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B3 2.1c – Student worksheet
Double circulatory system
Humans have two circulations, sometimes called a double circulation. Although we only have one
heart, it is effectively divided in two, with each side supplying a different part of the body.
1
2
3
Which part of the body is supplied by:
a
the left side of the heart (1 mark)
b
the right side of the heart? (1 mark)
Describe the exchange of oxygen and carbon dioxide with the blood:
a
in the lungs (2 marks)
b
in other organs of the body. (2 marks)
a
Which kind of blood vessel usually exchanges substances with the lungs and body
tissues? (1 mark)
b
Explain why. (2 marks)
The blood that is pushed out of the heart into the body circulation has a high pressure of around
120 mm Hg (millimetres of mercury). As the blood passes through the arteries, the pressure drops
because of friction with the walls of the blood vessels. By the time the blood reaches the capillaries
in the organs, its pressure has dropped to about 20 mm Hg.
4
Suggest what might happen if blood pressure in the capillaries was as high as it is in arteries.
Explain your answer. (2 marks)
5
The pressure of the blood that enters the lung circulation is about one-sixth that of the blood
entering the body circulation. Suggest why this is. (4 marks)
6
Explain the difference in thickness of the muscle in the two ventricles. (2 marks)
Mammals and birds have a double circulation. All other animals that have hearts do not. It has
been suggested that the reason for this is that mammals and birds are homeothermic (keep their
body temperature constant and often above that of the environment).
7
a
Which process supplies the energy for keeping the body warm? (1 mark)
b
What role does the blood circulation play in supporting this process? (2 marks)
c
Suggest why a double circulation helps mammals and birds to be homeothermic. (4 marks)
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