Ques 1: What is the role of respiration in oxygen cycle?
Ans: Oxygen enters in the living world through the process of respiration, i.e., it oxidises the food material (glucose molecule) and produces energy and carbon dioxide.
Ques 2: Name the gases which cause greenhouse effect.
Ans: Greenhouse effect is caused by carbon dioxide, Chlorofluorocarbons (CFCs) nitrogen oxide and methane.
Ques 3: Name some biologically important organic compounds that contain both oxygen and nitrogen.
Ans: Proteins, amino acids and nucleic acids.
Ques 4: Name the compound, which is responsible for the depletion of ozone layer in the atmosphere.
Ans: Chlorofluorocarbons (CFCs)
Ques 5: Which part of solar radiation is absorbed by ozone layer?
Ans: Ultraviolet radiation
Ques 6: What do you mean by biotic component?
Ans: The biotic component means the living organisms, which are present in environment.
Ques 7: What do you mean by air pollution?
Ans: An increase in the content of harmful or undesirable substances (pollutants) in the air, is called air pollution.
Ques 8: Air is also called "breath of life'. Why?
Ans: Air is called breath of life because it contains oxygen, which is required by all living organisms for respiration.
Ques 9: Which winds bring rain in most parts of India?
Ans: The South-West or North-East monsoons.
Ques 10: State the harmful effects of ultraviolet rays.
Ans: Ultraviolet rays cause cancer and cataract-like diseases to living organisms.
Ques 11: Which non-living component of the Earth determine biodiversity of an area?
Ans: Water is the determinant of biodiversity of an area.
Ques 12: State two factors, which are responsible for polluting water.
Ans: Municipal sewage and discharge from industries are responsible for polluting water.
Ques 13: What is soil?
Ans: Soil is the outermost layer of our Earth, called the crust, which forms the upper surface of land and supports plant growth.
Ques 14: What is top soil? How is it responsible for the biodiversity in an area?
Ans: It is the topmost layer of the soil that contains humus and living organisms in addition to the soil particles. The quality of top soil is an important factor that decides biodiversity in that area.
Ques 15: What are the main substances of biogeochemical cycles?
Ans: Its main substances are carbon (C), nitrogen (N), oxygen (O) and water
Ques 16: Which group of plants contains nitrogen fixing bacteria in their roots?
Ans: Leguminous plants such as cereals, pea, bean, etc.
Ques 17: Name two organisms, which play vital role in nitrogen fixation.
Ans: The organisms, which play vital role in nitrogen fixation are
(i) Rhizobium and blue-green algae, help in fixation of free atmospheric nitrogen.
(ii) Nitrosomonas and Nitrobacter are nitrifying bacteria, which convert ammonia to nitrite and then nitrite to nitrates.
Ques 18: Why step farming is common on hills?
Ans: Step farming is common on hills because it slows down the speed of rain water, stops soil erosion and increases water absorption by the soil.
Ques 19: Soil formation is done by both biotic and abiotic factors. List the names of these factors by classifying them as biotic and abiotic.
Ans: (i) Abiotic factors of soil formation?Sun, water, wind, etc.
(ii) Biotic factors of soil formation?herbs, lichens, mosses, microorganisms, etc.
Ques 20: Write full form of CFCs.
Ques 21: State one use of ozone.
Ans: It protects the Earth from harmful radiations like high energy ultraviolet radiations
Ques 22: State the role of symbiotic bacteria in nitrogen cycle of nature.
Ans: Plants are unable to take atmospheric nitrogen directly. Symbiotic bacteria converts the atmospheric nitrogen into water soluble nitrates, which are easily utilised by plants.
Ques 23: Name any one method by which water helps in soil formation.
Ans: In physical weathering, water and high temperature cause expansion and contraction of rocks, facilitating their breakdown. As a result forming soil.
Ques 24: In which region, the ozone layer is present in the atmosphere?
Ans: Ozone layer is present in stratosphere region of the atmosphere.
Ques 25: Where the hole in ozone layer have recently detected?
Ans: The hole in ozone layer have recently detected over Antarctica.
Ques 26: Why the Earth is called as 'Blue Planet'?
Ans: The Earth is called as 'Blue Planet' because it is covered with 75% of water.
Ques 27: State the process by which carbon enters in the living system.
Ans: Respiration is the process by which carbon enters in the living system in the form of carbon dioxide.
Ques 28: Name the component of air, which is most essential for living organisms.
Ans: Oxygen is the component of air, which is most essential for living organisms.
Ques 29: Give two examples where water can be found in the frozen form on the Earth.
Ans: Water is found frozen in the ice-caps at two poles and on snow-covered mountains.
Ques 30: Why terrestrial life forms require freshwater?
Ans: Terrestrial life forms require freshwater because their body cannot tolerate high amount of dissolved salts in saline water.
Ques 31: Name two fossil fuels, which are responsible for air pollution.
Ans: Coal and petroleum are responsible for air pollution.
Ques 32: What do you mean by thermal pollution?
Ans: Thermal pollution is increase in temperature of water-bodies due to addition of hot water or hot effluent into it.
Ques 33: Give any two effects of soil erosion.
Ans: Two effects of soil erosion are
(ii) Reduction in soil futility
Ques 34: What is combustion?
Ans: Combustion is a process of burning of fossil fuels, to provide energy for various needs like cooking, transportation and industrial processes.
Ques 35: Name the process by which oxygen is replenished in nature.
Ans: Oxygen is replenished in nature through photosynthesis.
Ques 36: What is ozone hole?
Ans: Ozone hole is the depletion of ozone gas in ozone layer, as present over Antarctica.
Ques 37: Name two freshwater resources, which provide freshwater for human use.
Ans: The two freshwater resources, which provide fresh water for human use are:
(ii) Surface water (ponds, lakes, streams, etc.)
Ques 38: What is the direction of air in coastal areas during the day?
Ans: During the day, the direction of air current or wind is from sea to land.
Ques 39: Which particles form the nuclei for condensation of water vapours in the atmosphere?
Ans: Dust and smoke particles.
Ques 40: Name the two acids that are present in acid rain.
Ans: Two acids present in acid rain are:
(i) Nitric acid
(ii) Sulphuric acid