CBSE Class 10 Science Our Environment

Environment: Our surrounding is called environment.

Class 10 Science: Our Environment

Environment: Our surroundings are called the environment.

Topics covered:

1. Ecosystem and its components
2. Biotic and abiotic components
3. Food chain and food web
4. Energy transfer through trophic levels
5. Ozone layer and its concerns

Ecosystem: This is a system of interdependencies among various living beings and non-living things in a given habitat.

Components of an ecosystem: An ecosystem has two types of components, namely the biotic component and the abiotic component.

Abiotic component: All the non-living things make the abiotic component of an ecosystem. Air, water and soil are abiotic components.

Biotic component: All living beings make the biotic component of an ecosystem.

• Green plants play the role of producers, because they prepare food by photosynthesis.
• Animals and other living beings play the role of consumers, because they take food (directly or indirectly) from plants.
• Bacteria and fungi play the role of decomposers, as they decompose dead remains of plants and animals so that the raw materials of organisms can be channelised back to the environment.

Food chain: A food chain is a simple representation of the transfer of energy from the sun to the different biotic components of an ecosystem. The sun is the ultimate source of energy. Green plants convert solar energy into chemical energy during photosynthesis.

Producer → Primary consumer → Secondary consumer

Food web: In any ecosystem, there can be many food chains which are interlinked at various levels. Thus, many food chains form a network, which is called a food web.

Transfer of energy through a food chain: The different levels in a food chain are called trophic levels. Out of the energy consumed by an organism at a particular trophic level, about 90% is utilised for its own needs and the rest, about 10%, is left for the organism of the next trophic level.

Balance in the ecosystem: There is a delicate balance in an ecosystem as far as the number of organisms at a particular trophic level is concerned. An increase or decrease in the population of any organism can disturb this balance. For example, in the following food chain:

Plant → Deer → Lion

If all the deer are killed in a jungle, the lions would be left with no food. This would endanger the existence of lions. Once the lions and deer are finished, it would result in a population explosion of green plants. If all the lions die in a jungle, it would create another problem. Since no lion would be left to kill the deer, the population of deer would increase substantially. This would finish off all the green plants and finally even the deer would be left with no food.

Biodegradable substances: Substances which can be decomposed by microorganisms are called biodegradable substances. All organic substances are biodegradable.

Non-biodegradable substances: Substances which cannot be decomposed by microorganisms are non-biodegradable. All inorganic substances are non-biodegradable.

Ozone layer depletion: The ozone layer lies in the stratosphere. When ultraviolet radiations act on oxygen, the oxygen is converted into ozone.

\(\text{O}_2 \xrightarrow{\ \text{UV radiation}\ } \text{O} + \text{O}\)

\(\text{O}_2 + \text{O} \longrightarrow \text{O}_3\)

The ozone layer works like a protective shield for living beings.

Effect of CFCs: The use of CFCs (chlorofluorocarbons) has damaged the ozone layer. CFCs are used in refrigerators and aerosol sprays.

Problems of waste disposal: Plastic waste is a serious concern because plastic is non-biodegradable. Proper segregation of wastes before disposal helps us to save our environment.

Mind Map: Our Environment

Flow Chart

Flow of energy in an ecosystem.

Figure 15.1 Food chain in nature (a) in forest, (b) in grassland and (c) in a pond.

Environment Puzzle

Using the across and down clues, write the correct words in the numbered grid.

Word bank: LANDFILL, RECYCLE, PROTECT, PRESERVE, POLLUTION, FLOOD, REDUCE, REUSE, DEFORESTATION

Answer: Across: 2 DEFORESTATION, 4 LANDFILL, 7 POLLUTION, 8 REDUCE, 9 REUSE. Down: 1 RECYCLE, 3 PRESERVE, 5 FLOOD, 6 PROTECT.

Environment Puzzle 2

Find the hidden words from the given grid. Words can go across or down.

Answer: Words hidden in the grid: ENVIRONMENT (across), COMPOST (across), SCIENCE (across), EARTH (across), RECYCLING (down).

Our Environment: Question Bank

Using kulhads as disposable cups to serve tea in trains proved to be a bad idea. Why?

Answer: Making kulhads on a large scale leads to the loss of top soil.

Why is plastic not degraded by bacteria?

Answer: Plastic is not degraded by bacteria because they do not have enzymes to degrade plastic.

DDT has entered the food chain. Which food habit is safer, vegetarian or non-vegetarian?

Answer: The vegetarian habit is safer. Being closer to the producers, less DDT will accumulate in our body. Biomagnification leads to a higher level of DDT at higher trophic levels.

An aquarium requires regular cleaning whereas lakes normally do not. Why?

Answer: Normally a lake has more diverse forms of life and hence a larger number of food chains. This leads to natural cleaning. Thus, the ecosystem is more stable. An aquarium has a very limited number of food chains and is unable to sustain itself. But sometimes there is excessive growth of algae in a lake. Then it also needs to be cleaned.

How will accumulation of biodegradable waste affect our environment?

Answer: Accumulation of biodegradable waste will (a) not let minerals return to the mineral pool, and (b) become a site of pest breeding.

Look at the following figures. Choose the correct one and give a reason for your answer.

Answer: Fig. A is correct. In an ecosystem, the number of individuals at the producer level is maximum. This number reduces at each successive level. Therefore, the shape is a pyramid with a broader base and a tapering apex. On average, 10% of the food changes into body mass and is available for the next level of consumers.

It is the responsibility of the government to arrange for the management and disposal of waste. As an individual you have no role to play. Do you agree? Support your answer with two reasons.

Answer: I do not agree. As an individual, I also have a responsibility and can contribute in the following ways: (i) cut down waste generation, (ii) make a compost pit for biodegradable waste, (iii) recycle non-biodegradable waste.

Q. 5 How will accumulation of bio degradable waste effect our environment?

Ans. Accumulation of bio degradable waste will: