1. Different materials are cycled in the environment in separate biogeochemical cycles. Human activities affect these cycles.
2. Environment is comprised of living (biotic) as well as non-living (a biotic) components. Our environment has undergone a great change since olden times.
3. Specific enzymes are needed to break down a particular substance. Human-made materials like plastics are not broken down by the action of bacteria or other saprophytes.
4. Substances that are broken down by biological processes are called biodegradable. Substances that are not broken down by biological processes are called non-biodegradable. Such substances may be inert and simply persist in the environment for a long time or may harm the various members of the eco-system.
5. All organisms such as plants, animals, microorganisms and human beings as well as the physical surroundings interact with each other and maintain a balance in nature.
6. All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.
7. Biotic components comprise of living organisms like plants, animals and microorganisms and abiotic components comprise physical factors like temperature, rainfall, wind, soil and minerals.
8. A garden is an ecosystem. There are different plants such as grasses, trees, flower-bearing plants, and animals like frogs, insects and birds. All these living organisms interact with each other and their growth, reproduction and other activities are affected by abiotic components of the ecosystem.
9. Different kinds of ecosystems are forests, ponds, lakes, deserts etc. These are all natural ecosystems. Gardens and crop-fields are examples of human-made (artificial) ecosystems.
Activity. Set up a human-made ecosystem.
An aquarium is a human-made ecosystem. It can be set-up as follows :
Requirements: A large jar, water, oxygen pump, fish food.
(1) Take a cubical glass vessel or a large jar.
(2) Fit an oxygen pump (aerator) to supply oxygen to the system.
(3) Fill the vessel or jar with water upto 90%.
(4) Add a few aquatic plants and fish into the vessel.
(5) The aquarium is ready. It is an example of a human-made ecosystem.
Clean the aquarium once in a week to keep it running.
10. Organisms can be grouped as producers, consumers and decomposers according to the manner they obtain their sustenance from the environment. Hence, the energy available at each trophic level gets progressively due to loss of energy at each level.
11. All green plants and certain blue-green algae which can produce food by photosynthesis are called producers.
12. Organisms which consume the food produced, either directly from producers or indirectly by feeding on other consumers are the consumers.
13. Consumers that feed on plants are called herbivores. For example, rabbit, horse, etc.
14. Consumers that feed on small animals are called carnivores. For example, lion, tiger, wolf, etc.
15. Consumers that feed on plants and animals both are called omnivores. For example, cat, dog, etc.
16. Parasite is another class of consumers. These are the organisms that live on or in the body of another organism from which they obtain their food. For example, parasites of man include fleas and lice, various protozoans and tapeworms.
17. Microorganisms comprising bacteria and fungi, break down the dead remains and waste products of organisms. These microorganisms are called decomposers.
18. Natural replenishment of soil will not take place in the absence of decomposers. Decomposers break down the complex organic substances into simple inorganic substances that go into the soil and are used again by the plants.
19. Series of organisms feeding on one another at various levels form a food chain (Fig. 15.1).
20. Each step of level of the food chain forms a trophic level. Organisms at the first trophic level are called autotrophs. In fact, these are the producers. They fix up solar energy and make it available for consumers.
21. Heterotrophs are the consumers.
22. Various trophic levels are indicated in Fig. 15.2 : The producers occupy the first level as shown in the figure.
The herbivores or primary consumers are at the second level.
Small carnivores or secondary consumers are at the third level while larger carnivores or tertiary consumers form the fourth trophic level.
23. The interactions among various components of the environment involve flow of energy from one component to the other. When one form of energy is changed to the other, some energy is lost to the environment which cannot be used again.
24. Green plants capture about 1% of the energy of sunlight that falls on their leaves and converts it into food energy.
25. An average of 10% of the food eaten is turned into its own body and is made available to the next level of consumers. Thus, 10% can be taken as average value for the amount of organic matter that reaches the next level of consumers.
26. The loss of energy at each step is so great that very little usable energy is left after four trophic levels.
27. There are a greater number of individuals at a lower trophic level, the maximum is that of the producers.
28. Each organism is generally eaten by two or more other kinds of organisms which, in turn, are eaten by several other organisms. The different food chains starting from the same producers are called a food web (See Fig. 15.3).
29. The flow of energy is unidirectional. The energy captured by the autotrophs from the sun does not revert to the Sun and the energy which passes to herbivores does not revert back to autotrophs. Thus, energy is never available to the previous level (See Fig. 15.4).
30. Some harmful chemicals enter our body through the food chain. Several pesticides used to protect our crops from diseases and pests are washed down into the soil or into water bodies.
From the soil, these are absorbed by the plants and from the water bodies, these are taken up by aquatic plants and animals.
31. Human beings occupy the top level in any food chain.
Therefore, maximum concentration of the harmful chemicals get accumulated in our bodies. This phenomenon is called biological magnification.
32. Foodgrains like wheat and rice, vegetable and fruits and even meat contain varying amounts of pesticide residues through the food chain.
33. The layer of ozone gas at a higher level from the earth is called ozone layer. Ozone is a deadly poison but at a higher level of atmosphere, it shields the surface of the earth from ultraviolet radiations from the Sun. This radiation is highly damaging to organisms as it causes skin cancer in human beings.
34. Ozone is formed at higher level of atmosphere by the action of UV rays on oxygen as shown below :
35. The amount of ozone in the atmosphere has dropped significantly since 1980, due to use of synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers.
36. In 1987, the United Nations Environment Programme (UNEP) succeeded in bringing about an agreement to freeze CFC production at 1986 levels.
37. Specific enzymes are needed for breakdown of specific substances. Hence, one enzyme will not work for all substances. Also, not all substances can be broken down by enzymes. Such substances are called non-biodegradable. They may persist in the environment.
38. We find lots of garbage around us in the towns and cities. Improvement in our lifestyle has resulted in greater amounts of waste material generation. Changes in packaging have resulted in much of our waste becoming non-biodegradable. These factors have an adverse impact on our environment.