Fig. 1 shows a section through a vein in a person’s leg. The person works at a desk and remains seated for long periods. Veins return blood to the heart at ...
Question 1 Report
Fig. 1 shows a section through a vein in a person’s leg. The person works at a desk and remains seated for long periods. Veins return blood to the heart at low pressure. Valves and contractions of nearby skeletal muscles help prevent blood collecting in the lower leg.
(a) What is the function of a valve in this vein? [1]
(b) Describe how contraction of leg muscles helps blood move towards the heart. [2]
(c) Give two features of veins that are different from arteries. [2]
Table 1 shows results from an investigation of blood flow in the fingers. A volunteer placed one hand in cool water and the other hand in warm water for two minutes. A sensor measured skin temperature and the time taken for colour to return after a fingernail was pressed. Blood vessels near the skin can change diameter to control heat transfer from the body.
| water temperature / degrees C | skin temperature after 2 minutes / degrees C | time for colour to return / s |
|---|---|---|
| 12 | 22 | 3.8 |
| 38 | 33 | 1.4 |
(a) Describe the difference in colour-return time between the two hands. [1]
(b) What change happens to skin arterioles in warm conditions? [1]
(c) Explain how this change affects heat loss from the body. [2]
Answer Details
Veins and valves
- A valve prevents backflow of blood, ensuring blood travels towards the heart. [1]
- When leg muscles contract, they squeeze the vein and force blood along it. Valves prevent reverse flow, so the blood is directed towards the heart. [2]
- Any two differences from arteries are accepted: veins have thinner walls, wider lumens, valves, and lower blood pressure. [2]
Blood flow near the skin
- Colour returned faster after warm water: it took 1.4 s rather than 3.8 s after cool water. [1]
- In warm conditions, skin arterioles dilate, meaning that they widen. [1]
- Dilation allows more blood to flow through capillaries close to the skin surface. More heat can then be transferred from the blood to the surroundings, increasing heat loss. [2]
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