Nutrition of living organisms
Nutrition is taking in food and turning it into energy and substances needed for life. The proteins, fats and carbohydrates in food are needed to build cells and tissues, and energy is released when they are broken down. By the way they feed, organisms fall into two groups. Autotrophs make organic matter from inorganic substances: green plants, algae, cyanobacteria. In photosynthesis, with light, chlorophyll, carbon dioxide and water, carbohydrate and oxygen are formed. Plants take minerals from the soil through the roots. Heterotrophs eat ready-made organic matter: humans, animals, fungi, parasitic plants and bacteria. Animals can be herbivores, predators, parasites or feeders on remains. Dodder (zarpechak) and Rafflesia are parasitic flowering plants that have lost chlorophyll. Predators often hunt sick and weak animals and so “clean” nature; that is why they are called “nature’s sanitation workers”.
Experiment “Is light needed?”: put damp cotton wool in two cups and the same number of cress (or bean) seeds in each. Put one by a bright window and the other in a dark box, and keep both moist. Observe for 7–10 days: the shoots in the dark are yellowish, long and weak, those in the light green and healthy. Light is needed to form chlorophyll. Safety: do not eat the seeds, wash hands; if mould appears, do not touch it and tell an adult.