Chapter Notes: How Nature Works in Harmony
Science Class 8 (Old NCERT)
Table of Contents
1. How Do We Experience and Interpret Our Surroundings?
2. Who Lives Together in Nature?3. Does Every Organism in a Community Matter?
4. What Are the Different Types of Interactions Among Organisms and Their Surroundings?
5. Who Eats Whom?
6. What Happens to Waste in Nature?
7. How Does One Change Lead to Another?
8. How Do Interactions Maintain Balance in Ecosystems?
9. What Are the Benefits of an Ecosystem?
10. Key Terms to Remember
How does nature keep everything in balance, and what happens when that harmony is disturbed?
• From forests and rivers to animals, people and the land itself, every part of nature is interconnected.
• Sometimes, when forests are cut down or rainfall changes, animals such as elephants lose their homes and food. They may then move into farms or villages, leading to new problems (Elephants moving in search of food and shelter).
• Even small changes in one part of nature can affect everything else around it.
In this chapter, you will explore how water, sunlight, plants, animals and humans are linked in a web of relationships. You will learn why balance in nature is important, how living things depend on one another, and how human activities can affect the whole system for better or worse.
1. How Do We Experience and Interpret Our Surroundings?
Different habitats have different kinds of plants and animals.
Habitat
A habitat is the place where an organism lives.
It provides the surroundings and conditions that an organism needs to survive.
A habitat may be small, such as tree bark, or large, such as a pond or a forest.
Different habitats contain different kinds of plants and animals, or living beings.
Organisms adapt to survive in the conditions of their particular habitats.
Explore two nearby habitats and identify the living organisms and non-living components present in each:
(a) Pond habitat
(b) Forest habitat
Select two nearby habitats, such as a pond and a forest.
List the living and non-living components in each habitat.
Both a pond and a forest have the following:
Living beings, or biotic components: Plants, animals and other organisms.
Non-living things, or abiotic components: Air, water, sunlight, soil, temperature, stones and other non-living materials.
Similarities: Both habitats have biotic and abiotic components.
Differences: The types of living beings vary. For example, fish are commonly found in ponds, whereas many trees are found in forests. The types and amounts of non-living components also differ. A pond has more water, whereas a forest generally has more soil and air.
Biotic components: All the living things in a habitat, including plants, animals and microorganisms.
Abiotic components: All the non-living things in a habitat, including sunlight, air, water, soil and temperature.
Every organism needs certain conditions to survive, such as food, water, oxygen, shelter and space.
Example: Fish live in ponds because ponds provide food, oxygen and shelter. Pond water provides biotic resources, such as food from plants and animals, and abiotic conditions, such as oxygen dissolved in water.
Many other organisms, including frogs, turtles, snakes, insects, birds and plants, may share the same pond. Each organism interacts with other organisms and with the non-living parts of the habitat.
Each habitat has its own combination of living and non-living components, such as air, sunlight, water, soil and temperature.
Different species in the same habitat may use resources in different ways. For example, in a forest, a snake may be active at night while a rodent may be active during the day. Using the same habitat at different times can help both organisms survive.
Definition: A population is a group of organisms of the same kind or species living together in a particular habitat at a given time.
Example: All the fish of one species living in a pond form a fish population.
To find the population of a particular plant or animal, the following method may be used:
Mark a fixed area, for example, 1 m × 1 m in a school garden.
Count the number of individuals of each type of organism present in that area.
Record the number for that particular organism in the selected area and at that particular time.
Thus, population means the number of individuals of a particular species living in a defined area at a certain time.
Community
A community is formed by different populations of plants, animals and microorganisms living together and interacting in the same habitat.
It includes all the living or biotic components of a habitat.
A habitat is the physical place or environment where an organism lives.
If only one type of organism is present in a habitat, there may be intense competition for food, water and space. Shortage of resources can make survival difficult.
Diversity in a habitat, meaning the presence of many types of organisms, helps maintain balance because different organisms perform different roles and interact in different ways.
Flower structure: A typical flower has sepals, petals, stamens, which are the male reproductive parts, and carpels, which are the female reproductive parts.
Pollination: Pollination is the transfer of pollen grains from the anther to the stigma of the same flower or of another flower of the same species.
How it happens: Wind, water, insects, bats and birds may carry pollen from one flower to another.
Why it matters: Pollination is essential for the formation of fruits and seeds.
Yes. Every organism in a community plays an important role, helping to maintain balance and supporting the survival of other organisms. Activities and scientific studies help us understand these relationships.
Explanation Using the Pond Example
Pond A, with fish: There are fewer dragonflies because fish eat dragonfly larvae in the pond.
Pond B, without fish: There are more dragonflies because fish are not present to eat their larvae.
Dragonflies are predators of bees, butterflies and other insects that help pollinate flowers.
Fewer dragonflies in Pond A allow more bees and butterflies to survive and pollinate flowers.
More pollinators result in more pollination. Consequently, more flowers can produce seeds and more plants can grow.
Scientific studies have confirmed this type of relationship. Researchers found that plants around ponds with fish were better pollinated than plants around ponds without fish. This was mainly due to the chain of effects involving fish, dragonfly larvae, dragonflies and pollinators.
Organisms are interconnected: The presence or absence of one type of organism, such as fish, can affect many others, including pollinators and plants.
Every member of a community has a role or niche: Fish control dragonfly populations, dragonflies affect pollinators, pollinators are essential for plant reproduction, and plants provide food and shelter for many organisms.
This is an example of a food web and ecological balance. A change in one group can produce effects, sometimes called a cascade, throughout the community.
Overfishing means removing too many fish from ponds, rivers, lakes or oceans.
If too many fish are removed, the number of dragonflies may increase because their predators have disappeared. More dragonflies may reduce the number of pollinators, leading to less pollination of nearby plants.
Removing a key species such as fish can upset the delicate balance of a community. It may affect other animals, plants and even the non-living environment.
Organisms do not live alone. They constantly interact with both living, or biotic, and non-living, or abiotic, components in their environment.
Interactions Between Biotic and Abiotic Components
Definition: These are interactions between living things and non-living things in their environment.
Examples:
Plants need sunlight for photosynthesis, water and soil for growth, and air for respiration.
Earthworms live in moist soil.
Fish lay eggs in water, which is an abiotic component.
Soil provides nutrients needed by plants.
Definition: These are interactions between non-living components that affect the conditions of a habitat.
Examples:
Sunlight warms the surroundings and increases the temperature during the day.
Water evaporates faster in strong sunlight.
Air currents can create gentle waves on the surface of water.
Definition: These are relationships between living organisms in a community.
Examples:
Frogs eat insects.
Water snakes eat fish.
Frogs and fish compete for larvae.
Many microorganisms interact in a pond and help break down dead material.
Plants provide food and shelter for animals.
Mushrooms, which are fungi, decompose dead plants and animals.
An ecosystem consists of all the living, or biotic, and non-living, or abiotic, components in a particular area and all the interactions among them.
Aquatic ecosystems are water-based ecosystems. They include ponds, rivers and lakes.
Terrestrial ecosystems are land-based ecosystems. They include forests, grasslands and farmlands.
Ecosystems may overlap. For example, a river running through a forest forms an area where aquatic and terrestrial ecosystems interact.
Producers or autotrophs: Organisms that make their own food, usually green plants through photosynthesis.
Consumers or heterotrophs: Organisms that depend on other organisms for food.
- Herbivores: Animals that eat plants, such as deer and horses.
- Carnivores: Animals that eat other animals, such as vultures and shikras.
- Omnivores: Animals that eat both plants and animals, such as foxes and mice.
Decomposers: Organisms such as fungi and bacteria that break down dead plants, dead animals and wastes. They return nutrients to the ecosystem.
Food chain: A food chain is a simple sequence showing who eats whom in an ecosystem.
Examples of Food Chains
Grass → Hare → Tiger (Grass is eaten by the hare, and the hare is eaten by the tiger.)
Grass → Grasshopper → Frog → Snake → Eagle (Each organism is eaten by the next organism in the chain.)
Each organism in a food chain occupies a specific position, called a trophic level.
First trophic level: Producers, such as grass and millet.
Second trophic level: Herbivores, which eat plants, such as hares and mice.
Third trophic level: Small carnivores, which eat herbivores, such as frogs.
Fourth trophic level: Consumers that eat animals at the third trophic level.
When the number of organisms at each trophic level is counted and arranged according to trophic levels, with producers at the base, the arrangement forms a pyramid of numbers.
Producers form the base of a food chain, while top predators occur at the higher levels. Energy is lost at each step of a food chain, so less energy is available at higher trophic levels.
In nature, feeding relationships are not usually simple chains. They are more complex and form a food web.
Grass may be eaten by a rabbit or a mouse.
Grasshoppers may be eaten by a bird or a frog.
Owls may eat mice or frogs.
Because an organism may be eaten by two or more types of organisms, food chains overlap and link together to form a web.
6. What Happens to Waste in Nature?
What Are Decomposers?
Definition: Decomposers are organisms that break down dead plants, animals and animal waste into simpler substances and return nutrients to the soil.
Examples: Fungi such as mushrooms and microorganisms such as bacteria are decomposers. Organisms such as worms, beetles and flies also help break down dead matter and waste.
When plants or animals die, decomposers act on them. Decomposers also act on their wastes.
Fungi such as mushrooms and bacteria break down complex substances in dead materials into simpler substances.
Beetles and flies often feed on materials such as animal dung, including elephant dung, and help break them down further.
This entire process is called decomposition.
Nutrient recycling: Decomposition returns important nutrients to the soil, where plants can use them for growth.
Balance in nature: Decomposers prevent the accumulation of dead plants, dead animals and wastes in the environment.
No waste in nature: Nothing truly goes to waste in nature. Materials are reused in different forms with the help of decomposers and other organisms.
Saprotrophs: Decomposers are also called saprotrophs. Sapro means 'rotten' and troph means 'food'.
Migratory birds travel thousands of kilometres between different habitats and countries to avoid harsh climatic conditions or to find food.
Example: Demoiselle cranes visit Khichan village in Rajasthan every winter.
Enhance beauty: Migratory birds add colour and variety to habitats.
Maintain ecosystem balance: They may act as pollinators and seed dispersers, linking different habitats.
Pest control: They feed on insect pests and may help farmers by reducing crop damage.
If plants in a pond die, for example, because of pollution, the following changes may occur:
Less oxygen is produced in the water.
The fish population declines because fish need oxygen.
Fewer fish may lead to more insects because fish usually eat some insects.
Extra insects may spread to nearby farms and harm crops.
Farmers may use more pesticides, which can further harm the environment.
One small change, such as the death of pond plants, can cause a chain reaction or 'cascading effects' throughout the ecosystem.
In the 1980s, India exported a huge number of Indian bullfrogs.
This reduced frog populations.
Fewer frogs meant more insects, including insect pests in farms.
Farmers then used more pesticides, which harmed the environment, water, soil and the health of living beings.
The Government banned frog-leg exports to help restore ecological balance.
• Interactions between organisms and their environment help keep populations and resources stable. This condition is called ecological balance.
• Ecological balance is dynamic, which means that it is always changing. However, large disruptions such as overuse of resources, pollution and loss of species can damage this balance.
8. How Do Interactions Maintain Balance in Ecosystems?
Besides feeding relationships, organisms also compete for common resources such as food, water, physical space and sunlight. This competition helps control population size and keeps the ecosystem balanced. Without it, one species could multiply excessively and cause an imbalance in the ecosystem.
Other Relationships
Mutualism: Both organisms benefit. For example, bees obtain nectar from flowers and flowers are pollinated by bees.
Commensalism: One organism benefits while the other is not affected. For example, an orchid may grow on a tree without harming or benefiting the tree.
Parasitism: One organism benefits while the other is harmed. For example, a tick feeds on the blood of a dog and may cause irritation.
Forests: Forests provide clean air, fertile soil, food, timber, medicines and natural beauty.
Water bodies: Ponds, rivers, lakes and other water bodies provide water and food.
All ecosystems: Ecosystems provide aesthetic value, recreation and support human well-being.
Mangroves, such as those in the Sundarbans: Mangroves protect coastal regions from floods and storms, absorb carbon dioxide and provide shelter to unique wildlife. The Sundarbans are recognised as a World Heritage Site.
Deforestation, pollution, unsustainable land use and illegal hunting are harming many habitats.
The Sundarbans mangroves are under threat from cutting of trees, pollution and overuse of resources.
Such activities disturb natural cycles and reduce biodiversity.
Protected areas: National parks, biosphere reserves and wildlife sanctuaries conserve habitats and wildlife. Examples include Jim Corbett, Manas, the Nilgiri Biosphere Reserve and Chilika Lake.
Community action: People must work together to conserve resources, prevent pollution and protect natural areas.
Examples include farms, fish ponds and parks.
When managed properly, they can help reduce pollution, support biodiversity and provide recreational spaces.
Need: Artificial ecosystems require continuous care and human management.
Ecosystems consist of biotic, or living, and abiotic, or non-living, components that depend on one another to support life processes.
Humans benefit from ecosystems in many ways:
Forests provide fresh air, fertile soil, food, fibres, timber and medicines.
Aquatic ecosystems provide water and food.
Ecosystems also provide aesthetic value, or beauty, and recreational value, or enjoyment.
These benefits support human well-being and show the close connection between nature and human life.
However, overuse or misuse of natural resources disturbs the balance of nature.
The Sundarbans contain the largest mangrove forest in the world.
• They are located in the delta where the Ganges and Brahmaputra rivers meet, between India and Bangladesh.
• The Sundarbans are home to many kinds of flora, or plants, and fauna, or animals. Several of these species are endangered.
• The mangrove forest protects coastal areas from storms and floods by slowing down strong winds and waves.
• Mangrove trees absorb carbon dioxide from the air and release oxygen.
• Sundarbans National Park in India was declared a World Heritage Site by UNESCO, the United Nations Educational, Scientific and Cultural Organization, in 1987 because of its importance.
• Mangrove trees are cut for fuelwood and farming.
• Illegal hunting and overuse of forest resources threaten wildlife.
• Pollution from industrial waste and untreated sewage damages water and habitats.
• Problems across India include: Deforestation, overuse of natural resources, spread of invasive species, unsustainable land use, and pollution.
Call to action: Think about the actions that you and your community can take to protect forests, rivers and wetlands from damage.
Protected Areas for Conservation
• Definition: Protected areas are parts of land or water set aside to conserve wildlife and their habitats.
• India has many protected areas, including national parks, wildlife sanctuaries, biosphere reserves and community-conserved areas.
• Benefits: Protected areas conserve entire habitats, including endangered animals, birds and rare plants.
• Jim Corbett National Park, Uttarakhand
• Manas National Park, Assam
• Nilgiri Biosphere Reserve, Western Ghats
• Chilika Lake, Odisha
• Eaglenest Wildlife Sanctuary, Arunachal Pradesh
• Hemis National Park, Leh
• Keibul Lamjao National Park, Manipur
• Marine National Park (Gulf of Kachchh), Gujarat
• The ancient text Vrikshayurveda emphasises soil health and nourishment.
• It advocates the continuous nourishment of soil using organic manure such as Kunapa Jala. Kunapa Jala is a liquid fertiliser made by fermenting animal and plant waste. Fermentation breaks complex substances into simpler ones.
• Other composted materials can also help maintain soil fertility.
• Farming is a major livelihood in India, but it can become unsustainable without environment-friendly practices.
• Humans have practised farming for thousands of years to grow food.
• Between 1950 and 1965, India faced a food crisis because crop production was low.
• In the middle of the twentieth century, the Green Revolution used tractors, machines, synthetic fertilisers and pesticides to increase food production.
Some Green Revolution methods are now considered unsustainable due to:
• Overuse of synthetic chemicals.
• Excessive extraction of groundwater.
• Growing only one type of crop for commercial gain, a practice called monoculture.
Harms to environment and health:
- Overuse of pesticides and monoculture lead to soil degradation and loss of soil quality.
- Reduced soil fertility from loss of microorganisms and humus (which binds soil particles).
- Pesticides reduce natural predators, leading to pest outbreaks and pesticide resistance.
- Heavy irrigation and ploughing disturb soil organisms like earthworms and snails.
- Monoculture reduces crop diversity and harms pollinators like bees.
- Organic and natural farming methods are being adopted to minimise interference with natural ecosystems.
• Habitat: A place that provides the right conditions for an organism to live and grow.
• Components of habitats: Biotic components include plants, animals and microorganisms. Abiotic components include air, water, soil and temperature.
• Ecosystem: A system formed by the interactions between biotic and abiotic components in a particular area.
• Types of ecosystems: Terrestrial ecosystems include forests, grasslands and deserts. Aquatic ecosystems include ponds, lakes and seas.
• Classification of organisms: Organisms in an ecosystem may be producers, consumers or decomposers.
• Producers: Organisms that make their own food.
• Consumers: Organisms that obtain energy by eating plants or other animals.
• Decomposers: Organisms that break down dead matter and recycle nutrients.
• Food chains: Sequences that show who eats whom.
• Food webs: Interconnected food chains that show complex feeding relationships.
• Trophic levels: The positions occupied by organisms in a food chain, showing their roles in the transfer of energy.
• Mutualism: A relationship in which both organisms benefit.
• Commensalism: A relationship in which one organism benefits and the other is unaffected.
• Parasitism: A relationship in which one organism benefits and the other is harmed.
• Benefits of ecosystems: Ecosystems provide clean air, water, food, medicines, climate regulation, recreation and support for human well-being.
• Threats to ecosystems: Pollution, deforestation, habitat destruction, climate change, invasive species and overexploitation of resources.
• Conservation of ecosystems: The protection of habitats and biodiversity through protected areas, community conservation and sustainable practices.
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