1. What is the function of ozone in upper atmosphere?
Ans: It shields the surface of the earth from ultraviolet rays from the Sun.
2. Why should biodegradable and non biodegradable waste be discarded in two separate dustbins?
Ans: So that the time and energy required in segregation may be saved and waste may be disposed off quickly
3. The following organisms form a food chain. Which of these will have the highest concentration of non-biodegradable chemicals ? Name the phenomenon associated with it. Insects, Hawk, Grass, Snake, Frog.
4.. Write the full name of the group of compounds mainly responsible for the depletion of ozone layer.
5. List two examples of natural ecosystem.
6. Differentiate between biodegradable and non-biodegradable substances with the help of one example each.
List two changes in habit that people must adopt to dispose non-biodegradable waste, for saving the environment.
Ans: Biodegradable substances – Any substance that can be broken down into simpler substances by biological process is called biodegradable. Ex. – Human Excreta/ Vegetable peels, etc.
Non-biodegradable substances – Any substance that can can’t be broken down into simpler substances by nature or decomposers. Ex. – Plastic/ glass (or any other) (any one)
Habits that people must adopt to dispose non-biodegradable waste, for saving the environment:
- Use of separate dustbins for biodegradable and non biodegradable waste,
- Reuse of things such as poly-bags, etc.,
- Recycle of waste
- Use of cotton /jute bags for carrying vegetables
7. What will be the amount of energy available to the organisms of the 2nd trophic level of a food chain, if the energy available at the first tropic level is 10,000 joules?
Ans: 10% of 10,000 joules = 1000 J
8. ‘‘Energy flow in food chains is always unidirectional.’’ Justify this statement.
Explain how the pesticides enter a food chain and subsequently get into our body.
Ans: The flow of energy is unidirectional. The energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs.
Therefore, in food chain the energy moves progressively through the various trophic levels it is no longer available to the previous level. Thus, The flow of energy in food chain is unidirectional.
The pesticides enter a food chain and subsequently get into our body in following way:
(i) Pesticides used for crop protection when washed away into the soil or water bodies absorbed by plants.
(ii) On consumption they enter our food chain and being non – biodegradable these chemicals get accumulated progressively and enter our body.
9. What is ozone ? How and where is it formed in the atmosphere? Explain how does it affect an ecosystem.
Ans: Ozone (O3) is a molecule formed by three atoms of oxygen.
Ozone is formed at at the higher levels of the atmosphere by action of UV radiation on oxygen (O2) molecule.
The higher energy UV radiations split apart some moleculer oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown—
O2 ⎯⎯UV⎯→ O + O then, O + O2 ⎯⎯⎯→ O3 (Ozone)
Ozone shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.
10. Construct an aquatic food chain showing four trophic levels.
Ans: Hydrilla →Scorpio→ Fish → Crane
11. To protect the food plants from insects, an insecticide was sprayed in small amounts but it was detected in high concentration in human beings. How did it happen?
Ans: As insecticides are not degradable, these get accumulated progressively at each tropic level. As human beings occupy the top level in any food chain, the high concentration of insecticide gets accumulated in their bodies. This phenomenon is known as biological magnification
12. Why do most food chains have 3- 4 steps only?
Ans: The loss of energy at each step is so great that very little usable energy remains after four trophic levels. Therefore, food chains generally consist of only three or four steps.
13. What will be impact on ecosystem if bacteria and fungi are removed from the Environment?
14. Why is a pond self sustaining unit while an aquarium may not be?
Ans: A pond contains microorganisms that break-down the dead remains and waste products of organisms into simple inorganic substances that are used by other organism.
Since, pond is a natural ecosystem while an aquarium is created by man and is artificial, thus a pond self sustaining while an aquarium may not be.
15. Which level shows the maximum biological magnification? Why?
Ans: The top tropic level in any food chain has the maximum concentration of chemicals. From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by plants and animals.