Class 8 Science Chapter 12 – How Nature Works in Harmony from NCERT Curiosity with easy Notes and complete Book Solutions. Get simple explanations, important concepts, questions and answers, and revision material for effective learning, practice and exam preparation.
How Nature Works in Harmony 12
Class 8 Science – Curiosity | Easy Notes, Concepts & Book Questions
Chapter in simple words:
Nature works like a connected system. Plants, animals, microorganisms, air, water, soil, sunlight and temperature depend on one another. A change in one part can affect many other parts of an ecosystem.
12.1 How Do We Experience and Interpret Our Surroundings?
Habitat: A habitat is the place where an organism lives and gets suitable conditions for survival.
Biotic components: Living parts of a habitat, such as plants, animals and microorganisms.
Abiotic components: Non-living parts such as air, water, soil, sunlight and temperature.
Example: A pond provides fish with food, oxygen, shelter and space. Fish get food from living organisms and oxygen from water.
Activity 12.1: Let us explore
Book activity:
- Identify two habitats around you.
- List the living beings and non-living things present there.
- Record your observations.
| Habitat | Living beings | Non-living things |
|---|---|---|
| Pond | Fish, frogs, algae, ducks | Water, soil, sunlight, air |
| Forest | Trees, birds, insects, animals | Soil, air, water, sunlight, temperature |
What common characteristics do you observe in the two habitats in Activity 12.1?
Answer: Both habitats have living and non-living components. However, the types of organisms and physical conditions may be different.
12.2 Who All Live Together in Nature?
Population: A group of organisms of the same type living in a particular habitat at a given time.
Community: Different populations living and interacting in the same habitat.
Individual → Population → Community → Ecosystem
Activity 12.2: Let us record
Students can mark an area of 1 m × 1 m in a school garden, identify organisms and count them.
| Name of organism | Population |
|---|---|
| Plant 1 | 20 |
| Plant 2 | 05 |
| Animal 1 | ________ |
| Animal 2 | ________ |
In the given example, there is a population of 20 ______ plants and is only 5 ______ plants in the same 1×1 m2 area.
Answer: The blanks should be filled with the names of the two types of plants observed.
Can a habitat have only one type of living organism? What might happen then?
Answer: It is possible, but organisms would compete for the same food, water and space. Resources could become scarce.
Pollination
Pollination: Transfer of pollen grains from stamens to the carpels of the same or another flower.
Pollinators: Wind, water, insects, bats and birds can help in pollination.
Importance: Pollination helps plants form fruits and seeds.
12.3 Does Every Organism in a Community Matter?
Activity 12.3: Let us read
Think of a reason for these observations.
Answer: Fish eat dragonfly larvae. Fewer dragonflies allow more bees, flies and butterflies to survive. These insects help pollinate flowers, increasing seed production.
Compare the number of dragonflies, bees, and butterflies in both the ponds. Do you find any relationship between the number of dragonflies and bees/butterflies?
Answer: Yes. When dragonflies are fewer, bees and butterflies can be more numerous because dragonflies prey on them.
What does this study show? How does the population of fish in a pond affect the seed production in nearby plants?
Answer: Fish reduce dragonfly larvae. Fewer dragonflies allow more pollinating insects, which can increase seed production.
Similarly, can overfishing by humans change this balance? How do you think it may affect the living and non-living parts of the habitat?
Answer: Yes. Fewer fish can increase dragonflies and disturb other populations, causing changes throughout the habitat.
12.4 What Are the Different Types of Interactions Among Organisms and their Surroundings?
Biotic
Living components such as plants, animals and microorganisms.
Abiotic
Non-living components such as air, water, soil, sunlight and temperature.
Interactions
Organisms interact with one another and with their physical surroundings.
Activity 12.4: Let us relate and identify
Criterion 1: Interactions between abiotic and biotic components.
Criterion 2: Interaction between two abiotic components.
Criterion 3: Interaction among biotic components.
| Criterion 1 | Criterion 2 | Criterion 3 |
|---|---|---|
| Earthworms live in moist soil. | The day temperature is high due to the bright sunlight. | A frog eats insects. |
| Many microbes are present in the pond. | Water is evaporating fast due to the sunlight. | A water snake eats fish. |
| A fish lays eggs in water. | Air current is blowing slowly on the water surface creating gentle waves. | Frogs and fish may compete for small insect larvae. |
Ecosystem
Ecosystem: A system formed by the interactions between living organisms and non-living components in an area.
Aquatic ecosystems: Ponds, rivers and lakes.
Terrestrial ecosystems: Forests, farms, grasslands and large trees.
Remember: Ecosystems can be small or large, and different ecosystems can overlap and interact with one another.
Can you find overlapping ecosystems in Fig. 12.6?
Answer: Yes. The figure shows aquatic and terrestrial ecosystems interacting, such as a river, forests, mountains, grassland and farmland.
How do plants and animals depend on non-living components?
Answer: Plants need sunlight, carbon dioxide, water, soil and nutrients. Animals need air, water, food and suitable temperature.
How do plants influence abiotic components?
Answer: Plants release oxygen, hold soil with their roots, retain soil moisture and help cool the atmosphere.
12.5 Who Eats Whom?
Producers: Organisms such as green plants that make their own food by photosynthesis.
Consumers: Organisms that depend on other organisms for food.
Herbivores: Animals that eat plants.
Carnivores: Animals that eat other animals.
Omnivores: Animals that eat both plants and animals.
Food chain: A simple sequence showing who eats whom in an ecosystem.
Grass → Grasshopper → Frog → Snake → Eagle
Activity 12.5: Let us classify
| Name of organism | Food habit |
|---|---|
| Deer | Herbivore |
| Hare | Herbivore |
| Vulture | Carnivore |
| Bengal Fox | Omnivore |
| Bird (Shikra) | Carnivore |
| Squirrel | Herbivore |
| Mouse | Omnivore |
| Mushroom | Decomposer |
| Tree | Producer |
Activity 12.6: Let us link (relate)
Take an example of a grassland ecosystem.
Grass, frog, hare, grasshopper, snake and eagle can be connected through feeding relationships.
Grass → Grasshopper → Frog → Snake → Eagle
Which is another food chain that can be drawn for the organisms given in this activity?
Answer: Grass → Hare → Leopard.
Trophic Levels
Trophic level: The position of an organism in a food chain.
| Trophic level | Example |
|---|---|
| First | Producers – green plants |
| Second | Herbivores – deer, hare |
| Third | Small carnivores – frogs |
| Higher levels | Large carnivores – tigers, vultures |
Activity 12.7: Let us draw
In the crop-field example, millet is the producer, mouse is the herbivore/consumer and eagle is a higher-level consumer.
Millet → Mouse → Eagle
The numbers of organisms can be represented as a pyramid with the highest number at the base.
Food Web
Food web: A network formed when several food chains in an ecosystem are linked together.
Many food chains → Interconnected feeding relationships → Food web
Activity 12.8: Let us trace and link
In a food web, one organism may be eaten by two or more types of organisms.
How many other organisms might be connected to one organism through a feeding relationship in an ecosystem?
Answer: There may be several, because one organism can have feeding relationships with more than one organism.
Observe the relationship between different food chains in an ecosystem. Are these food chains interlinked?
Answer: Yes. Different food chains are often interlinked and form a food web.
12.6 What Happens to Waste in Nature?
Decomposition: The breaking down of dead plants, animals and waste into simpler substances.
Decomposers: Organisms such as fungi and bacteria that break down dead matter.
Decomposers return important nutrients to the soil. In nature, materials are reused and recycled.
Does nature really waste anything?
Answer: No. Decomposers recycle dead matter and return nutrients to the environment.
12.7 How Does One Change Lead to Another?
Pollution → Plants die → Less oxygen → Fish decrease → More insects → More pesticides → Further environmental problems
Cascading effect: A change in one part of an ecosystem can cause a series of changes in other parts.
Activity 12.9: Let us read
What happens when we intervene in nature?
Answer: Human actions can disturb natural relationships. For example, reducing frogs can increase insect pests, leading to greater pesticide use and environmental damage.
Why did the decline in frog populations lead to an increase in agricultural pests?
Answer: Frogs eat insects. Fewer frogs meant fewer insects were eaten, so pest populations increased.
Why was the export of frog legs banned?
Answer: To prevent further decline of frogs and reduce ecological damage.
12.8 How Do Interactions Maintain Balance in Ecosystems?
Competition: Organisms compete for common resources such as food, water, space or sunlight.
Mutualism: Both organisms benefit.
Example: Honeybees and flowers.
Example: Honeybees and flowers.
Commensalism: One organism benefits while the other is not affected.
Example: Orchids growing on trees.
Example: Orchids growing on trees.
Parasitism: One organism benefits while the other is harmed.
Example: Ticks on dogs.
Example: Ticks on dogs.
| Interaction | Effect | Example |
|---|---|---|
| Mutualism | Both benefit | Bee and flower |
| Commensalism | One benefits, other unaffected | Orchid and tree |
| Parasitism | One benefits, other is harmed | Tick and dog |
Based on the example given in Fig. 12.16, what do you observe?
Answer: Different organisms have different relationships. Some benefit both organisms, some benefit one without affecting the other, and some benefit one while harming the other.
12.9 What Are the Benefits of an Ecosystem?
Ecosystems provide: clean air, water, food, fertile soil, fibres, timber, medicines, climate regulation, recreation and aesthetic value.
Human–nature connection: Humans depend on healthy ecosystems for survival and well-being.
How can we stop damaging forests, rivers, and wetlands?
Answer: We can reduce pollution, avoid unnecessary cutting of trees, conserve water, protect wildlife and use natural resources responsibly.
The Sundarbans
Sundarbans: A large mangrove ecosystem located around the Ganges–Brahmaputra delta between India and Bangladesh.
Mangrove forests help protect coastal areas by reducing the force of strong winds and waves during storms and floods.
The Sundarbans are home to many plants and animals, including endangered species.
Threats include cutting mangrove trees, illegal hunting, overuse of resources, industrial pollution and untreated sewage.
Protected Areas
Protected areas: Land or water areas set aside to conserve wildlife and habitats.
| Type | Purpose |
|---|---|
| National Park | Protects wildlife and habitats |
| Wildlife Sanctuary | Protects wildlife and their habitats |
| Biosphere Reserve | Protects larger ecosystems and biodiversity |
| Community Conserved Area | Conservation involving local communities |
12.9.1 Human-made ecosystems
Humans create ecosystems such as fish ponds, farms and parks to meet their needs.
Can you name any human made ecosystem in your area?
Answer: Examples include agricultural farms, gardens, parks and fish ponds.
12.9.2 How do healthy ecosystems serve our farms?
Green Revolution: A period when machines, improved farming methods, synthetic fertilisers and pesticides helped increase food production in India.
Overuse of synthetic chemicals, excessive groundwater extraction and repeated cultivation of one crop can harm soil health and biodiversity.
How do these practices harm both the environment and human health?
Answer: Excessive chemicals can harm soil organisms, water quality, biodiversity and may affect human health.
Activity 12.10: Let us survey
Visit a nearby farm with your parents or teacher/interact with farmers in your community to find out about the farming practices they adopt.
Sample questions:
How have your farming practices changed over time? And why?
What effects do you notice when using synthetic fertilisers and pesticides?
Have you seen any changes in soil health after using these synthetic fertilisers and pesticides?
What inference do you draw from your interactions with farmers?
Sample answer: Farmers may use different methods to improve production. Sustainable methods can help protect soil, water, biodiversity and future food production.
Based on your learning, what practices do you think can help farmers protect the soil, the environment, and our food security for the future?
Answer: Crop rotation, organic manure, composting, careful water use, natural pest control and reducing unnecessary chemical use can help.
Important Concepts at a Glance
Habitat Place that provides suitable conditions for an organism.
Population Same type of organisms living together in an area at a given time.
Community Different populations living and interacting in the same habitat.
Ecosystem Living and non-living components interacting with each other.
Producer Makes its own food, usually by photosynthesis.
Consumer Gets food from other organisms.
Decomposer Breaks down dead matter and recycles nutrients.
Food chain Shows who eats whom.
Food web Interconnected food chains.
Trophic level Position of an organism in a food chain.
KEEP THE CURIOSITY ALIVE
1. Refer to the given diagram (Fig. 12.19) and select the wrong statement.
(i) A community is larger than a population.
(ii) A community is smaller than an ecosystem.
(iii) An ecosystem is part of a community.
Answer: (iii) An ecosystem is part of a community.
An ecosystem is larger than a community because it includes both biotic and abiotic components.
An ecosystem is larger than a community because it includes both biotic and abiotic components.
2. A population is part of a community. If all decomposers suddenly disappear from a forest ecosystem, what changes do you think would occur? Explain why decomposers are essential.
Answer: Dead matter would accumulate and nutrients would not return properly to the soil. Plants would get fewer nutrients. Decomposers are essential for nutrient recycling.
3. Selvam from Cuddalore district, Tamil Nadu, shared that his village was less affected by the 2004 Tsunami compared to nearby villages due to the presence of mangrove forests. This surprised Sarita, Shabnam, and Shijo. They wondered if mangroves were protecting the village. Can you help them understand this?
Answer: Yes. Mangrove roots and dense vegetation can reduce the force of water and waves. They can therefore help protect coastal areas during storms and floods.
4. Look at this food chain:
Grass → Grasshopper → Frog → Snake
If frogs disappear from this ecosystem, what will happen to the population of grasshoppers and snakes? Why?
Answer: Grasshoppers would increase because fewer frogs would eat them. Snakes would decrease because frogs are one of their food sources.
5. In a school garden, students noticed fewer butterflies the previous season. What could be the possible reasons? What steps can students take to have more butterflies on campus?
Answer: Possible reasons include fewer flowering plants, pesticides, pollution or habitat loss. Students can grow flowering and native plants, avoid harmful pesticides and provide suitable shelter.
6. Why is it not possible to have an ecosystem with only producers and no consumers or decomposers?
Answer: Consumers transfer energy through food chains, while decomposers recycle nutrients. Both are important for a balanced ecosystem.
7. Observe two different places near your home or school (e.g., a park and a roadside). List the living and non-living components you see. How are the two ecosystems different?
Answer: A park may have more plants, birds and insects, while a roadside may have more pollution, traffic and fewer organisms. Their living and non-living conditions are different.
8. ‘Human-made ecosystems like agricultural fields are necessary, but they must be made sustainable.’ Comment on the statement
Answer: Farms provide food, but excessive chemicals, water use and monoculture can damage ecosystems. Sustainable methods protect soil, water and biodiversity.
9. If the Indian hare population (Fig. 12.20) drops because of a disease, how would it affect the number of other organisms?
Answer: Predators that eat hares may decrease due to less food. Plants eaten by hares may increase. Other changes may spread through the food web.
Probe and ponder
How might the loss of forest cover and changes in rainfall patterns lead to elephants to enter human farms and villages?
Answer: Loss of forests and changing rainfall can reduce food and water. Elephants may then move into farms and villages looking for food and water.
Imagine you are a tree in a dense forest. What kind of relationships would you have with water, sunlight, other animals, and other components of the forest?
Answer: I would use water and sunlight to grow, exchange gases with the air, provide food and shelter to animals, and interact with soil and microorganisms.
Do you think the Earth can thrive without humans? Can humans survive without the Earth?
Answer: Earth can continue its natural processes without humans, but humans depend on Earth for air, water, food, shelter and other resources.
If two kinds of birds compete for the same fruit, how might their way of living change over time?
Answer: They may change their feeding time, feeding place or food choices to reduce competition.
Can human actions cause natural disasters?
Answer: Human actions may increase the risk or severity of some disasters, for example through deforestation, poor land use and destruction of natural barriers.
Share your questions
Student activity: Write your own questions about habitats, ecosystems and nature.
Discover, design, and debate
Plan a clean-up day at school or a nearby park. Wearing gloves and using bags, collect the litter you find. Discuss the kinds of waste you found. Which was the most common? How can we reduce such waste?
Suggested response: Separate waste into biodegradable and non-biodegradable waste. Reduce single-use plastic, reuse useful materials and recycle whenever possible.
In Arunachal Pradesh, the Nyishi and Mishmi tribes treat the Tiger as sacred. In Chhattisgarh, the Baiga tribe worships the Bagesur Dev and believes the Tiger is the protector of the forest. Find out about other Indian tribes that have a special connection with animals.
Activity: Research a tribe and an animal connected with its culture. Write how this connection may help protect nature.
Pick a tree near your home or school. Observe it once a week for 4 weeks. Note any new leaves, flowers, fruits, or visiting birds and insects. Record your observations. You may even upload your findings to www.seasonwatch.in and become a young citizen scientist.
| Week | Leaves | Flowers | Fruits | Birds/Insects |
|---|---|---|---|---|
| 1 | ||||
| 2 | ||||
| 3 | ||||
| 4 |
Interact with farmers and record indigenous practices followed by them for sustainable farming. Create a sustainable herbal garden/natural farm at home or at school. It could be a group activity with students from different grades.
Suggested response: Students can record practices such as composting, using organic manure, saving seeds, crop rotation and careful water use.
Prepare some questions based on your learnings so far …
Why? When?
How long?
Where? Why not?
Prepare some questions based on your learnings so far …
Reflect on the questions framed by your friends and try to answer …
Quick Revision – Chapter 12
| Topic | Remember |
|---|---|
| Habitat | Place providing suitable conditions for an organism. |
| Biotic components | Living components. |
| Abiotic components | Non-living components. |
| Population | Same type of organisms in an area. |
| Community | Different populations living together. |
| Ecosystem | Interaction of biotic and abiotic components. |
| Producer | Makes its own food. |
| Consumer | Depends on other organisms for food. |
| Decomposer | Breaks down dead matter and recycles nutrients. |
| Food chain | Shows who eats whom. |
| Food web | Network of interconnected food chains. |
| Mutualism | Both organisms benefit. |
| Commensalism | One benefits; the other is unaffected. |
| Parasitism | One benefits; the other is harmed. |
Prepare with this NCERT Curiosity worksheet for Chapter 12. The worksheet includes important questions and revision exercises to help students understand key concepts, practise what they have learned, and prepare effectively for class tests and exams.
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