Forests Our Lifeline — Class 7 Science NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 7 Science chapter "Forests Our Lifeline" — 8 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 7 Science chapter "Forests Our Lifeline" — 8 important questions with detailed answers for CBSE board exam…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 7 Science — Forests Our Lifeline. Step-by-step answers to all 8 textbook questions from this chapter, written for CBSE board preparation and free to use.
Forests Our Lifeline — All 8 Questions Solved
Q1. What is a forest? Define ecosystem.
Forest: large area of land covered with trees and other vegetation, supporting diverse flora and fauna. Forest ecosystem: community of living organisms (biotic) and their physical environment (abiotic) interacting together.
Biotic: trees, animals, plants, microorganisms. Abiotic: sunlight, water, soil, temperature, humidity. Forest provides: oxygen, water, timber, medicines, food, habitat for wildlife.
Q2. What are the layers of forest? Describe each.
Forest layers (from top to bottom):
1. Canopy: tall trees with thick foliage; intercepts most sunlight
2. Understory: shorter trees and shrubs; receives filtered light
3. Shrub layer: bushes and small plants
4. Herb layer: grasses, herbs, ferns; experiences low light
5. Forest floor: leaf litter, decomposing matter, soil organisms (bacteria, fungi); richest in organic matter
Each layer supports different plants and animals adapted to light and moisture conditions.
Q3. Explain the food chains and food webs in a forest.
Food chain: linear sequence of organisms transferring energy. Producer → Primary consumer → Secondary consumer → Tertiary consumer.
Example: Plant → Grasshopper → Frog → Snake → Eagle
Food web: interconnected food chains showing multiple feeding relationships in ecosystem.
Energy flow: Sun → Plants (producers) → Herbivores → Carnivores → Decomposers
Loss: only 10% energy transferred at each level due to respiration and body maintenance.
Q4. What is the role of decomposers in forest ecosystem?
Decomposers: bacteria, fungi that break down dead organisms and waste material. Roles:
1. Decomposition: break down dead plants, animals, waste into simpler substances
2. Nutrient cycling: release nutrients (nitrogen, phosphorus) back to soil
3. Soil enrichment: add organic matter, improve soil fertility
4. Energy release: release stored chemical energy from dead matter
5. Waste management: prevent accumulation of dead matter
Without decomposers, nutrients would be locked in dead organisms, depleting soil fertility and disrupting ecosystem cycles.
Q5. How do forests help prevent soil erosion?
Forest role in soil conservation:
1. Root system: tree roots bind soil particles together, increase cohesion
2. Leaf litter: dead leaves and twigs cover soil, reduce water velocity
3. Canopy: dense foliage intercepts rainfall, reduces direct impact on soil
4. Water retention: porous humus-rich forest soil absorbs more water
5. Prevents landslides: root network anchors soil on slopes
6. Reduces runoff: slower water flow reduces surface erosion
Without forests, heavy rain washes away topsoil (fertile layer), exposing underlying rock, reducing fertility.
Q6. Discuss how forests affect the water cycle and climate.
Forests and water cycle:
1. Evapotranspiration: plants release water vapor, increasing atmospheric humidity
2. Rainfall increase: vegetation enhances cloud formation and precipitation
3. Groundwater: forest canopy and litter allow more water infiltration into soil, recharging aquifers
4. Rivers: forests regulate water flow, prevent floods and droughts
Forests and climate:
1. Carbon sequestration: absorb CO₂, reduce greenhouse gases
2. Temperature regulation: large-scale evaporation cools atmosphere
3. Oxygen production: plants produce oxygen through photosynthesis
4. Prevent global warming: forests are 'lungs of Earth'
Q7. What are forest products? List uses of forests.
Forest products:
Wood/Timber: fuel, construction, furniture, paper, pulp. Non-timber products: fruits, nuts, honey, medicinal plants, gum, latex, herbs, spices.
Forest benefits:
1. Shelter/habitat: home for millions of species
2. Food: fruits, nuts, game animals
3. Medicine: 25% of modern medicines from forest plants
4. Recreation: tourism, eco-tourism
5. Soil conservation: prevent erosion
6. Water regulation: maintain water cycle
7. Air purification: produce oxygen, absorb pollutants
8. Climate control: moderate temperature and humidity
Q8. Why are forests disappearing? What are conservation measures?
Causes of deforestation:
1. Logging: timber extraction
2. Agriculture: clearing for farmland
3. Urbanization: land development
4. Mining: extraction of minerals
5. Grazing: livestock overuse
6. Pollution and climate change
Conservation measures:
1. Protected areas: national parks, wildlife reserves
2. Reforestation: planting new trees
3. Sustainable forestry: selective logging, controlled harvest
4. Community participation: local people manage forests
5. Afforestation: converting wastelands to forests
6. Legal protection: enforcement of forest laws
7. Education: awareness about forest conservation
Forests Our Lifeline — Practice MCQs with Answers
Attempt these 20 multiple-choice questions after working through the solutions above. Each carries the correct option and the reasoning behind it, so a wrong answer tells you which idea to revisit.
MCQ 1. Which of the following gases do forests primarily absorb from the atmosphere?
- A. Oxygen
- B. Nitrogen
- C. Carbon dioxide
- D. Methane
Answer: C. Carbon dioxide — Forests, through the process of photosynthesis performed by trees and plants, absorb large amounts of carbon dioxide from the atmosphere, helping to regulate global climate.
MCQ 2. What is the uppermost layer of a forest, consisting of the crowns of tall trees, called?
- A. Understorey
- B. Canopy
- C. Forest floor
- D. Emergent layer
Answer: B. Canopy — The canopy is the dense, uppermost layer of a forest formed by the branches and leaves of tall trees. It largely determines the amount of light reaching the lower layers.
MCQ 3. Which of these is NOT a product we obtain directly from forests?
- A. Wood
- B. Honey
- C. Petrol
- D. Medicinal herbs
Answer: C. Petrol — Wood, honey, and medicinal herbs are natural products obtained from forests. Petrol is a fossil fuel derived from crude oil, not directly from forests.
MCQ 4. What is the primary role of decomposers like bacteria and fungi in a forest ecosystem?
- A. To produce oxygen
- B. To absorb sunlight
- C. To break down dead organic matter
- D. To act as primary consumers
Answer: C. To break down dead organic matter — Decomposers break down dead plants and animals into simpler substances, returning nutrients to the soil. This process is crucial for nutrient cycling in a forest.
MCQ 5. Forests are often referred to as the 'green lungs' of the Earth because they:
- A. Provide shelter to animals
- B. Release large amounts of oxygen
- C. Are green in colour
- D. Help in flood control
Answer: B. Release large amounts of oxygen — Forests are called 'green lungs' because trees and plants perform photosynthesis, releasing oxygen into the atmosphere, which is essential for most life forms.
MCQ 6. How do forests help in preventing soil erosion?
- A. By absorbing sunlight
- B. By acting as windbreaks
- C. By binding soil particles with their roots
- D. By increasing rainfall
Answer: C. By binding soil particles with their roots — The extensive root systems of trees and other plants in forests hold soil particles together firmly, preventing them from being washed away by rain or blown away by wind, thereby preventing soil erosion.
MCQ 7. Consider the following food chain: Grass → Deer → Tiger. What would happen if all the deer disappeared from this forest?
- A. The population of grass would decrease.
- B. The population of tigers would increase.
- C. The population of tigers would decrease.
- D. The population of grass would remain unchanged.
Answer: C. The population of tigers would decrease. — If all deer (herbivores) disappeared, their primary predators, the tigers, would lose their main food source, leading to a decrease in the tiger population due to starvation.
MCQ 8. Which of these processes is primarily responsible for the formation of humus in forest soil?
- A. Photosynthesis
- B. Respiration
- C. Decomposition
- D. Transpiration
Answer: C. Decomposition — Humus is formed through the decomposition of dead organic matter (leaves, twigs, animal remains) by microorganisms like bacteria and fungi, enriching the soil.
MCQ 9. What is the term for the various layers of vegetation (e.g., canopy, understorey, forest floor) found in a forest?
- A. Biodiversity
- B. Stratification
- C. Succession
- D. Adaptation
Answer: B. Stratification — The arrangement of different types of vegetation in distinct horizontal layers in a forest, based on height, is called stratification.
MCQ 10. Why are forests crucial for maintaining the water cycle?
- A. They absorb water from the atmosphere.
- B. They primarily store all the world's freshwater.
- C. They release water vapour through transpiration, contributing to cloud formation and rainfall.
- D. They create artificial reservoirs.
Answer: C. They release water vapour through transpiration, contributing to cloud formation and rainfall. — Trees release a significant amount of water vapour into the atmosphere through transpiration. This water vapour rises, condenses to form clouds, and eventually leads to rainfall, thus playing a vital role in the water cycle.
MCQ 11. If deforestation occurs on a large scale in an area, which of the following is a likely long-term consequence for the local climate?
- A. Increased rainfall and cooler temperatures.
- B. Decreased rainfall and warmer temperatures.
- C. No significant change in climate.
- D. Increased snowfall.
Answer: B. Decreased rainfall and warmer temperatures. — Deforestation reduces transpiration and the amount of moisture released into the atmosphere, leading to reduced cloud formation and rainfall. It also contributes to higher temperatures due to less shade and increased carbon dioxide.
MCQ 12. Which of the following best describes the interdependence of plants and animals in a forest ecosystem?
- A. Animals only depend on plants for food.
- B. Plants only depend on animals for carbon dioxide.
- C. Both plants and animals are independent of each other.
- D. Plants provide food and oxygen for animals, while animals provide carbon dioxide and aid in seed dispersal.
Answer: D. Plants provide food and oxygen for animals, while animals provide carbon dioxide and aid in seed dispersal. — Plants produce food and oxygen for animals, and animals in turn release carbon dioxide for plants and help in processes like pollination and seed dispersal, demonstrating a strong interdependence.
MCQ 13. The constant decaying of dead plants and animals on the forest floor leads to the formation of a dark, nutrient-rich substance. What is this substance called?
- A. Clay
- B. Sand
- C. Humus
- D. Silt
Answer: C. Humus — Humus is the dark, organic material that forms in soil when plant and animal matter decays. It is rich in nutrients and greatly improves soil fertility and water retention.
MCQ 14. Why is a forest considered a dynamic living entity?
- A. Because it contains only living organisms.
- B. Because trees in a forest are constantly moving.
- C. Because it is continuously changing and interacting, with organisms growing, reproducing, and decaying.
- D. Because it is an artificial environment created by humans.
Answer: C. Because it is continuously changing and interacting, with organisms growing, reproducing, and decaying. — A forest is dynamic because its components are constantly interacting and changing over time. Organisms grow, reproduce, die, and decay, influencing the environment and other living things within the ecosystem.
MCQ 15. What would be the most significant immediate consequence if all the decomposers were suddenly removed from a forest?
- A. The forest would become greener.
- B. The air would have more oxygen.
- C. Dead organic matter would accumulate, and nutrient cycling would stop.
- D. Animals would have more food.
Answer: C. Dead organic matter would accumulate, and nutrient cycling would stop. — Without decomposers, dead plants and animals would not break down. This would lead to the accumulation of organic waste and the cessation of nutrient recycling, making the soil infertile over time.
MCQ 16. Which layer of the forest receives the least amount of sunlight?
- A. Canopy
- B. Understorey
- C. Forest floor
- D. Shrub layer
Answer: C. Forest floor — The forest floor, being at the bottom, receives very little sunlight because it is blocked by the dense canopy, understorey, and shrub layers above it.
MCQ 17. Forests also act as 'natural purifiers' of water. How do they achieve this?
- A. By adding chemicals to the water.
- B. By filtering water through their roots and soil, removing impurities.
- C. By boiling the water.
- D. By directly consuming contaminated water.
Answer: B. By filtering water through their roots and soil, removing impurities. — Forest soil acts as a natural filter. Tree roots and layers of soil and humus absorb rainwater slowly, filtering out impurities and allowing clean water to seep into groundwater tables.
MCQ 18. Which of the following is a direct consequence of global warming caused by deforestation?
- A. Increased snowfall in tropical regions.
- B. Melting of glaciers and rising sea levels.
- C. Expansion of forest areas.
- D. Decrease in atmospheric carbon dioxide.
Answer: B. Melting of glaciers and rising sea levels. — Deforestation reduces the absorption of carbon dioxide, leading to an increase in greenhouse gases and global warming. A direct consequence of global warming is the melting of glaciers and ice caps, which contributes to rising sea levels.
MCQ 19. The variety of plants and animals found in a forest is known as its:
- A. Monoculture
- B. Biodiversity
- C. Homogeneity
- D. Stratification
Answer: B. Biodiversity — Biodiversity refers to the variety of life in an ecosystem, including the diversity of species, genetic diversity within species, and ecosystem diversity.
MCQ 20. What is the primary factor that determines the types of plants and animals that can thrive in a particular forest?
- A. The colour of the soil.
- B. The distance from human settlements.
- C. Climatic conditions (temperature, rainfall) and soil type.
- D. The presence of artificial lighting.
Answer: C. Climatic conditions (temperature, rainfall) and soil type. — Climatic conditions, such as temperature and rainfall, along with the type of soil, are the most critical abiotic factors determining which plant and animal species can survive and flourish in a specific forest environment.
How to Use These Solutions
Attempt each question yourself first and only then compare with the worked answer. Marks in the CBSE board exam are awarded for the METHOD as much as the final result, so reproduce the steps rather than memorising the last line. Where a solution states a law, a formula or a definition, learn that wording — examiners look for it.
Related practice for this chapter: chapter MCQs, previous-year questions, revision notes and sample papers.