ICSE Class 6 Biology Chapter 8 Our Environment

Our Environment

Learning Objectives

After completing this chapter you will be able to:

conclude that earth is a unique planet.

distinguish between biotic and abiotic components.

identify and differentiate between producers, consumers and decomposers.

describe the flow of energy in nature.

describe the interdependence between plants and animals.

state the ways in which plants and animals are useful to human beings.

identify the major causes of water, air, and noise pollution.

describe how to conserve our environment.

Our Earth

Our earth is one of the eight planets that move around the sun and is a part of the solar system.

Each planet in the solar system travels in its own path or orbit. Some planets are nearer to the sun than the earth. Some planets are farther away. Mercury is the closest to the sun and Neptune is the farthest. Mercury receives the maximum solar heat and is so hot that no plant or animal would be able to survive there. On the other hand, Neptune is the coldest. It is not possible for any living organism to survive in such extreme freezing cold conditions. Earth is a unique planet because it is at the right distance from the sun and it has all the conditions necessary for the survival of living organisms.

Earth - the unique planet to have conditions necessary for supporting life

The earth is perhaps the only planet in the solar system that has life on it. Let us see how earth provides all those conditions which are essential for the sustenance of life.

Optimum Distance From The Sun

The distance between the sun and the earth is such that the earth receives just the right amount of solar energy. So, it is neither too hot nor too cold. The light from the sun makes the earth's land and water warm enough to sustain life.

Presence Of Oxygen, Carbon Dioxide, Nitrogen, Ozone And Other Gases

All living organisms need oxygen for respiration. Burning cannot take place without oxygen. Carbon dioxide is used by plants for photosynthesis. Nitrogen present in the air is converted by certain microorganisms into nitrogen compounds. Plants use these nitrogenous compounds as fertilizers. Nitrogen also controls burning. Ozone, an allotropic form of oxygen prevents the ultraviolet rays of the sun from reaching the earth. All these gases and some other gases which make the sustenance of life possible, are present on the earth.

Air also helps to maintain the right temperature on the earth. It absorbs a lot of solar heat and does not let days get too hot. It also does not allow the heat of the earth to escape and hence protects us from freezing cold nights.

Presence Of Water

Water which is extremely essential for living organisms is present in abundance on the earth. All the life processes such as digestion, blood circulation, excretion and so on, taking place in living organisms, need water. Water is also required by plants when they make their food through photosynthesis.

Gravitational Force

The mass of the earth is such that it exerts right gravitational force which is sufficient to hold its atmosphere in place. If the gravitational force of the earth was of a smaller value, then all the gases on the earth would have escaped into outer space.

Presence Of Minerals

Carbon, hydrogen, oxygen and nitrogen are essential elements required by living organisms. They are present in sufficient amounts in various usable forms. The soil also contains minerals and nutrients required for the growth of plants.

Inside The Earth

Earth is made up of three layers. The outermost solid layer is called crust. The next layer is mantle which consists of a layer of molten rocks. The innermost layer is core which is separated into a liquid outer core and a solid inner core.

Parts Of The Earth

The entire earth including air around it can be divided into three spheres, namely, lithosphere, hydrosphere and atmosphere.

Lithosphere: It is the outer solid layer of the earth covered with soil and rocks. It is a rich source of minerals and provides essential nutrients for the growth of plants. All living beings depend on plants for their food.

Hydrosphere: About seventy per cent of the earth's surface is water and most of it is present in oceans. Only a small portion of the earth's water is fresh water, generally found in rivers, lakes, groundwater and also in the form of ice that covers the north and south poles. The part of the earth that contains water is called the hydrosphere.

Atmosphere: The lithosphere and hydrosphere are covered by a mixture of gases. This mixture of gases forms the atmosphere. It has nitrogen, oxygen, argon, a small amount of carbon dioxide, water vapours and other gases.

Table 8.1 Percentage of gases in air

Biosphere

The habitable parts of the earth, that is, lithosphere, hydrosphere and atmosphere where living beings exist is called biosphere.

Biosphere extends 11 km deep into the sea and some 10 km up into the air from the soil.

Teacher's Note

The biosphere is all around us - from the soil beneath our feet to the air we breathe and the water we drink. Understanding these three spheres helps us see how interconnected our environment is with every living thing.

Environment

The word 'environment' basically means surroundings. In fact, everything that surrounds and affects the life of an organism forms a part of its environment. Our environment includes variety of living and non-living things present around us. For example, the environment of a fish in a pond includes living things, such as insects, fishes and plants, and non-living things like water, gases, minerals and rocks. The environment has three interactive components, namely, biotic, abiotic and cultural.

Biotic Components

Biotic components of our environment includes all living organisms, namely plants, animals, and microorganisms. Microorganisms or microbes (micro means small, bios means life) include organisms like viruses, bacteria, protozoa, algae and fungi. Biotic components could be divided into three groups, namely, producers, consumers and decomposers.

Plants (Producers)

All animals directly or indirectly depend on plants for their food supply. All green plants have a green pigment called chlorophyll in them. Green leaves prepare food in the presence of sunlight using water and carbon dioxide by the process of photosynthesis. Therefore, green plants are called producers or autotrophs.

Carbon dioxide + Water with sunlight and chlorophyll yields Starch + oxygen

Animals (Consumers)

Living organisms that cannot make their own food depend on either plants or other animals for their food. They are called consumers or heterotrophs. Based on their feeding habits, consumers can be of many types.

Animals that eat only plants are called herbivores or primary consumers, for example, deer, horse, elephant and so on.

Animals that eat other living animals which eat primary consumers, are carnivores or secondary consumers, for example, tiger and leopard. Some carnivores feed on dead animals. These are called scavengers. Vulture and eagle are scavengers.

Those animals that eat secondary consumers, are called tertiary consumers, for example, snake and owl.

Some consumers eat both plants and animals. They are called omnivores. Bear, crow, cockroach and human beings are omnivores.

Microorganisms (Decomposers)

In addition to producers and consumers, there are microscopic organisms and worms called decomposers that are present in the soil. They feed upon the remains of dead plants and animals and in the process break them down into simple substances. Decomposers are called nature's scavengers. They decompose dead, decaying organisms and release their body minerals into the environment. These minerals are reused by plants for their growth. Thus, decomposers help not only in cleaning the environment but also in the recycling of the minerals.

Teacher's Note

When we see a fallen leaf decompose on the forest floor, we're watching decomposers like bacteria and fungi do their work - nature's way of recycling nutrients back to the soil and plants.

Abiotic Components

Abiotic components of our environment include light, temperature, air, water, humidity and soil. Life would not sustain without these components. Let us read about them.

Light

Sun is the primary source of light on the earth. Not only does light serve as a source of energy, it also influences plant life in a number of other ways. In the presence of sunlight green plants are able to make food. Light influences closing and opening of stomata, germination of seeds, flowering and so on. Light may determine the types of plants and animals found in a particular area.

The behaviour of certain animals is also influenced by light. Most of the common animals that you see around can tolerate bright light and move about freely during the day. However, earthworms, termites and cockroaches cannot stand intense light. They lead a nocturnal (active at night) life.

Air

Almost all living organisms need oxygen of the air for their survival. Plants take in carbon dioxide from the air and use it to make food. Nitrogen of the air is converted into nitrates by the microorganisms present in the soil. These nitrates are used by the plants. The ozone layer of the air protects us from harmful ultraviolet radiations from the sun.

Water

Water is the most abundant natural resource on the earth's surface. It is extremely important for

This is a preview of the first 3 pages. To get the complete book, click below.