Plant systems B:
Photosynthesis, nutrition and respiration
All living things require energy. The energy source for all life on Earth is ultimately the Sun. Without the ability of plant pigments to capture the Sun's light energy, life as we know it on Earth would not exist.
A green pigment, chlorophyll, is stored within small organelles called chloroplasts within many plant cells. It is mainly found in leaves and stems, thereby giving these parts a green appearance.
Chlorophyll, an iron-based molecule, can absorb light and become
energised, and then pass on this energy to combine the water and carbon
dioxide molecules to form sugar.
The chemical equation for photosynthesis is:
Oxygen is a by-product of this process. Any excess oxygen not required by the plant is released into the atmosphere, and is therefore available for animals to use.
Six molecules of oxygen combine with one molecule of sugar to form ENERGY, plus six molecules of carbon dioxide and six molecules of water.
Note that carbon dioxide is a by-product of respiration, which is then available for plants to use in photosynthesis. In other words, plants and animals are interdependent and the balance of oxygen and carbon dioxide in nature is vitally important.
The energy released in respiration is available for movement, growth, and all the life functions ("metabolism").
A healthy plant in good growing conditions produces more sugar through photosynthesis than it uses up in cellular respiration. It also produces more oxygen than it needs, so a supply of both food and oxygen for animals is maintained. The logging of vast areas of rainforest can greatly upset this balance in nature because photosynthesis is reduced.