Respiration and nutrition of plants. Metabolism in plants
All living cells of a plant — root, stem, leaf, flower, fruit, seed — breathe day and night: they take oxygen from the air and release carbon dioxide. In respiration organic substances are broken down to water and carbon dioxide and energy needed for life is released; in photosynthesis, on the contrary, organic substances are made and light energy is stored. Respiration does not need light; photosynthesis works only in light. By day both processes go on together, but photosynthesis releases much more oxygen, so only that is noticeable; at night only respiration continues. Sugar made in photosynthesis is turned into starch, cellulose, proteins, fats and vitamins and used to build the plant body. The uptake of substances and energy from the environment, their change in the cell and the removal of waste is called metabolism — a property of all living organisms.
Experiment (with the teacher): put freshly cut leafy shoots into two glass jars and cover them; keep one in the light and one in the dark. After a few hours the teacher lowers a burning splint to check the air. Discuss the result. Alternative: put a thermometer in a thermos with germinating bean seeds and record the temperature change. Safety: a burning splint only for the teacher, away from flammable things; handle glass carefully.