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What is magnification?
The degree to the size of an image is larger than the object itself. Numerically, it is the image size divided by the actual size of the object, measured using the same units.
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What is resolution?
The degree to which it is possible to distinguish between two objects that are very close together. Higher resolution = greater detail.
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What is the resolution of a light microscope and an electron microscope?
Light microscope = 200 nanometres , electron microscope =0.1nm
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What are the differences between TEM and SEM?
TEM: electrons pass through sample, 2D image, magnification = x500000. SEM: electrons bounce off sample, 3D image, magnification = x1000000
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What are limitations of an electron microscope?
Samples have to be placed in a vacuum because of molecules in the air. Expensive. Preparing samples and using electron microscope require training.
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In electron microscopy what materials are used for staining samples?
Metal particles or metal salts.
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What is the cytoskeleton?
The cytoskeleton refers to the network of protein fibres found within cells that gives structure and shape to the cell, and also moves organelles around inside cells.
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Describe the structure of the nucleus.
Has a nuclear envelope with nuclear pores, inside is a nucleolus.
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What is the function of the nucleus?
Contains cell's genetic material - instructions for making proteins which regulate the cell's activities. The nucleolus makes ribosomes and RNA.
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Describe the structure and function of the Rough Endoplasmic Reticulum.
The RER is a system of membrane bound flattened sacs called cisternae which are studded with ribosomes - the RER is continuous with the outer nuclear membrane. The RER processes and transports proteins made at the ribosomes.
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Which organelle recieves proteins from the RER, and modifies and packages the proteins into vesicles that can be transported?
Golgi Apparatus
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Describe the structure of mitochondria.
Spherical or sausage shaped. Two membranes separated by a fluid filled space. Inner membrane is highly folded to form cristae. The central part of the mitochondrion is called the matrix.
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What is the role of mitochondria?
Aerobic respiration; to release energy in the form of Adenosine Triphosphate.
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Describe the structure of chloroplasts.
Two membranes separated by a fluid filled space. Inner membrane continuous -> with membrane network called thylakoid membranes. A stacks of thylakoid are called Grana - these are linked by lamellae.
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What are Lysosomes and what do they do?
Lysosomes are spherical sacs surrounded by a single membrane - they contain digestive enzymes to break down materials.
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Give an example of a specialised Lysosome.
Acrosome in the sperm head which release enzymes to help penetrate the egg.
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Describe the structure and function of Ribosomes.
Bound to rough ER, consist of two subunits. Function is to synthesise proteins - act as assembly line where mRNA
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Which organelles form spindle fibres which move chromosomes during mitosis?
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Explain the role of the nucleus, mRNA, and vesicles in protein synthesis.
The nucleus contains genes that have the specific instructions to make the protein. DNA is transcribed onto an mRNA molecule and leaves through nuclear pore and attaches to ribosome on the rough ER.Protein is pinched off in a vesicle.
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Explain the role of the golgi apparatus and the cell membrane in protein synthesis.
The vesicles containing the protein are transported to and fuse with the golgi apparatus which processes and packages the protein. Vesicles are pinched off from the Golgi Apparatus and move towards the cell membrane where they are released.
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What are the features of prokaryotic cells ?
No nucleus, one membrane, no membrane bound organelles, have a PEPTIDOGLYCAN cell wall (Murien), circular DNA, ATP production takes place in mesosomes (in folded regions of the cell surface membr), some prokaryotic have flagella.
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What are the features of eukaryotic cells?
Have a nucleus, have linear DNA, much larger than prokaryotic cells, cellulose cell wall.
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What are some of the roles of membranes?
Separating cell contents from cytoplasm and outside environment, cell signalling, holds the components of metabolic pathways in place, regulates transport of materials in/out cells.
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Describe the structure of phospholipids.
The phosphate head is hydrophilic and the fatty acid tails are hydrophobic, therefore the phospholipid molecules form a bilayer with the tails facing inwards.
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What are the main components of the fluid mosaic model?
Phospholipid bilayer, proteins, glycolipids, glycoproteins, channel proteins, carrier proteins, enzymes, coenzymes, receptor sites.
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What are glycoproteins and glycolipids?
Proteins and lipids and with carbohydrates attached.
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Explain what is meant by cell signalling
Cells use signals (chemical messengers) to gather information about and respond to changes in their cellular environment and or communication between cells.
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Describe the components that all cell signalling mechanisms have in common.
A signal molecule and a receptor site.
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Explain the role of membrane-bound receptors in Hormonal responses
Membrane-bound receptors receive signal molecules which cause a response inside the cell such as a hormone like insulin being secreted.
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Explain the role of membrane-bound receptors in responses to drugs.
The receptor site can be blocked as a result of drugs interfering with the site whereby the normal signal molecule would fit. For example, a drug such as ecstasy blocks the receptor site on a neurone where a neurotransmitter would usually fit.
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Explain the importance of the cytoskeleton in providing strength to cells, aiding transport within cells and enabling cell movement.
Provides support to cells, determines the shape and changes the shape by moving the membrane for endo and exocytosis, move organelles, moves vesicles along microtubule tracks using ATP, hold organelles in place, make up centrioles and spindle fibres.
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Explain the effect of changing temperature on membrane structure and permeability.
Molecules have more kinetic energy - increased movement makes membrane leaky, phospholipid bilayer melts - membrane proteins are denatured and unable to function. Membrane becomes permeable - molecules which would not normally do so can move out.
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Why can some water molecules pass through the phospholipid bilayer even though they are charged?
They are very small molecules.
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Give an example of channel proteins in the body.
Sodium channel proteins in the nervous system.
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How do channel proteins allows ions and through?
Channel proteins form pores in the membrane which are often gated and shaped to only allow one type of molecule.
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What is active transport?
The movement of molecules or ions across membranes, which uses ATP to drive protein pumps within the membrane.
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How do protein pumps in active transport differ from those used in facilitated diffusion?
They use ATP, carry molecules against concentration gradient, can carry molecules at a much faster rate than diffusion, carry specific molecules one way across the membrane,
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Why is energy significant in ensuring one way flow across the membrane?
Energy in the form of ATP changes the shape of the protein after it has transported the molecule across the membrane so that the molecule cannot re enter the carrier protein.
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What is endo/exocytosis?
Bulk transport of material via vesicles that can fuse with or break from the cell surface membrane.
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Give some examples of bulk transport
Hormones like insulin which are packaged in vesicles in the Golgi Apparatus and transported across the membrane in large quantities. White blood cells engulf invading cells using vesicles.
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What names are given to movement of solid and liquid material in bulk transport?
Phagocytosis - solid material, Pinocytosis - liquid material
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Explain why active transport allows substances to be accumulated in an area, whereas facilitated diffusion doesn't.
Active transport uses ATP so molecules can only pass through one against the concentration gradient. Facilitated diffusion allows molecules to pass through both ways so the concentration of molecules will distribute evenly over time.
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Why can phospholipid molecules in a bilayer move only in the plane of the bilayer?
The phosphate head group cannot pass through the hydrophobic region in the center of the bilayer.
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Explain why dissolving more solute decreases the water potential of a solution.
Solute dissolves and water molecules cluster around the solute molecules. This reduces the capacity for the water molecules to move freely and the water potential decreases.
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If a plant cell is in a solution of a higher water potential compared to that of itself, what will happen to the cell?
Water molecules will diffuse into the cell by osmosis down the water potential gradient. This causes the plant cell to swell and become turgid. The plant cell wall prevents the cell from bursting.
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If an animal cell is placed in placed in a pure water, what will happen to the animal cell?
Water molecules will diffuse into the animal cell by osmosis down the water potential gradient, the animal cell will swell and burst opened; it is haemolysed.
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If an animal cell is placed in a concentrated solution, a solution of low water potential, what will happen to the animal cell?
Water molecules diffuse out of the cell by osmosis down the water potential gradient , the animal cell will shrink as it has become crenated.
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If a plant cell is placed in a solution of a lower water potential than its own, what will happen to the plant cell?
Water molecules will diffuse out of the plant cell by osmosis down the water potential gradient, and the plant cell 's cytoplasm and vacuole will shrink as they lose water, and the membrane will pull away from the cell wall - the cell is plasmolysed.
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Explain and suggest how freshwater amoebae continually move large volumes of water out of the cell.
The water potential of the amoebae's cytoplasm is lower than the surrounding water. Water will move out by osmosis. Excess water is moved into the Amoebae's contractile vacuole - periodically empties large volumes of water by exopinocytosis using ATP
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How many chromosomes are in the nucleus of: a) an onion cell (b) a human nucleus (c) a chimpanzee
a - 12 b - 46 c- 48
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In eukaryotes, what are DNA molecules wrapped around?
Proteins called histones.
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DNA and histones together are called...
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In mitosis, before chromatids can be seperated, they must be....
Supercoiled (to form visible chromosomes0
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How thick are chromatin threads before and after supercoiling?
Before: 30nm thick. After:500nm thick
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Why must chromosomes only be supercoiled for short periods of time?
Supercoiled chromosomes cannot perform their normal functions in the cell.
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How are mutations avoided when replicating chromosomes?
Proof-reading enzymes move along the new DNA strands and check that the copying has been done properly.
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What affects the length of time of the cell cycle?
Species, cell type, availability of nutrients.
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Define mitosis.
Mitosis refers to the process of nuclear division where two genetically identical nuclei are formed from one parent cell nucleus.
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Why is mitosis important?
For asexual reproduction, growth and repair. Also replacement of cells such as red blood cells.
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Describe what happens in prophase.
Chromosomes supercoil ( shorten and thicken) to become pairs of sister chromatids. The nuclear envelope breaks down and dissapears. Centrioles divide into two; each daughter centriole moves to opposite poles of the cell to form the spindle.
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What is a spindle fibre?
This is a structure made of protein fibres found in eukaryotic cells during cell division.
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Describe what happens in metaphase.
During metaphase chromosomes move to the equator and each becomes attached to a spindle thread by its centromere.
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Describe what happens in anaphase.
Chromatids are separated from eachother when the centromere splits, each chromatid is now a chromosome (identical to original chromosome in parent cell). The spindle fibres pull the chromatids towards oppsite poles of the cell, they assume a V-shape
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Describe what happens in telophase.
A new nuclear envelope forms around each set of chromosomes. The spindle breaks down and dissapears. The chromosomes uncoil so can no longer be seen under the microscope.
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What happens during cytokinesis?
The whole cell splits to form two new cells which are identical to the original parent cell.
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In plants, which cells are capable of mitosis and cytokinesis?
Meristem cells
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Why might most plants cells except meristem cells cannot undergo mitosis and cytokinesis.
The formation of the cell wall prevents cell the cell dividing.
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What are differences between cytokinesis in plant and animal cells?
In animal cells cytokinesis starts from the outside, but in plant cells cytokinesis starts with the formation of a cell plate where the spindle equator was. New cell membrane/wall material is laid down along this cell plate.
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What are the different categories of differentiaton?
Number of a particular organelle, the shape of the cell, some of the contents of the cell.
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What is meant by differentiation?
The changes occurring in cells of a multicellular organism so that each different type of cell becomes specialized to perform a specific function.
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Explain how a sperm cell is specialised for carrying out its role
A sperm cell has a single undulipodium to help propel it through the uterine tract towards the egg. The sperm also has an acrosome which releases enzymes to help penetrate the egg, also many mitochondria to help generate energy in the form ATP.
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How are neutrophils specialised for their role?
Multi-lobed nucleus which allows for greater flexibility, lysosomes which release enzymes to kill ingested microorganisms.
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How are red blood cells adapted to make them efficient in the collection of oxygen and its transport to the tissues?
No nucleus or mitochondria to allow more space for haemoglobin which carries the oxygen, RBCs have about the same diameter of a capillary so there is a short diffusion path, RBCs are bioconcave discs so have a large SA:V ratio - faster diffusion.
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Describe the structure of squamous epithlial tissue.
Flattened cells ideal for lining inside tubes such a blood vessels. SE tissue also forms thin walls i.e. in alveoli, to provide a short diffusion path. SE tissue is held in place by the basement membrane - made of collagen and glycoproteins.
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What is the name for the form of asexual reproduction in plants?
Vegetative propagation
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By which process do bacteria divide?
Binary fission
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Why can bacteria be used for genetic engineering?
They can swap plasmids which has genes for antibiotic resistance.
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The fusion of two gametes form a....
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What is the difference between diploid and haploid cells?
Diploid cells contain two sets of chromosomes (46 chromosomes), haploid cells contain half the number of chromosomes (23).
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Card 2


What is resolution?


The degree to which it is possible to distinguish between two objects that are very close together. Higher resolution = greater detail.

Card 3


What is the resolution of a light microscope and an electron microscope?


Preview of the front of card 3

Card 4


What are the differences between TEM and SEM?


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Card 5


What are limitations of an electron microscope?


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