Our Environment — Class 10 Biology NCERT Solutions (Free)
Free step-by-step NCERT solutions for Class 10 Biology chapter "Our Environment" — 7 important questions with detailed answers for CBSE board exam preparation.
TL;DR: Free step-by-step NCERT solutions for Class 10 Biology chapter "Our Environment" — 7 important questions with detailed answers for CBSE board exam pre…
Written & reviewed by the Syllab.in Academic Team (CBSE/NCERT subject experts) · Updated
NCERT Solutions for Class 10 Biology — Our Environment. Step-by-step answers to all 7 textbook questions from this chapter, written for CBSE board preparation and free to use.
Our Environment — All 7 Questions Solved
Q1. Define ecosystem. Describe the biotic and abiotic components of an ecosystem.
Ecosystem is a functional unit consisting of all living organisms and their physical environment interacting together. It is self-sustaining and capable of recycling nutrients.
Biotic components (living):
1. Producers (Autotrophs):
- Green plants that manufacture their own food through photosynthesis
- Form the base of food chain and food web
- Example: grasses, trees, algae
2. Consumers (Heterotrophs):
a) Primary consumers (Herbivores) - eat producers
Example: grasshoppers, rabbits, cows
b) Secondary consumers (Carnivores) - eat primary consumers
Example: snakes, frogs, birds
c) Tertiary consumers (Top carnivores) - eat secondary consumers
Example: eagles, hawks, lions
d) Omnivores - eat both plants and animals
Example: humans, bears, pigs
3. Decomposers:
- Break down dead organic matter
- Return nutrients to soil
- Example: bacteria, fungi, earthworms
4. Scavengers:
- Feed on dead animals
- Example: vultures, hyenas
Abiotic components (non-living):
1. Climate factors:
- Temperature
- Humidity
- Rainfall
- Wind
- Light intensity
2. Soil factors:
- Soil type and composition
- pH (acidity/alkalinity)
- Soil nutrients
3. Water:
- Water availability
- Salinity (for aquatic ecosystems)
4. Atmospheric gases:
- Oxygen
- Carbon dioxide
- Nitrogen
5. Topography:
- Altitude
- Slope
Interaction:
- Biotic and abiotic components interact continuously
- Abiotic factors affect distribution and abundance of biotic components
- Biotic organisms modify abiotic environment
- Example: Plants absorb CO2 from air and release O2; their presence provides shade affecting temperature
Q2. What is a food chain? Explain with examples and describe the 10% rule (10% energy law).
Food chain:
- A linear sequence showing energy flow from one organism to another
- Each organism eats the one before and is eaten by the one after
- Starts with producer (plant) and ends with top carnivore
- Simple representation of who eats whom
Example food chain in a forest:
Grass → Grasshopper → Bird → Hawk
(Producer) → (Primary consumer) → (Secondary consumer) → (Tertiary consumer)
Another example in aquatic ecosystem:
Alga → Small fish → Large fish → Eagle
Trophic levels:
- Trophic level 1: Producers (plants)
- Trophic level 2: Primary consumers (herbivores)
- Trophic level 3: Secondary consumers (carnivores eating herbivores)
- Trophic level 4: Tertiary consumers (carnivores eating carnivores)
The 10% Law (Law of Energy Transfer):
- Only 10% of energy from one trophic level passes to the next level
- 90% of energy is lost as heat during cellular respiration and other life processes
Energy loss from a food chain:
Grass: 1000 units of energy
↓ (only 10% transferred)
Grasshopper: 100 units
↓ (only 10% transferred)
Bird: 10 units
↓ (only 10% transferred)
Hawk: 1 unit
Consequences of 10% law:
- Only 4-5 trophic levels possible in any ecosystem (energy becomes too small to support organisms)
- Number of organisms decreases at higher trophic levels
- Pyramid of numbers shows fewer organisms at top
- Pyramid of biomass shows less total mass at higher levels
- Food chains are always shorter in aquatic ecosystems
- More herbivores needed to support fewer carnivores
Importance:
- Explains why energy transfer is inefficient
- Shows why ecosystems cannot support unlimited top predators
- Explains why there are more plants than animals
- Shows that herbivores are more efficient food source than carnivores
Q3. What is a food web? How does it differ from a food chain?
Food web:
- A complex network of interconnected food chains
- Shows multiple feeding relationships in an ecosystem
- Many organisms can eat multiple food sources
- Realistic representation of feeding relationships
- Shows that energy flow in ecosystems is not linear but branching
Example food web in a forest:
- Grass is eaten by grasshopper, rabbit, and deer
- Grasshopper is eaten by bird and lizard
- Rabbit is eaten by hawk and fox
- Bird is eaten by hawk
- Lizard is eaten by snake
- Snake is eaten by hawk and fox
- Hawk and fox are top carnivores
Key features of food web:
- Multiple arrows from each organism showing different food sources
- Organisms can occupy multiple trophic levels
- Shows alternative feeding pathways
- More flexible than food chain
Differences between food chain and food web:
Food chain:
- Linear sequence (straight line)
- Single feeding pathway
- One organism eats the one before
- Simpler but less realistic
- Example: Grass → Grasshopper → Bird → Hawk
- Shows only one path of energy flow
Food web:
- Branching network (interconnected)
- Multiple feeding pathways
- Organism can eat and be eaten by multiple species
- More complex but more realistic
- Shows overlapping food chains
- More complete picture of ecosystem
Advantage of food web over food chain:
- Shows that if one species is removed, energy can still flow through alternate pathways
- Shows that removing one organism affects multiple species
- More accurately represents natural ecosystems where organisms have diverse diets
- Helps understand ecosystem stability and impacts of extinction
Both food chains and food webs follow the 10% law of energy transfer.
Q4. What is pollution? Distinguish between biodegradable and non-biodegradable substances.
Pollution:
- The introduction of harmful substances into the environment
- Causes adverse effects on living organisms and physical environment
- Can be in air, water, or soil
- Sources: factories, vehicles, agriculture, households, plastic waste
- Types: air pollution, water pollution, soil pollution, noise pollution, light pollution, thermal pollution
Biodegradable substances:
- Can be broken down by natural decomposers (bacteria, fungi)
- Decompose through chemical and biological processes
- Harmless byproducts after decomposition
- Complete breakdown takes days to months
- Examples:
a) Food waste: vegetable peels, fruit waste
b) Paper and cardboard
c) Wood and leaves
d) Natural fibers: cotton, wool, silk
e) Manure and compost
f) Leather
g) Human waste
- Environmentally safe if properly managed
- Can be used for composting to produce useful fertilizer
Non-biodegradable substances:
- Cannot be broken down by natural decomposers
- Persist in environment indefinitely
- Accumulate over time (bioaccumulation)
- Harmful to organisms and ecosystems
- Plastic takes 500+ years to decompose
- Examples:
a) Plastics: bags, bottles, containers
b) Glass
c) Metals: aluminum, iron
d) Pesticides: DDT
e) Synthetic fibers: polyester, nylon
f) Nuclear waste
g) Some detergents
Comparison:
Biodegradable:
- Breaks down naturally
- Useful after decomposition (nutrients returned to soil)
- Safe for environment
- Quick decomposition
Non-biodegradable:
- Does not break down naturally
- Accumulates in environment
- Toxic to organisms
- Persistent pollution problem
Solutions for non-biodegradable waste:
- Reduce use of plastics (reduce)
- Reuse items multiple times (reuse)
- Recycle materials (recycle)
- Use biodegradable alternatives
- Proper disposal methods
- Landfill management
The problem of plastic pollution is increasing worldwide because plastics are cheap, durable, and widely used, but persist in environment for centuries.
Q5. What is the ozone layer? Why is ozone depletion a concern? What are ozone-depleting substances?
Ozone layer:
- Layer of ozone (O3) gas in Earth's stratosphere
- Located 10-50 km above Earth's surface
- Formed when UV radiation splits O2 molecules
- Protects life on Earth from harmful ultraviolet (UV) radiation
Functions of ozone layer:
1. Absorbs UV-B and UV-C radiation from Sun
2. Prevents harmful radiation from reaching Earth's surface
3. Makes life on land possible
4. Prevents skin cancer, cataracts, and immune system damage
5. Protects phytoplankton in oceans
Ozone depletion:
- Reduction in ozone layer thickness
- Created an "ozone hole" over Antarctica
- Discovered in 1985
- About 40% of ozone depleted over Antarctica
- Smaller ozone hole over Arctic
Concerns about ozone depletion:
1. Increased UV radiation reaching Earth:
- Causes skin cancer and melanoma
- Causes cataracts and eye problems
- Suppresses immune system
- Causes sunburn and premature aging of skin
2. Effects on ecosystems:
- Damages phytoplankton, base of food chains in oceans
- Reduces crop yield (plants damaged by UV)
- Affects aquatic life
- Damages animals and plants
3. Long-term effects:
- Permanent if not addressed
- Takes decades for ozone to regenerate
Ozone-depleting substances (ODS):
1. Chlorofluorocarbons (CFCs):
- Used in refrigerators and air conditioners
- Used as aerosol propellants
- One Cl atom destroys 100,000 ozone molecules
2. Halons:
- Used in fire extinguishers
- Extremely damaging to ozone
3. Methyl bromide:
- Used as pesticide
- Damages ozone
4. Hydrochlorofluorocarbons (HCFCs):
- Replacement for CFCs
- Still damaging but less than CFCs
Mechanism of ozone depletion:
- Cl atoms from CFCs released in stratosphere
- Cl reacts with O3: Cl + O3 → ClO + O2
- ClO reacts with another O3: ClO + O3 → Cl + 2O2
- Cl atom regenerated and continues destroying ozone
- One Cl atom can destroy thousands of O3 molecules
Solutions:
- Montreal Protocol (1987) - international agreement
- Phase out CFCs, halons, and other ODS
- Use CFC-free refrigerants
- Proper disposal of old refrigerators
- Alternative technologies
- Ozone layer showing signs of recovery
Ozone depletion is global issue requiring worldwide cooperation.
Q6. What is bioaccumulation and biomagnification? How do they occur and why are they dangerous?
Bioaccumulation:
- Accumulation of non-biodegradable substances in the body of an organism
- Substance enters organism through various routes (ingestion, absorption)
- Cannot be broken down or excreted efficiently
- Concentration increases over time
- Happens within a single organism
Example of bioaccumulation:
- DDT pesticide sprayed on crops
- Enters plant tissues
- Animals eating plants consume DDT
- DDT accumulates in animal tissues over years
- Concentration in animal becomes much higher than in environment
Biomagnification (bioamplification):
- Increase in concentration of substance through successive trophic levels
- Non-biodegradable substance gets more concentrated up the food chain
- Happens across multiple organisms in food chain
- Top predators accumulate highest concentrations
Example of biomagnification:
Water: DDT concentration = 0.000003 ppm
↓
Algae (producers): DDT concentration = 0.04 ppm
↓
Small fish (primary consumers): DDT concentration = 0.5 ppm
↓
Large fish (secondary consumers): DDT concentration = 2.0 ppm
↓
Eagle (top predator): DDT concentration = 25 ppm
Concentration increases 8 million times from water to eagle!
How bioaccumulation and biomagnification occur:
1. Non-biodegradable substance enters ecosystem
2. Cannot be broken down by decomposers
3. Organism ingests substance but cannot excrete it efficiently
4. Substance stored in body tissues (usually in fat)
5. With each meal, organism ingests more substance
6. Concentration builds up over time (bioaccumulation)
7. When predator eats prey containing accumulated substance, predator gets large dose
8. Predator then accumulates even more substance
9. Concentration increases at each level of food chain (biomagnification)
Why they are dangerous:
1. Toxic effects on organisms:
- DDT: eggshell thinning in birds, reproductive failure
- Mercury: neurological damage
- PCBs: immune system suppression
2. Affects top predators most:
- Eagles, hawks, fish-eating birds affected
- Reproductive failure
- Population decline
- Nearly caused extinction of bald eagles
3. Long-term effects:
- Substance persists for years or decades
- Genetic damage
- Cancer
- Ecosystem imbalance
4. Affects humans:
- Fish and seafood are contaminated
- Consuming contaminated animals
- Accumulates in human body
- Health problems
Solutions:
- Ban non-biodegradable pesticides (DDT banned in many countries)
- Use biodegradable alternatives
- Regulate industries producing toxic substances
- Proper waste management
- Monitor contamination levels
Biomagnification is why pesticides like DDT, though effective against insects, are dangerous and have been banned in many countries.
Q7. What are the impacts of waste accumulation on the environment? Explain the 3Rs principle (Reduce, Reuse, Recycle).
Impacts of waste accumulation on environment:
1. Land pollution:
- Landfills overflow and fill up
- Soil contamination from hazardous waste
- Loss of agricultural land
- Leachate contaminates groundwater
- Aesthetic damage to landscape
2. Water pollution:
- Waste enters rivers and oceans
- Plastic waste harms aquatic life
- Contamination of drinking water sources
- Eutrophication from nutrient overload
- Marine animals choked by plastic
3. Air pollution:
- Burning of waste releases toxic gases
- Methane from decomposing waste in landfills
- Greenhouse gas emissions (climate change)
- Odors affecting nearby communities
4. Ecosystem damage:
- Death of aquatic organisms
- Bioaccumulation of toxins
- Habitat destruction
- Species extinction
- Food chain disruption
5. Human health:
- Toxic exposure near landfills
- Contaminated water and food
- Diseases from pollution
- Respiratory problems from air pollution
6. Resource depletion:
- Wasteful use of raw materials
- Deforestation for paper and timber
- Mineral resource exhaustion
- Energy waste
The 3Rs Principle:
Priority order (most to least important):
1. REDUCE:
- Minimize production of waste
- Use less materials
- Buy only what is needed
- Avoid single-use items
- Use durable, long-lasting products
- Digital documents instead of paper
- Smaller packaging choices
- Most effective because prevents waste creation
- Examples:
a) Use less plastic bags
b) Buy in bulk to reduce packaging
c) Avoid disposable products
d) Use public transport (reduces packaging from car parts)
2. REUSE:
- Use items multiple times before disposal
- Extend life of products
- Reduces need for new materials
- Examples:
a) Reuse plastic bags from shopping
b) Use glass jars for storage
c) Donate clothes and books
d) Refill water bottles
e) Use both sides of paper
f) Repair items instead of throwing away
g) Sell used items
3. RECYCLE:
- Process used materials into new products
- Requires some energy but saves raw materials
- Reduces landfill waste
- Reduces extraction of new resources
- Only done when material cannot be reused
- Examples:
a) Paper and cardboard recycling
b) Plastic bottle recycling
c) Glass recycling
d) Metal recycling (aluminum, steel)
e) E-waste recycling (computers, phones)
Benefits of 3Rs:
1. Reduces landfill waste
2. Saves natural resources
3. Saves energy (no need to extract and process new materials)
4. Reduces pollution from manufacturing
5. Reduces greenhouse gas emissions
6. Creates jobs in recycling industry
7. Saves money
8. Sustainable for future generations
Waste management hierarchy:
REDUCE (most important) → REUSE → RECYCLE → DISPOSE (least preferred)
Everyone must practice 3Rs to solve waste accumulation problem.
Our Environment — 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 best defines an ecosystem?
- A. All living organisms in a particular area.
- B. All non-living components of an environment.
- C. Both living and non-living components interacting as a functional unit.
- D. A group of similar species living together.
Answer: C. Both living and non-living components interacting as a functional unit. — An ecosystem comprises all living organisms (biotic components) in an area along with the non-living physical components (abiotic components), interacting as a functional unit.
MCQ 2. Which organisms constitute the first trophic level in a typical food chain?
- A. Carnivores
- B. Herbivores
- C. Producers
- D. Decomposers
Answer: C. Producers — Producers, such as green plants and algae, form the base of every food chain as they synthesize their own food using sunlight through photosynthesis.
MCQ 3. The primary cause of ozone layer depletion is the release of which chemicals into the atmosphere?
- A. Carbon dioxide
- B. Methane
- C. Chlorofluorocarbons (CFCs)
- D. Sulphur dioxide
Answer: C. Chlorofluorocarbons (CFCs) — Chlorofluorocarbons (CFCs) are widely recognized for their role in depleting the ozone layer as they release chlorine atoms that break down ozone molecules.
MCQ 4. Which of the following is an example of biodegradable waste?
- A. Plastic bottles
- B. Glass shards
- C. Vegetable peels
- D. Aluminium cans
Answer: C. Vegetable peels — Biodegradable waste can be broken down by natural biological processes, such as decomposition by microorganisms, unlike non-biodegradable materials.
MCQ 5. According to the 10% law, what percentage of energy is transferred from one trophic level to the next higher trophic level in a food chain?
- A. 1%
- B. 10%
- C. 25%
- D. 50%
Answer: B. 10% — The 10% law states that only about 10% of the energy from one trophic level is transferred to the next trophic level, with the rest being lost as heat.
MCQ 6. What is the main role of decomposers in an ecosystem?
- A. To produce food for consumers
- B. To consume other living organisms
- C. To break down dead organic matter and recycle nutrients
- D. To regulate temperature and precipitation
Answer: C. To break down dead organic matter and recycle nutrients — Decomposers, like bacteria and fungi, are crucial for breaking down dead organic matter, returning essential nutrients to the soil for reuse by producers.
MCQ 7. Which of the following is an example of an artificial ecosystem?
- A. Forest
- B. Pond
- C. Lake
- D. Aquarium
Answer: D. Aquarium — An aquarium is an artificial ecosystem created and maintained by humans, with controlled biotic and abiotic components, unlike natural ecosystems like forests or ponds.
MCQ 8. Why is the concentration of harmful chemicals like DDT highest in top carnivores?
- A. They consume more food than other organisms.
- B. They have a higher metabolic rate.
- C. They are at the highest trophic level, leading to biomagnification.
- D. They are more resistant to chemical effects.
Answer: C. They are at the highest trophic level, leading to biomagnification. — Harmful non-biodegradable chemicals like DDT undergo biomagnification, where their concentration increases progressively at each successive trophic level, making it highest in top carnivores.
MCQ 9. Which international agreement was designed to phase out the production of substances responsible for ozone depletion?
- A. Kyoto Protocol
- B. Paris Agreement
- C. Montreal Protocol
- D. Cartagena Protocol
Answer: C. Montreal Protocol — The Montreal Protocol is an international treaty specifically aimed at protecting the ozone layer by phasing out the production and consumption of ozone-depleting substances like CFCs.
MCQ 10. If grass → deer → lion is a food chain, what trophic level does the deer occupy?
- A. Producer
- B. Primary consumer
- C. Secondary consumer
- D. Tertiary consumer
Answer: B. Primary consumer — Deer are herbivores that feed directly on producers (grass), making them primary consumers in this simple food chain.
MCQ 11. What is the ultimate source of energy for most ecosystems on Earth?
- A. Geothermal energy
- B. Chemical energy
- C. Solar energy
- D. Nuclear energy
Answer: C. Solar energy — Solar energy is captured by producers (through photosynthesis) and then transferred through various trophic levels, making it the fundamental energy source for most ecosystems.
MCQ 12. Which of the following is NOT an abiotic component of an ecosystem?
- A. Temperature
- B. Sunlight
- C. Bacteria
- D. Water
Answer: C. Bacteria — Abiotic components are non-living physical and chemical factors of an ecosystem, whereas bacteria are living organisms (biotic components, specifically decomposers).
MCQ 13. Composting is a method of waste disposal where:
- A. Waste is burned at extremely high temperatures to reduce volume.
- B. Waste is buried in landfills for natural decomposition.
- C. Organic waste is decomposed by microorganisms to create nutrient-rich humus.
- D. Non-biodegradable waste is sorted and processed for reuse.
Answer: C. Organic waste is decomposed by microorganisms to create nutrient-rich humus. — Composting is a controlled biological process where organic waste decomposes in the presence of microorganisms, yielding a valuable soil conditioner called compost.
MCQ 14. A highly stable ecosystem is generally characterized by:
- A. Low biodiversity and simple food chains
- B. High biodiversity and simple food chains
- C. Low biodiversity and complex food webs
- D. High biodiversity and complex food webs
Answer: D. High biodiversity and complex food webs — High biodiversity provides alternative food sources and multiple roles, while complex food webs offer numerous pathways for energy flow, making an ecosystem more resilient and stable against disturbances.
MCQ 15. The primary role of decomposers in nutrient cycling within an ecosystem is to:
- A. Convert solar energy into chemical energy.
- B. Consume primary consumers for energy.
- C. Break down complex organic matter into simpler inorganic substances.
- D. Release oxygen into the atmosphere.
Answer: C. Break down complex organic matter into simpler inorganic substances. — Decomposers break down dead organic matter and waste products, converting complex organic compounds into simpler inorganic nutrients that can be reused by producers.
MCQ 16. The ozone layer primarily protects the Earth from which type of harmful radiation?
- A. Infrared radiation
- B. X-rays
- C. Gamma rays
- D. Ultraviolet (UV) radiation
Answer: D. Ultraviolet (UV) radiation — The ozone layer absorbs most of the Sun's harmful ultraviolet (UV) radiation, preventing it from reaching the Earth's surface where it can cause significant damage to living organisms.
MCQ 17. Why are food chains generally limited to 3-4 trophic levels?
- A. There is not enough physical space for more organisms.
- B. The efficiency of energy transfer between trophic levels is very low.
- C. Predators at higher levels cannot find enough prey.
- D. Nutrients become too scarce at higher levels to sustain life.
Answer: B. The efficiency of energy transfer between trophic levels is very low. — Due to the 10% law, only about 10% of energy is transferred at each step, making insufficient energy available to support large populations at very high trophic levels.
MCQ 18. The pyramid of energy in any functional ecosystem is always:
- A. Upright
- B. Inverted
- C. Spindle-shaped
- D. Either upright or inverted
Answer: A. Upright — The pyramid of energy is always upright because the amount of energy decreases at each successive trophic level, as energy is lost as heat at each transfer.
MCQ 19. Which method of waste disposal can lead to the formation of methane gas, a potent greenhouse gas?
- A. Incineration
- B. Composting
- C. Landfilling
- D. Recycling
Answer: C. Landfilling — In landfills, organic waste undergoes anaerobic decomposition by microorganisms, producing methane gas, which is a significant greenhouse gas.
MCQ 20. Increased exposure to UV radiation due to ozone depletion can lead to which of the following in humans?
- A. Increased crop yield
- B. Reduced skin cancer risk
- C. Damage to eyes and immune system
- D. Enhanced photosynthesis
Answer: C. Damage to eyes and immune system — UV radiation can cause skin cancers, cataracts, and suppress the immune system in humans, among other harmful effects on living organisms.
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.