Solutions-NCERT-Class-10-Science-Chapter-13-Our Environment-CBSE

The transfer of food or energy takes place through various levels in the food chain, which are known as trophic levels, e.g.

Organisms that feed on dead plants and animals are called decomposers, e.g. bacteria, fungi, etc. They breakdown the complex organic compounds present in the dead remains into simpler substances and obtain nutrition from them. These substances are released into the soil and the atmosphere. Thus, they play the following roles

• They help in recycling of materials, replenishment of the soil's nutrients, etc.
• They clean our surroundings by decomposing dead organisms and organic wastes.

• Substances which can be broken down with the help of enzymes secreted by the bacteria and other saprophytes over a period of time are biodegradable. These substances have short molecular organisation and can be assimilated by the saprophytes.
• Non-biodegradable substances cannot be acted upon by the enzymes in nature as they consist of polymers which are strongly bonded with each other.

• Biodegradable wastes in large quantities would contribute to the pollution of the environment.
• They serve breeding ground to flies which are carrier of many diseases such as cholera.

The two ways in which non-biodegradable substances would affect the environment are

• They make the environment poisonous and unfit for survival of living forms of life.
• They block the transfer of energy and minerals in the ecosystem.

Ozone is a tri-atomic molecule, i.e. made up of three atoms of oxygen joined together. Its molecular formula is O₃. It can affect any ecosystem in the following ways

(i) It protects against ultraviolet rays if, present in stratosphere.

(ii) Ozone dissipates the energy of UV rays by undergoing dissociation followed by reassociation.

2O₃ → 3O₂ + Energy

(iii) In atmosphere, it is highly toxic and cause injury to mucous membranes, eye irritation and internal injuries in animals and humans.

We can help in reducing the problem of waste disposal by adopting the following methods:

• Minimizing the use of non-biodegradable wastes.
• Recycling the non-biodegradable wastes like plastic.
• Production of compost, biogas from biodegradable wastes.
• Reducing the volume of wastes by burning them in incinerator.

(c) Fruit-peels, cake and lime-juice

(b) Grass, goat and human

(d) All of the above

If we kill all the organisms in one trophic level, the organisms of lower trophic level will grow more in number and the organisms of higher trophic level will not survive. It will disturb the web and create ecological imbalance.

(i) Yes, the impact of removing all the organisms in a trophic level will be different for different trophic levels. The lower trophic level of an ecosystem has a greater

number of individuals than the higher trophic levels.

• Removal of producers will affect all the organisms of successive trophic levels and it will threat their survival.
• The removal of higher trophic level will lead to increase in organisms of lower trophic level and the organisms of higher trophic level will die due to the shortage of food.

(ii) No, removal of all organisms of a trophic level will disturb the ecosystem.

• Killing of higher trophic level organisms will cause explosion in the population of lower level organisms. This will adversely affect the ecosystem and thus environment.

(a) Biological magnification refers to the increase in the concentration of certain toxicants at each successive trophic level.

(b) Yes, the levels of magnification will be different at each trophic level. When the chemicals do not get degraded and get accumulated progressively at each trophic level, it leads to biomagnification. It is more in organisms of higher trophic levels.

Problems caused by the non-biodegradable wastes are :

• Clogging of drains
• Death of cattle by ingestion of plastic bag
• Soil destruction
• Non-aesthetic look
• Bio-magnification of poisonous chemicals in our body or other animals which disturb body metabolism resulting in various diseases
• Pollution of air, water and land
• Resulting in balance of ecosystem.

Production of biodegradable waste in large amount will also affect the environment adversely. Some of the impacts on the environment are as follows:

• Production of harmful gases causing pollution.
• Microbes will not be able to decompose all the biodegradable waste causing ugly look.

• Thinning of ozone layer present in stratosphere is called depletion of ozone layer. Due to depletion of ozone layer, harmful ultraviolet radiations can reach the surface of the Earth, which may lead to skin diseases, cancer, etc.
• To reduce the depletion of ozone layer, use of chlorofluorocarbons has been minimised. In 1987, the UNEP has passed an agreement to freeze CFC production at 1986 levels.