Our Environment Test - 9

An ecosystem may be natural or man-made (artificial). Forests, ponds and lakes are natural ecosystems while gardens and crop-fields are human-made (artificial) ecosystems.

The use of chemicals like CFCs has endangered the ozone layer. The decrease in the amount of ozone in earth's atmosphere has been linked to synthetic chemicals like chlorofluorocarbons (CFCs). CFCs are used as refrigerants and in fire extinguishers.

There is a loss of energy as the energy is transferred from a lower trophic level to a higher trophic level; this limits the number of trophic levels in a food-chain. The food chains generally consist of only three or four steps since very little usable energy remains after four trophic levels.

The flow of energy in an ecosystem is always unidirectional. As the energy moves progressively through one trophic level to another, it is no longer available to the previous level. The energy that is captured by the autotrophs (producers) does not revert back to solar radiation. The energy which passes on to the herbivores (primary consumers) from the autotrophs does not come back to the autotrophs.

The chemicals used to protect crops from diseases and pests are washed down into the soil or the water bodies. From the soil, these are absorbed by the plants along with water and minerals. From the water bodies, these are taken up by aquatic plants and animals. The non-biodegradable chemicals thus enter the food chain. They get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals gets accumulated in human bodies. This phenomenon is known as biological magnification.

Substances that are broken down by biological processes are said to be biodegradable. Dead parts of plants and animals are biodegradable. Substances that are not broken down are said to be non-biodegradable. Plastics, detergents, and pesticides are non-biodegradable. Bacteria and fungi are decomposers. Green plants (autotrophs) are producers.

Each step or level of the food chain forms a trophic level. The autotrophs or the producers are at the first trophic level. They fix up the solar energy and make it available for heterotrophs or the consumers. The herbivores or the primary consumers come at the second trophic level. Small carnivores or the secondary consumers come at the third trophic level. Larger carnivores or the tertiary consumers form the fourth trophic level.

Organisms can be grouped as producers, consumers and decomposers according to the manner in which they obtain their sustenance from the environment. Producers or autotrophs prepare their own food. Consumers can be classed as herbivores, carnivores, omnivores and parasites. Herbivores obtain food directly from green plants. Parasites obtain food from a host.

A tree is a producer (autotroph). A grasshopper is a herbivore (primary consumer). A frog is secondary consumer.

The decrease in the amount of ozone in the atmosphere has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. The human beings occupy the top level in any food chain. The maximum concentration of the chemicals in a food chain is in the human body. This phenomenon is known as biological magnification. According to 10% law, the energy available to each successive trophic level is 10% of the previous trophic level. An ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.