a) Arteries, capillaries and veins are blood vessels found in the human circulatory system - OCR Gateway - GCSE Biology - Question 17 - 2023 - Paper 3

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Arteries have a very thick muscle wall to withstand high pressure from the heart. Capillaries have thin walls, and veins have thinner walls than arteries.

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Veins have a wider lumen than arteries, while capillaries have the narrowest lumen of all.

CVI can cause poor blood flow in the legs. Blood that is supposed to flow back to the heart may pool in the veins, leading to reduced circulation and increased pressure in the legs.

A common symptom of CVI is swelling in the legs, which can be accompanied by pain or discomfort.

To find the total volume pumped in one hour:

1. Calculate the number of contractions in one hour:

   $ext{Contractions per hour} = 76 ext{ beats/min} \times 60 ext{ min/hour} = 4560 ext{ beats/hour}$

2. Calculate the total volume pumped:

   $ext{Total volume} = 4560 ext{ beats/hour} \times 70 ext{ ml/beat} = 319200 ext{ ml/hour}$

Thus, the volume of blood pumped into the aorta in one hour is 319200 ml.

Another feature of red blood cells is their biconcave shape, which increases the surface area-to-volume ratio. This adaptation allows for more efficient gas exchange, enabling red blood cells to pick up oxygen in the lungs and deliver it to tissues throughout the body.