9th Std Science Solution in English | Lesson.24 Environmental Science

Lesson 24 Environmental Science

Environmental Science Book Back Answer

I. Choose the correct answer:

1. All the factors of biosphere which affect the ability of organisms to survive and reproduce are called as ________

  1. biological factors
  2. abiotic factors
  3. biotic factors
  4. physical factors

Ans: physical factors

2. The ice sheets from the north and south poles and the icecaps on the mountains, get converted into water vapour through the process of __________

  1. evaporation
  2. condensation
  3. sublimation
  4. infiltration

Ans: sublimation

3. The atmospheric carbon dioxide enters into the plants through the process of _________

  1. photosynthesis
  2. assimilation
  3. respiration
  4. decomposition

Ans: photosynthesis

4. Increased amount of __________ in the atmosphere, results in green house effect and global warming

  1. carbon monoxide
  2. sulphur dioxide
  3. nitrogen dioxide
  4. carbon dioxide

Ans: carbon monoxide

5. Free living soil bacteria such as Pseudomonas sp. are responsible for the ________ process in the nitrogen cycle.

  1. ammonification
  2. nitrogen fixation
  3. nitrification
  4. denitrification

Ans: denitrification

6. Which of the following is not an adaptation of hydrophytes?

  1. poorly developed root system
  2. reduced plant body
  3. water storing parenchymatous tissues
  4. finely divided submerged leaves

Ans: water storing parenchymatous tissues

7. In some xerophytes, leaves are modified into spines as an adaptation ________

  1. to reduce transpiration rate
  2. to store water
  3. to reduce consumption of water
  4. all of the above

Ans: all of the above

8. Identify the incorrect statement with respect to adaptations of earthworm.

  1. Earthworm has a stream lined body with no antennae or fins.
  2. Each segment of earthworm has setae.
  3. Many earthworms become inactive in a process called hibernation, during winter season.
  4. Earthworms remain in its burrow during day time, to avoid sunlight.

Ans: Many earthworms become inactive in a process called hibernation, during winter season.

9. Which of the following is one of the strategies to conserve water?

  1. Water recycling
  2. Increasing the number of bore wells
  3. Using large overhead water tanks
  4. Watering the plants using hose

Ans: Water recycling

10. Specific constituents such as nitrogen, phosphorus, suspended solids and heavy metals found in the wastewater are removed during _________ treatment of water recycling process.

  1. primary
  2. secondary
  3. tertiary
  4. none of the above

Ans: tertiary

II. Match the following.

MicroorganismRole Played
1. Nitrogen fixationNitrosomonas
2. AmmonificationAzotobacter
3. NitrificationPseudomonas species
4. DenitrificationPutrefying bacteria
Ans : 1 – B, 2 – D, 3 – A, 4 – C

III. State whether the statements are true or false. Correct the false statements.

1. Nitrogen is a greenhouse gas.

Ans: False

Correct Ans: Carbon dioxide is a greenhouse gas.

2. Poorly developed root is an adaptation of mesophytes.

Ans: False

Correct Ans: Well developed root is an adaptation of mesophytes.

3. Bats are the only mammals that can fly

Ans: True

4. Earthworms use the remarkable high frequency system called echoes.

Ans: False

Correct Ans: Bats use the remarkable high frequency system called echoes.

5. Aestivation is an adaptation to overcome cold condition.

Ans: False

Correct Ans: Aestivation is an adaptation to overcome hot or dry condition.

VI. Give reason.

1. Roots grow very deep and reach the layers where water is available. Which type of plants develops the above adaptation? Why?

Xerophytes, They have well developed roots. Roots grow very deep and reach the layers where water is available as in Calotropis.

2. Why streamlined bodies and presence of setae is considered as adaptations of earthworm?

The earthworm has a cylindrical, elongated and segmented body. This helps them to live in narrow burrows underground and for easy penetration into the soil

3. Echo location serves as an adaptation in bats. Justify the given statement.

Bats are not blind. But to fly around and hunt for insects in the dark, they use a remarkable high-frequency system called echolocation. Bats give out high-frequency sounds (ultrasonic sounds). These sounds are reflected back from its prey and perceived by the ear. Bats use these echoes to locate and identify the prey.

4. Farm ponds serve as an excellent water conservation strategy. Why is it impossible for all farmers to construct it in their fields?

  • Farm ponds reduce water flow to other tanks and ponds situated in lower-lying areas.
  • They occupy a large portion of farmer’s lands.

IV. Answer in brief

1. What are the two factors of biosphere?

  • Biotic or living factors which include plants, animals and all other living organisms.
  • Abiotic or non-living factors which include all factors like temperature, pressure,water, soil, air and sunlight which affect the ability of organisms to survive and reproduce.

2. How do human activities affect nitrogen cycle?

Burning fossil fuels, application of nitrogenbased fertilizers and other activities can increase the amount of biologically available nitrogen in an ecosystem. Nitrogen applied to agricultural fields enters rivers and marine systems. It alters the biodiversity, changes the food web structure and destroys the general habitat

3. What is adaptation?

Any feature of an organism or its part that enables it to exist under conditions of its habitat is called adaptation.

4. What are the challenges faced by hydrophytes in their habitat?

Hydrophytes face certain challenges in their habitat. They are:

  1. Availability of more water than needed.
  2. Water current may damage the plant body.
  3. Water levels may change regularly.
  4. Maintain buoyancy in water.

5. Why is it important to conserve water?

  • It creates more efficient use of the water resources.
  • It ensures that we have enough usable water.
  • It helps in decreasing water pollution.
  • It helps in increasing energy saving.

6. List some of the ways in which you could save water in your home and school?

  1. Rain water harvesting.
  2. Improved irrigation techniques.
  3. Active use of traditional water harvesting structures.
  4. Minimising domestic water consumption.
  5. Awareness on water conservation.
  6. Construction of farm ponds.
  7. Recycling of water.

7. What are the uses of recycled water?

  • Agriculture
  • Landscape
  • Public parks
  • Golf course irrigation
  • Cooling water for power plants and oil refneries
  • Toilet fushing
  • Dust control
  • Construction activities

8. What is IUCN? What is the vision of IUCN?

IUCN is an international organization working in the field of nature conservation and sustainable use of natural resources.

9. According to you, which process of water cycle is adversely affected by human activities?

Major human activities affecting the water cycle on land are urbanisation, dumping of plastic waste on land and into water, polluting water bodies and deforestation.

10. Identify the given plant. How does it adapt itself to its habitat?

Submerged leaves are narrow or finely divided. e.g. Hydrilla

11. What is grey water?

Grey water is reusable waste water from residential, commercial and industrial bathroom sinks, bath tub,shower drains and washing of clothes. Use of non-toxic and low sodium soap and personal care products is required to protect vegetation when reusing grey water for irrigation

Vision of IUCN

The vision of IUCN is ‘A just world that values and conserves nature’.

V. Answer in detail.

1. Describe the processes involved in the cyclic flow of water between biotic and abiotic factors of biosphere?

Water cycle or hydrological cycle is the continuous movement of water on earth. In this process, water moves from one reservoir to another by processes such as evaporation, sublimation, transpiration, condensation, precipitation, surface runoff and infiltration, during which water converts itself to various forms like liquid, solid and vapour


Evaporation is a type of vaporization, where liquid is converted to gas before reaching its boiling point. Water evaporates from the surface of the earth and water bodies such as the oceans, seas, lakes, ponds and rivers.


Sublimation is conversion of solid to gas, without passing through the intermediate liquid phase. Ice sheets and ice caps from north and south poles, and icecaps on mountains, get converted into water vapour directly, without converting into liquid.


Transpiration is the process by which plants release water vapour into the atmosphere through stomata in leaves and stems.


Condensation is the changing of gas phase into liquid phase and is the reverse of vaporisation. At higher altitudes, the temperature is low. The water vapour present there condenses to form very tiny particles of water droplets. These particles come close together to form clouds and fog.


Due to change in wind or temperature, clouds combine to make bigger droplets, and pour down as precipitation(rain). Precipitation includes drizzle, rain, snow and hail.

Run off :

As the water pours down, it runs over the surface of earth. Runoff water combines to form channels, rivers, lakes and ends up into seas and oceans.


Some of the precipitated water moves deep into the soil. Then it moves down and increases the ground water level.


Some of the precipitated water flows through soil and porous or fractured rock. Infiltration and percolation are two related but different processes describing the movement of water through soil.

2. Explain carbon cycle with the help of a flow chart? 

9th Science Guide Environmental Science Answers in English a

3. List out the adaptations of xerophyte

Plants that grow in dry habitat are called xerophytes. These plants develop special structural and physiological characteristics to meet the following conditions:

  • To absorb as much water as they can get from the surroundings.
  • To retain water in their organs for very long time.
  • To reduce the transpiration rate.
  • To reduce consumption of water

Adaptations of xerophytes

  • They have well developed roots. Roots grow very deep and reach the layers where water is available as in Calotropis.
  • They store water in succulent water storing parenchymatous tissues. e.g. Opuntia, Aloe vera.
  • They have small sized leaves with waxy coating. e.g. Acacia. In some plants, leaves are modified into spines. e.g. Opuntia.
  • Some of the xerophytes complete their life cycle within a very short period when sufficient moisture is available

4. How does a bat adapt itself to its habitat

  • For the most part, bats live in caves, which provide protection from most predators during the day and maintain a stable temperature.
  • Bats are active during the night. This is a useful adaptation for them, as flight requires more energy during daylight hours.
  • By hibernating, bats lower their metabolic rate and lower their body temperature during winter.
  • Bats allow their internal temperatures to drop when they rest.
  • Bats use echolocation (high frequency ultrasonic sound waves) to recognize and locate prey.

5. What is water recycling? Explain the conventional wastewater recycling treatment?

Conventional waste water treatment consists of a combination of physical, chemical and biological processes which remove solids, organic matter and nutrients from waste water. Te waste water treatment involves the following stages:

Primary treatment

Primary treatment involves temporary holding of the waste water in a tank. Te heavy solids get settled at the bottom while oil, grease and lighter solids float over the surface. Te settled and floating materials are removed. The remaining liquid may be sent for secondary treatment.

Secondary treatment

Secondary treatment is used to remove the biodegradable dissolved organic matter. This is performed in the presence of oxygen by aerobic microorganisms (Biological oxidation). The microorganisms must be separated from treated waste water by sedimentation. After separating the sediments of biological solids, the remaining liquid is discharged for tertiary treatment.

Tertiary treatment

Tertiary or advanced treatment is the final step of sewage treatment. It involves removal of inorganic constituents such as nitrogen, phosphorus and microorganisms. The fine colloidal particles in the sewage water are precipitated by adding chemical coagulants like alum or ferric sulphate



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