A-Level Biology 5-6 Markers 2024, Exams of Advanced Education

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A-Level Biology 5-6 Markers

Explain how microorganisms in the soil produce a source of nitrates from the remains of crop plants - 1) Protein/amino acids/DNA, into ammonium compounds/ ammonia

2. By saprobionts
3. Ammonium/ammonia into nitrite
4. Nitrite into nitrate
5. By nitrifying bacteria
6. Nitrogen to ammonium/ ammonia
7. By nitrogen-fixing bacteria in soil Describe advantages and disadvantages of using chemical pesticides to control pests of crops - (Advantages)
8. Acts quickly
9. Can apply to particular area
10. Kills wide variety of plants (Disadvantages)
11. Needs to be reapplied
12. Not specific
13. Pests can develop resistance
14. (Bio)accumulation IGNORE ref. to leaching/eutrophication Describe how plants use light energy in the light-dependent reaction - 1) Excites electrons/ removes electrons from chlorophyll
15. Electrons move along carriers/ electron transfer chain, releasing energy
16. Energy used to join ADP and Pi to form ATP

4. Photolysis of water produces protons, electrons and oxygen
5. NADP reduced by electrons/electrons and protons/ hydrogen Describe competitive and non-competitive inhibition of an enzyme - 1) Inhibitors reduce binding of enzyme to substrate (Competitive)
6. Inhibitor similar tertiary structure to substrate
7. Binds to active site
8. Inhibition can be overcome by more substrate added (Non-competitive)
9. Inhibitor binds to side other than active site (allosteric) on enzyme
10. Changes shape of active site
11. Cannot be overcome by adding more substrate Explain why maltase:

• only breaks down maltose
• allows this reaction to take place at normal body temperature - 1) Tertiary structure of enzyme (means)

2. Active site is complementary to maltose
3. Description of induced fit
4. Enzyme is a catalyst
5. Lowers activation energy required
6. By forming enzyme-substrate complexes Explain how the diet of a person can increase the risk of coronary heart disease - 1) Too much saturated fat/ cholesterol in diet
7. Increase in cholesterol in blood
8. Atheroma plaques in artery walls

4. Reduces diameter of coronary arteries
5. Less oxygen/glucose to heart tissue
6. Increase in blood pressure
7. (Increased risk of) clot/ thrombosis/ embolism/ aneurysm Describe how the heart controls and coordinates the regular contraction of the atria and ventricles - 1) SAN -> AVN -> bundle of His
8. Impulses/ electrical activity (over atria)
9. Atria contract
10. Non-conduction tissue (between atria and ventricles)
11. Delay (at AVN) ensures atria empty before ventricles contract
12. Ventricles contract from apex upwards Describe the processes involved in the absorption of the products of starch digestion - 1) Glucose moves in with sodium (into epithelial cell)
13. Via. (carrier/channel) protein
14. Sodium removed (from epithelial cell) by active transport
15. Into blood
16. Maintaining low sodium concentration (in epithelial cell)/ sodium concentration gradient (between lumen and epithelial cell)
17. Glucose moves into blood
18. By (facilitated) diffusion Describe the role of the enzymes of the digestive system in the complete breakdown if starch - 1) Amylase
19. (Starch) to maltose
20. Maltase
21. Maltose to glucose

5. Hydrolysis
6. Of glycosidic bonds Explain how the epithelial cells that line the small intestine are adapted for absorption of glucose - 1) Microvilli
7. Large/increased surface area
8. Many mitochondria
9. (Mitochondria/ respiration) produce ATP (for active transport)
10. Carrier protein for active transport
11. Channel/ carrier proteins for facilitated diffusion
12. Co-transport of sodium (ions) and glucose or symport/ carrier proteins for sodium (ions) and glucose
13. Membrane-bound enzymes digest disaccharides/ produce glucose Describe how trees convert carbon dioxide into organic substances during photosynthesis. - 1) Carbon dioxide combines with ribulose bisphosphate/ RuBP
14. Produces two molecules of glycerate (3-) phosphate/ GP
15. Reduced to triose phopshate/ TP
16. Using reduced NADP
17. Using energy from ATP
18. Triose phosphate converted to other organic substances/ named organic substances/ ribulose bisphosphate
19. In light independent reaction/ Calvin cycle Explain how the use of pesticides can result in resistant strains of insect pests - 1) Variation/ variety in pest population
20. Due to mutation
21. Allele for resistance
22. Reference to selection
23. Pests with resistance (survive and) breed/ differential reproductive success

6. Increase in frequency of allele Explain how farming practises increase the productivity of agricultural crops - 1) Fertilisers/ mineral/ named ion (added to soil)
7. Role of named nutrient/ element e.g. nitrate/ nitrogen for proteins / phosphate/ phosphorus for ATP/DNA
8. Pesticides/biological control prevents damage/consumption of crop
9. Pesticides/weed killers/herbicides/weeding remove competition
10. Selective breeding / genetic modification (of crops)
11. Glass/greenhouses enhance temp/CO2/light
12. Ploughing aerates soil/improves drainage
13. Ploughing/aerates allows nitrifcation
14. Benefit of crop rotation in terms of soil nutrients/fertility/pest reduction
15. Irrigation/water to remove limiting factor
16. Protection of crops from birds/pests/frost by covers/netting etc. Explain how nitrates may cause the death of fish in fresh water. - 1) Growth of algae/surface plants blocks light
17. Reduced/no photosynthesis so (submerged) plants die
18. Saprobiotic (microorganisms/bacteria)
19. Aerobically respire / use oxygen in respiration
20. Less oxygen for fish to respire / aerobic organisms die Describe and explain how cell fractionation and ultracentrifugation can be used to isolate mitochondria from a suspension of animal cells/enzyme - 1) Cell homogenisation to break open cells
21. Filter to remove (large) debris/whole cells
22. Use isotonic solution to prevent damage to mitochondria/organelles
23. Keep cold to prevent/reduce damage by enzymes / use buffer to prevent protein/enzyme menstruation
24. Centrifuge (at lower speed/1000g) to separate nuclei/cell fragments/heavy organelles

6. Re-spin (supernatant / after nuclei/pellet removed) at higher speed to get mitochondria in pellet/at bottom Describe the principles and the limitations of using a transmission electron microscope to investigate cell structure - Principles
7. Electrons pass through/enter (thin) specimen
8. Denser parts absorb more electrons
9. (So) denser parts appear darker
10. Electrons have short wavelength so give high resolution Limitations
11. Cannot look at living material / must be in a vacuum
12. Specimen must be (very) thin
13. Artefacts present
14. Complex straining method / complex/long preparation time
15. Image not in 3D / only 2D images produced Describe how a vaccine leads to the production of antibodies against a disease-causing organism - 1) Vaccine contains antigen from pathogen
16. Macrophage presents antigen on its surface
17. T cell with complementary receptor protein binds to antigen
18. T cell stimulates production of B cells
19. (With) complementary antibody on its surface
20. B cells secrete large amounts of antibody
21. B cells divide to form clones all producing same antibody Describe the difference between active and passive immunity - 1) Active involves memory cells, passive does not
22. Active involves production of antibody by plasma/memory cells
23. Passive involves antibody introduced into body from outside

4. Active long term, because antibody produced in response to antigen
5. Passive short term, because (given) antibody is broken down
6. Active can take time to develop/work, passive fact acting Describe what happens to chromosomes in meiosis - 1) Chromosomes shorten/thicken/condense
7. Chromosomes associate in homologous pairs / form bivalents
8. Crossing over
9. Join to spindle fibres
10. (At) equator/middle of cell
11. (Join via.) centromere
12. (Homologous) chromosomes mive to opposite poles
13. (Pairs of) chromatids separated in 2nd division