Chapter – 13

Our Environment

In this post we have given the detailed notes of class 10 Science Chapter 13 (Our Environment) in English. These notes are useful for the students who are going to appear in class 10 board exams.

Chapter 13: Our Environment

What is Environment? 🌍

Environment refers to everything that surrounds us — all the living and non-living things with which we interact. It includes all the organisms (biotic components) as well as physical factors like air, water, soil, and sunlight (abiotic components) that make up our surroundings.

Biotic and Abiotic Components 🌱🪨

• Biotic components: All living organisms present in an environment — plants, animals, and microorganisms.
• Abiotic components: All the non-living physical factors of an environment — air, water, soil, temperature, sunlight, and minerals.

Ecosystem 🌳

All the organisms in an area, together with the abiotic (physical) factors with which they interact, make up an ecosystem. In other words, an ecosystem is a functional unit of nature where living organisms interact with each other as well as with their surrounding physical environment.

Examples: A garden, a pond, a lake, a forest, a crop field, and a river.

For instance, in a garden, we find many biotic components such as grass, trees, plants, flowers, frogs, insects, and birds, along with abiotic components like air, soil, and temperature. So a garden is an ecosystem.

Types of Ecosystem

• (i) Natural Ecosystem: Ecosystems that exist in nature without human interference. Examples: Forests, ponds, rivers, and lakes.
• (ii) Artificial (Man-made) Ecosystem: Ecosystems created and maintained by humans. Examples: Gardens, crop fields, and aquariums.

Classification of Organisms Based on Nutrition 🍃

On the basis of how they obtain their food/energy, organisms in an ecosystem are classified into three groups:

• Producers
• Consumers
• Decomposers

1) Producers 🌿

Organisms that make their own food using sunlight and inorganic substances (like carbon dioxide and water) through the process of photosynthesis are called producers. All green plants and blue-green algae (cyanobacteria) that carry out photosynthesis are producers. They form the base of every food chain since they trap the sun’s energy and convert it into chemical energy stored in food.

2) Consumers 🐐🦁

Organisms that depend directly or indirectly on producers for their food are called consumers. They cannot make their own food and must obtain it from other organisms.

Consumers are of the following four types:

• Herbivores: Organisms that depend only on plants for food. Examples: Cow, deer, goat, and rabbit.
• Carnivores: Organisms that eat only the flesh of other animals. Examples: Lion, tiger, and cheetah.
• Parasites: Organisms that do not make their own food but obtain nourishment by living in or on the body of another organism (the host), often harming it. Examples: Plasmodium, tapeworm, and lice.
• Omnivores: Organisms that eat both plants and animal flesh. Examples: Crow and dog.

3) Decomposers 🍄

Organisms that break down the complex organic substances present in the dead remains of plants and animals into simpler inorganic substances are called decomposers. They are also called scavengers/saprotrophs of the ecosystem. Examples: Bacteria and fungi.

Decomposers play an important role in the environment:

• They break down biodegradable waste into simpler substances.
• They release nutrients back into the soil, making it more fertile, and allow those nutrients to be reused by producers.

Food Chain 🔗

The series of organisms in which each organism feeds on the one before it, forming a chain, and each step forms one trophic (nutritional) level, is called a food chain. Different organisms taking part at various biological levels form this series/chain.

Examples:

• (a) Grass ⇒ Deer ⇒ Tiger
• (b) Grass ⇒ Grasshopper ⇒ Frog ⇒ Snake ⇒ Vulture/Eagle
• (c) Green plants ⇒ Scorpion ⇒ Fish ⇒ Heron

Food Web 🕸️

Different food chains in an ecosystem vary greatly in length and complexity. Usually, an organism is eaten by two or more other kinds of organisms, which in turn are eaten by several other organisms. So, instead of a straight-line food chain, food relationships among organisms become interconnected and branched. Such an interconnected network of many food chains in an ecosystem is called a food web.

Difference between Food Chain and Food Web

Food Chain

• Organisms at various trophic levels form a single, linear sequence.
• Energy flows in a single, linear direction.
• A food chain usually consists of only three or four steps.

Food Web

• Several interconnected food chains together form a web.
• Energy flow is branched, not linear.
• It looks like a web made up of many interlinked steps/chains.

Flow of Energy in an Ecosystem ⚡

In a terrestrial ecosystem, green plants (producers) capture only about 1% of the solar energy that falls on their leaves and convert it into food energy through photosynthesis.

The 10% Law of energy flow: Only about 10% of the energy available at one trophic level is transferred to the next trophic level, while the remaining 90% is used up for the organism’s own life processes (respiration, movement, growth) or is lost as heat. This is known as the 10% law of energy flow.

Example of trophic levels:

Producer ⇒ Primary Consumer ⇒ Secondary Consumer ⇒ Tertiary Consumer

Suppose the producers receive 1000 J of energy (1% of the sunlight falling on them). Applying the 10% law:

1000 J ⇒ 10% of 1000 J = 100 J ⇒ 10% of 100 J = 10 J ⇒ 10% of 10 J = 1 J

Why food chains generally have only 3–4 trophic levels: Because such a small fraction of energy is transferred at each step, very little usable energy remains available for the next level. After about four trophic levels, the amount of energy left is too small to support another level of consumers.

Why energy flow in a food chain is unidirectional (linear) and not cyclic: The solar energy captured by producers is converted into chemical energy and is never converted back into solar energy. Similarly, energy transferred to herbivores can never go back to the producers. Since energy moves progressively from one trophic level to the next and is not available to the previous level, the flow of energy is always in one direction (unidirectional), not cyclic. By the time energy reaches the last consumer, only a negligible amount remains, and it cannot be reused.

Role of decomposers in the food chain: Decomposers are microorganisms that act on the dead and decaying remains of producers and consumers and break them down into simple inorganic compounds. They absorb some of these products themselves, while the rest are released back into the environment for reuse by producers. Their role in the ecosystem is important because:

• They clean up the environment by breaking down biological waste into simpler substances.
• They replenish nutrients in the soil, making it fertile.

Biological Magnification (Biomagnification) 🐟☠️

As organisms feed on one another in a food chain, certain harmful chemical substances (like pesticides and industrial chemicals) that enter the food chain get passed on from one organism to the next. Since these chemicals are non-biodegradable, they keep accumulating at each trophic level, and their concentration increases progressively as we move up the food chain — this is called biological magnification. In other words, the increasing concentration of harmful chemicals at successive trophic levels of a food chain is known as biomagnification. Human beings, being at the top of most food chains, tend to have the highest concentration of these harmful chemicals in their bodies.

How Do Our Activities Affect the Environment? 🏭

The substances or wastes produced by living organisms and human activities are of two types, depending on whether or not they can be broken down by biological processes.

1) Biodegradable Substances 🍂

Substances that can be broken down into simpler, harmless substances by biological processes (through the action of decomposers) are called biodegradable substances.

Examples: Cow dung, cotton cloth, jute, paper, fruit and vegetable peels, and animal waste — all organic substances derived from living organisms are biodegradable.

Properties of biodegradable substances:

• They are chemically active/reactive in nature.
• They undergo biological decomposition.
• They remain in the environment for only a short time.
• They do not cause much harm to the environment.

2) Non-biodegradable Substances 🧴

Substances that cannot be broken down by biological processes are called non-biodegradable substances.

Examples: Plastic, polythene, synthetic fibres, metals, radioactive waste, and certain chemicals (like DDT and other fertilizers/pesticides) that are unreactive and do not decompose.

Properties of non-biodegradable substances:

• They are chemically inactive/unreactive in nature.
• They do not undergo biological decomposition.
• They remain in the environment for a very long time.
• They cause considerable harm to other components of the environment.

The Ozone Layer and How It Is Getting Depleted ☀️🛡️

Ozone (O₃) is a molecule formed by three atoms of oxygen. While oxygen (O₂) is essential for the respiration of living organisms, ozone is a deadly poison at the ground level. However, at higher levels of the atmosphere (the stratosphere), ozone performs an essential function — it shields the surface of the Earth from the sun’s harmful ultraviolet (UV) radiation.

UV radiation is dangerous because it can cause skin cancer in humans, damage the eyes, and harm crops and other living organisms. The ozone layer acts as a protective umbrella that absorbs most of this harmful UV radiation and prevents it from reaching the Earth’s surface.

Depletion of the ozone layer:

• The major cause of ozone layer depletion is the release of Chlorofluorocarbons (CFCs) — chemicals used in refrigerators, air conditioners, aerosol sprays, and fire extinguishers — into the atmosphere.
• CFC molecules break down ozone molecules in the stratosphere, thinning the ozone layer and creating what is commonly called the “ozone hole.”
• A thinner ozone layer allows more harmful UV radiation to reach the Earth, increasing the risk of skin diseases (including skin cancer), eye cataracts, and damage to the immune system.

Steps taken to control ozone depletion: In 1987, the United Nations Environment Programme (UNEP) reached an agreement, known as the Montreal Protocol, to freeze the production and use of CFCs at 1986 levels, in order to protect the ozone layer.

Managing the Garbage We Produce 🗑️

With growing population and changing lifestyles, the amount of waste generated by human activities has increased enormously, and its proper disposal has become a major environmental challenge.

Disposal of biodegradable waste:

• Biodegradable waste can be safely disposed of by composting — allowing decomposers to break it down naturally, converting it into manure that enriches the soil.
• Vermicomposting (using earthworms) is another effective and eco-friendly way of converting kitchen and garden waste into useful compost.

Disposal of non-biodegradable waste:

• Since non-biodegradable substances like plastics and metals are not broken down by decomposers, they accumulate in the environment and cause pollution of soil and water.
• Such waste should be reduced at the source, reused wherever possible, and recycled instead of being dumped or burnt (burning produces harmful gases and adds to air pollution).
• Practising the 3 R’s — Reduce, Reuse, and Recycle — helps in managing non-biodegradable waste responsibly and reduces the burden on the environment.

Why proper waste management is important: Improper disposal of both biodegradable and non-biodegradable waste disturbs the natural balance of ecosystems, pollutes soil, water, and air, and can enter food chains, ultimately affecting human health through biomagnification.

Key Points to Remember

• The environment consists of biotic (living) and abiotic (non-living) components.
• An ecosystem is formed by the interaction of biotic and abiotic components in an area; it can be natural (forest, pond) or artificial (garden, crop field).
• Organisms are classified as producers, consumers (herbivores, carnivores, parasites, omnivores), and decomposers based on their mode of nutrition.
• A food chain is a linear sequence of organisms feeding on one another; a food web is an interconnected network of many food chains.
• Only about 10% of energy is transferred from one trophic level to the next (the 10% law); this is why food chains usually have only 3–4 trophic levels.
• Energy flow in a food chain is always unidirectional (linear), never cyclic.
• Biological magnification is the increase in concentration of harmful, non-biodegradable chemicals at successive trophic levels.
• Biodegradable substances (like cow dung and paper) decompose naturally; non-biodegradable substances (like plastic and DDT) do not, and persist in the environment for long periods.
• Depletion of the protective ozone layer, mainly caused by CFCs, allows harmful UV radiation to reach the Earth’s surface; the Montreal Protocol (1987) aims to control CFC production.
• Practising the 3 R’s — Reduce, Reuse, and Recycle — along with composting and vermicomposting helps manage waste and protect the environment.

We hope that class 10 Science Chapter 13 (Our Environment) notes in English helped you. If you have any query about class 10 Science Chapter 13 (Our Environment) notes in English or about any other notes of class 10 Science in English, so you can comment below. We will reach you as soon as possible…