NCERT Solutions For Class 10 Science Chapter 15 Our Environment

NCERT Solutions For Class 10 Science Chapter 15 Our Environment Long Question And Answers

Question 1.

1. “Energy flow in a food chain is unidirectional.” Justify this statement. Explain how pesticides enter a food chain and subsequently get into our bodies.
2. What is an ecosystem? List its two main components.

Answer:

1. Because the energy moves progressively through the various trophic levels and is no longer available to the previous trophic level. The energy captured by autotrophs does not revert to the solar input.

• Pesticides, used for crop protection when washed down into the soil/water body, are absorbed by the plant/producer along with water and minerals.
• Being non-biodegradable, these chemicals accumulate progressively in the food chain and enter our bodies.

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2. A self-sustaining functional unit, consisting of living (biotic) and non-living (abiotic) components, is called an ecosystem.

Biotic components: Plants and animals.

Abiotic components: Light, soil, temperature, humidity, wind, air, etc.

Question 2.

1. What is the difference between the food habits of organisms belonging to second and fourth trophic levels? Give one example of organisms belonging to each of these two trophic levels.
2. What are the materials that remain unchanged over long periods?
3. What will happen to the garbage, and dead plants and animals in the absence of decomposers?

Answer:

1. Difference between second trophic level and fourth trophic level:

2. Non-biodegradable material.

3. The natural replenishment of soil will not take place and most of the fertile land will be used by us for dumping waste.

Question 3.

1. State in brief two ways in which non-biodegradable substances would affect the environment. List two methods of safe disposal of the non-biodegradable waste.
2. Differentiate between autotrophs, and heterotrophs and give one example of each

Answer:

The non-biodegradable substances affect the environment in the following ways:

1. They persist in the environment for a long time and thus damage the environment.
2. They cause land and water pollution.

Methods of safe disposal of the non-biodegradable waste:

1. By underground dumping.
2. By sending them to factories for recycling.

Autotrophs: Organisms that can make their food from carbon dioxide and water under the action of sunlight and in the presence of chlorophyll are called autotrophs.

Example: All green plants.

Heterotrophs:

Organisms that cannot make their food by the process of photo synthesis and are dependent on others for food are called heterotrophs.

Example: All animals.

Question 4. Explain the flow of energy between various components ofthe environment.
Answer:

Green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves.

The loss of energy at each step is so great that very little usable energy remains after four trophic levels.

In a food chain, the greatest number of individuals are at the lower trophic level of an ecosystem, and the greatest number is of the producers.

Question 5. Distinguish between biodegradable and non-biodegradable substances. List two effects of each of them on our environment.
Answer:

Effects of biodegradable substances:

1. They release harmful gases like methane, ammonia, carbon dioxide, hydrogen sulfide, etc., during the decomposition process.
2. They release a foul smell only during the decomposition process but they do not cause any type of soil pollution

Effects of non-biodegradable substances:

1. They persist in the environment for a long time and thus, harm the various members of the ecosystem.
2. They release very harmful gases when they are acted upon by physical processes like heat and pressure.
3. They cause pollution of air, soil, and water

Question 6. How is ozone formed at higher levels of the atmosphere?
Answer:

Ozone is a product of UV radiation on oxygen molecules at higher levels of the
atmosphere. The higher energy radiations split apart some 02 molecules into three oxygen (O) atoms. These atoms then combine with molecular 02 to form ozone.

⇒ \(\mathrm{O}_2+\mathrm{O} \longrightarrow \mathrm{O}_3\)

Question 7. Indicate the flow ofenergy in an ecosystem. Why is it unidirectional? Justify.

1. Usage of-pesticides
2. Manures.

Answer:

The flow of energy generally is as follows:

Sun→ Producer → Herbivore → Carnivore.

Since the flow is progressively from one trophic level to another and does not revert, it is said to be unidirectional. Further, the available energy decreases in the higher trophic levels making it impossible for energy to flow in the reverse direction.

Question 8.

1. What is an ecosystem? List its two main components.
2. We do not clean ponds or lakes, but an aquarium needs to be cleaned regularly Explain.

Answer:

1. A self-sustaining functional unit consisting of living (biotic) and non-living (abiotic) components, is called an ecosystem.

1. Biotic Components: Plants and animals.
2. Abiotic Components: Light, soil, temperature, humidity, wind, air, etc.

2. An aquarium is an artificial and incomplete ecosystem in contrast to a pond or lake which is a natural, self-sustaining, and complete ecosystem. In a natural ecosystem, decomposers help in recycling waste. So, an aquarium needs to be cleaned regularly.

Question 9. Differentiate among autotrophs, heterotrophs, hs, and decomposers andgive one example of each.
Answer:

Autotrophs: Organisms that can make their food from carbon dioxides and water under the action of sunlight and in the presence of chlorophyll are called autotrophs.

Example: All green plants.

Heterotrophs:

Organisms that cannot make their food by the process of photosynthesis and are dependent on others for food are called heterotrophs.

Example: All animals

Decomposers: Organisms that decompose the complex molecules present in the dead remains of plants and animals are called decomposers.

Example: Bacteria, fungi

Question 10. What are trophic levels? Give an example ofa food chain having four steps and name the different levels according to their nutrition habit.

Each step of the food chain is termed the trophic level.

Grass→ Insect → Frog →Snake

Grass – Producer

Insect – Primary consumer

Frog – Secondary consumer

Snake – Tertiary consumer

Question 11. Two things become clear from the energy flow diagram drawn below

Answer:

1. The flow of energy is unidirectional.
2. Only 10%of  energy flows from one trophic level to the next.

Question 12. In the food chain: Grass → Deer→ Lion, operating in a forest, what will happen if all the:

1. Lions are removed?
2. Deer are removed?

Answer:

1. Several deer increases, which will result in less amount of grass, leading to soil erosion.
2. Food available for lions would be less. The amount of grassland will increase.

Question 13. List two causes of depletion of the ozone layer. Mention any two harmful effects of depletion of this layer.
Answer:

Two causes of the depletion of the ozone layer are:

1. Use of CFCs (chlorofluorocarbon) in refrigeration.
2. Use of CFCs in fire extinguishers and aerosol sprayers.

The harmful effects of the depletion of the  ozone layer are as follows:

Due to the depletion of the ozone layer, UV radiation reaches the earth. This UV radiation causes skin cancer, and damage to the eyes and immune system.

This depletion of the ozone layer may also lead to variations in global rainfall, ecological disturbances, and dwindling global food supplies.

Question 14. Mention the difference between the food habits of organisms belonging to the first and third tropic levels. Give one example of each of them.
Answer:

Question 15. Draw a line diagram of a simple food web.
Answer:

Simple food web:

Question 16. What will happen if we kill all the organisms at one trophic level?
Answer:

If we kill all the organisms in one trophic level, the number of organisms in the higher trophic level will decline as they will not get food while the number of organisms in the lower trophic level will increase as they are not eaten up.

For example, if in the following food chain:

Grass → Deer →  Tiger

If we remove all the tigers, the number of deer will increase and the amount of grass will decrease

Question 17.

1. Which scientific term is used for the progressive accumulation of harmful chemicals at each trophic level of a food chain?
2. State any two practices which can help in the protection of our environment.

Answer:

1. Biological magnifications.

2.

1. Use of unpetrol patrol and alternate sources of energy.
2. Disposal of waste after separating into biodegradable and non-biodegradable waste material.

Question 18.

1. Construct the food chain of the forest
2. Construct the food chain of grassland

Answer:

1. Grass → Deer → Tiger

2. Grass→ Grasshopper→ Frog → Snake→ Vulture

Question 19. Write the appropriate names ofthe tropic levels Z and X in the figure given below.

Answer:

Z = Tertiary consume

X= Primary consumer.

Question 20. Give any two ways in which non-biodegradable substances would affect the environment.
Answer:

Non-biodegradable substances cannot degrade and return the minerals to the environment. Instead of a cycle, these materials follow a linear path. They are produced in a factory and then end up in the soil. They pile up and cause harm to the various members of the ecosystem.

They may cause biomagnification in the food chain and end upinhumans. For example, pesticides like DDT enter the food chain, biomagnify, and affect human beings and other organisms.

Question 21. What are trophic levels? Give an example ofa food chain and state the different trophic levels in it.
Answer:

The trophic level is the functional level occupied by an organism in a food chain. Trophic means feeding, so trophic levels are the levels or positions at which the species feed. Examples of trophic levels include ‘herbivores’ and ‘decomposers’.

 An example of a food chain depicting various trophic levels is as follows:

Question 22. What is the role of decomposers in the ecosystem?
Answer:

Without decomposers, the remains of the other organisms in a community would accumulate. Eventually, the world would run out of carbon dioxide or nite or phos, phase, or other inorganic materials essential for life. The decomposers break down the organic waste products and dead remains of organisms into the inorganic substances needed by the producers (plants). Most decomposition is carried out by saprophytic fungi and bacteria.

Question 23. What is depicted in the below-mentioned scheme?
Answer: Food Chain 10% law.