1. How is our atmosphere different from the atmospheres on Venus and Mars?
Answer: Our atmosphere is a mixture of many gases like nitrogen, oxygen, carbon dioxide and water vapour. In contrast, the atmospheres of Venus and Mars mainly contain carbon dioxide, which forms about 95–97% of their atmosphere. Earth’s atmosphere supports life, unlike Venus and Mars where no life is known to exist.
2. How does the atmosphere act as a blanket?
Answer: The atmosphere acts like a blanket around the Earth because it keeps the temperature under control. It does not allow the Earth to become too hot during the day or too cold at night. This happens because gases in the atmosphere trap heat and slowly release it, maintaining a balanced and suitable temperature for life.
3. What causes winds?
Answer: Winds are caused by the uneven heating of the Earth’s surface by the Sun. When air gets heated, it becomes lighter and rises, creating a low pressure area. Cooler air from nearby high pressure areas moves in to fill this space. This continuous movement of air from high pressure to low pressure forms wind.
4. How are clouds formed?
Answer: Clouds are formed when water from seas, rivers, and other water bodies evaporates due to heat and rises as water vapour. High up in the atmosphere, the air is cooler, so this water vapour condenses into tiny water droplets or ice crystals. These droplets gather together to form clouds.
5. List any three human activities that you think would lead to air pollution.
Answer: Three human activities that lead to air pollution are:
(i) Burning of fossil fuels like petrol, diesel and coal in vehicles and industries releases harmful gases.
(ii) Burning of garbage and crop residue produces smoke and poisonous substances in the air.
(iii) Construction work and mining release dust particles that pollute the atmosphere.
1. Why do organisms need water?
Answer: Organisms need water because it is essential for life processes. It helps in digestion, transportation of nutrients, and removal of wastes from the body. Water also maintains body temperature and is required for chemical reactions inside cells. In plants, it is necessary for photosynthesis and carrying minerals from soil.
2. What is the major source of fresh water in the city/town/village where you live?
Answer: The major source of fresh water in most cities, towns, and villages is groundwater. It is obtained through wells, tube wells, and hand pumps. In some places, fresh water also comes from rivers, lakes, or reservoirs after proper treatment before supplying it to households.
3. Do you know of any activity which may be polluting this water source?
Answer: Yes, many activities can pollute water sources. Dumping of garbage and sewage into rivers or drains is a major cause. Washing clothes, vehicles, and animals near water bodies also adds dirt and detergents. Industrial waste and chemicals released without proper treatment further contaminate groundwater and surface water.
1. How is soil formed?
Answer : Soil is formed by the breaking down of rocks over a long period of time. This process is called weathering. Factors like wind, water, sunlight, and living organisms help in breaking rocks into small particles. Humus formed from dead plants and animals mixes with these particles to form soil.
2. What is soil erosion?
Answer: Soil erosion is the removal of the top fertile layer of soil by agents like wind, water, and human activities such as deforestation and overgrazing. It reduces the fertility of soil and affects plant growth.
3. What are the methods of preventing or reducing soil erosion ?
Answer: Soil erosion is the removal of topsoil by wind or water, but we can prevent or reduce it using these simple methods:
(i) Afforestation : Planting more trees binds the soil with their roots, holding it firmly in place.
(ii) Terrace farming : On hilly slopes, cutting steps or terraces reduces the speed of running water, preventing soil wash-off.
(iii) Contour ploughing : Ploughing along the curves or contours of a slope, instead of straight lines, slows down water flow and traps soil.
(iv) Shelter belts : Growing rows of trees or shrubs in dry, windy areas acts as a shield, stopping wind from blowing away the topsoil.
(v) Avoiding overgrazing : Allowing grass and plants to regrow prevents animals from stripping the land bare.
(vi) Crop rotation and mulching : Growing different crops in seasons and covering the soil with dry leaves or straw keeps it covered and healthy.
1. What are the different states in which water is found during the water cycle?
Answer: During the water cycle, water is found in three different states: solid, liquid and gas. It exists as ice and snow in the solid state, as water in rivers, lakes, seas and oceans in the liquid state and as water vapour in the gaseous state in the atmosphere.
2. Name two biologically important compounds that contain both oxygen and nitrogen.
Answer: Two biologically important compounds that contain both oxygen and nitrogen are proteins and nucleic acids. These compounds are essential for the growth, development and functioning of living organisms.
3. List any three human activities which would lead to an increase in the carbon dioxide content of air.
Answer: Three human activities that increase carbon dioxide (CO₂) in the air are:
(i) Burning of fossil fuels like petrol, diesel and coal in vehicles, factories, and power plants.
(ii) Cutting of trees decreases the process of photosynthesis, which leads to an increase in carbon dioxide in the air.
(iii) Burning of wood and crop residue releases stored carbon directly as CO₂ into the atmosphere.
4. What is the greenhouse effect?
Answer: The greenhouse effect is the natural process by which certain gases in the Earth’s atmosphere, such as carbon dioxide, methane and water vapour, trap the Sun’s heat. These gases act like the glass roof of a greenhouse, allowing sunlight to enter but preventing heat from escaping back into space. This keeps the Earth warm enough to support life. Without the greenhouse effect, the Earth would be extremely cold. However, an excessive increase in these gases leads to global warming.
5. What are the two forms of oxygen found in the atmosphere?
Answer: The two forms of oxygen found in the atmosphere are:
(i) Diatomic oxygen (O₂): the normal oxygen that we breathe, essential for respiration and combustion.
(ii) Ozone (O₃): found mainly in the ozone layer in the upper atmosphere, which protects us from the harmful ultraviolet (UV) rays of the Sun.
1. Why is the atmosphere essential for life?
Answer: The atmosphere is essential for life because it provides oxygen for breathing and carbon dioxide for plants to make food. It traps heat to keep Earth warm, protects us from harmful UV radiation through the ozone layer and burns up most meteoroids before they hit the ground. It also enables the water cycle, bringing rain. Without it, no life could survive.
2. Why is water essential for life?
Answer: Water is one of the basic requirements for life. It is needed for various life processes such as digestion, transportation of substances, excretion, and temperature regulation. In plants, water is essential for photosynthesis and transport of minerals. Since living organisms cannot survive without water, it is considered the basis of life.
3. How are living organisms dependent on the soil? Are organisms that live in water totally independent of soil as a resource?
Answer: Living organisms depend on soil for food, water, shelter, and minerals. Plants grow in soil and animals depend directly or indirectly on plants for food. Many organisms also live in the soil. Organisms living in water are not totally independent of soil because minerals and nutrients present in water come from the soil and rocks through erosion and runoff.
4. You have seen weather reports on television and in newspapers. How do you think we are able to predict the weather?
Answer: We are able to predict the weather by collecting information about temperature, humidity, rainfall, wind speed and air pressure. This data is gathered using satellites, weather stations, radars and balloons. Scientists study these changes in the atmosphere and use computers to forecast the weather.
5. We know that many human activities lead to increasing levels of pollution of the air, water-bodies and soil. Do you think that isolating these activities to specific and limited areas would help in reducing pollution?
Answer: Yes, isolating polluting activities to specific and limited areas can help in reducing pollution to some extent. It makes the treatment and control of wastes easier and prevents pollution from spreading over large areas. However, proper waste management and strict pollution control measures are also necessary to protect air, water, and soil from pollution.
6. Write a note on how forests influence the quality of our air, soil and water resources.
Answer: Forests improve the quality of air by absorbing carbon dioxide and releasing oxygen during photosynthesis. They help in reducing air pollution and maintaining the balance of gases in the atmosphere. Forests also prevent soil erosion as tree roots hold the soil firmly. They increase the water-holding capacity of soil and help in maintaining the water cycle by bringing rainfall and replenishing groundwater.
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