Genetic diversity PPQs

Question 1

Some populations of animals that have never been hunted show very low levels of genetic diversity. Other than hunting, suggest two reasons why populations might show very low levels of genetic diversity. (2 marks)

Answer 1

1. (Hunting) reduced population size(s), so (much) only few alleles left;
   Accept bottleneck
2. Otters today from one / few surviving population(s);
   Accept founder effect
3. Inbreeding.

Question 2

The stringent response involves a number of enzyme-catalysed reactions. Explain how scientists could use this knowledge to design drugs that make the treatment of infections caused by the SR strain more successful. (2 marks)

Answer 2

1. Make a competitive / non-competitive inhibitor;

2. Competitive competes with / blocks active site / non-competitive inhibitor affects / changes active site;

Question 3

There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin. Explain why there was a time lag. (3 marks)

Answer 3

1. Initially one / few insects with favourable mutation / allele;
2. Individuals with (favourable) mutation / allele will have more offspring;
3. Takes many generations for (favourable) mutation / allele to become the most common allele (of this gene

Question 4

The KDR plus allele codes for the sodium ion channels found in neurones. When DDT binds to a sodium ion channel, the channel remains open all the time. Use this information to suggest how DDT kills insects. (2 marks)

Answer 4

1. Neurones remain depolarised;

2. So no action potentials / no impulse transmission.

Question 5

Suggest how the KDR minus allele gives resistance to DDT. (2 marks)

Answer 5

1. (Mutation) changes shape of sodium ion channel (protein) / of receptor protein;
2. DDT no longer complementary / no longer able to bind.

Question 6

Name two ways in which meiosis produces genetic variation. (2 marks)

Answer 6

1. Independent segregation (of homologous chromosomes);

2. Crossing over

Question 7

Identify one event that occurred during division 2 but not during division 1 of meiosis (1 mark)

Answer 7

Separation of (sister) chromatids / division of centromere.

Question 8

Describe what has happened during division 1 in the figure above. (2 marks)

Answer 8

1. Chromosomes in homologous pair;

2. One of each into daughter cells / haploid number.

Question 9

Aspartic acid and proline are both amino acids. Describe how two amino acids differ from one another. You may use a diagram to help your description. (1 mark)

Answer 9

Have different R group

Question 10

Species richness and an index of diversity can be used to measure biodiversity within a community.What is the difference between these two measures of biodiversity? (1 mark)

Answer 10

Species richness measures only number of (different) species / does not measure number of individuals.

Question 11

The traps in the canopy were set at 16–27 m above ground level. Suggest why there was such great variation in the height of the traps. (1 mark)

Answer 11

Trees vary in height.

Question 12

Ecologists investigated the size of an insect population on a small island. They used a mark-release-recapture method. The ecologists captured insects from a number of sites on the island. Suggest how they decided where to take their samples. (2 marks)

Answer 12

1. Draw grid over (map of) area;

2. Select squares / coordinates at random.

Question 13

Give two assumptions made when using the mark-release-recapture method. (2 marks)

Answer 13

1. No emigration / immigration;
2. No losses to predation;
3. Marking does not affect survival;
4. Birth rate and death rate equal;
5. (In this case) all belong to one population.

Question 14

What two measurements are needed to calculate an index of diversity? (2 marks)

Answer 14

1. Number of (individuals of) each species;

2. Total number of individuals / number of species;

Question 15

Some fields acted as controls. They were sprayed with a solution that did not contain the herbicide. Explain the purpose of these control fields. (1 mark)

Answer 15

results are due to the herbicide / are not due to another factor

Question 16

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how. (6 marks)

Answer 16

1. Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two glycerate (3-)phosphate
3. GP reduced to triose phosphate
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to glucose

Question 17

Give three ways in which courtship behaviour increases the probability of successful mating (3 marks)

Answer 17

1. Recognise / identify / attract same species;
2. Stimulates / synchronises mating / production / release of gametes;
3. Recognition / attraction of mate
4. Indication of (sexual) maturity / fertility / receptivity / readiness to mate;
5. Formation of a pair bond / bond between two organisms

Question 18

This classification system consists of a hierarchy as there are small groups within larger groups. Give one other feature of a hierarchy that is shown in the diagram. (1 mark)

Answer 18

No overlap.

Question 19

What is meant by a hierarchy? (2 marks)

Answer 19

1. Groups within groups;

2. No overlap (between groups);

Question 20

Explain the role of independent segregation in meiosis. (2 marks)

Answer 20

1. genetic variation;
2. (Allows) different combinations of maternal and paternal
   chromosomes / alleles;

Question 21

A zedonk is the offspring produced from breeding a mountain zebra with a donkey.
• The body cells of a mountain zebra contain 32 chromosomes.
• The body cells of a donkey contain 62 chromosomes.
Use this information to suggest why zedonks are usually infertile ( 2marks)

Answer 21

1. Zedonk has 47 / odd number of chromosomes;
2. Chromosomes cannot pair / are not homologous / chromosome
   number cannot be halved

Question 22

What is a species? (2 marks)

Answer 22

1. Group of similar organisms / organisms with similar features
2. Reproduce / produce offspring;
3. That are fertile;

Question 23

The forest was cleared to make more land available for agriculture.
After the forest was cleared the species diversity of insects in the area decreased. Explain why. (3 marks)

Answer 23

1. Decrease in variety of plants / fewer plant species;
2. Fewer habitats / niches;
3. Decrease in variety of food / fewer food sources;

Question 24

Explain what is meant by: a phylogenetic group (1 mark)

Answer 24

evolutionary links / history / relationships / common ancestry;

Question 25

Cytochrome c is more useful than haemoglobin for studying how closely related different organisms are. Suggest one reason why. (1 mark)

Answer 25

1. All organisms respire / have cytochrome c;
2. (Cytochrome c structure) less varied (between
   organisms) ;

Question 26

Describe what happens to chromosomes in meiosis (6 marks)

Answer 26

1. chromosomes condense
2. associated with homologous pairs
3. crossing over occurs
4. chromosomes at the equator, spindle fibres attach at centromere
5. chromatids move to opposite ends of the cell
6. chromatids separate

Question 27

Meiosis results in genetic variation in the gametes which leads to variation in the offspring formed by sexual reproduction. Describe how meiosis causes this variation and explain the advantage of variation to the species. (5 marks)

Answer 27

1. Crossing over
2. Independent segregation
3. Different adaptation
4. some survive
5. pass on allele/gene

Question 28

What is the role of the centromere? (2 marks)

Answer 28

1. spindle fibres attach to centromere
2. sister chromatids are pulled apart
3. hold the sister chromatids together

Question 29

Apart from genetic factors what other type of factor causes variation within a species? (1 mark)

Answer 29

environmental pressure/change

Question 30

Describe and explain how selection will have affected the genetic diversity of sugar beet. (2 marks)

Answer 30

1. would decrease genetic diversity

2. no. of different alleles within the pop. has been reduced

Question 31

Suggest how a mutation can lead to the production of a protein that has one amino acid missing (2 marks)

Answer 31

1. loss of 1 triplet

2. loss of amino acid