Students should read Chapter 15 Our Environment Class 10 Science Notes provided below. These notes have been prepared based on the latest syllabus and books issued by NCERT, CBSE and KVS. These important revision notes will be really useful for students to understand the important topics given in the chapter Our Environment in Class 10 Science. We have provided class 10 science notes for all chapters.

Revision Notes Chapter 15 Our Environment Class 10 Science

Chapter 15 Our Environment is an important chapter in Class 10 Science. The following notes will help you to understand and easily learn all important points to help you score more marks.

Important terms & concepts

Environment: It is the sum total of all external conditions and influences that affect the life and development of an organism, i.e., the environment includes all the physical or abiotic and biological or biotic factors.

Biodegradable Substances are those substances which are broken down into simpler, harmless substances in nature in due course of time by the biological processes such as action of microorganisms.
Examples: Domestic waste products, urine and fecal matter, sewage, agricultural residue, paper, wood, cloth and cattle dung.

Non-biodegradable Substances: are those substances which cannot be broken down into simpler, harmless substances in nature. These substances may be in solid, liquid or gaseous form and may be inert and accumulate in the environments or may concentrate in the food chain and harm the organisms.
Examples: DDT, plastics, polythene bags, insecticides, pesticides, mercury, lead, arsenic, aluminium, radioactive waste, etc.

Ecosystem: It is the structural and functional unit of biosphere, comprising of all the interacting organisms in an area together with the non-living constituents of the environment. Thus, and ecosystem is a selfsustainingsystem where energy and matter are exchanged between living and non-living components. 

Biotic Component: It means the living organisms of the environment-plants, animals, human beings and microorganisms like bacteria and fungi, which are distinguished on the basis of their nutritional relationship.

Abiotic Component: It means the non-living part of the environment – air, water, soil and minerals. The climatic or physical factors such as sunlight, temperature, rainfall, humidity, pressure and wind are a part ofthe abiotic environment. 

Types of Ecosystems: Ecosystems are of two types
I) Natural Ecosystem: The natural ecosystems are terrestrial (land) as well as aquatic. The common examples of land ecosystem are forests, grasslands, deserts, etc. The common examples of aquatic ecosystem are ponds, lakes, rivers, ocean, etc.
II) Artificial Ecosystems: The artificial ecosystems are made by human beings. The common examples of artificial ecosystems are crop fields, gardens, parks, aquarium etc.

Producers: Those organisms which produce food by photosynthesis, i.e., organisms which can make organic compounds like sugar and starch from inorganic substance using the radiant energy of the sin in presence of chlorophyll.
Examples: All green plants and certain blue-green algae are called producers.

Consumers: those organisms which depend upon the producers for food, either directly or indirectly by feeding on other consumers for their sustenance. Consumers therefore feed upon those below it in a food chain and are called heterotrophs. It can be classified into primary consumer or herbivores, carnivores, omnivores and parasites.
Herbivores are the animals that consume or eat vegetation or plants, e.g., cows, horses.
Carnivores are the animals that eat meat of other animals, e.g., tigers, wolves.
Omnivores are the animals that eat both plants and animals, e.g., humans, cockroaches.
Parasites are those organisms that live on (ectoparasites) or in (endoparasites) the body of another organism, e.g., host from which it obtains its nutrients, e.g., parasites of man includes fleas and lice (ectoparasites) various protozoans (endoparasites) and tapeworms.

Decomposers: They are those microorganisms that obtain energy from the chemical breakdown of dead organisms or animals or plant wastes. These microorganisms are the decomposers as they breakdown the complex organic substances into simple inorganic substances that go into the soil and are used up once more by the plants.
Examples: Bacteria and Fungi.

Food web: Network of various food chains which are interconnected at various trophic levels.
Example: Grass may be eaten by grasshopper as well as rabbit or cattle and each of these herbivores may be eaten by many carnivores such as frog, bird or tiger depending on their food habits.

Food Chain: It is the sequence of organisms through which energy is transferred in the form by the process of one organism consuming the other. It shows the relationship of producer and consumer, i.e., ‘who eats whom’. Thus it is a series of organisms taking part at various biotic levels from the producer and ends in consumer.

A simple generalized food chain operating in an ecosystem is as follows:
Producers   Herbivores  Carnivores
Example of food chains:
I) Food chain in forest or grassland ecosystems:
  Grass      Grasshopper     Frog          Snake          Eagle
(Producer) (Herbivore)  (Carnivore) (Carnivore) (Top Carnivore)

II) Food chain in aquatic ecosystems:
  Phytoplankton  Zooplankton  Crustacean    Fish            Crane
(Producer)         (Herbivore)   (Carnivore) (Carnivore) (Top Carnivore)

Trophic Levels: These are the various steps or levels in the food chain where transfer of food or energy takes place. The producers or autotrophs are the first trophic level, the herbivores or primary consumers are the second trophic level, the carnivores or secondary consumers are the third trophic level and the large carnivores or tertiary consumers are the fourth trophic level of the food chain.

Significance of Food Chain:
• The study of food chain helps in understanding food relationships and interactions among various organisms in an ecosystem.
• With such studies one can follow the basic mechanism of transfer of food energy and nutrients through various components of nature.
• One can also understand the movement of toxic substances in an ecosystem and the problem of their biological magnification.

Flow of Energy: The flow of energy through different steps in the food chain is unidirectional. This means that energy captured by autotrophs does not revert back to the solar input and it passes to the herbivores.
It moves progressively through various trophic levels.
• Green plants capture 1% of energy of the sunlight that falls on their leaves and convert it into food energy.
• When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment. On an average 10% of food eaten is turned into its own body and made available for next level of consumers.
• Thus, 10% can be taken as average value, the amount of organic matter present at each step and reaches the next level of consumers.
• As very less energy is available for next level of consumer, food chain consists of only three or four steps. The loss of energy at each step is so great that very little energy remains after four trophic levels.
• There are a greater number of individuals at lower trophic level, i.e., at the producer level of the ecosystem.
• In an ecosystem, the Sun’s energy is transformed by producers into chemical energy by the process of photosynthesis.
• In herbivores and carnivores this energy is then transformed further at various trophic levels.
• The chemical energy is transformed into mechanical energy and heat.

• Thus energy flows from sun through producers to consumers in a single direction only.
• So, there is maximum energy at the producer level and further the energy goes on decreasing. The herbivores get more energy with food than carnivores at third and fourth trophic levels.

Progressive Decline in the Amount of Energy:
• At every trophic level large amount of energy is lost for maintain metabolic activities and lost as heat.
• The amount of heat lost is generally 90% and the amount of energy retained is 10% by every trophic level.
• So, only 10% energy is available from previous trophic level to the next.

• The decline in energy level leads to
i. Lesser number of organisms in each trophic level.
ii. Limited number of trophic level in food chains.

Pesticide: It refers to a chemical that is used to kill a pest organism which includes insecticides (for killing the insects), weedicides (for killing the weeds), fungicides (for killing fungi), nematicides (for killing nematodes) and rodenticides (for killing rodents).

Pest: any destructive organism that caused great economic damage by destroying crop plant are called pests. Example—Weeds, insects, mites, nematodes, etc.

Biological Magnification: It refers to the process of increase in the concentration of a toxic chemical with increasing trophic level in a food chain.
• Harmful or poisonous substance such as DDT sprinkled to kill pests on plants enters the food chain.
• As human beings occupy the top level in any food chain, the maximum concentration of harmful chemicals gets accumulated in the body, the phenomenon of which is known as biological magnification.

Accumulation of Harmful Chemicals is Food Chain: Some poisonous chemicals enter out bodies through the food chain.
• It is by the use of several pesticides and other chemicals for crop protection and storage, etc.
• The plants absorb these harmful chemicals from soil along with water and minerals.
• They enter the food chain in producer level and then transferred to next trophic levels.
• The highest levels get more of these chemicals.
    Water  →       Planktons                  → Fish
            (Aquatic plants and animals)

Effects of Human Activities on Environment: Changes in the environment affect us and our activities change the environment around us. There exists a great interrelationship between man and environment where both influence each other. When the environment is polluted beyond the capacity of cleaning agents of nature, ecological balance is lost and the environment becomes polluted.
Our activities pollute the environment in various ways and some of the environmental problems are depletion of ozone layer and disposal of waste.

Ozone: Ozone (O₃) is an isotope of oxygen, i.e., it is a molecule formed by three atoms of oxygen.

• Ozone exists in the so-called ozone layer of the stratosphere.
• Ozone at higher levels of atmosphere is a product of UV radiation action on oxygen (O₂) molecule.
• Ozone performs an essential function of shielding the surface of the earth from ultraviolet radiation of the sun.

Ozone Layer: It is a layer of the earth’s atmosphere in which most of the atmosphere’s ozone is concentrated.
• Ozone layer protects the earth from harmful radiation s like high energy ultraviolet radiations from passing
through it. This property gives it an important function of protecting the biosphere.

• In this layer most of the sun’s ultraviolet radiation is absorbed by the ozone molecules, causing a rise in the temperature of the stratosphere.

• The use of chemicals like CFCs has endangered the ozone layer.

CFCs (Chlorofluorocarbons): Compounds obtained by replacing the hydrogen atoms of hydrocarbons by chlorine and fluorine atoms.
• Their stability at high temperature makes them suitable for a variety of uses such as in aerosols and refrigerator coolants. They are often known as freons.
• CFCs are very stable and are found to persist in the atmosphere. They do not degrade easily and rise to the stratosphere, where they are broken down by UV radiation resulting attack on the ozone molecules damaging the ozone umbrella of earth.

Depletion of Ozone Layer: There are several reasons for depletion of ozone layer.
• The foremost is the use of chlorofluorocarbons (CFCs). The other factor responsible for ozone destruction is the pollutant nitrogen monoxide (NO).
• When the harmful chemicals like chlorofluorocarbons (CFCs) are released into the air, it accumulates in the upper atmosphere and reacts with ozone resulting in reduction in thickness of the ozone layer.
• Thus the ozone layer in the atmosphere becomes thinner and gets depleted allowing more ultraviolet rays to pass through it.
• The Antarctic hole in ozone layer is caused due to chlorine molecules present in chlorofluorocarbons (CFCs) that are used by human beings.

Probable Damages due to Ozone Layer Depletion: Due to Ozone layer depletion. Ultraviolet rays reach earth and cause certain ill-effects which are bad for us and for crops.
• Exposure to UV rays can lead to greater incidence of skin cancer, cataracts or other damages to the eye and immune deficiency.
• An excess of ultraviolet light decrease crop yield and reduce population of phytoplankton, zooplankton and certain fish larvae that are important constituents of aquatic food chains.
• It may also disturb global rainfall, causing ecological disturbances and bring about reduction in global food supplies.

Garbage management:
• More quantity of waste material is generated due to the improvement of out day to day lifestyle.
• Nowadays, more and more disposable items are used due to change in our life style.
• Changes in packaging have resulted much of our non-biodegradable waste.
• Proper method of garbage disposal by segregating biodegradable, non-biodegradable and recycling material to be used.

Replacement of Non-biodegradable Waste by biodegradable Waste an Examples:
• Few years back, tea was served in trains in reusable glasses.
• For hygienic reasons glasses were replaced by disposable plastic cups.
• But disposal of these cups were a major environmental challenge.
• Plastic cups were then replaced by disposable clay but making of these cups in large scale had resulted loss of fertile top soil.
• Now, disposable paper-cups are used which are biodegradable.