June 2023

Question 1

1.2. State 1 function of the capsule and 1 function of the pilus. (2)

Answer 1

Capsule
1. protects from drying out / protects from phagocytosis / attachment to surfaces or other cells
Pilus
2. movement / attachment to surfaces or other cells / exchange of plasmids / conjugation

Question 2

2.4. Some students investigate the effect of the conc. of salt on the growth of strawberries. Suggest 2 reasons why 50 strawberry seeds are planted but the students choose only 20 plants for the investigation. (2)

Answer 2

2 max:
1. (idea that) Not all the seeds will germinate
2. Want them to be the same height / size / they have the same starting point
3. It allows a comparison to be made
4. To reduce competition

Question 3

3.1. A scientist researches the effect of a herbicide on the abundance of different species
of plant. The scientist collects data from two fields. One field is treated with herbicide
and the other is not treated with herbicide. Describe a method to sample the fields randomly (3)

Answer 3

Any three from:

1. Use a quadrat
2. Key to identify the species
3. (Tape measure to) set out a grid / co-ordinates
4. Random number generator

Question 4

3.4. The scientist uses the index of diversity rather than using species richness. Why? (2)

Answer 4

Species richness
1. Is the total number of different species
Index of diversity
2. Is the total number of different species and includes the number of individuals in each species

Question 5

3.5. Name 2 molecules, other than DNA, that can be used to classify a species. (2)

Answer 5

Accept answers in either order
1. mRNA
2.Protein / polypeptide

Question 6

4.4. Explain the importance of the tertiary structure of an enzyme. (2)

Answer 6

1. Provides specific shape for the active site
2. (so that) substrate fits/is complementary to/binds into/attaches to the active site

Question 7

5.2. Describe how crossing over and independent segregation of homologous chromosomes cause genetic variation in the gametes. (2)

Answer 7

Crossing over
1. (Chromatids are produced with) different / new combinations of alleles

Independent segregation
2. Different combinations of chromosomes (1 and 2) / maternal and paternal chromosomes are produced

Question 8

5.3. Each gamete has only one allele of each gene. Describe how this occurs. (3)

Answer 8

3 max:
1. Homologous chromosomes / pairs are separated from one another
2. (Sister) chromatids are then separated / split from one another
3. The idea of each chromatid carrying one allele
4. Spindle (fibres) pull the chromosomes / chromatids to opposite poles of the cell

Question 9

6.3. State 1 advantage of the increase in the affinity of haemoglobin for oxygen. (1)

Answer 9

(ensures / results in) greater uptake of oxygen (by Hb) in the lungs / exchange surface

Question 10

7.5. Many of the bacterial species in the digestive system have only recently been
classified. Suggest why it might be difficult to give a species name to a bacterium. (1)

Answer 10

one of:
1. Asexual reproduction / can’t reproduce together and make fertile offspring / can’t sexually reproduce
2. Horizontal transmission / conjugation
3. Difficult to observe / identify physical characteristics
4. Issues accessing the bacteria

Question 11

7.7. Scientists compare the effect of fibre intake on the diversity of organisms living in the human digestive system. Other factors could affect this diversity. Scientists would need to consider these other factors when analysing data from participants.
Suggest two other factors that could affect diversity. (2)

Answer 11

2 of:
1. Diet e.g., sugar / salt / fat / alcohol / meat / dairy / probiotics levels
2. Microorganism exposure / competition with pathogens
3. Lifestyle
4. Exposure to antibiotics