Blooming science-8-part-2 part press

6. Excretory system Kidnys, urinary To remove metabolic

bladder , liver & wastes from body.

large intestine

7. Nervous system Brain,Spinal lord To maintain co-ordination

& nerves & communication in all
organs.

8. Reproductive Testes, ovavy To produce young ones of
system & genital organs own kind

9. Glandular System Various glands To produce hormones.

Main Points to Remember

1. The structural and functional unit of life is called cell.

2. A tissue is a collection of similar cells organized to carry out one or more
particular function.

3. An organ is a group of tissues performing a special function.

4. A system is a group of structures or organs.

5. Animal tissues are classified into four types. They are epithelial tissue,
connective tissue, muscular tissue and nervous tissue.

6. Epithelial tissue is a thin protective layer of cells which covers the inner and
outer surfaces of organs.

7. Epithelial tissue is further divided into two-simple epithelium and compound
epithelium.

8. Simple epithelium is further divided into squamous or pavement ethelium,
cuboidal epithelium, columnar epithelium, glandular epithelium and sensory
epithelium.

9. Compound epithelium is further divided into stratified epithelium and
transitional epithelium.

10. Plant tissue is divided into meristematic tissue, areolar and permanent tissue on
the basis of nature, position and function of cells.

11. Meristematic tissue is a group of actively dividing cells found at the tip of roots
and shoot. It is responsible for growth of plant.

12. Apical, intercalary and lateral meristems are three kinds of meristematic
tissues.

13. Permanent tissue is a group of cells derived from meristematic tissue.

14. Permanent tissue is divided into simple permanent, complex permanent and
special permanent tissue.

Blooming Science & Environment Book 8 223

PRO J ECTWORK

Take a soft stem of a herbaceous plant. Cut few thin transverse sections with the
help of blade. Keep these in a watch glass and stain with the help of safranin.
Then transfer a thin and complete slide into a glass slide. Put a drop of slycerin
temporary slide of stem. Observation in your copy and discuss about its structure.

Exercise

1. Fill in the blanks.
a. Organisms which have many cells in their body are called __________.
b. The outermost covering of the plant cell is _________________.
c. The living structures in the cytoplasm are called _____________.
d. The two types of reproduction in amoeba are __________ and ______.
e. _______________ are the ‘power house of cell’.
f. __________ and permanent tissue are two of plant tissue.
g. There are ¬¬_____ types of tissue in animal.

2. State whether the following statements are ‘True’ or ‘False’.
a. All cells possess nucleus.
b. The cells without nucleus are called exnucleated cells.
c. Plastids are found only in plant cells.
d. All species of amoebae are unicellular organism.
e. Meristematic tissue is found in animal.
f. Chromosomes are seen always in the cell.
g. Big vacuoles are seen in animal cells

3. Write notes on.

a. Golgi complex b. Mitochondria

c. Plastids d. Epithelial tissue

e. Nucleus

4. Answer the following questions.

a. What is a cell?

b. Draw a neat and labeled diagram of plant cell.

c. Draw a neat and labeled diagram of animal cell.

224 Blooming Science & Environment Book 8

d. What are the important organelles in the cytoplasm?
e. Differentiate between plant cell and animal cell.
f. What are the major functions of ribosome, endoplasmic reticulum and

plastids?
g. What are the three types of plastids? Mention their function and location

where they are found.
h. What is a tissue?
i. Classify animal tissue.
j. Show the relation of cell, tissue and organ in plants.
k. What is meristematic tissue.
l. Write the types of epithelial tissues.
m. Show the relation of cell, tissue and organ in animals.

Glossary

Connective tissue : the tissue which connects two or more tissues and organs

Diffusion : the process of flowing substances from the higher
concentraction to the lower concentration

Fibrinogen : a protein found in plasma that helps in blood clotting

Prothrombin : a chemical found in blood and plays an important role in the
blood clotting

bone marrow : a region inside bone, where blood cells are formed

Hormones : secretion of ductless glands and responsible for the coordination
of growth and development

Dexygenated : impure or having no oxygen

Oxygenated : pure or having oxygen

Superficial : close to the surface

Blooming Science & Environment Book 8 225

Chapter Life Process

18

Learning Outcomes Estimated Periods: 10+2

On the completion of this unit, the students will be able to:
 describe asexual and sexual reproduction in plants and animals.
 describe in short about circulatory system of human beings.
 explain and demonstrate process photosynthesis in plants.

A. Reproduction

Reproduction is a life process in which all living organisms produce new individuals
of their own kind. By reproduction, living organisms maintain the existence and
continuity of their race. There are two types of reproduction.

a) Asexual reproduction b) Sexual reproduction

Asexual Reproduction

Asexual reproduction is a type of reproduction that occurs without the fusion of
male and female gametes. It produces indentical offspring. It enables the organism to
multiply faster under the favourable conditions of environment. Asexual reproduction
in organisms takes place by the following methods.

i) Fission ii) Budding iii) Regeneration

iv) Sporulation v) Framentation v) Vegetative propagation

i) Fission

Reproduction in unicellular

organisms mostly occurs by

fission. In this reproduction, an

organism divides into two and two

into four and so on. Fig: Fission

The daughter organisms produced

are exactly identical to their parent. Fission is very common in Amoeba, Paramecium,

Euglena, Yeast, Plasmodium, etc.

226 Blooming Science & Environment Book 8

ii) Budding

In budding an outgrowth or bud is produced from the parent body. After its complete
development, it detaches from parent body. Then bud grows and assumes the form
and size of the parent. For example, Hydra, Yeast, etc.

Fig: Yeast budding Fig: Hydra budding

iii) Regeneration

In regeneration, parent body breaks into two or more
fragments and each fragment develops into a new
individual. For example, Tapeworm, Hydra etc.

Fig: Tape worm

iv) Sporulation

The reproduction that occurs by spores is called sporulation. In
some lower non-flowering plants like Fern and Mucor, spores
are formed. These spores germinate and grow into new plants
under suitable conditions.

v) Framentation Fig: Mucor

In fragmentation process, a living body is
fragmented into two or more fragments and each is
developed into new organism. This process takes
place in lower plants like in spirogyra.

vi) Vegetative Propagation Fragmentation of Spirogyra

It is the method of reproduction in some higher flowering plants through vegetative
organs such as roots, stems and leaves.

Vegetative propagation by root: Sweet potato, Dahlia, etc.

Vegetative propagation by stem: Onion, Potato, Ginger, etc.

Vegetative propagation by leaf: Bryophyllum, Begonia, etc.

Blooming Science & Environment Book 8 227

Fig: Sweet potato Fig: Onion bulb Fig: Bryophyllum leaf

Sexual Reproduction

The reproduction that involves the fusion of male and female gamete is called sexual
reproduction. Most developed plants and animals reproduce sexually.

In flowering plants, stamen produces the male gamete and pistil produces the female
gamete.

In most sexually reproducing plants and animals, male and female individuals are
separate. Male produces the male gamete (sperm) and female produces the female
gamete (ovum). Such organisms are called unisexual or dioecious. For example,
Human, Bird, Frog, Papaya, Pumpkin etc.

When both male and female sex organs are found in the same organism, it is called
bisexual or hermaphrodite. For example, Earthworm, Hydra, Mustard, Buckwheat
etc.

Male gamete is called sperm and female gamete is called egg or ovum. In sexual
reproduction fusion of male gamete and female gamete takes place. This process is
called fertilization. There are two types of fertilization occurs in animals i.e; external
fertilization and internal fertilization. The fusion of male gamete and female gamete
outside the body of an organism is called external fertilization. External fertilization
occurs in animals like frog, fish etc. The fusion of male gamete with female gamete
inside the body of an organism is called internal fertilization. Internal fertilization
occurs in birds, insects, man etc. During fertilization, fusion of male gamete and
female gamete takes place and as a result zygote is formed. This zygote develops into
a new living organisms.

Differences between Sexual and Asexual Reproduction

S.N. Sexual Reproduction S.N. Asexual Reproduction

1. It needs male and female gametes 1. It does not involve male and

to accomplish reproduction. female gamates.

2. Fertilization occurs, so zygote is 2. Fertilization and zygote

formed. formation do not occurs.

3. It causes variation. 3. It does not cause variation.

228 Blooming Science & Environment Book 8

Fertilization

The process of fusion of male and female gamete is called fertilization. It is of two
types.

a) External fertilization b) Internal fertilization

External Fertilization

The fertilization which occurs outside the body of female is called external
fertilization. e.g. most of the fishes and amphibians.

Internal Fertilization

The fertilization which occurs inside the body of female is called internal fertilization.
e.g. insects, birds, reptiles and mammals.

The sperm and ovum fuse together to form a zygote that develops into an embryo
and later embryo develops into a new individual.

Differences between Internal and External Fertilization.

S.N. Internal Fertilization S.N. External Fertilization
1.
In this method the sperm and 1. In this method the sperm and
2. ovum fuse within the body of ovum fuse externally (outside the
3. female. body).

Mating is necessary for this 2. It is accomplished without
mating.
reproduction.
Frog, fish, etc are the examples of
Dog, cow, man, duck, etc are the 3. it.
examples of it.

Points to Remember
1. Reproduction is a life process in which all living organisms produce new

individuals of their own kind.
2. Asexual reproduction is a type of reproduction that occurs without the fusion

of male and female gametes. It takes place by the fission, budding, sporulation,
regeneration and vegetative propagation.
3. Sexual reproduction involves the fusion of male and female gametes.
4. When the male and female reproductive organs are found in the separate
organisms, they are called unisexual organisms.
5. When the male and female reproductive organs are found in the same organism,
it is called bisexual or hermaphrodite organism.
6. The process of fusion of male and female gamete is called fertilization.
7. External fertilization occurs outside the body of the female.
8. Internal fertilization occurs inside the body of the female.

Blooming Science & Environment Book 8 229

PRO J ECTWOR

Study of mustard flower

a. Take a mustard flower.

b. Separate out the outermost whorl of structure from it. Study them. They are
sepals; calyx.

c. Separate the whorls from it one by one and sketch Corolla
their diagram separately. You will get corolla
(petals), androecium and gynoecum in the order. Petals
Androecium
d. Also write the major functions of these different
Clayx
parts. Gynoecium

Exercise

1. Fill in the blanks.

a. The process of fusion of male and female gametes is called ……………..

b. In insects, ………….. fertilization takes place.

c. Male and female are involved in …………. reproduction.

d. …………. fertilization occurs inside the body of the organism.

e. Plant often grows into new plant from their roots, stems and leaves, this
is called ……….. propagation.

f. In tapeworm, if the parent body is broken up, each piece can grow into a
new individual. This is called …………….

2. Answer the following questions.

a. What is reproduction?

b. What are the two basic types of reproduction?

c. Name any two organisms which do not reproduce sexually.

d. What is hermaphrodite? Give two examples of it.

e. What is sporulation? Name an organism which reproduces by this
process.

f. What is asexual reproduction? Name any two organisms which reproduce
sexually.

g. What is fertilization? Classify it.

230 Blooming Science & Environment Book 8

h. What is asexual reproduction? Name four types of asexual reproduction.
i. Briefly explain with the help of diagram how fission takes place in

amoeba.
j. Explain the following by giving one example of each.
i) Vegetative reproduction or propagation
ii) Regeneration
k. What is pollination? Classify it.

3. Differentiate between the following.
a. Fission and budding
b. Sexual reproduction and asexual reproduction
c. External fertilization and internal fertilization
d. Sperm and ovum

4. The following figure shows a mode of a sexual reproduction in an animal.
Name that animal and mention its mode of reproduction.

Glossary

Pollination : transformation of pollen grains from anther to stigma

Fertilization : fusion of nuclei of male and female gametes

Unicellular : consists of single cell

Spore-sac : the sac like structure of non-flowering plants in which spores are
formed

Uterus : the organ of females, where zygote develops in the form of new
organism

Blooming Science & Environment Book 8 231

B. Transport System

Protoplasm

Protoplasm is a fluid found inside the boundary of the cell membrane of a cell. It is a
semi-transparent liquid which looks slightly grayish or brown in colour. It was first
discovered by a scientist, Prokunjee. The protoplasm consists of different substances
in it. The chemical composition of protoplasm of one cell is different from the
chemical composition of protoplasm of another cell. The protoplasm found in human
cell contains elements like hydrogen, oxygen, nitrogen, carbon, iron, sulphur and
phosphorus. These elements are found in water, carbohydrate, protein, fat, mineral
salts present in the protoplasm. In human body these elements are found in different
percentage. The human body contains 65% oxygen, 18% carbon, 10% hydrogen 3%
nitrogen and 4% other substances by weight. Protoplasm plays an important role in
different life process such as in digestive system, respiration, locomotion, sensitivity,
reproduction etc.

Importance and Necessity of Protoplasm

Protoplasm is the most important substance found in the cell of all living beings. Many
chemical reactions take place in protoplasm. These chemical reactions are termed
as metabolism. Activities like digestion, respiration, excretion, growth, sensitivity,
locomotion, co-ordination, reproduction etc. all occur in cell. During metabolism,
some chemical changes take place due to which protoplasm is formed or destroyed.
Plants prepare food by photosynthesis process. During photosynthesis, protoplasm
is formed. This process is called anabolism. All cells carry out respiration. During
respiration carbohydrate is broken down in the presence of oxygen and enzyme and
part of protoplasm is destroyed. This process is called catabolism.

In order to survive an organism, these activities anabolism and catabolism should
take place in the protoplasm. The anabolism and catabolism together is called
metabolism. Metabolism is very necessary process for life. In this way, protoplasm
plays an important role in life process of an organism.

Transport System
Different tissues in the body need essential nutrients and oxygen. Cells in different
tissues produce unwanted substances during respiration and other chemical process.
So, in the body of unicellular or multi-cellular organisms essential nutrients and
unwanted materials produced in the cell have to be transported from one part to
the other part within the body. In other words, nutritive elements and oxygen have
to be transported to the cells of different parts of the body and harmful substances
and carbon dioxide have to be transported from the cells to the excretory organs
otherwise these substances cause harm to the body.

232 Blooming Science & Environment Book 8

Transport in Multicellular Organisms

Transport system is well developed in the body of multi-cellular organisms. Essential
nutrients, water and oxygen needed by the cells in different parts of the body are
supplied by the transport system. Similarly, carbon dioxide and other harmful
substances produced during metabolism are also carried to the excretory organs by
transport system. The transport of nutrients and harmful substances are done by the
blood. So, the blood plays an important role in transport system.

Transport in Unicellular Organisms

In the body of unicellular organisms like amoeba, paramecium, chlamydomonas,
transport system is not well developed. They have no blood. So, blood does not play
any role in transport system in these organisms. These organisms have cytoplasm
in their body. They get essential nutrients by the movements of cytoplasm. The
exchange of gases in their body is done by diffusion process. Digested food is also
excreted by this diffusion process.

Transportation in Plants

Developed plants have conducting tissues. Xylem and phloem are conducting tissues
in developed plants and they act as tube for transporting water and food materials
from one part to the other part of the plant. Xylem conducts water and minerals salts
from root to the leaves and phloem conducts prepared food from the leaves to the
other parts of the plant. Thus, xylem transports water and dissolved mineral salts to
the leaves and phloem transports food from leaves to the root, stem, fruits etc.

Activity

Take water in a beaker and put 2-3 drops Flower
of red ink in it. Cut a white rose flower
with stem and dip the cut stem in water. Beaker
Leave it for a day and observe. What do Coloured
you find? You will find that the flower has water
become reddish in colour. This shows that
xylem helps to transport water.

Blood Circulatory System in Human

Blood circulatory system plays an important role in the body of organisms. Essential
nutrients and useful materials need to be transported from one part of the body to the
other part. The blood transports these essential nutrients, oxygen and hormones to
the different tissues of the body and also transports unwanted and harmful substances
produced in the body to the excretory organs. This process continues in the body and
is called transportation or circulatory system. In unicellular and simple organisms,
transport system is simple while in complex organisms, transport system is well
developed. In developed organisms, blood is flowing all the time in blood vessels.

Blooming Science & Environment Book 8 233

So, essential nutrients are carried by the blood to different parts of the body and
unwanted substances are carried by the blood from tissues to the excretory organs.
So, blood plays a main role in transportation.

Blood

Blood is a red fluid which circulates round the body through blood vessels. Blood
is red due to the iron containing pigments called haemoglobin. Blood is composed
of plasma and blood cells. Plasma is a yellowish transparent liquid. It contains 90%
water and 10% other substances like carbohydrate, protein, fat, salt etc. The plasma
helps to transport the nutritive substances dissolved in water. It also carries the carbon
dioxide gas produced during respiration to the lungs. It helps to carry urea from the
liver to the kidneys and hormones secreted by the endocrine glands to the tissues.

In short, plasma helps to control the flow and the amount of water, helps to control
the clotting of blood and to protect from harmful germs invaded to our body. There
are blood cells except plasma in blood. There are three types of blood cells in the
blood, i.e red blood cells, white blood cells and platelets.

Red blood cells (erythrocytes) are many in number in blood. These blood cells are
very small and have no nucleus. They are made in bone marrow and destroyed in the
spleen. Haemoglobin present in red blood cells absorbs oxygen from the lungs and
helps to transport to the different cells of the body. The decrease in the number of red
blood cells in the blood causes anaemia.

White blood cells (leucocytes) are bigger than red blood cells and are less in number
in the blood. These cells are of various types and are colourless. They have distinct
nucleus but have no fixed shape. They are also made in bone marrow. These cells
fight against germs in infected area and protects, the body from disease. Some of
them destroy the disease causing microbes while some of them remove the destroyed
cells or microbes from the infected area and help to heal the wounds.

Platelets (thrombocytes) are very tiny cells. These are smaller than both red blood
cells and white blood cells. They are also of various kinds. They are less in number
in the blood. They are spherical in shape and have no nucleus. They are also made
in bone marrow. They help in clotting of blood at wounds and damaged skin or cut.
Thus, platelets play an important role to clot blood in wounds and cuts.

Heart

The heart is an important organ in our body. It is made up of cardiac muscles. The
heart pumps blood from heart to the different parts of the body. The heart supplies
oxygenated blood to the cells through blood vessels. The heart also helps to collect
deoxygenated blood from different cells, send it to lungs for purification and then
transports again to the cells. In this process, many nutrients and waste products in
the cells are transported.

234 Blooming Science & Environment Book 8

The heart is a strong muscular organ. It is situated between two lungs in the thorax.
It is enclosed in a membrane called pericardium. The space inside is filled with
pericardial fluid which protects the heart from external injury.

The heart has four chambers. These are:

(i) Right auricle (ii) Left auricle

(iii) Right ventricle (iv) Left ventricle

Aorta

Superior venacava Pulmonary artery
Left auricle
Right auricle Coronary artery
Inferior venacava
Left ventricle
Aorta

Right ventricle

External view of mammalian heart (pulmonary veins are not shown)

There are two upper chambers and two lower chambers. The heart is internally divided
into right chamber and left chamber which are separated with a thick muscular wall
called septum.

The septum prevents the intermixing of blood between left and right sides. These
four chambers work as a single organ. The right auricle collects the deoxygenated
(impure) blood from the body and the left auricle collects the oxygenated (pure)
blood from the lungs. The Muscle of the heart contracts and relaxes in a rhythmic
manner. This is known as heart beat. The deoxygenated blood passes from right
auricle to right ventricle whereas oxygenated blood passes from left auricle to left
ventricle when the valves of auricle to ventricle open. Blood moves from auricle to
ventricle when heart pumps blood but blood does not return back from ventricle to
auricle due to the presence of values between auricles and ventricles. There are four
different types of values in human heart, they are;
1. Tricuspid value: between right auricle and right ventricle.
2. Bicuspid value: between left auricle and left ventricle.
3. Pulmonary value: between right ventricle and pulmonary artery.
4. Aortic Value: between left ventricle and aorta.
These valves prevent the back flow of blood at the time of pumping.

Blooming Science & Environment Book 8 235

Blood Vessels

The heart pumps blood through vessels. These vessels carry blood to the different
parts of the body. There are three types of blood vessels.

(i) Arteries (ii) Veins (iii) Capillaries

(i) Arteries

The vessels which supply blood

to the different parts of the body

are called arteries. Arteries carry Artery

oxygenated blood to the body.

The wall of the arteries is made Endothelium Muscular layer Connective tissue

up of thick muscles and so, it

can bear great pressure of the Vein

blood. Arteries have no valves.

Arteries divide into branches Valve

in different parts of the body. Capillary
These divide arteries are called

arterioles. Arterioles also branch Blood vessels

into smaller capillaries when they reach cells and tissues. These capillaries

carry oxygenated blood and dissolved salts and sugar to the cells.

(ii) Veins

The vessels which carry blood to the heart are called veins. Veins carry
deoxygenated blood to the heart. They have thinner wall than that of artery
with valves. Capillaries collect blood from tissues and carry to the heart.

(iii) Capillaries

The branched vessels which reach the different tissues of the body are called
capillaries. They connect minute vessels like arterioles and ventrioles in the
form of network. Half of the capillaries collect blood and carry to the veins
while the half capillaries carry blood from arteries to the tissues. The capillaries
help to exchange nutrients, gases etc. between the blood and cells of the body.

Difference between Arteries and Veins.

S.N. Arteries S.N. Veins

1. The heart pumps blood into 1. The heart receives blood from

arteries. veins.

2. They carry pure blood except 2. They carry impure blood except

pulmonary artery. pulmonary vein.

3. They have thick muscular wall. 3. They have thin muscular wall.

236 Blooming Science & Environment Book 8

4. Blood flows with high pressure. 4. Blood flows with less pressure.

5. Valves are absent. 5. Valves are present.

6. Pulse can be noted. 6. Pulse cannot be noted.

Activity
To observe the heart

1. Collect a heart of a goat from a meat shop and observe the external part.

2. Cut the heart lengthwise with a sharp blade and observe auricle and
ventricle.

3. Observe the thickness of the wall muscles of left auricle and right auricle.

4. What are the large vessels that are connected to the heart? Find.

Blood Circulation

The organs which take part in the circulation of blood are as follows:

(a) Heart (b) Arteries

(c) Veins (d) Capillaries

Pulmonary vein

Pulmonary artery Lung
Left auricle
Venacava Aorta
Right auricle
Right ventricle Left ventricle
Hepatic vein
Hepatic artery
Liver Stomach and Intestine
Renal vein
Renal artery
Kidney
Oxygenated blood
Deoxygenated blood Lower parts of the body

The deoxygenated blood collected from different part of the body reaches to the
right auricle of the heart via superior and inferior venacava. The right auricle
contracts and the blood flows to the right ventricle through tricuspid valve. When
the right ventricle contracts the blood reaches lung through pulmonary artery. In
lungs, the blood gets oxygen and leaves carbon dioxide. The oxygenated blood i.e.
pure blood is carried by pulmonary vein to the left auricle. When the left auricle
becomes full, it contracts and the blood flows to the left ventricle through bicuspid
valve, which is pumped by the heart to the aorta. The aorta carries this oxygenated

Blooming Science & Environment Book 8 237

blood to the different parts of the body. The arteries carry oxygenated blood to all
parts of the body and the veins carry deoxygenated blood from all over the body.
The deoxygenated blood is carried by ventrioles to the veins which carry back to the
right auricle of the heart. The valves located in heart help to flow the blood in and
outside heart.

Main Points to Remember

1. Every cell has protoplasm. It is a semi-transparent liquid found within cell-
membrane of a cell.

2. Protoplams contains substances like water, carbohydrate, protein, fat, mineral salts
and other elements like nitrogen, oxygen, carbon, iron, phosphorus, sulphur etc.

3. Transport is the process of supplying essential nutrients to the cell and removing
unwanted substances from the cell.

4. Transport system is simple in simpler organisms whereas it is well developed
in higher organisms.

5. Heart, artery, vein and capillary take part in blood circulation.

6. Blood is liquid containing haemoglobin. Blood is red due to the presence of
haemoglobin.

7. Blood is composed of plasma and blood cells.

8. Blood transports food, respiratory gases and wastes in the body.

9. Blood cells are the three types-red blood cells, white blood cells and platelets.

10. Red blood cells are very small without nucleus. They transport oxygen to the
different parts of the body.

11. White blood cells are colourless, large with nucleus. They destroy germs and
protect the body from disease.

12. Platelets are very smaller cells without nucleus. They help in clotting of blood.
Arteries carry oxygenated blood from heart to the different parts of the body.

13. Veins carry deoxygenated blood from different parts of the body to the heart.

PRO J ECTWORK

Touch the wrist of your one hand by the thumb of another hand carefully: can you
feel its pulse? Find out the rate of pulse per minute. Run for a while and again
find the pulse by repeating the same process. What difference can you observe?
Draw your conclusion and discuss in your class.

238 Blooming Science & Environment Book 8

Exercise

1. Fill in the blanks.

(i) ________________ is the semi-transparent fluid inside the cell.

(ii) Transport of water and mineral salts in plants occurs through ________.

(iii) Transport of food material in plants occurs through _____________.

(iv) Blood looks red due to the presence of _____________.

(v) ___________ are the blood vessels that carry blood from heart to the
different parts of the body.

(vi) Fluid part of the blood is called _______________.

(vii) _____________ are the blood cells that carry oxygen to different parts of
the body.

(viii) ___________ are the blood cells that help in clotting.

2. Choose the best answer from the given alternatives.

(a) Transport of water and minerals salts in plants takes place through

(i) phloem (ii) xylem

(iii) xylem and phloem both (iv) None

(b) Transport of food in plants takes place through

(i) xylem (ii) phloem

(iii) xylem and phloem both (iv) None

(c) Blood contains

(i) Red blood cells (ii) White blood cells

(iii) Platelets (iv) all

(d) Oxygenated blood is carried by

(i) artery (ii) veins

(iii) artery and veins both (iv) none

3. Answer the following questions.
a. What is meant by transportation?

b. What is blood? Write its composition.

c. What is plasma?Write its function.

d. Name the three types of blood cells.

e. What is protoplasm? Why is protoplasm important?

Blooming Science & Environment Book 8 239

f. Draw a diagram of heart and label its different parts.
g. Why is blood circulation necessary?
h. Write the function of RBC, WBC and platelets.
i. How do transportation occurs in unicellular organisms?

4. Differentiate.
(a) Artery and veins
(b) Red blood cells and white blood cells
(c) Pulmonary artery and pulmonary vein

Glossary

Bone marrow : the fluid found inside bone

Autrioventricular : found in between auricle and ventricle

Pulmonary : related with heart

Bicuspid : two lobed
Tricuspid : three lobed
Arterioles : branches of arteries
Venules : branches of veins

240 Blooming Science & Environment Book 8

C. Photosynthesis Sunlight

All living beings need food to survive. Food Green leaf
provides us energy to perform various body (Chlorophyll)
activities. Root

Only green plants can synthesize food by
themselves. They are so called autotrophs. They
take in raw materials like water and dissolved
mineral nutrients from the soil and carbon
dioxide from atmosphere and prepare food in
the presence of light. Energy from sunlight is
captured by chlorophyll present in chloroplasts.
Chloroplasts are found in the cells of green
plants.

Photosynthesis is a process of preparing food
by green plants from simple inorganic materials
like carbon dioxide and water with the help of
light energy (sunlight).

Things Required for Photosynthesis
Green plants require the following things for photosynthesis.

Raw Materials

Carbon dioxide and water are raw materials. Carbon dioxide in the air is taken
through the undersurface of leaves called stomata. Water is absorbed by roots from
soil. It is carried up through stem into leaves.

Energy

Sunlight is the main source of energy. Energy of sunlight is converted into chemical
energy.

Chlorophyll

It is the green coloured pigment found in the chloroplast of the plant cells. It absorbs
solar energy and converts it into chemical energy.

During photosynthesis, carbon dioxide and water react with each other in the presence
of sunlight and chlorophyll to produce glucose and oxygen. Oxygen is released as a
byproduct.

The overall process of photosynthesis is summarized in the following equations.

Blooming Science & Environment Book 8 241

Carbon dioxide + Water Chlorophyll Glucose + Oxygen
6H2O sunlight

6CO2 + Chlorophyll C6H12O6 + O2
sunlight

Thus, green plants covert light energy into chemical energy.

Activity

To test leaf for starch (Starch Iodine Test)

Theory : Because of photosynthesis, starch is formed Scan for practical experiment
and is present in green leaf.

Material required : Green leaf, breakers, petri dish, 90%
alcohol, water, iodine solution and
spirit lamp.

Method visit: csp.codes/c08e25

1. Take a green leaf from a plant. Keep it in sunlight.

2. Put the leaf in hot water for five minutes. It is done to make leaf soft.

3. Put the leaf in small beaker containing 90% alcohol and put the small beaker
in a beaker of hot water for about ten minutes. The alcohol will boil and
decolorize the leaf.

4. Transfer the decolorized leaf into another beaker containing water and wash
it.

5. Again transfer it in a petri dish and add iodine solution.

Leaf Leaf in hot water Leaf in Wash the decolourised Leaf in iodine

alcohol leaf with water solution

Observation : The colour of the portions of the leaf turns blue-black.

Conclusion : The change in the colour of the leaf is due to the presence of starch
in it. Only the portions of the leaf containing starch turn blue-black.
This shows that starch is made in the leaf during photosynthesis.

242 Blooming Science & Environment Book 8

Activity

To demonstrate that carbon dioxide is necessary for photosynthesis.

Theory : Carbon dioxide is the source of carbon for photosynthesis.

Materials required : A potted plant, plastic bag, caustic potash (KOH), iodine
solution and alcohol.

Method

1. Keep a potted plant in the dark place for two days.

2. Put some caustic potash
in a plastic bag and insert
the leaf of the plant into
the bag and tie its mouth
so that no air enters. (The
caustic potash will absorb
carbon dioxide present
in the plastic bag and the
leaf inside will not get any
carbon dioxide).

3. Place the potted plant in the
sunlight for few hours.

4. Pluck two leaves, one from
inside the plastic bag and the other from outside and test them for starch.

Observation : The leaf inside the plastic bag shows negative result. That is, it
does not change its colour. The open leaf shows positive result.
That is, it becomes dark-blue indicating the presence of starch.

Conclusion : Air contains carbon dioxide which is necessary for making
starch.

Activity

To demonstrate that light is essential for photosynthesis.

Theory : Energy from sunlight is used to prepare food during
photosynthesis.

Materials required : A potted plant, petri dish, beaker, burner, black paper or
aluminium foil, iodine solution and clips.

Procedure

1. Keep a potted plant in dark for two days. This is done to remove any precious
starch present in the leaves.

Blooming Science & Environment Book 8 243

2. Pluck a leaf and test it for the presence of starch as in the previous activity.
3. The leaf does not turn blue-black with iodine solution. This shows the

absence of starch in it.
4. Now, clip two strips of black paper onto a leaf surface.
5. Keep the plant out of sunlight for a few hours.
6. Pluck the experimental leaf and remove the strips of black paper.
7. Dip the leaf in the iodine solution. (Test for starch)

Fig 233

Observation : The colour of covered portion of leaf which did not get any light,
will not show change in colour. The uncovered portion which
was exposed to light shows change in colour.

Conclusion : The starch is formed only in those parts of the leaf which are
exposed to light. The green leaf makes starch only in the presence
of light.

Activity

To demonstrate oxygen gas is given out during photosynthesis.

Theory : Glucose and oxygen are formed during photosynthesis

Materials required : Beaker, test tube, glass-funnel, water plant (Hydrilla) and
water.

Method

1. Place a few twigs of aquatic plants such as Hydrilla at the bottom of a
beaker containing water.

2. Invert glass funnel over the twigs.

3. Fill a test tube full with water and invert over the tip of the funnel.

4. Place the whole apparatus in the sunlight for some time.

244 Blooming Science & Environment Book 8

Observation : Bubbles of gas are given off from the twigs and get collected in
the test tube by displacing water downwards.

Test for the released gas

Procedure : Take a glowing Oxygen
match stick
Observation
Conclusion close to the test Beaker
tube containing
gas. Inverted
funnel
: The glowing Water
match stick Hydrilla leaves
burns brightly. Wood block

: Oxygen gas is Release of oxygen during photosynthesis

given out during photosynthesis.

Precaution : 1. The stem of the funnel should be completely under water.

2. There should be no air, bubbles in the test tube.

Main Points to Remember

1. All the biochemical process that take place inside the living cell, is called
metabolism. It includes two types of reactions:
(a) Anabolism (b) Catabolism.

2. Anabolism: All those biochemical reactions in which complex molecules are
made from simple ones, such reactions are called anabolic reactions. This
process is called anabolism.

3. Catabolism: All those biochemical reactions in which complex molecules are
made simple ones, such reactions are called catabolic reactions. This process
is called catabolism.

4. Chlorophyll, sunlight, CO2, water and minerals are necessary things for
photosynthesis

5. Glucose and oxygen are by products of photosynthesis.
6. Photosynthesis is very necessary process for the life process of animals and

plants.

PRO J ECTWORK

Observe the process of preparation of ‘Jamara’ at your home/ neighbour’s home
during Dashain festival. Why are the young planys ( Jamara) found yellow in
colour ? What would happen if the jamara is grown on sunny place? Find out the
reason and discuss in your class.

Blooming Science & Environment Book 8 245

Exercise
1. Fill in the blanks.

a) Absorption of raw materials takes place in _____________.
b) Carbondioxide is needed for _______________.
c) The glucose is a part of the ______________ system.
d) The chloroplast is the place where __________________ takes place.
2. Indicate if the following are “True” or “False”.
a) The respiratory system gets rid of waste products.
b) Photosynthesis occurs in presence as well as in absence of light.
c) Respiration occurs at body temperature.
d) Oxygen is evolved during photosynthesis.
e) Carbon dioxide is necessary for photosynthesis.
f) Breathing and Respiration are similar phenomenon.
g) When a person is excited his breathing rate decreases.
3. Answer the following questions.
a. Which chemical is used to test the presence of starch?
b. What is photosynthesis?
c. Mention the photosynthetic organ, photosynthetic organelle and

photosynthetic site of plants.
d. What is the role of light in photosynthesis process?
e. Why is the presence of chlorophyll necessary for plants?
f. What is the difference between the photosynthesis that occurs in dark and

in the presence of light?
g. Why is photosynthesis considered as opposite process of respiration?
h. Why is photosynthesis essential for both animals, human begins and

plants? Explain with example.
i. How can you prove that carbon dioxide is taken by the plants during the

preparation of food (photosynthesis)? Explain with a neat sketch.
j. How will you show that the starch is prepared during photosynthesis?

Write an activity with a neat sketch.
k. Write an experiment with a labeled sketch to show that oxygen is given

out during photosynthesis.
l. Write an experiment showing the necessity of light during photosynthesis

with a neat sketch.

Glossary

Chunk : a thick solid piece that has been cut of broken of something
Oxidized : a chemical reaction with oxygen
Microbe : an extremely small living thing that can be seen only under microscope

and may cause disease
Enzyme : a protein catalyst produced within a living organism that accelerates

chemical reaction is called an enzyme
Xylem : a tissue of plant, which transports water and minerals the from soil to

leaf

246 Blooming Science & Environment Book 8

Chapter Astronomy / Geology

19 Structure of the Earth

Learning Outcomes Estimated Periods: 6+1

On the completion of this unit, the students will be able to:
 define minerals and tell the physical properties and advantages of minerals.
 introduce important minerals found in Nepal.
 describe soil erosion and deposition and conservation of soil.
 describe the process of formation of soil and demonstrate soil profile.

Minerals

Take a handful of sand on a white paper and observe it. What type of substances
do you see in it? You get some colourless, white, or coloured substances, but it is a
mixture of many substances and most of them are minerals and rocks. You also may
see fine sheets of shiny substances in it. They are different minerals. The granular
fine particles are silica or quartz, the sheets are mica. Silica and mica are examples
of mineral.

Minerals are those chemical substances [element or compound] which are found
naturally in the earth’s crust. They are solid and crystalline. Minerals are not made
artificially and they do not come from living things. There are two types of minerals.
They are; metallic minerals from which metals are obtained and non-metallic
minerals from which metal can not be obtained.

Some examples of minerals are talc, gypsum, quartz, diamond, ruby, emerald,
graphite, garnet, sapphire, calcite, clay and topaz. Minerals are the components of
rocks.

Minerals differ in colour, luster, hardness and cleavage. The minerals may cleave
in block or sheets. About 3000 minerals are found on the earth but only about 100
minerals of them are common and useful us.

A pearl is a chemical compound but not considered as minerals, because a living
being oyster produces it. Coal is also not considered as true mineral because it is
formed from dead parts of the plants.

Blooming Science & Environment Book 8 247

Coal, petroleum and natural gases are considered as fuel minerals by economists, but
geologists do not consider them as minerals.

Minerals are very important for the industrial development of a country. It is said
that minerals are found in abundance in Nepal. So far, only a few extensive surveys
for drilling out various minerals have been carried out. According to the surveys, the
following minerals are found in Nepal:

Occurrence of Minerals in Nepal

Mineral is a substance that is naturally present in the earth and is not formed from
animal or vegetable matter, for example, gold, silver, copper, iron, etc. Mineral
resource is one of the important natural resources. The mineral resources helps in
the development of agriculture, industries and trade which are the backbone of a
country’s economy. In the absence of mineral resource the country will have to
depend solely on imports.

Nepal being a mountainous country, is very rich in mineral resources. Varieties
of minerals are deposited in various parts of the country. But we are not able to
extract them due to poor economic condition, lack of advanced technology, skilled
manpower and adequate infrastructures.

More than 80 types of minerals are reported in large amount in different parts of
Nepal. The names of metal and their minerals and the place of occurence of them in
Nepal based on various geological surveys, varieties of minerals found in different
parts of the country are tabled below:

Occurrence of ores of minerals in Nepal.

Metals / Minerals Names of ores Place of occurrence
Iron Magnetite
Phulchoki – Lalitpur,
Haematite Tanahun, Bhojpur, Ilam,
Ramechhap, Pyuthan,
Chitwan, Makawanpur,
Baitadi

Copper Copper ores in the form Udayapur, Gorkha, Dhading,

of chalcopyrite, copper Makawanpur, Solukhumbu,

bronite. Taplejung

Gold Alluvial gold Rapti river, Mustang,
Native gold Bajhang, Marsyangdi,
Sunkoshi river, Swayambhu-
Hall chowk area

248 Blooming Science & Environment Book 8

Magnesium Magnesite Udayapur, Dolkha
Zinc/Lead Lead-zinc deposite
Cobalt Cobaltite Ganesh Himal, Phulchoki
Calcium Limestone
Palpa, Gulmi
Bismuth Bismuth ore
Chobhar, Udayapur, Jogimara
of Dhading district, Okhre
of Makwanpur, Udayapur,
Surkhet

Bhimphedi

Characteristics of Minerals

The minerals have their own characteristics. The important characteristics are given
below.

1. The minerals have their own colour. Different minerals are different in colour.
For example haematite (mineral containing iron in excess) is reddish brown in
colour and chalcopyrite (mineral containing copper in excess) is golden green.

2. Generally the metallic minerals are lustrous in nature.

3. Generally minerals are hard in nature.

4. In general minerals are crystalline in structure.

Uses of Minerals

As mentioned above about 3000 minerals are found on the earth but only about 100
minerals are common and useful to us. Some of the important uses of minerals are
listed below.

1. The metals are extracted from the minerals.

2. Mineral oils are used as sources of domestic and industrial fuels.

3. The minerals are very important for the industrial development of a country.

4. Various minerals are used in the construction of roads, bridges, buildings etc.

5. Various minerals are used to make decorating materials.

Blooming Science & Environment Book 8 249

Soil

Soil is a natural resource, which is required for
production of food, industrial raw materials as well as
for generation of energy resources.

Soil is necessary for all the living beings. Soil is
powdered form of rocks. Plants are able to grow and
make food from the whole living beings only because
plants can grow in soil. Soil is made up of small particles of rocks, remains of dead
plants and animals.

Animals directly or indirectly depend upon plants for their foods. Plants grow and
make food for the whole living beings. Some animals like rabbit, ants, mouse,
earthworms etc make their homes in the soil.

Formation of Soil

Soil is formed from rocks. Rocks are

slowly broken down by the action of

sun, wind, rain and water. This is called as

weathering of the rocks.

Rocks breakdown due to the moving water,

animals, weather, wind, snow, roots of plants

etc. Rocks break down into small pebbles. They breakdown into smaller grains called

sand and sand forms soil by mixing with dead and decaying matters.

The dead animals and plants matters are called as humus. It is dark brown or black

in colour. It is very useful for growing plants.

Types of Soil

There are three types of soil on the basis of colour, size and composition. They are
loam soil, clay soil and sandy soil.

Loam Soil

It is fertile soil. It is the combination of sand, clay and
humus in good proportion. Humus is the remains of dead
and decayed matter. It can hold enough water and air. The
water never gets water-logged nor dries up easily. It is
good for cultivation of crops.

Clay Soil
Clay soil has tightly packed particles. Particles of the soil
are very small. Water does not flow freely through this
soil. It remains wet for long time and soil gets heavy.

250 Blooming Science & Environment Book 8

Sandy Soil

This soil contains high proportion of sand particles and
less proportion of other particles. It absorbs less water and
water can pass easily through it. Sandy soil is found in
desert. Plants like cactus grows in this region.

It dries up very quickly in dry season. The soil provides much space for air in between
sand particles.

Soil Texture

Soil is formed very slowly by the weathering on the rocks. The formation of soil
may take millions of years. It can be said that soil is the weathered rock. The main
components of the soil are clay, sand, humus and minerals.

Soil contains tiny grains of rock and minerals and it becomes fertile when humus is
mixed in it. In soil, air spaces are also found. Soil may also contain many organisms.
They also help to make the soil fertile and loose. Soil may be of different colours
due to the presence of particular minerals in it. Like that, soil may be classified on
the basis of the size of particles and degree of fertility. It is classified into clay sandy
and loam soil. On the basis of depth also it is classified into top soil, sub soil and bed
rock.

Soil Profile

A clear structure (diagram) showing internal Humus
adjustment of the different layers of soil from Top soil
up to down is called soil profile. Soil profile of
different places is different. At some places, Sub soil
bedrock is seen superficial and at some places it
is at very deep. Bedrock is the hard big rock on Bed rock
which soil is found. Usually soil profile shows
that, fertile soil with fine particles and humus is
found at the top, which is black in colour.

But somewhere it may be of different colours due
to the presence of a particular mineral in it. This soil is loose in which plant roots
can spread easily, it is top soil. Below the topsoil compressed sandy soil having less
humus is found which is called sub soil. At the bottom or just above the bedrock
gravels, boulders, etc. are found. In oceans, the deep bedrock is found to be naked
but in coastal regions it is covered with sand or sand rocks.

Blooming Science & Environment Book 8 251

Activity

Obtain a potful of soil from your garden Humus
or lawn near about and observe carefully
the various components using a hand Water
lens if necessary. Usually the following
things are found: Clay particles
Sand
(a) Minerals (soil and clay particles)
from the parent rock. There may be Gravel particles
coarse and fine sand, silt, clay, etc. Sedimentation test

(b) Humus (from dead animal and plant bodies)

(c) Plants and smaller animals.

(d) Water and air trapped in between the soil particles.

Perform sedimentation test to find out the various components by vigorously shaking
a sample of soil with water in a wide mouthed glass jar.

See if you can see layers of different components present in the soil. Compare your
observation with the diagram for sedimentation test.

The texture of soil depends on the amount of various particles and their sizes. The
sizes of soil particles are different as shown below: Different names are given to soil
with particles of different sizes.

Particles Size
5.00mm - 2.0mm or more
Gravel 2.00mm - 0.2mm
Sand 0.2mm-0.02mm
Silt 0.02mm or less
Clay

Soil Erosion and Deposition

Introduction
Our earth is unique in the solar system because there is life on earth. No other planet
is known to support life. The composition of the atmosphere, the ocean, and even
rocks beneath our feet are strongly influenced by the activities of living matter. The
earth is dynamic in nature because it changes its shape gradually. Due to various
natural processes, substance in one part of the earth is taken to other parts. One of
the effects of such process is erosion. Erosion is the wearing away of the land surface

252 Blooming Science & Environment Book 8

by natural agents that involves the transport of such materials to other places. These
natural agents include moving water (e.g. rivers, ocean waves), ice (e.g. glaciers)
wind, organism and gravity. When there is erosion in soil, it can lead to a loss of
agricultural land.

We have seen that wind takes away the particles of soil and sand with it. Rainwater,
stream and rivers, waves of ocean, water falls, etc. break rocks and remove rock
particles. The process is called erosion. Therefore, erosion is the process of taking
away the products of weathering by wind and water-like agents. Glacier is another
form of water which causes erosion. Valley glaciers are found on mountains and
continental glaciers are found in polar regions. When the glaciers slide, they also
smoothen the surface of the rock causing weathering as well as erosion. In deserts,
wind plays vital role in erosion.

We find that the materials removed by erosion are transported by wind and water and get
deposited at other place. This process is called deposition. Erosion and deposition take
place side by side, because one process of them is a must for or after another process.

Effects of Erosion and Deposition
Major effects of erosion and deposition are as follows:
1. Erosion causes landslide.
2. Erosion forms plains, plateaus and residual mountain like landscapes.
3. Erosion decreases the soil fertility.
4. Deposition forms different types of plains, plateaus and mountains.
5. Deposition may increase or decrease the soil fertility.
6. Erosion and deposition help to form soil.

Erosion by Wind
Blowing air erodes the upper surface of earth. The forcefully moving air picks up and
removes loose rock and soil particles. The wind carrying rock particles can also wear
away the upper surface of rocks while it blows through it.

Erosion by Water System
Various water systems are responsible for bringing out erosion of soil and rocks.
Rainwater causes the upper surface of soil and rocks to wear away gradually.
Waterfalls, rivers and streams also scrape the surface of land through which they
flow causing massive erosion. Glaciers also cause erosion. Ice in glacier grind and
scour the earth surface causing weathering and erosion of soil and rocks. Ocean tides
are also responsible for erosion and deposition of matter. Tidal currents are stream-
like flow of seawater into and out of bays with the rising and falling of the tides. They
erode and wash away the material in seashore.

Blooming Science & Environment Book 8 253

The eroded materials are carried out by various agents and get deposited into new
places. The laying down of such materials on the earth’s surface is called deposition.

Conservation of Soil

We grow different types of crops in soil. If the soil is fertile, we can get good crops
yielding. Therefore, it is very important to protect and conserve the soil. We also
know that soil is the eroded rock and it is loose at the surface. Therefore, the soil can
be eroded more easily. The rate of erosion is maximum on slopes.

Activity

To demonstrate that erosion occurs more on naked land.

Material required: two elongated wooden boxes, wooden blocks, bottle with
holes at lid, tube

Method

1. Two boxes are Elongated wooden Bottle with
box with soil holes in its lid
adjusted as shown in Soil with
Wooden block plant

the figure inclined at Wooden
Wire net block

the same angle. One Less muddy water
box contains only Tub

More muddy water

soil and the other box

contains soil with plants grown on it.

2. Pour water in each of the boxes one by one.

Study the concentration of mud in collected water. You will find more erosion in
naked soil. Like in the above activities, fertile soil on the surface of the earth is
continuously removing away by water and wind like media. We must conserve
the soil for good crop yielding, otherwise gradually our fertile lands will loose
their fertility.

Afforestation

Roots of the plants help to protect the soil from removal. Soil can be conserved by
planting trees. Trees decrease the force of rain water. In addition, they slow down the
flow of wind and water.

Soil Cover

Regular ploughing makes soil loose. It can be eroded easily. In between the harvesting
and slowly new crop land remains bare. It can be easily eroded by wind and water.
So, we should keep fertile land under cover-crops or useful grass.

254 Blooming Science & Environment Book 8

Terrace Farming
This method of farming is done in hilly or sloppy land. In this method crops are grown
on sloping land which is cut into large steps called terraces. Terrace farming reduces
the speed of flowing water, thereby decreases the amount of soil being carried away.

Forest Conservation
Green forest are the wealth of Nepal. Forest helps in preserving soil and habitats,
balancing the weather and keeping the environment stable. Now a days there is the
continuous destruction of forest. People cut down trees for shelter, fire wood, etc.
Due to deforestation, there is always disastrous floods, carrying away top soil and
dry river beds.
The cutting of trees is called deforestation.
Causes of Deforestation
a) Need of settlement and cultivation
b) Need of timber and fuel wood.
c) Need of grazing of domestic animals.
d) Need of forest fire.
e) Lack of awareness in the people about the importance of forest.

Conservation of Forest
As forest is the important natural resources of our country it should be conserved in
the following ways:
a) Afforestation: We need to plant more trees.
b) Overgrazing: Overgrazing of cattle, sheep, horse, etc not only kills the new

seedlings but also decreases the plant grass-cover of that area.
c) Control of forest fire: Forest fire can be controlled by spraying fire

extinguishing solutions from air-crafts.
d) Provide awareness to the people of all levels about forest conservation.
e) Enforce strong laws against timber and forest product smugglers.

Landslide
A landslide includes a wide range of ground movements, such as rock falls, deep
failure of slopes and shallow debris flows. The biggest reason for landslide is that
there is slope and material goes down the slope because of gravity. The rocks and
soil slopes are made weak through saturated by snowmelt or heavy rains.

Blooming Science & Environment Book 8 255

Causes of Landslides
There are many factors that cause landslides.
Some major causes are-

i) Heavy Rainfall

Heavy rainfall increases the weight of the soil
that causes landslides.

ii) Construction of Highways

Hillside houses, dams, reservoirs and drainage results in the movement of materials
on slopes.
iii) Earthquake
Earthquake is also responsible for the breaking of rock, ultimately causing landslides.
iv) Deforestation and Overgrazing
Landslide is caused due to deforestation and overgrazing.
v) Excessive Ploughing
It is caused by excessive ploughing and tilling of field in the slopes of hills and
mountains.
Effects
Landslides can cause loss of property, loss of human life and make agricultural
land useless of cultivation. The streams and rivers are often blocked by landslides
which results into flood. Landslide destroys development structures (roads, bridges,
industries) and human settlements.
Preventing Measures
There are various measures to prevent landslides.
i) Terrace farming should be properly managed on mountain slopes.
ii) Retaining walls should be constructed in the areas where landslides occur frequently.
iii) Afforestation should be encouraged.
iv) Deforestation and overgrazing should be checked.
v) Contour ploughing should be practiced in the mountain.

Main Points to Remember

1. Mineral is a substance that is naturally present in the earth and is not formed
from animal or vegetable matter, for example, gold, silver, copper, iron, etc.

2. Minerals have their own characteristies.
3. Minirals are very important as they are used for various purpose.
4. Different types of minirals are found in Nepal.
1. Erosion is the removal of particles.
2. Erosion and deposition undergo hand to hand.

256 Blooming Science & Environment Book 8

3. Rain, river, wind, frost, glacier and temperature changes are the agents of erosion.
4. The collection of eroded materials to far away places is called deposition.
5. Terrace farming, construction of retaining walls, afforestation, contour

ploughing prevent landslides.
6. Soil is the uppermost lose covering of the earth.
7. The layers found in the soil are humus, top soil, sub soil and bed rocks.
8. A diagram that shows the distinct internal arrangement of different layers of

soil from surface to down is called soil profile.
9. Top soil is the fertile layer of the soil.
10. The removal of soil by running water and wind is known as soil erosion.
11. Soil should be conserved as no plants and animals can survive without soil.
12. Forest can be conserved by controlling deforestation, setting of fire, overgrazing,

and promoting afforestation, public awareness, etc.
13. Landslides occur mostly in hilly and mountainous regions of Nepal during

rainy season.
14. Heavy rainfall, construction activities, earthquake, deforestation, overgrazing,

extensive ploughing etc are the causes of landslide.

PRO J ECTWORK

Collect some soil from your garden or ground near by you. Mix it with water
stir it for sometime and keep undisturb in a plastic or glass jar for few hours.
Observe after few hours, you can observe various layers of soil in a soil profile.
Draw the diagram of your observation and discuss with your friends.

Exercise

1. Fill in the blanks.
a. There is more change of ……………… in the barren hills.
b. The lowermost strong rock is called …………………….
c. The red colour in soils is due to the presence of …………….. in it.
d. ……………….. is the diagram that shown internal arrangement of
different layers of soil from top to bottom.
e. Top soil is the ………………. layer of soil.
f. Composition of soil depends upon the layer of ………………. from
which it is formed.
g. ………………. and deposition undergo hand to hand.
h. The sliding down of material under the force of gravity on a mountain or
hill slide is called …………….
i. In ……………. crops are grown on sloppy ground which is cut into large
step called terrace.
j. The practice of renewing a forest by planting seedling or trees is called
……………..

Blooming Science & Environment Book 8 257

2. Answer the questions.
a. What are minerals?
b. Which minerals are found in Nepal?
c. Why are minerals very important?
d. Explain how plants can protect the soil.
e. What is erosion?
f. Why is wind considered a causative agent of erosion?
g. What is soil profile?
h. What is deposition?
i. What is landslide?
j. How is soil formed?
k. What are the preventive measures of landslide?
l. How does rainfall cause soil erosion?
m. What are the agents that cause erosion?
n. What are the advantages of forest?
o. What are the main causes of soil erosion? Discuss
p. Erosion and deposition undergo hand to hand. Discuss
q. Explain the ways of soil conservation?
r. How can soil erosion be prevented?
s. Explain the causes of landslide?
t. Write any three causes of deforestation.

3. Draw a diagram of soil profile.

4. Give reason for the following:
a. Farmers sometime plough the soil deeply.
b. Humus increases the fertility of soil.
c. Heavy rain causes landslide.

Glossary

Luster : shining
Cleavage : the splitting of a crystal along planes of atom in the lattice
Magma : molten substance found in the earth
Erode : the removal of rock particles
Fossils : preserved dead bodies of organisms in sedimentary rock
Furnace : a baking chamber
Speckled : spotted
Gravel : pieces of stones

258 Blooming Science & Environment Book 8

Chapter Climate and Weather

20

Learning Outcomes Estimated Periods: 5+1

On the completion of this unit, the students will be able to:
 define climate and describe factors affecting weather.
 give general introduction of climate of Nepal.
 describe about monsoon.

Introduction

We are familiar with rainy days in summer, hot sunny day, very cold climate of
winter, etc. Why does it so happen? The clouds of the morning vanish as the sun
rises up and may even rain on the same day. Sometimes it is very dry and windy,
whereas sometimes it is very hot and humid. These changes in the atmosphere are
called weather changes. We should know the direction of the wind, humidity of the
air, maximum and minimum temperature, possibility of the rain, etc. to know about
the weather. These factors generally constitute of weather.
Weather is the state of the atmosphere to the degree that clear it is hot or cold, wet
or dry, calm or stormy, clear or cloudy.

Climate
Climate encompasses the statistics of
temperature, humidity, atmospheric pressure,
wind, precipitation, atmospheric particle count
and other meteorological elemental measurements
in a given region over long periods. Climate can
be contrasted to weather, which is the present
condition of these elements and their variations
over shorter periods.

The climate of a location is affected by its latitude,
terrain, and altitude, as well as nearby water bodies
and their currents.

Nepal’s climate varies with its topography and altitude. It ranges from the tropical
to the arctic. The low-land Terai region with its maximum altitude to approximately

Blooming Science & Environment Book 8 259

305m, which lies in the tropical southern part of the country, for instance, has a hot
and humid climate that can rise above 45 Degree Celsius (113 Degree Fahrenheit)
during summer. The mid-land regions are pleasant almost all the year round, although
winter nights are cool. The northern mountain region, around an altitude above
3,300m has an alpine climate with considerably lower temperature in winter as can
be expected.

Climate and its Determining Factors.

The average weather condition in an area over a considerable period of time is
climate. Some times we generalize climate and weather in similar way. But climate
and weather are not same. Weather is atmospheric condition in a small area where
as climate is average weather condition in large area. In a same day it may rain
in morning and many sun shine in afternoon. It is weather condition. What ever
the weather condition, it may in summer or winter or monsoon season there. It is
climatic condition. The different parts of the world have different types of climate.
The area or part which has more or less similar type of hotness, coldness, rainfall,
perception, temprature etc is a climatic region. There are different climatic regions in
the world because different factors determine the type of climate in different places.
We do not experience similar type of climate at the same time in the world. It is so,
because different factors are responsible to determine the climate of different places.
The major factors which affect the climate of the world are :

a) Height from the Sea Level :

We know the density of air is higher at the lower altitude as it contains water
vapour, dust particles due to which it absorbs more heat . But air at the higher
attitude is thiner and absorbs less heat.So lower altitude is hotter and higher
is cooler. The temprature decreases when we go higher from the sea level.
Approximately per 165m above from sea level temperature decreases by 1oC.
So, Kathmandu valley is hotter than Dhunche of Rasuwa.

b) Distance from the Equator :

The equator is the shortest distance from the sun. The sun rays falls vertically
on the equator but slanting towards the poles side. The vertically falling rays
have to heat small area only but slanting rays have to heat greater area through
wide atmosphere. So more heat of slanting rays is spent in the atmosphere and
less heat reaches on the surface. That is why area near to equator is hotter and
far from equator is cooler.

Besides height from the sea level and distance from the equator, there are other
factors also. The other factors which affect the climate are distance from the sea,
slope of the land, features of topography, local factors of particular place etc.

260 Blooming Science & Environment Book 8

Climate of Nepal

Nepal is small country in its area. But Nepal experiences varieties of climate. The
land features of Nepal plays significant role to determine its variation in climate.
Mainly the distance from the sea altitude plays important role in climatic condition
of Nepal. With in the same latitude also we experience different climate because of
altitude.

Slope of land is another factor that affects the climate of Nepal. With in a short distance
between Jomson and Pokhara, these two places have different type of climate. It is so
because southern facing slope of northen hemsphere of the earth receives direct sun
light and another side is in shadow area.

The southern parts of Nepal called terai. This region has sub-tropical climate. The
nature of sub tropical climate is hot and wet. So, our terai region is very hot during
summer. In winter season, it is not very cold during sunshine but coldness increases
at night. It happens so, because of nature of the land to get heated faster and cooled
also faster. The hilly region has temperate climate. The temperate climate means
neither very cold nor hot. It is also called moderate climate. The himalayan region
experiences sub-polar climate. Sub-polar climate is cold through out the year and it
is warm during the sunshine.

The climate of Nepal varies from place to place. But the climatic conditions that
change seasons are same. Seasons time period is of 3-4 months. It does not seem
many changes. Nepal has summer season characterising by hot and hot. Nepal
receives more rainfall in monsoon season, winter witness with cold and dry. It rains
very little or no in winter.

Climatic condition is key factor for the development of the plants and animals.
Human activities are influenced by climatic condition of particular area. That is why
people of himali region wear Bhakhkhu and Cha most of the time and people of terai
wear light clothes like Dhoti, Kurtha, Voto etc. Paddy is not grown in himalayan
region because of climatic condition. Laligurans flower and Danfe bird are found
in himalayan region because they can easily adjust in cold climate. Danfe bird and
laliguras are not found in Chitwan N.P.

Seasons in Nepal

Nepal has four climatic seasons.

Spring ( March – May): The temperature is mildly warm in low lands while
moderate in higher altitudes with plenty of opportunities to have tryst with the
mountain views. It is also the time for flowers to blossom and the national flower of
Nepal – rhododendron sweeps the ascending altitudes with its magnanimous colour
and beauty.

Blooming Science & Environment Book 8 261

Summer (June – August): This is also the monsoon season in Nepal. The weather
is hot and wet all the times. It rains almost everyday with occasional thunderstorms
in the evening. The rain spreads the pleasantness around with lush green vegetation.

Autumn (September – November): This is the best tourist season in Nepal with
the summer gone by and the winter to set in. The weather is highly pleasant so are
the mountain views. This is the peak season for trekking as mountain views are
guaranteed so better book your flight in advance. This is also the season of festivities
as Nepal celebrates the biggest Hindu festivals Dashain followed by Tihar.

Winter (December – February): The weather is cool and the sky is clear with
occasional snowfalls at higher elevations. This season is good for trekking in lower
elevations. The morning and night is cold and the days are warm when sunny.

Monsoon and its Effects

The monsoon means seasons. The word monsoon is derived from “Arabic Word-
MAUSAM” which means change of season. Season means, the change of climatic
condition from one feature to another. The monsoon as defined as “A seasonal wind
of the Indian Ocean in Southern part whose direction is reversed periodically.”
The Monsoon is formed being water evaporated, during summer the rays of the sun
falls perpendiculary on the northern hemisphere of the earth (Nepal lies in northern
hemisphere). The air on the surface of the land rises up as its presure decreases. So the
other side the cold air from the ocean has high pressure. The air at a high pressure now
flows to the land area with moisturised air, when this moisturised air passes across the
high mountains, it condenses which falls as rain. It is called monsoons rain.

In Nepal monsoon comes from south east of Nepal. Nearest large amount of water
volume of Nepal is Bay of Bangel. During the summer, the water vapour raising from
Bay of Bangel enters to Nepal from eastern part and flows towards the north and the
west. When this vapour reaches in northern hills, it turns into rain and causes rainfall.
Due to which eastern part of Nepal receives more rain than western in Summer.

Night Heat from Sun sea breeze
land breeze

Colder air Hotter air

Water water Sea Colder air Sea Warm land
Cool land

But in winter Asia as well Nepal receives less heat. Air in upper surface is cold
and has high pressure, where as air above the sea or ocean are warm creating low
pressure. This causes blow of air from land and sea. Since this air blow from land to

262 Blooming Science & Environment Book 8

sea, it is dry and not moisturised. So it causes less rain. The Temperature ranges from
30oC in summer and 10oC in winter in Nepal. Rain varies from over 100 cm to 150
cm during summer monsoon. Monsoon causes a lot of rain. As the result the volume
of water in river increases sometimes which causes flood. The Koshi river increases
sometimes which causes flood. The Koshi river of our country is called “Sorrow of
Nepal”. It is called so because it destroys life and properties in large amount. When
there is over flow of water in Koshi river, it destroys fertile land, house, crops, life
of people and their property. Monsoon also causes land slide, the southern parts of
Nepal faces problems of flood during summer. It is because of monsoon rain so much
or not rain are not good climatic condition. Landslide, soil erosion, flood are caused
by monsoon. The rain accompains by storm and hurricane are more destructive. They
cause destroy of electric poles, breaking of trees and branches. Even such storms and
hurricane causes lost of life accidently. Thousand of people in our neighbouring
countries like India, Bangladesh, Thailand suffer from such storm. Sometimes in
Nepal also, we face storm causing accident and destroy of crops.

Study of Weather

The science of the study of weather is called meteorology. While studying the
meteorological factors such as the minimum temperature, maximum temperature,
direction of wind or rain, humidity, formation of clouds, rainfall, etc we make a
survey. Let us discuss briefly about the factors that affect the weather.

Direction of Air: The movement of air is one of the most important factors in the
weather change. How does the air move? What factor plays the role in the movement
of air? Let us take an experiment.

Activity
Convection current

Make a rectangular box with
the two projected holes on the
upperside as shown in the figure.
The front side is made of glass.
Put a candle or lamp just below
one projection and allow the
smouldering taper to pass from the other. You will see that the smouldering taper
passes and comes out from the other. This is due to the fact that the hot air comes
up because it becomes lighter. The cooler air takes the place of hot air. Thus a
current is setup of movement of air takes place.

Blooming Science & Environment Book 8 263

Hot Air is Lighter

In the experiment given above you have noticed that hot air goes up and cool air
occupies the space left by hot air. This can be proved with the help of the following
experiment also.

Activity
Hot air is lighter

Suspend two paper cups upside
down with the help of a stick
and thread so that it looks like a
balance. See that they are equally
balanced. Bring a burning flame
below one of the paper cups. You
will notice that the cup moves up
and the other comes down. This
is due to the fact that heated air
molecules become lighter and they go up. As they go up, the air molecules push
the cup and hence it rises up. The cup with cool air comes down.

Similar phenomenon takes place in the nature also. Due to the sun, the heated
molecules of air go up and cool air molecules come to the space left by
hot molecules. Thus air current moves. Such a current in the nature is called
convectional current.

Types of Weather

We have experienced hot, windy, moist, dry and rainy weathers. When the rain falls,
the air becomes humid. When there is no rain, the air becomes dry. Presence of water
vapour in the air increases humidity. Thus, different types of weather are seen.

Instruments used to Determine Weather

There are different kinds of instruments used to study the weather at a particular
place. Four instruments are discussed below.

Maximum and Minimum Thermometer: This thermometer consists of
two indicators. One indicator shows the minimum temperature of the day
and the next column shows the maximum temperature. One tube of the
thermometer is filled with alcohol and the other is filled with mercury. As
the temperature in the atmosphere varies, two indictors show the maximum
and minimum limits respectively.

264 Blooming Science & Environment Book 8

Rain Gauze: This is the device to find the rain in a day. One cylindrical
vessel and a cone or funnel are fitted and kept in the open space. As the
rain falls, the water is collected in the cylindrical flask and the amount of
rain water is measured to determine the rainfall on that day.

Hygrometer: Hygrometer is the instrument used to measure the
humidity in the air. The humidity means the percentage of water
vapour in the air. The humidity device consists of the parts which
are highly affected by the change in the humidity of the air. For
example, the clean dry air becomes long or short due to humidity
of the air. On the same principle the components of a hygrometer
is made.

Anemometer: This is the device which is used to measure the
direction of wind. From which direction to which direction the air
is blowing can be found out with the help of anemometer. This also
finds the speed of the air with the help of rotation speed of the cup
shaped structures on the top of rotating part.

The anemometer and rain gauze are placed on the open air space
while the hygrometer and maximum and minimum thermometer are placed in the
shade. Using the devices discussed in the section, we can find the following things.
a. Maximum temperature of the day
b. Minimum temperature of the day
c. Content of the water vapour in the air (humidity)
d. Direction of the movement of the air
e. Speed of the air in the direction of the air.

Weather Forecasting

In our country, there is a meteorological station where the elements of weather and
climate are studied by meteorologists and reported to the radio and television stations
for the forecasting of weather. If we study the elements of weather, we also can guess
about the future weather more or less. The sun, water and air are the main factors of
the weather which cause wind, rain, cool, warm, clouds, etc. in the atmosphere.

Nowadays satellite photographs are also used to know the position and speed of the
cloud in the sky. Meteorologists use such photographs for the forecasting of the weather.

Blooming Science & Environment Book 8 265

Main Points to Remember

1. The branch of science which deals with the study of weather is called Meteorology.
2. Weather constitutes direction of the sun, direction of wind, water vapour in the

air, temperature, etc.
3. The sun, air and water are some of the important elements of the weather.
4. Hot air moves up and the space is occupied by the cool air. Thus setup air

currents are called convectional current.
5. Water turns into vapour. It goes high up, cools and becomes clouds. After

moving a certain distance, it comes down in the form of rain.
6. The average weather condition in a considerable area over a period of time is

called climate.
7. The percentage of water vapour in the air is called humidity.
8. Summer, winter, autumn and spring are four seasons throughout a year.
9. Height from sea level, distance from sea level, slope of land, features of

topography are weather determining factors.
10. Thermometer, rain gauze, anemometer, hygrometer are the instruments that

help in finding the changes in the weather. They help in finding temperature,
rainfall, direction of air and humidity.
11. Climatic condition is the key factor for the growth and development of plants,
animals and human activities.

PRO J ECTWORK

Measurement of Rain fall and Direction of wind

1. Take a rectangular tin-can with wide open mouth. Collect rain water falling
freely. Measure the height of the water in the tin-can with the help of a scale.

2. Make a fan model. Face it towards the direction of air. It begins to rotate.

Exercise

1. Fill in the blanks.

a. The direction of air can be found out with the help of ………………

b. Hot air is ………………….. than cool air.

c. The movement of air from hot and cold sets up a current called …..………

d. Thermometer can be used to measure …………….. and ………………
temperature called maximum and minimum thermometer.

266 Blooming Science & Environment Book 8

e. …………………….. is used to measure the rain on the day.

f. Percentage of water vapour in the atmosphere is called ……………..

g. Humidity is found out with the help of a device is called ………….…..

h. Anemometer is used to find ………………….. and ………………….

2. Answer the following questions.
a. What is weather?
b. What kinds of instruments are used in finding weather?
c. Why do we need to study about the weather?
d. In nature, the air moves and a current is setup. What do you call it?
e. Give a pictorial representation of water cycle in nature.
f. What do we call weather science technically?
g. What instrument is used to find the speed and direction of wind?
h. Using anemometer, hygrometer, thermometer and rain gauze what kind
of information do you get about weather?
i. What should be done to find the weather?
j. How can you determine that the weather is being changed?
k. Why does air move? Explain with the help of a figure.
l. Give an experiment that shows the movement of air.
m. Give an experiment to show that hot air is lighter.
n. How does the rainfall take place?

o. What is a rain gauze? How do you measure the rainfall in a day?

3. Write short notes on:

a. Anemometer b.Hygrometer

c. Maximum and Minimum thermometer d. Climate

e. Monsoon

Glossary

Weather : the condition of atmosphere of a place at a time

Cloud : water vapour along with dust in the sky

Rain : water droplets showering on earth due to cooling of cloud

Meteorology : branch of science dealing with weather

Barometer : an instrument to measure atmospheric pressure

Hygrometer : an instrument to measure humidity

Anemometer : an instrument to measure direction and speed of wind

Weather forecasting : to predict weather conditions

Blooming Science & Environment Book 8 267

Chapter The Earth and
the Universe
21

Learning Outcomes Estimated Periods: 5+2

On the completion of this unit, the students will be able to:
 explain the history of the earth
 describe the mechanism of occurring days and night.
 write in short about the moon and the phases of the moon.

The universe is commonly defined as the totality of everything that exists, including
all matter and energy, the planets, stars, galaxies and the contents of the intergalactic
space. The words or terms cosmos, the celestial sphere, world and nature are used
in place of universe. Scientific observations of earlier stages in the development of
the universe, which can be seen at great distances, suggest that the universe has been
governed by the same physical laws throughout most of its extent and history. There
are various multiverse theories, in which physicists have suggested that our universe
is one among many universes that exist.

All the aggregate of all existing things or the whole creation embracing all celestial
bodies (Heavenly bodies) and all of the space is called the universe.

The earth is a member of the solar system; therefore origin of the earth is directly
related with the origin of the solar system. Many theories have been proposed to
explain the formation of the solar system. All these theories can be grouped into the
following two general classes:

A. Formation of the solar system quickly and violently

B. Formation of the solar system slowly and moderately

Some Hypotheses about the Origin of the Earth

Some hypotheses are mentioned below in chronological order of their statements:

1. Old Planetesimal Hypothesis

A French philosopher, Buffon put forth old planetesimal hypothesis in 1749
AD. This hypothesis states that the sun and another star collided together; as

268 Blooming Science & Environment Book 8

a result a very large amount of matter was thrown out of the sun. These hot
matters cooled and the earth with other planets was formed.

2. Nebular Hypothesis

A German philosopher

Immanuel Kant proposed

nebular hypothesis about the

origin of the solar system in

1755, and it was imporved by

a French astronomer Laplace

later in 1796 AD. According

to this hypothesis, the sun

and the planets were formed

from a large whirling cloud

of hot gases and dust. When Nebular theory

the cloud cooled and grew smaller, it began to spin faster. As the surface of the

cloud cooled by radiation, a ring of matter was formed at its surface.

The ring was escaped out from the surface of the main mass and the first planet
was formed. The process was repeated again and again till the entire solar
system was formed. The remaining mass was the sun.

3. New Planetesimal Hypothesis:

A geologist T.C. Chamberlin Moon

and an astronomer F.R. Circumterrestrial
Moulton of Chicago ring

University formulated new

planetesimal hypothesis in Earth
1905 AD. It was slightly

different from the old

planetesimal theory suggested Planetesimals theory
by Buffon. According to this

hypothesis, the two stars did not collide but they came very close to one another,

and due to the gravity of the star, great tides (bulges) raised on the sun. The

materials, which were raised from the sun, remained as large spiral arms. These

spiral arms when cooled, they broke away from the sun. The broken materials

shrank and formed solid particles called planetesimals. These planetesimals

combined together to produce the planets.

Blooming Science & Environment Book 8 269

4. Tidal Hypothesis

The English astronomers Sir James Jeans and

Sir Harold Jeffreys proposed the tidal hypothesis

in 1917 AD. They also supposed that a passing

star had exerted a tidal pull upon the sun but

the effect was to cause a long filament of gases

to be drawn from the sun. The outer part of the

filament escaped into space, the inner part came Tidal hypothesis
back into the sun and the middle part formed a

series of bead like structures of different sizes, which formed the planets.

All the four hypotheses mentioned above are in the first category. It says that
the solar system was formed quickly and violently. The major weakness of
above hypothesis is that the material raised from the sun would be millions of
degrees hot. The hot material would quickly spread out into the space as a gas
before it could cool to form the planets.

5. Dust Cloud Hypothesis:

This hypothesis is put further in 1944 AD about the origin of the earth. Kalluan
Weizsacker, Cuiper and many other Geologists are pioneer of this hypothesis.
This hypothesis proposed that the sun and the planets were formed from a
large cloud of gases and dust. The light of the star pushed the atoms of the
gases and dust to form large particles. These large particles were attracted to
each other by the pull of gravity and they began to crowd together. Eventually,
a huge ball of materials formed the sun and the solar energy produced in it
by the nuclear fusion. Part of the cloud of dust and gases, from which the
sun was formed, stayed all around this new star and slowly rotated. The huge
whirlpools originated in this rotating cloud, which formed smaller globes of
gases and dust to form the planets. In this way, the earth was originated in cold
state. It was suggested that the heat of the interior of the earth is due to decay
of radioactive elements inside it.

Although any hypothesis is not completely convincing, yet the dust cloud
aggregation theory is very popular and more convincing.

Some Data Related to the Earth

Estimated age = about 4600 million years

Area of the surface = 509,700,000 km2

Area of lithosphere = 148,400,000 km2

Area of hydrosphere = 361,300,000 km2

Diameter along equator = 12,756 km

270 Blooming Science & Environment Book 8

Mass = 6 × 1021 metric ton

Relative density = 5.7

Main gases = Nitrogen and oxygen

Satellite = 1 (moon)

Average surface temperature = 20oC

Main distance from the sun = 1 AU [1.5 × 108 km]

Diurnal and Annual Motion of the Earth

The earth moves round on Rotation NP

its axis as well as in its orbit 23 1o Tropic Arctic circle
around the sun. The motion 2 Equator cancer
of the earth on its axis is of
called diurnal motion and a
complete round on its axis 6621o 6621o 6621o
is called a rotation. The 2321o
earth takes about 24 hours Plane of ecliptic 0o
[23 hr, 56 min and 4.09s] to 2312o
Plane of ecliptic Antarctic Tropic
circle
of capricorn

Equator

6612o

complete one rotation. The Axis

motion of the earth in its orbit is called annual motion and a complete round around

the sun is called a revolution. The revolution of the earth has a direct concern with

the change in seasons and varying length of day and night. The rotation of the earth

causes day and night on the earth. The earth takes about 365 days [365d, 6 hr, 9 min

and 9.54 s] to complete one revolution.

The axis of the earth is inclined to plane of the ecliptic at an angle of 66.5°, it causes different
seasons and varying lengths of day and night. If the axis were perpendicular to this plane, all
parts of the earth would have equal days and nights at all times of the year.

Day and Night; an Effect of the Rotation of the Earth

Day and night on the earth occurs due to its
rotation. When the earth rotates on it axis,
only one portion of its surface faces the
rays of the sun and experiences day. The
other portion which is away from the
sun’s rays will be in darkness experiences
night.

To understand better about the cause of
day and night, place a globe or ball as the
earth in a dark room and use a flash of light or a table lamp representing the sun. Do
you see all the parts facing light?

Blooming Science & Environment Book 8 271

The earth rotates eastwards, every part of the earth’s surface will be exposed to
the sun at some time or the other. The part of the earth’s surface that emerges from
darkness into the sun’s rays experiences sunrise. Later, when it is gradually obscured
from the sun’s rays, it experiences sunset.

Seasons

Earth is a planet. It is a member of the E4
solar system. It lies in the third position.
It is about 150 million kilometers from S E3
the sun. It is only planet with air, water
and suitable temperature for living E1
beings.

The earth revolves around the sun in

elliptical path. Sometimes it comes E2
near the sun and sometimes it goes far Fig: Change in season
away from the sun. While revolving

around the sun, its axis makes angle with the orbit. Due to this reason, sunlight

cannot fall equally on the earth.

The Revolution of the Earth and its Effects

When the earth revolves around the E4
sun, it moves in an elliptical orbit and
a complete revolution takes about E1 E3
365.25 days or a year. A normal
year is taken to be 365 days and an
extra day added every four years as
a leap year. We know that, the axis
of the earth is inclined to the plane
of the ecliptic. It causes the different
seasons and varying lengths of day
and night.

In E1 condition of the earth in the E2
given diagram June 21, when the

northern hemisphere is tilted towards the sun. It is called summer solstice. In this

condition the northern hemisphere has the longest day and the shortest night. But the

southern hemisphere has the shortest day and the longest night. In this condition the

northern hemisphere receives the stronger, direct rays of the sun for a longer time.

It makes the region warmer i.e., summer. In that period the southern hemisphere has

winter.

In E3 condition on 22nd December when the northern hemisphere is tilted away from
272 Blooming Science & Environment Book 8