MG SCHOOL SCIENCE • CLASS 10

Our Environment

Chapter 13 – Complete chapter notes, key concepts, comparison tables and quick revision.

Class 10 Science Chapter 13 Study Notes

1. Introduction

Our environment is a complex and dynamic system that supports all living beings. It consists of physical, chemical and biotic factors that interact continuously to maintain life and ecological balance.

Physical factors

Natural elements such as landforms, climate, temperature, rainfall, wind and soil.

Chemical factors

Substances and chemical conditions present in air, water and soil, along with their interactions.

Biotic factors

Living organisms, including plants, animals and microorganisms, and their interactions within ecosystems.

Core concept: The environment functions through continuous interactions among physical, chemical and biotic components to sustain ecological balance.

2. Ecosystem: What Are Its Components?

An ecosystem is a functional unit formed by the interaction of living organisms, called biotic components, with the non-living physical and chemical environment, called abiotic components. Organisms influence the environment and are, in turn, affected by it.

Types of ecosystems

Natural ecosystems

Ecosystems that exist and function without deliberate human intervention.

Examples: Forests, lakes, rivers, oceans and grasslands.

Artificial or man-made ecosystems

Ecosystems created and maintained by humans.

Examples: Crop fields, aquariums, gardens and parks.

Components of an ecosystem

Abiotic components: Non-living physical and chemical factors such as light, temperature, water, air, soil and minerals. Climate, soil-related conditions and topographic features are important abiotic factors.
Biotic components: Living organisms such as producers, consumers and decomposers.

Producers, consumers and decomposers

Producers or autotrophs: Green plants, algae and some cyanobacteria synthesise organic food from carbon dioxide and water using sunlight. This process is called photosynthesis. Producers form the base of food chains.
Consumers or heterotrophs: Organisms that cannot prepare their own food and obtain it by feeding on producers or other consumers.
Decomposers: Organisms such as bacteria and fungi that break down dead plants, dead animals and wastes into simpler substances. They return nutrients to the soil and make them available again to producers.

Division of consumers

Herbivores: Consumers that feed on plants. Examples: goats and deer.
Carnivores: Consumers that feed on other animals. Examples: tigers and crocodiles.
Omnivores: Consumers that eat both plants and animals. Example: humans.
Parasites: Organisms that live on or inside another organism, called the host, and obtain nutrients from it. Lice are animal parasites. Cuscuta (dodder) is a parasitic plant.

Decomposers help in nutrient recycling and maintain the fertility of the soil.

Classification of ecosystem components

Category	Role / Definition	Examples
Producers (Autotrophs)	Synthesise organic food using sunlight (photosynthesis).	Green plants, algae, cyanobacteria.
Consumers: Herbivores	Feed directly on plants (primary consumers).	Goats, deer.
Consumers: Carnivores and Omnivores	Feed on animals (carnivores) or both plants and animals (omnivores).	Tigers, crocodiles (carnivores); humans (omnivores).
Decomposers	Break down dead organic matter and recycle nutrients into soil.	Bacteria, fungi.

3. Food Chains and Food Webs

A food chain is a linear sequence of organisms through which food, energy and nutrients pass when one organism eats another.

Grass
Producer➜Deer
Herbivore➜Lion
Carnivore

Trophic levels in a food chain

Trophic levels are the successive feeding levels in a food chain. At each consumer level, organisms obtain food and energy from the level below them.

First trophic level: Producers or autotrophs, such as green plants, capture solar energy and convert it into chemical energy stored in food.
Second trophic level: Primary consumers or herbivores, such as deer, feed on producers.
Third trophic level: Secondary consumers or small carnivores, such as foxes, feed on herbivores.
Fourth trophic level: Tertiary consumers or larger carnivores feed on secondary consumers.

Key energy principles in food chains

Base support: Energy captured by producers supports all the higher trophic levels.
Solar energy conversion: Autotrophs convert solar energy into chemical energy stored in organic molecules. This energy is transferred to consumers and is also made available to decomposers through dead organisms and wastes.
Energy loss as heat: At every transfer from one trophic level to the next, a considerable portion of energy is lost to the environment, mainly as heat during respiration and other metabolic activities.
1% solar capture rule: Green plants typically capture and convert about 1% of the sunlight falling on their leaves into chemical energy stored in food.
10% energy flow rule: Only about 10% of the energy or organic matter at one trophic level is generally converted into biomass at the next higher trophic level.
Trophic level limitation: Because usable energy decreases progressively, food chains usually have only three or four major trophic levels.

Remember the 10% rule: Approximately 10% of the energy at any given trophic level is transferred to the next higher level. The remaining energy is lost as heat or used in metabolic processes.

Food web

Food chains in a natural ecosystem are interconnected because most organisms feed on more than one kind of organism. The network of these interconnected food chains is called a food web. Food webs show the complexity of feeding relationships and the movement of energy and materials within an ecosystem.

4. Energy Flow in Ecosystems

Energy flow in an ecosystem has two important characteristics: it is unidirectional and the amount of available energy progressively decreases at successive trophic levels.

1. Unidirectional flow

One-way movement: Energy flows in one direction: from the Sun to producers and then to consumers. Decomposers obtain energy from dead organisms and wastes at all trophic levels.
Non-reversible energy: Energy captured by producers does not return to the Sun. Energy lost as heat cannot be reused by earlier trophic levels.

2. Progressive diminishment

Metabolic energy loss: Usable energy decreases at each trophic level because energy is lost as heat during respiration and other life processes and also leaves the body as waste.
Constraint on food chain length: These energy losses limit the number of trophic levels in a food chain.

Biological magnification

Harmful chemicals used in agriculture, such as certain pesticides, enter the food chain. They are absorbed by plants and accumulate in the bodies of organisms that feed on those plants. The concentration of these non-biodegradable chemicals increases at each trophic level. This is called biological magnification. Their concentration is highest in top consumers, including humans.

Environmental hazard: Biological magnification leads to the maximum accumulation of non-biodegradable toxic chemicals, such as pesticides, in top carnivores and humans at the highest trophic level.

5. How Do Our Activities Affect the Environment?

Human activities such as deforestation, industrial production, the use of synthetic chemicals, improper waste disposal and over-exploitation of natural resources change the composition, structure and functioning of ecosystems. These changes can lead to pollution, loss of biodiversity, soil degradation and climate change.

Ozone layer and how it is getting depleted

Stratospheric shield: The ozone layer is a region of the stratosphere containing a relatively high concentration of ozone (O₃). It absorbs most of the Sun's harmful ultraviolet (UV) radiation. This protective shield reduces UV-related damage such as skin cancer, cataracts and reduced plant productivity.
Ozone vs molecular oxygen: Ozone is a molecule containing three oxygen atoms (O₃). Molecular oxygen (O₂) is essential for aerobic life.
Beneficial vs harmful ozone: Ozone at ground level in the troposphere is a pollutant and can harm human health and vegetation. Ozone in the stratosphere is beneficial because it absorbs UV radiation.

Formation and breakdown of ozone

Ultraviolet radiation splits molecular oxygen into free oxygen atoms, which combine with molecular oxygen to form ozone:

O₂ ──(UV light)──➜ O + O
O₂ + O ──➜ O₃ (Ozone)

Ozone can also be broken down by natural and human-made processes. Synthetic chemicals, especially chlorofluorocarbons (CFCs), release chlorine in the stratosphere and catalyse the destruction of ozone.

Ozone depletion and international response

Decline in ozone levels: From the late 1970s and into the 1980s, observations showed a significant decline in stratospheric ozone levels.
Role of CFCs: The decline was linked to CFCs and other ozone-depleting substances widely used in refrigerants, aerosols and foam-blowing agents.
The Montreal Protocol (1987): An international agreement adopted in 1987 to address this problem. It sought to freeze and then reduce the production and use of CFCs and related chemicals.
Global impact: As a result of the Montreal Protocol and its subsequent amendments, the production of many CFCs has been phased out and safer alternatives have been introduced.

6. Managing the Garbage We Produce

Modern lifestyles and increased consumption generate large quantities of waste. Effective waste management reduces environmental harm, conserves resources and protects human health.

Enzyme specificity: The enzymes of decomposers cannot break down many synthetic materials, such as most plastics. These materials therefore remain in the environment for a long time.
Persistence of synthetic materials: Many man-made materials, especially plastics, resist decomposition and persist in the environment for decades or centuries. They can pollute land and water and create hazards for wildlife and humans.

Types of materials in garbage

Biodegradable wastes

Wastes that can be decomposed by microorganisms.

Examples: Fruit and vegetable peels, paper, cotton, jute, dung and food scraps.

Non-biodegradable wastes

Wastes that cannot be decomposed by microorganisms.

Examples: Plastics, polythene, metals, synthetic fibres, certain pesticides and radioactive wastes.

Principles and methods of waste management

1. Reduce

Minimise the generation of waste at its source. Avoid unnecessary disposable products and excessive packaging.

2. Reuse

Use articles more than once before discarding them. Refillable containers and repaired products are examples.

3. Recycle

Convert waste materials into raw materials for making new products. Paper, glass, metals and some plastics can be recycled.

4. Segregation

Separate biodegradable and non-biodegradable wastes at the source. This makes composting and recycling more efficient.

5. Composting

Decompose organic wastes biologically to produce compost, which can be used as a soil conditioner.

6. Sanitary landfills

Dispose of waste in engineered sites designed to isolate it from the surroundings and reduce pollution. Mainly used for non-recyclable wastes.

7. Controlled incineration

Burn waste under controlled conditions with suitable energy-recovery and pollution-control systems. It is appropriate only for certain types of waste and requires careful control of emissions.

Waste classification and disposal methods

Waste category	Characteristics and action of decomposers	Examples and effective disposal methods
Biodegradable wastes	Broken down into simple substances by microbial enzyme action; eco-friendly.	Peels, paper, cotton, dung and food scraps. Disposal: Composting, biogas generation.
Non-biodegradable wastes	Resist microbial decomposition; persist for decades or centuries.	Plastics, polythene, metals and pesticides. Disposal: Recycling, sanitary landfills, incineration.

7. What You Have Learned – Quick Revision

Ecosystem unity: An ecosystem comprises interacting biotic and abiotic components and functions as a unit.
Primary producers: Producers or autotrophs capture solar energy and form the base of food chains. Consumers and decomposers depend on them directly or indirectly.
Energy transfer efficiency: Green plants convert about 1% of sunlight into chemical energy, and only about 10% of the energy at one trophic level becomes available as biomass at the next level.
Food webs: Food chains are interconnected into food webs, which show the complexity of feeding relationships in ecosystems.
Human impacts: Human activities affect the environment through pollution, resource depletion, habitat destruction and other changes to ecosystems.
Ozone protection: Chemicals such as CFCs have damaged the stratospheric ozone layer. International action, including the Montreal Protocol, has been taken to reduce the use of these substances.
Waste management: Waste can be biodegradable or non-biodegradable. Reduction, reuse, recycling, segregation, composting and sanitary disposal are essential for protecting the environment.
Sustainability: Understanding ecosystems and human impacts helps us design conservation and sustainable-use measures that maintain ecological balance.

Chapter takeaway: Protecting the environment requires understanding ecosystem interactions, conserving resources, preventing pollution and managing waste responsibly.

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Saturday, 7 November 2026

Our Environment Notes