NCERT Book Class 6 Science Natures Treasures PDF Download

Chapter 11: Nature's Treasures

School vacations are always fun for Bhoomi and Surya. This vacation, they visit their Ajji (grandmother). Ajji lives in a village on the edge of a forest in the Western Ghats. The air in the village is fresh and cooler than in the city. They can see beautiful hills, streams, and many interesting plants, animals and birds around them.

One afternoon, Bhoomi and Surya ask Ajji to tell them more about the place. Ajji says, "Children, do you know that this place has several treasures of nature that enrich our lives? The pure air is refreshing and the soil is so fertile that it supports a variety of living beings. Moreover, this place gets plenty of sunlight which is useful in many ways. Different varieties of trees provide food and shelter to animals including various birds and insects. Can you think of more such treasures of nature?"

[Figure: A village, See in your textbook]

Bhoomi replies, "Ajji, we use water for drinking and growing vegetables." Ajji says, "Yes. We need these treasures for our survival and for making our lives more comfortable. Without these treasures of nature, any form of life on Earth is not possible." We all are a part of nature.

Ajji explains the importance of air around us and how it is essential for our survival. Let us find out more about air.

11.1 Air

One morning, Bhoomi and Surya see Ajji performing some breathing exercises. Ajji asks them to join her. She says, "I am taking deep breaths in, and letting them out. This helps in getting more fresh air in the lungs to stay healthy." Bhoomi and Surya sit with Ajji and start taking deep breaths.

Let us also perform a breathing exercise.

Activity 11.1: Let us experience

• Take a deep breath in, and then breathe out slowly.
• Take a deeper breath in again.
• Hold your breath for as long as you can and then breathe out slowly.
• How long can you hold your breath?
• How do you feel when you hold your breath?

[Figure: Breathing exercise, See in your textbook]

From this activity, we find that it is difficult to hold our breath for a long time. The air which we breathe in has oxygen. Our body needs oxygen to perform its functions. When we hold our breath for a long time, the body does not get enough oxygen to perform its functions. Thus, we need oxygen for our survival. Similarly, most of the living beings also need oxygen for their survival.

Teacher's Note

Oxygen is only 21% of the air we breathe, but it is the only part your body actually uses. When you hold your breath, your body quickly runs out of this oxygen and feels uncomfortable. This shows why even though air has many gases, we are most dependent on the oxygen in it.

Do you know?

We can survive without food or water for a few days, but we cannot survive without oxygen for even a few minutes.

You notice the presence of air when the leaves of a tree rustle, the clothes hanging on a clothes line sway, or the pages of an open book begin to flutter once a fan is switched on.

Moving air is called wind. Sometimes it blows fast, for example, during a storm, and sometimes it blows gently as a breeze. You must have played with a firki (paper pinwheel) many times. Let us make a firki by performing Activity 11.2.

The air which surrounds the Earth is a mixture of gases. Can you name some gases which are present in the air? Air contains nitrogen, oxygen, argon, carbon dioxide and other gases in small quantities. Fig. 11.1 gives the composition of air in percentage. Notice that in Fig. 11.1 there are 100 squares. Out of 100 squares, 78 are occupied by nitrogen, 21 are occupied by oxygen, and 1 by argon, carbon dioxide and other gases.

[Figure 11.1: Composition of air, See in your textbook]

More to know!

Percentage is the number of parts in 100. It is denoted by the symbol '%'.

Teacher's Note

When you see a percentage, always think "out of 100". So 78% nitrogen means if we divide air into 100 equal parts, 78 of those parts are nitrogen. This 100-part idea makes percentages much easier to picture and compare.

Key Points

• Air is a mixture of gases, mainly nitrogen (78%), oxygen (21%), and small amounts of other gases like argon and carbon dioxide (1%).
• Oxygen is the part of air that our body needs to survive; we cannot live without it for more than a few minutes.
• Moving air is called wind, and it can be as gentle as a breeze or as strong as a storm.
• Percentage means the number of parts out of 100, shown by the symbol '%'.

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