NCERT Solutions for CBSE Class 10 Biology — 24 solved questions with detailed explanations.
Difficulty: Easy · Topic: Natural Resources
Coal is a non-renewable resource because it was formed over millions of years from ancient plant material and cannot be replenished on a human timescale. Once coal reserves are exhausted, they are gone. Solar energy, wind energy, and forests (if managed sustainably) are renewable resources — they are naturally replenished.
Difficulty: Easy · Topic: Three Rs
Using a cloth bag again and again instead of using (and discarding) a new plastic bag each time is an example of reuse. You are using the same item multiple times for the same purpose, extending its life and reducing waste. If you avoided shopping altogether, that would be 'reduce.' If you sent the plastic bag to a factory to be made into new products, that would be 'recycle.'
Difficulty: Easy-Medium · Topic: Forest Conservation
The Chipko Movement (1970s, Garhwal region of Uttarakhand) was a grassroots movement where local villagers, especially women led by Gaura Devi, hugged (chipko) trees to prevent them from being felled by logging contractors. The movement highlighted the importance of community participation in forest conservation and demonstrated that local people who depend on forests are their best protectors.
Difficulty: Easy-Medium · Topic: Water Harvesting
Underground storage of harvested rainwater has several advantages: (1) Water does not evaporate (unlike open surface storage, which loses significant water to evaporation). (2) It is not a breeding ground for mosquitoes. (3) It is protected from contamination by human activities and animals. (4) It recharges the groundwater table, making water available through wells and borewells. (5) Soil acts as a natural filter, improving water quality.
Difficulty: Easy-Medium · Topic: Fossil Fuels
Burning fossil fuels (coal, petroleum, natural gas) releases carbon dioxide (CO2) into the atmosphere. CO2 is a greenhouse gas that traps heat from the sun, preventing it from escaping back into space. This increases Earth's average temperature — a phenomenon called global warming. Since the Industrial Revolution, atmospheric CO2 levels have risen from ~280 ppm to over 420 ppm, causing significant climate change.
Difficulty: Easy-Medium · Topic: Fossil Fuels
Petroleum (crude oil) was formed from the remains of tiny marine organisms (plankton, algae) that died and settled on the ocean floor millions of years ago. Over time, they were buried under layers of sediment. High temperature and pressure converted the organic matter into liquid and gaseous hydrocarbons — petroleum and natural gas. Coal, in contrast, was formed from ancient forests (terrestrial plants).
Difficulty: Easy-Medium · Topic: Sustainable Development
Sustainable development was defined by the Brundtland Commission (1987) as 'development that meets the needs of the present without compromising the ability of future generations to meet their own needs.' It requires a balance between economic growth, environmental protection, and social equity. It does not mean stopping development — it means developing wisely, using renewable resources where possible, reducing waste, and protecting ecosystems.
Difficulty: Easy-Medium · Topic: Water Resources
Johads are traditional earthen check dams used in Rajasthan for rainwater harvesting. They collect and store rainwater during the monsoon, allow it to percolate and recharge groundwater, and provide water during dry periods. Other traditional systems include: Kulhs (Himachal Pradesh — irrigation channels), Eris (Tamil Nadu — tanks), and Bundhis (Madhya Pradesh — earthen dams).
Difficulty: Easy-Medium · Topic: Forest Conservation
Forests do not increase CO2 levels — they actually absorb CO2 during photosynthesis and release oxygen. Forests are carbon sinks, helping to mitigate climate change. All other options are genuine functions of forests: tree roots prevent soil erosion, forests provide habitat for millions of species, and trees release water vapour through transpiration, contributing to cloud formation and rainfall.
Difficulty: Easy-Medium · Topic: Conservation
The Ganga Action Plan (1985) was launched to reduce pollution levels in the Ganga river. The river receives enormous amounts of untreated sewage, industrial effluents, and other pollutants from the cities along its course. The plan aimed to treat sewage before it enters the river, control industrial pollution, and restore the river's water quality. Despite significant investment, pollution levels remain high due to the scale of the problem and growing population.
Difficulty: Easy-Medium · Topic: Conservation
Coliform bacteria (such as Escherichia coli) are found in the intestines of humans and animals. Their presence in water indicates contamination with sewage or faecal matter, which means the water may contain disease-causing pathogens (bacteria, viruses, parasites). The coliform count is a standard measure of water quality. Safe drinking water should have a coliform count of zero per 100 mL. High coliform levels mean the water is unsafe and needs treatment.
Difficulty: Easy-Medium · Topic: Forest Conservation
The Amrita Devi Bishnoi Wildlife Protection Award is given by the Government of India for outstanding contribution to wildlife conservation. It is named after Amrita Devi Bishnoi, who sacrificed her life in 1730 to protect khejri trees in Khejarli village, Rajasthan. She and 362 other Bishnoi villagers were killed while hugging trees to prevent them from being felled on royal orders. This supreme sacrifice inspired future conservation movements.
Difficulty: Medium · Topic: Dams
Large dams, while providing benefits like irrigation and hydroelectricity, raise serious concerns: (1) Displacement of thousands of people from villages and towns submerged by the reservoir. (2) Loss of forests, wildlife, and biodiversity in the submergence zone. (3) Disruption of downstream ecosystems — reduced water flow, altered sediment transport, and impact on fish migration. (4) Social inequity — benefits often flow to distant cities while local communities bear the costs. The Narmada Bachao Andolan movement highlighted these issues in India.
Difficulty: Medium · Topic: Natural Resources
Acid rain is caused primarily by sulphur dioxide (SO2) and nitrogen oxides (NOx) released from burning fossil fuels (especially coal in power plants and vehicle exhaust). These gases dissolve in atmospheric moisture to form sulphuric acid (H2SO4) and nitric acid (HNO3), which fall as acid rain. Acid rain damages monuments (like the Taj Mahal — called 'Marble Cancer'), kills aquatic life, damages forests, and corrodes metals.
Difficulty: Medium · Topic: Conservation
The most effective combination is: (1) Using public transport — reduces fossil fuel consumption and CO2 emissions per person. (2) Switching to LED lights — LEDs use 75% less energy than incandescent bulbs. (3) Composting kitchen waste — reduces landfill waste and methane emissions while creating useful fertiliser. Together, these actions reduce energy consumption, waste generation, and greenhouse gas emissions — all contributing to a smaller carbon footprint.
Difficulty: Medium · Topic: Water Resources
Check dams are small barriers built across streams or drainage channels. Their primary function is to slow down the flow of water, allowing more time for water to percolate into the ground and recharge groundwater. They reduce surface runoff, decrease soil erosion, and increase groundwater availability. Unlike large dams, check dams are simple, low-cost, community-manageable structures. They do not generate electricity or make water potable, but they play a crucial role in sustainable water management.
Difficulty: Medium · Topic: Forest Conservation
Biodiversity (the variety of life forms in an area) is important because: (1) It ensures ecosystem stability — more species means more resilience to disturbances. (2) It provides genetic resources for medicine, agriculture, and industry. (3) It supports ecological services — pollination, water purification, nutrient cycling, climate regulation. (4) Each species plays a specific role in its ecosystem — losing one can have cascading effects. Biodiversity is valuable for all of humanity, not just scientists, and its loss is irreversible.
Difficulty: Medium · Topic: Sustainable Development
Solar energy is a renewable energy source — the sun provides virtually limitless energy that can be captured using solar panels (photovoltaic cells) or solar thermal systems. Unlike coal and petroleum (which are non-renewable fossil fuels), solar energy produces no greenhouse gas emissions during electricity generation and will not run out. Other renewable sources include wind, hydro, biomass, and geothermal energy. Nuclear fission, while low-carbon, involves non-renewable uranium fuel and radioactive waste, so it is not typically classified as renewable.
Difficulty: Medium · Topic: Conservation
Using disposable plastic plates and cups contributes LEAST to conservation — in fact, it is harmful. Disposable plastics are made from petroleum (non-renewable), generate non-biodegradable waste that pollutes the environment, and require energy to produce. All other options actively conserve resources: taking the school bus reduces fuel consumption, switching off appliances saves electricity, and composting reduces waste while creating useful manure.
Difficulty: Medium-Hard · Topic: Forest Conservation
Both are true and R correctly explains A. Successful forest conservation requires the involvement of local communities because: (1) They depend on forests for fuel, fodder, food, medicines, and minor forest products — so they have a direct stake in sustainability. (2) They possess traditional ecological knowledge built over generations about sustainable harvesting practices. (3) Historical examples (Chipko Movement, Bishnoi community, community forest management in Arabari, West Bengal) show that forests managed with local participation are better conserved than those managed solely by distant bureaucracies.
Difficulty: Medium-Hard · Topic: Fossil Fuels
Both statements are true and R correctly explains A. We should reduce fossil fuel dependence because: (1) They are non-renewable — formed over millions of years and cannot be replenished. Known reserves are finite. (2) Their combustion releases CO2 (primary greenhouse gas causing global warming), along with SO2, NOx (causing acid rain), and particulate matter (causing respiratory diseases). Transitioning to renewable energy (solar, wind, hydro) addresses both resource depletion and climate change.
Difficulty: Medium-Hard · Topic: Natural Resources
The most likely cause is over-extraction of groundwater through borewells (pumping water faster than natural recharge) combined with loss of forest cover (deforestation reduces water retention in soil, increases surface runoff, and decreases groundwater recharge). Together, these reduce the water table dramatically. Planting trees, building check dams, and rainwater harvesting would all improve water availability, not diminish it. This is a common problem in many Indian villages today.
Difficulty: Medium-Hard · Topic: Natural Resources
The Assertion is true — coal and petroleum should indeed be used judiciously (wisely and sparingly). However, the Reason is false — coal and petroleum are non-renewable resources, NOT renewable. They were formed over millions of years from ancient organisms and cannot be replenished on a human timescale. This is precisely why they must be used judiciously — once exhausted, they are gone. Additionally, their combustion causes pollution and climate change, providing another reason for judicious use.
Difficulty: Hard · Topic: Natural Resources
Rainwater harvesting is more aligned with sustainable development principles because: (1) It is decentralised — water stays where it falls, benefiting local communities directly. (2) It recharges groundwater across a wide area. (3) It causes no displacement of people. (4) It has minimal environmental impact — no submergence of forests or farmland. (5) It involves community participation, building local ownership and self-reliance. (6) It is low-cost and can be implemented quickly. Large dams provide benefits (hydroelectricity, flood control) but at significant social and environmental costs — displacement, biodiversity loss, and downstream disruption. For drought-prone areas, distributed groundwater recharge is often more effective than a single large reservoir.
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