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AQA A+Level Biology_ Paper 1Solutions
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AQA A+Level Biology: Paper1Solutions
1.1 Describe the induced fit model of enzyme action and how an enzyme acts as a
catalyst. - ANS-- The substrate binds to the active site and forms an ES complex. -
The active site changes shape slightly so it's complimentary to the substrate. -
This reduces the activation energy.
1.2 Tick one box to show which are the substrate the scientists must add to the reaction
mixture is to produce ATP. - ANS-- Adenosine diphosphate.
1.3 Suggest and explain a procedure the scientist could have used to stop each
reaction. - ANS-- The nature of the enzyme by putting it in ice.
1.4 Explain the change in ATP concentration with increasing inorganic phosphate
concentration - ANS-- With increasing phosphate concentration more ES complex is
form.
- And at 40 mol dm3, all active sites are occupied.
2.1 Explain the advantage for large animals of having a specialised system that
facilitates oxygen uptake. - ANS-- Large organisms have a smaller surface area to
volume ratio.
- This means they overcome a long diffusion pathway.
2.2 Suggest how the environmental conditions have resulted in adaptations of systems
using model A rather than model B. - ANS-- Water is more dense than air. - So it
supports the gills.
2.3 A student studies 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. -
ANS-- The difference of oxygen concentration between the artery and vein is larger in
the fish than the human.
- So the fish remove a greater amount of oxygen that they intake.
2.4 Explain how the countercurrents principle allows sufficient oxygen uptake in the fish
gas exchange system. - ANS-- Blood and water continuously flow in opposite directions.
, - So the concentration gradient is maintained along the length of the lamellae.
3.1 Describe how one amino acid is added to a polypeptide that is being formed at a
ribosome during translation. - ANS-- TRNA brings the specific amino acid to the
ribosome.
- The anticodon on the tRNA binds to the codon on the mRNA.
- The amino acids join to form a peptide bond using ATP.
3.2 Use information in table to to suggest why this amino acid replacement changes the
properties of crystallin. - ANS-- The hydrogen bonds form instead of the ionic bonds. -
And it changes the tertiary structure of the crystallin.
3.3 MRNA codon for the non-mutant triplets.
mutated mRNA codon.
Mutated DNA triplet. - ANS-- AGG
- GGG
- CCC
4.1 Suggest two ways the student could improve the quality of his scientific drawing of
the blood vessels in this dissection. - ANS-- Add labels.
- Don't use shading.
4.2 Describe one feature that allows you to identify the blood vessels.
Blood vessel X
Blood vessel Y
Feature - ANS-- Artery
- Vein
- They have different wall thicknesses.
4.3 Describe two precautions the student should take when clearing away after the
dissection. - ANS-- Disinfect all instruments.
- Disinfect hands.
5.1 Describe how a sample of chloroplasts could be isolated from leaves. - ANS-- Break
open the cells and filter it.
- Keep it in the cold to ensure it has the same water potential.
- Keep it in a controlled pH.
- Centrifuge it to remove cell debris.
- And centrifuge at increase in speeds so the chloroplast can settle out.
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