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Description
Flashcards by Mia Weaver, updated more than 1 year ago
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Created by Mia Weaver
about 5 years ago
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| Question | Answer |
| Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells. (5 marks) | Any 5 from: - Cell homogenisation to break open cells - Filter to remove large debris / whole cells - Use isotonic solution to prevent damage to mitochondria/organelles - Keep cold to prevent/reduce damage by enzymes / use buffer to prevent protein/enzyme denaturation - Centrifuge at lower speed to separate nuclei / cell fragments / heavy organelles - Re-spin supernatant at higher speed to get mitochondria in pellet / at bottom. |
| Describe the principles and limitations of using a transmission electron microscope to investigate cell structure. (5 marks) | Principles: (max 3) - Electrons pass through/enter thin specimen - Denser parts absorb more electrons - So denser parts appear darker - Electrons have short wavelength so give high resolution Limitations: (max 3) - Cannot look at living material / Must be in a vacuum - Specimen must be very thin - Artefacts present - Complex staining method / complex / long preparation time - Image not in 3D / only 2D images produced. |
| Describe how you could use cell fractionation to isolate chloroplasts from leaf tissue. (3 marks) | - How to break open cells and remove debris (e.g. homogenisation and filtering) - Solution is cold/isotonic/buffered; - The Second pellet is chloroplast. |
| Name two structures in a eukaryotic cell that cannot be identified using an optical microscope. (2 marks) | Any 2 from: Mitochondrion / ribosome / endoplasmic reticulum / lysosome / cell-surface membrane. |
| Describe what happens during anaphase that results in the production of two genetically identical cells. (2 marks) | - Sister / identical chromatids / identical chromosomes - To opposite poles / ends / sides |
| A sample of epithelial tissue was analysed. Some of the cells had 8.4 units of DNA, others had only 4.2 units. Use your knowledge of the cell cycle to explain why some cells had 8.4 units of DNA and others had only 4.2 units. (2 marks) | - 8.4 / cells with twice DNA content = replicated DNA / late interphase / prophase / metaphase / anaphase - 4.2 = DNA not replicated / early interphase / telophase / cell just divided / finished mitosis |
| Mitosis is important in the life of an organism. Give two reasons why. (2 marks) | Any 2 from: - Growth/increase in cell number - Replace cells / repair tissue / organs / body - Genetically identical cells - Asexual reproduction / cloning |
| Name two structures present in an epithelial cell from the small intestine that are not present in a cholera bacterium. (2 marks) | Any 2 from: - Nucleus / nuclear envelope / nuclear membrane / nucleolus - Mitochondrion - Smooth / rough ER - Lysosome - Microvillus/brush border - Golgi - Linear / non-circular DNA / chromosome - 80S/ denser/heavier/larger ribosomes |
| Give one advantage of using a TEM rather than a SEM. (1 mark) | - Higher resolution / higher magnification / higher detail of image OR - Allows internal details/structures within cells to be seen / cross-section to be taken |
| Give one advantage of using a SEM rather than a TEM. (1 mark) | - Thin sections do not need to be prepared / shows surface of specimen / can have 3-D images |
| An optical microscope cannot be used to see a plasma membrane. Explain why. (2 marks) | - Does not have the resolution / cannot distinguish between points this close together - As light has longer wavelength |
| Give one property of molecules which can diffuse through a cell membrane. (1 mark) | - Lipid soluble / small / non-polar / not charged |
| A group of scientists homogenised pancreatic tissue before carrying out cell fractionation to isolate an organelle. Explain why scientists: Homogenised the tissue. (1 mark) | - Breaks open cells / disrupts cell membrane / releases cell contents / releases organelles / break up cells |
| A group of scientists homogenised pancreatic tissue before carrying out cell fractionation to isolate an organelle. Explain why scientists: Filtered the resulting suspension. (1 mark) | - Removes cell debris / complete cells / tissue |
| A group of scientists homogenised pancreatic tissue before carrying out cell fractionation to isolate an organelle. Explain why scientists: Kept the suspension ice cold during the process. (1 mark) | - Reduces/prevents enzyme activity |
| A group of scientists homogenised pancreatic tissue before carrying out cell fractionation to isolate an organelle. Explain why scientists: Used isotonic solution during the process. (2 marks) | - Prevents osmosis / no net movement of water / water does not enter organelle / water does not leave organelle - So the organelle is not damaged / does not burst / does not shrivel |
| Contrast the processes of facilitated diffusion and active transport. (3 marks) | - Facilitated diffusion involves channel or carrier proteins whereas active transport only involves carrier proteins - Facilitated diffusion does not use ATP / is passive whereas active transport uses ATP - Facilitated diffusion takes place down a concentration gradient whereas active transport can occur against a concentration gradient. |
| Explain why an antibody attaches only to a specific protein. (2 marks) | - An antibody has tertiary structure - Which is complementary to binding site on the protein. |
| If the DNA of the cell is damaged, a protein called p53 stops the cell cycle. Mutation in the gene for p53 could cause cancer to develop. Explain how. (3 marks) | - Cancer cells often have faulty / damaged DNA - Protein / p53 faulty / not made - Cell (with faulty DNA) divides / completes cell cycle - Uncontrolled division produces cancer |
| Drugs are used to treat cancer. At what phase in the cell cycle would each of the following drugs act? (i) A drug that prevents DNA replication (ii) A drug that prevents spindle fibres shortening. (2 marks) | - Interphase / S phase / synthesis phase - Anaphase / A |
| A mutation of a tumour suppressor gene can result in the formation of a tumour. Explain how. (2 marks) | - Tumour suppressor gene inactivated / not able to control / slow down cell division - Rate of cell division too fast / out of control. |
| Some cancer cells have a receptor protein in their cell-surface membrane that binds to a hormone called growth factor. This stimulates the cancer cells to divide. Scientists have produced a monoclonal antibody that stops this stimulation. Use your knowledge of monoclonal antibodies to suggest how this antibody stops the growth of a tumour. (3 marks) | - Antibody has specific tertiary structure / binding site / variable region - Complementary shape/fit to receptor protein / GF / binds to receptor protein / to GF - Prevents GF binding to receptor. |
| Scientists use a specific antibody to detect an antigen on the bacterium that causes stomach ulcers. Explain why the antibody will only detect this antigen. (3 marks) | - Antibody / variable region has specific amino acid sequence / primary structure - The shape / tertiary structure of the binding site is complementary to / fits / binds with these antigens - Forms complex between antigen and antibody |
| People with AIDS die because they are unable to produce an immune response to pathogens. Explain why this leads to death. (3 marks) | - Infected by / susceptible to other pathogens - Pathogens reproduce / cause diease in host - Damage cells / tissues / organs - Release toxins |
| What is an antigen? (2 marks) | - molecule/part of molecule/protein/ glycoprotein/named molecule - that stimulates an immune response |
| Describe how B-lymphocytes respond when they are stimulated by antigens. (4 marks) | - divide by mitosis / form clones - produce plasma cells - plasma cells make antibodies - plasma cells produce memory cells |
| Most of the water uptake in a root takes place in the region just behind the root tip. Explain why. (2 marks) | -Presence of root hairs -The area is permeable and has a large surface area |
| Name the stage of mitosis that immediately follows anaphase. (1 mark) | - Telophase |
| A clone of genetically identical animals can be obtained from one embryo. Explain how. (2 marks) | - The embryo is split into cells - Each cell is undifferentiated - Then they are split by mitosis |
| Describe and explain 3 organelles you would see in large numbers in an exocrine cell in the pancreas. (6 marks) | Any 3 from: - Golgi vesicles: To transport and release substances. - Rough E.R.: As the ribosomes on it synthesise proteins. - Golgi apparatus: To modify and package proteins. - Mitochondria: To release energy for protein synthesis. |
| Describe and explain 3 organelles you would see in large numbers in an epithelial cell lining the small intestine. (6 marks) | - Golgi apparatus: Modify and package proteins. - Mitochondria: To release energy for active transport. - Rough E.R.: Ribosomes on it synthesise proteins. |
| What is a pathogen? (1 mark) | - A microorganism that causes disease |
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