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893 Cards in this Set
- Front
- Back
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What is a cell?
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The basic unit of all living things
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What are the two types of cells?
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Prokaryotic
Eukaryotic |
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What do prokaryotic cells lack?
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Membrane bound organelles
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What is an organelle?
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A specialised part of a cell that performs a particular function
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What are the types of microscopes? (4)
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Light microscope
Transmission electron microscope Scanning electron microscope Laser scanning confocal microscope |
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What is microscopy
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The use of the microscope
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What is microscopy used for?
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To observe different types of cells and cell structure of eukaryotic organisms
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How do light microscopes work? (3)
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Object is placed in beam if light
Beam passes through object to produce an image Specimen needs to be thin and transparent |
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What are light microscopes used for? (2)
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Looking at the structure of cells
Looking at the position and shape of organelles |
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What is cell staining?
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When cells are stained to better visualize cells under a light microscope
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What is differential staining?
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When different parts of cells are stained different colours to identify different cellular components and cell types
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How do transmission electron microscopes work?
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The electrons pass through the material
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How do scanning electron microscopes work?
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The electrons are bounced off the surface of the material
Scattered electrons are used to form a detailed image |
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What is the maximum magnification of a light microscope?
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x2000
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What is the maximum magnification of a transmission electron microscope?
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x500,000
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What is the maximum magnification of a scanning electron microscope?
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x100,000
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What is the maximum resolution of a light microscope?
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200nm or 0.2um
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What is the maximum resolution of a transmission electron microscope?
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0.2nm
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What is the maximum resolution of a scanning electron microscope?
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10nm
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How does a laser scanning confocal microscope work? (3)
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Cells are stained with fluorescent dyes
Thick section of tissue is scanned with laser beam Laser beam scans across different depths of the section |
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What is the advantage of focusing the laser beam across different depths? (3)
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The laser can be focused at a very specific depth
This eliminates the blur seen in optical microscopes that is caused by out-of-focus tissue above the focal point This makes the image clealer |
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How can 3d images be created with a laser microscope? (2)
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Images are taken at successive depths
These are fed into a computer to generate a 3d image |
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Why do electron microscopes have a higher resolution than light microscopes?
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The wavelength of electrons are much shorter than light
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What are the advantages of a light microscope? (5)
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Inexpensive to buy and operate
Portable Specimens can be living or dead Doesn't require vacuum Simple sample preparation |
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What are the disadvantages of a light microscope? (2)
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Only x2000 magnification
Only 200nm resolution |
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What are the advantages of an electron microscope? (2)
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x500,000 magnification
0.5 nm resolution |
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What are the disadvantages of an electron microscope? (5)
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Expensive to buy and operate
Large Specimens are dead Requires vacuum Complex sample preparation which often distorts the sample |
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How many millimetres is one metre?
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1000
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How many micrometres is one millimetre?
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1000
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How many nanometres is one micrometre?
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1000
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What is magnification?
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Measure of by how much the image is enlarged relative to the specimen size
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What is resolution?
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The ability to distinguish between two points
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What is another word for resolution?
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Resolving power
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What is the range of magnification? (2)
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Infinite
However image may become blurry depending on resolution |
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The lower the number...
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The higher the resolution
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What is the formula for magnification?
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Size of image/Size of object
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What is an eyepiece graticule?
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Grid incorporated into an eyepiece for measuring objects under a microscope
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What is a stage micrometer?
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Consists of a microscope slide on which is engraved a fine and accurate scale
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Give the steps for calibrating an eyepiece graticule with a stage micrometer (3)
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Micrometer divisions are at known distance apart
Count number of graticule units equivalent to one micrometer division Calculate distance of one graticule division |
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Give the steps for measuring an object after calibrating an eyepiece graticule (3)
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Use same objective lens as for calibrating
Count number of graticule divisions equivalent to length of cell Convert eye piece divisions to micrometres |
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Give the components of a eukaryotic cell (15)
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Nucleus
Nucleolus Nuclear Envelope Rough endoplasmic reticulum Smooth endoplasmic reticulum Golgi apparatus Ribosomes Mitochondria Lysosomes Chloroplasts Plasma membrane Centrioles Cell wall Flagella Cilia |
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What is the largest organelle?
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Nucleus
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Outline the function of the nucleus (2)
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Controls activities of the cell
Contains genetic information that can be transmitted to the next generation |
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Describe the structure of the nucleus (3)
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Nucleus contains one or more nucleoli
Surrounded by double nuclear membrane crossed by a number of nuclear pores It is continuous with the endoplasmic reticulum |
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Outline the function of the nucleoli
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Makes ribosomal RNA and packages it with ribosomal protein to make ribosomes
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Outline the function of the rough endoplasmic reticulum (2)
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Attachment for ribosomes
Aids transportation of protein from ribosomes to golgi bodies |
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Outline the function of the smooth endoplasmic reticulum
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Series of flattened sacs that are sites of synthesis and transportation of steroids and lipids
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Outline the function of the golgi apparatus (3)
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Processes proteins
Used for secretion using vesicles Formation of lysosomes |
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Outline the function of the ribosomes
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Sites of protein synthesis
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Outline the function of the mitochondria (2)
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Site of aerobic respiration
Highly folded inner membrane that helps with ATP synthesis |
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What are lysosomes? (2)
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Sacs containing high concentrations of hydrolytic (digestive) enzymes
These sacs are kept alkaline and separate from the rest of the cell to prevent damage |
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Outline the function of the lysosomes
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Used to break down ingested material
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Outline the function of the chloroplasts (2)
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Site of photosynthesis
Contains chlorophyll that absorbs light |
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Outline the function of the plasma membrane (2)
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Responsible for the control of solute movements between the cell and its environment
Responsible for synthesis and assembly of cell wall components (in plants) |
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Outline the function of the centrosomes
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A pair of structures held at right angles to one another, which act as organizers of the nuclear spindle in preparation for the serpepration of chromosomes or chromatids during nuclear division
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Outline the function of the cell wall (3)
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Prevents bursting when water enters cell by osmosis
Fully permeable transport route Gives cell shape and strength |
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Outline the function of the tonoplast membrane
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Surrounds the vacuole and regulates entry/exit of substances into/out of the vacuole
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Outline the function of the vacuole (2)
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Contains cell sap, which is a solution of minerals, sugars and waste products
Regulates osmotic properties of the cell |
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What is the cell wall made of in prokaryotes?
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Murein
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What is another word for murein?
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Peptidoglycan
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What is peptidoglycan?
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A polymer made of amino acids and sugars
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What is the cell wall made of in plant cells?
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Cellulose
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What are flagella and cilia composed of?
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Microtubules
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What are microtubules?
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Small tubular structure in the cytoplasm composed of tubulin
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Why is the structure of cilia/flagella called 9 2 structure?
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It consists of a ring of nine pairs of microtubules surrounding two central microtubules
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Outline the function of the flagella (2)
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Found in some single celled organisms
Move the cell around |
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Outline the function of the cilia (2)
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Used for cell signalling
Used for keeping areas clean of mucus |
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Explain production and secretion of proteins (7)
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Nucleolus manufactures ribosomes for protein synthesis in the RER
Nucleus manufatures mRNA which is needed by ribosomes to make proteins Ribosomes in the RER make proteins RER processes the proteins which are then sent in vesicles to the Golgi vody The golgi body further processes the proteins and sends them in vesicles to the plasma membrane The vesicles fuse with the plasma membrane to secrete the finished product |
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What is the cytoskeleton?
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A series of protein threads in the cytoplasm
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What are the two types of protein threads?
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Microtubules
Microfilaments |
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What are the functions of the cytoskeleton? (4)
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Cellular movement
Moving liquids across surface of the cell Intracellular movement so organelles can move from one part of the cell to another Strenghtening and supporting the cell to keep it in shape |
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What protein are microfilaments made up of?
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Actin
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What are plasmids?
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Circular, double stranded DNA molecules found naturally in prokaryotes
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What features do animal cells have that plant cells don't have? (2)
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Centrioles
Flagella |
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What features do plant cells have that animal cells don't have? (4)
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Cellulose cell wall
Chloroplasts Vacuole Plasmodesmata |
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What is a plasmodesma?
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Gaps in the cell wall through which cytoplasm connects the protoplast of one cell with an adjacent cell
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What is protoplast?
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The part of the cell that is inside the cell wall
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What are the features of eukaryotes (compared to those of prokaryotes)? (10)
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Nucleus present
DNA linear and in nucleus Multiple linear chromosomes Has histones Cell wall in plant cells made of cellulose or chitin (fungi) Membrane bound organelles Large ribosomes (80 S) No pili Has a cytoskeleton 10 - 100 micrometers |
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What are the features of prokaryotes (compared to those of eukaryotes)? (10)
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Nucleus not present
DNA circular and free in cytoplasm Single circular chromosome Lacks Histones Cell wall made of murein Organelles not membrane bound Ribosomes small (70 S) Sometimes have pili No cytoskeleton 0.2 - 2 micrometers |
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What unit is used to measure ribosomes?
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Svedberg units (S)
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What is the size of the ribosome of a prokaryote in nanometres?
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18nm
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What is the size of the ribosome of a eukaryote in nanometres?
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22nm
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What are pili?
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Short hairs on the surface of prokaryotes used for mating
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What elements are 99% of living things made of? (4)
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Carbon
Hydrogen Oxygen Nitrogen |
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What is a covalent bond?
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A strong chemical bond formed by sharing one or more electrons between two atoms and so creating a molecule
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What is polarity?
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An uneven charge distribution within a molecule
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What is a dipole?
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When one pole of the molecule is slightly positive and the other slightly negative
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Why do H-bonds form in water?
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Because the oxygen atom has greater electron-attracting power than the hydrogen atoms, which gives the oxygen more electronegativity, forming an H-bond
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How are water *atoms* attracted to each other?
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Covalent Bonds
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How are water *molecules* attracted to each other?
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Hydrogen Bonds
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Why does water have unique properties? (3)
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Water has small molecular size
Water has H-bonds Water is attracted to charged particles (polar) |
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What are the unique properties of water? (7)
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Excellent solvent for polar substances
Repels non polar susbtances High heat capacity High heat of vaporisation High heat of fusion Less dense below 4 degrees High surface tension |
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What are the advantages of water being an excellent solvent for polar substances? (2)
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Ions in solution become more chemically reactive
This helps cells where chemical reactions take place in water |
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What are the advantages of water repelling non-polar substances? (3)
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Helps with structure of 3-D protein
Helps with lipid cell membranes Helps with structure of nucleic acids |
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Why does water have high heat capacity?
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Because much of the energy is used to break hydrogen bonds which restricts movements of the molecules
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What are the advantages of water having high heat capacity? (2)
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Helps provide a constant external environment for cells and organisms
Biological processes are less likely to be inhibited by extreme temperatures |
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What is heat of vaporisation?
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The measure of heat energy required to vaporise a liquid, to overcome attractive forces so they can escape as a gas
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Why does water have a high heat of vaporisation?
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Because of hydrogen bonding
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What are the advantages of water having a high heat of vaporisation? (2)
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Water vaporises less easily so heat is lost easier to the environment which is good for transpiration
For example: sweating, panting |
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What is heat of fusion?
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A measure of energy required to melt a solid
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Why does water have a high heat of fusion?
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Due to high heat of capacity because of H-bonds
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What is the advantage of water having a high heat of fusion?
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Contents of cells are less likely to freeze
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What is the advantage of ice being less dense below 4 degrees? (3)
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Layer of ice forms at the top of ponds and lakes first
This allows arctic aquatic animals to survive Also regulates circulation in large bodies of water |
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What is high surface tension?
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When molecules stick together (cohesion) near the surface
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What are the advantages of high surface tension? (2)
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Allows translocation of water through xylem in plants
Many small organisms rely on surface tension to settle/skate on |
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Why is carbon an excellent building block?
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It has one electron yet to be shared that can form covalent bonds with other elements to easily form biological molecules
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What are carbon skeletons?
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When carbon atoms bond with other carbon atoms and elements (eg. H-C-C-O)
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Name the different types of carbon skeletons (4)
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Short chain
Long chain Branched chain Ring form |
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What is a monomer?
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A single smaller molecule that may form covalent bonds with other monomers to build up to larger molecules called polymers
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What is a polymer? (2)
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A large molecule built up from many similar monomers joined together by covalent bonds to form a chain or a branched chain
Each bond forms as a result of a condensation reaction |
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What is a dimer?
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A molecule formed of two monomers joined together by a condensation reaction
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Give examples of monosaccharides (3)
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Glucose (Hexose)
Fructose (Pentose) Ribose (Triose) |
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Give examples of disaccharides (3)
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Sucrose
Maltose Lactose |
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Give examples of polysaccharides (3)
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Starch (amylose)
Glycogen Cellulose |
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What is a protein monomer called?
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Amino acid
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Give examples of amino acids (3)
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Glycine
Valine Alanine |
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What is hydrolysis?
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A chemical reaction where the covalent bond between the two molecules is broken with the addition of a water molecule, separating the two molecules
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Learn the chemical structure of glucose and fructose and how they condense to form a glycosidic bond before continuing
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Learn the chemical structure of glucose and fructose and how they condense to form a glycosidic bond before continuing
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What are the roles of carbohydrates as biological molecules? (3)
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Energy source
Energy store Structural component |
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What is cell respiration?
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A process involving many enzyme catalysed reactions that occur within cells and results in the release of energy which is used to make adenosine triphosphate (ATP)
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What is the general formula for carbohydrates?
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Cx(H2O)y
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Give an example of a carbohydrate energy source
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Glucose
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Give an example of a carbohydrate energy store
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Glycogen
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What type of molecule is a monosaccharide? (2)
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Simple sugar
(Single molecule) |
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What type of molecule is a disaccharide? (2)
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Complex sugar
(two molecules covalently joined) |
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What type of molecule is a polysaccharide? (2)
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complex carbohydrate
(many molecules covalently joined together) |
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How does a monosaccharide taste like?
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Sweet
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How does a disaccharide taste like?
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Sweet
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How does a polysaccharide taste like?
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Not sweet
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What is the solubility of a monosaccharide in water?
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Soluble
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What is the solubility of a disaccharide in water?
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Soluble
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What is the solubility of a polysaccharide in water?
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Not soluble
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How many glycosidic bonds does a monosaccharide have?
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None
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How many glycosidic bonds does a disaccharide have?
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Single glycosidic bond
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How many glycosidic bonds does a polysaccharide have?
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Many glycosidic bonds
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What is the structure of a monosaccharide? (2)
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Exists as a single ring shape
Or straight chain |
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What is the structure of a disaccharide ?
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Two rings joined
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What is the structure of a polysaccharide ?
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Long chains which may be branched and coiled, making them very compact
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What are the roles of monosaccharides? (3)
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Energy release
Used as monomers for other carbohydrates |
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What are the roles of disaccharide? (3)
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Energy release
Energy storage Transport within plants |
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What are the roles of polysaccharide? (2)
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Energy storage
Structural component of cell walls |
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What are the two forms of glucose?
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α-glucose
β-glucose |
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What is the difference between alpha and beta glucose? (2)
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α-glucose: The hydrogen on carbon 1 is above the
plane of the ring. β-glucose: The hydrogen on carbon 1 is below the plane of the ring. |
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What are isomers?
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Molecule containing the same number and types of atoms, but the atoms are arranged differently
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Give examples of isomers (2)
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α-glucose
β-glucose |
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Describe the function of glucose (4)
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Small molecule that breaks down into smaller molecules to form CO2 and H2O
Diffuses easily Water soluble Therefore is easily transported and is the main respiratory substrate, resulting in energy release |
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What is the role of ribose/deoxyribose (pentoses)?
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To form nucleic acids
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What are the functions of triose sugars?
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Intermediate molecules in both respiration and photosynthesis
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What is a disaccharide?
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Carbohydrates formed by two monosaccharides that join together by a glycosidic bond
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What is a glycosidic bond?
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A covalent bond formed when two carbohydrate molecules are joined together by a condensation reaction
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What is a condensation reaction?
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A reaction in which two molecules combine to form a larger molecule, producing H2O as a by product
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What is the opposite of condensation?
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Hydrolysis
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What is the bond formed between two α-glucose? (2)
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1, 4 glycosidic
Between C1 of one glucose and C4 of other glucose |
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What disaccharide is formed when amylase breaks down starch?
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Maltose
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How do you form sucrose?
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Glucose + Fructose
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How do you form lactose?
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Glucose + Galactose
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How do you form maltose?
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Glucose + Glucose
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What enzyme turns fructose into glucose?
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Isomerase
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Explain the reducing sugar test (FINISH AT HOME) (4)
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Add Benedict's solution to the sugar
Heat in water bath Precipitate indicates reducing sugar Colour indicates amount of reducing sugar Solution is originally pale blue, then turns green, then yellow, then brick red |
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What is the test for non-reducing sugars?
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Heat and add acid to sugar
Neutralise acid with an alkali such as NaOH Carry out benedict's test |
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What is the non-reducing sugar?
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Sucrose
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What is a polysaccharide?
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Large polymers formed of many monosaccharides that combine by condensation reactions to create long chains
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What is the function of starch?
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Main storage polysaccharide in plants
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What is the function of glycogen
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What is the function of glycogen
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What is the function of cellulose
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Main structural constituent of plant cell walls
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What is a polymer?
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A substance with a molecular structure made up of many similar smaller molecules.
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What 2 polymers is starch made of?
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Amylose
Amylopectin |
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What is the structure of amylose? (3)
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Polymer of glucoses joined by a-1, 4 glycosidic bonds
Chains are curved and coiled up into helical structures like springs H-bonds hold together the amylose |
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What is the structure of amylopectin? (3)
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Polymer of glucoses joined by a-1, 4 glycosidic bonds
Has branches of a 1, 6 glycosidic bonds. This causes molecule to be branched |
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How does the structure of starch help with it's functionality? (3)
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Insoluble so good for storage
Helix is compact Branches mean the compound can easily be hydrolysed to release glucose monomers |
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What is the structure of glycogen
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Similar to amylopectin but with many more branches which are also shorter
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How does the structure of glycogen help with it's functionality?
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Extremely compact due to short branches
Very fast hydrolysis due to branches (larger surface area) |
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What is the structure of cellulose? (3)
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Adjacent chains of long, un-branched polymer of glucose joined by b-1, 4 glycosidic bonds
Between 60 and 70 molecules become tightly cross-linked to form bundles called microfibriles Microfibriles are in turn held together in bundles called fibres by H-bonding Permeable to water |
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How does the structure of cellulose help with it's functionality? (4)
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Cellulose fibres have very high tensile strength
This makes it difficult to stretch or break And makes it possible for a cell to withstand large pressures that develop within it due to osmosis (without it the cell would burst) Helps make the cell rigid which is responsible for cell expansion during growth |
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Why does starch/glycogen need to be hydrolysed easily?
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To be easily broken down into other substances eg. glucose for respiration
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What is the test for starch? (2)
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Add Potassium Iodide (KI) solution
Positive result forms a poly-iodide complex Positive result changes solution from orange brown to blue black |
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What is a triglyceride?
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A lipid whose molecules are made up of a glycerol molecule and three fatty acids
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What is a fatty acid?
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Organic molecule which all have a -COOH group attached to a hydrocarbon tail
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What is a -COOH group called?
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Carboxylic
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What is the function of triglycerides (not tissue)?
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Used as energy storage compounds in plant, animals and fungi because they are insoluble
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Why are insoluble molecules good for storage?
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Because they don't dissolve in water, and they can be hydrolysed back into their original form
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What is the advantage of storing energy in triglycerides rather than polysaccharides?
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They contain more energy per gram, so can store more energy in less mass
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What is adipose tissue?
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Stores of triglycerides built up beneath the skin in the form of oil droplets
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What are the functions of adipose tissue (3)
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Helps body against heat loss
Helps with buoyancy with aquatic animals Forms a protective layer around some of the body organs |
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What is a phospholipid?
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A substance where molecules are made up of a glycerol molecule, two fatty acids and a phosphate group
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What are the properties of a phospholipid molecule? (3)
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Fatty acid chains are hydrophobic
Phosphate group (head) is hydrophillic Therefore phospholipid molecule arranges itself into a bilayer with the hydrophobic tails facing inwards to avoid contact with water |
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Why are the fatty acid chains hydrophobic?
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They have no electrical charge, so are not attracted to the dipoles of water molecules
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Why is the phosphate group hydrophillic?
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They have an electrical charge, so are attracted to the dipoles of water molecules
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What is the structure of an amino acid
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Simple organic compound
Amine group and carboxyl group attached to central carbon atom Third component is always hydrogen Fourth group is an R group |
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What is an amine group?
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H2N
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How many different amino acids/R-groups are there?
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20
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What is a dipeptide?
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When two amino acids link together by condensation to form a *peptide* bond and produce water
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How is a peptide bond broken?
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With hydrolysis (adding a molecule of water)
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What type of bond is a peptide bond?
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Strong covalent bond
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What is a polypeptide?
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A molecule made up of amino acids linked together by peptide bonds
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How many polypeptide chains does a complete protein molecule contain?
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A complete protein molecule contains one or more polypeptide chains that interact with each other
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Where in cells are amino acids linked together?
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In the ribosomes
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How are protein molecules digested?
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They are hydrolysed in the stomach and small intestine into amino acids and absorbed into the blood
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What is the biuret test for proteins?
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Add sodium hydroxide solution
Add very dilute copper sulphate solution If the mixture contains protein, the top of the solution will go purple |
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What is the primary structure?
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The sequence of amino acids in a polypeptide or protein
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How many combinations of amino acids (primary structures) can be made?
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Infinite
|
|
|
What is the secondary structure?
|
The structure of a protein molecule resulting from the regular coiling or folding of the chain of amino acids (polypeptide)
|
|
|
What are the two types of secondary structures?
|
α- helix
β- pleated sheet. |
|
|
What is an α- helix?
|
When a polypeptide chain or part of it coils into a corkscrew shape due to hydrogen bonding between amine and hydroxyl groups
|
|
|
Why do some proteins or parts of proteins show no regular arrangement at all?
|
They have a set of R-groups in the polypeptide chain that change the structure
|
|
|
What is the tertiary structure?
|
The compact structure of a protein molecule resulting from the 3-D coiling of the already folded chain of amino acids
|
|
|
What is the acronym for types of bonds?
|
HH-DIL
|
|
|
Explain the types of bonds that can form in a tertiary structure (5)
|
Hydrogen bonds between a wide variety of R-groups
Disulphide bonds between two cysteine molecules Ionic bonds between R groups containing amine and carboxyl groups as they have a charge (O- and H+) Hydrophobic interactions between R groups which are non polar London forces between R groups which are non polar |
|
|
What is a cysteine molecule?
|
A molecules that contains sulphur atoms
|
|
|
What are the factors disrupting tertiary structure? (2)
|
pH
Temperature (causes denaturation) |
|
|
What is the quaternary structure?
|
The 3-D arrangement of two or more polypeptides, or of a polypeptide and a non-protein component such as haem, in a protein molecule
|
|
|
How many polypeptide chains does Haemoglobin have?
|
Four in each molecule
|
|
|
List the types of bonds that can form in a quaternary structure (5)
|
Hydrogen
Disulphide Ionic Hydrophobic interactions London Forces |
|
|
What are the features of a globular protein? (5)
|
A protein whose molecules are folded into a relatively spherical shape
Water-soluble Metabolically active Has the function of hormones/enzymes Shape matters |
|
|
Give examples of globular proteins (2)
|
Insulin
Haemoglobin |
|
|
What are the features of a fibrous protein? (7)
|
Long thin protein molecule
Insoluble Metabolically inactive Has the function of structure Might have quaternary structure Never has teriary structure Shape doesn't matter |
|
|
Give examples of fibrous proteins (2)
|
Keratin
Collagen |
|
|
What is a conjugated protein?
|
A protein with something in it that's not an amino acid (prosthetic group)
|
|
|
What are the features of haemoglobin (globular protein)?
|
Soluble in water
Can combine with oxygen Can pick up and release oxygen |
|
|
Explain the solubility of haemoglobin (3) |
Tertiary structure of haemoglobin makes it soluble |
|
|
Explain the ability of haem to combine with oxygen (3)
|
Oxygen molecules combine with Fe2+ in the haem group
One oxygen molecule (O2) can combine with each haem group So one haemoglobin molecule can combine with four oxygen molecules (eight atoms) |
|
|
Explain the ability of haemoglobin to pick up and release oxygen (2)
|
Overall shape of haemoglobin molecule enables it to pick up oxygen when the oxygen concentration is high and to release oxygen when the oxygen concentration is low
One one oxygen molecule has combined with one haem group, the whole molecule changes its shape in such a way that it is easier for oxygen to combine with the other three haem groups |
|
|
What are the features of collagen (fibrous protein)? (4)
|
Insoluble
High tensile strength Compact Forms fibres |
|
|
Explain how collagen is insoluble
|
Collagen molecules are very long and are too large to be able to dissolve in water
|
|
|
Explain the high tensile strength of collagen (3)
|
Three polypeptide chains wind around one another held by hydrogen bonds
This forms a three-stranded molecule that can withstand force Also allows the molecules to stretch slightly when pulled |
|
|
Explain how collagen is compact (2)
|
Every third amino acid in each polypeptide is glycine, whose R group is just a single hydrogen molecule.
Small size allows 3 polypeptide chains in a molecule to tightly pack |
|
|
Explain how collagen forms fibres (2)
|
Many lysine fibres in each polypeptide
This allows covalent bonds to form between lysine R groups of different collage molecules, forming fibres |
|
|
What is a co-factor?
|
A non-protein chemical compound that is needed for the protein's biological activity
|
|
|
What is a nucleic acid?
|
Molecules made up of carbon, hydrogen, oxygen and nitrogen
|
|
|
What are the two types of nucleic acids?
|
DNA
RNA |
|
|
What does DNA stand for?
|
Deoxyribonucleic acid
|
|
|
What does RNA stand for?
|
Ribonucleic acid
|
|
|
What is are the roles of nucleic acid? (3)
|
Carry genetic code
Important in controlling cellular activity Responsible for protein synthesis |
|
|
Describe DNA (3)
|
Double stranded polynucleotide
Carries information for protein synthesis Contains pentose sugar deoxyribose |
|
|
Describe RNA (3)
|
Single stranded polynucleotide
Important in the role of protein synthesis Contains the pentose sugar ribose |
|
|
What is a polynucleotide?
|
A polymer of nucleotide monomers covalently bonded together
|
|
|
What is a nucleotide?
|
The basic building block of nucleic acid molecules
|
|
|
How many molecules are nucleotides made of?
|
3
|
|
|
What are the three nucleotide molecules?
|
Pentose sugar molecule
Organic nitrogenous base Phosphate group |
|
|
How are the three nucleotide molecules joined together?
|
Covalent bonds formed by condensation reactions
|
|
|
What is a condensation reaction?
|
A reaction in which two molecules combine to form a larger molecule, producing H2O as a by product
|
|
|
Describe pentose sugar (2)
|
Either ribose or deoxyribose
Contains 5 carbon atoms |
|
|
What is an organic nitrogenous base?
|
A nitrogen-containing organic compound
|
|
|
What are the 5 types of nitrogenous bases?
|
Adenine (A)
Cytosine (C) Guanine (G) Thymine (T) Uracil (U) |
|
|
What bases does DNA contain?
|
A
C G T |
|
|
What bases does RNA contain?
|
A
C G U |
|
|
What are the two types of organic bases?
|
Pyrimidines
Purines |
|
|
What are the differences between purines and pyrimidines? (3)
|
Purines are larger than pyrimidines
Purines consist of two carbon-nitrogen rings whereas pyrimidines consist of a single carbon-nitrogen ring Pyrimidines consist of T, C, U whereas Purines consist of A, G |
|
|
How are polynucleotides formed? (3)
|
Nucleotides are joined together by condensation reactions to form a chain
Phosphate group of one nucleotide is joined to the sugar molecule of the next nucleotide in the chain, and this is repeated for each nucleotide added This forms a sugar-phosphate backbone |
|
|
How is DNA formed from polynucleotides? (5)
|
The two polynucleotides are held together by hydrogen bonds between adjacent bases
Adenine links with Thymine Cytosine links with Guanine Phosphate is combined with carbon-3 of one deoxyribose and carbon-5 of the next Strands are antiparallel |
|
|
What does antiparallel mean?
|
They run in opposite directions to each other
|
|
|
What is the shape of DNA called?
|
Double helix
|
|
|
What is 5' (5 prime)?
|
Nitrogenous-phosphate group
|
|
|
What is 3' (3 prime)?
|
OH group
|
|
|
What does 5' --> 3' mean? (2)
|
The nitrogenous phosphate group forms phosphodiester bonds with the OH group
Therefore the nucleotide is built up in the 5' to 3' direction |
|
|
What is semi-conservative replication?
|
Each new DNA molecules is formed of one conserved strand from the original molecule which acts as the template, and one of the strand of new nucleotides
|
|
|
Describe DNA replication (8)
|
Strands seperate and H-bonds break
DNA helicase is involved in breaking H-bonds Both strands act as a template Free nucleotides attach Complementary base pairing - AT and GC DNA polymerase joins nucleotides H-bonds reform Semi-conservative replication occurs |
|
|
Where do free nucleotides come from?
|
From the food we eat (plants make it)
|
|
|
What is the code for DNA called?
|
Triplet code
|
|
|
What is triplet code?
|
The three nitrogenous bases read along the DNA strand that code for amino acids
|
|
|
How many different amino acids are there?
|
20
|
|
|
How many combinations of triplet codes are there?
|
64
|
|
|
Why is triplet code called degenerate?
|
Because there may be up to six different triplet code for the same amino acid
|
|
|
What is the advantage of triplet code being degenerate?
|
If a mutation causes a base change, the triplet may still code for the same amino acid and therefore not change the protein produced
|
|
|
What is a terminator signal?
|
Triplet code that indicates the end of the message
|
|
|
What are the two stages of protein synthesis?
|
Transcription
Translation |
|
|
What is transcription?
|
The process of copying the code exactly to form a template of mRNA
|
|
|
Describe transciption (10)
|
DNA is unwound by RNA polymerase
DNA is unzips into two strands mRNA is made by transcription Promoter region causes RNA polymerase to bind Template strand of DNA is transcribed Direction of transcription is 5' --> 3' Complementary base pairing between template strand and RNA nucleotides RNA contains uracil instead of thymine Terminator stops RNA polymerase and stops transcription mRNA is released |
|
|
Where does the mRNA go after transcription? (2)
|
Leaves the nucleus via nuclear pores for the ribosomes
In the ribosomes, it acts as the template for protein to be synthesised |
|
|
What are RNA triplets called?
|
Codon
|
|
|
What are the properties of codons? (9)
|
Composed of mRNA base triplets
64 different types Each codes for the addition of an amino acid to a growing polypeptide chain Degenerate Meaning more that one codon can code for a particular amino acid Universal Meaning it is the same in almost all organisms AUG is the start codon Some codons code for the end of translation |
|
|
What are the three stages in translation?
|
Initiation
Elongation Termination |
|
|
Describe the first stage of translation - initiation (4)
|
mRNA is used as a template
Initiator tRNA binds to small subunit of ribosome AUG is start codon UAC is start anticodon on tRNA |
|
|
Describe the second stage of translation - elongation (9)
|
mRNA translated in a 5' to 3' direction
Second tRNA binds to ribosome Large subunit moves down mRNA after a second tRNA binds mRNA read in base triplets Each codon specifies addition of a particular amino acid to the growing polypeptide chain Peptide bonds form between amino acids tRNA brings amino acids Amino acid on first tRNA is transferred to amino acid on second tRNA Loss of tRNA and new tRNA binds |
|
|
Describe the third stage of translation - termination
|
Stop codon is reached
Release factor binds to mRNA Polypeptide is released |
|
|
What is the use of the anticodon?
|
Triplet complementary to the codon and ensures correct order of amino acids during translation
|
|
|
Where does the polypeptide go? (4)
|
It is sent to the golgi apparatus
It is packaged (not packed) in vesicles It is further processed It leaves the cell via exocytosis |
|
|
What are the three types of RNA?
|
Messenger RNA (mRNA)
Transfer RNA (tRNA) Ribosomal RNA (rRNA) |
|
|
What is the role of mRNA?
|
Copies the information from the DNA code (transcription)
|
|
|
What is the structure of tRNA? |
Short chains that fold on to themselves, creating a clover shaped molecule |
|
|
What is the role of tRNA?
|
Carry amino acids to the mRNA and the ribosomes to form a polypeptide chain
|
|
|
What is the role of rRNA?
|
Form ribosomes when attached to the ribosomal protein molecules
|
|
|
What is a catalyst
|
A substance that increases the rate of a chemical reaction without getting used up in the process
|
|
|
What is a globular protein?
|
A spherical protein that is somewhat soluble in water and can act as an enzyme
|
|
|
What are enzymes?
|
Globular proteins that are folded into complex tertiary structures that allow smaller molecules to fit into them
|
|
|
What is a substrate?
|
The molecules that fit into the active site of an enzyme
|
|
|
What is the active site?
|
The place where the substrate molecules fit into the enzyme and is a complementary shape to the substrate
|
|
|
Describe the structure of an active site
|
Groove composed of small number of amino acids within a polypeptide
|
|
|
What are the features of the active site determined by?
|
The R groups of the amino acids making up the active site
|
|
|
Give an example of an enzyme R group and its function
|
Non-polar R group
Provides a hydrophobic interior to the active site so it only accepts non-polar substances |
|
|
What is specificity?
|
The relationship between an enzyme and the only type of molecule that fits into its active site
|
|
|
What are intracellular enzymes?
|
Enzymes that catalyse reactions within cells
|
|
|
Give an example of an intracellular enzyme
|
Catalase
|
|
|
What is the role of catalase?
|
Break down hydrogen peroxide into oxygen and water
|
|
|
Where does hydrogen peroxide come from in the body?
|
It is a product of metabolic reactions in the body
|
|
|
Why does hydrogen peroxide need to be broken down?
|
It is a strong oxidising agent, so is extremely toxic
|
|
|
What are the two types of intracellular enzymes?
|
Fixed
Free in solution |
|
|
Give an example of a fixed intracellular enzyme
|
Sucrase attached to the cell membranes of cells lining the gut
|
|
|
What is an extracellular enzyme?
|
Enzymes that catalyse reactions outside of cells
|
|
|
Give two examples of extracellular enzymes
|
Amylase
Trypsin |
|
|
What is the role of amylase?
|
Hydrolyses starch into maltose
|
|
|
What is hydrolysis?
|
The chemical breakdown of a compound due to reaction with water
|
|
|
What is the role of trypsin?
|
Breaks down protein molecules into peptides and amino acids
|
|
|
What forms when the substrate fits into the active site?
|
Enzyme-substrate complex
|
|
|
What are the two ideas of how enzymes interact with their substrates?
|
Lock and key hypothesis
Induced fit hypothesis |
|
|
Explain the lock and key hypothesis (5)
|
The substrate fits exactly into the active site
Interactions between the R groups within the active site of and the substrate stabilise the enzyme-substrate complex Substrate is altered and forms a product Complex is now called enzyme-product complex Enzyme releases the product and the process can be repeated |
|
|
What is an enzyme product complex?
|
The complex that forms in the active site after the reaction is complete but before the product(s) leave
|
|
|
Explain the induced fit hypothesis
|
The theory that the active site of an enzyme changes shape during the binding of a substrate molecule, and this puts strain on the substrate molecule contributing to the reaction
|
|
|
What is activation energy?
|
The energy that is needed to overcome the energy barrier to allow a reaction to occur
|
|
|
How do enzymes alter the activation energy?
|
They lower it
|
|
|
Explain what happens during a chemical reaction
|
Reactants collide
When they collide with enough kinetic energy, the reaction will occur |
|
|
What are the factors required for a substrate to be catalysed by an enzyme?
|
The active site must be a complimentary shape to the substrate or must change shape to become complimentary to the substrate
Substrate and active site must be line up They must collide with enough energy |
|
|
What is another term for 'complimentary shape'?
|
Precise conformation
|
|
|
What is the definition of activation energy *in terms of enzymes?*
|
The minimum amount of energy needed to form the transition state
|
|
|
What happens during the transition state? (3)
|
When a substrate and active site collide with enough energy and form an unstable high-energy intermediate
This quickly changes into the product Energy is released |
|
|
Draw the activation energy graph for an enzyme
|
Look it up |
|
|
What are the factors that affect enzyme activity?
|
Temperature
pH Enzyme Concentration Substrate Concentration |
|
|
Draw and describe the graph for how temperature affects the rate of reaction with enzymes
|
As the temperature increases, the react of reaction also increases.
However when the graph passes the optimum temperature, the graph starts to rapidly decline |
|
|
Explain the temperature-rate of reaction graph (5)
|
Higher temperature means particles have more kinetic energy
This means increased frequency of collisions Increased likelihood of enzyme and substrate colliding and breaking bonds However after a certain high temperature, the enzyme denatures This causes the enzyme to no longer work properly which reduces rate of reaction |
|
|
What is meant by the term denature? (2)
|
When the active site of an enzyme changes shape due to extreme temperatures or pH levels so the substrate can no longer fit into the active site
This damage is irreversible |
|
|
Why do organisms have varying optimum pH and temperatures? (2)
|
Some organisms such as extremophiles have enzymes that don't denature even at extreme temperatures and pH levels
Different organisms also have enzymes that have different optimum pH that differ in plants and animals |
|
|
Draw and describe the graph for how pH affects the rate of reaction with enzymes
|
The closer you get to the optimum pH, the higher the rate of reaction
|
|
|
Explain the pH-rate of reaction graph (2)
|
Enzymes work best at a certain pH, so the closer you get to that pH, the higher the rate of reaction
However, at extremes of pH, the enzyme denatures |
|
|
Draw and describe the graph for how enzyme/substrate concentration affects the rate of reaction (2)
|
The higher the concentration, the higher the rate of reaction
The graph levels off after a certain concentration and stays at a constant rate without increasing |
|
|
Explain the enzyme/substrate concentration graph (5)
|
Higher concentrations means increased likelihood of enzyme clashing with substrate
Therefore the higher the concentration, the higher the rate of reaction However after a certain concentration the graph stops increasing This is because the substrates have already occupied all the active sites (increased substrate conc.) Or because there are not enough substrate molecules to bind to the excess of active sites (increased enzyme conc.) |
|
|
What is an inhibitor?
|
A substance that slows down the rate at which an enzyme works
|
|
|
What are the two types of inhibitors?
|
Competitive
Non-competitive |
|
|
What is a competitive inhibitor?
|
An inhibitor that has a similar shape to the enzyme's normal substrate, preventing the substrate from binding
|
|
|
What is the effectiveness of a competitive inhibitor affected by?
|
The relative concentrations of the inhibitor and substrate, as greater concentrations means more likely that inhibitor molecule will bump into active site rather than substrate
|
|
|
What is a non-competitive inhibitor? (2)
|
An inhibitor that does not have the same shape as the substrate, and do not bind to the substrate
However they bind to a different part of the enzyme |
|
|
What does a non-competitive inhibitor binding to an enzyme do? (2)
|
Changes enzyme's shape, including the shape of the active site
So substrate can no longer bind with it |
|
|
Why is a non-competitive inhibitor not affected by inhibitor vs substrate concentration?
|
Even if you add more substrate, it still won't be able to bind to the active site
|
|
|
What is the job of the plasma membrane?
|
To act as a partially permeable membrane
|
|
|
Where are membranes located in cells? (3)
|
Between cell and environment
Between organelles and cytoplasm Within organelles |
|
|
What are the other roles of membranes? (2)
|
Sites of chemical reactions
Sites of cell communication (signalling) |
|
|
How thick is the membrane in the fluid mosaic model?
|
7nm
|
|
|
Why is the fluid mosaic structure described as 'fluid'?
|
The phospholipids move around in the lipid layer and the proteins can also move
|
|
|
How many layers does lipid part of the membrane have?
|
Two
|
|
|
What is the double layer called?
|
Phospholipid bilayer
|
|
|
Give the parts of the fluid mosaic model (5)
|
Phospholipids
Cholesterol Glycolipids Glycoprotein Proteins |
|
|
When do phospholipids naturally form a bilayer?
|
When they are in contact with water or an aqueous medium
|
|
|
What are the two parts of a phospholipid?
|
Hydrophilic Polar Head
Non-polar Hydrophobic Tail |
|
|
What does hydrophillic mean?
|
Attraction to water
|
|
|
What does hydrophobic mean?
|
Repulsion from water
|
|
|
Is water polar or un-polar?
|
Polar
|
|
|
Why is a bilayer the most stable structure? (3)
|
Heads of lipids are attracted to water
Tails are repelled, so a bilayer helps them be as far away from water as possible Tails attract each other further stabilising |
|
|
What are the two types of double bonds?
|
Saturated
Unsaturated |
|
|
The unsaturated lipid molecule has a weird tail. True or False?
|
True
|
|
|
What is the property of lipids formed with unsaturated chains?
|
Lower melting point
|
|
|
What are intrinsic proteins?
|
Proteins that are embedded in the lipid bilayer
|
|
|
What are the two types of intrinsic proteins?
|
Peripheral proteins
Transmembrane proteins |
|
|
What are peripheral proteins?
|
Proteins attached to the surface of the lipid bilayer
|
|
|
What are Transmembrane proteins?
|
Proteins that span the membrane and are exposed at both sides
|
|
|
How are transmembrane proteins held in the membrane?
|
By interactions between hydrophobic hydrophobic tail and hydrophobic parts of the proteins
|
|
|
What is an extrinsic protein?
|
Protein that are on the surface of the lipid bilayer, but are not embedded in it
|
|
|
What is a channel protein?
|
A transmembrane protein that forms a passageway for water and polar substances to pass through via diffusion
|
|
|
What are carrer proteins?
|
Proteins that can change shape to move substances from one side of the membrane to another
|
|
|
What are glycoproteins?
|
Proteins that have a short carbohydrate chain attached
|
|
|
What is the role of the carbohydrate chains? (4)
|
Can form hydrogen bonds with water to stabilise membrane structure
Important in cell signalling Act as receptors in for certain molecules Triggering specific changes when the molecule binds |
|
|
What are glycolipids?
|
Lipids with a short carbohydrate chain attached
|
|
|
What are surface antigens formed by?
|
Glycolipids and Glycoproteins
|
|
|
What are antigens?
|
A molecule that is foreign to the body and that stimulates an immune response and the production of antibodies
|
|
|
What is the function of cholesterol in the membrane?
|
To maintain a suitable level of fluidity in the membrane
|
|
|
What do phospholipids and cholesterol have in common?
|
They both have a hydrophillic and hydrophobic portion
|
|
|
What does the hydrophillic and phobic part of cholesterol allow it to do?
|
Allows cholesterol to bind to the to the phospholipids to keep it from becoming too fluid
|
|
|
How does cholesterol prevent the membrane from becoming too rigid?
|
Cholesterol is present between the fatty acid chains so adjacent fatty acids don't come together and crystallise
|
|
|
What is cell signalling?
|
Information transfer between cells
|
|
|
What make up the receptors in the plasma membrane?
|
Glycoproteins
|
|
|
What are receptors?
|
Cell signal receivers
|
|
|
What is a target cell?
|
A cell that responds to a particular messenger
|
|
|
What will a messenger have to allow it to respond to a specific receptor?
|
A unique complimentary shape
|
|
|
What changes can receptors cause? (3)
|
Release of a second messenger
Opening/Closing of a protein channel Activation of an enzyme |
|
|
How can drugs be used to slow/stop receptors?
|
The drug molecule can be a complimentary shape to the receptor, therefore blocking the receptor
|
|
|
What happens to the phospholipid bilayer when the temperature is increased by a moderate amount (below 40 degrees)?
|
Lipid component of the membrane becomes more fluid
Increase in kinetic energy of phospholipid molecules This reduces its effectiveness as a barrier to polar molecules Speed of diffusion also increases |
|
|
What happens to the phospholipid bilayer when the temperature is increased by a large amount (above 40 degrees)?
|
Proteins start to denature
This disrupts the membrane structure |
|
|
What happens when the membrane structure is fully damaged?
|
Substances can pass freely through it
|
|
|
What happens when an organic solvent touches the membrane?
|
They dissolve the lipids which can severely disrupt the membrane structure
|
|
|
What are the passives forms of movement across membranes? (2)
|
Diffusion
Facilitated Diffusion |
|
|
What are the active forms of movement across membranes?
|
Active transport
Endocytosis Exocytosis |
|
|
What is the difference between passive and active forms of transport?
|
Active forms of transport require ATP as an immediate source of energy whereas passive forms don't
|
|
|
What does ATP stand for?
|
Adenosine Triphosphate
|
|
|
How do substances move in and out of membranes?
|
Through diffusion
|
|
|
What is diffusion?
|
The net movement of a substance from a region of high concentration to a region of low concentration, and involves random movement of molecules.
|
|
|
Can particles move against the concentration gradient in normal diffusion?
|
Yes, but only a very small percentage of particles
|
|
|
What factors affect the rate of diffusion? (3)
|
long/short distance for substance to travel
greater/lower concentration gradient Large/small surface area |
|
|
What is facilitated diffusion?
|
Diffusion that assists larger/polar molecules to pass through the membrane by using proteins
|
|
|
What are the two types of proteins used with facilitated diffusion? (2)
|
Channel Protein
Carrier Protein |
|
|
What type of molecules are carried by carrier proteins
|
Larger molecules
|
|
|
How are large molecules transported by carrier proteins?
|
Molecule attaches to a specific carrier protein
The carrier protein reacts and changes shape to move the molecule |
|
|
What type of molecules are carried by channel proteins? (2)
|
Ions
Small polar molecules |
|
|
What is active transport?
|
When the cell needs to move a chemical against the concentration gradient and energy has to be used
|
|
|
What is a respiratory inhibitor?
|
Chemicals that stop active transport, which prevents ATP synthesis for respiration
|
|
|
What is osmosis?
|
The net movement of water molecules from an area of high water potential to an area of low water potential down the water potential gradient across a partially permeable membrane
|
|
|
Does a concentrated solution have more or less water molecules?
|
Less water molecules
|
|
|
What does the term 'partially permeable' mean?
|
It lets some substances through but prevents the movement of others
|
|
|
Define water potential
|
A measure of the relative tendency of water to move from one area to another
|
|
|
What term is used to describe animals cells bursting when it comes to osmosis?
|
Crenation
|
|
|
What term is used to describe plant cells changing due to osmosis? (3)
|
Turgor
Flaccid Plasmolysis |
|
|
What is crenation?
|
When water potential outside is lower than water potential inside, so the cell shrivels
|
|
|
What happens when water potential outside is higher than water potential inside an animal cell?
|
The cell bursts
|
|
|
What is plasmolysis?
|
The shrinking of cytoplasm away from the cell wall of a plant cell when water is lost due to osmosis, resulting in space between the cell wall and cell membrane
|
|
|
When is an animal cell stable?
|
When water potential outside is equal to inside
|
|
|
When does a plant cell become turgid?
|
When water potential is higher outside the cell than inside the cell
|
|
|
Define hypotonic
|
When water potential is higher than cell
|
|
|
Define hypertonic
|
When water potential is lower than cell
|
|
|
Define isotonic
|
When water potential is same as cell
|
|
|
When does a plant cell become flaccid?
|
When it is neither turgid, nor plasmolysed
|
|
|
Why do plant cells want to be turgid?
|
For support in non-woody plants so they don't wilt
|
|
|
What happens when a plant cell is immersed in sucrose solution? [Exam question template] (8)
|
Higher water potential inside than outside the cell in the sucrose solution
Water will move down the water potential gradient From inside to outside the cell Across a partially permeable cell/tonoplast phospholipid membrane Via Osmosis This will cause volume of water in cytoplasm and vacuole to decrease Cell membrane will start to pull away from the cell wall Therefore it will become plasmolysed |
|
|
What are the forms of bulk transport (2)?
|
Endocytosis
Exocytosis |
|
|
What is endocytosis?
|
The process by which cells absorb molecules by engulfing them
|
|
|
What are the two forms of endocytosis?
|
Phagpcytosis
Pinocytosis |
|
|
What is pinocytosis used for?
|
Taking in small particles and fluids
|
|
|
Explain the process of pinocytosis (3)
|
Plasma membrane invaginates inwards
Membranes fuse around the molecule Small vesicle is formed |
|
|
What is phagocytosis used for?
|
Larger particles
|
|
|
Explain the process of phagocytosis (2)
|
Pseudopodia extend from the cell and wrap themselves around a larger particle
Membranes fuse to form a vesicle |
|
|
What is a phagosome?
|
A vesicle formed around a particle absorbed by phagocytosis
|
|
|
What is exocytosis?
|
The manner in which substances are secreted and egested from a cell
|
|
|
Exocytosis is like the reverse process of __________________
|
Pinocytosis
|
|
|
What is mitosis?
|
The type of cell division used for growth and repair
|
|
|
What are the uses of mitosis?
|
Growth
Replacement of old cells Replacement of damaged tissue Asexual reproduction |
|
|
What is meiosis?
|
The formation of gametes in sexual reproduction
|
|
|
What is differentiation?
|
The process by which a cell develops to become more distinct in form and function
|
|
|
What is a zygote?
|
A diploid cell resulting from fusion of gametes
|
|
|
What is a gamete?
|
Sex cell
|
|
|
What are the male and female sex cells?
|
Sperm
Ovum |
|
|
How does a zygote develop into a baby?
|
By mitosis
|
|
|
What is the cell cycle?
|
The cycle of division, growth and maturity, and then another division
|
|
|
Why does the length of cell cycles vary in different types of cells?
|
Some cells are more specialized, so take longer to divide
|
|
|
Why are red blood cells unable to divide?
|
They lose their nucleus over the course of development
|
|
|
What cells other than red blood cells can't divide?
|
Highly specialized cells such as muscle cells
|
|
|
What are the phases/checkpoints of the cell cycle? (4)
|
G1
S phase G2 M phase |
|
|
What happens during the G1 phase? (2)
|
Chromosomes are checked for damage
If damage is detected, cell does not proceed into S phase until damage is repaired |
|
|
What happens during the S phase? (2)
|
A check is made that all the chromosomes have replicated
If not, the cell cycle is stopped |
|
|
What happens during the G2 phase? (2)
|
Another check is made for DNA damage that may have occurred during replication
If damage exists, cell cycle is stopped until damage is repaired |
|
|
What happens during the M phase (metaphase)?
|
A check ensures that the chromosomes have correctly attached to the spindle fibres before anaphase proceeds
|
|
|
What is interphase?
|
The parts of the cell cycle when mitosis is not occurring
|
|
|
What occurs during interphase?
|
DNA replicates
Transcription of mRNA Chromatin becomes chromosomes |
|
|
What are haploid cells?
|
Cells that have only half the number of chromosomes
|
|
|
What are diploid cells?
|
Cells that have the complete set of necessary chromosomes
|
|
|
What does diploid number mean?
|
Number of chromosomes in a given cell
|
|
|
How do you calculate the haploid number?
|
Half the diploid number
|
|
|
What is the human diploid number?
|
46
|
|
|
What is the human haploid number?
|
23
|
|
|
What are the five stages in mitosis?
|
Prophase
Metaphase Anaphase Telophase Cytokinesis |
|
|
LEARN PICTURES OF MITOSIS FOR PLANTS AND ANIMALS
|
LEARN PICTURES OF MITOSIS FOR PLANTS AND ANIMALS
|
|
|
What happens during early prophase? (5)
|
Chromosomes condense
Chromosomes coil Chromosomes shorten AND thicken Chromosomes become visible Consist of two chromatids joined by a centromere |
|
|
What happens during late prophase? (4)
|
Chromosomes condense more
Centrioles move to opposite poles Nucleolus continues to shrink and disappears Nuclear envelope disintegrates |
|
|
What happens during metaphase? (2)
|
Chromosomes align at equator
They are attached to the spindle by their centromeres |
|
|
What is a centromere?
|
the region of a chromosome to which the spindle attaches, via the kinetochore, during cell division
|
|
|
What is the kinetochore?
|
A complex of proteins associated with the centromere of a chromosome during cell division, to which the spindle attaches.
|
|
|
What are spindle fibres made of?
|
Microtubules
|
|
|
What happens during anaphase? (3)
|
Centromere splits
Chromatids separate Move to opposite poles by contraction of spindle |
|
|
What is the difference between chromosomes and chromatids?
|
A chromosome consists of two sister chromatids
|
|
|
What happens during telophase?
|
Chromosomes uncoil
|
|
|
What happens during cytokinesis? (4)
|
Cytoplasm near equator invaginates
Cytoplasm splits Organelles are shared between the two cells Golgi apparatus produces vesicles to form new sections of plasma membrane |
|
|
Describe the products of mitotic cell division (3)
|
DNA is identical in both cells
DNA is identical to parent cells Two seperate cells formed |
|
|
What are the differences in plant mitosis?
|
Centrioles don't exist (but spindles exist)
Golgi apparatus produces vesicles to form new sections of cell wall as well |
|
|
What is asexual reproduction?
|
Reproduction which involves the production of offspring from a single individual
|
|
|
Give an example of an organism that reproduces asexually
|
Fungus
|
|
|
What are stem cells
|
Undifferentiated cells
|
|
|
What are erythrocytes?
|
Red blood cells
|
|
|
What is the function of erythrocytes?
|
Transport oxygen around the body
|
|
|
How are erythrocytes formed?
|
They are formed from stem cells in the bone marrow
|
|
|
Why do erythrocytes have to be made from stem cells?
|
They have no nucleus so cannot divide
|
|
|
What is the process of making erythrocytes called?
|
Erythropoiesis
|
|
|
Describe the stages of erythropoisis (5)
|
Stem cell is multipotent, so divides to form proerythrocytes
Changes have occurred and this cell can now only form an erythrocyte Haemoglobin builds up in the cytoplasm Nucleus is ejected Further changes form a mature erythrocyte |
|
|
What does multipotent mean?
|
Capable of forming a number of different types of body cells
|
|
|
What is haemoglobin?
|
Oxygen-carrying pigment of red blood cells
|
|
|
What is the shape of an erythrocyte and what is the function of it's shape? (2)
|
Biconcave disc
Provides a large surface area to volume ratio due to double indentation which allows more oxygen to diffuse through the surface |
|
|
Why doesn't an erythrocyte have a nucleus (and other organelles)?
|
Allows more mitochondria to be packed into the cytoplasm, so more oxygen can be carried
|
|
|
What is the function of haemoglobin? (2)
|
Binds with oxygen
Releases oxygen when O2 concentrations are low |
|
|
Why do erythrocytes have elastic membranes?
|
So they can squeeze through narrow capillaries
|
|
|
What are neutrophils?
|
A type of white blood cell
|
|
|
How are neutrophils made?
|
Same way as red blood cells, formed by stem cells
|
|
|
What changes do stem cells undergo to become neutrophils?
|
Nucleus gains indentations
Accumulation of lysosomes containing hydrolytic enzymes |
|
|
What are hydrolytic enzymes?
|
Digestive enzymes
|
|
|
What are the features of neutrophils?
|
Flexible shape
Contains lysosomes with hydrolytic enzymes Nuclear membrane is more flexible than normal |
|
|
What is the use of neutrophils having a flexible shape?
|
Allows them to penetrate between the junctions of the cells of the capillary wall and form pseudopodia to engulf microorganisms
|
|
|
What are pseudopodia?
|
Projections of the cytoplasm
|
|
|
What is the use of neutrophils having digestive enzymes?
|
To engulf and destroy invading cells
|
|
|
What is the process of engulfing known as?
|
Phagocytosis
|
|
|
What is the use of neutrophils having a more flexible membrane
|
Helps cell squeeze through tiny gaps between capillary cells
|
|
|
What are meristematic cells?
|
Plant stem cells (undifferentiated cells) that exist in the meristematic tissue (meristem)
|
|
|
What is the cambium?
|
Meristem between xylem and phloem cells
|
|
|
How does the cambium produce xylem and phloem?
|
Divides by mitosis and differentiates
To form phloem cells on the outside To form xylem cells on the inside |
|
|
The production of xylem and phloem from cambium cells is stimulated by ______________
|
hormones
|
|
|
What are hormones?
|
An organic substance produced on one part of an organism and transported to other parts, where it has specific effects
|
|
|
What happens to meristematic cells when they differentiate to become xylem? (2)
|
Lose their cytoplasm
Cell walls may be lost |
|
|
What happens to meristematic cells when they differentiate to become phloem? (2)
|
Some loss of cytoplasm and organelles
Sieve plates develop at the ends of cells |
|
|
What are the features and uses of a sperm cell? (4)
|
Flagellum - provides propulsion
Spiral mitochondira - provides energy for movement Reduced cytoplasm - reduce mass for swimming Acrosome contains enzymes - to penetrate egg cell |
|
|
What are the features and uses of root hair cells? (3)
|
Long projection from cell
-penetrates between soil particles to reach more water -Increases surface area to volume ratio for more diffusion of water molecules |
|
|
Where are root hair cells found?
|
Just behind the root tip where they are continually being formed
|
|
|
What part of the root does mitosis occur (unspecialised cells)
|
At the root cap/tip
|
|
|
What are the features and uses of a leaf palisade cell? (2)
|
Many chloroplasts - absorb as much light as possible for photosynthesis
Cell is tall and thin - Allows light to penetrate further |
|
|
What are the features and uses of a guard cell?
|
Inner cell wall is thicker than outer one - causes stoma to open when cell is turgid
Contain chloroplasts which may assist in stomatal opening |
|
|
What are the three types of stem cells?
|
Totipotent
Pluripotent Multipotent |
|
|
What are totipotent stem cells?
|
Cells that can differentiate into any type of body cell
|
|
|
Where are totipotent stem cells found?
|
In the zygote and early embryo
|
|
|
What are pluripotent stem cells?
|
Cells that can form any type of body cell but cannot form extra-embryonic cells
|
|
|
What are embryonic cells?
|
Cells that make up the placenta and umbilical cord
|
|
|
What are multipotent cells?
|
Stem cells that can form more than once cell type, but not all types
|
|
|
Where are multipotent stem cells found?
|
In the bone marrow etc.
|
|
|
Give examples of tissue (6)
|
Squamous epithelium
Ciliated epithelium Cartilage Muscle Xylem Phloem |
|
|
What is epithelium?
|
A sheet of cells that forms an outer layer
|
|
|
What is squamous epithelium? (2)
|
A type of epithelium that consists of a layer of flattened cells
Lies on the basement membrane |
|
|
What is the basement membrane?
|
A thin, delicate membrane of protein fibres and polysaccharides separating an epithelium from underlying tissue
|
|
|
Why is squamous epithelium thin?
|
To provide a short diffusion path
|
|
|
What is ciliated epithelium?
|
Epithelium made up of cells with a lot of cilia on their surfaces
|
|
|
What is the use of ciliated epithelium? (2)
|
Used when something needs to be moved across the surface
The movement of the cilia shifts material along the surface of the epithelium |
|
|
What is the function of cartilage?
|
A type of connective tissue that supports tissue in the nose, ear, joints etc.
|
|
|
What is connective tissue?
|
A tissue that connects, supports, binds or separates other tissues or organs
|
|
|
Describe cartilage (2)
|
Consists of collagen fibres which stiffens and strengths the tissue
Contains elastin fibres which give it flexibility |
|
|
What is the function of muscle?
|
Move parts of the body
|
|
|
What are the three types of muscle?
|
Skeletal (voluntary)
Smooth (involuntary) Cardiac (only found in heart) |
|
|
What is special about skeletal muscles?
|
Highly specialised and multi-nucleate
|
|
|
What is another word for skeletal muscles?
|
Muscle fibres
|
|
|
What is a fascicle?
|
A group of fibres
|
|
|
What are myofibrils made of? (2)
|
Myofilaments called actin
And myosin |
|
|
What is the function of xylem?
|
Plant tissue that transports water and minerals up the plant stem and also strengthens it
|
|
|
What are the four parts of a xylem cell? (4)
|
Vessel elements
Tracheids Fibres Parenchyma |
|
|
What is the use of parenchyma cells?
|
Forms a packing tissue between other cells
|
|
|
What is the use of vessel elements?
|
Main water-transporting cells
|
|
|
What are the features of vessel elements? (3)
|
Wide lumen
Perforated end walls Contains pits to prevent blockages |
|
|
What is the function of phloem?
|
Transports organic nutrients up and down the plant
|
|
|
What is the use of tracheids? (2)
|
Transport water
In angiosperms, used as strengthening tissue |
|
|
What is an angiosperm?
|
A large group of plants that have flowers and produce seeds
|
|
|
What are the features of tracheids?
|
Thinner lumen than vessels
Has perforated end walls Has pits to prevent blockages |
|
|
How do the pits prevent blockages?
|
They help the water move laterally
|
|
|
Why are the vessel, tracheids and fibres thickened with lignin?
|
Strengthens walls, allows the cell to support
|
|
|
Why are xylem cells dead and missing a cytoplasm?
|
Unnecessary for strengthening and would obstruct water transport
|
|
|
What is the role of phloem?
|
Transports organic nutrients up and down the plant
|
|
|
What are three parts of a phloem cell?
|
Sieve tube elements
Companion cells Parenchyma |
|
|
What is the role of the sieve tube elements?
|
Transport nutrients
|
|
|
What is the structure of the sieve tube elements?
|
Reduced cytoplasm
Few organelles End walls form sieve plates |
|
|
Why do sieve tube elements have reduced cytoplasm?
|
To allow for more transport space
|
|
|
Why do sieve tube elements have sieve plates at the end?
|
To connect cytoplasms of adjacent sieve tube elements
|
|
|
What is the role of companion cells? (2)
|
Supports the sieve elements
May also play a role in transporting nutrients in the phloem |
|
|
What is an allele?
|
A type of version of a gene for a given characteristic
|
|
|
What is a homologous pair?
|
Two chromosomes with the same sequence of genes on them
|
|
|
Why is it easy to pair up homologous chromosomes?
|
They have similar staining properties because they have the sane basic structure
|
|
|
What homologous pair is an exception when pairing?
|
X and Y chromosomes have different structures but still are pairs
|
|
|
List the stages of meiosis (10)
|
Prophase I
Metaphase I Anaphase I Telophase I Cytokinesis I Prophase II Metaphase II Anaphase II Telophase II Cytokinesis II |
|
|
What is the stage before mitosis but is not part of mitosis?
|
Interphase
|
|
|
What happens during Prophase I? (5)
|
Chromosomes condense, become shorter, thiccer and visible in the light microscope
Synapsis of homologous chromosomes to become bivalents Chiasmata form to hold chromosomes together crossing over takes place Nuclear membrane breaks up into small sacs of membrane which become endoplasmic reticulum Centrioles replicate, move to opposite poles and form spindle fibres |
|
|
What is synapsis?
|
When two homologous chromosomes come together
|
|
|
What is chiasmata?
|
The places where chromatids cross over
|
|
|
What happens during Metaphase I? (3)
|
Bivalents move to the equatorial (or metaphase) plate across the centre of the cell
Independent orientation occurs in paternal and maternal chromosomes in each bivalent Microtubules attach to the centromere of each chromosome |
|
|
What is independent orientation?
|
When the chromosomes line up in different ways (eg. two paternals on the right, or one paternal on the right and one on the left)
|
|
|
How many independent orientations are there in humans?
|
2^23
|
|
|
What happens during anaphase I?
|
Chromosomes (each with two chromatids) are pulled by shortening of microtubules towards the poles
|
|
|
What is the difference between anaphase I and anaphase in mitosis?
|
In mitosis, chromatids are pulled, whereas in meiosis, chromosomes (two chromatids) are pulled
|
|
|
What happens during telophase I? (2)
|
Chromosomes reach opposite poles
Nuclear membrane reforms to make two daughter haploid nuclei |
|
|
What are haploid nuclei?
|
Nuclei that have half the number of chromosomes of the parent cell
|
|
|
What happens during cytokinesis I?
|
The cell surface membrane pinches in leaving small cytoplasmic bridges between the cells
|
|
|
What occurs between meiosis I and meiosis II?
|
Interphase II where chromosomes uncoil
|
|
|
What happens during prophase II? (2)
|
Centrioles replicate and move to poles that are perpendicular to those in meiosis I
Nuclear membrane breaks up |
|
|
What happens during metaphase II? (2)
|
Individual chromosomes align on the equator with their chromatids independently/randomly assorted
Microtubules attach to the centromeres |
|
|
What happens during anaphase II?
|
Sister chromatids break apart at the centromere and move to opposite poles
|
|
|
What happens during telophase II? (2)
|
Nuclear membranes reform
Cells divide to give four haploid cells that are genetically different to one another and from the parent cells |
|
|
What is an advantage of sexually reproducing using gametes produced by meiosis?
|
Genetic variation is produced
|
|
|
What is aerobic respiration?
|
Process that requires oxygen and releases CO2 as a waste product
|
|
|
What is breathing?
|
Taking air into the body, exchanging gases and then expelling the air again
|
|
|
Do fish/plants breathe? If not, what do they do?
|
No, they ventilate
|
|
|
Why do humans need an extensive ventilation system?
|
They are a complex and large organism, so tend to be more active so have increased metabolic energy so require a sophisticated ventilation system
|
|
|
What are the factors affecting diffusion of gases? (6)
|
Surface area: volume ratio
Thin gas exchange surface Good blood supply Ventilation mechanism Surface is moist |
|
|
What is the thickness of alveolar walls?
|
One cell thick (simple squamous epithelium)
|
|
|
Why do the lungs need a good blood supply?
|
To make gas exchange quicker and maintain the concentration gradient of both gases
|
|
|
Why do the lungs need to be ventilated?
|
To maintain the gas concentration gradient by constantly breathing in oxygen and breathing out CO2
|
|
|
Why do the lungs need to be moist?
|
Oxygen and CO2 can only get through the membranes in solution
|
|
|
What is the gas exchange surface in mammals?
|
Alveoli
|
|
|
Give the order of the pathway from mouth/nose to alveoli
|
Mouth/nose > Trachea > Two bronchi > bronchioles > alveoli
|
|
|
What are the alveoli?
|
A group of air sacs with an extensive capillary network
|
|
|
What is the trachea?
|
The widest tube in the gas exchange system
|
|
|
Why does the trachea not have thin walls?
|
It is not involved in gas exchange so doesn't require a thin diffusion distance
|
|
|
What lies behind the trachea?
|
The oesophagus
|
|
|
What are the bronchi?
|
A pair of rubes connected to the trachea with bronchioles on the end
|
|
|
Why are there 2 bronchi?
|
One connects to each lung
|
|
|
What are the bronchioles?
|
Small tubes at the end of the bronchi, which branch into alveoli
|
|
|
Where are the lungs situated? (2)
|
In the thoraic cavity
Protected by the rib cage |
|
|
What are intercostal muscles?
|
Muscles between the ribs which move the rib cage during breathing
|
|
|
What is the pleural membrane?
|
Double membrane that surrounds the lungs
|
|
|
What is between the pleural membranes?
|
Pleural cavity
|
|
|
What is in the pleural cavity?
|
Fluid
|
|
|
What is the job of the pleural cavity fluid?
|
Provides lubrication between lungs and the rib cage
|
|
|
What is the diaphragm?
|
A sheet of muscle at the base of the thoracic cavity
|
|
|
What is cartilage?
|
A form of connective tissue that provides strengthening and support
|
|
|
What are the similarities and differences between cartilage and bone? (2)
|
Both cartilage and bone are resistant to tension and compression
Cartilage however is more flexible |
|
|
What is the function of the cartilage in a gas exchange system?
|
To keep the larger tubes open
|
|
|
What are the three "larger tubes"?
|
Trachea
Bronchi Larger bronchioles |
|
|
Why do the larger tubes require cartilage to support them?
|
They would otherwise collapse
|
|
|
What is special of cartilage supporting the trachea and bronchi?
|
They form rings around the tube to act as a scaffolding
The trachea cartilage is C-shaped to avoid obstructing the oesophagus |
|
|
What is epithelium?
|
A layer of cells that forms a covering
|
|
|
What is ciliated epithelium?
|
Epithelium that contains cilia and is coated with mucus
|
|
|
What is the function of the mucus on the ciliated epithelium?
|
Traps dust and bacteria that enter the lungs via the air
|
|
|
What is the function of the cilia on the ciliated epithelium?
|
Beats constantly to move the mucus on its surface and dispose it
|
|
|
What are goblet cells?
|
Cells that produce the mucus that line the trachea/bronchi
|
|
|
Why don't bronchioles have mucus?
|
They are deep in the lungs so most bacterial/particles probably have already been removed
|
|
|
What is the purpose of smooth muscle in the lungs?
|
Allows expansion in conditions when extra oxygen is needed (eg. excercise)
|
|
|
What parts of the lung contain smooth muscle? (3)
|
Trachea, bronchi and larger bronchioles
|
|
|
What is the purpose of elastic fibres in the lungs?
|
Causes the lungs to "recoil" during expiration which expels air quicker and more efficiently
|
|
|
What parts of the lung have elastic fibres?
|
All parts of the lung
|
|
|
Explain the process of inspiration (5)
|
External intercostal muscles contract, raising rib cage
Diaphragm contracts and flattens Volume of thoraic cavity increases and pressure is decreased to a level below the atmospheric pressure Air is drawn into gas exchange system Lungs expand due to reduced pressure on them |
|
|
Explain the process of expiration (5)
|
External intercostal muscles relax, lowering rib cage
Diaphragm relaxes and moves outwards and up The volume of the thoraic cavity decreases and pressure is increased to a level above the atmospheric pressure Lungs recoil due to their elasticity and increased pressure on them Air is pushed out of gas exchange system |
|
|
What is a spirometer?
|
A device used to measure breathing rates
|
|
|
What are the parts of a spirometer? (5)
|
Mouth piece
Nose piece Chamber lid Counter weight Soda lime |
|
|
What is the purpose of the mouth and nose piece? (2)
|
Person puts mouthpiece into mouth and breath normally
Nose piece disallows people to breath through their nose |
|
|
How and when does the chamber lid rise and fall? (2)
|
As they breath in, chamber lid will fall
As they breath out, chamber lid will rise |
|
|
What is the purpose of the counter weight?
|
Make sure there's no resistance when breathing out
|
|
|
What is the purpose of the soda lime?
|
Acts as a CO2 absorber to absorb any CO2 when exhaling
|
|
|
Why is the CO2 absorber essential?
|
It is a closed system, so leaving CO2 in the breathing container may be dangerous
|
|
|
Why does the spirometer trace keep going down? (2)
|
CO2 is absorbed by the absorber. so any gas exhaled is lost
Therefore the overall volume of gas (oxygen) in the container keeps decreasing, so the spirometer trace also decreases |
|
|
What are the four thing a spirometer can measure?
|
Vital capacity
Tidal Volume Breathing Rate Oxygen uptake |
|
|
What is vital capacity?
|
The maximum volume of air that can be breathed our in a single breath
|
|
|
What is tidal volume?
|
The volume of air that is normally breathed in or out at rest
|
|
|
What is breathing rate?
|
The number of breaths per minute
|
|
|
What is a single breath?
|
Taking air in and breathing it out
|
|
|
What is oxygen uptake?
|
The amount of oxygen consumed by the subject
|
|
|
What is the tidal volume of a spirometer trace?
|
The normal up and down curve of breathing
|
|
|
What is the vital capacity on a spirometer trace?
|
The size of the wave when a deep breath is taken
|
|
|
What is the formula for total lung capacity?
|
Vital capacity + Total lung capacity
|
|
|
What is residual volume?
|
Small amount of air that is left over in the lungs during expiration
|
|
|
How do you calculate breathing rate?
|
Count number of breaths (up and down) in a given time (minutes)
|
|
|
Why do breaths get deeper as the spirometer readings continue?
|
The concentration of oxygen in the tank has dropped, so larger breaths are needed to get more oxygen
|
|
|
What are the two types of fish?
|
Cartilage fish
Bony fish |
|
|
What are the exchange organs of bony fish?
|
Gills
|
|
|
How is the surface area of gills increased?
|
Split into many divisions (gill filaments)
Split into further divisions (gill lamellae) |
|
|
How are the lamellae specialised for exchange? (2)
|
Well supplied with blood vessels
Very thin |
|
|
What is the buccal cavity?
|
Space in the fish's mouth
|
|
|
What is the gill cavity?
|
Space containing gills
|
|
|
What is the operculum?
|
A flap of tissue that covers the gills in bony fish
|
|
|
Explain the process of gill ventilation (9)
|
Fish lowers buccal cavity
Operculum shuts Volume of cavity increases Pressure in cavity decreases Water flows into buccal cavity Fish raises buccal cavity Increased pressure pushes water into gill cavity Pressure now builds up in gill cavity This opens the operculum and forces water out |
|
|
What is counter current flow?
|
When the blood flows in the opposite direction to the water, so the concentration gradient is maintained anywhere along the lamella
|
|
|
What is concurrent flow (used in cartilage fish)?
|
When blood flows through the gills in the same direction as water does
|
|
|
What is the problem with concurrent flow?
|
Concentration gradient is not maintained throughout the lamella as it reaches equilibrium half way through
|
|
|
How does gas exchange occur in insects?
|
Air containing oxygen is directly delivered to all tissues via the trachae
|
|
|
What are the trachae?
|
A series of tubes
|
|
|
What are spiracles?
|
Holes in the abdomen
|
|
|
What are tracheoles?
|
Smaller tubes
|
|
|
The walls of the trachae are thickened by rings of _________
|
chitin
|
|
|
What is the job of the chitin?
|
Keeps the trachae open and supports it
|
|
|
Explain the ventilation process in insects (4)
|
Insect makes pumping movements with thorax
When body expands, air is sucked into spiracles into trachae Air passes down trachaeoles into trachael fluid Fluid allows CO2 and O2 to exchange into and from tissues |
|
|
Why do multicellular animals require transport systems?
|
Because they have a high demand for oxygen and nutrients
|
|
|
What are the factors affecting rate of diffusion? (4)
|
Distance to travel
Time taken to travel Surface area:volume ratio Steepness of concentration gradient |
|
|
Why do animals have circulatory systems?
|
To carry oxygen, nutrients and waste
|
|
|
What are the four types of circulatory systems?
|
Single circulatory system
Double circulatory system Open circulatory system Closed circulatory system |
|
|
Give an example of an animal with a single circulatory system
|
Fish
|
|
|
Give an example of an animal with a double circulatory system
|
Human
|
|
|
Explain how a single circulatory system in a fish works (5)
|
The blood goes through the heart once in one circuit of the body
Deoxygenated blood is pumped by the heart to the gills Blood absorbs O2 and excretes CO2 Oxygenated blood is pumped by the heart to the systematic capillaries where blood is supplied to the organs Deoxygenated blood flows back to the heart and one circuit is completed |
|
|
Explain how a double circulatory system works in humans (4)
|
The blood goes through the heart twice in one circuit of the body
Blood leaving the RHS heart travels to lungs to be oxygenated Oxygenated blood returns to LHS heart Blood is pumped to organs via systematic capillaries Deoxygenated blood returns to RHS heart and one circuit is completed |
|
|
How many chambers does the human heart have?
|
4
|
|
|
What are the four chambers of the heart called (in order of blood flow)?
|
Right ventricle
Left atrium Left ventricle Right atrium |
|
|
What is the advantage of double circulation? (6)
|
Requires less capillary networks as blood immediately travels back to heart after passing through an organ
Therefore system maintains higher blood pressure Higher average speed of flow Helps maintain steeper concentration gradient Increases rate of diffusion Makes exchange of materials more efficient |
|
|
What is an open circulatory system?
|
When blood is not always confined within blood vessels, but also enters the body cavity
|
|
|
What is a closed circulatory system?
|
When blood is confined within blood vessels
|
|
|
What animals have an open circulatory system?
|
Arthropods (insects)
|
|
|
What are the three types of blood vessels?
|
Arteries
Capillaries Veins |
|
|
What animals have a closed circulatory system?
|
Mammals
|
|
|
What is the name for the main blood vessel of insects?
|
Dorsal vessel
|
|
|
What is blood called in insects?
|
Haemolymph
|
|
|
What is the haemocyl?
|
The body cavity
|
|
|
What is the name of an insect heart?
|
Tubular heart
|
|
|
What is the role of the tubular heart?
|
Pump haemolymph an dbathe organs
|
|
|
How does haemolymph re-enter the heart?
|
Through one way valves called ostia when the heart relaxes
|
|
|
What is the human heart?
|
A muscular organ that pumps blood around the body in regular circumstances
|
|
|
What is the function of arteries?
|
Carry blood at high pressure to the tissues
|
|
|
What is the innermost layer called (lining the lumen)?
|
Tunica intima
|
|
|
What is the lumen?
|
The hole
|
|
|
Describe the tunica intima in arteries (3)
|
Endothelium is one cell thick
Consists of collagen fibres and connective tissue Smooth muscle with reduces friction |
|
|
What is the second closest layer to the lumen called?
|
Tunica media
|
|
|
Describe tunica media in arteries (3)
|
Much thicker in arteries than veins
Smooth muscle cells Elastic tissue |
|
|
What is the role of muscle cells in artery tunica media? (2)
|
Strengthens artery so resists high pressures
Can contract to control blood flow |
|
|
What is the role of elastic tissue in artery tunica media? (3)
|
Elastic tissue stretches when pressure is high
Pressure is lowered slightly Fluctuations of stretching and recoil even out |
|
|
What is the outermost layer of the artery?
|
Tunica adventitia
|
|
|
Describe structure and role of the tunica adventitia of an artery (2)
|
Consists of protein collagen
Tough material that prevents the blood vessel from over-stretching to prevent damage |
|
|
What is an arteriole?
|
Smaller, branched arteries that lead into capillaries
|
|
|
What is the function of arterioles?
|
Regulate blood flow
|
|
|
Describe arterioles (2)
|
Similar structure to arteries
Greater proportion of smooth muscle and less elastic tissue |
|
|
Why do arterioles have less elastic tissue?
|
They don't have to withstand as high pressures as arteries
|
|
|
What exists at the junction of arterioles and capillaries?
|
Pre-capillary sphincters
|
|
|
What is the role of the sphincters?
|
They can contract and prevent blood flowing into a certain capillary bed if necessary
|
|
|
What is the role of capillaries?
|
Exchange materials with the cells
|
|
|
Describe the structure of lumen
|
Small lumen (big enough to let 1 erythrocyte pass)
One cell thick walls |
|
|
Why do capillaries have tiny lumens?
|
Causes friction with blood
Slows blood and reduces pressure |
|
|
What is a venule?
|
Smaller veins that are connected to capillaries
|
|
|
What are the differences between veins and venules? (2)
|
Smaller (some only consist of endothelium)
Few or no elastic fibres |
|
|
What is the function of veins?
|
Return blood from the heart
|
|
|
Describe the structure of a vein (4)
|
Large lumen
Thin tunica media Tunica adventitia relatively thicker than in arteries Valves along their length |
|
|
Why do veins have a large lumen?
|
No pulse
Therefore rate of flow is slower So lumen is larger to carry more blood To make sure blood is transferred at same rate as arteries |
|
|
Why do veins have less elastic tissue?
|
Low pressure
|
|
|
Why do veins have valves?
|
To ensure one-way flow towards the heart
|
|
|
Why are valves not necessary in arteries?
|
The pulse (pressure) pushes the blood in the right direction
|
|
|
How is blood pushed along in the veins if there is no pulse? (2)
|
When muscles around the vein contract during their normal activity, the vein doesn't resist so blood is pushed along
Valves prevent backflow so overall blood moves forward |
|
|
List the certain features of arteries in order (6):
Direction of flow Blood pressure Pulse Thickness of tunica media Size of lumen Valves |
Away from heart
High Present Thick Narrow Absent |
|
|
List the certain features of veins in order (6):
Direction of flow Blood pressure Pulse Thickness of tunica media Size of lumen Valves |
Towards heart
Low Absent Thin Wide Present |
|
|
What is tissue fluid?
|
Extracellular fluid which bathes the cells of most tissues, arriving via blood capillaries and being removed via the lymphatic vessels
|
|
|
What fluid returns excess tissue fluid to the blood?
|
Lymph
|
|
|
What are the components of blood?
|
Red blood cells (erythrocytes)
White blood cells (leukocytes) Platelets Plasma |
|
|
What is the role of erythrocytes? (3)
|
Transport oxygen
Play a role in transporting CO2 Transport carried out by red pigment haemoglobi |
|
|
What is the role of leukocytes?
|
Different types of white blood cell play different roles in the immune system
|
|
|
What is the role of platelets?
|
Cell fragments that are important in the clotting process
|
|
|
What is the role of plasma?
|
The liquid medium of the blood, which transports dissolved substances (including amino acids, sugars etc,)
|
|
|
What is tissue fluid formed by?
|
Plasma
|
|
|
What is the difference in composition between lymph and tissue fluid?
|
Lymph contains more white blood cells
|
|
|
Why does lymph have more white blood cells? (2)
|
White blood cells fight infections
Lymph goes to the lymph nodes to fight infection |
|
|
Describe composition of red blood cells in blood/tissue fluid/lymph (3)
|
yes/no/no
|
|
|
Describe composition of white blood cells in blood/tissue fluid/lymph (3)
|
many/few/many
|
|
|
Describe composition of proteins in blood/tissue fluid/lymph (3)
|
many/few/more than in tissue fluid (antibodies added)
|
|
|
Describe composition of dissolved solutes in blood/tissue fluid/lymph (3)
|
yes/yes/yes
|
|
|
Why are there no erythrocytes in tissue fluid but there are some proteins and white blood cells? (2)
|
Red blood cells are too large to pass through capillary walls
White blood cells and proteins can sometimes squeeze through capillary walls |
|
|
Why does lymph have more white blood cells and proteins?
|
Lymph is tissue fluid on the way back to the blood system
There are lymph nodes along the lymphatic system Lymph nodes contain lymphocytes Some of these lymphocytes along with antibodies are added to lymph |
|
|
What are lymphocytes?
|
A form of small leucocyte (white blood cell) with a single round nucleus, occurring especially in the lymphatic system.
|
|
|
What is the lymphatic system? (2)
|
Network of tissues and organs that help rid the body of waste materials.
Consists of lymph which contains infection fighting leukocytes |
|
|
What happens at the arterial end during formation of tissue fluid? (3)
|
Ultrafiltration occurs due to contraction of left ventricle
This plasma becomes tissue fluid Due to loss of plasma, water potential becomes less negative |
|
|
What is ultrafiltration?
|
When high hydrostatic pressyre forces plasma (containing nutrients/other substances) out of the capillary
|
|
|
What is NOT exerted during ultrafiltration? (2)
|
Blood cells
Large protein molecules |
|
|
Why are blood cells/large proteins not exerted?
|
They are too large to get through the gaps in the capillary walls
|
|
|
What is the special name for capillary walls?
|
Fenestrations
|
|
|
What nutrients/other substances exist in the plasma and how do they get out? (3)
|
Oxygen leaves red blood cells via diffusion
Glucose leaves via diffusion through fenestrations ions (Na+, Cl- leaves via diffusion through fenestrations) |
|
|
What happens to the oxygen in the tissue fluid?
|
Tissue fluid bathes mitochondria
Oxygen enters mitochondria via diffusion Respiration takes place CO2 reenters capillaries via diffusion |
|
|
What is hydrostatic pressure?
|
The pressure exerted by a fluid
|
|
|
Why is the blood in the arterial end have a very high hydrostatic pressure (2)
|
The left ventricle has contracted
The arterioles/capillaries are very narrow |
|
|
What happens at the veinous end during formation of tissue fluid? (3)
|
Tissue fluid is 95% reabsorbed at the veinous end along with waste products from respiration/urea
This is because the veinous end has low pressure and more negative water potential So tissue fluid reenters the capillaries via osmosis |
|
|
What is osmosis?
|
When water diffuses from a region of less negative (high) water potential to a region of more negative (low) water potential through the water potential gradient through a partially permeable membrane
|
|
|
Why does the veinous end have lower HP/lower water potential?
|
Proteins in the blood plasma exert an oncotic pressure
This means that overall, the osmotic potential is lowered on the veinous end |
|
|
What happens to the remaining 5% of tissue fluid?
|
Gets drained into lymphatic system
|
|
|
What is histamine?
|
A hormone that causes fenestrations to widen
|
|
|
What is the role of histamine?
|
Allows phagocytes to exit and enter capillaries easier
|
|
|
What is the side effect of histamine? (4)
|
Proteins are able to diffuse into the tissue fluid due to fenestrations widening
This lowers oncotic pressure Causes less tissue fluid to reenter the capillaries Therefore causes build up of tissue fluid resulting in swelling |
|
|
Where is the aorta?
|
The blood vessel which divides into three above the heart
|
|
|
What is the role of the aorta?
|
Carries oxygenated blood at high pressure to the body
|
|
|
Where is the pulmonary artery?
|
Below the aorta to the right
|
|
|
What is the role of the pulmonary artery?
|
Carries deoxygenated blood to the lungs
|
|
|
Where is the coronary artery?
|
Lines the outside of the heart
|
|
|
What is the role of the coronary artery?
|
Supplies oxygenated blood to the heart
|
|
|
What is the role of the coronary vein?
|
Returns deoxygenated blood
|
|
|
What are the valves between the atria and ventricles called?
|
Atrio-ventricular valves
|
|
|
What are the valves in the aorta/pulmonary vein called?
|
Semi-lunar valves
|
|
|
List the heart chambers in order of wall thickness
|
Left ventricle > Right ventricle > Left/Right Atrium
|
|
|
Why is the left ventricle thicker than the right ventricle? (2)
|
When the left ventricle contracts, it pumps blood to the rest of the body
Therefore requires more muscle |
|
|
What is the purpose of the valve tendons? (2)
|
Ventricles produce considerable pressure when they contract
Tendons attach ventricular valves to ventricle walls to prevent the valves from blowing inside out |
|
|
What is the septum?
|
The wall that separates the left and right ventricles
|
|
|
What is the name of the atrioventricular valve on the right?
|
Tricuspid valve
|
|
|
What is the name of the atrioventricular valve on the left?
|
Bicuspid valve
|
|
|
What is the cardiac cycle?
|
The process by which the heart beats and relaxes in a regular cycle
|
|
|
What is the contraction phase of the cardiac cycle called?
|
Systole
|
|
|
What is the relaxation phase of the cardiac cycle called?
|
Diastole
|
|
|
Give the steps of the cardiac cycle (19)
|
Dexoygenated blood enters right atrium via superior/inferior vena cava
Right atrium contracts Pressure in right atrium is greater than pressure in right ventricle, causing the tricuspid valves to open Blood is forced through into the right ventricle Pressure is greater in the right ventricle than in the right atrium, causing the tricuspid valves to close Right ventricle contracts Pressure in right ventricle is greater than pressure in pulmonary artery semi-lunar valve opens Blood enters pulmonary artery Pressure is greater in pulmonary artery that in right ventricle semi-lunar valve closes Deoxygenated blood travels to the lungs and right atrium relaxes Oxygenated blood fills into left atrium Mitral valve opens and blood flows into left ventricle Mitral valve closes Left ventricle contracts, forcing the aortic semi-lunar valve to open Oxygenated blood is sent all around the body Semi-lunar valve closes and left ventricle relaxes Both ventricles and both atrium contract at the same time |
|
|
The heart is myogenic. What does myogenic mean?
|
Cardiac muscles can contract without stimulation from outside nerves
|
|
|
What controls the contraction of the heart?
|
Autonomic nervous system
|
|
|
What is the autonomic nervous system? (2)
|
The part of the nervous system that controls involuntary activity
Consists of parasympathetic and sympathetic nervous systems |
|
|
What does the parasympathetic nervous system do?
|
Decreases the heart rate
|
|
|
What does the sympathetic nervous system do?
|
Increases the heart rate
|
|
|
What is the sino-atrial node?
|
A patch of specialised muscle tissue in the upper wall of the right atrium from which the heart beat originates
|
|
|
What is another word for the sino-atrial node?
|
Pacemaker
|
|
|
How does the pacemaker regulate contraction? (7)
|
Nodal tissue generates electrical impulses when it contracts
This sets off a wave of muscle contraction across both atria Impulse is passed to the atrio-ventricular node This node delays signal for a short time to allow atria to complete contraction Then sends impulse to ventricles Impulse travels down bundle of His to bottom of ventricles and then back up the Purkyne fibres This causes contraction as it moves up the walls of the ventricles |
|
|
How does the impulse not directly from the atria to the ventricles?
|
There is non conductive tissue between the atria and ventricles (apart from the AV node)
|
|
|
Why does the impulse not travel directly to the ventricles from the atria ventricular node?
|
It is best if the contraction of the ventricles starts from the bottom to the top
|
|
|
What is electrocardiography?
|
A process used to detect electrical heartbeat activity in muscle cells by placing electrodes on the skin to create an electrocardiogram
|
|
|
What are the 4 wave parts of an electrocardiogram
|
P wave
QRS complex T wave U wave |
|
|
What is the cause of the P wave
|
Caused by depolarisation of the atria
|
|
|
What does polarisation mean?
|
A state in which something has different properties in different directions
Eg. In nerves polarisation means electrical charges on either side of the membrane |
|
|
What does depolarisation mean?
|
Balancing or reversal (removal in essence) of electrical charges
|
|
|
What does repolarisation mean?
|
Restoration of electric charges
|
|
|
What is the cause of the QRS complex?
|
Ventricular depolarisation/contraction
|
|
|
What is the cause of the T wave?
|
Repolarisation of the ventricles (causing relaxation)
|
|
|
What is the cause of the U wave?
|
It is uncertain
|
|
|
What is tachycardia?
|
The heart is beating too rapidly
|
|
|
What is tachycardia bpm?
|
Over 100 when resting
|
|
|
What does the graph of tachycardia look like?
|
The peaks are too close together
|
|
|
What is bradycardia?
|
The heart is beating too slowly
|
|
|
What is bradycardia bpm?
|
Less than 60 bpm
|
|
|
What does the graph of bradycardia look like?
|
The peaks are too far apart
|
|
|
What is an ectopic heart beat?
|
When the heart beats too early followed by a pause
|
|
|
What is fibrillation?
|
When the heartbeat has lost its rhythm
|
|
|
Is ectopic heart beat or fibrillation harmful? (2)
|
Ectopic is rarely harmful
Severe fibrillation is very dangerous and can result in death |
|
|
What is the solubility of oxygen in water?
|
Low
|
|
|
Describe haemoglobin (3)
|
Protein with four polypeptide chains - two alpha two beta
Each chain had an iron containing haem group One oxygen molecule can bins to each of the four haem groups |
|
|
What is oxyhaemoglobin?
|
When oxygen is bound to haemoglobin
|
|
|
What is deoxyhaemoglobin?
|
When oxygen is not bound to it
|
|
|
How does haemoglobin change with partial pressure of oxygen?
|
Affinity for oxygen increases
|
|
|
What happens when one haem group absorbs oxygen? (2)
|
Structure of haemoglobin is altered so that it becomes easier to absorb a second molecule
This increased affinity continues with the second and the third molecules of O2 |
|
|
What is affinity?
|
A natural attraction
|
|
|
What is an oxygen dissociation curve?
|
A graph that shows the changing affinity for oxygen shown by haemoglobin at different partial pressures of O2
|
|
|
What is the shape of an oxygen dissociation curve?
|
Sigmoid (s shaped)
|
|
|
Why is an oxygen dissociation curve sigmoid shaped? (4)
|
Slow increase at start
Due to relative difficulty of absorbing first oxygen Steep increase afterwards Due to ease of absorbing second third and fourth molecule of O2 |
|
|
What does pO2 mean?
|
Partial pressure of oxygen
|
|
|
What is the approximate pO2 in respiratory tissue?
|
Between 2 and 3
|
|
|
Why is the pO2 of respiratory tissue low? (3)
|
Lower pO2 means lower saturation
Respiratory tissue need oxygen to respire Oxyhaemoglobin dissociates easier because affinity is lower |
|
|
What is the approximate pO2 in lungs?
|
12
|
|
|
Why is the pO2 of the lungs higher? (3)
|
Higher pO2 means higher affinity
This means higher saturation Oxygen uptake is maximised |
|
|
What does the bohr effect do to the graph?
|
Shifts the oxygen curve to the right
|
|
|
What is the bohr effect? (3)
|
In actively respiring tissues with high demand for oxygen, CO2 is produced
Increasing levels of CO2 lower the affinity of haemoglobin for oxygen This allows more oxygen to be released |
|
|
What is the partial pressure of the placenta compared to the PP in the lungs?
|
Much lower
|
|
|
What does the sigmoid curve of a fetus look like compared to adults?
|
It is shifted to the left
|
|
|
How is fetal haemoglobin different to adult haemoglobin? (2) |
Fetal haemoglobin has a higher affinity for oxygen than adult haemoglobin |
|
|
How does Fetal haemoglobin help it survive?
|
Since Fetal haemoglobin has a greater affinity than mother's haemoglobin, it is able to extract O2 from the mother's blood
|
|
|
What happens to the Fetal haemoglobin after first few months of birth?
|
It is replaced by adult haemoglobin
|
|
|
Why is fetal haemoglobin replaced?
|
It is replaced because the child has developed lungs so doesn't need fetal globin
|
|
|
What if fetal haemoglobin was not replaced?
|
Transfer of oxygen to cells would be slow as affinity is higher, so harder to get rid of the oxygen molecules
|
|
|
What are the three ways I'm which CO2 is transported?
|
Dissolved in plasma
Hydrogen carbonate ions Bound to haemoglobin |
|
|
How much CO2 is dissolved in the plasma?
|
5%
|
|
|
What is the formula for Hydrogen carbonate?
|
HCO3-
|
|
|
How much CO2 is transported as HCO3-?
|
70-90%
|
|
|
What complex is formed when CO2 binds to haemoglobin?
|
Carbaminohaemoglobin
|
|
|
How much CO2 is transported as carbaminohaemoglobin?
|
5-25%
|
|
|
Explain the process of the bohr shift in an erythrocyte (7)
|
CO2 diffuses into the red blood cell
CO2 is converted to carbonic acid, catalysed by the enzyme carbonic anhydrase Carbonic acid dissociates to form H+ and HCO3- ions Chloride shift occurs H+ ions combine with haemoglobin to form haemoglobinic acid This enhances O2 release (bohr shift) Acid becomes the substrate for carbaminohaemoglobin formation Acid also has a buffering effect, preventing H+ ions from lowering pH |
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Where does photosynthesis occur in plants?
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In the leaves
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Where is water/ions absorbed from the soil?
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In the roots
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Why do plants require a transport system?
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To transport water and ions to the leaves and nutrients to the roots, which may be a large distance
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What is photosynthesis?
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A chemical process used by plants and algae to make glucose and oxygen from carbon dioxide and water, using light energy.
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In what form is glucose transported in the plant?
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Sucrose
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What are the two seperate transport systems in plants?
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Xylem
Phloem |
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What are the plant structural adaptations that allow the stem to increase SA:volume ratio?
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Shoot is branched with thin flat leaves to increase SA
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Outline how the root system provides a large surface area for mineral ion and water uptake (4)
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Roots have large surface area to volume ratio
Branching increases surface area Root hairs increase surface area Cortex cell walls increase surface area |
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Why do plants not have a system for transporting Oxygen and CO2 unlike animals? (3)
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They have a very large surface area:volume ratio
Leaves have chloroplasts that can generate their own oxygen using CO2 Low metabolic rates of plant tissue, so low demand for respiration |
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What is a dicotyledenous plant?
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A flowering plant with two embryonic seed leaves (cotyledons), which usually emerge from the seed at germination
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What are the parts of a stem
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Look it up |
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What are the parts of a root
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Look it up |
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What are the parts of a leaf
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Look it up |
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LEARN BOTH DIAGRAMS AND MICROSCOPIC IMAGES OF XYLEM/PHLOEM IN ROOTS AND STEMS AND LEAVES
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LEARN BOTH DIAGRAMS AND MICROSCOPIC IMAGES OF XYLEM/PHLOEM IN ROOTS AND STEMS AND LEAVES
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What are the four types of xylem cells?
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Vessels
Tracheids Fibres Parenchyma |
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What is the most important type of xylem cell?
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The xylem vessel element
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Give the features of a xylem vessel element (5)
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End wall is lost/perforated
Cell is dead No cytoplasm Cell wall is thickened with lignin Has many pits |
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Why is the end wall in the xylem vessel lost/perforated?
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To allow free passage of water to the next cell
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Why is the xylem vessel dead and without a cytoplasm?
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Allows water to move through it more easily
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Why is the the xylem vessel thickened with lignin?
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Makes the xylem rigid and able to give support
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What is the pattern of lignin thickening?
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Rings, coils or strips
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What is the role of the pits in the xylem vessel?
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Allow water to move transversely (sideways) from cell to cell
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What are the two types of transport phloem?
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Sieve tube elements
Companion cells |
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What are the features of the sieve tube elements? (3)
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Alive
No nucleus Few organelles and little cytoplasm |
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How do the features of the sieve tube elements help the phloem?
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Lack of organelles aids transportation
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What is the role of the companion cell?
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Acts as a 'life support system', providing materials to the phloem cell and keeping it alive
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How is the companion cell attached to the sieve tube?
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Via plasmodesmata
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What is plasmodesmata?
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A microscopic channel through plant cell walls, connecting the cytoplasm of two cells
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Water moves from an area of _________ water potential to an area of __________ water potential (2)
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High
Low |
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What is transpiration?
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The evaporation of water
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How do water potential gradients help with transpiration? (2)
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Water potential in the leaf is greater than outside the leaf
So water vapour diffuses out of the leaf |
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How do solute potential gradients help with water absorption? (4)
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Solute concentration inside the root is higher than in the soil/outside
This is due to active transport of ions across the root Therefore water potential outside the root is higher than inside the root Water is absorbed by osmosis |
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How does water potential gradient help with transportation of water to the stem? (3)
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High water potential in root
Low water potential in stem So water travels up the stem down the water potential gradient |
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What is the water potential gradient?
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The gradient of water potential from high to low
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Give the order of locations of water transportation pathway (7)
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Soil > Root hair cells > Roots > Root cortex > Endodermis > Xylem > Stem
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What are the two water transportation pathways?
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Apoplastic pathway
Symplastic pathway |
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What is the apoplastic pathway? (2)
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Goes through cell walls which are readily permeable
Most of the water travels down this path |
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What is the apoplast (not pathway)? (2)
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The 'non living' extracellular space that surrounds the symplast
Consists of cell walls and spaces between the cells |
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What is the symplastic pathway?
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Goes through the cytoplasm and from cell to cell via the plasmodesmata
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What is the symplast (noth pathway)?
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A continuous network of interconnected plant cell protoplasts
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What is a protoplast?
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The cytoplasm of the cells, linked by plasmodesmata
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What is the problem with the apoplastic pathway?
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There is no opportunity to 'select' what comes into the plant, everything dissolved in the water is transported
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How is the problem with the apoplastic pathway solved?
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By the presence of the casparian strip in the walls of the endodermal cells
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Describe the casparian strip? (2)
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A continuous band that goes around the wall of the endodermal cells
Made of suberin |
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Describe suberin
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Waterproof, waxy substance
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What happens to the path of the water in the symplastic pathway? (4)
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Blocks the apoplast pathway
Forces water to enter cytoplasm Water passes through semi-permeable membrane Water re-enters symplastic pathway or enters xylem |
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Why does the suberin force the water into the cytoplasm?
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So it can get filtered by the semi permeable cell membrane
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What is the transpiration stream?
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The stream of water formed due to pressure differences in the stem and roots
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Explain the transpiration stream in detail once the water has entered the xylem (6)
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Water enters xylem within vascular cylinder
Transpiratoin causes low pressure in stem Root pressure causes water to move up the plant Transpiration stream of water is formed from roots to leaves Water movement in xylem due to pulling force Cohesion between water molecules |
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What type of process is the transpiration stream?
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Passive process (no energy used)
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What is the cohesion tension theory?
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The theory that water molecules are polar, therefore are cohesive
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What does cohesive water molecules mean?
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When they move, they pull other water molecules with them
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Why does there need to be a continuous stream of water molecules?
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Due to the cohesion theory, if there is a break in the water molecule stream, all other water molecules below the break fill fail to rise up the xylem
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What happens if there is an air bubble in the xylem? (2)
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An air lock forms (the transpiration stream is blocked by the air bubble)
The water then moves laterally from one xylem vessel to another through the pits in the xylem vessel walls |
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What is adhesion of water molecules in xylem?
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When the water molecules stick to the walls of the xylem
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What is the role of adhesion in the xylem
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Maintains the shape of the transpiration stream column even when transpiration is not taking place (eg. at night)
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What plant organ aids with gas exchange?
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Stomata
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What is the stomata?
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A port in the epidermis of the leaf, surrounded by a pair of guard cells
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What is the consequence of the stomata opening?
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Water vapour diffuses out of the stomata (transpiration)
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Why do the stomata close at night?
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To reduce water loss when CO2 is not needed for photosynthesis (no sunlight)
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How does temperature affect rate of transpiration? (4)
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Increased kinetic energy of water molecules
Faster diffusion of water molecules Faster evaporation Very high temperatures cause stomata to close, so transpiration decreases |
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How does light affect the rate of transpiration? (4)
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Causes stomatal opening
Increasing light increases transpiration No light causes stomatal closure reducing transpiration Wider opening with brighter light hence more transpiration |
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How does wind affect the rate of transpiration? (3)
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Removes water vapour from around leaf
Increases water vapour gradient so increases transpiration up to a maximum Lack of wind reduces transpiration |
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How does humidity affect the rate of transpiration? (2)
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High humidity reduces water vapour gradient so lower transpiration rate until transpiration rate is zero (equilibrium)
Lowering humidity can increase transpiration rate up till a maximum |
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What is the instrument used to measure transpiration?
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Potometer
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Give the steps for setting up a potometer (9)
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Take a leafy shoot
Cut the end of the stem at an angle to increase the surface area Fill the potometer and put it under water to stop any air bubbles getting trapped in the next step Keeping it under water, firmly put the twig into the apparatus Seal the joint with Vaseline if necessary Make a note of the position of the bubble After a set time, make note of the new position The position of the bubble can be adjusted using the screw clip of the reservoir Work out volume of water taken up |
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What is the formula for calculating water water absorbed (mm^3)?
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pi * r^2 * distance moved (mm)
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What is the formula for rate of uptake?
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Volume of water absorbed / time
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What are the ways in which plants restrict water vapour loss?
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Leaves have a waxy waterproof cuticle
Stomata are mostly on the lower surface of the leaf Stomata close in the darkWater |
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What is a xerophyte?
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Plants that live in dry conditions
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What are some common xerophatic adaptations? (4)
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Number of stomata is reduced
Stomata may be surrounded by hairs to trap water vapour leaving the stoma Waxy cuticle is thicker Smaller leaves |
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What is a
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Who knows? |
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What is a hydrophyte?
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A plant that lives in fresh water with the leaves beneath or floating on the surface
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What are some common hydrophytic adaptations? (4)
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Stoma tends to be on the upper surface
Leaves have large air spaces for buoyancy Thin waxy cuticle Reduced root and xylem system was less water needs to be absorbed and transported |
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Why is the stomata on the upper surface of leaves in aquatic plants? (2)
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Water loss is not a problem as the plant is surrounded by water
Richest supply of gases is in the air rather than in the water |
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What is translocation?
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The transport of dissolved photosynthetic assimilates in a plant
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What are photosynthetic assimilates?
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Nutrients made by photosynthesis in the leaf
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Give examples of nutrients that are translocated (2)
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Sucrose
Amino acids |
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What is the main difference between translocation and water transport by xylem?
|
Translocation requires energy from respiration
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Translocation is movement from __________ to _______ (2)
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sources
sinks |
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What are the sources of sucrose?
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Leaves
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What is a sink?
|
Any area that requires sucrose or other nutrients
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What is the main sink?
|
Growing points (meristems) in the roots, stem and leaves (particularly in the storage organs)
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What is a tuber?
|
A storage organ such as a potato
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Explain how sucrose travels to the sinks/storage organs (4)
|
High concentration of sucrose in the source
Low concentration of sucrose in the sink due to sucrose being used up Low concentration of sucrose in storage organs due to it being converted to starch Sucrose diffuses down the concentration gradient |
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Outline the mass flow hypothesis
|
Sucrose moves into the xylem by active transport
Water moves down a water potential gradient by osmosis Pressure builds up and moves dissolved sucrose away from the sources Sucrose is actively pumped out of the phloem at the sink Water leaves phloem by osmosis |
