Jan 2023

Question 1

1.3. Describe how the nucleus controls the activities of the cell. (2)

Answer 1

any two from:
1. Produces mRNA / tRNA
2. Contains the DNA/genetic material of the cell OR contains chromosomes OR contains the code for proteins / enzymes
3. Makes ribosomal RNA / rRNA / ribosomes

Question 2

1.5. Describe how mitochondria helps in protein synthesis. (2)

Answer 2

(1) (Organelle A/mitochondrion) makes ATP
(2) (ATP) provides energy for peptide bond formation OR provides energy for joining amino acids

Question 3

1.8. Explain how ultracentrifugation separates cell organelles. (2)

Answer 3

1. Spin at increasing speed
2. Separates organelles depending on mass / density

Question 4

3.2. Explain one way that meiosis results in genetic variation. (2)

Answer 4

1. Crossing over (between homologous chromosomes)
2. Causes new combinations of alleles
   OR
3. Independent segregation (of homologous chromosomes)
4. Different combinations of (maternal and paternal) chromosomes / alleles

Question 5

4.2. Explain why ecologists find it more useful to calculate the index of diversity than to only record the number of species present. (2)

Answer 5

1. (Index of diversity takes into account) number of species present
2. (And) number of individuals of each species

Question 6

4.3. Suggest why the ecologists can only estimate the population sizes of the fish in a specific section of the river. (1)

Answer 6

Difficult to catch all the fish OR fish can migrate up / down river

Question 7

5.5. Vancomycin is an antibiotic that can be used to treat S. aureus infections. Vancomycin prevents the formation of pentaglycine bridges between peptide chains in murein. Suggest how vancomycin prevents the growth of a population of bacteria. (2)

Answer 7

1. Prevents synthesis of (new) cell walls
2. So bacteria cannot reproduce
   OR
3. Weakens cell wall
4. So cell contents leak out OR lysis / bursting of cells

Question 8

6.1. Define the term tissue. (1)

Answer 8

A collection of similar/identical cells that perform a specific function

Question 9

6.2. Explain why plants need a specialised tissue to transport the products of photosynthesis (2)

Answer 9

1. (Plants are large so) have a small surface area to volume ratio OR (Plants/acacias have) long distances for transport
2. (small SA:V so) mass transport needed for efficient supply of materials OR diffusion too slow

Question 10

6.6. Suggest why having small leaves and thick waxy cuticles could be a disadvantage to plants. (2)

Answer 10

1. (Small so) reduces surface area for gas exchange OR fewer stomata for gas exchange OR reduces surface area for photosynthesis / light absorption
2. (Thick, waxy cuticle so) increases diffusion distance for gases OR diffusion of gases cannot occur

Question 11

7.4. Carbon monoxide attaches to oxygen-binding sites on haemoglobin. Carbon monoxide poisoning is treated in hospital using pure oxygen. Explain why the binding of carbon monoxide to haemoglobin is an example of competitive inhibition. (2)

Answer 11

1. (CO) competes with oxygen for binding site(s) or
   CO similar shape to O2 so fits / combines with binding site on Hb or Prevents oxygen from binding or Blocks (oxygen) binding sites
2. Increasing oxygen conc. decreases effect (of inhibitor / carbon monoxide)