Our Environment

Q1. Why are some substances biodegradable and some non-biodegradable? 

Ans. Substances which can be decomposed and broken down into simpler substances by microorganisms acting on it is called bio-degradable and those substances which cannot be acted upon by microorganisms and are not broken down into simpler substances are called non-biodegradable substances. 

Q2. Give any two ways in which bio-degradable substances would affect the environment. 

Ans. Two ways in which bio-degradable substances would affect the environment are: 

1. During the decomposition of the substances, a lot of foul smell spreads in the surrounding areas. 

2. The place where these bio-degradable substances are present with some moisture becomes breeding ground for insects like mosquitoes, houseflies which are vectors in carrying parasites that cause different diseases. 

Q3. Give any two ways in which non-biodegradable substances would affect the environment. 

Ans. 

1. The non-biodegradable substances accumulate and don't decompose hence they remain in the ecosystem and cause pollution, choke the system of many animals and kill them. 

2. These substances due to accumulation cause water and soil pollution. E.g.: pesticides, detergents, polythene. 

Q4. What are trophic levels? Give an example of a food chain and state the different trophic levels in it.  

Ans. The various levels or a stage in a food chain at which the transfer of food takes place is called the trophic level, e.g., the food chain. 

Q5. What is the role of decomposers in the ecosystem?  

Ans. Decomposers break down complex organic substances like plants' and animals' dead bodies and convert them into simpler inorganic substances. 

   All the elements that are present in the body on which decomposers act are released back to nature. Decomposers maintain balance in nature and play an important role in the environment. 

Q6. What is ozone and how does it affect any ecosystem? 

Ans. Ozone is a molecule of oxygen with 3 atoms, its formula is O₃. The ultraviolet radiation splits oxygen into free oxygen atoms, these atoms combine with oxygen molecules to form ozone. 

Ozone Ecosystem:
  At ground level, ozone is poisonous but at higher levels, it is very useful as it protects all living organisms from harmful UV radiations of the sun. It doesn't allow the ultraviolet radiation to enter the surface of the earth. The UV radiations cause an ionizing effect that leads, to skin cancer in human beings. 

Q7. How can you help in reducing the problem of waste disposal? Give any two methods.  

Ans. To reduce the problem of waste disposal we can 

1. Segregate the bio-degradable waste from non-biodegradable waste before dumping it. 

2. Remove all materials which can be recycled and send them for recycling, e.g., paper, glass, metal, rubber. 

Q1. Which of the following groups contain only bio-degradable items?
(a) Glass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit peels, cake and lime juice
(d) Cake, wood and grass

Ans. (a), (c) and (d).

Q2. Which of the following constitutes a food chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat 

Ans. (b) Grass, goat and human

Q3. 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

Ans. (d) All of the above

Q4. What will happen if we kill all the organisms at one tropic level? 

Ans. If all the organisms at one trophic level are killed then all the organisms of the next trophic level which are dependent on these are killed. Next trophic levels will not get food to eat and the entire food chain gets disturbed. At the same time, their organisms at the lower trophic level will reproduce and the population will increase in abundance thereby, disturbing the ecosystem. 

Q5. Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can the organism of any trophic level be removed without causing any damage to the ecosystem? 

Ans. The impact of removing all the organisms at a trophic level will be the same. If the organisms of any trophic level are removed it will certainly damage the ecosystem. 

Q6. What is biological magnification? Will the levels of this magnification, be different at different levels of the ecosystem? 

Ans. The pesticides and chemicals are absorbed by plants from the soil and enter the food chain. Being non-biodegradable they accumulate progressively, at each trophic level. As humans occupy the top level of any food chain, the maximum concentration of chemicals is found in our bodies. This is called biological magnification. 

   The level of magnification will be different at different trophic levels, the maximum concentration will be at the highest trophic level and the chemical will be less at the lower trophic levels. 

Q7. What are the problems caused by the non-biodegradable waste that we generate? 

Ans. 

1. As the non-biodegradable waste cannot be broken down into simpler forms, it keeps on accumulating in nature causing pollution. 

2. They cause diseases. 

3. It also causes biological magnification. 

Q8. If all the waste we generate is bio-degradable, will this have no impact on the environment?  

Ans. If all the waste we generate is bio-degradable and is managed in such a way that it is allowed to decompose, then it will have no impact on the environment. 

Q9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage? 

Ans. The ozone layer in the stratosphere is very helpful in shielding harmful UV rays. In the absence of an ozone layer heavy damage to organisms may occur. It may cause diseases like skin cancer, cataracts, reduced crop production etc. 

   The damage is limited by UNEP (United Nations Environment Programme), which forged an agreement to freeze CFC production in 1986. 

   CFC - Chlorofluorocarbons used as refrigerants and in fire extinguishers.