NUTRITION
When we walk or ride a bicycle, we are using up energy. Even when we are not doing any apparent activity, energy is needed to maintain a state of order in our body. We also need materials from outside in order to grow, develop, synthesise protein and other substances needed in the body. This source of energy and materials is the food we eat.
How do living things get their food?
The general requirement for energy and materials is common in all organisms, but it is fulfilled in different ways. Some organisms use simple food material obtained from inorganic sources in the form of carbon dimade and water. These organisms, the autotrophs, include green plants and some bacteria. Other organisms utilise complex substances These complex substances have to be broken down into simpler ones before they can be used for the upkeep and growth of the body. To achieve this, organisms use bio-catalysts called enzymes. Thus the heterotrophs survival depends directly or indirectly on autotrophs Heterotrophic organisms include animals and fungi.
Autotrophic Nutrition
Carbon and energy requirements of the autotrophic organism are fulfilled by photosynthesis. It is the process by which autotrophs take in substances from the outside and convert them into stored forms of energy. This material is taken in the form of carbon dioxide and water which is converted into carbohydrates in the presence of sunlight and chlorophyll Carbohydrates are utilised for providing energy to the plant We will study how this takes place in the next section. The carbohydrates which are not used immediately are stored in the form of starch, which serves as the internal energy reserve to be used as and when required by the plant. A somewhat similar situation is seen in us where some of the energy derived from the food we eat is stored in our body in the form of glycogen taken up in the form of tnorganic nitrates or nitrites. Or it is taken up as organic compounds which have been prepared by bacteria from atmosphere nitrogen
Heterotrophic Nutrition
Each organism is adapted to its environment. The form of nutrition differs depending on the type and availability of food material as well as how it is obtained by the organusin. For example, whether the food source is stationary (such as grass) or mobile (such as a deer), would. allow for differences in how the food is accessed and what is the nutritive apparatus used by a cow and a lion. There is a range of strategies by which the food is taken in and used by the organism Some organisms break down the food material outside the body and then absorb n Examples are fungs like bread moulds, yeast and mushrooms, Others take in whole material and break it down inside their bodies. What can be taken in and broken down depends on the body design and functioning Some other organisms derive mutrition from plants or animals without killing them. This parasitic nutritive strategy is used by a wide variety of organisms like cuscuta famar bell, ticks, Doe leeches and tape-worms.
How do Organisms obtain their Nutrition?
Since the food and the way it is obtamed differ, the digestive system is different in various organisms. In single-celled organisms, the food may be taken in by the entire surface. But as the complexity of the organism increases, different parts become specialised to perform different functions. For example, Amoeba takes in food using temporary linger like extensions of the cell surface which fuse over the food particle forming a food vacuoleInside the food vacuole, complex substances are broken down into simpler ones which then diffuse into the cytoplasm. The remaining undigeste material is moved to the surface of the cell and thrown out. In Paramecium, which is also a unicellular organism, the cell has a definite shape and food taken in at specific spot. Food is moved to this spot by the movement of ella which cover the entire surface of the cell