NCERT Class 10: Science-Exercise Solutions
Chapter 15-Our Environment-Exercise Solutions
NCERT Book Page Number-264-265
Q.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
Ans. (a) Grass, flowers and leather
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Q.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
Ans. (b) Grass, goat and human
Q.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
Ans. (d) All of the above
Q.4. What will happen if we kill all the organisms in one trophic level?
Ans. If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem. As an example, in a food chain Grass → Deer → Lion, If we remove all lions then population of deer will increase which will cause over-grazing. This will lead to deforestation. It may even lead to soil erosion causing further conversion of fertile land into barren desert.
Q.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 dam¬age to the ecosystem?
Ans. Impact of removing all organisms of a trophic level is different for different trophic levels.
For example, if we remove producers from a food chain, no organism will get food, if we remove herbivores from a food chain then carnivores will die and producers will also die due to competition for space and nutrients. No, we can’t remove any trophic level without causing damage to the ecosystem as one is dependent on other for its survival. If we remove any one this will create imbalance in the ecosystem.
Q.6. What is biological magnification ? Will the levels of this magnification be different at differ¬ent levels of the ecosystem ?
Ans. Biological magnification is defined as the phenomenon of accumulation or increase in the concentration of some toxic substances at each trophic level.
The levels of biomagnification will be different at different trophic levels. For example, in pond water, DDT was sprayed and the producers (phytoplanktons) were found to have 0.04 ppm concentration of DDT. Since many types of phytopplanktons are eaten by some fishes and clams, their body accumulates 0.23 ppm of DDT. Sea gull that feeds on clams accumulates more DDT
as one sea gull eats many clams. Hawk, the top carnivore, got the highest concentration of DDT.
Q.7. What are the problems caused by the non-biodegradable wastes that we generate ?
Ans. The problems caused by non-biodegradable wastes are:
• They cause biomagnification.
• They increase pollution.
• They make environment unclean.
• They kill useful microorganisms.
Q.8. If all the waste we generate is biodegradable, will this have no impact on the environment ?
Ans. If all the waste generated would be biodegradable this will also create problem. As the number of decomposers will be quite low so wastes cannot be broken down into harmless simpler substance at right time. It will become breeding ground for flies those spread many diseases. It will also emit foul smell which makes the life of people miserable.
Q.9. Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Ans. The damage to the ozone layer is a cause for concern because:
• It causes skin darkening, skin cancer, ageing, and cataracts in human beings.
• It can result in the death of many phytoplanktons that leads to increased global warming.
To limit the damage to the ozone layer, the release of CFCs into the atmosphere must be reduced. CFCs used as refrigerants and in fire extinguishers should be replaced with environmentally safe alternatives. Also, the release of CFCs through industrial activities should be controlled.