Homeostasis (Edexcel A (SNAB) A Level Biology)

Exam Questions

46 mins5 questions
1a
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4 marks

Maintaining a constant body temperature is of crucial importance to the survival of living organisms.

Explain the importance to certain organisms of maintaining a constant body temperature.

1b
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1 mark

The regulation of body temperature involves negative feedback loops.

State what is meant by the term 'negative feedback loop'.

1c
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2 marks

The following statements describe changes that occur in the skin in response to a change in temperature.

  1. Vasodilation of the arterioles near the skin will allow blood to flow to the capillaries.
  2. The activity of the sweat glands is reduced.
  3. Erector pili muscles in the skin contract to trap air between hairs.
  4. Blood is diverted through shunt vessels in the dermis of the skin.
(i)

Which of these statements would apply in hot conditions? 

(1)

  A I only
  B IV only
  C I, II and III
  D II, III and IV

(ii)

The regulation of body temperature is controlled by the brain.

Name the part of the brain responsible for thermoregulation.

(1)

1d
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3 marks

In prolonged cold conditions, the body will release the hormone thyroxine to regulate body temperature.

Describe the mechanism by which thyroxine is responsible for thermoregulation.

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2a
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2 marks

Plant sterols and plant stanols are found in a range of food, including vegetables, cereals, seeds and nuts. Plant sterols and stanols have a similar structure to cholesterol and reduce the absorption of cholesterol in the small intestine, so more cholesterol is lost in the faeces. This helps to lower the levels of cholesterol in the blood and in turn, reduces the risk of cardiovascular disease (CVD). 

A group of scientists wanted to investigate the effects of eating plant sterols and stanols on the risk of CVD. The scientists randomly divided healthy volunteers into two groups. Every day for eight weeks, one group was given plant sterols and stanols to eat. The other group acted as a control.

Each week, the scientists measured the diameter of the lumen of the main artery in the arm of the volunteers.

State how the control group should have been treated.

2b
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3 marks

The results of the experiment in part (a) are shown in the table below.
 

  Mean maximum diameter of lumen of main artery in the arm (cm)
Experimental group
(± standard deviation)
Control group
(± standard deviation)
 Before experiment 0.69 (± 0.02) 0.71 (± 0.02)
 After 8 weeks 0.74 (± 0.03) 0.72 (± 0.05)

A student reading the results concluded that there was sufficient evidence to assume a causal relationship between plant sterols and stanols, and a reduced risk of CVD.

Evaluate the student's conclusion.

2c
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6 marks

An electrocardiogram (ECG) measures the electrical fluctuation within a cardiac muscle as a heart is beating. The diagram below shows an ECG trace for a normal, healthy person and an ECG trace for a person suffering from heart disease.

ecg

Describe and explain the path that electrical impulses follow to cause contraction in the ventricular muscle in a healthy heart.

2d
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2 marks

Explain how the information from part (c) shows that the damage caused to the diseased heart is likely to have affected the sinoatrial node (SAN).

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3a
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2 marks

The graph below shows the change in the volume of the left ventricle during the cardiac cycle.


ch78mlti-stroke-volume

(i)

Identify the time(s) at which the semilunar valves opened.

(1)

(ii)

Use the information in the graph to explain your answer at part (i).

(1)

3b
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3 marks

The person that was used to draw the graph at part (a) has a cardiac output of 7.92 dm3 min-1.

The cardiac output was calculated using the following formula:

Cardiac output = heart rate × stroke volume

Use the information provided in part (a) and (b) to calculate the heart rate of this person.

3c
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2 marks

Cardiovascular disease (CVD) can cause damage to the cardiac muscle of the left ventricle which decreases the stroke volume of the heart.

Use the information in part (b) to explain the effect this may have on the heart rate of a person.

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4a
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5 marks

A mountaineer hikes up a mountain. 

With an increase in altitude there is a decrease in temperature.

Describe the homeostatic mechanism that will regulate the mountaineers' body temperature near the top of the mountain.

4b
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2 marks

When hiking in extremely cold conditions, it is very important that mountaineers wear waterproof gloves that are properly insulated to avoid frostbite in their fingers and hands.


2BEOfmto_640px-third-degree-frostbite

Frostbite (pictured above) is damage to the skin and tissue when exposed to very low temperatures. Severe frostbite can cause tissue death and in extreme cases, amputation of fingers and toes is the only course of action doctors can take. 

Deduce the reason why these gloves would prevent frostbite.

4c
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2 marks

The tissue death caused by severe frostbite is known as gangrene. In such cases, the affected parts must be amputated.

Use your knowledge of skin structure and blood vessels to explain why gangrene is more likely in extremities, such as fingers and toes.

4d
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2 marks

Prolonged exposure to extremely cold conditions leads to hypothermia. This occurs when a dramatic decrease in body temperature leads to a decrease in metabolism, which in turn results in less heat energy being released leading to a further drop in body temperature.

In this sense, hypothermia is an example of a positive feedback loop.

Explain why positive feedback loops cannot be considered a homeostatic mechanism.

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5a
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1 mark

The following image shows the electrocardiogram (ECG) of a healthy heart and a heart with an abnormal rhythm.

EHlgTG2j_ecg-normal-abnormal

Which of the following provides the correct description of the ECG shape of a healthy heart?

      P wave QRS complex T wave
  A Caused by repolarisation of the atria resulting in systole Caused by depolarisation of the ventricles resulting in diastole Caused by depolarisation of the ventricles resulting in systole
  B Caused by depolarisation of the atria resulting in systole Caused by depolarisation of the ventricles resulting in systole Caused by repolarisation of the ventricles resulting in diastole
  C Caused by depolarisation of the atria resulting in diastole Caused by repolarisation of the ventricles resulting in systole Caused by depolarisation of the ventricles resulting in diastole
  D Caused by repolarisation of the atria resulting in diastole Caused by depolarisation of the ventricles resulting in systole Caused by repolarisation of the ventricles resulting in diastole
5b
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2 marks

Use the graph at part (a) to identify and explain the possible heart problem in the abnormal ECG.

5c
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2 marks

Damage to the atrioventricular node (AVN) will severely affect the heart rate of an individual.

Explain the effect this would have on the heart rate.

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