RBSE Class 9 Science Notes Chapter 13 Environment

Rajasthan Board RBSE Class 9 Science Notes Chapter 13 Environment

Meaning of Environment:
Every living being like microbes, plants and animals, including man is an organism. Surroundings of every organism constitute the environment.

Environment consist of two components:

Biotic component: It includes living organisms present in the surroundings of an organism, e.g., plants, animals, humans and microbes.
Abiotic component: It includes non-living factors that surround and influence an organism, e.g., air, water, light, temperature, etc. Both the components of environment influence different organisms in different ways.
The physical factors of environment are heat and light. Chemical factors are soil and water and ecological factors are atmosphere, fire and biotic.
All the organism utilize substances which are found on earth and the substance which are required by living organisms for their livelihood are called resources. All those substances which are available in environment and are essential for the continuation of life are called natural resources, like air, water, soil, plants, minerals, etc.
The study of environment is included under a large discipline ecology. The word ecology is derived from Greek word oikos meaning place to live and logos means to study. Ernst Haeckel was a German biologist, who coined the term ecology. Ecology is the study of interrelationship of organisms between the biotic and abiotic components of their environment.

Environment Pollution:

Many factors present in environment affects human health, adversely.
Uncontrolled human activities lead to ecological imbalance and cause environmental pollution.
Pollution is an undesirable change in the physical and biological characteristics of our air, land and water, which may harmfully affect human life. The substance or agents which cause pollution of the environment are called pollutants.
The contamination of air with dust, smoke and harmful gases, which adversely effect human beings and other living organisms is called air pollution. The substance whose presence in air produces air pollution are called air pollutants. It is caused by industries, automobiles, fertilizers, pesticides, etc. The main air pollutants are power and heat generation, which produce SO₂, NO, O₃, etc. Air pollution can cause respiratory disease like aslhma, aronchitis, lung cancer, etc.
Water pollution is defined as the addition of harmful substances to water, which makes it unfit for use and constitutes a health hazard. Water pollution occurs by industrial wastes, and those sources which discharge pollutants directly into the water. Water pollution causes many diseases like – cholera,typhoid, trouble in stomach, skin diseases, etc. It can be control by treatment of waste water, reverse osmosis and recycling of water.
Sound pollution is the unwanted sound dumped in the environment. It is caused n railway, buses, industries, public address systems, etc. Noise pollution may cause damage to thympanic membrane of the ear, creating deafness. It also causes headache, discomfort, irritation, etc. Sudden loud noise affects heart beat, increases blood pressure. It can be controlled by maintaining the machines properly.
Soil pollution is the natural medium in which we grow crops for producing food. It is a precious resource. Now, since the human population is increasing at a very fast rate, we have to grow more and more crops in the soil in order to fulfill the food requirements. Soil does not get any time to regenerate its lost nutrients. As a result, the nutrient content of the soil continuously, gets depleted. Thus, increased agricultural activity has created an imbalance in nature. When same crops are grown in the same soil year after year, it removes particular nutrients from the soil. Thus, growing same type of crops in the same soil, year after year, results in depletion of certain specific nutrients in the soil and creates imbalance in the nature. Growing the same crop in the same soil, year after year is referred to as monoculture.

The nutrient deficient soil can be replenished by the following methods:

By keeping the field fallow or free for one or more seasons.
By practicing crop rotation.
By practicing multiple cropping.
By supplying manures and fertilizers.
Thermal Pollution: The earth receives heat from the sun. Spare heat from the earth is radiated towards the outer space. The layer of gases (CO₂,CH₄,NO) and water vapor of the atmosphere stop these radiations and sends back again to the earth. Due to this, the temperature of the earth increases. This process is called greenhouse effect. It has been estimated,that the temperature of earth has increased tremendously in the last 50 years.

Consequences of thermal pollution:

Huge deposits of ice in frozen seas, near the poles and glaciers, will melt, so the water level in oceans will rise and many islands and cities on sea shore will be drowned.
Cyclones and heavy storms are caused, due to rise in temperature all over the world.
High temperature may reduce crop production and also the working efficiency of human beings, will be reduced.
The temperature of water will rise, which will be injurious for aquatic creatures.

Measures to control thermal pollution:

More and more trees should be planted, to absorb excess of carbon dioxide.
Release of gases like CO₂, CH₄, NO by the factories into air should be banned.
Use of CFC compounds should be restricted.

Ecology:
Organisms and environment are two constituents of nature. Study of relationship between the organisms and their environment is called Ecology. Ecology is made up of two Greek words-Oikos means house or habitat and logos means study or discourse.

Ecosystem:

According to Tansley: The system formed as a result of interaction of living and non-living factors is called ecosystem.
According to Odum: Ecosystem is a basic unit of ecology, in which living’and non-living environment affecting each other by interaction, maintain the functional mobility of the system, by the continuous effect of energy and chemical substances. The source of energy in the ecosystem is sun light.
Ecosystem can be as small as a drop of water or it can be as big as an ocean or a big forest. So much so, the biosphere (whole earth with living beings), makes an ecosystem.

Structure of Ecosystem:
An ecosystem consists of two main components:

Abiotic or non- living components, and
Biotic or living components.

Abiotic components are as follows:
Climatic or physical factors:
These are of two types:

Atmospheric, such as temperature, sunlight, moisture and precipitation.
Edaphic, such as soil texture.
These factors determine the distribution of the type of organism living in the area.

Inorganic substances
These are various nutrients elements and compounds, such as carbon (C), nitrogen (N), sulphur (S), phosphorus (P), carbon dioxide (CO₂), oxygen (O₂), etc. Minerals such as calcium (Ca), potassium (K) and magnesium (Mg) are also included in nutrients. These are involved in the cycling of the materials in the ecosystem.

Organic substances (Compounds)
These are proteins, carbohydrates, fats, amino acids, etc. These are involved in the cycling of the materials, in lipids and humic substances. These enter in living factors through soil and after death and decomposing, mix back in soil and environment.

Biotic components:

The living components of the biosphere are called biotic components. The living components of the biosphere are:
- Producers,
- Consumers, and
- Decomposers,
  depending upon their mode of nutrition.
Producers or Autotrophs: Green plants are called producers, because they are able to synthesis their food in the presence of sunlight and chlorophyll, by taking carbon dioxide from the atmosphere and water from the soil. They are also called as autotrophs as they synthesis their own food. As green plants can convert solar energy into chemical energy of food, so according to E.J. Koromondy, they can also be called converters.
Consumers or Heterotrophs: Consumers or heterotrophs are those animals which eat food¬stuffs manufactured by green plants. They cannot manufacture their own food. Phagotrophs are such heterotrophic organisms which digest their food in their body.

Consumers are of three types:

Primary Consumers: All the herbivores, which feed on producers (green plants) are called primary consumers. Some common examples of primary consumers are insects, goat, cow, rabbit, grass hopper, deer, parrot, etc.
Secondary Consumers: The carnivores eat herbivores or primary consumers and are called secondary consumers. Some common examples of secondary consumers are snake, frog, fox, lizard, etc. They are also called primary carnivores.
Tertiary Consumers: They are also called secondary carnivores. Big carnivores eat the secondary consumers and are called tertiary consumers. Lion and tiger are common exampies of tertiary consumers.
Omnivore: An animal which can eat plants as well as flesh of other animals is called omnivore. For example, man is an omnivore.

Decomposers or Micro consumers or osmotrophs or Saprotrophs:
These are the micro-organisms which feed on dead bodies of plants and animals and break down complex organic substances into simpler inorganic substances. Putrefying bacteria and fungi decompose the dead plants and animals into ammonia and other simpler substances. Through decomposers, the elements enter the earth again which are again, taken up f plants. Thus, the cycle of matter continues.

Bio-geochemical cycle:
The main elements—oxygen, nitrogen, sulphur, phosphorus, etc., enter from earth to the producer level in the ecosystem and then get transferred to other levels. The transfer and circulation takes place through soil, water, air and living organisms. The cycling (circulation) of these chemicals in ecosystem and ultimately in biosphere are referred as bio-geochemical cycles.

Types of bio-geochemical cycles:
Mainly these are of two types:
1. Gaseous cycles, and
2. Sedimentary cycles.

Gaseous cycles: These are the cycles of gases whose reservoir pool is atmosphere. For example, carbon dioxide cycle, oxygen cycle and nitrogen cycle.
Sedimentary cycles: Cycles of minerals such as phosphorus and sulfur. The reservoir pool is lithosphere (soil or rock). These cycles are imperfect, because during these cycles some quantity get deposited into sea, land or at the bottom of ponds.
Water cycle: Water is essential for life. Ocean is the major reservoir of water which covers about 70% of earth’s surface. The water cycle is governed by sun’s heat energy. Water cycle do not involve organisms, but normal physical processes like evaporation, condensation, etc.
Oxygen cycle: Oxygen is necessary for life. Oxygen exist in molecular form and as part of CO₂ and H₂O. For respiration, oxygen is taken from air or water. On exhalation, O2 returns in the form of CO₂ and H₂O. Oxygen is released in the form of product in photosynthesis.
Carbon cycle: This is a gaseous cycle. Carbon dioxide is about 0.03 % in the atmosphere. This cycle involves the cycling of carbon, which is a basic component of all the organic compounds that build all the living things. Atmospheric CO2 and dissolved CO2 in the water are the basic source of carbon. Carbon moves from atmosphere to producers, to consumers and from both to the decomposers, and finally back to the atmosphere. Carbon is also found in water, fossil fuels and sedimentary rocks.
Nitrogen cycle: Nitrogen is essential for the synthesis of proteins in plants and animals. Atmospheric air contains about 79% nitrogen, but it is not of much use for plants and animals. Animals need nitrogen in the form of aminoacids to form proteins, and plants in the form of soluble salts, nitrates for the synthesis of amino acids and proteins.

The greenhouse effect:
Some gases prevent the escape of heat from the earth. An increase in the percentage of such gases in the atmosphere would cause the average temperatures to increase worldwide, and this is called the greenhouse effect. Carbon dioxide is one such gas. An increase in carbon dioxide content in the atmosphere would lead to global warming.

Ozone layer:
In the upper layer of the atmosphere, a gas called ozone is found. Its molecule contain three atoms of oxygen. It performs an essential function, where it is found. It absorbs harmful radiations from the sun. This prevents those harmful radiations from reaching the surface of the earth, where they may damage many forms of life. Various man-made compounds like CFCs, carbon compounds having both fluorine and chlorine, are very stable and do not degrade by any biological process. These are found to persist in the atmosphere and when react with the ozone molecules, it resulted in reduction of the ozone layer. Recently scientists have discovered a hole in the ozone layer above the antartica. It would be better not to take chances towards and move to stop further damage to the ozone layer.