Two transport systems compared
Both animals and plants must move substances around their bodies, but they solve the problem in different ways. Animals use a blood circulatory system with a pump, while plants rely on vascular tissue and physical forces such as the transpiration pull. Comparing them shows the same purpose met by very different designs.
The animal blood circulatory system
At the centre is the heart, a muscular pump that pushes blood through three kinds of vessel. Arteries carry blood away from the heart at high pressure; veins return blood to the heart; and thin-walled capillaries allow substances to be exchanged with the cells. The blood carries oxygen, bound to haemoglobin in the red blood cells, as well as digested food, carbon dioxide and wastes.
Key idea
Arteries away from the heart, veins back to the heart. Haemoglobin in red blood cells carries oxygen to the body cells.
The plant transport system
Plants have no heart. Instead, xylem carries water and minerals upward from the roots, pulled by transpiration, while phloem carries dissolved food from the leaves to the rest of the plant. There is no circulation in a loop as in animals.
Example
Think of arteries and xylem as both being "delivery" tubes under pressure, but the artery is powered by a heart while the xylem is powered by evaporation at the leaves.
Remember
- Animal: heart pumps blood through arteries, veins and capillaries.
- Plant: no pump; xylem (water up) and phloem (food) do the transport.
- Both deliver useful substances and remove wastes from cells.