Balanced eating, breathing and transport of substances

In organisms, water and substances are delivered to where they are needed by a transport system. In a plant, root hairs absorb water and minerals from the soil. In the stem the conducting vessels of the xylem carry them from the root to the leaves; the sieve tubes of the phloem carry organic matter (sugar) made in leaves to other organs. Loss of water vapour through the stomata is called transpiration; it pulls water up from soil through the root and stem to the leaf. In humans the circulatory system – the heart and blood vessels – carries substances. The heart has four chambers: two atria and two ventricles. Vessels carrying blood away from the heart are arteries; those bringing blood to the heart are veins; in the thin capillaries gases and substances are exchanged between blood and tissues. The systemic (large) loop supplies all organs with oxygen and food; the pulmonary (small) loop takes blood to the lungs, releases carbon dioxide, loads it with oxygen and returns it to the heart. Mammals and birds have a four-chambered heart, fish two-chambered, amphibians and most reptiles three-chambered. The heartbeat can be felt as the pulse.