Question 511 Mark
Define oxygen cycle.
Answer
View full question & answer→The cycle of consumption of oxygen by respiration and its release by photosynthesis is called oxygen cycle.
Questions · Page 2 of 2
[1 Marks Each] QUE - ANS
Question 521 Mark
Why do you think mountaineer carry oxygen cylinders with them, while climbing high mountains?
Answer
View full question & answer→ There is less oxygen at high places like mountains, so they carry oxygen cylinder with them to breathe there.
Question 531 Mark
Why does the transparent glass of windows, if not wiped off regularly, appears hazy?
Answer
View full question & answer→Air contains dust and smoke along with the gases. These gets deposited on the glass windows and make them appear hazy.
Question 541 Mark
Why there are long chimneys in factories?
Answer
View full question & answer→Chimneys take the harmful gases and smoke of factories away from our noses.
Question 551 Mark
What is atmosphere?
Answer
View full question & answer→ Our earth is surrounded by a thin layer of air. This layer is called atmosphere. It extends up to many kilometres above the surface of the earth.
Question 561 Mark
What is air made up of?
Answer
View full question & answer→ Air is made up of mixture of gases like-Nitrogen, oxygen, carbon dioxide, water vapour, dust particles and other gases.
Question 571 Mark
Why we should not breathe through our mouth?
Answer
View full question & answer→If we will breathe through our mouth then dust particles present in air will enter our body and will cause harmful diseases.
Question 581 Mark
The mountaineers carry oxygen cylinder with them while climbing high mountains.Why?
Answer
View full question & answer→ The availability of air decreases gradually as we go up in the atmosphere.
Question 591 Mark
When the open mouth of an empty bottle is tilted in a bucket filled with water, we see bubbles coming out of it. Explain the phenomenon.
Answer
View full question & answer→The bottle contains air so when it was titled air came out in the form of bubbles.
Question 601 Mark
Explain with flow diagram oxygen-carbon dioxide balance in the atmosphere.
Answer
View full question & answer→ Oxygen-carbon dioxide balance is the balance between the rate of consumption and formation of oxygen and carbon dioxide in nature.
Question 611 Mark
Name the gases present in atmosphere.
Answer
View full question & answer→Nitrogen, oxygen, carbon dioxide, water vapour, dust particles and other gases.
Question 621 Mark
Make sentences using the given set of words.
$99\%$, oxygen, nitrogen, air, together.
$99\%$, oxygen, nitrogen, air, together.
Answer
View full question & answer→Oxygen and nitrogen together make up $99\%$ of the air.
Question 631 Mark
Name the substances which are present in traces in air. What are these together called?
Answer
View full question & answer→Xenon $(Xe)$, Krypton $(Kr)$, Neon $(Ne)$ and Helium $(He)$ are present in traces in the air. These together form $0.02\%$ of air and are called inert gases.
Question 641 Mark
Which of the two gases are present in higher amount in the atmosphere oxygen or carbon dioxide gas?
Answer
View full question & answer→Oxygen.
Question 651 Mark
Have you ever seen tiny shining particles in the beam of sunlight, what are these particles?
Answer
View full question & answer→Dust particles.
Question 661 Mark
Why pages of an open book begin fluttering when the fan is switched on?
Answer
View full question & answer→Because of air.
Question 671 Mark
Air occupies space. Explain the statement.
Answer
View full question & answer→ Blow a balloon, air from your body enters balloon at it gets bigger because air occupies space.
Question 681 Mark
Activity.Find a sunny room in your school/home. Close all the doors and windows with curtains pulled down to make the room dark. Now, open the door or a window facing the sun, just a little, in such a way that it allows sunlight to enter the room only through a slit. Look carefully at the incoming beam of sunlight.
Do you see some tiny shining particles moving in the beam of sunlight (Fig.)? What are these particles?
Do you see some tiny shining particles moving in the beam of sunlight (Fig.)? What are these particles?
Answer
View full question & answer→Yes, some tiny shining particles are seen moving in the beam of sunlight. These are the dust particles which are resent in air.
Question 691 Mark
How does oxygen become available to the animals in water and soil?
Answer
View full question & answer→ Air remains dissolved in water. Air is also present between the particles of soil. Hence animals living there get oxygen.
Question 701 Mark
How can you show that air is dissolved in water?
Answer
View full question & answer→ Take water in a pan and heat it. After sometimes just before it boils we can observe some bubbles at the inner surface of the pan. This is because of the air dissolved in water.
Question 711 Mark
How does oxygen occur in nature?
Answer
View full question & answer→Oxygen is found in free state in air as diatomic molecule ($O_{2}$) to the extent of $21\%$ by volume or $23\%$ by weight. In the combined state, it is present in water $(89\%$ by weight$)$, earth’s crust $($about $50\%)$ and in plants and animal tissues $(50-70\%).$