Our Environment NCERT Class 10 Ch 15 Notes for CBSE

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The environment is everything that is around us.

Ecosystem (Living Organisms + Abiotic Components)

All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem.

Thus, an ecosystem consists of biotic components comprising living organisms and abiotic components comprising physical factors like temperature, rainfall, wind, soil and minerals.

All living organisms as well as the physical surroundings interact with each other and maintain a balance in nature.

Biotic Factors

1. Producers

Organisms that are able to form nutritional organic substances from simple inorganic substances such as carbon dioxide; they are also known as autotrophs (greek trophḗ – ‘nourishment’ or ‘food’). They get energy from chemicals or the sun, and with the help of water, convert that energy into useable energy in the form of sugar, or food.

Examples: plants, blue-green algae, etc.

2. Consumers (Primary consumers, Secondary consumers, Tertiary consumers)

Consumers are organisms that feed on producers; they are called heterotrophs (hetero – ‘other’ + Greek trophos – ‘feeder’).

Examples: birds, cats, insects

3. Carnivores

Carnivores (Latin caro, genitive carnis – ‘meat’ or ‘flesh’, vorare meaning “to devour”) are organisms that derive energy and nutrient requirements from a diet consisting mainly or exclusively of animal tissue, whether through predation or scavenging.

4. Omnivores

Omnivores (Latin omnis (all), and vora, from vorare, (to eat or devour)) are the animals that have the capability to obtain chemical energy and nutrients from materials originating from plant and animal origin.

5. Parasites

Parasites (Greek parasitos – ‘one who eats at the table of another’) live on or in another organism, the host, causing it some harm, and is adapted structurally to this way of life.

6. Saprophytes

Saprophytes are the organisms, particularly fungi, which obtain nutrients directly from dead organic matter.

Abiotic Factors

Abiotic factors include water, light, radiation, temperature, humidity, atmosphere, and soil.
The macroscopic climate often influences each of the above.
Pressure and sound waves may also be considered in the context of marine or sub-terrestrial environments.
Biodegradable substances
The wastes that decompose (broken down) naturally in the environment and are considered safe for the environment are called biodegradable substances.
Examples: food scraps, cotton, wool, wood, human and animal waste, manufactured products based on natural materials (such as paper, and vegetable-oil-based soaps).
Non-biodegradable substances
Materials that remain for a long time in the environment, without getting decompose by any natural agents, also causing harm to the environment are called non-biodegradable substances.
Examples: metals, plastics, bottles, glass, poly bags, chemicals, batteries, etc.

Food Chain

A food chain is a linear network of links in a food web starting from producer organisms and ending at apex predator species, detritivores, or decomposer species.

Each step or level of the food chain forms a trophic level.

  • Trophic Level 1: The autotrophs or the producers are at the first trophic level. They fix up solar energy and make it available for heterotrophs or consumers.
  • Trophic Level 2: The herbivores (primary consumers) come at the second.
  • Trophic Level 3: Small carnivores (secondary consumers) at the third trophic level.
  • Trophic Level 4: Large carnivores (tertiary consumers) form the fourth trophic level.

Flow of Energy in a Food Chain

The interactions among the various components of the environment involve the flow of energy from one component of the system to another.
The autotrophs capture the energy present in sunlight and convert it into chemical energy. This energy supports all the activities of the living world. From autotrophs, the energy goes to the heterotrophs and decomposers.
However, when one form of energy is changed to another, some energy is lost to the environment in forms which cannot be used again.

  • The green plants in a terrestrial ecosystem capture about 1% of the energy of sunlight that falls on their leaves and converts it into food energy.
  • When green plants are eaten by primary consumers, a great deal of energy is lost as heat to the environment, some amount goes into digestion and in doing work and the rest goes towards growth and reproduction. An average of 10% of the food eaten is turned into its own body and made available for the next level of consumers.
  • Therefore, 10% can be taken as the average value for the amount of organic matter that is present at each step and reaches the next level of consumers.
  • 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.
  • There are generally a greater number of individuals at the lower trophic levels of an ecosystem, the greatest number is of the producers.
  • The length and complexity of food chains vary greatly. Each organism is generally 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, the relationship can be shown as a series of branching lines called a food web.
  • The flow of energy is unidirectional. 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. As it moves progressively through the various trophic levels it is no longer available to the previous level.
  • Another interesting aspect of the food chain is how unknowingly some harmful chemicals enter our bodies through the food chain. Farmers use several pesticides and other chemicals 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. As 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. This is the reason why our 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.

Biomagnification (Biological Magnification)

Biomagnification, also known as bio-amplification, is the increasing concentration of a substance, such as a toxic chemical, in the tissues of tolerant organisms at successively higher levels in a food chain.

Ozone (O3)

Ozone is a molecule formed by three atoms of oxygen. While O2 is essential for all aerobic forms of life, Ozone is a deadly poison.

However, at the higher levels of the atmosphere, ozone performs an essential function. It shields the surface of the earth from ultraviolet (UV) radiation from the Sun. This radiation is highly damaging to organisms, for example, it is known to cause skin cancer in human beings.

Ozone at the higher levels of the atmosphere is a product of UV radiation acting on oxygen (O2) molecule. The higher energy UV radiations split apart some molecular oxygen (O2) into free oxygen (O) atoms. These atoms then combine with the molecular oxygen to form ozone as shown below

O2 ⎯⎯UV⎯→ O + O
O + O2 → O3

The amount of ozone in the atmosphere began to drop sharply in the 1980s. This decrease has been linked to synthetic chemicals like chlorofluorocarbons (CFCs) which are used as refrigerants and in fire extinguishers. In 1987, the United Nations Environment Programme (UNEP) succeeded in forging an agreement to freeze CFC production at 1986 levels.

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