Class 8 Science Notes on Chapter 12 How Nature Works in Harmony: Complete Revision Guide

Nature is made up of living organisms and non-living components that depend on one another. Plants, animals, microorganisms, air, water and soil work together to keep ecosystems healthy and balanced. When one part of this system changes, it can affect the entire ecosystem.

Class 8 Science Chapter 12 How Nature Works in Harmony Notes simplify these concepts by explaining habitats, ecosystems, food chains, food webs, ecological interactions, biodiversity and sustainable farming in clear and easy language. These notes are ideal for quick revision, strengthening your understanding and preparing confidently for exams.

Topics Covered in Class 8 Science Chapter 12 How Nature Works in Harmony Notes

What is a Habitat	Biotic and Abiotic Components
Producers, Consumers and Decomposers	Food Chain
Food Web	Trophic Levels
Ecological Interactions	Levels of Organisation in an Ecosystem
Types of Ecosystems	How Ecosystems Maintain Balance
Importance of Ecosystems	Major Threats to Ecosystems
Protected Areas	Sustainable Farming Practices

Class 8 Science Chapter 12 How Nature Works in Harmony Notes Chapter Summary 

No living organism can survive on its own. Plants, animals and microorganisms depend on air, water, soil and sunlight, while these natural resources create the conditions needed for life to survive and grow.

The Class 8 Science Chapter 12 How Nature Works in Harmony Notes explains how organisms depend on each other, how food moves through ecosystems and why protecting nature is essential for human survival.

What is a Habitat

A habitat is the natural place where an organism lives, grows and reproduces. Every habitat provides suitable conditions such as food, water, shelter and space for survival.

Different organisms require different habitats because each species is adapted to specific environmental conditions.

Some examples include:

• Forests
• Ponds
• Grasslands
• Deserts
• Rivers
• Agricultural fields

Each habitat contains both living and non-living components that work together.

Biotic and Abiotic Components of an Ecosystem

Every ecosystem is made up of living and non-living components that work together to support life. While living organisms depend on their surroundings for survival, non-living factors create the conditions needed for them to grow and thrive.

The table below shows the two main components of an ecosystem.

Biotic Components (Living)	Abiotic Components (Non-living)
Plants	Air
Animals	Water
Fungi	Soil
Bacteria	Sunlight
Other microorganisms	Temperature

Neither of these components can function independently. For example, plants need sunlight, water and nutrients from the soil to prepare food, while animals depend on plants and other organisms for food and oxygen. 

Producers, Consumers and Decomposers in an Ecosystem

Every organism in an ecosystem depends on food for survival. Based on how they obtain food, living organisms are grouped into producers, consumers and decomposers. 

The table below explains each group along with its role and examples.

Group	How They Obtain Food	Role in the Ecosystem	Examples
Producers	Make their own food through photosynthesis.	Form the first trophic level and provide food and oxygen for other organisms.	Grass, trees, algae
Consumers	Depend on plants or other animals for food. They are classified as herbivores, carnivores and omnivores.	Transfer energy through the food chain by feeding on other organisms.	Herbivores: Deer, rabbit, cow Carnivores: Tiger, snake, eagle Omnivores: Human, crow, fox.
Decomposers	Break down dead plants, animals and organic waste into simpler substances.	Recycle nutrients, improve soil fertility, keep the environment clean and support plant growth.	Bacteria, fungi

Together, these three groups keep ecosystems healthy and functioning smoothly.

Food Chain, Food Web and Trophic Levels

Every organism in an ecosystem depends on another for food and energy. This movement of energy follows a specific pattern, helping maintain the balance of nature.

To understand this process, let's look at three important concepts: the food chain, food web and trophic levels.

a. Food Chain

A food chain shows the order in which one organism is eaten by another. It explains how energy passes from plants to animals in an ecosystem.

For example:

Grass → Grasshopper → Frog → Snake → Eagle

In this food chain:

• Plants are the producers because they make their own food.
• Herbivores eat plants and obtain energy from them.
• Carnivores feed on herbivores or other animals.
• Top predators occupy the highest level of the food chain.

A food chain helps us understand how energy moves from one living organism to another.

b. Food Web

In nature, things are not always as simple as a single food chain. Most animals eat more than one type of food and may also be prey for different animals. As a result, many food chains become connected, forming a food web.

A food web:

• Shows multiple feeding relationships within an ecosystem.
• Provides alternative food sources for organisms.
• Makes ecosystems more stable and balanced.
• Helps organisms survive even if one food source becomes scarce.

Because it includes many interconnected food chains, a food web gives a more realistic picture of how organisms depend on one another in nature.

c. Trophic Levels

As energy moves through a food chain or food web, each organism occupies a particular feeding position. This position is known as a trophic level.

The table below shows the different trophic levels.

Trophic Level	Organisms
First	Producers (Plants)
Second	Herbivores (Primary Consumers)
Third	Small Carnivores (Secondary Consumers)
Fourth	Large Carnivores (Tertiary Consumers)

As we move from one trophic level to the next, only a small amount of energy is passed on. This is why the number of organisms becomes smaller at higher trophic levels, with only a few top predators at the top of the food pyramid.

Ecological Interactions: How Organisms Depend on One Another

An ecosystem is not just a collection of plants and animals. Every living organism interacts with others in different ways to survive, find food and reproduce. Some interactions benefit both organisms, while others may benefit only one or even harm another. 

Let's look at the main types of ecological interactions.

a. Competition

Competition occurs when two or more organisms need the same resources, such as food, water, sunlight or space. Since these resources are often limited, organisms compete to survive.

Examples:

• Two birds competing for insects.
• Plants growing close together compete for sunlight.

b. Mutualism

In mutualism, both organisms benefit from the relationship. Each one helps the other in some way, making it a successful interaction.

Example: Bees collect nectar from flowers while helping pollinate them.

c. Commensalism

In commensalism, one organism benefits while the other remains unaffected. The relationship is beneficial for one organism without affecting the other.

Example: Orchids grow on trees for support without taking nutrients from them.

d. Parasitism

In parasitism, one organism, called the parasite, benefits by living on or inside another organism, known as the host. In the process, the host suffers harm.

Example: Ticks feed on the blood of dogs.

Each of these interactions plays an important role in nature. By influencing how organisms live and survive, they help regulate populations and maintain the balance of ecosystems.

Levels of Organisation in an Ecosystem

To understand how an ecosystem works, it helps to look at how nature is organised. Living organisms are arranged into different levels, starting with a single organism and gradually building up to a complete ecosystem.

The table below explains each level in a simple way.

Level	What It Means
Individual	A single living organism, such as one fish or one tree.
Population	A group of organisms of the same species that live in the same area.
Community	Different populations living and interacting in the same habitat.
Ecosystem	A community of living organisms interacting with non-living components such as air, water, soil and sunlight.

To see how these levels connect, think of a pond. A single fish is an individual, while all the fish of the same species in the pond form a population. 

Types of Ecosystems

Depending on where living organisms interact with their surroundings, ecosystems are broadly grouped into terrestrial and aquatic ecosystems.

The table below shows the two main types along with some common examples.

Type of Ecosystem	Description	Examples
Terrestrial Ecosystems	It is found on land and supports a wide variety of plants and animals.	Forests, Grasslands, Deserts, Farms
Aquatic Ecosystems	They are found in water and provide habitats for aquatic plants and animals.	Rivers, Ponds, Lakes, Oceans

While many ecosystems occur naturally, some are created and managed by humans. 

Examples include agricultural fields, parks, gardens and fish ponds, where living organisms continue to interact with their environment just as they do in natural ecosystems.

How does an Ecosystem Stay Balanced

An ecosystem stays healthy because every living organism has a role. Plants, animals and microorganisms depend on one another, creating a balance that keeps nature functioning smoothly. 

When one part of this balance is disturbed, it affects the entire ecosystem. For example:

• Plants produce food through photosynthesis and release oxygen into the atmosphere.
• Herbivores feed on plants, helping control excessive plant growth.
• Carnivores keep herbivore populations under control, preventing overgrazing.
• Decomposers break down dead plants and animals, returning nutrients to the soil.

When any one of these groups declines, the effects can spread throughout the ecosystem. For instance, if frog populations decrease, insect numbers may rise rapidly. This can damage crops and increase the need for pesticides.

Why are Ecosystems Important

A healthy ecosystem supports life in many ways. Beyond providing habitats for plants and animals, it also offers essential resources and services that humans depend on every day.

Some of the key benefits of healthy ecosystems include:

• Clean air and fresh water
• Fertile soil for farming
• Food and medicinal resources
• Pollination of crops by insects
• Climate regulation
• Protection from floods and soil erosion
• Conservation of biodiversity

A great example is the Sundarbans mangrove forest. It acts as a natural barrier against coastal storms, provides a home for diverse wildlife and helps reduce carbon dioxide in the atmosphere, making it an important ecosystem for both people and nature.

Major Threats to Ecosystems

Ecosystems remain balanced only when living organisms and their surroundings work together in harmony. However, various human activities can disturb this balance, affecting biodiversity and the survival of many species.

The table below outlines some of the major threats to ecosystems and their impact.

Threat	How It Affects the Ecosystem
Deforestation	Destroys forests, reduces biodiversity and displaces wildlife.
Pollution	Contaminates air, water and soil, harming both plants and animals.
Habitat Destruction	Forces organisms to leave or lose their natural homes.
Climate Change	Alters weather patterns and affects the survival of many species.
Overuse of Natural Resources	Depletes forests, water and other resources faster than they can recover.
Illegal Hunting	Reduces wildlife populations and disrupts food chains.
Invasive Species	Compete with native species for food and habitat, upsetting ecological balance.

If these threats continue unchecked, ecosystems may lose their biodiversity, making it harder for plants, animals and humans to depend on the resources they provide.

Protected Areas: Safe Homes for Wildlife

Many plants and animals need safe places to live and reproduce. To protect them and preserve their natural habitats, governments and conservation organisations have created protected areas that limit human activities.

Some of the most common protected areas are:

• National Parks: Large natural areas that protect forests, wildlife and entire ecosystems.
• Wildlife Sanctuaries: Places where wild animals are protected in their natural habitats.
• Biosphere Reserves: Protected regions that conserve biodiversity while allowing people to use resources responsibly.
• Marine Protected Areas: Coastal and ocean regions that protect fish, corals and other marine life.

These protected areas play an important role in conserving biodiversity, protecting endangered species and preserving nature for future generations.

Sustainable Farming for a Healthy Environment

Farming and nature are closely connected. Healthy soil, clean water and pollinating insects are all essential for growing crops. However, using too many chemical fertilisers, pesticides and excessive groundwater can harm the environment over time.

Sustainable farming focuses on methods that protect nature while maintaining healthy crop production. Some of these practices include:

• Using organic manure to enrich the soil naturally.
• Rotating crops to keep the soil healthy and reduce pest attacks.
• Preparing compost from organic waste to improve soil fertility.
• Using natural methods to control pests instead of relying heavily on chemicals.
• Conserving water by using it wisely during irrigation.
• Growing different crops together to improve soil health and support biodiversity.

By following these practices, farmers can protect the environment, improve soil quality and ensure enough food for future generations.