Biology · B Form and function. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Blood leaves the heart in arteries, passes through capillaries in the tissues and returns in veins. Each vessel is built for its job. Arteries carry blood at high pressure, so their walls are thick with muscle and elastic fibres. Veins carry blood at low pressure, so they have thin walls, a wide lumen and valves. Capillaries are where exchange happens.
Plants move water in xylem vessels. Water evaporates from the leaves (transpiration). This pulls on the column of water in the xylem, and the pull reaches down to the roots. Water molecules stick to each other by cohesion, so the column does not break. The plant uses no energy for this.
Students say that water is pushed up the xylem. It is pulled up under tension by transpiration from the leaves. Also remember that a correlation between a diet factor and heart disease does not prove a cause.
Answer: The heart rate increased by 60 beats per minute.
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