Table 1 shows results from an investigation into the effect of standing still on blood flow in the lower leg. A Doppler ultrasound probe was used to estimat...

Table 1 shows results from an investigation into the effect of standing still on blood flow in the lower leg. A Doppler ultrasound probe was used to estimate blood velocity in a vein. Each volunteer was tested while sitting, after standing still for 20 minutes and after walking for five minutes. The investigation was carried out in a room at 20 degrees C. The researchers were interested in how leg muscle contractions and vein valves help return blood to the heart. Long periods of immobility can increase the risk of a blood clot forming in a leg vein.

(a) Which activity produced the lowest mean blood velocity? [1]
(b) Describe the effect of walking on blood velocity compared with standing still. [1]
(c) Suggest why walking increases blood flow in leg veins. [2]

A nurse recorded the pulse rates of a patient receiving treatment for dehydration after a stomach illness. The patient had lost water and salts, reducing the volume of plasma in the blood. Table 1 shows measurements taken before and after the patient was given an oral rehydration drink. Fig. 1 shows a simplified pressure cuff used to measure blood pressure. The cuff is wrapped around the upper arm and inflated. The nurse also checked that the patient was producing urine, because this indicates that the kidneys are receiving enough blood.

(a) What happened to pulse rate after the drink? [1]
(b) Suggest why dehydration can lower blood pressure. [1]
(c) Describe why the rehydration drink can improve circulation. [2]