Class 6 Science Chapter 11 Notes
🌿 Nature's Treasures
(New NCERT "Curiosity" | 2025-26)
📌 Chapter Overview
This chapter explores the rich gifts of nature — called natural resources — that all living beings depend upon for survival. Through the story of Bhoomi and Surya visiting their grandmother Ajji in a village on the edge of a forest in the Western Ghats, students discover the importance of air, water, sunlight, forests, soil, rocks, minerals, and fossil fuels. The chapter also teaches students why conserving these treasures is our responsibility.
💡 Opening Story: Bhoomi and Surya visit their grandmother Ajji's village during school vacation. The village is surrounded by hills, streams, forests, and diverse plants and animals. Ajji shows them the fresh air, fertile soil, and abundant sunlight and tells them — "These are nature's greatest treasures. Without them, no life is possible!" This begins their journey of discovering nature's priceless gifts.
🔑 Key Points
- Natural resources = materials or substances provided by nature that are essential for all living beings
- Natural resources include air, water, sunlight, forests, soil, rocks, minerals, and fossil fuels
- Renewable resources = can be naturally replenished within a reasonable time (air, water, sunlight, forests)
- Non-renewable resources = limited in quantity; take millions of years to form; cannot be quickly replaced (coal, petroleum, natural gas, minerals)
- Human-made resources = things created by humans using natural resources (furniture, vehicles, solar panels)
- All natural resources must be used wisely and conserved for future generations
- Fossil fuels = coal, petroleum, natural gas — formed from remains of ancient organisms buried underground millions of years ago
🔎 11.1 What Are Natural Resources?
- Natural resources are materials and substances that exist in nature and are used by living organisms
- We get them directly from nature — without making or manufacturing them
- They include: Air, Water, Sunlight, Forests, Soil, Rocks, Minerals, Fossil Fuels
💡 Key Insight: Nature does NOT have unlimited resources to meet all human needs. Some resources are limited and must be managed and used carefully. Conservation is essential!
| Type | Description | Examples |
|---|---|---|
| Natural Resources | Provided by nature | Air, water, forests, soil, coal |
| Human-made Resources | Created by humans using natural resources | Furniture, vehicles, solar panels, buildings |
🔎 11.2 Air — The Invisible Treasure
✅ Composition of Air:
| Gas | Percentage |
|---|---|
| Nitrogen | 78% |
| Oxygen | 21% |
| Argon, Carbon dioxide & other gases | 1% |
📌 Air also contains water vapour, dust particles, and smoke in very small amounts.
✅ Importance of Air:
- Oxygen in air is essential for breathing and respiration of all living beings
- Carbon dioxide is used by plants for photosynthesis (making food)
- Nitrogen is essential for making proteins in living organisms
- Air helps in the water cycle — carries water vapour for cloud formation and rain
- Air (wind) is used to generate electricity through windmills
- Air helps seeds and pollen disperse from one place to another
✅ Wind — Air in Motion:
- Moving air is called wind
- Slow-moving air = Breeze (pleasant, cool)
- Fast-moving air = Storm / Gale (destructive)
- Wind energy is a renewable source of energy — used in windmills to generate electricity
- Wind energy does not pollute the environment
✅ Conservation of Air:
- Avoid burning waste, dry leaves, and plastics — they pollute air
- Use public transport or cycle instead of private vehicles
- Plant more trees — they absorb carbon dioxide and release oxygen
- Use CNG (Compressed Natural Gas) instead of petrol/diesel — less pollution
🔎 11.3 Water — The Liquid of Life
✅ Sources of Water:
- Oceans, seas, rivers, lakes, ponds, groundwater, glaciers, rainfall
💡 Important: Most of Earth's water is in the oceans — but it is saline (salty) and cannot be used for drinking or farming. Freshwater (in rivers, lakes, groundwater) is very limited and precious!
✅ Uses of Water:
- Drinking and cooking
- Bathing and cleaning
- Agriculture and irrigation — growing food
- Industries — manufacturing, cooling machines
- Generating hydroelectric power (dams)
- Habitat for aquatic plants and animals
✅ Rainwater Harvesting:
- Rainwater harvesting = collecting and storing rainwater for future use
- Rainwater collected on rooftops flows through pipes into storage tanks or pits
- This stored water recharges groundwater and is used for daily needs
- Traditional Indian systems: stepwells (baoli), tanks, kunds — used for centuries
- Ajji's village collects rainwater to meet water needs during dry seasons
✅ Conservation of Water:
- Turn off taps when not in use
- Fix leaking taps and pipes immediately
- Use bucket instead of shower/pipe while bathing
- Water plants in the morning or evening (less evaporation)
- Reuse water — e.g., water used for washing rice can be used to water plants
- Practise rainwater harvesting
🔎 11.4 Sunlight — The Energy Treasure
- The Sun is the primary source of energy for all life on Earth
- Without sunlight, no plant can grow → no food → no life!
✅ Uses of Sunlight:
- Photosynthesis — plants use sunlight to make food
- Provides heat and warmth — essential for survival
- Drying clothes, food, and crops
- Solar cookers — cook food using sunlight (no fuel needed!)
- Solar panels — convert sunlight into electricity
- Solar water heaters — heat water using sunlight
- Sunlight helps our body produce Vitamin D — essential for strong bones
✅ Solar Energy:
- Solar energy is renewable — the Sun will keep providing energy for billions of years
- It does not pollute the environment — clean and eco-friendly
- Solar panels are used in homes, schools, streetlights, and even satellites
- Limitation: Cannot be used at night or on very cloudy days
🔎 11.5 Forests — The Green Treasure
✅ What is a Forest?
- A forest is a large area covered with trees and a wide variety of plants and animals
- Forests are complex ecosystems — all organisms in a forest depend on each other
- Forests are called the "lungs of the Earth" — they absorb carbon dioxide and release oxygen
✅ Importance of Forests:
- Provide oxygen for all living beings
- Habitat for thousands of species of plants, animals, and insects
- Provide food — fruits, nuts, honey, edible plants for wildlife and humans
- Provide timber, bamboo, rubber, gum, resin, dyes for industries
- Provide medicinal plants used in Ayurveda and modern medicine
- Prevent soil erosion — tree roots hold soil firmly in place
- Regulate water cycle — forests attract rainfall and maintain groundwater levels
- Control floods — soil in forests absorbs heavy rainwater slowly
- Reduce temperature — forests keep surrounding areas cool
- Carbon sinks — absorb huge amounts of carbon dioxide, helping control climate change
✅ Deforestation — A Major Threat:
- Deforestation = large-scale cutting of trees and clearing of forests
- Causes: building roads, cities, industries, agriculture, logging for timber
- Effects of deforestation:
- Soil becomes loose → soil erosion → land becomes barren
- Less rainfall → drought
- Loss of habitat → animals lose homes → extinction of species
- More carbon dioxide in air → global warming
- Increased flooding (no roots to hold soil and absorb water)
- Loss of medicinal plants and forest resources
✅ Conservation of Forests:
- Van Mahotsav — festival of tree plantation held every year in India (July)
- Chipko Movement — famous movement where people of Uttarakhand hugged trees to prevent them from being cut down; started in 1973; led by Sunderlal Bahuguna
- Social Forestry — planting trees in community lands, roadsides, and waste lands
- National Parks and Wildlife Sanctuaries — protected areas where forests and animals are conserved
- Plant trees regularly in schools, homes, and public spaces
📌 Why is it difficult to regrow forests?
- Trees take decades to grow to their full size
- Forest soil may become degraded and infertile after clearing
- Complex ecosystem with thousands of species cannot be easily restored
- Many species go extinct and cannot come back once lost
🔎 11.6 Soil — The Living Treasure
✅ How is Soil Formed?
- Soil is formed by the slow breaking down of rocks over thousands of years
- Rocks are broken down by heat, cold, wind, water, and the action of plant roots
- This process is called weathering
- It takes hundreds to thousands of years to form even a thin layer of soil
✅ What Does Soil Contain?
- Sand and tiny rock particles
- Clay
- Humus (decomposed plant and animal remains)
- Water and air
- Tiny living organisms — earthworms, bacteria, fungi, insects
- Minerals and nutrients essential for plant growth
💡 Humus = decomposed organic matter in soil. It makes soil fertile (good for growing plants).
✅ Types of Soil:
| Type | Properties | Best Used For |
|---|---|---|
| Sandy soil | Large particles, does not hold water well, drains fast | Desert plants, some root vegetables |
| Clay soil | Fine particles, holds water well, sticky when wet | Pottery, bricks, some crops |
| Loamy soil | Mix of sand, clay, and humus — best for farming | Agriculture, most crops |
| Silty soil | Fine particles, retains moisture, fertile | Farming near riverbanks |
✅ Importance of Soil:
- Base for plant growth — provides minerals and nutrients
- Supports agriculture — all food we eat grows in soil
- Habitat for millions of organisms (earthworms, insects, bacteria)
- Purifies water — as water passes through soil layers, impurities are filtered
- Used for making bricks, pottery, tiles (clay)
- Stores water — recharges groundwater
✅ Soil Erosion:
- Soil erosion = removal of topsoil by wind or water
- Caused by deforestation, overgrazing, heavy rain, floods
- Tree roots bind soil and prevent erosion
- Loss of topsoil = loss of fertile land → less food production
🔎 11.7 Rocks and Minerals — The Earth's Treasure
✅ Rocks:
- Rocks are hard, solid materials that make up the Earth's surface
- Rocks are made up of minerals
- Used for: building houses, roads, dams, temples, tools
✅ Minerals:
- Minerals are naturally occurring substances found in rocks and soil
- Each mineral has a specific chemical composition and properties
- Examples: Gold, Silver, Iron, Copper, Aluminium, Diamond, Coal
✅ Uses of Minerals:
| Mineral | Uses |
|---|---|
| Iron | Making steel — used in buildings, vehicles, tools |
| Copper | Electrical wires, utensils, coins |
| Aluminium | Aircraft, foils, cans, cooking utensils |
| Gold / Silver | Jewellery, electronics, coins |
| Diamond | Jewellery, cutting tools (hardest natural substance) |
| Calcium (limestone) | Making cement, chalk, glass |
| Silicon | Computer chips, solar panels |
📌 Minerals are non-renewable — they take millions of years to form inside the Earth and exist in limited quantities. Once used up, they cannot be replaced.
🔎 11.8 Fossil Fuels — The Hidden Treasure
✅ What Are Fossil Fuels?
- Fossil fuels are fuels formed from the remains of ancient plants and animals buried deep inside the Earth for millions of years under heat and pressure
- They are called "fossil" fuels because they come from fossils (preserved remains of ancient organisms)
- The three fossil fuels are: Coal, Petroleum (oil), and Natural Gas
✅ Formation of Fossil Fuels:
Ancient plants and animals die
→ Buried under layers of mud and rock
→ Heat and pressure over MILLIONS of years
→ Slowly transformed into fossil fuels
✅ Types of Fossil Fuels:
| Fossil Fuel | Form | Main Uses |
|---|---|---|
| Coal | Solid black rock | Generating electricity, steel making, steam engines |
| Petroleum (Crude Oil) | Liquid (black/brown) | Petrol, diesel, kerosene, plastics, LPG |
| Natural Gas | Gas | CNG for vehicles, LPG for cooking, generating electricity |
✅ Products from Petroleum:
- Petrol (Gasoline) — cars and motorcycles
- Diesel — trucks, buses, trains
- Kerosene — lamps, jet fuel
- LPG (Liquefied Petroleum Gas) — cooking gas
- Plastics — bottles, bags, packaging
✅ Why Are Fossil Fuels Non-Renewable?
- They take millions of years to form — we cannot make them quickly
- They exist in limited quantities inside the Earth
- Once we use them all, they will run out completely — no way to replenish them
- Current rate of use is much faster than rate of formation
✅ Problems with Fossil Fuels:
- Air pollution — burning fossil fuels releases smoke, carbon dioxide, sulphur dioxide
- Global warming — excess carbon dioxide traps heat in atmosphere → Earth warms up → climate change
- Oil spills — petroleum leaking from tankers and pipelines pollutes oceans and harms marine life
- Acid rain — sulphur dioxide from burning coal mixes with rainwater → acid rain → damages forests and buildings
✅ Alternatives to Fossil Fuels:
- Solar energy — from sunlight (renewable, non-polluting)
- Wind energy — from wind through windmills (renewable)
- Hydroelectric power — from flowing water in rivers (renewable)
- Biogas — from decomposed organic waste (renewable)
- Hydrogen fuel — clean energy of the future
🔎 11.9 Renewable vs Non-Renewable Resources
| Feature | Renewable Resources | Non-Renewable Resources |
|---|---|---|
| Definition | Can be replenished naturally within a reasonable time | Cannot be quickly replenished; limited in quantity |
| Examples | Air, water, sunlight, wind, forests | Coal, petroleum, natural gas, minerals |
| Availability | Available continuously or can be regrown | Fixed amount in Earth — will run out |
| Environmental impact | Generally eco-friendly | Burning causes pollution, global warming |
| Conservation | Must still be used carefully | Must be used very carefully — strictly limited |
📖 Important Definitions
| Term | Definition |
|---|---|
| Natural Resources | Materials and substances provided by nature, essential for all living beings |
| Human-made Resources | Things created by humans using natural resources (vehicles, buildings) |
| Renewable Resources | Resources that can be naturally replenished within a reasonable time |
| Non-Renewable Resources | Resources that exist in limited quantities and take millions of years to form |
| Fossil Fuels | Fuels formed from remains of ancient organisms — coal, petroleum, natural gas |
| Deforestation | Large-scale cutting and clearing of forests |
| Soil Erosion | Removal of topsoil by wind or water, often due to deforestation |
| Weathering | Breaking down of rocks by heat, cold, wind, and water over thousands of years |
| Humus | Decomposed organic matter in soil — makes soil fertile |
| Rainwater Harvesting | Collecting and storing rainwater for future use |
| Conservation | Careful and sustainable use of natural resources to preserve them for the future |
| Chipko Movement | Famous forest conservation movement in Uttarakhand (1973) — people hugged trees |
| Van Mahotsav | Annual tree plantation festival in India held in July |
| Biodiversity | Wide variety of plants, animals, and other organisms in an area |
| Solar Energy | Energy obtained from sunlight — renewable and non-polluting |
| Wind Energy | Energy obtained from moving air — used in windmills |
❓ NCERT Exercise Questions & Answers
Q1. Fig. 11.9 — Match resources and classify as renewable or non-renewable:
| Resource | Renewable / Non-Renewable |
|---|---|
| Coal | Non-Renewable |
| Sunlight | Renewable |
| Water | Renewable |
| Forests | Renewable |
| Minerals | Non-Renewable |
| Natural Gas | Non-Renewable |
| Wind | Renewable |
Q2. True [T] or False [F] — correct if false:
(i) Nature has all the resources to meet human needs. Answer: False ❌ — Nature does NOT have unlimited resources. Some resources are limited. We must use them carefully and conserve them.
(ii) Forests are important only because they give us wood. Answer: False ❌ — Forests are important for many reasons: they provide oxygen, habitat for wildlife, prevent soil erosion, regulate rainfall, provide medicinal plants, absorb carbon dioxide, and maintain ecological balance.
(iii) Soil is formed by the breaking down of rocks over thousands of years. Answer: True ✅
(iv) Fossil fuels are renewable sources of energy. Answer: False ❌ — Fossil fuels (coal, petroleum, natural gas) are non-renewable. They take millions of years to form and cannot be replaced once used.
Q3. List four activities that are possible due to the presence of air.
Answer:
- Breathing — Humans and animals inhale oxygen from air to survive
- Photosynthesis — Plants use carbon dioxide from air to make food
- Windmills — Wind (moving air) generates electricity
- Wind dispersal — Air carries seeds, pollen, and helps in dispersal of plants
Q4. Classify — coal, natural gas, forests, and minerals as renewable or non-renewable:
| Resource | Classification | Reason |
|---|---|---|
| Coal | Non-Renewable | Takes millions of years to form; limited quantity |
| Natural Gas | Non-Renewable | Formed from ancient organisms; limited; takes millions of years |
| Forests | Renewable | Trees can grow back over time if conserved properly |
| Minerals | Non-Renewable | Form over millions of years inside Earth; limited |
Q5. Why do we say that petroleum is a non-renewable resource?
Answer: Petroleum is called non-renewable because:
- It is formed from remains of ancient marine organisms buried deep under Earth
- The process takes millions of years under heat and pressure
- It exists in limited quantities inside the Earth
- Once we extract and use it all, it cannot be replenished within a human timeframe
- The rate at which we consume petroleum is far faster than the rate at which it can form
Q6. It is difficult to regrow forests. Justify this statement.
Answer: Regrowing forests is very difficult because:
- Trees take many decades or even centuries to grow to full size
- After deforestation, the soil becomes degraded, loose, and infertile
- A forest is a complex ecosystem with thousands of interdependent species — restoring all of them is extremely challenging
- Many animal and plant species go extinct once a forest is destroyed — they cannot come back
- Climate and water conditions in a cleared forest change, making it harder for trees to grow again
- Even if trees are planted, they take many years to become a true forest
Q7. Make a list of five daily activities using natural resources and suggest ways to reduce their use:
| Activity | Natural Resource Used | How to Reduce |
|---|---|---|
| Bathing | Water | Use bucket instead of shower; shorter baths |
| Cooking | LPG (fossil fuel), water | Use solar cooker when possible; avoid water wastage |
| Travelling | Petrol/diesel (fossil fuel) | Use public transport, cycle, or walk for short distances |
| Using electricity | Coal (power plants) | Switch off lights and fans when not in use |
| Writing on paper | Forests (wood pulp) | Use both sides of paper; recycle paper |
Q8. What are the consequences of cutting a large forest area?
Answer: Cutting large forest areas causes:
- Soil erosion — roots no longer hold soil; topsoil washes away
- Reduced rainfall — forests attract rain; cutting them causes drought
- Loss of biodiversity — animals and plants lose their habitat and may go extinct
- Global warming — fewer trees to absorb carbon dioxide → temperature rises
- Flooding — soil can no longer absorb rainwater → more floods
- Loss of medicines — many medicinal plants found only in forests are lost forever
- Disruption of water cycle — less water vapour released → less cloud formation → less rain
Q9. Why is solar energy a better option than fossil fuels?
Answer:
| Solar Energy | Fossil Fuels |
|---|---|
| Renewable — available every day | Non-renewable — will run out |
| Does not pollute the environment | Burning causes air pollution and global warming |
| Free to use (no cost for sunlight) | Expensive — prices keep rising |
| Lasts forever (billions of years) | Will be exhausted within a few hundred years |
| Eco-friendly and sustainable | Harms ecosystems and climate |
Q10. Cutting down trees on a large scale impacts the quality of soil. Why?
Answer:
- Tree roots hold soil firmly in place. When trees are cut, roots are gone
- Soil becomes loose and exposed to wind and rain
- Rainwater washes away the fertile topsoil (soil erosion)
- Soil loses humus → becomes less fertile → cannot support plant growth
- Less water is absorbed into the ground → soil becomes dry and degraded
- The land eventually becomes barren (unable to grow any crops)
✅ MCQ Questions
1. Which gas is most abundant in air? a) Oxygen b) Carbon dioxide c) Nitrogen ✅ d) Argon
2. Which of these is a renewable resource? a) Coal b) Petroleum c) Natural gas d) Sunlight ✅
3. Fossil fuels are formed from: a) Rocks melting b) Rainwater collecting c) Remains of ancient organisms ✅ d) Volcanic eruptions
4. The Chipko Movement was related to: a) Water conservation b) Soil conservation c) Forest conservation ✅ d) Mineral conservation
5. Soil is formed by: a) Evaporation of water b) Weathering of rocks ✅ c) Burning of fossils d) Melting of ice
6. Which of these is NOT a fossil fuel? a) Coal b) Wind energy ✅ c) Petroleum d) Natural gas
7. Rainwater harvesting is done to: a) Filter salt from seawater b) Collect and store rainwater for future use ✅ c) Purify groundwater d) Generate electricity
8. Van Mahotsav is: a) A wildlife protection law b) A water conservation scheme c) Annual tree plantation festival ✅ d) A soil testing programme
9. Which part of soil makes it fertile? a) Sand b) Clay c) Humus ✅ d) Gravel
10. Oxygen percentage in air is: a) 78% b) 1% c) 21% ✅ d) 50%
11. Which is a non-renewable resource? a) Water b) Wind c) Forests d) Minerals ✅
12. Solar energy cannot be used when: a) It is hot b) It is windy c) It is night or very cloudy ✅ d) It is summer
🧠Quick Revision Table
| Natural Resource | Type | Main Use | Conservation Method |
|---|---|---|---|
| Air | Renewable | Breathing, photosynthesis, wind energy | Plant trees; avoid burning |
| Water | Renewable | Drinking, farming, electricity | Rainwater harvesting; save water |
| Sunlight | Renewable | Photosynthesis, solar energy | Use solar panels and cookers |
| Forests | Renewable | Oxygen, habitat, timber, medicine | Chipko movement; Van Mahotsav |
| Soil | Renewable (very slowly) | Agriculture, construction | Plant trees; prevent erosion |
| Minerals | Non-Renewable | Electronics, construction, tools | Recycle metals; reduce waste |
| Coal | Non-Renewable | Electricity, steel making | Use solar/wind energy instead |
| Petroleum | Non-Renewable | Petrol, diesel, plastics | Use public transport; CNG |
| Natural Gas | Non-Renewable | Cooking (LPG), CNG | Use biogas as alternative |
🌟 Ancient Indian Connection!
India has a 5,000-year-old tradition of nature conservation! Ancient Indians worshipped trees (Peepal, Neem, Tulsi) as sacred — this was a scientific way to protect them. Stepwells (Baoli) for rainwater harvesting date back to the Indus Valley Civilisation (2600 BCE). The state of Odisha is famous for its ancient water harvesting systems and sacred forests called "Jahera" — village deity forests that are protected by communities for centuries as part of their culture. The Bishnoi community of Rajasthan has been protecting trees and wildlife for over 500 years — the Chipko Movement was inspired by their sacrifice! 🇮🇳
📌 Exam Tips
- Most asked: "Why is petroleum non-renewable?" — Always mention: takes millions of years to form, limited quantity, cannot be replenished
- Know the difference between renewable and non-renewable with at least 3 examples of each
- Chipko Movement — know the year (1973), place (Uttarakhand), leader (Sunderlal Bahuguna), and the key action (hugging trees)
- Composition of air — 78% Nitrogen, 21% Oxygen, 1% other gases — this comes in MCQs every time!
- Soil erosion due to deforestation — always connect: no roots → loose soil → washed away by rain → barren land
- "Forests are renewable — but difficult to regrow" — this paradox is very commonly asked! 🎯