CBSE Class 10 Science Our Environment Notes 2025 PDF & Study Material

The environment includes our physical surroundings like air, water, soil, and all the organisms such as plants, animals, human beings, and micro-organisms like bacteria and fungi (called decomposers). An ecosystem is a self-contained unit of living things and their non-living environment. All the interacting organisms in an area together with the non-living constituents of the environment, form an ecosystem. It, therefore, consists of biotic and abiotic components.

An essential part of life on Earth is the environment. It provides the necessary resources needed for living and supports all living organisms. So, essentially, it is a study of the natural world, the relationship of organisms living there, and human actions towards them. For Class 10 students, it is essential to understand how important the environment is and its need for preservation so that they make the right decisions leading to a sustainable future. In this article we will discuss some important topics related to our environment and its components, the impact of human activities on our environment, and ways of protecting and conserving it. To prepare and ace the final exams, students can find question banks with competency-based and important questions and other study materials provided by Educart.

Class 10 Science Chapter 15: Our Environment – Notes

The environment includes everything around us, such as air, water, soil, plants, animals, humans, and microorganisms like bacteria and fungi (decomposers). Human and animal activities produce waste materials, which can be harmful to some extent. These wastes are categorised into two main types:

Biodegradable Wastes

These are substances that can be broken down naturally by bacteria, fungi, and other microorganisms. Factors like temperature and sunlight also help in their decomposition.

Examples:

• Food waste
• Leaves
• Urine and faeces
• Sewage
• Agricultural residue
• Paper, wood, and cloth
• Cow dung

Non-Biodegradable Wastes

These substances do not decompose naturally and remain in the environment for a long time, potentially harming ecosystems. They can be in solid, liquid, or gaseous forms.

Examples:

• Plastic and polythene bags
• Glass
• Pesticides and insecticides (e.g., DDT)
• Heavy metals like mercury, lead, and arsenic
• Radioactive waste

Harmful Effects of Biodegradable Waste:

• Produces a foul smell during decomposition.
• Pollutes the environment and makes surroundings dirty.
• Can block drainage systems, creating stagnant water that becomes a breeding ground for mosquitoes, leading to diseases like malaria and dengue.

Effects of Non-Biodegradable Waste:

• Remains in the environment for years, causing long-term pollution.
• Harmful chemicals can enter the food chain and affect human health.
• Some, like radioactive waste, pose severe environmental and health risks.

By properly managing waste, reducing pollution, and using eco-friendly products, we can help protect our environment.

Difference Between Biodegradable and Nonbiodegradable Wastes

What is an Ecosystem?

An ecosystem is a self-sustaining unit that includes living organisms (plants, animals, and decomposers) interacting with non-living elements (soil, air, and water). Examples include forests, ponds, lakes, and grasslands.

Types of Ecosystems

Ecosystems can be natural or man-made:

• Natural Ecosystems: Forests, rivers, deserts, lakes, mountains, seas, etc.
• Man-Made Ecosystems: Gardens, crop fields, parks, aquariums, etc.

Terrestrial and Aquatic Ecosystems

• Terrestrial (Land-Based) Ecosystems: Deserts, grasslands, mountains, forests.
• Aquatic (Water-Based) Ecosystems: Ponds, lakes, rivers, oceans.

Components of an Ecosystem

Ecosystems consist of biotic (living) components and abiotic (non-living) components.

Biotic Components (Living Organisms)

Biotic components include three groups:

(a) Producers (Autotrophs)

These are organisms that produce their own food using sunlight through photosynthesis. Examples include:

• Green plants
• Blue-green algae

Some microscopic aquatic plants that float on water surfaces are called phytoplankton.

(b) Consumers (Heterotrophs)

Consumers depend on other organisms for food. They are classified as:

1. Herbivores (Primary Consumers): Eat only plants (e.g., deer, rabbits, cows).
2. Carnivores (Secondary/Tertiary Consumers): Eat other animals (e.g., snakes, lions, frogs).
3. Omnivores: Eat both plants and animals (e.g., humans, bears).
4. Parasites: Live on or inside other organisms and rely on them for survival (e.g., lice, tapeworms).

Some carnivores are further classified:

• Primary Carnivores (Secondary Consumers): Feed on herbivores (e.g., wild cats, frogs, birds).
• Secondary Carnivores (Tertiary Consumers): Feed on primary carnivores (e.g., owls, tigers, lions).
• Top Carnivores: Apex predators that are not hunted by other animals (e.g., lions).

(c) Decomposers

Decomposers are fungi and bacteria that break down complex organic matter from dead plants and animals into simpler substances. They help in recycling nutrients and maintaining ecological balance.

Importance of Decomposers

1. Waste Disposal: They break down dead organisms, cleaning the environment and making space for new life.
2. Soil Fertility: Decomposers release nutrients back into the soil, improving fertility.
3. Mineral Solubilization: They produce acids that help dissolve essential minerals.
4. Nutrient Recycling: They recycle materials in the biosphere, ensuring a continuous cycle of life.

Abiotic Components of an Ecosystem

These are the non-living elements that influence life in an ecosystem.

Types of Abiotic Components:

1. Edaphic Factors: Soil texture, topography, water, and air.
2. Inorganic Substances: Carbon dioxide, nitrogen, oxygen, water, phosphorus, sodium, potassium, calcium (involved in nutrient cycles).
3. Organic Compounds: Proteins, carbohydrates, and lipids, which link abiotic and biotic components.
4. Climatic Factors: Sunlight, temperature, air pressure, humidity, rainfall, and moisture, which affect organism distribution.

Functions of an Ecosystem

1. Energy Flow: This shows how solar energy is captured and used by organisms.
2. Nutrient Cycling: Provides information on essential minerals and their recycling.
3. Interdependence: Explains relationships between organisms and their environment.
4. Conservation Awareness: Helps humans understand resource conservation, pollution control, and ways to maximize productivity.
5. Biogeochemical Cycles: Energy flows in one direction, while nutrients cycle continuously.

Food Chain

A food chain is the sequence of living organisms in which one organism consumes another, transferring energy from one level to the next.

Key Features of a Food Chain:

• Unidirectional Flow: Energy transfer occurs in only one direction.
• Represents "Who Eats Whom": Shows the sequence of consumption.
• Sequential Energy Transfer: Organisms are arranged based on their roles in energy transfer.

Example of a Simple Food Chain (Grassland Ecosystem):

Grass (Producer) → Deer (Herbivore) → Lion (Carnivore)

• Grass (T1): Producer that synthesizes food through photosynthesis.
• Deer (T2): Herbivore that feeds on grass (Primary Consumer).
• Lion (T3): Carnivore that preys on deer (Secondary Consumer).

Example of a Four-Step Food Chain:

Grass (Producer) → Insect (Herbivore) → Frog (Carnivore) → Eagle (Secondary Carnivore)

Significance of Food Chains

Understanding Food Relationships: Helps in studying interactions among organisms in an ecosystem.

Energy Transfer Moves energy and nutrients between organisms in an ecosystem.

Ecosystem Stability: Contributes to the dynamic balance of an ecosystem.

Tracking Pollutants: Helps in understanding the movement of harmful substances (e.g., pesticides) in the food chain.

Food Web

A food web consists of multiple interlinked food chains within an ecosystem. It shows how organisms have multiple food sources and predators rather than a single food chain.

Characteristics of a Food Web:

• More complex than a food chain.
• Provides ecosystem stability—if one organism is removed, others can still survive.
• Shows that organisms can be part of multiple food chains.

Trophic Levels

Each step in a food chain where energy is transferred is called a trophic level.

Trophic Levels in a Food Chain:

Producers (T1): Green plants and algae (make their food through photosynthesis).

Primary Consumers (T2): Herbivores that eat plants (e.g., deer, insects).

Secondary Consumers (T3): Small carnivores that eat herbivores (e.g., frogs, snakes).

Tertiary Consumers (T4): Large carnivores that eat smaller carnivores (e.g., eagle, lion).

Energy Flow & the 10% Law

• Energy decreases as it moves up the trophic levels.
• Only 10% of energy is transferred to the next level; the rest (90%) is used by the organism for life processes like movement, respiration, and reproduction.
• This limits the number of trophic levels in a food chain.

Environmental Issues and Their Impact

Changes in the environment directly affect our lives, just as our activities influence the surroundings. Over time, human actions have led to environmental degradation, resulting in serious problems such as ozone layer depletion and waste accumulation.

Ozone Layer Depletion

The ozone (O₃) layer is mainly found in the stratosphere, a section of the atmosphere located between 12 km and 50 km above sea level. This region, known as the ozonosphere, plays a crucial role in shielding the Earth from harmful ultraviolet (UV) radiation. Without this protective layer, UV rays can cause serious health problems, including skin cancer, cataracts, weakened immune systems, and damage to plant life.

The thinning of the ozone layer, particularly over Antarctica, was first discovered in 1985 and was referred to as the "ozone hole."

Measures to Prevent Ozone Layer Damage

One of the main causes of ozone depletion is the excessive use of chlorofluorocarbons (CFCs)—synthetic chemicals found in refrigerants, fire extinguishers, and aerosol sprays. A single chlorine atom from CFCs can destroy 100,000 ozone molecules.

To combat this issue, the United Nations Environment Programme (UNEP) played a key role in securing the Kyoto Protocol, which required countries to limit CFC production to 1986 levels.

Biological Magnification

Biological magnification refers to the gradual increase in the concentration of harmful chemicals, such as pesticides, within organisms at each level of the food chain. This can have toxic effects on both wildlife and humans.

Waste Management and Disposal

Rapid industrialisation and the growing demand for consumer goods have led to a sharp rise in waste production, especially in urban areas. Proper waste disposal is essential to prevent pollution and environmental damage. Different methods are used depending on the type of waste:

• Incineration: Burning waste at high temperatures to reduce it to ash. This is commonly used for household, chemical, and medical waste.
• Open Dumping: A traditional method where solid waste is discarded in specific areas. However, this contributes to pollution.
• Landfilling: Waste is dumped in low-lying areas and compacted with bulldozers to manage space efficiently.
• Composting: Organic waste is placed in a compost pit (2m × 1m × 1m) and covered with soil. Within three months, it decomposes into nutrient-rich manure.
• Recycling: Non-biodegradable materials like plastic and metal are processed and reused to create new products.
• Reuse: Simple and effective, this method involves using items multiple times—for example, reusing paper to make envelopes.

Common Mistakes in Chapter 14 Our Environment

Chapter 14, "Our Environment," covers key environmental concepts, but students often make common mistakes when studying this topic. Here are some frequent errors to watch out for:

Misunderstanding Biodegradable and Nonbiodegradable Substances

• Mistake: Thinking that all natural materials are biodegradable.
• Correction: Some natural substances, like glass and metals, are not biodegradable.

Confusion Between Food Chain and Food Web

• Mistake: Believing a food chain and a food web are the same.
• Correction: A food chain is a single linear path, whereas a food web is a network of interconnected food chains.

Incorrect Explanation of Biological Magnification

• Mistake: Assuming biological magnification affects all organisms equally.
• Correction: It primarily affects organisms at higher trophic levels as toxins accumulate and concentrate as they move up the food chain.

Misinterpretation of the Ozone Layer and Its Depletion

• Mistake: Thinking the ozone layer is present in the troposphere.
• Correction: The ozone layer is found in the stratosphere and protects against harmful UV radiation.

Lack of Clarity on Waste Management Methods

• Mistake: Mixing up composting and recycling.
• Correction: Composting breaks down organic waste into manure, while recycling involves processing materials like plastic and metal for reuse.

Incomplete Understanding of Ecosystem Components

• Mistake: Forgetting the difference between biotic and abiotic components.
• Correction: Biotic components include living organisms, whereas abiotic components include non-living factors like sunlight, water, and air.

Overlooking the Impact of Human Activities

• Mistake: Underestimating the role of human actions in environmental problems.
• Correction: Activities like deforestation, industrial pollution, and excessive plastic use contribute significantly to environmental degradation.

By avoiding these mistakes, students can improve their understanding of the "Our Environment" chapter and perform better in exams. Environmental problems like ozone layer depletion, biological magnification, and waste accumulation pose serious threats to life on Earth. Human activities have significantly contributed to these issues, but by adopting sustainable practices, we can minimise further damage. Reducing CFC emissions, managing waste responsibly, and promoting recycling and reuse are essential steps towards a healthier planet. Governments, organisations, and individuals must work together to implement eco-friendly solutions. Protecting the environment is not just a choice but a necessity for future generations. By acting now, we can ensure a cleaner, safer, and more sustainable world for all.