Autotrophic and Heterotrophic Organisms

Many organisms must eat food to get the energy for life processes because they cannot produce their own food molecules from inorganic substances. They are called heterotrophs. This means that they need a ready- made organic substance to provide them with energy and materials for building cytoplasm. They are, therefore, dependent directly or indirectly on the synthetic activities of green plants. In order to obtain food, most animals have to go foraging and therefore must be mobile. This need for mobility puts a limit on the maximum body size that an animal can attain and still function efficiently. Heterotrophic organisms must rely on autotrophs for energy. All life depends on autotrophs because only they are able to convert light and energy into food.

Green plants and many onecelled organisms take in the energy by capturing it directly from the sun, they use inorganic molecules to produce organic food molecules. Such organisms are called autotrophs. This means that they do not depend on an outside source of organic food but are able to synthesize all of their organic requirements from simple inorganic molecules. During photosynthesis, carbon dioxide and water are used to produce carbohydrates. Nitrate absorbed from the immediate environment provides the nitrogen needed for protein synthesis. Since all the necessary chemicals are ‘to hand’, green plants produce their own food “on site” and have no need to be mobile. This sessile existence allows many plants to attain a body size greater than any animal.

Photosynthesis: Using Energy For Food

Plants that contain chlorophyll can trap energy from the sun and store it. This stored energy can then be used to make sugars. The whole process is called photosynthesis. Study the equation for photosynthesis (2.1).

Date: 2014-12-22; view: 966