Science and Technology

• The process of protecting the fertile top layer of soil and building the
organic materials is called conservation of soil. Afforestation, terracing of
slopes, wise disposal of wastes, controlling overgrazing, dam construction
on the bank of river and adoption of proper agricultural practices are the
methods of soil conservation.

• Vertical section of soil from the surface showing different layers is called
soil profile. There are five layers or horizons in a soil profile.

• Removal of useful substances from the soil and addition of harmful
substance to it is called soil pollution.

• Industrial and household wastes, deforestation, garbage, excessive use of
fertilizers and pesticides, etc. are the causes of soil pollution.

• Soil pollution causes the loss of fertility, climate change, pollution of
drinking water, effects on human health and wild life.

• Soil pollution can be prevented by afforestation, awareness of the impacts
of pollution, reducing the use of fertilizers and pesticides, adoption of 3R,
proper management of wastes and consuming organic products.

• The internal structure of the earth is made of crust, mantle and core.
• The earth moves around the sun in an elliptical orbit in 365.25 days. It

also moves around its axis in 24 hours.
• Changes of season occur because of the earth’s tilt with the orbital plane

and its revolution around the sun on an elliptical path.
• There are four seasons in a year-Spring, Summer, Autumn and Winter.
• Summer is the hottest season and winter is the coldest season of the year.
• Autumn and Spring have moderate temperature.
• The family of the sun consisting of the sun, eight planets, asteroids,

satellites, comets, meteors and meteorite is called solar system
• The sun is a medium-sized star made of hydrogen and helium. It is

15,00,00,000 km away from the earth.
• The temperature of the core is 15 million degree Celsius but the surface

temperature is only 6,000 degree Celsius.
• The heavenly bodies that go around the sun are called planets.
• The rocky planets inside of the asteroid belts are called inner planets and

the planets outside of the asteroid belts are called outer planets.
• The inner planets also called earth-like planets are Mercury, Venus, Earth

and Mars.

251 kf7o\ j|md ljsf; sG] b|af6 :jLst[

• Outer planets also called gas giants are Jupiter, Saturn, Uranus and
Neptune.

• Asteroids are also called dwarf planets. They are smaller than the planets.
Ceres, Pluto and Eris are the largest asteroids.

• The heavenly bodies that revolve round a planet are called moons. Moons
are also called natural satellites.

• The earth has only one moon. Outer planets have larger numbers of
moons.

• The cosmic snowball of gases, rocks and dust that appears as a long bright
tail with head only when it arrives near the sun is called comet.

• Rocks and dust which burn brightly when they enter the earth’s atmosphere
are called meteors.

• The meteors that strike the earth without burning in the earth’s atmosphere
are called meteorites.

Check your knowledge

1. Tick () the correct statement and cross () the wrong one.
a. The process of protecting the fertile top layer of soil is called soil
erosion.
b. The vertical section of soil from the surface showing different layers is
called soil profile.
c. Mantle is the hottest part of the earth’s interior.
d. Rocks are in the state of compressed solid in inner core.
e. A shadow is formed when an opaque body obstructs the light.
f. The earth revolves around the sun in a circular orbit.
g. The sun is considered as a medium-sized star.
h. The temperature of the surface of the sun is much higher than that of the
core.
i. Jupiter is the largest terrestrial planet.

2. Fill in the blank spaces with the correct words.
a. Soil is formed by ___________________ of the rocks.
b. The colour of the soil depends on _________________ present in it.
c. The process of forming a sediment by the transportation of eroded materials
is called ________________ .
d. The _______________ is the thickest layer of earth’s inner part.

252 kf7o\ jm| d ljsf; sG] ba| f6 :jLst[

e. It often rains in _________________ season in Nepal.
f. December, January and February fall in ________________ season.

g. The seasons in Nepal are different from the ______________ practices.
h. Spring season comes after _________________ season.
i. Heat is produced in the sun when the ______ gas changes into ______ .

j. Asteroid belt lies between the orbit of the ________ and ___________ .
k. The meteors are also called _______________ .

3. Choose the correct option from the given alternatives.

a. Which of the following is the parent material of a soil?
i. minerals ii. air
iii. micro-organism iv. organic matter

b. What is soil erosion?
i. natural process of removing harmful wastes.
ii. is the process of formation of soil.

iii. a process of removing and transporting soil by water or wind.
iv. a process of rising environment temperature.

c. The rocks are in a solid state in the inner core because of:
i. high temperature and pressure ii. high temperature
iii. high pressure iv. low pressure

d. Which of the following is not a condition for change of season?
i. earth’s tilt iii. revolution of the earth
iv. revolution on elliptical path iv. rotation of the earth

e. Which of the following pairs of months has optimum temperature in our
country?
i. Baishakh and Jestha ii. Falgun and Chaitra

iii. Bhadra and Aswin iv. Aswin and Kartik

A. i and ii B. ii and iv C. ii and iii ii and iv

f. The distance between the sun and the earth is:
i. 150, 000 km ii. 150 million km
iii. 15 million km iv. 140,00,000 km

g. Which of the following is not a dwarf planet? iv. pluto
i. Enke ii. Eris iii. Ceres

4. Differentiate between the following.

a. afforestation and deforestation
b. Spring and autumn (seasons)
c. Axis and orbit

d. star and planet 253
e. inner planet and outer planet
f. meteors and meteorites

kf7\ojm| d ljsf; sG] ba| f6 :jLs[t

5. Give reason for the following.
a. Erosion and deposition occur successively.
b. Winter months are cold in the northern hemisphere.
c. Meteors produce streak of light.
d. Comet develops a tail when it approaches the sun.

6. Answer the following questions and do the rest as instructed.
a. What is soil? Write different components of soil.
b. What is soil conservation? Mention any three methods of soil conservation.
c. What is soil profile? List the master horizons of soil.
d. What is soil pollution? Write any three causes of soil pollution.
e. What are the effects of soil pollution? Mention the methods of prevention of
soil pollution.
f. What are the different layers of the earth’s inner part?
g. Draw a diagram of the earth’s interior part and label each part as per the
value of thickness.
h. How does the earth move around the sun?
i. What are the causes of changes of seasons?
j. Draw a chart to show the changes of seasons and describe the condition of
each season.
k. Mark the seasons in all the positions in the diagram below.

North pole
E4

South pole

North pole North pole

E1 E3

South pole South pole

North pole

l. What is solar system? South pole E2

m. What are the size and the temperature of the sun?

n. How does the sun produce heat?

o. What is a satellite? Which planets have larger numbers of satellites?

p. What is a comet? When does it appear in the sky?

q. Why do the meteorites not appear during the day time?

r. Identify the following and write any two characteristics of these objects.

(i) (ii)

254 kf7o\ jm| d ljsf; sG] b|af6 :jLst[