Q.11. Explain the term food webs. (AKTU. - 2012 - 13)
Ans. A food web is a diagram illustrating the feeding relationships between the plants and animals in a certain area. Basically who eats whom. They show the relationships between these organisms much more realistically than a food chain or trophic pyramids. A true food web that consideres all the plants and animals in a system is bound to be unwiedly and confusing. Food webs show how many animals are interconnected by different paths.
Example: Trees produce acorns which acts as food for many mice and insects. Because there are many mice, the weasels, snakes, and racoons, have food. The insects in the acorns also attract birds, skunks, and opposums. With the skunks, opposums, weasels and mice around, hawks, foxes, and owls can find food. They are all connected.
One doesn’t find simple independent food chains in an ecosystem, but many interdependent and complex food chains that look more like a web and are therefore called food webs. A food web that shows the energy transformations in an ecosystem looks like as shown in this picture.
As you can see from this picture, food webs, with all their dependencies, can be very complex, but somehow nature balances things out so that food webs last a long time. Many species share the same habitat, their populations survive for many years, and they all live together.
Q.12. What is meant by ‘flow of energy’ in an ecosystem? (AKTU. 2010 - 11)
Ans. The existence of the living world depends upon the flow of energy and circulation of materials through ecosystem. Green plants trap solar radiations and in presence of carbon dioxide, water, and chlorophyll, they prepare their carbohydrate food material. This energy is utilized by the organisms in the next trophic level. The flow of energy in an ecosystem takes place through food chain.
The most important feature of this energy flow is that it is unidirectional or one way flow; because once the energy flows from the first to next trophic level, it can not be reverse back to the first trophic level.
Also, the flow of energy follows the o laws of thermodynamics:
Ist law of therrnodynams states that energy can neither be created nor bedestroyed but it can be transformed from one form to another. The solar energy trapped by green plants gets converted into chemical energy.
IInd law of thermodynamics states that energy dissipates as it is used. As the energy flows through food chain, there occurs loss of energy at every trophic level. The loss of energy takes place respiration, loss of energy in locomotion, running, hunting and other activities. At energy level there is about 90% loss of energy and energy transferred from one trophic level to other is only about 10%.
The flow of energy regulates the rates of materials i.e. nutrients. It also regulates the modification of environment because, the environment is modified by the organisms according to their needs.
Q.13. What do you mean by the term material cycle? (AKTU. - 2011 - 12, 12 - 13)
Ans. The producers of an ecosystem take up several basic inorganic nutrients from their non-living environment. These materails get tranformed into the bio mass of the producers. Then they are utilised by the consumers population and are ultimately returned to the environment with the help of the reducers or decomposers. This cyclic exchange of nutrient material between the living organisms and their non-living environment is called biochemical cycle (material cycle). As indicated by the name the nutrients circulate through life (bio) and through earth (geo) repeatedly (cycle).
The biogeochemical (material or nutrient) cycles conserve the limited source of raw materials in the environment.
