Biology Paper 2

Question 1

Exercise causes an increase in heart rate.

Describe the role of receptors and of the nervous system in this process.

Answer 1

Chemoreceptors detect rise in
CO2/H+/acidity/carbonic acid/fall in pH
OR
Baro/pressure receptors detect rise in blood
pressure;
2. Send impulses to cardiac centre/medulla;
3. More impulses to SAN;
4. By sympathetic (nervous system for
chemoreceptors/CO2)
OR
By parasympathetic (nervous system for
baro/pressure receptors/blood pressure);

Question 1

Dengue is a serious disease that is caused by a virus. The virus is carried from
one person to another by a mosquito, Aedes aegypti. One method used to try to
reduce transmission of this disease is the Sterile Insect Technique (SIT). This
involves releasing large numbers of sterile (infertile) male A. aegypti into the
habitat. These males have been made infertile by using radiation.

Explain how using the SIT could reduce transmission of dengue.

Answer 1

Compete (with fertile males) to mate/for
food/resources
OR
intraspecific competition;

2. Do not reproduce/breed
   OR
   Reduces population (of mosquitoes);

Question 2

Describe how the mark-release-recapture method could be used to determine the
population of A. aegypti at the start of the investigation.

Answer 2

Capture/collect/sample, mark and release;
2. Leave time for mosquitoes/Aedes to disperse
before second sampling/collection;
3. (Population =) number in first sample × number
in second sample divided by number of marked
in second sample/number recaptured;

Question 3

The release of radiation-sterilised A. aegypti has not been very successful in
controlling the transmission of dengue.

Suggest one reason why.
[1 mark]

Answer 3

Radiation) affects their ‘attractiveness’/courtship
/survival/ life span;

Question 4

The scientists then compared the length of time that the control mice and the
trained mice could carry out prolonged exercise. The trained mice were able to
exercise for a longer time period than control mice.

Explain why.

Answer 4

More Aerobic respiration so more ATP released/ ATP produced faster
Anaerobic respiration delayed
Less/no lactate

Question 5

Scientists investigated the effect of regular exercise on skeletal muscle fibres in
mice. The scientists compared the muscle fibres of mice after six weeks of regular
exercise (trained mice) with those of mice that had not exercised (control mice).
The scientists stained the muscle fibres from both sets of mice to show succinic
acid dehydrogenase activity. The darker the stain the greater the succinic acid
dehydrogenase activity.

Figure 3 shows a typical set of results they obtained.

Figure 3

Succinic acid dehydrogenase is an enzyme used in the Krebs cycle.

Suggest one reason for the difference in the staining between the muscle fibres of
the control mice and the trained mice.
[1 mark]

Answer 5

More mitochondria
More AEROBIC respiration
More slow muscle fibres

Question 6

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the
growth of weeds.
[2 marks]

Answer 6

Less ATP
Less reduced NADP
Less GP converted to TP