AQA A-Level Biology Paper 1: 2021 Exam Questions and Answers, Exams of Advanced Education

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Aqa a level biology paper 1 2021

Describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst - 1. Substrate binds to the active

2. Active site changes shape (slightly) so it is complementary to substrate
3. Reduces activation energy; Tick () one box to show which other substrate the scientists must add to the reaction mixtures to produce ATP - B Suggest and explain a procedure the scientists could have used to stop each reaction - 1. Boil
4. Denatures the enzyme/ATP synthase; Explain the change in ATP concentration with increasing inorganic phosphate concentration - 1. (With) increasing Pi concentration, more enzyme-substrate complexes are formed;
5. At or above 40 (mmol dm-3 ) enzyme concentration is a limiting factor Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake - 1. Large(r) organisms have a small(er) surface area to volume (ratio);
6. therefore faster diffusion due to overcoming the long diffusion pathway Suggest how the environmental conditions have resulted in adaptations of systems using Model A rather than Model B - 3. Water is dense(r) (than air);
7. (So) water supports the systems/gills; A student studied Figure 3 and concluded that the fish gas exchange system is more efficient than the human gas exchange system. Use Figure 3 to justify this conclusion - 1. In fish, blood leaving (V) has more oxygen than water leaving (E);
8. (But) in humans, blood leaving (V) has less oxygen than air leaving (E);
9. Difference in oxygen (concentration) between artery and vein is greater in fish than in humans;
10. (So) fish remove a greater proportion from the oxygen they take in;

Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system. - 1. Blood and water flow in opposite directions; 2.Diffusion gradient (maintained) along (length of) lamella Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation - 1. tRNA brings specific amino acid (to ribosome);

2. Anticodon (on tRNA) binds to codon (on mRNA);
3. Amino acids join by condensation reaction (using ATP) to form a peptide bond Use information in Table 2 to suggest why this amino acid replacement changes the properties of crystallin - 1. Hydrogen bonds form instead of ionic bonds;
4. Changes the tertiary structure (of the crystallin); Complete Table 3. - mRNA codon for the non-mutant triplet AGG Mutated mRNA codon GGG Mutated DNA triplet CCC Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection - 1. Only use single lines
   2. Add labels 2 Identify the type of blood vessel labelled as X and the type of blood vessel labelled as Y in Figure 4. Describe one feature that allowed you to identify the blood vessels. [ - 1. Blood vessel X - artery/arteriole and Blood vessel Y - vein/venule;
5. (Difference in) lumen size Describe two precautions the student should take when clearing away after the dissection - 1. Carry instruments by holding handle
6. Disinfect instruments

Describe how a sample of chloroplasts could be isolated from leaves. - 1. Break open cells using a blender blend

2. In cold, same water potential
3. place it in a Centrifuge and spin and remove cell debris;
4. (Centrifuge/spin) at high(er) speed, chloroplasts settle out; Give one feature of the chloroplast that allows protein to be synthesised inside the chloroplast and describe one difference between this feature in the chloroplast and similar features in the rest of the cell - 1. DNA;
5. Is not associated with protein/histones but nuclear DNA is Use Figure 6 to suggest why iron-deficient plants have a reduced growth rate. - 1. Less (thylakoid) membrane
6. Smaller surface area (of membrane in chloroplast)
7. (Less chlorophyll so) reduced light absorption;
8. (So) slower rate of photosynthesis Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases - 1. C = prophase and D = metaphase and E = anaphase;
9. (In) prophase, chromosomes condense;
10. (In) prophase OR metaphase, centromeres attach to spindle fibres;
11. (In) metaphase, chromosomes/pairs of chromatids at equator/centre of spindle/cell;
12. (In) anaphase, centromeres divide; 6. (In) anaphase, chromatids (from each pair) pulled to (opposite) poles/ends (of cell);
13. (In) prophase/metaphase/anaphase, spindle fibres shorten Use your knowledge of phagocytosis to describe how an ADC enters and kills the tumour cell - 1. Cell engulfs the antibody
14. Lysosomes fuse with vesicle(containing ADC);
15. Lysozymes digest the antibody to release the drug

Use this information to explain why treatment with an ADC often causes side effects - 1. ADC will bind to non-tumour cells;

2. Cause death to healthy cells Suggest one reason why there are no data for Group G and Group H after day 8 - Mice died Suggest and explain two further investigations that should be done before this ADC is tested on human breast cancer patients - 1. Tested on other mammals to check for safety/side effects;
3. Tested on (healthy) humans to check for safety/side effects; Describe how a triglyceride molecule is formed - 1. One glycerol and three fatty acids;
4. Condensation (reactions) and removal of three molecules of water;
5. Ester bond(s) (formed) Suggest one reason why they used a data logger and explain why this was important in this investigation

• 1. To increase accuracy because differences in lengths are small Use this information and Table 6 to show how each population is better adapted for its natural environment when compared with the other population. - 1. Population 1 grew longer roots in warm temperatures and population 2 grew longer roots in cool temperatures;

2. Standard deviations do not overlap so difference (in mean) unlikely to be/not due to chance;
3. Population 1 (is better adapted to warm conditions because it) has more saturated fatty acids so more energy available (and more growth);
4. Population 2 (is better adapted to cool conditions because it) has more unsaturated/liquid fatty acids so more lipase activity (and more growth); Although these two populations are completely separate and show genetic variation, they are both called Helianthus annuus. Explain why they are both given this name - same species so if mated they can produce fertile offspring Which of these models, P, Q or R, is supported by the results shown in Figure 12?

Give the letter and name of the model supported and explain why the results do not support the other models - 1. (Model) Q and (Name) Semi-conservative (replication); Explanation 2. (Model) P (is unsupported because) There should be two peaks in generation 1 3. (Model) R (is unsupported because) There should be >2 peaks in generation 2/ Describe the structure of DNA. - 1. Polymer of nucleotides;

2. Each nucleotide formed from deoxyribose, a phosphate (group) and an organic/nitrogenous base;
   3. Phosphodiester bonds (between nucleotides);
3. Double helix strands held by hydrogen bonds;
4. (Hydrogen bonds/pairing) between adenine, thymine and cytosine, guanine; Name and describe five ways substances can move across the cell-surface membrane into a cell - 1. (Simple) diffusion of small/non-polar molecules down a concentration gradient;
5. Facilitated diffusion down a concentration gradient via protein carrier/channel;
6. Osmosis of water down a water potential gradient;
7. Active transport against a concentration gradient via protein carrier using ATP;
8. Co-transport of 2 different substances using a carrier protein Contrast the structure of the two cells visible in the electron micrographs shown in Figure 14 - 1. Magnification (figures) show A is bigger than B;
9. A has a nucleus whereas B has free DNA;
10. A has mitochondria whereas B does not; 4. A has Golgi body/endoplasmic reticulum whereas B does not;
11. A has no cell wall whereas B has a murein/glycoprotein cell wall;
12. A has no capsule whereas B has a capsule;