Earth as a Planet

Choose the correct option

Question 1

At the Bedford level canal area a famous experiment was carried out. How many poles were used and at what distance apart?

1. 3 poles, 5m
2. 2 poles, 10m
3. 4 poles, 5m
4. 3 poles, 10m

Answer

3 poles, 5 km

Note — There is a misprint in the book. The distance should be 5 km.

Question 2

Which part of a ship is visible when one watches an approaching ship at the shore?

1. the hull
2. the mast
3. the entire ship
4. the deck

Answer

the mast

Question 3

At what angle can the Pole Star be seen at the Poles and at the Equator?

1. 60°, 30°
2. 90°, 0°
3. 45°, 45°
4. 0°, 90°

Answer

90°, 0°

Question 4

Magellan's ship Victoria after completing a round-the-world voyage in 1522 returned to which country?

1. France
2. Spain
3. London
4. United States of America

Answer

Spain

Question 5

Earth's diameter at the Equator is ............... and at the poles is ............... .

1. 12,750 km, 12,715 km
2. 12,752 km, 12,726 km
3. 12,714 km, 12,755 km
4. 12,756 km, 12,714 km

Answer

12,756 km, 12,714 km

Question 6

What is the shape of the earth?

1. Sphere
2. Oblate
3. Oval
4. Oblate Spheroid

Answer

Oblate Spheroid

Question 7

What is the shape of earth called?

1. Oblate
2. Spherical
3. Geoid
4. Spheroid

Answer

Geoid

Question 8

The atmosphere of Venus has maximum concentration of which gas?

1. Oxygen
2. Carbon dioxide
3. Nitrogen
4. Helium

Answer

Carbon dioxide

Question 9

Name the gas that absorbs the harmful ultraviolet rays of the sun.

1. Ozone
2. Oxygen
3. Carbon dioxide
4. Nitrogen

Answer

Ozone

Question 10

What is the thickness of the Biosphere?

1. 20 km
2. 19 km
3. 15 km
4. 25 km

Answer

15 km

Question 11

What term refers to a self-regulating and self-sustaining unit of the biosphere?

1. Ecosystem
2. Food cycle
3. Biome
4. Ecology

Answer

Ecosystem

Question 12

Name the cycle through which solar energy moves from non-living to living organisms and back.

1. Carbon cycle
2. Nitrogen cycle
3. Nutrition cycle
4. Energy cycle

Answer

Nutrition cycle

Question 13

Name the basic raw material for life.

1. Nitrogen
2. Carbon
3. Oxygen
4. solar energy

Answer

Carbon

Question 14

Which is the fifth largest planet in the solar system?

1. Mars
2. Jupiter
3. Earth
4. Neptune

Answer

Earth

Question 15

Which planet is also called as the Watery planet?

1. Saturn
2. Venus
3. Mercury
4. Earth

Answer

Earth

Question 16

Which is the planet after Earth and before Jupiter?

1. Venus
2. Mars
3. Saturn
4. Uranus

Answer

Mars

Question 17

Which of the following is not a chief member of the solar system?

1. Satellites
2. Asteroids
3. Meteorites
4. None of the above

Answer

None of the above

Question 18

Where was the Bedford Level Experiment carried out?

1. England
2. France
3. India
4. Canada

Answer

England

Short Answer Questions

Question 1

How can you prove that the earth is a sphere by looking at the horizon?

Answer

The view of the earth's surface as seen from a height is circular. We can prove that the earth is a sphere by looking at the horizon as with increase in altitude, the circular horizon also widens. Had the earth's surface been flat, the horizon would have been the same irrespective of the altitude.

Question 2

Briefly describe the shape of the earth.

Answer

The earth is said to be spherical, but it is not a perfect sphere. The diameter at the equator is greater than the diameter at the poles. The bulge at the equator and compression at the poles gives earth the shape of an oblate spheroid or 'Geoid'.

Question 3

What is the earth's mean temperature? State its one advantage.

Answer

The mean temperature of the earth is 17 degrees Celsius. This temperature is ideal for life to exist.

Question 4

Why is the earth called a watery planet?

Answer

Earth is called a watery planet because 70% of the earth's surface is covered by water.

Question 5

What is 'biosphere'?

Answer

Biosphere is the life zone of the earth. It is that part of the earth's terrestrial system - including air, land and water - in which life develops and where life processes in turn get transformed.

Question 6

Name the conditions necessary for life on earth.

Answer

The conditions necessary for life on earth are as follows:

1. Optimum distance from the sun
2. Ideal temperature of 17 degrees Celsius
3. Presence of Atmosphere
4. Presence of water
5. Presence of lithosphere and biosphere
6. Life-giving cycles operate in nature

Question 7

Give any two features of the earth that make it a 'Unique Planet'.

Answer

Two features of the earth that make it a 'Unique Planet' are as follows:

1. Presence of Atmosphere
2. Presence of water

Structured Questions

Question 1(a)

How does the sighting of a ship from the seashore prove about that the earth is round in shape?

Answer

While standing at the seashore, watching an approaching ship, we first see only its mast. Then, as it comes closer, we can see the deck in the middle, then its funnel, and finally the hull comes into full view. This can only happen when the earth's surface is curved. Thus, it is proved that the earth is round in shape.

Question 1(b)

State briefly the Bedford Level Experiment.

Answer

An experiment was carried out in the Bedford Level canal area in England.

Procedure- Three poles of equal length were fixed at intervals of 5 km. It was ensured that the poles had the same height above the water in the canal.

Observation- When the poles were viewed from one end of the canal, the middle pole looked slightly higher.

Result- This experiment demonstrated that the surface of the earth is curved.

Question 1(c)

Give a geographical reason for each of the following:
(i) The sunrise and sunset occur at different times at different places.
(ii) The earth is not a perfect sphere.
(iii) Venus is hotter than mercury.

Answer

(i) The sunrise and sunset occur at different times at different places because the earth rotates from west to east and therefore, people in the east can see the sun earlier than those in the west.

(ii) The earth is not a perfect sphere because the diameter of the earth varies at the equator and at the poles. This difference is due to the centrifugal force of the earth's rotation at a great speed which forms a bulge at the equator and a compression at the poles.

(iii) Venus is hotter than mercury because Venus is mainly composed of carbon dioxide which produces Greenhouse effect on the surface of Venus. Thus, the temperature on its surface remains very high.

Question 1(d)

Draw a well labelled diagram to show that the horizon of the earth is circular in shape.

Answer

Question 2(a)

Describe the role of atmosphere in making earth a habitable planet.

Answer

The atmosphere of the earth is composed of gases like nitrogen (78%), oxygen (21%), carbon dioxide, helium and argon (less than 1%). Atmosphere plays a major role in making earth a habitable planet as-

1. The atmosphere receives heat from the sun by solar radiation and loses heat by earth's radiation. In this way, a balance is maintained.

2. The earth's atmos[here is made up of life-supporting gases like nitrogen, oxygen and carbon dioxide.

3. Ozone present in the earth's atmosphere absorbs harmful ultraviolet rays of the sun.

4. The atmosphere also prevents loss of heat from the earth's surface and helps to keep earth warm.

Question 2(b)

Describe the role of water in making earth a habitable planet.

Answer

Earth is a watery planet with 70% of the earth's surface being covered by water. Water plays a major role in making earth a habitable planet as-

1. Distribution of water is responsible for moderating the climate and surface condition of the earth.

2. Water bodies like lakes, ponds, rivers etc. are important parts of the ecosystems and biosphere.

3. Water moves in a continuous hydrological cycle. There is a proper balance between evaporation, condensation and precipitation without which life would not be possible.

4. Water bodies help to maintain the temperature of the earth's surface. They rapidly absorb enormous amount of heat during the day, and keep the earth fairly cool. At night, they release the heat absorbed during the day, which along with other atmospheric effects, keep most of the surface from freezing at night.

Question 2(c)

Describe the role of temperature in making earth a habitable planet.

Answer

Temperature plays a major role in making earth a habitable planet as the earth is the third planet from the sun. It has an average temperature of 17 degrees Celsius which is suitable for life to exist. Other planets of the solar system are either too hot or too cold to support life.

Question 2(d)

Describe the role of distance from the sun in making earth a habitable planet.

Answer

Distance from the sun plays a major role in making earth a habitable planet as-

1. The earth is at an optimum distance from the sun. Hence, it is neither too hot nor too cold.

2. The distance between the earth and the sun makes life possible on earth. If it was closer to the sun, any life present would get burnt from too much heat of the sun. If it was farther from the sun, life would freeze because of lack of heat.

Question 3(a)

How does each of the following prove the circular shape of the earth:
(i) Lunar Eclipse
(ii) Pole Star

Answer

(i) Lunar Eclipse

The shadow of the earth on the surface of the moon is clearly visible from earth during lunar eclipse. It appears as an arc of a circle. Since the earth is bigger than the moon, it is rarely oriented in the same position as the moon but the shadow is always circular. This proves the circular shape of the earth.

(ii) Pole Star

The Pole Star can be seen at an angle of 90 degrees at the North Pole. It lies in line with the axis of the earth, and its angle decreases towards the equator. At the equator, the angle is 0 degrees. This can happen only in an arc of a circle. This proves the circular shape of the earth.

Question 3(b)

What is an ecosystem? Give an example.

Answer

The self-regulating and self-sustaining structural and functional unit of the biosphere is called an ecosystem. This system depends upon the sun for its energy.

For example, Ecosystem of a forest include plants and trees which are eaten by herbivores (deer, rabbit). These animals are eaten by carnivores (lion, tiger). When these animals perish, they are decomposed by decomposers and return to the environment. Again they are consumed by producers and so on.

Question 3(c)

Give a geographical reason for each of the following:
(i) Earth is a habitable planet.
(ii) From space Earth looks blue.
(iii) Water bodies reduce the day-night temperature variations.

Answer

(i) Earth is a habitable planet as it is covered with green vegetation, enormous blue-green oceans containing over a million islands, a large number of streams and rivers, huge land masses called continents with mountains, ice caps and deserts. It also has ideal temperature for the existence of life.

(ii) From space Earth looks blue because 70% of the earth's surface is covered by water.

(iii) Water bodies reduce the day-night temperature variations as water can absorb enormous amounts of heat without causing much change in its temperature. Water bodies rapidly absorb enormous amount of heat during the day, and keep the earth fairly cool. At night, they release the heat absorbed during the day, which along with other atmospheric effects, keep most of the surface from freezing at night.

Question 3(d)

Draw a well labelled diagram to show the cyclic circulation of water between the three realms of the earth.

Answer

Thinking Skills

Question 1

You have gone from Delhi to Arunachal Pradesh on a study tour with your school during the winter vacation. As you woke up in the morning at 6 o'clock, you noticed the sun has risen whereas at Delhi sun rise is around 7.30 a.m. Similarly around 4.30 it was sunset while sunset is around 6 p.m. in Delhi. What do you think could be the reason for the sun rising and setting earlier than Delhi? Which feature of the earth can you relate to from this?

Answer

The sun rises from the east and sets in the west. Sunrise and sunset occurs at different times at different places because the earth rotates from west to east. Arunachal Pradesh is situated to the east of Delhi and hence, people in Arunachal Pradesh experience the sunrise and sunset earlier as compared to the people who live in Delhi.

This also proves that the earth is geoid in shape as had the earth been flat, the sunrise and sunset would have occurred at the same time all over the world.

Question 2

The earth depends upon the sun for its energy. Imagine a day, when the sun would not rise. Write down the consequences for the earth and its inhabitants.

Answer

If the sun did not rise for a day, it would have catastrophic consequences for the earth and its inhabitants:

1. The sun is the primary source of energy for all life on earth. The absence of sunlight would cause a rapid drop in temperature, leading to widespread damage to aquatic ecosystems.
2. Without sunlight, photosynthesis will not be possible. The lack of food for plants and herbivores would ultimately lead to the extinction of many species, causing a ripple effect on the food chain.
3. Plants regulate the oxygen and carbon dioxide in the atmosphere. The loss of plants will lead to decrease in oxygen production and affect all living organisms.
4. The sudden and prolonged absence of sunlight would have a profound impact on human society, with panic and chaos as people struggle to adapt to the situation.

Thus, it is clear that the Sun is essential for life on earth.