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173 Cards in this Set
- Front
- Back
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What is the resolution possible with a light microscope? |
200nm |
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What is the resolution that can be achieved by a transmission electron microscope? |
0.1nm |
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What is the resolution that can be achieved by a scanning electron microscope? |
0.1nm |
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What is the magnification that can be achieved by a light microscope? |
x1500 |
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What is the magnification that can be achieved by a transmission electron microscope? |
x500,000 |
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What is the magnification that can be achieved by a scanning electron microscope? |
x100,000 |
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Define resolution |
The ability to see detail The smallest distance two separate objects can be apart for you to be able to distinguish them as distinct from each-other |
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How do you work out the magnification? |
Magnification = Image size/actual size |
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Why is it sometimes necessary to stain samples for light microscopy? |
When the sample is completely transparent- staining creates contrast and allows you to see detail |
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Why is it sometimes necessary to stain samples for electron microscopy? |
When the sample is completely transparent- otherwise the electrons will just pass through. Staining creates contrast and allows you to see detail |
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How would you stain a sample for light microscopy? |
Add a dye such as methylene blue or eosin- some parts take up more dye than others |
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How would you stain a sample for electron microscopy? |
Dip the sample in a solution of heavy metals (e.g. lead)- the metal ions scatter the electrons |
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What is the structure and function of the nucleus? |
A large organelle surrounded by a nuclear envelope, which has many pores. The nucleus contains chromatin and often a nucleolus
Chromatin contains DNA and proteins- the nucleus controls the actions of the cell. The pores allow substances in and out of the nucleus |
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What is the function of the nucleolus? |
Makes ribosomes |
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What is the structure and function of the rough endoplasmic reticulum? |
A system of ribosome-studded membranes enclosing a fluid-filled space
Folding and processing proteins that have been made in the ribosomes |
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What is the structure and function of the smooth endoplasmic reticulum? |
A system of membranes enclosing a fluid filled space
Synthesizing and processing lipids |
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What is the structure and function of the Golgi apparatus? |
A group of fluid-filled flattened sacs
Processing and packaging new lipids and proteins Making lysosomes |
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What is the structure and function of ribosomes? |
A small organelle made of a large and a small subunit
Synthesizing proteins |
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What is the structure and function of mitochondria? |
A double membrane, with the inner membrane folded to form cristae. Inside is the matrix, which contains enzymes for respiration
The site of aerobic respiration |
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What is the structure and function of lysosomes? |
A round organelle surrounded by a membrane, containing digestive enzymes
Digesting invading cells and breaking down worn-out components of the cell |
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What is the structure and function of chloroplasts? |
A small, flattened structure surrounded by a double membrane. Inside are thylakoid membranes stacked up into grana. The grana are linked together by lamellae
The site of photosynthesis |
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What is the structure and function of the plasma (cell surface) membrane? |
Fluid mosaic structure of mainly phospholipids and proteins
Regulates the movement of substances in and out of the cell Has receptor molecules to allow the cell to respond to chemicals such as hormones |
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What is the structure and function of the centrioles? |
Small, hollow cylinders containing a ring of tiny protein cylinders called microtubules
Form spindle fibres in cell division to move chromosomes |
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What is the structure and function of flagella and cilia? |
Small, hair-like structures with an outer membrane and a ring of nine pairs of protein microtubules, with a single pair or microtubules in the middle
Cilia- move substances along the cell surface Flagella- propel cells forward to make them move |
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How do organelles work together in the secretion of proteins? |
-Proteins are made in the ribosomes, which are attached to the rER -rER folds and processes proteins -Proteins are transported from rER to Golgi in vesicles -Undergo further processing at Golgi -Packaged into vesicles -Vesicles move to cell surface and are excreted by exocytosis |
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What is the function of the cytoskeleton? |
Providing mechanical strength to cells, aiding transport within cells and enabling cell movement |
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What is the cytoskeleton? |
A network of protein threads running through the cytoplasm |
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How is the structure of a Eukaryotic cell different from that of a Prokaryotic cell? |
Prokaryotic are much smaller, don't have a nucleus, have circular DNA, have fewer organelles, have smaller ribosomes, have a different type of cell wall, have mesosomes, have plasmids |
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What is a prokaryotic cell? |
A cell without a nucleus e.g. bacterial cell |
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What is a eukaryotic cell? |
A complex cell with a nucleus e.g. animal cell/plant cell |
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How is a plant cell different to an animal cell? |
Plant cell has a cellulose cell wall, chloroplasts, plasmodesmata, and a vacuole |
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What are the roles of membranes within cells? |
-Divide the cell into different compartments (around organelles) which makes the cell more efficient -Some membranes are folded, which increases the surface area -Can form vesicles to transport substances around the cell -Control what substances enter and leave organelles |
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What are the roles of membranes at the surface of cells? |
-Barrier against water-soluble molecules -Controls what enters and leaves -Allows cell communication -Allows cell recognition |
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How can plasma (cell surface) membranes be described? |
Partially permeable |
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Describe the fluid mosaic model of membrane structure |
-Phospholipids form a bilayer- they are constantly moving, which makes the bilayer fluid -Protein molecules scattered amongst the bilayer, like a mosaic -Some proteins have a polysaccharide chain- they are glycoproteins -Some lipids have a polysaccharide chain- they are glycoproteins -Cholesterol is found within the membrane |
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What is the role of phospholipids in the cell surface membrane? |
The hydrophillic heads face outwards, making the inner of the membrane hydrophillic, which makes a barrier to most water-soluble molecules |
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What is the role of cholesterol in the cell surface membrane? |
Cholesterol molecules fit between phospholipids and bind to the hydrophobic tails. This makes the bilayer less fluid- cholesterol maintains the fluidity of the phospholipid bilayer |
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What is the role of glycolipids and glycoproteins in the cell surface membrane? |
Cell recognition- flag the cell as 'self' to white blood cells |
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What are the roles of proteins in the cell surface membrane? |
Control what enters and leaves- there are carrier proteins and channel proteins that allow the passage of large or charged water-soluble substances Some proteins are receptor proteins, which allow the cell to detect chemicals released from other cells |
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How does a changing temperature effect membrane permeability? |
Very low temp.- phospholipids don't have much energy, so there is limited movement and the membrane is rigid. However channel proteins may denature, increasing permeability
0-45 degrees- phospholipids can move around- membrane is partially permeable as temp increases, phospholipids move more and this increases permeability
Very high temp.- bilayer starts to melt and the membrane is more permeable. Proteins denature, increasing permeablility |
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What is meant by the term 'cell signalling'? |
How cells communicate with eachother -One cell releases a messenger molecule -The molecule travels to another cell -It is detected by the cell because it binds to a receptor on the cell membrane |
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Explain the role of membrane-bound proteins as sites where hormones and drugs can bind |
-They have specific shapes -Only messenger molecules with a complementary shape can bind -Different cells have different types of receptors -The binding of a messenger molecule can trigger a response in the cell or block the receptor and stop it from working |
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Define passive transport |
The movement of molecules or ions across membranes that doesn't require energy from ATP
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Define active transport |
The movement of molecules or ions across membranes which requires energy from ATP |
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Define diffusion |
The movement of molecules from a region of high concentration to a region of lower concentration down a concentration gradient
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Define osmosis |
The movement of water molecules from a region of higher water potential to a region of lower water potential, down a water potential gradient, across a partially permeable membrane |
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Define facilitated diffusion |
The passive movement of molecules across membranes down their concentration gradient, which is aided by transport (carrier) proteins. No energy from ATP is needed |
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Define endocytosis |
The process of taking materials into a cell by surrounding them with part of the plasma membrane, which then pinches off to form a vesicle inside the cell. This is an active process requiring ATP |
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Define exocytosis |
The process of removing materials from the cell by fusing vesicles containing the material with the plasma membrane (cell surface membrane) |
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What happens if a plant cell is placed in pure water? |
Water moves into the cell by osmosis down a water potential gradient
The plant cell wall prevents bursting The cell becomes turgid |
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What happens if a plant cell is placed in concentrated salt solution? |
Water moves out of the cell by osmosis, down a water potential gradient
The plant cell membrane pulls away from the cell wall The cell becomes plasmolysed |
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What happens if an animal cell is placed in pure water? |
Water moves into the cell by osmosis, down a water potential gradient
The cell bursts open It becomes haemolysed |
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What happens if an animal cell is placed in concentrated salt solution? |
Water moves out of the cell by osmosis, down a water potential gradient The cell shrinks It becomes crenated |
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What are the stages of the cell cycle? |
MITOSIS The cytoplasm divides (cleaves) GROWTH INTERPHASE Biosynthesis (synthesis of proteins, replication of organelles) Synthesis of new DNA (replication of chromosomes) |
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What are the main stages of mitosis? |
Prophase- replicated chromosomes supercoil
Metaphase- replicated chromosomes line up on equator of cell Anaphase- the replicas are pulled apart towards opposite poles of the cell Telophase- the two new nuclei are formed |
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What is meant by the term 'homologous pair of chromosomes'? |
Pairs of chromosomes that have the same genes at the same loci, that pair up during meiosis
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What is mitosis used for in plants and animals? |
Asexual reproduction in plants Growth Repair Replacement |
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What is the process of cell division in yeast? |
They undergo cytokinesis by producing a small 'bud' that nips off the cell, in a process called budding
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What can cells produced by mitosis be described as being? |
Genetically identical |
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What is a stem cell? |
An unspecialised cell that is capable of becoming any one of the different cell types. They can be described as omnipotent or totipotent
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What is differentiation (with reference to stem cells)? |
The changes occurring in cells of a multicellular organism so that each different type of cell becomes specialised to perform a specific function |
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How are erythrocytes (RBCs) adapted to their function? |
They have no nucleus, mitochondria, golgi apparatus or rough endoplasmic reticulum to make space for haemoglobin. Their shape becomes a biconcave disc which increases their surface area for transporting oxygen
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How are neutrophils adapted to their function? |
They have enormous numbers of lysosomes for breaking down microorganisms once they have been ingested |
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How are sperm cells adapted to their function? |
Contain many mitochondria to generate energy for movement
The head contains a specialised lysosome which can release enzymes onto the outside of the cell to break down the egg to penetrate it Has a flagellum to propel the cell up the uterine tract |
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How are root hair cells adapted to their function? |
Hair-like projection increases surface area for absorption of minerals and water from the soil
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How are guard cells adapted to their function? |
Contain chloroplasts Have spiral-thickened cellulose in the inner edge of their cell walls so that only the outer walls stretch- this can create a pore (a stoma) |
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Define tissue |
A collection of cells that are similar to eachother and perform a common function |
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Define organ |
A collection of tissues working together to perform a particular function
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Define organ system |
A number or organs working together to perform an overall life function |
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How are cells arranged in the squamous and ciliated epithelium? |
SQUAMOUS The cells are flattened, so they are very thin. They are held in place by the basement membrane, which attaches them to connective tissue CILIATED The cells are column-shaped and all have tiny projections called cilia, which co-ordinate to waft mucus |
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How are cells arranged in the xylem? |
Continuous hollow tubes of dead lignin-reinforced cells with a wide lumen |
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How are cells arranged in the phloem? |
Consists of sieve tubes and companion cells. Cells line up end-to-end to form a long tube. Some ends of the cells remain to form sieve plates. Next to each sieve plate is a companion cell which moves the products of photosynthesis in and out of the phloem
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Why is co-operation between cells, tissues and organs important? |
It activities and functions of all the cell types need to be organised to ensure the whole organism can survive
Co-operation allows processes like photosynthesis and respiration to occur |
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Why do multicellular organisms need specialised exchange surfaces, whereas single-celled organisms do not?
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Single celled have a large surface-area-to-volume ratio so they can achieve sufficient exchange through their outer surfaces alone
Multicellular organisms have smaller surface-area-to-volume ratios and require more exchange, and the outer surface is not sufficiently large for this. There is also a greater distance for the gases to travel to reach target cells |
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What are the features of an efficient exchange surface?
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Large surface area
Thin barrier to reduce diffusion distance Fresh supply of molecules to keep the concentration gradient steep Removal of required molecules to keep the concentration gradient steep |
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How are the lungs adapted for efficient exchange?
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Large surface area- the alveoli are packed in in bunches to increase surface area
Plasma membranes allow easy diffusion of oxygen and carbon dioxide 1 cell thick alveolus walls to shorten diffusion distance 1 cell thick capillary walls to shorten diffusion distance Capillaries are narrow so red blood cells are squashed against walls- they are closer to the oxygen |
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What features do the alveoli have that make them an efficient exchange surface?
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High surface area
Good blood supply Thin walls |
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Where are goblet cells found and what is their function in the mammalian gaseous exchange system?
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Found under the epithelium
Secrete mucus to trap tiny particles from the air to reduce risk of infection |
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Where is cartilage found and what is its function in the mammalian gaseous exchange system?
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Found in a crescent shape in the trachea and bronchi
Holds them open and prevents them collapsing during periods of low pressure in inhalation |
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What is the role of the ciliated epithelium in the mammalian gaseous exchange system?
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The ciliated cells have cilia which are tiny hair-like structures which can coordinate to waft mucus up the airway to the back of the throat to be swallowed
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What is the function of smooth muscle in the mammalian gaseous exchange system?
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The smooth muscle can contract, constricting the airway and restricting the flow of air to and from the alveoli. This is important if there are harmful substances in the air
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Where are elastic fibres found and what is their function in the mammalian gaseous exchange system?
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They are found in the walls of the airway and can re-coil to their original shape after being deformed by the contraction of the smooth muscle. They re-open the airway after it has been contricted
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Describe the mechanism of breathing
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INSPIRATION
Diaphragm contracts, becomes flatter Intercostal muscles contract to raise ribs Volume of chest cavity increases Pressure in chest cavity drops below atmospheric pressure Air moves into lungs EXPIRATION Diaphragm relaxes and is pushed upwards Intercostal muscles relax and ribs fall Volume of chest cavity decreases Pressure in lungs increases and rises above atmospheric pressure Air moves out of lungs |
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Define tidal volume
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The different volumes of air moved in and out of the lungs with each breath when at rest
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Define vital capacity
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The largest volume of air that can be moved into and out of the lungs in any one breath
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Define single circulatory system and give an example of one
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A circulation in which blood flows through the heart once during each circulation of the body, e.g. the circulation system in fish
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Define double circulatory system and give an example of one
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A transport system in which blood travels twice through the heart for each complete circulation of the body, e.g. the mammalian circulatory system
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Define closed circulatory system and give an example of one
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A circulatory system in which the blood is always contained in blood vessels, e.g. in fish, mammals
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Define open circulatory system and give an example of one
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A circulatory system in which the blood is not always contained in blood vessels, e.g in insects
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Why is the muscle on the left side of the heart thicker than the right side?
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The blood from the left ventricle is pumped to the whole body, and needs sufficient pressure to overcome the resistance of the systemic circulation
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Describe the cardiac cycle
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ATRIAL SYSTOLE
Atria contract, which pushes blood into the ventricles. Once they are full, they begin to contract which causes the atrioventricular valves to snap shut VENTRICULAR SYSTOLE The walls of the ventricles contract from the bottom upwards, raising the pressure and pushing blood upwards towards the arteries Semilunar valves open, blood is pushed out of the heart DIASTOLE Atria and ventricles relax, blood flows into heart from veins |
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What is the role of the sino-atrial node (SAN)?
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Initiates a wave of excitation at regular intervals It is also known as the pacemaker
It is found at the top of the right atrium |
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What is the role of the atrioventricular node (AVN)?
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Delays the wave of excitation to allow time for the atria to finish contracting and for blood to flow into the ventricles before they begin to contract
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What is the role of the purkyne tissue?
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Carries the wave of excitation away from the AVN and spreads it out over the walls of the ventricles, causing them to contract from the bottom upwards
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Describe how the action of the heart is co-ordinated with reference to the SAN, AVN and purkyne tissue
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SAN generates a wave of excitation, which spreads over the walls of the atria and causes them to contract. The impulse travels to the AVN where it is delayed, before being passed on to the purkyne tissue, where it is spread through the ventricles, causing them to contract from the bottom upwards
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What would an elevation of the ST section on an ECG indicate?
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Heart attack
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What would a small and unclear P wave on an ECG indicate?
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Atrial fibrillation
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What would a deep S wave on an ECG indicate?
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Abnormal muscle thickness of the ventricles
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What does ECG stand for?
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Electrocardiogram
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What is the structure and function of an artery?
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STRUCTURE
Narrow lumen Folded endothelium Elastic tissue Smooth muscle Thick walls containing collagen FUNCTION Carry blood away from the heart at high pressure |
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How is an artery structurally adapted to its function?
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Folded endothelium and elastic fibres allow the walls to stretch and recoil when needed
Narrow lumen maintains a high pressure Smooth muscle to constrict the artery and limit the blood supply to certain organs as needed |
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What is the structure and function of a vein?
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STRUCTURE
Large lumen Thinner layers of collagen, smooth muscle and elastic tissue Contain valves FUNCTION Carry blood back to the heart under low pressure |
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How is a vein structurally adapted to its function?
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Valves to prevent backflow of blood in low pressure
Large lumen to ease flow of blood Thin walls allow it to be flattened against skeletal muscle, to increase pressure and force blood through |
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What is the structure and function of a capillary?
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STRUCTURE
Very thin walls of one flattened endothelial cell Very narrow lumen, the diameter of a red blood cell FUNCTION Allow exchange of materials between blood and cells of tissues via the tissue fluid |
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How is a capillary structurally adapted to its function?
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Very thin walls allow easy diffusion and osmosis
Narrow lumen squeezes red blood cells as they travel through, which makes them give up oxygen more easily |
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What are the differences between blood, tissue fluid and lymph?
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Blood has more red blood cells and more oxygen, amino acids and glucose
Tissue fluid has more carbon dioxide Lymph has more lymphocytes, carbon dioxide and fats |
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How is tissue fluid formed from plasma?
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Hydrostatic pressure pushes fluid out of the network of capillaries through tiny gaps in the capillary walls. The fluid consists of plasma with dissolved nutrients. The fluid surrounds body cells and allows exchange of gases and nutrients
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How does haemoglobin carry oxygen?
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It binds with oxygen to form oxyhaemoglobin
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What affects the affinity of oxygen with haemoglobin?
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The partial pressure of oxygen- the higher the partial pressure, the more abundant oxygen is in the surrounding cells, and the higher the oxygen affinity
The partial pressure of CO2- the higher the partial pressure, the more abundant oxygen is in the surrounding cells, and the lower the oxygen affinity |
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What is the Bohr effect?
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The effect of the concentration of hydrogen ions on the dissociation of oxygen from oxyhaemoglobin
The Bohr shift is the shift of the oxyhaemoglobin dissociation curve downwards and to the right |
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Why does fetal haemoglobin have a different affinity for oxygen?
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Fetal haemoglobin has a higher oxygen affinity because it must be able to 'pick up' oxygen from the fluid in the mother's blood
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How is carbon dioxide transported in the blood?
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It is either dissolved in the blood, combined with oxyhaemoglobin to form carbaminohaemoglobin, or transported in the form of hydrogencarbonate ions (HCO3-)
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What happens when carbon dioxide enters red blood cells?
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Combines with water to form a weak acid called carbonic acid. The reaction is catalysed by carbonic anhydrase
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What happens to carbonic acid in red blood cells?
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Dissociates to release hydrogen ions and hydrogencarbonate ions (HCO3-)
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What happens to hydrogen ions in the red blood cells?
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They are taken up by haemoglobin to produce haemoglobonic acid, which acts as a buffer (maintains a constant pH)
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Define oxygen tension
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The amount of oxygen in the air expressed as the pressure created by the presence of oxygen, expressed in kilopascals (kPa)
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Define partial pressure
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The proportion of total pressue provided by a particular gas as part of a mixture of gases
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How does the number of leaves affect the rate of transpiration?
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A plant with more leaves has a larger surface area over which water vapour can be lost
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How can the number and size of stomata affect the rate of transpiration?
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If a plant has many large stomata on its leaves, then water vapour is lost more quickly
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How can the position of stomata affect the rate of transpiration?
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If the stomata are on the lower surface of the leaf, water vapour is lost more slowly
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How can the presence of a cuticle affect the rate of transpiration?
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A waxy cuticle acts as a barrier to reduce evaporation from the leaf surface
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How can light affect the rate of transpiration?
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In high levels of light, the stomata open to allow gaseous exchange for photosynthesis, resulting in increased loss of water vapour
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What are the ways that temperature can affect the rate of transpiration?
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An increased temperature will:
-increase the rate of evaporation from the cell surfaces, so the water vapour potential in the leaf rises -increase the rate of diffusion through the stomata because the water molecules have more kinetic energy -decrease the relative water vapour potential in the air, allowing more rapid diffusion of molecules out of the leaf |
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How can relative humidity affect the rate of transpiration?
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A higher relative humidity in the air will decrease the rate of transpiration because there will be a smaller water vapour potential gradient between the air spaces in the leaf and the air outside
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How can air movement/wind affect the rate of transpiration?
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Air moving outside the leaf will carry away water vapour that has just diffused out of the leaf, maintaining a high water vapour potential gradient
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How can a plant reduce its rate of transpiration when water is in short supply?
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It can close stomata, wilt leaves or shed leaves to reduce water loss through stomata
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What is the transpiration stream?
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The flow of water through a plant from the roots, through the xylem and out of the plant through the upper parts of the plant (e.g. leaves)
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What is transpiration?
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The loss of water by evaporation from the aerial parts of a plant
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How can the rate of transpiration be measured?
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Using a potometer, you can measure the water uptake from a leafy shoot by looking at the movement of the meniscus inside the water column
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What is the main thing you need to be careful of when assembling a potometer, and how can you reduce the chance of this happening?
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Air bubbles in the potometer water column
Cut the shoot underwater, assemble the potometer under water, then dry the leaves of the shoot |
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What are the three processes involved in transpiration?
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-osmosis from the xylem to mesophyll cells
-evaporation from the surface of the mesophyll cells into the intercellular spaces -diffusion of water vapour from the intercellular spaces out through the stomata |
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What are the adaptations most plants have to reduce water loss?
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A waxy cuticle
Stomata on the lower surface of leaves Closed stomata at night Losing leaves in winter |
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What is a xerophyte?
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A plant that is adapted to reduce water loss so that it can survive in very dry conditions
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How does having smaller leaves reduce water loss?
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The surface area of the leaf is reduced, so less water is lost by transpiration from the surface of the leaf
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How does having densely packed spongy mesophyll reduce water loss?
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Reduces the cell surface area that is exposed to the air inside the leaves. Less water will evaporate into the leaf air spaces, reducing the rate of water loss
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How does having hairs on the surface of the leaf reduce water loss?
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Traps a layer of air close to the surface of the leaf. This air can become saturated with moisture, which reduces the water vapour potential gradient between the inside and outside of the leaf, resulting in a reduced rate of transpiration
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How does having pits on the leaf reduce water loss?
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They can trap air that has become saturated with water vapour, which reduces the water vapour potential gradient between the inside and outside of the leaf, resulting in a reduced rate of transpiration
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How does rolling of leaves reduce water loss?
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The lower epidermis is not exposed to the atmosphere and can trap air, which becomes staurated. This reduces the water vapour potential gradient between the inside and outside of the leaf, resulting in a reduced rate of transpiration
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How does maintaining a high salt concentration inside the plant's cells reduce water loss?
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This gives the cells a low water potential, which reduces the evaporation of water from the cell surfaces because the water potential gradient between the cells and the leaf air spaces is reduced
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What is translocation?
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The transport of assimilates (sugars and other chemicals made by the plant cells) throughout the plant, in the phloem tissue
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How does sucrose enter the phloem?
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The companion cell uses ATP to actively move H+ ions out of its cytoplasm into the surrounding tissues, creating a diffusion gradient of H+ ions. The H+ ions then diffuse back into the companion cells through cotransporter proteins, which allow the H+ ions to also bring a sucrose molecule back in with them. From the companion cells, the sucrose molecules can then diffuse through plasmodesmata into the phloem
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How does mass flow occur at the source?
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Sucrose entering the sieve tube elements reduces the water potential, causing water to move in by osmosis. This increases the hydrostatic pressure, causing the water to move away from the source to an area of lower hydrostatic pressure
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How does mass flow occur at the sink?
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Sucrose is taken up by cells surrounding the phloem by diffusion or active transport, reducing the sucrose concentration and increasing the water potential in the sieve tube element, so water molecules move into the surrounding cells by osmosis. This reduces the hydrostatic pressure, which makes water move into the area from an area of higher hydrostatic pressure
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What is a source?
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An area where sucrose is released into the phloem
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What is a sink?
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An area where sucrose is removed from the phloem
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Give examples of how the roots of a plant can be a source and a sink
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Source- carbohydrates stored in the roots can be released into the phloem
Sink- sugars are stored in the roots as starch |
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What is the evidence for the mass flow hypothesis?
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When the phloem is cut (in the bark of a tree) sap oozes out, indicating a pressure gradient
Phloem sap has a high pH, which is what you would expect since hydrogen ions are actively transported out of the cells ATP is abundant in phloem because it is required for active transport of H+ ions |
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What is the evidence against the mass flow hypothesis?
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The role of sieve plates is unclear- it seems they act as a barrier for no apparent reason
Sugar travels to many different sinks It doesn't make sense that the phloem cells are alive- there is no reason for them to be |
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need to do pages 69-75
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ok
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Why is the xylem vessel lignified? |
The lignin strengthens the xylem wall to prevent it collapsing in low pressure It also waterproofs it to prevent loss of water through the walls of the xylem It also improves the adhesion of water molecules and prevents the stem breaking |
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What is the function of pits in the xylem vessel? |
Allow the movement of water out of the xylem to photosynthesising tissues Allow the movement of water into the xylem from respiring tissues |
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Why are the lungs considered to be an organ? |
It is a collection of different tissues working together to perform a common function (gas exchange) |
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What are the roles of glycoproteins in the cell surface membrane? |
Receptors for cell signalling- can receive signals and trigger a response inside the cell Act as antigens to help the immune system identify the cell as 'self' Help with cell adhesion to hold cells in tissues together |
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Why might the rate of transpiration in the afternoon be lower than in the morning? |
Lower temperature Less light The air has a higher water potential in the afternoon Stomata are closed Less air movement (wind) |
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Why does the hydrostatic pressure drop as blood moves away from the heart? |
There is less fluid in the blood as it is lost through the capillaries in the tissue fluid There are more, smaller vessels which have a larger total cross-sectional area |
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What precautions should you take when using a spirometer to measure vital capacity? |
Use medicinal grade oxygen Disinfect the mouthpiece Check the spirometer is fully functional Use a nose clip Make sure the person is healthy (not heavily asthmatic) |
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What is the tissue in plants that contains stem cells? |
Cambium |
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Why does the trunk of a tree swell above a cut if you cut away some of the bark? |
The sucrose can't be transported past the cut because the phloem is removed The damage triggers increases cell division to produce cells to store the excess sugars in |
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What is the average diameter of a eukaryotic cell? |
20-40micrometres |
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What is the size of the ribosomes in prokaryotic cells? |
18nm |
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Which is bigger- a nanometre or a micrometre? |
Micrometre |
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What is the role of the mitochondria in eukaryotic cells, and mesosomes in prokaryotic cells? |
Site of aerobic respiration |
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Why do single-celled organisms not need a specialsed exchange surface to carry out gaseous exchange? |
Large surface area to volume ratio Very small- can meet needs for CO2 and O2 just by diffusion through plasma membrane |
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What does a scanning electron microscope allow you to see? |
Surface detail, 3D shape |
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What does a transmission electron microscope allow you to see? |
Individual organelles |
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What happens to the plasma membrane of a cell at high temperatures (above 60 degrees)? |
Phospholipid bilayer melts//structure becomes disrupted//becomes damaged |
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What is the process of budding in yeast? |
DNA replicates, cell replicates by mitosis. The new nucleus moves into a bud on one side of the cell. The new cell is pinched off the old one, and a scar is left on the surface of the yeast cell |
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Which tissue in plants, xylem or phloem, has bordered pits? |
Xylem |
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Where can meristematic tissue be found in plants? |
Tip of root Tip of stem |
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How would you use a spirometer trace to measure the rate of oxygen uptake? |
Draw a line along the tips of the peaks and calculate the gradient of the line |
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What are two adaptations of the sieve tube elements that enable mass flow to occur? |
Joined end to end, have sieve pores, little cytoplasm, no nucleus |
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What is meant by a homologous pair of chromosomes? |
A pair of chromosomes that have the same genes at the same loci One from the mother and one from the father They have the same banding pattern and are usually the same length |
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Why is it not possible to expel all the air from the lungs? |
Trachea is held open by cartilage Bronchi are held open by elastic fibres |
