2021 a level paper 1

• describe the induced-fit model of enzyme action and how an enzyme acts as a catalyst.

  substrate will bind to the active site, active site will slightly change in shape to become complementary to substrate this reduces activation energy.
• Suggest and explain a procedure the scientists could have used to stop each reaction.

  put in ice bath to reduce kinetic energy so no more enzyme-substrate complexes form
• Explain the change in ATP concentration with increasing inorganic phosphate concentration.

  increase in inorganic phosphate increases amount of enzyme-substrate complexes formed, however at 40mmol dm-3 enzyme concentration becomes a limiting factor
• explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake.

  larger organisms have a smaller surface area to volume ratio which allows for faster diffusion.
• Suggest how the environmental conditions have resulted in adaptations of systems using Model A rather than Model B.


  water is denser than air therefore water supports the system
• 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.

  in fish, blood leaving has more oxygen than water leaving but in humans blood leaving has less oxygen than air leaving
• Explain how the counter-current principle allows efficient oxygen uptake in the fish gas exchange system

  blood and water flow in opposite directions meaning diffusion is maintained along the gill filament
• Describe how one amino acid is added to a polypeptide that is being formed at a ribosome during translation.

  tRNA bring a specific amino acid to the ribosome and amino acids join by condensation reaction forming a peptide bond
• Use information in Table 2 to suggest why this amino acid replacement changes the properties of crystallin.

  hydrogen bonds form instead of ionic bonds which changes the tertiary structure
• Suggest two ways the student could improve the quality of his scientific drawing of the blood vessels in this dissection.

  use one continuous line and do not shade
• 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.

  blood vessle x = artery

  blood vessle y = vein

  the feature that allowed me to identify is the size of the lumen
• Describe two precautions the student should take when clearing away after the dissection.

  carry scalpel by the handle, disinfect surfaces and hands.
• Describe how a sample of chloroplasts could be isolated from leaves.

  blend cells and filter

  place the cells in a cold, isotonic solution. centrifuge the solution at a low speed to remove dense organelles. centrifuge at a higher speed so the chloroplasts can settle into a pellet and be removed.
• 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.


  feature = ribosomes

  structural difference = smaller than the ribosomes in cytoplasm
• Use Figure 6 to suggest why iron-deficient plants have a reduced growth rate.

  they have less thylakoid membrane, therefore smaller surface area and less chlorophyll. reduced amounts of chlorophyll reduces light absorption
• Describe the role of the spindle fibres and the behaviour of the chromosomes during each of these phases.

  c = prophase

  d =metaphase

  e = anaphase

  in prophase chromosomes condense. during metaphase centromeres attach to spindle fibres and chromosomes line up at equator of the cell. in anaphase centromeres divide and chromatids are pulled to opposite poles of the cell.
• Use your knowledge of phagocytosis to describe how an ADC enters and kills the tumour cell.

  cell will engulf the antibody, lysosomes will fuse with vesicle and lysozymes will break down the antibody.
• Some of the antigens found on the surface of tumour cells are also found on the surface of healthy human cells. Use this information to explain why treatment with an ADC often causes side effects

  ADC will bind to healthy cells and cause death of the 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.

  test on rats to check the side effects and test on humans to check for side effects
• Describe how a triglyceride molecule is formed.

  one glycerol molecule and three fatty acids join together via a condensation reaction and remove three molecules of water forming ester bonds
• Suggest one reason why they used a data logger and explain why this was important in this investigation.

  incresase accuracy as it reduces chances of human errors
• 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
• Give the letter and name of the model supported and explain why the results do not support the other models


  model =q

  name = semi conservative replication

  explanation for first unsupported model= there should be 2 peaks in generation 1

  explanation for second unsupported model =
• Describe the structure of DNA.

  polynucleotide, each nucleotide is formed from deoxyribose, a phosphate group and a nitrogenous base. the bonds between nucleotides are phosphodiester bonds. dna is a double helix structure. hydrogen bonds bases and forms between adenine and thymine and cytocsine and guanine
• Name and describe five ways substances can move across the cell-surface membrane into a cell.

  active transport against a concentration gradient.

  osmosis of water down a water potential gradient.

  facilitated diffusion down a concentration gradient via a protein channel.

  simple diffusion of small molecules down a concentration gradient
• Contrast the structure of the two cells visible in the electron micrographs shown in Figure 14.

  a has a nucleus whereas b has free dna. a has mitochondria whereas b does not. a has no cell wall whereas b has meruin cell wall. a has no capsule whereas b has a capsule. a has larger ribosomes.