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Date	May 2017	Marks available	3	Reference code	17M.2.SL.TZ2.1
Level	Standard level	Paper	Paper 2	Time zone	Time zone 2
Command term	Compare and contrast	Question number	1	Adapted from	N/A

Question

Consumption of dark chocolate has been shown to have health benefits. A study was undertaken to see the effects of epicatechin (Epi), a substance in dark chocolate, on the aerobic capacity of leg muscles of mice.

A group of adult mice was used to measure the effects of a low dose of Epi given over 15 days. The mice were divided into four groups and given either water or Epi and were either kept idle (no exercise) or made to exercise on a treadmill.

After 15 days, the results were analysed. The blood capillary density in leg muscle was measured under the light microscope.

Leg muscle tension was measured over time during a treadmill exercise in all four groups. The muscle is considered to reach a point of fatigue when there is a decrease in tension to 50 % of the initial tension.

The scientists tested the expression of four different mitochondrial proteins. The protein samples were taken from leg muscles. The technique that was used to quantify the amount of protein expressed was Western blotting. In this procedure the thickness of the band is an indicator of the amount of protein.

State the significance of the statement: p<0.05.

[1]

a.i.

Outline the trends in capillary density in the results of this experiment.

[2]

a.ii.

Describe how increased capillary density could affect the aerobic capacity of muscle.

[2]

State the time when the point of fatigue occurred in the Epi–exercise group.

[1]

c.i.

Compare and contrast the results for the water–no exercise group and the Epi–no exercise group.

[3]

c.ii.

Discuss the effect of exercise on the results of the experiment.

[2]

Analyse the effect of exercise on the presence of the mitochondrial proteins in the leg muscle.

[2]

Mitochondria are essential for aerobic respiration. Suggest one possible role of the proteins that were studied.

[1]

The scientists concluded that Epi significantly increased aerobic capacity in leg muscle.

Evaluate the strength of the evidence provided by all of the data for dark chocolate improving the aerobic capacity of athletes.

[3]

Markscheme

there is a significant «statistical» difference between two experimental values
OR
there is a less than 5 % chance that the difference is random
OR
95 % or more probability that results are due to the experiment «IV» and not random/can reject the null hypothesis
OR
there is a relationship/correlation between doing exercise and capillary density

OWTTE

a.i.

a. exercise «significantly» increased the density with both water and Epi

“both” or OWTTE must be mentioned

b. Epi «significantly» increased the density with and without exercise

c. Epi–exercise had the greatest increase in the density
OR
Epi increases the density more than exercise alone

a.ii.

a. increases amount of blood taken to the muscle

b. increases the delivery of oxygen/glucose/nutrients for aerobic respiration

c. increases the removal of carbon dioxide/wastes
OR
increased gas exchange

175 «seconds»

Accept 170 to 180 «seconds».

c.i.

a. in both cases the tension decreased over time

b. Epi–no exercise lasts longer/more time until «onset of» fatigue «than water–no exercise»

c. the rate of decrease in tension is the same/similar in both

d. Epi–no exercise has more contractions per second before fatigue point «than water–no exercise»

Do not accept numerical comparisons without justification.

c.ii.

a. «exercise with» water has no impact

b. «exercise with» Epi promotes higher levels of tension for more time

c. «exercise with» Epi increases the time to fatigue

a. exercise has no/very little effect with water

b. exercise with Epi increased III/IV

c. «it appears that» exercise with Epi has no/very little effect on II
OR
Epi relative to water increases all 4
OR
exercise has little/no effect on protein I/II

d. exercise with Epi «appears to» decrease I

a. protein channels
OR
pumps in membranes of mitochondria
OR
hormone binding sites

b. structural/integral/peripheral/glyco/surface proteins

c. enzymes/catalysts

Accept verifiable names of specific membrane enzymes.

d. electron transport chain proteins

Limitations:

a. study done on mice and may not apply to humans

b. levels of Epi administered in experiment may exceed levels in a sample of dark chocolate
OR
levels of Epi administered in experiment may have different levels in a sample of dark chocolate
OR
chocolate may have other components with unknown effects on aerobic capacity

c. mitochondrial proteins may not improve aerobic capacity

Strengths:

d. data supports as dark chocolate contains EPI

e Epi improves capillary density and would therefore increase aerobic capacity

f. Epi improves fatigue resistance

g. Epi in combination with exercise improves it further

h. Epi increases mitochondrial proteins therefore/presumably increasing aerobic capacity

OWTTE