Home TNPSC General-Blogs Class X- Science Chapter 15: Our Environment-Notes

Class X- Science Chapter 15: Our Environment-Notes



The environment includes our physical surroundings like air (or atmosphere), water bodies, soil (land and all the organisms such as plants, animals, human beings and micro-organisms like bacteria and fungi (called decomposers). The waste materials produced by the various activities of man and animals are poisonous to some extent and can be divided into two main groups

  1. Biodegradable Wastes: Substances that are broken down by the biological processes are said to be biodegradable. These substances are decomposed through the actions of fungi, bacteria, and other living organisms. Temperature and sunlight also play an important role in the decomposition of biodegradable substances.

Examples: Food waste, trees leaves, urine and fecal matter, sewage agricultural residue, paper, wood, cloth, cow-dung etc.

  1. Non-Biodegradable Wastes: Substances that are not broken down by biological processes. These substances may be in solid, liquid or gaseous form. These substances are inert and simply persist in the environment for a long time or may harm the various members of the ecosystem.

Examples: These includes DDT (Di-chloro-di phenyl trichloroethane-in-pheneyle the choro ethane), insecticides, pesticides, mercury, lead, arsenic aluminium, plastics, polythene bags, glass, radioactive wastes. These non-biodegradable wastes are major pollutants of the environment.


Harmful effects of biodegradable and Non-Biodegradable Substance

  • The waste destroys the natural beauty and our surroundings become dirty.
  • Decomposition of these wastes results in the production of a foul smell, which spreads to the surrounding areas.
  • These wastes may also block the drains creating pools of waste, which becomes the breeding sites of mosquitoes. The latter is the carrier of diseases like malaria and dengue.

Difference between Biodegradable and Non-Biodegradable wastes

S.No Biodegradable wastes Non- Biodegradable wastes
1 The wastes are broken down naturally by microbial action. The wastes are not broken down by the microbes.
2 Biodegradation forms harmless and non-poisonous products. No such action is possible.
3 They release raw materials back to nature. They do not release raw materials.
4 They pollute the environment only when they are produced in quantity beyond the capacity of the environment to degrade them. Non-biodegradable wastes pollute the environment even in small quantity.
5 Bio-concentration does not occur. Bio-concentration or biomagnifications occurs when wastes enter food chains.
6 Recycling is possible both naturally and through human efforts. Recycling is possible only through human efforts.


Ecosystem: An ecosystem is a self-contained unit of living things (plants, animals and decomposers), and their non-living environment (soil, air and water).

Example:  forest, a pond, a lake, green land etc.

In an ecosystem, energy and matter are continuously exchanged between living and non¬living components. An ecosystem can be both natural and man-made. Some examples of natural ecosystems are grassland, forest, sea, river, desert, mountain, pond, lake etc. The desert, grassland and mountains represent the terrestrial ecosystem (land-based ecosystem).

The ponds, rivers, lakes and sea represent the aquatic ecosystem (water-based ecosystem). Man-made artificial ecosystems are gardens, crop fields, parks, aquariums, etc.


Components of Ecosystem:

There are two components of an ecosystem:

  • Biotic component
  • Abiotic component.
  1. Biotic component: It includes three types of organisms:

(a) Producers: All green plants, blue-green algae can produce their food (Sugar and starch) from inorganic substances using light energy (Photosynthesis). Therefore, all green plants are called producers. They are also called autotrophs. Planktons are very minute or microscopic organisms freely floating on the surface of the water in a pond, lake, river or ocean.

Planktons are of two types:

  • The microscopic aquatic plants freely floating on the surface of the water are called phytoplanktons.
  • The microscopic aquatic animals freely floating on water are called zooplanktons. The freely floating protozoa are an example of zooplankton.

(b) Consumers: They are organisms that consume other organisms or their products as their food. All animals belong to this category. Consumers depend upon producers for their food directly or indirectly. They get their food by eating other organisms or their products. For example, man, goat, deer, fish, lion, cow, buffalo, etc., are common consumers. The consumers can be classified into the following types:

  • Herbivores: These are organisms (animals) that get their food by eating the producers (or plant) directly. Herbivores are also called first-order consumers. Some common examples of herbivores are: deer, rabbit, rat, squirrel, goat, cattle, etc
  • Carnivores: These are organisms (animals) that consume other animals. Therefore, carnivores feed on the flesh of herbivores. These are also called primary carnivores or second-order consumers. Some common examples are snakes, wild cats, jackals, frogs, birds, fishes, etc. There are animals that prey upon primary carnivores. They are called second-order consumers or third-order consumers. For example, owls, peacocks, tigers, lions, etc., are some second-order carnivores and may be eaten by third-order carnivores. The carnivores which have not been preyed upon further are called top carnivores. For example, the lion is a top carnivore.
  • Parasite: The organisms which feed on both plants and animals are called omnivores. Human beings are a common example of omnivores because they eat both plants (For example; pulses, grams, oilseeds, fruit, etc.) and animal products (milk, meat, egg, etc.).
  • Omnivores: Fungi and bacteria which break down (decompose) the dead plants, animal’s complex compounds into simpler ones. The decomposers help in the replenishment of natural resources. These are also known as microorganisms or saprotrophs. These are also called reducers.

Importance of Decomposers

  • Decomposers help in disposing of the wastes and dead bodies of plants and animals. Therefore, they clean the environment and create space for the living of newer generations of organisms.
  • The decomposers release minerals and other raw materials trapped in organic matter. These are picked up by plants. This also helps to maintain the fertility of the soil.
  • The decomposers produce some acids which are useful insolubilization of some minerals.
  • Decomposers help in recycling the materials in the biosphere so that, the process of life may go on and on like an unending chain.
  1. Abiotic Components: These are non-living components of an ecosystem. These include the physical environment. Edaphic factors like soil texture, topography, water, and air. Inorganic substances like carbon dioxide, nitrogen, oxygen, water, phosphorus, sodium, potassium, and calcium. These are involved in the cyclic of materials in the ecosystem. Organic compounds like proteins, carbohydrates, and lipids. These largely form the living body and link the abiotic and biotic components.

Climatic factors: These are sunlight temperature, pressure humidity, moisture, rainfall, etc. these factors affect the distribution of the organisms.

Functions of an Ecosystem

  • The ecosystem indicates available solar energy and the efficiency of an ecosystem to trap the same.
  • It gives information about the available essential minerals and their recycling periods.
  • It provides knowledge about the web of interactions and inter-relationship among the various population as well as between the population and the abiotic environment.
  • It helps human beings to know about the conservation of resources, protection from pollution and inputs required for maximizing productivity.
  • In the ecosystem, two processes of energy flow and biogeochemical cycles (nutrients movement) proceed side by side. The energy flow is unidirectional while the movement of nutrients is cyclic.
  • Food chain, Food web, Trophic levels. The flow of energy ten per cent law, Depletion of the ozone layer, Biological magnification. Mode of waste disposal.


Food Chain: The sequence of living organisms in a community, in which one organism consumes another organism to transfer food energy, is called a food chain.

A food chain is a uni-direction where the transfer of energy takes place in only one direction.

OR Food chain is a sequential process that represents “who eats whom”.

OR Food chain refers to an arrangement of different biotic groups in a sequence of energy transfers. These biotic groups are producer herbivores, carnivores.

For example, T1 (Grass) → T2 (Deer) → T3 (Lion)

Examples of Food Chains: Simple food chain operating in grassland or forest

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

In this food chain, grass represents the producers (first trophic level). Grass synthesizes its own food by the process of photosynthesis. The grass is eaten up by deer, which represents the herbivores or the primary consumers. Deer in turn is consumed by lions, carnivores or secondary consumers. A food chain in grassland which has four steps is:

Grass (Producers) → Insect (Herbivores) → Frog (Carnivores) → Eagle (Secondary Carnivore)


Significance of Food Chains

  • The study of food chains helps in understanding food relationships and interactions among the various organisms in an ecosystem. The food chains, transfer energy and materials between various living components of an ecosystem.
  • The food chains transfer energy and materials between various living components in an ecosystem or biosphere.
  • The food chains give dynamicity to an ecosystem or biosphere.
  • The movement of toxic substances like pesticides, weedicides, etc., through food chains, can prove very harmful.

Food Web: The inter-connected food chains operating in an ecosystem that establishes a network of relationships between various species are called a food web. In a food web, one organism may occupy a position in more than one food chain. An organism can obtain its food from different sources and in turn, may be eaten up by different types of organisms.

Fig: Food web

Trophic Levels: The various steps in the food chain at which the transfer of food (or energy) takes place are called trophic levels. There is a gradual decrease in the amount of energy transfer from one tropic level to the next trophic level in a food chain.

Fig: Tropic Levels

So, only 10% of energy is transferred to the next tropic level while 90% of energy is used by the present tropic level in its life processes.

The various trophic levels are given below :

  • The plant or the producers constitute the first tropic level.
  • The herbivores or primary consumers form the second tropic level.
  • Carnivores or secondary consumers make up the third tropic level.
  • Large carnivores or the tertiary consumers which feed upon the small carnivores constitute the fourth tropic level.

Flow Open Energy

Energy is used and conveyed from one tropic level to another in a food chain. This is called the flow of energy. Green plants capture about 1% of the solar energy incident on the Earth through the biochemical process of photosynthesis. A part of this trapped energy is used by plants in performing their metabolic activities and some energy is released as heat into the atmosphere. The remaining energy is chemical energy stored in the plants as ‘carbohydrates’. When plants are eaten up by herbivores, the chemical energy stored in the plants is transferred to these animals. These animals (herbivores) utilize some of this energy for metabolic activities, some energy is “released as heat and the remaining energy is stored. The process of energy transferred is similarly repeated with carnivores and so on.


Ten per cent law: Ten per cent law states that only 10 per cent of the energy entering a particular tropic level of organisms is available for transfer to the next higher trophic level.

Fig: Ten per cent law

For example, suppose 1000 J of solar energy is received by green plants, then only 1% of solar energy available on earth is utilized by plants. So only 10 J (1% of 1000 J) is trapped by plants and the rest 990 J of energy is lost to the environment. So, plants utilize only 10 J of energy. Next, only 10% of the 10 J energy of the plant, that is, 1 J, is available to the herbivore animal while 9 J is lost to the environment. Again, just 10% of the 1 J of energy of herbivore animals is utilized by carnivore animals. Thus, carnivore animals have only 0.1 J of energy while 0.9 J is lost to the environment.


Environmental Problems: Changes in the environment affect us and our activities change the environment around us. This led to the slow degradation of the environment that arose many environmental problems. Example: Depletion of the Ozone Layer and waste disposal.

Depletion of Ozone Layer: Ozone (O3) layer is largely found in the stratosphere which is a part of our atmosphere from 12 km -50 km above sea level. This region is called the ozonosphere. Ozone is deadly poisonous at the ground level. Ozone is formed as a result of the following photochemical reaction.

Fig: Depletion of Ozone Layer

The ozone layer is a protective blanket around the earth that absorbs most of the harmful U.V. (Ultraviolet) radiation of the Sun, thus, protecting the living beings of the Earth from health hazards like skin cancer, cataract in the eyes, weakening the immune system, destruction of plants etc. The decline of Ozone layer thickness in Antarctica was first discovered in 1985 and was termed as OZONE HOLE.

Steps were taken to limit the damage of the ozone layer: Excessive use of CFCs (Chloro Fluoro Carbon) a synthetic, inert chemical. For example; Freon which is used as a refrigerant and also in fire extinguishers caused Ozone depletion in the upper atmosphere. A single chlorine atom can destroy 1,00,000 Ozone molecules. U.N.E.P. (United Nation Environment Programme) did an excellent job in forging an agreement to freeze CFC production at 1986 levels (KYOTO Protocol) by all countries.

Biological Magnification: The increase in the concentration of harmful chemical substances like pesticides in the body of living organisms at each tropic level of a food chain is called biological magnification.

Fig: Example of Biological Modification

Garbage Disposal: Industrialization and rise in demand for consumer goods have created a major problem in the form of wastes/garbage accumulation and its disposal especially in urban areas.

The disposal of waste should be done in a scientific way. There are different methods of waste disposal. The method to be used depends on the nature of the waste. Some of the important modes of waste disposal are:

  • Incineration: Burning of waste at high temperatures to form ash is called incineration. This process is carried out in an incinerator. Incineration is used to destroy household, chemical and biological wastes.
  • Open dumping: A conventional method in which solid waste is dumped in selected areas of a town. It actually causes pollution
  • Land fillings: Wastes are dumped in low living areas and are compacted by rolling with bulldozers
  • Composting: Organic wastes are filled into a compost pit (2m × 1m × 1m). It is then covered with a thin layer of soil. After about three months the same garbage-filled inside the pit changes into organic manure.
  • Recycling: The solid wastes are broken down into their constituent simpler materials. These materials are then used to make new items. Even non-biodegradable solid wastes like plastic, metal can be recycled.
  • Reuse: A very simple conventional technique of using an item again and again. For example; paper can be reused for making envelopes, etc…


Environment: The combination of all the physical and biological conditions affecting the responses of living organisms is called the environment.

Biodegradable wastes: The wastes which are broken down by the activity of microorganisms and enter into the biogeochemical cycle are known as biodegradable wastes.

Non-biodegradable wastes: The wastes which cannot be broken down by the enzymes produced by microorganisms into simpler and harmless products in nature are called non-biodegradable wastes.

Garbage: Domestic wastes including kitchen waste are termed garbage.

Incineration: The destruction of waste materials by burning at high temperatures is called incineration.

Biotic Community: A group of various populations of organisms living in a region is called the biotic community.

Ecosystems: The self-contained and distinct functional unit capable of independent existence made by the interaction of living and non-living components is called an ecosystem. The ecosystem component consists of two components- Abiotic and biotic


  • Abiotic: Components consist of inorganic and organic substances and climatic factors.
  • Biotic: Components consist of a living organism.
  • Autotrophs: Those organisms which can produce their own food are called autotrophs or producers. All green plants are producers.
  • Consumers: Those organisms which are unable to synthesise their food themselves and consume the food produced by producers or eat other organisms as food, are known as consumers.
  • Decomposers: Bacteria and fungi which break down the complex organic compounds present in the dead plants and animals and their products into simpler substances are known as decomposers.

Click here to Download : Chapter 15 Our Environment PDF Material