ICSE Class 6 Biology Chapter 8 Our Environment

Our Environment

Syllabus

1. Earth is a unique planet in the solar system - it has the right combination of several factors which support life:

- Correct distance from the sun, to ensure adequate heat and light.

- An atmosphere which protects living things from harmful radiation and has a combination of gases needed to sustain life.

- Sufficient water for living beings.

- Several minerals available in the soil, which organisms use to grow and reproduce.

2. The environment has three interactive components - abiotic, biotic and cultural:

- Abiotic components - light, temperature.

- Biotic components - plants, animals, micro-organisms.

- Cultural components - owing to human influences on the environment.

Some details about each of these factors; interactions between these factors; how they influence life on earth.

3. Producers, consumers, scavengers and decomposers. Herbivores, carnivores, omnivores. Simple food chains and food webs. Energy chains - all start with the Sun.

- Games involving the building of Food Chains.

- Investigating the effect of light, water, excess heat, different kinds of soil on potted plants (E) (Teachers to explain the need for control and also ensure that only one variable is altered at a time. Good training in scientific method).

4. Plants and animals are interdependent. Maintaining the balance in nature - what happens when this balance is upset - how human beings can do this.

Our Earth

Our earth is one of the eight planets that revolves around the sun. The other seven planets are Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune. The sun and its eight planets together constitute the Solar system. Each planet in the solar system travels in its own path or orbit. Look at the Fig. 8.1 given below. Some planets are nearer to the sun, while some are farther from it. Can you name the planet nearest to the sun and the planet farthest from the sun? Mercury is closest to the sun, and as such, it is the hottest planet. It is so hot that no living organism, plant or animal, would be able to survive on it.

On the other hand, neptune is farthest from the sun, and as such, it is the coldest planet. Do you think it is possible for any plant or animal to survive in such extreme cold conditions?

Our earth is the third planet from the sun. As a whole, it is neither too hot nor too cold. In fact, it is the only planet of the solar system which is most suitable for supporting life.

The earth we live on has plains, mountains, deserts, rivers, lakes, oceans, etc. Since the earth is very large, therefore, we can see only a very small part of it. This part usually appears almost flat to us. But astronauts travelling in spaceships have observed the earth from long distances. They took photographs, which show that earth is spherical in shape somewhat like a ball.

The earth is not at rest. It keeps revolving around the sun, in an elliptical path called the orbit of earth. It completes one revolution around the sun in 365 1/4 days. Though the earth is always moving, we do not notice this motion because we are also a part of it.

As the earth moves around the sun along its orbit, it also rotates like a top about its own "axis". Due to this rotation, different parts of the earth face towards the sun one by one. You should know that the day and night occur due to this rotation. Furthermore, the axis of the earth is tilted to its orbit at an angle of 23 1/2 degrees. This helps in the formation of seasons on the earth.

Conditions Essential For Life

Have you ever thought of things which we need to live. Possibly, food is the basic necessity of life. Essentially, we get our food from the plants or animals. The animals, in turn, get their food again from the plants. Plants need water, air, soil and sunlight to prepare their food.

Our planet, Earth is indeed unique. All necessary requirements, for the existence of life, are available on it naturally, such as:

1. Presence of water: Water is extremely essential for living organisms. It is present in abundance on earth. The bio-chemical reactions taking place inside the living organisms need water.

2. Presence of oxygen: Earth has enough oxygen which is required by all living organisms for respiration.

3. The distance from the sun: The distance between the sun and the earth is such that earth is neither too hot nor too cold. The temperature at most of the places on earth remains between -20°C to +48°C which is favourable to sustain life. The heat from the sun is enough to warm the earth's land and water. The sunlight also provides energy to the plants to prepare their own food.

4. Presence of minerals: Carbon, hydrogen, oxygen and nitrogen are the essential elements required by living organisms and are present in sufficient amounts in various usable form. Soil too contains nutrients required for the growth of the plants.

5. Gravitational force: The earth has the right mass to exert the right gravitational force to hold its atmosphere. If the gravitational force of earth would have been less, then all the gases on the earth would have escaped into the outer space.

Biosphere

The part of the earth, including air, water, land, surface, that supports life is known as the Biosphere. It has three divisions: The entire part of earth's surface which is covered with rocks and soil is called Lithosphere. The depression in the lithosphere, filled with water is called the Hydrosphere, and surrounding the lithosphere and hydrosphere is an outer envelope of air, known as Atmosphere.

Lithosphere: It plays a very important role in the growth of plants since it contains minerals and essential nutrients for their growth.

Hydrosphere: About 70% of the earth's surface is water found in oceans, seas, rivers, lakes, etc.

Atmosphere: The layer of gases that surround the lithosphere and hydrosphere is called the atmosphere. The gases in the atmosphere are nitrogen, oxygen, a small amount of CO2, argon, water vapour and other gases. It also contains another gas, ozone in the upper parts, which prevents the sun's harmful ultraviolet rays from reaching the earth.

Environment

Our surroundings include plants, animals, water, land, air, sun, sky, clouds and many other things. All these affect our life and constitute our environment.

All that surrounds and affects the life of an organism (plant or animal), is its environment.

Factors of Environment

(A) Abiotic (non-living) factors or physical factors as air, water, soil, light, temperature, etc.

(B) Biotic (living) factors such as plants, animals and all such other life forms which influence the organism's life either directly or indirectly.

(C) Cultural factors: Man is a social being. Any activity of a person as an individual can affect his social environment.

Let us study more about the different factors of the environment and know how they influence and interact with each other?

Teacher's Note

Understanding that Earth orbits the sun and has unique conditions for life helps us appreciate why we must protect our planet. Every day, we depend on the atmosphere, water, and soil that make Earth habitable.

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