Our Environment

1.0Introduction

The environment is the sum total of all living and non-living factors that surround and influence an organism. It has two components biotic and abiotic.

Both these biotic and abiotic components influence the organism and, in turn, get influenced. This interdependent interaction among organisms as well as with the abiotic components maintains a balance in nature.

The study of environment includes the study of its various components, and their protection, preservation and management.

2.0Ecosystem

All the interacting organisms in an area together with the non-living constituents of the environment form an ecosystem. Ecosystem term was given by Arthur Tansley. It is a self-sustained unit of living things (plants, animals and decomposers) and their non-living environment (soil, air and water).

It 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. It may be small and also very large.

3.0Types of ecosystem:

In the biosphere, ecosystem may be classified on the basis of their nature, duration and size. On the basis of nature, ecosystem may be classified as -

• Natural ecosystem
• Artificial ecosystem
• Natural ecosystem: These ecosystems 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 man-made or man-engineered ecosystem. In this ecosystem, man maintains or disturbs the natural balance by the addition of energy and planned manipulations. Common examples of artificial ecosystem are croplands, orchards, gardens, aquarium, etc.

4.0Components of ecosystem

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

(A) Abiotic (non-living) components These include the non-living physico-chemical factors of the environment.

Abiotic factors include -

• Inorganic substance
• Physical environment
• Climatic factors
• Inorganic substance: Inorganic substances, (carbon, nitrogen, oxygen, calcium, phosphorus, etc.) and their compounds (water, carbon dioxide, etc.) constitute the main abiotic component.
• Physical environment: These include air, water and soil.
• Climatic factors: These include light, temperature, humidity, wind, rainfall, water, etc. and also edaphic factors (soil, substrate, topography, minerals, pH , etc.).

(B) 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 consumer depends on producers for food, directly or indirectly. All the animals are consumers.

"All the flesh of a carnivore is grass." Justify the statement.

• Explanation Carnivores depend upon herbivores for their food and herbivores eat plants to obtain energy. Herbivores build up their tissues with the help of chemical energy obtained from plants and carnivores build up their tissues with the help of chemical energy obtained from herbivores (by eating them). This justifies the statement, "All the flesh of a carnivore is grass".

Consumers: (a) 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.

(b) 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. The small carnivores which feed on herbivores (primary consumers) are called secondary consumers. The large carnivores or top carnivores which feed upon the small carnivores or secondary consumers are called tertiary consumers. e.g., lion, tiger, hawk, etc.

(c) 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 faeces, urine into simpler substances are called decomposers. e.g., bacteria and fungi.

Why are decomposers known as cleaners of the environment?

• Explanation Decomposers act upon dead remains and convert organic substances into simple inorganic substances. They help in replenishing the soil. If there are no decomposers, then all the dead bodies would pile up on this earth.

Importance of decomposers

• They decompose the dead bodies of animals and plants thus acts as cleansing agents of the environment.
• They help in recycling the material in biosphere thus, play a vital role in biogeochemical or nutrient cycles.
• They maintain the fertility of soil.

If there were no decomposers, the earth would have been a heap of dead organisms.

5.0Food 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.

(i) Grass $\to$ Deer $\to$ Lion (Producer) (Herbivore) (Carnivore)

(ii) Grass (Producer) $\to \begin{array}{c}\text{ Insects }\\ \text{ (Herbivore) }\end{array}\to \begin{array}{c}\text{ Frog }\\ \text{ (Carnivore) }\end{array}$ (Top carnivores)

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

Trophic levels:

Each step or level of the food chain forms a trophic level. The distinct sequential steps in the food chain where transfer of energy occurs are referred to as trophic levels. e.g., green plants (producers) form the first trophic level, the producer level; the plant eaters (herbivores), also called primary consumers, belong to second trophic level, the primary consumer level; and the flesh eaters (carnivores), also called secondary consumers, represent the third trophic level and so on.

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

Characteristics of food chain

• A food chain involves a nutritive interaction between the living organisms (biotic components) of an ecosystem. In a food chain, there occurs repeated eating, i.e., each group eats the other group and subsequently is taken by some other group organisms.
• A food chain is always straight and proceeds in a progressive straight line.
• Usually, there are 3 or 4 trophic levels in the food chain. In few chains, there may be maximum of 5 trophic levels.
• Some organisms are omnivores. These occupy different trophic positions in different food chains.
• At each transfer, generally $80-90\%$ of energy is lost as heat in accordance with second law of thermodynamics. Types of food chains: There are two types of food chains. (a) Grazing food chains

Grazing Food Chains

(b) Detritus food chain

• Detritivores are heterotrophs that obtain nutrients by consuming detritus (decomposing plant and animal waste as well as faeces) e.g., invertebrates like earthworm, insects such as mites, beetles, butterflies. They should be distinguished from other decomposers like bacteria and fungi which are unable to ingest discrete lumps of matter, but instead use saprotrophic feeding, in which they absorb nutrients through extracellular digestion.
• Kites and vultures feed on dead organisms and therefore, they act 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 - (i) It is a means of transfer of energy from one trophic level to another. (ii) It provides information about the living components of an ecosystem. (iii) A natural method of population control due to different nutritional habits. (iv) It enables recycling of resources via decomposition.

6.0Food web:

The inter-connected food chains operating in an ecosystem which establish a network of relationships between various species is called a food web or the network of a large number of food chains existing in an ecosystem is called a food web.

Unlike food chains, food webs are never straight. Food webs help in checking the over population of species of organisms (both animals and plants).

The length and complexity of food chains vary greatly. Each organism eats two or more other kinds of organisms which in turn are eaten by several other organisms. So instead of a straightline food chain, the relationship can be shown as a series of branching lines called a food web. A food web provides alternative pathways of food availability.

7.0Transfer of energy in ecosystem

Ten Percent law: It was put forth by Lindeman (1942). It is 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.

The number of trophic levels in a food chain is limited. Why?

• Explanation It is because only $10\%$ of energy is passed on to next higher trophic level in a food chain. As a result of this, there is a progressive decline in the energy level and the amount of energy available is not enough to sustain more than few trophic levels in a food chain. Each organism needs energy to carry on vital activities and for building up and repairing the body tissues.

The ultimate source of entire energy, used by living organisms, is the Sun. In a community, each food chain, in fact, 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. On an average, $10\%$ of the food (energy) is turned into body of herbivores. In the same way, $10\%$ of total energy available to the herbivores is made available for the next level of consumers. In other words, on an average, $10\%$ of the amount of organic matter that is present at each step reaches the next consumer level.

Trophic levels 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. Also, as it moves through the various trophic level it is no longer available to previous level. The energy available at each trophic level gets diminished progressively due to loss of energy at each level.

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 nonbiodegradable chemical at different trophic levels in a food chain is called biomagnification.

Study carefully the given food chain. Wheat \rightarrow rat \rightarrow snake \rightarrow hawk. To which of the two consumers, snake or hawk, will more energy (percent) be available and why?

• Explanation More energy will be available for the snake. Snake is a secondary consumer while hawk is a tertiary consumer. According to second law of thermodynamics, larger amount of energy is lost to the environment at each trophic level. Snake is at third trophic level and hawk is at fourth trophic level. Therefore, more energy (present) will be available to the snake at third trophic level.

Diagram showing flow of energy in an ecosystem -

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. It includes peelings of fruits and vegetables, other kitchen waste, ash, paper, cow dung, human excreta, glass, plastics, leather and rubber articles, brick, sand, worn out clothes and metal objects, etc. When accumulated, these heaps of solid waste make the surroundings dirty and pollute the soil.

Types of solid wastes

(1) Biodegradable wastes: They are those waste materials which can be broken down into simpler, non-poisonous substances by the action of microorganisms. e.g. cattle dung, waste vegetables, fruits and compost etc. (2) Non-biodegradable wastes: The waste materials which cannot be broken down into simpler substances easily in nature. These substances may be inert and simply persist in the environment for a long time or may harm the various members of the ecosystem. e.g., Aluminium cans, DDT, Plastics and Radioactive wastes.

Why are some substances biodegradables?

• Explanation Lot of waste is produced by man or naturally. Some of waste substances are acted upon by the microorganisms and broken down into simpler substances. Such substances are called biodegradable. e.g., vegetable and fruit peels.

Differences between biodegradable and non-biodegradable waste

Modes of waste disposal: Some prominent methods of waste disposal are -

• Landfills: In urban areas, the majority of the solid waste is buried in low lying areas to level the uneven surface of land. This method of waste disposal is commonly called landfills.
• Recycling of wastes: Number of solid wastes (paper, plastics, metal etc.) can be recycled by sending them to respective recycling units. For instance, 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: Household waste such as peels of fruits and vegetables, leftover food, fallen dead leaves of kitchen garden plants and potted plants etc. can be converted into compost and used as manure.
• Incineration: It is the process of burning of substance at high temperature (usually more than $1000^{\circ }\mathrm{C}$ ) and ultimately converting them into ashes. This ash can be disposed off by landfills. In cities, municipal committees/corporations generally do large scale disposal of waste by incineration.

8.0Ozone layer depletion:

Ozone layer is a layer of the earth's atmosphere where ozone is concentrated. 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) radiations from the Sun.

• Ozone $\left({\mathrm{O}}_3\right)$ is a molecule formed by three atoms of oxygen. It is formed in atmosphere by the action of ultraviolet radiation on oxygen gas.
• The high energy ultraviolet radiations (UV radiations) coming from the sun splits oxygen gas into free oxygen atoms.

${\mathrm{O}}_2\underset{\text{ radiations from sun }}{\overset{\text{ Ultrailet }}{\to }}\mathrm{O}+\mathrm{O}\text{ (oxygen atom) }$

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

$\mathrm{O}+{\mathrm{O}}_2⟶\underset{\text{ (Ozone) }}{{\mathrm{O}}_3}$

Ozone is a deadly poison. The amount of ozone in the atmosphere began to drop sharply in the 1980s. The thinning of ozone layer is commonly called ozone depletion. 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 $\left({\mathrm{CH}}_4\right)$ and oxides of nitrogen $\left({\mathrm{NO}}_{\mathrm{x}}\right)$ 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: Due to ozone depletion living organisms expose to ultraviolet radiations which may cause following effects - (i) Ultraviolet radiation is highly damaging to organisms. It causes skin cancer in human beings. (ii) These cause damage to eyes and also cause increased incidence of cataract disease in eyes. (iii) These cause damage to immune system by lowering the body's resistance to diseases.

Among the ozone depleting substances (ODS) chlorofluorocarbons are the most harmful. Give the reason.

• Explanation Chlorofluorocarbons produce 'active chlorine' ( Cl and ClO radicals) in the presence of UV radiations. These radicals, through chain reactions, destroy the ozone by converting it into oxygen. This is the reason why chlorofluorocarbons are the most harmful ODS.

Steps to be taken to limit the damage to the ozone layer - (a) Reduce the use of chlorofluorocarbon in refrigerators, air conditioners, etc. (b) Avoid using CFCs in aerosols, sprays, etc. (c) Complete freeze on large scale CFC production.

The annual Antarctic ozone hole reached an average area of 23.2 million square kilometres between 7 October 2022 to 13 October 2022. This depleted area of the ozone layer over the south pole was slightly smaller than last year and generally continued overall shrinking trend of recent years.

9.0Biology Diagrams made Easy

10.0Chapter At a Glance

11.0SOME BASIC TERMS

• Ecology: Study of interrelationship of organisms between the biotic and abiotic components of their environment.
• Producer: Organisms which make their own food.
• Herbivore: Animals which eat plants only.
• Carnivore: Animals which eat other animals only.
• Omnivore: Animals which eat both plants and animals.
• Decomposer: Microorganisms which break down the complex organic compounds.
• Incineration: Processing of burning of substances at high temperature.
• Dobson spectrometer: Instruments to measure atmospheric ozone.
• CFC: Chlorofluorocarbon.
• Ozone Depletion: Thinning of ozone layer