Read the given passage and answer the questions that follow: 8
1. Our Earth is like a greenhouse, with one difference. A greenhouse is encased in glass, while the
Earth is encased in a thin blanket of carbon dioxide (CO). This carbon dioxide serves the same
function for the Earth as docs glass for a greenhouse. It helps to keep the Earth warm. Scientists call
it the 'greenhouse effect'.
2. The amount of carbon dioxide in the air is only .03 per cent, yet all plant and animal bite depends
on it. The percentage of carbon dioxide in the air is kept almost constant by a series of natural processes. We call it call carbon (or carbon dioxide) cycle.
3. Carbon dioxide is added to the atmosphere by two main processes - breathing and burning. All
living things breathe out carbon dioxide into the atmosphere. The air breathed in contains only .03per cent carbon dioxide, whereas the air breached out contains 4 per cent. Thus breathing leads to
an increase in the amount of carbon dioxide in the air. Also large quantities of carbon dioxide are
produced by the burning of wood, coal and oil.
4. The main way in which carbon dioxide is removed from the atmosphere is by photosynthesis2
“. It is
a process by which green plants, with the help of sunlight, break up carbon dioxide into carbon . and
oxygen. Carbon is retained by the plants as their food, and they set free oxygen for the use of i
animals. All animals depend, directly or indirectly, on plants for their food. And all plants, in turn,
depend on carbon dioxide breathed out by animals.
5. Carbon dioxide is removed from the atmosphere by water also. This gas is moderately soluble in
water. Thus our rivers, lakes and seas also take up a lot of carbon dioxide from the air. Water
animals use this dissolved carbon dioxide to make their shells. When these animals breathe or die
and decay, carbon dioxide is released back into the atmosphere. Thus the cycle is completed.
Choose the correct option to answer each of the following questions:
(a) The carbon cycle is series of natural processes that help……………
a. To increase the amount of CO2 in the air.
b. To reduce the amount of CO2 in the air.
c. To keep the amount of CO2 in the air almost content.
d. To keep air free from pollution.
(b) ‘Photosynthesis’ is the process by which green plants break up …………
a. The carbon cycle into carbon and oxygen.
b. Carbon dioxide into carbon and oxygen.
c. The sunlight into light and heat.
d. The green–house effect into light and heat.
(c) How do all animals depend on plants?
a. They eat the food that plants produce.
b. They breathe in the carbon dioxide that plants produce.
c. Both a and b above.
d. Neither a nor b
(d) How do all plants depend on animals?
a. Carbancycle
b. Carbondioxide
(e) What is meant by ‘soluble’?
a. That can be solved
b. That can be dissolved
c. That can be eaten
d. That can be preserved
(f) How do plants get their food?
a. By breaking up CO2 into carbon and oxygen and using the carbon as their food.
b. By breaking up CO2 into carbon and oxygen and using oxygen.
c. By breaking up the sunlight with the help of their leaves.
d. By ranking up water and vitamins with the help of their roots.
Answer the following questions briefly.
(g) How does the earth differ from a greenhouse?
(h) What is the normal percentage of carbon dioxide in the air?
Answers
Answer:
a: option is A
b: option is B
c: option is c
d: option is b
e: option is b
f: option is a
g: earth differ from greenhouse
h:95percent come from natural resources,humans:0.0016
(a) The correct answer is: (option c) To keep the amount of CO2 in the air almost constant.
The carbon cycle is series of natural processes that help to keep the amount of CO2 in the air constant.
(b) The correct answer is: (option b) Carbon dioxide into carbon and oxygen.
‘Photosynthesis’ is the process by which green plants break up carbon dioxide into carbon and oxygen.
(c) The correct answer is: (option a) They eat the food that plants produce.
All animals depend on plants as they eat the food that plants produce.
(d) The correct answer is: (option b) Carbon dioxide.
All plants depend on animals for carbon dioxide.
(e) The correct answer is: (option b) That can be dissolved.
‘Soluble’ means that can be dissolved.
(f) The correct answer is: (option a) By breaking up CO2 into carbon and oxygen and using the carbon as their food.
Plants get their food by breaking up CO2 into carbon and oxygen and using the carbon as their food.
(g) The earth differs from a green house. There is only one difference and that is: a greenhouse is encased in glass, while the Earth is encased in a thin blanket of carbon dioxide. This carbon dioxide serves the same function for the earth as does glass for a greenhouse.
(h) The amount of carbon dioxide in the air is only 0.03 percent, yet all the plant and animal depends on it. The percentage of carbon dioxide in air is kept almost constant by a series of natural processes called carbon cycle.
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