Q  1. What are the two ways by which carbon dioxide is fixed?


Following are the two ways by which carbon dioxide can be fixed in nature:

i. In the process of photosynthesis, carbon dioxide is fixed by the plants.

ii. Dissolved carbon dioxide is used by many marine animals to make their carbonate shells.

Q  2. (i) Name two biologically important compounds that contain both oxygen and nitrogen.

(ii) What is the role of nitrogen fixing bacteria?


(i) (a) Nucleic acids (DNA and RNA)

(b) Proteins

(ii) Nitrogen fixing bacteria are found in root nodules of legumes and they convert atmospheric nitrogen into soluble nitrates and nitrites.

Q  3. Define biogeochemical cycle.


Biogeochemical cycle is a pathway by which elements or molecules move through both biotic and abiotic compartments of an ecosystem.

Q  4. What is the main cause of increase in CO2 in atmosphere? Explain the harmful effect of increase in CO2 content in atmosphere.


Industrial revolution is the main cause of increase in carbon dioxide in the atmosphere. Increase in carbon dioxide gives rise to global warming which causes imbalance in nature, affects monsoons and rainfall.

Q  5. Give terms for the following:

i. Conversion of ammonia into nitrates

ii. Process of ammonia formation

iii. Conversion of nitrates into ammonia


i.. Nitrification ii. Ammonification iii. Denitrification

Q  6. List two activities of man which lead to environmental pollution.


a. Deforestation, which can lead to increase in concentration of carbon dioxide

b. Excessive combustion of fossil fuels.

Q  7. Explain the role played by lichens, mosses and trees in soil formation.


(i) Lichens grow on the surface of rock and extract minerals from them. This creates small crevices at places where a thin layer of soil builds up.

(ii) Mosses grow over these crevices and deepens them to build up more soil.

(iii) The roots of trees grow into cracks in the rocks and widen to form soil.

Q  8. Which cycle is known as the perfect cycle in biosphere? Why?


Nitrogen cycle is called a perfect cycle in the biosphere because it keeps or maintains the overall amount of nitrogen constant in atmosphere, soil and water. Decay causers, Nitrogen cycle depends upon different kinds of bacteria the nitrifies, the denitrifies, and the nitrogen fixers. There is a regular circulation of nitrogen through the air, soil, plants and animals through nitrogen cycle.

Q  9. What is soil erosion? Write two steps to control soil erosion.


Removal of the top layer of soil rich in humus is called soil erosion. Steps to control soil erosion :

(a) Growing deep rooted plants at slopes.

(b) Preventing deforestation.

(c) Preventing large scale grazing of animals. (Any two)

Q  10. Our Earth is covered with approximately 75% water still there is an urgent need to conserve water. Why?


(a)Approximately 98% of the total water on earth is saline water and 2% is available for human consumption.

(b)Due to human activities the potable water becomes unfit for drinking and gets polluted. Hence, there is need to conserve water.

Q  11. (a)State the group of compounds that leads to ozone depletion.

(b)What is the significance of intact ozone layer?


(a) Chloro fluoro carbons causes ozone depletion.

(b) Ozone layer absorbs harmful ultraviolet radiations released from the sun and prevents them from reaching the surface of the earth as these radiations cause harmful effects to human beings, plants and animals.

Q  12. What makes the biosphere dynamic but stable system?


Biosphere consists of both biotic and abiotic components. The constant interactions between the biotic and abiotic components results in continuous transfer of food and energy. This interaction makes the system dynamic. Different elemental cycles such as water cycle, nitrogen cycle, carbon cycle etc. provide stability to the biosphere.

Q  13. What are the effects of air pollution on human beings?


Effects of air pollution are:

i. Air pollution can have serious conseQuences on the health of human beings. Human beings may suffer from respiratory problems, high blood pressure, renal problems, eye irritation, problems in nervous system, etc.

ii. Air pollution causes falling of leaves, reduced growth of plants, degeneration of chlorophyll, etc.

iii. Air pollution leads to acid rain which further damages soil, plants and buildings, etc.

Q  14. “Urbanization and industrialization is mainly responsible for the increase in environment pollution”. Justify this statement and suggest ways and means to check it.


(a) Urbanization and industrialization is mainly responsible for the increase in environment pollution” This is due to the following reasons:

i. Increased consumption of fossil fuels has increased the production of pollutants like CO2, SO2, NO2, CO2 etc. ii. Release of CFC molecules in the atmosphere has led to depletion in ozone layer which results in the entry of U.V. rays into earth’s atmosphere.

iii. Oxides of sulphur and nitrogen dissolve in rain water to produce acid rain.  

(b) Measures to check environmental pollution:

i. Reduce consumption of fossil fuels.

ii. Planting more trees. iii. Usage of non-conventional sources of energy e.g solar, wind, tidal energy.

Q  15. List three major physical processes in the water cycle in nature.


i. Evaporation of water from water bodies.

ii. Precipitation.

iii. Flow of water from land to oceans.

Q  16. What is atmosphere? Name the five layers of atmosphere.


The atmosphere is a mixture of gases that surrounds the planet Earth. The atmosphere is divided into following five layers:

i. Troposphere

ii. Stratosphere

iii. Mesosphere

iv. Thermosphere

v. Exosphere

Q  17. Write a short note on greenhouse effect.


The greenhouse effect is a natural phenomenon that traps radiation within the earth’s atmosphere. Natural greenhouse gases include water vapor, carbon dioxide, nitrous oxide, and methane which are essential to support life. The greenhouse effect is the cause of global warming. It is irreversible, environmental condition in which damaging human-produced gases build up and trap heat within the earth’s protective atmospheric shield, called the ozone layer. An increase in amount of such gases in the atmosphere would cause the increase in the average temperature of the earth.

Q  18. State the role of the atmosphere in climate control.


Atmosphere prevents sudden increase in temperature during the day light hours. It slows down the escape of heat into outer space during the night.

Q  19. What is leghaemoglobin?


It is haemoglobin like pink coloured protein present in the root nodules of leguminous plants.

Q  20. Mention the three reservoirs for the carbon.


The three reservoirs for the carbon are:

i. Deposits of peat, coal and oil

ii. Carbonate rocks iii. Ocean

Q  21. Write a note on how forests influence the Quality of air.


Forests influence the air Quality by:

(i)It helps in purifying air by adding oxygen to it.

(ii)Green house effect is controlled as plants take carbon dioxide gas during photosynthesis.

(iii)It maintains the temperature of surrounding area by the formation of clouds by transpiration giving cooling effect.

Q  22. List two biotic components of biosphere.


Biotic components of biosphere include producers, heterotrophs, herbivores, carnivores and decomposers (any two)

Q  23. How is atmosphere on Earth different from the atmosphere on Venus and Mars? State two ways by which percentage of carbon dioxide is fixed on the earth.


Atmosphere of Venus and Mars

(i) Consists of 95-97% carbon dioxide,   

(ii) Life supporting gases are not present there.   Atmosphere of Earth

(i) Consists of a mixture of many gases like oxygen, nitrogen, carbon dioxide and water vapours which are life supporting gases.

(ii) Carbon dioxide is green house gas which maintains temperature on earth during night.

(iii) Oxygen is needed by organisms for survival.   Two ways by which percentage of CO2 is fixed on earth are :

(i) Green plants convert CO2 into glucose in the presence of sunlight.

(ii) Many marine animals use carbonates dissolved in sea water to make their shells.

Q  24. The atmosphere acts as a blanket. How?


Air in the atmosphere is a bad conductor of heat and it keeps the average temperature of the earth fairly constant during the day and the whole year.

Q  25. Define soil erosion.


Soil erosion is the gradual wearing away of land by water, wind and general weather conditions.

Q  26. Classify soil on the basis of agricultural point of view.


On the basis of agriculture, soil is categorised into following two types:  i Residual soil: Residual soil is further divided into: a. Black soil b. Red soil c. Laterite soil ii. Transported soil: Transported soil is further divided into: a. Alluvial soil b. Desert soil c. Mountainous soil

Q  27. Near coastal areas, wind blows from sea towards the land during the day while wind current moves from land to the sea during the night. Explain giving reason.


During the day, air above the land gets heated up faster and starts rising. As this air rises, a region of low pressure is created and the air over the sea moves into this area of low pressure. The direction of the wind would be from the sea to the land. During night, both land and sea start to cool. Since water cools down slower than the land, the air above water would be warmer than the air above land so the wind current moves from land to the sea.

Q  28. (a) What are two different states in which water is formed during the water cycle?

(b) What is the major source of fresh water in the city/town/village where you live?

(c) Do you know any activity which may be polluting this water source?


(a) Gaseous and liquid state.

(b) Rivers, lakes, ponds and ground water are the major sources of ground water.

(c) Dumping of waste materials, sewage or waste from factories and mercuric salts, pollutes water.

Q  29. Write a note on how forests influence the Quality of soil.


(i)Plants in forest hold the soil preventing soil erosion.  

(ii)It holds the soil which helps in increasing the underground water level.  

(iii)It adds nutrients to the soil due to lot of vegetation present in forest gets decomposed.  

Q  30. What is the importance of water?


Importance of water:

i. Human body is composed of about 75% water. Water allows our blood to flow through the blood vessels thus supplying the body with vital nutrients. Water also allows waste matter to be eliminated from the body through the excretory system.

ii. Water is used for drinking, washing, cleaning, etc.

iii. Water acts an important agent in soil formation.

iv. Water provides habitat to many organisms on earth.