4.4.4- Adaptations

Question 1

A mutation can lead to the production of a non-functional enzyme. Explain how.
(6)
Scientists investigated the effect of a specific antibiotic on two strains of the same
species of bacterium.

Answer 1

1. Change / mutation in base / nucleotide sequence (of DNA / gene);
   Q.
   Ignore: references to changing base-pairing
   Accept: affect for change, if in correct context
   Accept: changes triplets / codons
2. Change in amino acid sequence / primary structure (of enzyme);
   Accept: different amino acid(s) coded for
   Q Reject: different amino acids produced / formed / made
3. Change in hydrogen / ionic / disulfide bonds;
   Accept: references to sulfur bonds
4. Change in the tertiary structure / shape;
   Neutral: alters 3D structure / 3D shape
5. Change in active site;
6. Substrate not complementary / cannot bind (to enzyme / active site) / no
   enzyme-substrate complexes form.
   Accept: no E S complexes form

Question 2

Scientists investigated the effect of a specific antibiotic on two strains of the same
species of bacterium.
• One strain, SR, shows a stringent response in the presence of this antibiotic.
Part of this response involves stopping cell division. This gives this strain a
greater resistance to the effects of this antibiotic.
• The other strain, non-SR, cannot carry out a stringent response.
The scientists grew cultures of the SR strain and the non-SR strain containing the
same number of bacterial cells. They then stopped each strain from dividing and
exposed them to different concentrations of the antibiotic. After a fixed time, the
scientists estimated the number of living bacteria remaining in the cultures.
Figure 1 shows their results.

(b) Describe differences in the effect of increasing the concentration of antibiotic on the
SR strain and the non-SR strain.

Answer 2

1. Non-SR strain falls more / SR strain falls less / up to 10(μg / cm−3);
   Must include 10 but only required once in either MP1 or MP2
   Ignore: units or absence of
   This must be a comparative statement
2. Above 10(μg / cm−3), SR strain levels out / off and non-SR strain
   continues to decrease;
3. Greater difference between strains with increasing concentration of
   antibiotic.
   This must be a comparative statement

Question 3

Q2.To reduce the damage caused by insect pests, some farmers spray their fields of crop
plants with pesticide. Many of these pesticides have been shown to cause environmental
damage.
Bt plants have been genetically modified to produce a toxin that kills insect pests. The use
of Bt crop plants has led to a reduction in the use of pesticides.
Scientists have found that some species of insect pest have become resistant to the toxin
produced by the Bt crop plants.
The figure below shows information about the use of Bt crops and the number of species
of insect pest resistant to the Bt toxin in one country.

(a) Can you conclude that the insect pest resistant to Bt toxin found in the years 2002
to 2005 was the same insect species? Explain your answer. (1)

Answer 3

1- No – no mark)

Graph / bar chart only shows number of species, not the name of the species.

Question 4

One farmer stated that the increase in the use of Bt crop plants had caused a
mutation in one of the insect species and that this mutation had spread to other
species of insect. Was he correct? Explain your answer. (4)

Answer 4

1. Mutations are spontaneous / random;
2. Only the rate of mutation is affected by environment;
3. Different species do not interbreed / do not produce fertile offspring;
4. So mutation / gene / allele cannot be passed from one species to
   another.
   Ignore references to correlation does not prove causation

Question 5

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)

Answer 5

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 6

Other than hunting, suggest two reasons why populations might show very low
levels of genetic diversity (2)

Answer 6

1. Population might have been very small / genetic bottleneck;
2. Population might have started with small number of individuals / by one
   pregnant female / founder effect;
3. Inbreeding.

Question 7

.Malaria is a disease that is spread by insects called mosquitoes. In Africa, DDT is a
pesticide used to kill mosquitoes, to try to control the spread of malaria.
Mosquitoes have a gene called KDR. Today, some mosquitoes have an allele of this
gene, KDR minus, that gives them resistance to DDT. The other allele, KDR plus, does
not give resistance.
Scientists investigated the frequency of the KDR minus allele in a population of
mosquitoes in an African country over a period of 10 years.
The figure below shows the scientists’ results.

Suggest an explanation for the results in the figure above. (4)

Answer 7

1. Mutation produced KDR minus / resistance allele;
2. DDT use provides selection pressure;
3. Mosquitoes with KDR minus allele more likely (to survive) to reproduce;
4. Leading to increase in KDR minus allele in population.

Question 8

The KDR plus allele codes for the sodium ion channels found in neurones.
(c) 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)

Answer 8

1. Neurones remain depolarised;

2. So no action potentials / no impulse transmission.

Question 9

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

Answer 9

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