Class 10 NCERT Solutions Biology Chapter 13: Our Environment
Our Environment Exercise 212
Solution 1
Trophic levels are different steps of a food chain. A trophic level is the level of species in an ecosystem on the basis of the source of nutrition such as producers, primary consumers, secondary consumers, etc.
The producers form the first trophic level as they manufacture food. The primary consumers form the second trophic level, the secondary consumers form the third, and the tertiary consumers form the fourth trophic level.
Food chain: is a unidirectional flow of food energy in the organisms which are present in a given ecosystem. Terrestrial food chain.
(Producer) (Herbivore) (Carnivore)
1st Trophic level 2nd trophic level 3rd trophic level
Concept insight: Students should recall food chain and its various levels.
Solution 2
Role of decomposers in the ecosystem:
(i) They clean the environment.
(ii) They decompose biodegradable substances into useful substances.
(iii) They release nutrients into soil by decomposing dead and decaying matter, thus making the soil fertile.
(iv) They maintain the nutrient pool by returning back the nutrients in the pool.
Concept insight: Recall the role of decomposers in an ecosystem.
Our Environment Exercise 214
Solution 1
Substances are classified as biodegradable and non-biodegradable because some substances can be decomposed by microorganisms and some cannot.
Substances that are broken down into simple soluble forms are called biodegradable substances and the substances that are not decomposed by microorganisms into harmless substances are called non biodegradable substances.
Concept insight: Difference between biodegradable and non-biodegradable substances.
Solution 2
Biodegradable substances would affect the environment in the following ways.
(i) They may produce foul smell during decomposition process.
(ii) They may produce harmful gases such as ammonia, methane, carbon dioxide.
Concept insight: Recall biodegradable substances.
Solution 3
Non-biodegradable substances would affect the environment in the following ways.
(i) Substances like DDT, BHC enter in the food chain and cause biomagnification.
(ii) They cause pollution.
(iii) They also kill useful microorganisms.
Concept insight: Recall non-biodegradable substances.
Our Environment Exercise 216
Solution 1
Ozone (O3) is a triatomic molecule, made up of three atoms of oxygen.
Ozone (O3) thus forms a layer in the upper atmosphere. It is very essential for the life on this planet. It shields the surface of the earth from ultra-violet radiation (UV) coming from sun as these radiations are very harmful causing skin cancer and cataract in humans. It also cause harm to the crops.
Concept insight: Students should recall ozone layer, its composition and function.
Solution 2
Following measures could be taken to reduce waste disposal:
(i) By separating biodegradable substances from non-biodegradable substances.
(ii) By reducing, reusing and recycling non-biodegradable substances.
Concept insight: Differences between biodegradable and non-biodegradable substances.
Our Environment Exercise 216 Contd.
Solution 1
(a), (c) and (d)
Concept insight: Differentiate between biodegradable and non biodegradable substances.
Solution 2
(b) Grass, goat and human.
Concept insight: Recall food chain and organisms that constitute a food chain.
Our Environment Exercise 217
Solution 3
(d) All of the above.
Concept insight: Important from Exam Point of View.
Solution 4
If we kill all the organisms of one trophic level it will create an imbalance in the ecosystem.
For example, in a food chain: 
If lions are removed from the above food chain, 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.
Concept insight: Recall food chain and levels of a food chain.
Solution 5
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.
If all the organisms of a trophic level are removed it will create an imbalance in the ecosystem. Removing any trophic level from a food chain will cause imbalance in an ecosystem.
Concept insight: Recall food chain and the importance of different levels of food chain.
Solution 6
Biological magnification is defined as the phenomena of accumulation or increase in the concentration of some toxic substances at each trophic level.
It has been observed that some harmful or poisonous substances like: DDT sprinkled to kill pests on food plants get washed down into the soil or into the water bodies.
From the soil, these chemicals are absorbed by plants along with water and minerals whereas aquatic plants and animals take up these chemicals from water bodies.
On eating these plants or aquatic plants and animals, the toxic substances enter into our body.
Yes, the magnification is different at different levels of the ecosystem. The animals at the higher trophic levels get more poison along with their food than animals at lower trophic level. Thus, as the levels of food chain increases, the magnification also increases.
Concept insight: Recall the concept of biological magnification and its impact on different levels of food chain.
Solution 7
Following are some problems caused by non-biodegradable wastes:
(a) They cause biomagnification.
(b) They increase pollution.
(c) They make environment unclean.
(d) They kill useful microorganisms.
Concept insight: Recall the non-biodegradable wastes.
Solution 8
If all the waste generated would be biodegradable this will also create problem as the process of decomposition is quite slow so waste will start accumulating.
Biodegradable waste would affect the environment in the following two ways:
(i) Some biodegradable substances like cow-dung blocks the sewerage pipes and produce foul smell thus pollutes the surrounding environment.
(ii) Some biodegradable substances like fruit and vegetable wastes serve the breeding site of flies and mosquitoes which causes various diseases in surrounding environment.
Concept insight: Recall the concept of biodegradable wastes.
Solution 9
Due to the depletion of ozone layer ultraviolet rays reaches the earth surface and causes the following harmful effects:
(i) Causes skin cancer.
(ii) Causes eye disease called cataract.
(iii) Damage the immune system, thus lowering body's resistance to diseases.
Steps to reduce the damage:
(i) Use of aerosols should be banned.
(ii) Many countries have banned the use CFC's as refrigerants.
(iii) Pollution should be reduced.
Concept insight: Recall ozone layer, its importance, cause for ozone hole and steps to reduce the damage.
