Question 1. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.
Answer 1 Trophic levels in a food chain represent various steps where transfer of food energy takes place.
Example: A simple food chain found in a grassland is given below:
Grass → Insects → Frogs → Snakes
(i) Grass → I trophic level
(ii) Insects → II trophic level
(iii) Frogs → III trophic level
(iv) Snakes → IV trophic level
Question 2. What is the role of decomposers in the ecosystem?
Answer 2 Decomposers are microorganisms that act on dead and decaying bodies of producers and consumers and break them into simple inorganic compounds. They absorb some of the substances and release the rest into the environment to be recycled and to be used in future by producers. Thus, decomposers have a key role in the recycling of material in the biosphere and provide the raw materials to the producers. So, in this way they make the soil fertile.
Question 1. Why are some substances biodegradable and some non-biodegradable?
Answer 1 Substances which can be broken down into simpler substances by the biological means are called biodegradable substances.
For example, Cotton, wood, paper, wool, etc.
Substances which cannot be broken down into simpler substances by biological means are called non-biodegradable substances.
For example: plastic bags, synthetic fibres etc.
Question 2. Give any two ways in which biodegradable substances would affect the environment.
Answer 2 (i) Decomposition process of biodegradable materials produces foul smell and some harmful substances, which makes the environment nasty and unhealthy for people living in nearby areas.
(ii) Decomposition process in sewage water and open biodegradable waste provides breeding ground for mosquitoes, insects and microbes resulting into a number of diseases like malaria, cholera, diarrhoea, etc.
Question 3. Give any two ways in which non-biodegradable substances would affect the environment.
(i) Chemicals like BHC and DDT induce carcinoma (muscle cancer) and growth of tumours in humans.
(ii) Unwise handling of non-biodegradable waste materials may cause skin, respiratory and intestinal infections.
Non-biodegradable substances do not decompose easily. Such substances, if not disposed carefully, may contaminate our land and ground water resources besides polluting our environment.
Question 1. What is ozone and how does it affect any ecosystem?
Answer 1 Ozone (O3) is a molecule formed by three atoms of oxygen. It is a deadly poison. However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the Earth from ultraviolet (UV) radiations emitted by the sun.
These radiations are very dangerous for living organisms. They are known to cause skin cancer, cataract and weakening of immune system in human beings. They also destroy plants and reduce photosynthesis process.
Question 2. How can you help in reducing the problem of waste disposal? Give any two methods.
Answer 2 (i) By minimising the use of items resulting into waste generation, and promoting the use of recyclable articles.
(ii) Separating biodegradable and non-biodegradable waste before their disposal and dumping.
(iii) Recycling the non-biodegradable waste material.
Question 1. Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer 1 The group which contains biodegradable items are:
(i) Fruit peels, cake and lime juice.
(ii) Cake, wood and grass.
Question 2. Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer 2 (b) Grass, goat and human constitute a food chain.
The food chain is given below: Grass → Goat → Human beings
Question 3. Which of the following are environment-friendly practices?
(a) Carrying cloth-bags to put purchases in while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of getting your mother to drop you on her scooter
(d) All of the above
Answer 3 (d) All of the above
The eco-friendly habits that we should adopt in our day-to-day life.
(i) Switch off the light when not in use.
(ii) Walk to school or use bicycle.
(iii) Always carry cotton bags instead of using plastic bags
Question 4. What will happen if we kill all the organisms in one trophic level?
Answer 4 Killing of all organisms in one trophic level will stop the transfer of food energy to next trophic level. Therefore, organism in the next trophic level will die while the individuals of the lower trophic level will exhibit enormous growth in their population. It will break down the food chain which will create imbalance in the ecosystem. Both the conditions will result in ecological upset.
For example: If we remove deer (second trophic level) from a food chain, the population of carnivores will deplete while the primary producer, that is, grass and plants will show high growth.
Question 5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organisms of any trophic level be removed without causing any damage to the ecosystem?
Answer 5 Yes. Impact of removing all organisms in a trophic level will be different for different trophic levels. If all the producers are killed, it will cause death or migration of the primary consumers in the ecosystem. In the absence of producers, subsequent level of consumers will also be affected. But if primary consumers are removed, organisms of higher trophic level will die, while those of lower level (producers) show exponential growth much beyond the carrying capacity of the environment.
Removal of the organisms in a trophic level will upset the whole ecosystem as all categories of organisms are linked through a food chain. The survival of organisms of one trophic level depends on the existence of the members of other trophic level.
Question 6. What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer 6 Some harmful non-biodegradable substances enter the food chain at the level of primary producers and gets accumulated in the food chain at different trophic levels. Progressive increase in the concentration of non-biodegradable substances in a food chain is called biological magnification.
As these substances are non-biodegradable, levels of their concentration keep on increasing from lower trophic level to higher level. Humans being on the top of food chain, also get these harmful substances in our body resulting into various health problems.
Question 7. What are the problems caused by the non-biodegradable wastes that we generate?
Answer 7 Non-biodegradable wastes cannot be broken down into simpler substances. Excessive use of non-biodegradable material results into higher quantity of waste creating problem of its safe disposal.
Some of the non-biodegradable wastes like heavy metals and pesticides enter into the food chain and their concentration increase in the upper trophic levels causing health problems to humans and threat to the existence of the certain animals specially birds. Further, non-biodegradable wastes reduce the soil fertility by changing the natural pH balance. Heavy metals from such wastes contaminate our ground water resources making it non-potable.
Question 8. If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer 8 Biodegradable wastes are decomposed by microorganisms into simpler substances themselves and provide raw materials for producers, but they also have adverse effects on the environment as given below:
(i) Slow decomposition of biodegradable waste by microorganisms release foul smell and harmful gases. When inhaled by human beings, they may cause irritation, nausea, giddiness, etc.
(ii) Decomposing waste provides breeding ground for a number of harmful organisms. Abundance of harmful micro-organisms may cause diseases in animals, plants and human beings.
(iii) Increase in the number of micro-organisms in aquatic medium will cause oxygen deficiency in water bodies.
Question 9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer 9 Ozone layer is a protective shield around the Earth. It prevents harmful ultraviolet radiation of the sun from reaching the Earth. Air pollutants, like chlorofluorocarbons (CFCs), are causing depletion of ozone layer.
Depletion of ozone layer is allowing greater amount of UV radiation to reach the Earth. UV radiation can affect the ecosystem by affecting photosynthesis in plants, destroying planktons and decomposers. In human beings, UV radiation may cause skin cancer, cataract of eyes and damage to immune system. Many developed as well as developing nations of the world have agreed to sign and obey the directions of UNEP (United Nations Environment Programme) to freeze the production of CFCs or to limit their production to some extent.