Class 10 : Science (In English) – Lesson 13. Our Environment

EXPLANATION & SUMMARY

🔵 Detailed Explanation

🌍 Introduction

🔵 The environment is the sum of all external conditions and influences affecting living organisms.
🟢 It consists of biotic components (plants, animals, microorganisms) and abiotic components (air, water, soil, sunlight, temperature).

🟡 Human activities like industrialisation, urbanisation, deforestation, and overuse of resources disturb natural balance.

🌿 Ecosystem
🔵 Definition: A functional unit of nature where living beings interact with each other and with their physical surroundings.

🟢 Two main components:
Biotic: producers (plants), consumers (herbivores, carnivores, omnivores), decomposers (fungi, bacteria).
Abiotic: soil, water, air, sunlight.

🟡 Types of ecosystem: Natural (forest, pond, lake, desert, grassland) and artificial (crop field, aquarium).
💡 Example: Pond ecosystem → producers (algae, plants), primary consumers (insects, fish), secondary consumers (bigger fish), decomposers (fungi, bacteria).

🔴 Food Chain and Food Web
🌿 Food chain: Linear sequence of who eats whom.

Grass → Grasshopper → Frog → Snake → Eagle.
🟢 Food web: Interconnection of multiple food chains; more stable.
🟡 Trophic levels: Each step in food chain is a trophic level.
Producers → Primary consumers → Secondary consumers → Tertiary consumers.

✏️ Note: Energy flow is unidirectional.

⚡ Energy Flow in Ecosystem
🔵 Energy enters ecosystem through sunlight → captured by producers (photosynthesis).
🟢 Only 10% of energy at one trophic level is transferred to next (10% law).

🟡 Remaining energy lost as heat or used for life processes.
🔴 Pyramid of energy is always upright.
💡 Example: Grass (1000 J) → Grasshopper (100 J) → Frog (10 J) → Snake (1 J).

🟣 Ozone Layer and its Depletion
🌍 Ozone (O₃): Found in stratosphere; protects from harmful UV radiation.
🟢 Depletion: Caused by chlorofluorocarbons (CFCs) used in refrigerators, ACs, aerosol sprays.

🟡 Effects: skin cancer, eye cataract, reduced immunity, harm to plants and animals.
🔴 Global efforts: Montreal Protocol (1987) to reduce CFCs.

🟠 Waste Generation and Management
🌿 Human activities produce biodegradable waste (food, paper, wood) and non-biodegradable waste (plastics, glass, metals).

🟢 Non-biodegradable wastes accumulate → pollute soil, water, harm organisms.

🟡 Methods of management:
Reduce → minimise waste.
Reuse → use same item again (bottles, containers).

Recycle → convert waste to usable form (plastic, paper, metal).
💡 Example: Carry cloth/jute bags instead of plastic bags.

🔵 Environmental Issues
🌍 Air pollution: Due to vehicles, industries, burning fossil fuels → respiratory issues, global warming.
🟢 Water pollution: Due to sewage, industrial effluents, plastics → waterborne diseases.
🟡 Soil pollution: Excess fertilisers, pesticides, plastics → reduces fertility.
🔴 Deforestation: Loss of biodiversity, climate imbalance.

🟢 Summary
Ecosystem = interaction of living + non-living.
Food chain and food web → transfer of energy.
Only 10% energy transferred between trophic levels.
Ozone protects from UV, CFCs cause depletion.
Waste management: Reduce, Reuse, Recycle.
Environmental problems: pollution, deforestation.

📝 Quick Recap
🌿 Ecosystem = biotic + abiotic.
🍃 Food chain = linear, Food web = interconnected.
⚡ 10% law of energy transfer.
🛡️ Ozone = protective shield.
♻️ Waste management → 3Rs.
🌍 Pollution = global concern.

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QUESTIONS FROM TEXTBOOK

Question 1
Which of the following groups contain only biodegradable items?
(a) Grass, flowers and leather
(b) Grass, wood and plastic
(c) Fruit-peels, cake and lime-juice
(d) Cake, wood and grass
Answer
🔵 Biodegradable = decomposable by microorganisms.
🟢 Plastic is not biodegradable.
🟡 Correct set: fruit-peels, cake, lime-juice.
✔️ Correct option: (c)

Question 2
Which of the following constitute a food-chain?
(a) Grass, wheat and mango
(b) Grass, goat and human
(c) Goat, cow and elephant
(d) Grass, fish and goat
Answer
🌿 Food chain must show producer → consumer → higher consumer.
🟢 (b) Grass → goat → human forms valid chain.
✔️ Correct option: (b)

Question 3
Which of the following are environment-friendly practices?
(a) Carrying cloth-bags while shopping
(b) Switching off unnecessary lights and fans
(c) Walking to school instead of using scooter
(d) All of the above
Answer
🔵 All three reduce pollution, save energy, reduce plastic use.
✔️ Correct option: (d) All of the above

Question 4
What will happen if we kill all the organisms in one trophic level?
Answer
🌍 Balance of ecosystem breaks.
🔴 Previous level organisms (prey) multiply unchecked.
🟢 Next level organisms (predators) starve and die.
⚡ Whole food web collapses.

Question 5
Will the impact of removing all the organisms in a trophic level be different for different trophic levels? Can organisms of any trophic level be removed without causing damage?
Answer
🟢 Yes, impact differs by level.
If producers removed → entire chain breaks.
If herbivores removed → carnivores die, plants overgrow.
If carnivores removed → herbivores multiply, plants depleted.
🔴 No trophic level can be removed without causing harm.

Question 6
What is biological magnification? Will the levels of this magnification be different at different levels of the ecosystem?
Answer
🔵 Definition: Increase in concentration of harmful non-biodegradable chemicals (like pesticides, DDT, heavy metals) as we move up the food chain.
🟢 Higher trophic levels accumulate more toxins.
🌿 Example: pesticides in plants → cow → humans (highest effect).

Question 7
What are the problems caused by the non-biodegradable wastes that we generate?
Answer
🔴 Accumulate in environment → soil/water pollution.
🟡 Cause biological magnification in food chains.
🌍 Block drains, harm aquatic life.
🟢 Non-decomposable, persist for long time.

Question 8
If all the waste we generate is biodegradable, will this have no impact on the environment?
Answer
🌿 Even biodegradable waste in excess causes harm.
🔵 Produces foul smell, releases methane.
🟡 Excess waste may choke drains, affect soil fertility.
✔️ So, it will still impact environment unless managed properly.

Question 9
Why is damage to the ozone layer a cause for concern? What steps are being taken to limit this damage?
Answer
🔴 Ozone absorbs harmful UV rays.
🟢 Depletion → skin cancer, cataract, immune damage, harm to crops and animals.
🌍 Steps taken:
Ban on CFCs under Montreal Protocol.
Use eco-friendly coolants, refrigerants, sprays.
Awareness campaigns to reduce ozone-depleting substances.

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OTHER IMPORTANT QUESTIONS FOR EXAMS

Question 1
Which of the following is non-biodegradable?
Paper
Plastic
Vegetable peels
Cotton cloth
Answer: 2 🟠

Question 2
Energy flow in an ecosystem is:
Cyclic
Multidirectional
Unidirectional
Absent
Answer: 3 🔵

Question 3
Which trophic level has the maximum energy?
Producers
Primary consumers
Secondary consumers
Tertiary consumers
Answer: 1 🌿

Question 4
Which of the following causes ozone depletion?
O₂
CFCs
CO₂
SO₂
Answer: 2 ⚡

Question 5
Which is an example of an artificial ecosystem?
Pond
Forest
Aquarium
Desert
Answer: 3 🐟

Question 6
The pyramid of energy is always:
Inverted
Upright
Irregular
None
Answer: 2 🟢

Question 7
Which of these is not a decomposer?
Bacteria
Fungi
Algae
Actinomycetes
Answer: 3 🌊

Question 8
Food web is:
Single chain of feeding
Interconnection of food chains
Flow of minerals
Pyramid of numbers
Answer: 2 🟡

Question 9
Which gas absorbs harmful UV rays?
O₂
CO₂
Ozone
Nitrogen
Answer: 3 🟣

Question 10
Which waste can be recycled?
Glass
Vegetables
Paper
Both 1 and 3
Answer: 4 ♻️

Question 11 (Assertion–Reason)
A: Energy transfer from one trophic level to another follows 10% law.
R: Only 10% of energy is stored at each level, rest lost as heat.
Answer: 1 ✔️

Question 12
A: Plastics are biodegradable.
R: They are decomposed easily.
Answer: 4 ❌ (Both false)

Question 13
A: Producers occupy the first trophic level.
R: They prepare food by photosynthesis.
Answer: 1 🌿

Question 14
A: Biological magnification occurs with non-biodegradable pollutants.
R: Concentration increases at higher trophic levels.
Answer: 1 🔴

Question 15
A: Montreal Protocol aimed at protecting ozone layer.
R: It restricted use of chlorofluorocarbons.
Answer: 1 🌍

Question 16
A: Food chains are longer in aquatic ecosystems than in terrestrial ones.
R: Aquatic ecosystems provide more stable conditions.
Answer: 1 🐠

Question 17
A: Consumers directly use solar energy.
R: Producers capture solar energy.
Answer: 3 ❌

Question 18
A: Waste segregation is necessary for waste management.
R: It makes recycling and disposal easier.
Answer: 1 ♻️

Question 19
A: Excess use of pesticides can harm human health.
R: They accumulate in food chain (magnification).
Answer: 1 ⚡

Question 20
A: Earth wire prevents shock.
R: It provides alternate path for leakage current.
Answer: 1 🟡

🟢 Section B (Q21–26: Very Short Answers, 2 marks)
Question 21
Define ecosystem.
Answer:
🔵 A self-sustaining system of biotic and abiotic components interacting with each other.

Question 22
What is meant by biodegradable waste?
Answer:
🟢 Waste decomposed naturally by microorganisms, e.g., food peels, paper.

Question 23
State one difference between biodegradable and non-biodegradable substances.
Answer:
🔴 Biodegradable: decompose (paper, wood).
🟡 Non-biodegradable: persist (plastic, glass).

Question 24
What is a food chain?
Answer:
🌿 Sequence of organisms where one is eaten by another for energy transfer.

Question 25
Why is ozone layer important?
Answer:
🟢 Shields Earth from harmful UV rays.

Question 26
What is meant by 3Rs in waste management?
Answer:
🔵 Reduce, Reuse, Recycle.

🟡 Section C (Q27–33: Short Answers, 3 marks)
Question 27
Explain 10% law of energy transfer.
Answer:
🌍 Only 10% of energy at one trophic level is passed to next.
🟡 Example: Grass (1000 J) → Goat (100 J) → Human (10 J).

Question 28
Differentiate between food chain and food web.
Answer:
🔵 Food chain: linear sequence.
🟢 Food web: interlinked chains.
🟡 Food web more stable.

Question 29
What are effects of ozone depletion?
Answer:
🌞 Skin cancer, cataract.
🌿 Affects crops, aquatic life.
🟡 Increases UV penetration.

Question 30
What are decomposers? State their role.
Answer:
🔵 Organisms like fungi, bacteria.
🟢 Decompose dead matter → recycle nutrients → maintain ecosystem balance.

Question 31
What are consequences of excessive use of non-biodegradable waste?
Answer:
🔴 Soil and water pollution.
🟡 Toxicity in organisms.
🌍 Biological magnification.

Question 32
State two differences between biodegradable and non-biodegradable waste with example.
Answer:
🟢 Biodegradable: decomposed (peels, paper).
🔴 Non-biodegradable: not decomposed (plastic, metals).

Question 33
Give one example each of producer, herbivore, carnivore.
Answer:
🌿 Producer: Grass.
🐐 Herbivore: Goat.
🦅 Carnivore: Eagle.

🔴 Section D (Q34–36: Long Answers, 5 marks)
Question 34
Explain biological magnification with example.
Answer:
🔵 Non-biodegradable chemicals (pesticides, DDT) enter food chain.
🟢 Concentration increases at each level.
🦅 Highest at top predators/humans.
🟡 Example: DDT in fields → fish → birds → humans.

Question 35
Draw a labelled diagram of food chain in a forest and explain energy transfer.
Answer:
🌿 Grass → Deer → Tiger.
Energy transfer: Sunlight → grass (photosynthesis) → herbivore (10%) → carnivore (10% of herbivore energy).
🔴 Shows flow is unidirectional.

Question 36
What are causes and control measures of ozone layer depletion?
Answer:
Causes: CFCs from ACs, refrigerators, aerosols.
Effects: UV damage to health and crops.
Control: Montreal Protocol, eco-friendly coolants, ban on CFCs.

🟣 Section E (Q37–Q39: Case-Based, 4 marks)
Question 37
Case: A farmer sprays pesticides on crops.
(a) Which phenomenon occurs when pesticides enter food chain?
(b) Which organisms affected most?
(c) Why?
(d) Name one control measure.
Answer:
(a) Biological magnification.
(b) Humans (top consumers).
(c) Concentration increases at each level.
(d) Use bio-pesticides.

Question 38
Case: A student throws plastic bag in drain.
(a) Is plastic biodegradable?
(b) What problems arise?
(c) Suggest eco-friendly alternative.
(d) State 3Rs principle.
Answer:
(a) No.
(b) Chokes drains, waterlogging.
(c) Use cloth/jute bags.
(d) Reduce, Reuse, Recycle.

Question 39
Case: Scientists warn of thinning ozone over poles.
(a) What causes ozone depletion?
(b) Why dangerous?
(c) Which protocol signed globally?
(d) Suggest one alternative to CFCs.
Answer:
(a) CFCs.
(b) Allows UV radiation → skin cancer, cataracts.
(c) Montreal Protocol.
(d) Hydrofluorocarbons (HFCs).

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MIND MAPS

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