CBSE Notes Class 10 Science Chapter 13 - Our Environment

Our environment includes all living organisms, natural resources, and physical surroundings that interact to support life on Earth. Understanding how plants, animals, microorganisms, and humans depend on one another helps explain the balance of nature and the impact of human activities on ecosystems.

CBSE Notes Class 10 Science Chapter 13 – Our Environment provide clear and exam-oriented explanations of key concepts such as food chains, food webs, trophic levels, biodegradable and non-biodegradable substances, and ecosystem stability. These our environment class 10 notes are designed as quick-revision material, helping CBSE students grasp core ideas easily, strengthen conceptual clarity, and score better in board exams with structured, syllabus-aligned content.

1.0Download CBSE Notes for Class 10 Science Chapter 13: Our Environment - Free PDF!!

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2.0Ecosystems and Their Components

• Ecosystem is the basic unit of ecology and the biotic and abiotic components present in it influence each other. 
• Both the components are essential for the sustenance of life. 
• Ecosystem term was given by Arthur Tansley Ecosystem is a self-sustained unit of living things (plants, animals and decomposers) and their nonliving environment (soil, air and water). 
• Biotic components : The biotic components include all kinds of living organisms with which the organism interacts (all animals, plants, microorganisms). 
• Abiotic components : The abiotic components are the physical factors such as climatic factors (e.g., Air, Water, Temperature, Humidity, Light, Wind, Precipitation etc.).

Biotic (living) components

• The biotic community of an ecosystem includes 3 types of organisms 
• Producers : Those organisms which can prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight in the presence of chlorophyll. e.g., Green plants and certain blue green algae. 
• Consumers : Those organisms which consume food or eat food prepared by producers are called consumers. The consumers depend on producers for food, directly or indirectly. All the animals are consumers.
• Consumers can be further divided into three groups 
• Herbivores - Those animals which eat only plants are called herbivores. e.g., Buffalo, goat, sheep, horse, deer, camel, grasshopper, etc. Since herbivores obtain their food directly from plants or producers therefore herbivores are primary consumers. 
• Carnivores - Those animals which eat only other animals as food are called carnivores or those animals which eat the meat or flesh of other animals are called carnivores. e.g., Lion, tiger, frog, vulture, kingfisher, etc. 
• Omnivores - Those animals which eat both plants and animals, are called omnivores or those animals which eat plant food as well as the meat or flesh of other animals. e.g., Man, dog, crow, sparrow, bear and ant, etc.
• Decomposers -  The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like feces, urine into simpler substances are called decomposers. e.g., Bacteria and fungi.

3.0Food Chains and Food Webs

• Food Chains and Food Webs describe how energy and nutrients flow through living organisms in an ecosystem. A food chain is a series of organisms, each feeding on the one below it, showing a direct and linear transfer of energy. These chains are structured into distinct levels known as trophic levels.
• At the base of every food chain are autotrophs or producers, such as green plants and algae. They convert solar energy into chemical energy through photosynthesis, forming the primary source of energy that supports all life on Earth.
• The second trophic level consists of herbivores, which feed directly on producers. Small carnivores occupy the third trophic level, feeding on herbivores, while larger carnivores form the fourth trophic level, preying on smaller carnivores.
• As energy flows through these trophic levels, a significant portion is lost at each step in the form of heat, respiration, digestion, and reproduction. On average, only about 10% of the energy from one trophic level is transferred to the next. This limited energy transfer explains why food chains rarely extend beyond three or four trophic levels.
• In real ecosystems, organisms do not depend on a single food source. Instead, multiple food chains interconnect to form a food web, which represents a more complex and realistic pattern of energy flow. Food webs increase ecosystem stability, as the availability of alternative food sources helps organisms survive environmental changes or population fluctuations.

4.0Energy Flow and its Unidirectional Nature

• The energy flow through an ecosystem is unidirectional, meaning it moves from producers to consumers and decomposers, never returning to the previous level. 
• Once autotrophs capture energy from sunlight, it is progressively passed on but diminishes at each trophic level. 
• As a result, energy becomes less available as it moves up the food chain.
• In addition to energy loss, harmful chemicals can also travel up the food chain in a process known as biological magnification. 
• Chemicals used in agriculture, such as pesticides, can be absorbed by plants and eventually consumed by animals and humans. 
• Since these chemicals are non-biodegradable, they accumulate in increasing concentrations at each trophic level, posing serious health risks to those at the top, including humans.

Ten Percent law 

• It was put forth by Lindeman (1942). It is also termed as the second law of thermodynamics or law of entropy. 
• According to this law, transfer of energy from one trophic level to another trophic level is never 100 percent. 
• It is so because most of the energy gets lost as heat in the environment during each transfer. On an average, about 10% of energy is actually available to the next trophic level.

5.0Human Impact on the Environment

• Humans are an integral part of the environment, and our activities significantly impact it. 
• Environmental degradation due to pollution, deforestation, and industrial waste has been well-documented. 

Ozone Layer Depletion

• This is a protective shield in the upper atmosphere, and is critical in blocking the Sun's harmful ultraviolet (UV) radiation. 
• UV radiation can cause severe health issues, including skin cancer. 
• The ozone layer is formed when UV radiation reacts with oxygen molecules (O2), breaking them apart into individual oxygen atoms. These atoms combine with other oxygen molecules to form ozone (O3).
• However, human-made chemicals, especially chlorofluorocarbons (CFCs), have caused significant depletion of the ozone layer. 
• CFCs, used in refrigeration and fire extinguishers, release chlorine atoms when they reach the upper atmosphere. They react with ozone and break it down. 
• Recognising the threat posed by CFCs, the international community agreed to limit their production under the Montreal Protocol in 1987. Since then, efforts have been made to phase out CFCs and manufacture CFC-free products to protect the ozone layer.

Waste Disposal and Its Challenges

• Waste disposal is another major environmental challenge. We produce vast amounts of waste daily, including non-biodegradable materials like plastics. 
• While bacteria and fungi break down biodegradable materials into simpler substances that nature can reuse, non-biodegradable materials persist in the environment for a long time, often harming ecosystems.
• For instance, plastic waste accumulates in landfills and water bodies, posing risks to wildlife. 
• Animals may ingest plastics, mistaking them for food, which can lead to injury or death. 
• Moreover, non-biodegradable materials can release toxic substances over time, polluting soil and water sources.

6.0Detailed CBSE Class 10 Science Chapter 13 – Key Notes

Environment

"Everything which surrounds and influences the organism directly or indirectly is included in the environment."

The environment is the sum total of all living and non-living factors that surround and influence an organism.

Biotic components

The biotic components include all kinds of living organisms with which the organism interacts (all animals, plants, micro-organisms).

Abiotic components

The abiotic components are the physical factors such as climatic factors.
(e.g. Air, Water, Temperature, Humidity, Light, Wind, Precipitation etc.).

NOTE

Ecology is the study of interrelationships of organisms between the biotic and abiotic components of their environment.

The 'Ecology' term was coined by Ernst Haeckel (1868).

Ecosystem

• Ecosystem is the basic unit of ecology and the biotic and abiotic components present in it influence each other.

Both the components are essential for the sustenance of life.

• Ecosystem term was given by Arthur Tansley.
• Ecosystem is the structural and functional unit of biosphere.

It is an open system with respect to energy and depend on sunlight which is the ultimate source of energy to biosphere.

Types of ecosystem: In the biosphere, ecosystem may be classified on the basis of their nature, duration and size.

Natural ecosystem

These ecosystem operate in the nature by themselves without any human interference. Common examples of natural ecosystem are a pond, a lake, a meadow, a desert, a grassland, a forest and an ocean, etc.

Artificial ecosystem

These are maintained by man and hence, are also termed as man-made ecosystem. Common examples are croplands, orchards, gardens, aquarium etc.

NOTE

On the basis of size, ecosystem may be classified as:
(1) Small ecosystem (flowerpot, water in a dish).
(2) Large ecosystem (forest, desert, ocean).

Components of Ecosystem

The various components of an ecosystem may be grouped into two main types.

Abiotic (non-living) components

01 - Inorganic Substance
02 - Physical Environment
03 - Climatic Factors

NOTE

On the basis of duration, ecosystem may be classified as:
(1) Temporary ecosystem (short lived ecosystem, rainfed pond).
(2) Permanent ecosystem (a lake, a forest, a desert).

Biotic (living) components

Producers: Those organisms which can prepare their own food from simple inorganic substances like carbon dioxide and water by using sunlight in the presence of chlorophyll. e.g., Green plants and certain blue green algae.

Consumers: Those organisms which consume food or eat food prepared by producers are called consumers. The consumers depends on producers for food, directly or indirectly. All the animals are consumers.

Consumers:

Herbivores (primary consumers)
Those animals which eat only plants are called herbivores. e.g., Buffalo, goat, sheep, horse, deer, etc.

 Carnivores (secondary consumers)
Those animals which eat only other animals as food are called carnivores e.g., Lion, tiger, frog, vulture, etc.

Omnivores
Those animals which eat both plants and animals are called omnivores e.g., Man, dog, crow, sparrow, bear etc.

Decomposers: The micro-organisms which break down the complex organic compounds present in dead organisms like dead plants and animals and their products like faeces, urine into simpler substances are called decomposers. e.g., Bacteria and fungi.

Importance of decomposers

• Acts as cleansing agents of the environment.
• Help in recycling the material in biosphere thus, play a vital role in biogeochemical or nutrient cycles.
• Maintain the fertility of soil.
• If there were no decomposers, the earth would have been a heap of dead organisms.

Food Chain

• It is a sequence of organisms through which energy is transferred in the form of food by the process of one organism consuming the other.

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

Maize (producer) → Locust (primary consumer) → Lizard (secondary consumer) → Snake (tertiary consumer)

As the food chain goes on, the energy transferred to the next organism decreases.

NOTE

In a food chain, there is unidirectional flow of energy from sun to producers and subsequently to series of different types of consumers.

Trophic levels:

The distinct sequential steps in the food chain where transfer of energy occurs are referred to as trophic levels.

• Plants → Men (Two trophic levels)
• Plants → Goat → Men (Three trophic levels)
• Plants → Mice → Snakes → Peacocks (Four trophic levels)
• Plants → Insects → Frogs → Snakes
• Plants → Grasshoppers → Frogs → Snakes → Hawks (Five trophic levels)
• Plants → Grasshoppers → Frogs → Eagles (Five trophic levels)

Characteristics of food chain

• Involves nutritive interaction.
• Proceeds in progressive in straight line.
• Usually there are 3-4 trophic levels.
• Omnivores occupy different positions.
• 80-90% energy is lost as heat at each trophic level.
• Unidirectional flow of energy.

Types of food chains

Grazing food chains

Detritus food chain

• Detritivores are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal plants as well as faeces) e.g., invertebrates like earthworm, insects such as mites, beetles, butterflies.
• Kites and vultures feeds on dead organisms and therefore, they acts as scavengers.
• There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.

Significance of food chains

The significance of food chains can be seen with the help of following functions: –

• It is a means of transfer of energy from one trophic level to another.
• It provides information about the living components of an ecosystem.
• A natural method of population control due to different nutritional habits.
• It enables recyling of resources via decomposition.

Food Web

The inter - connected food chains operating in an ecosystem which establish a network of feeding relationships between various species is called a food web.

A food web provides alternative pathways of food availability.

Unlike food chains, food webs are never straight.

Difference between Food Chain and Food Web

NOTE

• In an ecosystem, generally the producers are maximum in number.
• As we move along the chain, the number of individuals at each trophic level decreases.

Transfer of energy in ecosystem

Ten Percent law

• It was put forth by Lindeman (1942).
• Also termed as second law of thermodynamics or law of entropy.
• According to this law, transfer of energy from one trophic level to other trophic level is never 100 percent.
• It is so because most of energy gets lost as heat in the environment during each transfer. On an average, about 10% of energy is actually available to the next trophic level.

Flow (Transfer) of energy in an ecosystem

• The ultimate source of entire energy, used by living organisms, is the Sun.
• In a community, each food chain represents stepwise transfer of food (energy).
• Of the total solar radiations falling on the earth, only about 1% are captured by green plants in a terrestrial ecosystem and converted into food energy by photosynthesis. This energy is stored as chemical energy of food.
• When green plants are eaten by herbivores (primary consumers), a great energy is lost as heat to the environment in accordance with the second law of thermodynamics.
• Since so little energy is available for the next level of consumers, food chains generally consist of only three or four steps. The loss of energy at each step is so great that very little usable energy remains after four trophic levels.
• The flow of energy is unidirectional because the energy that is captured by the autotrophs does not revert back to the solar input and the energy which passes to the herbivores does not come back to autotrophs.
• Several pesticides and other chemicals are used to protect our crops from diseases and pests. These chemicals are either washed down into the soil or into the water bodies.
• From the soil, these are absorbed by the plants along with water and minerals, and from the water bodies these are taken up by aquatic plants and animals. This is one of the ways in which they enter the food chain.
• These chemicals are not degradable, these get accumulated progressively at each trophic level. As human beings occupy the top level in any food chain, the maximum concentration of these chemicals get accumulated in our bodies. This phenomenon is known as biological magnification.
• The food grains such as wheat and rice, vegetables and fruits, and even meat, contain varying amounts of pesticide residues. They cannot always be removed by washing or other means.
• The phenomenon that involves progressive increase in concentration of harmful non-biodegradable chemical at different trophic levels in a food chain is called biomagnification.

NOTE

Biodegradable waste can also be used in biogas plants to generate biogas and manure. Biogas is a cheap source of fuel, and manure, a cheap fertilizer.

How do our activities affect the environment?

There are two major environmental problems:
(a) Solid waste and their disposal
(b) Depletion of ozone layer.

Solid waste and their disposal

Solid waste generally comes from residences, cattle sheds, industries, agricultural fields and many other places.

There are two types of solid wastes:

NOTE

The use of a lot of clay for making millions of kulhads daily led to the loss of fertile top soil from fields. So, the practice of using kulhads has been discontinued.

Modes of waste disposal

Some prominent methods of waste disposal are:

Land fills

In urban areas, majority of the solid wastes are buried in low lying areas to level the uneven surface of land. This method of waste disposal is commonly called land fills.

Recycling of wastes

• Number of solid wastes can be recycled by sending them to respective recycling units.
• Paper is sent for recycling into special paper mills; broken plastic (e.g., plastic bags, buckets, bowls, dishes, mugs, discs, etc.) are sent to plastic processing factories.

Preparation of compost

Kitchen waste can be converted into compost and used as manure.

Incineration

It is the process of burning of substances at high temperature (usually more than 1000°C) and ultimately converting them into ashes. This ash can be disposed off by land fills.

Ozone layer Depletion

Ozone (O₃) is a molecule formed by three atoms of oxygen. Ozone, is a deadly poison. It is formed in atmosphere by the action of ultraviolet radiation on oxygen gas.

The high energy ultraviolet radiation (UV radiation) coming from the sun splits oxygen gas into free oxygen atoms.

The free oxygen atoms are highly reactive. One oxygen atom reacts with an oxygen molecule to form an ozone molecule.

O + O₂ --------------------> O₃(Ozone molecule)

Ozone layer

• The amount of ozone in the atmosphere began to drop sharply in the 1980s. The thinning of ozone layer is commonly called ozone depletion.
• The ozone layer is very important for the existence of life on earth because it absorbs most of the harmful ultraviolet radiation coming from the sun and prevents them from reaching the earth. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun.
• Ozone is being depleted by air pollutants. Chlorofluorocarbons (CFCs) are air pollutants that are mainly responsible for the depletion of ozone layer in the stratosphere.
• Chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. Besides, methane (CH₄) and oxides of nitrogen (NOₓ) also cause destruction of ozone.
• In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels. It is now mandatory for all the manufacturing companies to make CFC-free refrigerators throughout the world.

Effect of ozone depletion

• Ultraviolet radiation is highly damaging to organisms. It cause skin cancer in human beings.
• These cause damage to eyes and also cause increased incidence of cataract disease in eyes.
• These cause damage to immune system by lowering the body's resistance to diseases.

Steps to be taken to prevent depletion of ozone layer are

• Reduce the use of chlorofluorocarbon in refrigerators, air conditioners, etc.
• Avoid using CFCs in aerosols, sprays, etc.
• Complete freeze on large scale CFC production.

7.0Benefits of CBSE Notes for Class 10 Science Chapter 13 - Our Environment

• Building a Strong Foundation: Understanding the concepts in "Our Environment" is crucial for future science studies, and these notes can help build a strong foundation.
• Clarity on Definitions and Terms: Notes often provide clear and concise definitions of important scientific terms used in the chapter.
• Understanding Relationships: They can help you understand the interrelationships between different components of the environment and human impact.
• Focus on Important Diagrams and Processes: CBSE Notes may emphasise key diagrams and the steps involved in various environmental processes.
• Supplement to Textbook: They act as a valuable supplement to your textbook, offering an alternative way to learn and reinforce the material.
• Increased Confidence: Having well-prepared notes can boost your confidence for tests and exams.

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