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67 Cards in this Set
- Front
- Back
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How many micrometres are there in a millimetre? |
1000 |
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How many nanometres in a millimetre? |
1,000,000 (so there are 1000 nanometres in a micrometre) |
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What is the formula for calculating magnification? |
Magnification=size of image divided by size of real object
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What is resolution? (microscopes) |
The miniumum distance apart that two objects can be in order to appear as two seperate items |
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What is the resolution of a light microscope? |
About 0.2 micrometres |
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What is cell fractionation? |
The process by which cells are broken up and the different organelles they contain are seperated out |
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Why is the tissue to be studied placed in a cold, buffered solution of the same water potential of the cell prior to osmosis? |
•Cold- to reduce enzyme activity which might break down the organelles •Of the same water potential as the tissue- to prevent organelles from bursting or shrinking as a result of osmosis •Buffered- so the pH does not fluctuate, which may alter the structure of organelles or affect the functioning of enzymes |
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What is the first stage of cell franctionation? |
Homogentation- cells are broken up in a homogenisor (blender), which releases the organelles from the cell. The resultant fluid, known as homogenate, is then filtered to remove any complete cells and large bits of debris |
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Describe the process of ultracentrifugation for animal cells |
•The tube of filtrate is placed in the centrifuge and spun at a slow speed •The heaviest organelles (nuclei), are forced to the bottom of the tube, where they form a thin sediment •The fluid at the top of the tube (supernatent) is removed, leaving just the sediment of nucei •The process is repeated at a higher speed with the supernatent. Next the sediment will be the mitochondia as they are the next heaviest organelles |
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Which are the heaviest and lightest organelles of the following: lysosomes, nuclei, mitochondria |
Nuclei are heaviest. Then mitochondria Then lysosomes are the lightest |
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Why do light microscopes have a poor resolution? |
Due to the relatively long wavelength of light |
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What are the two main advantages of an electron microscope? |
•The electron beam has a very short wavelength so the microscope has a high resolving power •As electrons are negatively charged the beam can be focused using electromagnets |
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What resolving power do the best electron microscopes have? |
About 0.1 nm - 2000 times better than a light microscope |
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Why does a near vacuum need to be created in an electron microscope? |
Because electrons are absorbed and deflected by molecules in the air |
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How does a transmission electron microscope work? |
An electron gun produces a beam of electrons which is focused onto the specimin by a magnet condenser. This beam passes through a thin section of the specimin. Parts of this specimin allow the electrons to pass through and so appear bright. Other parts absorb electrons and so appear dark. An image is produced on a screen and this can be photographed to give a photomicrograph. |
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Why can the resolving power of the TEM not always be acheived in practice? |
•Difficulties in preparing the specimin limit the resolution which can be acheived •A higher energy electron beam is required and this may destroy the specimin |
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What are the four main limitations of the TEM? |
•As the system must be in a vacuum living specimins cannot be observed •The specimin must be extremely thin •A complex staining process must be observed and even then the image is not in colour •Artefacts may be present in the image which result from the way the specimin is prepared rather than what is actually there
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What is the resolving power of the SEM? |
Around 20nm - worse than the TEM , but still 10 times better than a light microscope |
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How does a scanning electron microscope work? |
A beam of electrons is directed onto the surface of the specimen from above, (rather than penetrating it from below) which is then passed back and forth across the specimen in a regular pattern. The electrons are scattered by the specimen, so by computer analyis of the pattern of scattered electrons and secondary electrons produced we can build up a 3D image of the specimen. |
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What are the three functions of the nucleus? |
•It acts as the control centre of the cell through the production of mRNA and tRNA and hence protein synthesis •It manufactures ribosomal DNA and chromosomes •It retains the genetic material of the cell in the form of DNA and chromosmes |
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What is the nuclear envelope? |
A double membrane which surrounds the nucleus. Its outer membrane is continuous with the endoplasmic reticulum of the cell and often has ribosomes on its surface. It control the entry and exit of materials in and out of the nucleus and contains the reactions taking place within it. |
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What are the nucear pores? |
They allow the passage of large molecules such as mRNA out of the nucleus. |
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What is the nucleolus? |
A small spherical region within the nucleoplasm. It manufactures ribosomal RNA and assembles the ribosomes. There may be more than one per nucleus |
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What are 5 parts of the nucleus? |
•Chromosomes-protein-bound, linear DNA •Nucleoplasm- jelly-like material which makes up most of the nucleus •Nuclear pores-allow large molecules to pass in and out •Nuclear envelope-double membrane which controls what enters and leaves the nucleus and contains the reactions within •Nucleolus- manufactures RNA and assembles the ribosomes |
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What are cristae in the mitochondria? |
Extensions of the inner membrane, which provide a large surface area for the attatchment of enzymes and other proteins involved in respiration |
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What is in the matrix of the mitochondrion? |
Protein, lipids, ribosomes and DNA which allows the mitochondria to control the production of some of their own proteins. Many enzymes involved in respiration are also found here. |
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What types of cells may contain many mitochondia? |
Cells with a high level of metabolic activity will contain many mitochondia as they require a plentiful supply of ATP, produced in respiration which takes place in the mitochondria. Examples include muscle cells, which require ATP for movement, and epithelial cells, which need ATP for active transport when absorbing substances by active transport |
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What are the grana? |
Stacks of up to 100 disk-like structures called thylakoids. These contain chlorophyll and are where the light-dependant stage of photosynthesis takes place. |
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What is the stroma? |
A fluid-filled matrix in the chloroplast where the light-independant reaction of photosynthesis takes place |
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How are chloroplasts adapted to their function of carrying out photosynthesis? |
•The granal membranes provide a large surface area for the attatchment of chlorophyll, electron carriers and enzymes which carry out the first stage of photosynthesis. •The fluid of the stroma posseses all the enzymes needed to make sugars in the second stage of photosynthesis •Chloroplasts contain both DNA and ribosomes so they can quickly and easily manufacture some of the proteins needed for photosynthesis |
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What is endoplasmic reticulum? |
An elaborate 3D system of sheet-like membranes spreading through the cytoplasm of the cell. It is continuous with the outer nucear membrane. The membranes enclose a network of tubules and flatterned sacs called cisternae. |
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Which type of endoplasmic reticulum has ribosomes on its surface? |
Rough ER |
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What are the two functions of rough ER? |
•To provide a large surface area for the synthesis of proteins and glycoproteins •To provide a pathway for the transport of materials, especially proteins, through the cell |
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What are the two functions of smooth ER? |
•To synthesise, store and transport lipids •To synthesise, store and transport carbohydrates |
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What cells will have extensive endoplasmic reticulum? |
Those which make and store large quantities of lipids, carbohydrates and proteins such as liver and secretory cells, e.g epithelium |
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What is the golgi apparatus and what does it do? |
A stack of membranes which make up flatterened sacs (cisternae) with small rounded hollow structures called vesicles. The proteins and lipids produced by the ER are passed through the golgi apparatus in strict sequence. The golgi then modifies these proteins by adding non-protein components to them and also it 'labels' them, allowing them to be accurately sorted and sent to their correct destinations. |
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What happens to modified proteins and lipids in the golgi apparatus once they have been sorted? |
They are transported in golgi vesicles which are pinched off from the ends of the golgi cisternae. They may move to the cell surface where they fuse with the membrane and release their contents to the outside. |
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What are 5 functions of the golgi apparatus? |
•To add carbohydrate to protein to form glycoproteins •To produce secretory enzymes e.g those secreted by the pacreas •To secrete carbohydrates e.g those used in making cell walls in plants •To transport, modify and store lipids •To form lysosomes |
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What cells will have a well developed golgi apperatus? |
Secretory cells such as the epithelial cells which line the intestines |
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What are lysosomes? |
Lysosomes are formed when the vesicles produced by the golgi apparatus contain enzymes such as proteases and lipases, as well as lysozymes- enzymes which hydrolyse the cell walls of certain bacteria. Lysosomes isolate these enzymes from the rest of the cell before releasing them to the outside of the cell or into a phagocytic vesicle within the cell |
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What are the 4 functions of lysosomes? |
•To hydrolyse material ingested by phagocytic cells such as white blood cells and bacteria •To release enzymes to the outside of the cell (exocytosis) in order to destry material around the cell •To digest worn out organelles so the useful chemicals in them can be recycled •To completely break down cells after they have died (autolysis) |
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What cells will have many lysosomes? |
Secretory cells such as epithelial cells and phagocytic cells |
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What are the two types of ribosomes and where are they found? |
80s- found in eukaryotic cells 70s- found in prokaryotic cells, mitochondria and chloroplasts- they are slightly smaller |
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What is the structure of a ribosome? |
They have two subunits, a large one and a small one, each of which contains ribosomal RNA and protein |
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What is the function of ribosomes? |
They are the site of protein synthesis |
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What are the functions (3) of the cell wall? |
•To provide mechanical strength to stop the cell bursting under the pressure created by the osmostic entry of water •To give mechanical strength to the plant as a whole •To allow water to pass along it and so contribute to the movement of water through the plant |
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What makes up the cell walls of plants, algae and fungi? |
•Plant- microfibrils of cellulose embedded in a matrix •Algae- either cellulose or glycoproteins or a mixture of both •Fungi- No cellulose but a mixture of a nitrogen-containing polysaccharide called chitin, a polysaccharide called glycan and glycoproteins |
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What does a vacuole contain? |
A solution of mineral salts, sugars, amino acids, wastes and sometimes pigments such as anthocyanins. |
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What is a vacuole? |
A fluid filled sac bound by a single membrane called the tonoplast. There is usually one large central vacuole in mature plant cells |
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What are the functions (3) of the vacuole? |
•They support herbaceous plants, and herbaceous parts of woody plants, by making cells turgid •The sugars and amino acids may acts as a temporary food store •The pigments may colour petals to attract pollinating insects |
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What is a tissue? |
A group of sinilar cells which perform a specific function |
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What is an organ? |
A combination of tissues which are coordinated to perform a variety of functions, although often with one predominant major function |
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What is an organ system? |
Organs working together in a single unit, grouped together to perform particular functions more efficiently |
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What is the structure of a bacteria? (Talk about cell wall, capsule, cell-surface membrane, circular DNA, plasmids, ribosomes) |
•Cell wall- physical barrier made up of murein (a polyner of polysaccharides and peptides), excludes certain substances and protercts against mechanical damage and osmotic lysis •Capsule- a layer of mucilaginous slime secreted by the bacteria around the cell wall to protect bacteria from other cells and help groups of bacteria stick together for further protection •Cell-surface membrane-acts as a differentially permeable layer which controls the entry and exit of chemicals •Circular strands of DNA- like normal DNA but not associated with histones •Plasmids-Smaller circular peices of DNA which can reproduce themselves indepentdantly. They may posses genes which aid the survival of the bacteria in adverse conditions (may produce enzymes which break down antibiotics). Plasmids are used as vectors in genetic engineering |
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List 8 ways that prokaryotic cells differ from eukarytoic cells |
•Prokaryotic cells have no nucleus or nuclear envelope, only an area where DNA is found •In prokaryotes, DNA is not associated with proteins such as histones •In prokaryotes, some DNA may be in the form of plasmids- in eukaryotes all DNA is linear •Prokaryotes have no membrane-bound organelles •Prokaryotes have no chloroplasts, only bacterial chlorophyll associated with the cell-surface membrane in some bacteria •Prokaryotic ribosomes are 70s therefore much smaller •Bacterial cell walls are made of murein not cellulose or chitin •Prokaryotes may have a capsule, eukaryotes do not |
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What is the structure of a virus? |
Will contain nuceic acids such as DNA or RNA but can only replicate inside a host cell. The nucleic acid is enclosed within a protein coat called the capsid. Some viruses are further surrounded by a lipid envelope. On the surface of the virus there will be attachement proteins |
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What is interphase? |
The period preceding mitosis where the cell is not dividing. Considerable cellular activity such as DNA replication happens during this phase. |
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What is the difference between mitosis and meiosis? |
Mitosis produces two daughter cells with the same number of chromosomes as the parent cell which are genetically identical. Meiosis produces four daughter cells which each have half the number of chromosomes of the parent cell. |
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What order do the stages of mitosis go in? |
iPMAT: Interphase Prophase Metaphase Anaphase Telophase (then cytokinesis) |
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What happens during prophase? |
•Chromosomes become visible •Centrioles move to opposite poles of cell and develop spindle fibres spanning the cell •Nuceolus disappears and nuclear envelope disintegrates |
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What happens during metaphase? |
•Centromere (which joins the two chromatids) attatches to microtubules from the poles •Chromosomes are therfore pulled along spindle apparatus to equator of cell |
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What happens during anaphase? |
•The spindle fibres attatched to the chromatids contract •Ths pulls the centromeres into two and each chromatid goes to its respective opposite pole. •This requires energy from respiration, and mitochondria gather around the spindle fibres |
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What happens during telophase? |
•Chromosomes reach the poles and become indistinct •Nuclear envelope and nucleolus reform •Spindle fibres disintegrate •Cytoplasm divides by cytokinesis |
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What is cell division called in prokaryotic cells? |
Binary fission |
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What is the process of binary fission? |
•The circular DNA molecule replicates and both copies attatch to the cell membrane •The plasmids also replicate •The cell membrane begins to grow between the two DNA molecules and pinch inward, dividing the cytoplasm in two •A new cell wall forms between the two molecules of DNA, dividing the original cell into two identical daughter cells, each with a single DNA copy and varying numbers of plasmids |
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How do viruses replicate? |
They attatch to a living host cell with their attatchement proteins. They then inject their nuceic acid into the host cell, which provides the 'instructions' for the cells metabolic processes to start producing the viral components, nuceic acid, enzymes and structural proteins, which are then assembled into new viruses. |
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What are the three stages of the cell cycle? |
•Interphase •Nuclear division- when the nucleus divides into two •Cytokinesis- the process by which the cytoplasm divides to produce two new cells |
