15Chapter Cells
Learning Outcome Estimated Periods: 6+3
On the completion of this unit, students will be able to:
explain the general structure of cell.
draw simple diagrams of plant and animal cells
show differences between plant and animal cell.
explain the functions of cell organelles.
Introduction
Cell is the basic unit of life. All living things are composed of cells. A unicellular
organism is composed of only one cell whereas a multicellular organism is
composed of many cells. Life processes like respiration, excretion, reproduction,
etc. are performed within the single cell in case of unicellular organisms, but
there are separate groups of cells responsible for separated functions in case of
multicellular organisms. Such a group of similar cells is called a tissue. Thus, a tissue
may be defined as a collection of similar cells having the same structure adapted
to performance of the same function or set of functions. The cells have their shape
and size depending on their functions. The cells or a tissue follow the same laws of
growth and development. Some examples of animal tissue are epithelium, muscle,
bone, blood and nerve. Similarly meristem, parenchyama, xylem and phloem are
some examples of plant tissues.
Cell
All living organisms, animals, plants and human beings are made
up of cells. A cell is defined as a protoplasmic unit surrounded by
a thin membrane. Cells are regarded as the building blocks of the
body. They are seen with the help of a microscope. The cells are
smallest structural units of a living body. Like small bricks make a Cell
big house, small cells make plants’ and animals’ body. All animals are cellular. Cells
are structural and functional units of life. Without cell, no living beings can survive.
Structure of the cell
Cells are basic structural unit of living-beings. Cells are important to plants and
animals, as brick to buildings. Each living cell as a functional unit makes plant and
animal body a living whole. It is the cell from which the life begins. They contain
numerous organelles. And the presence of these helps in the continuity of life with a
living matter called protoplasm. All the life activities such as nutrition, respiration,
movement, growth, reproduction and death etc. responds to external stimuli are
controlled by cell. The size of cell depends upon their functions. Some are very long.
Nerve cell is the longest cell.
Blooming Science & Environment Book 6 151
Each living cell is bounded by cell membrane. Cell membrane is elastic, thin, and
delicate living membrane. It performs the following functions:
a. It controls the entry and exit of materials to and from the cell.
b. It gives shape and rigidity to the cell.
c. It protects the cell.
In a plant cell, there is a cell wall in addition to the cell membrane. It is a non-living
part of the plant cell. It is found outside the cell membrane. It is non-living and rigid.
It protects the cell and also gives fixed shape to the cell. That’s why plants cell have
fixed shape.
Differences between cell membrane and cell wall
Cell Membrane Cell Wall
1. It is found in both plant and animal 1. It is found only in plant cell.
cell.
2. It is thin, elastic and delicate. 2. It is thick and rigid.
3. It forms the outer covering in animal 3. It forms the outer covering in plant
cell but in plant cell it lies below the cell. Cell membrane lies below it.
cell wall.
There is thick fluid inside the cell that is called cytoplasm. Cytoplasm consists of
water, proteins, fat, sugars etc. It occupies the space between the cell membrane
and the nuclear membrane. The metabolic activities take place in cytoplasm. It
contains large number of minute living structures bounded by a membrane known
as organelles. These are permanent structures of the cells. The most important cell
organelles are mitochondria, golgi-bodies, endoplasmic reticulum, centrosome,
ribosome, lysosomes etc.
The non-living substances in the cell are known as cell inclusions. Starch grains, fat
globules and crystal of excretory substances are the cell inclusions.
Cell Cell wall
membrance Cell
Membrance
Mitochondrion
Centriole Vacuole
Necleolus Nuclear Membrane
Nucleus Necleus
Nuclear Cytoplasm Nuceleolus Cytoplasm
Membrane Golgi bodies
An Plant Cell
Endoplasmic An Animal Cell
reticulum
152 Blooming Science & Environment Book 6
Activity 1
To study plant cells (Onion cells)
Materials required: onion bulb, forceps, slides, coverslip, watch glass, glycerin,
safranin, etc.
Method:
1. Get an onion and take a peel out.
2. Break the peel. You will see thin papery layer on
the concave side.
3. Tear of the thin peel, keep it in a watch glass.
4. Add a few drops of water and safranin to it.
4. Place a small piece of this peel on a glass-slide.
5. Put a drop of glycerin and cover it with a cover slip.
6. Observe it under a microscope.
Observation:
Note down what you see. You will notice small chambers like structure. These are the
cells.
Activity 2
To study animal cells (human cheek cell)
Materials required:
Tooth pick, watch glass, glass slides, coverslip methylene
blue, blotting paper, etc.
Method:
i. Clean two glass slides and a coverslip by blotting
paper.
ii) Scrap the inner surface of your cheek gently with the help of tooth pick.
iii) Put the scrapped out material on the clean slide and make it thin by rubbing
with the help of the end of another slide.
iv) Put a drop of methylene blue and cover it with the help of cover slip.
v) Now observe the slide under the microscope.
Observation:
Note down what you see. You will notice small circular structures which are
cells.
Blooming Science & Environment Book 6 153
Plant Cell
Generally a plant cell is rectancular or hexagonal in shape. The main components of
plant cell are described below:
Cell wall: The plant cell has cell wall. It is made of cellulose which is non-living
things. The cell-wall gives the cell a definite shape. The cell-wall consists of a semi-
permeable membrane. Cell-wall provides protection and support to the cell.
Cytoplasm: It is a substance in which protein, minerals, fats, water, etc. found.
There are various organelles in the cytoplasm such as mitochondria, golgi bodies,
etc Mitochondria is necessary for respiration of the cell. It acts as power house of
the body because they produce energy. Cytoplasm takes active part in all cellular
activities such as growth, nutrition, respiration, reproduction etc.
Vacuoles: Plant cells have a large and or many small vacuoles. They contain water,
minerals, glucose and other substances needed for the cell. It is also known as aqueous
solution cell-sap. Vacuoles acts as the storehouse for excess water, waste products
etc. It also keeps the cell in shape. It regulates the amount of glucose in the cell.
Nucleus: It is the controlling centre of the cell. It is generally round in shape. It
is located at the centre of the cell. It consists of nuclear membrane, necleoplasm
and nucleolus. Nucleus consists of sugar, minerals, protein etc. It consists of thread
like elongated structure called chromosomes. Chromosomes contain genetic codes
and transmit from generation to generation. They appear only during cell-division.
Nucleus acts as a life-centre for the cell. Nuclear membrane provides partition
between nucleus and cytoplasm. Nucleolus synthesizes ribonucleic acid and protein.
Nucleus plays active role during reproduction of the cell.
Plastids: In the cytoplasm of
the plant cell, there are various Plastid Cell wall
types of plastids , such as Cell
chloroplasts, chromoplasts, Membrance
leucoplast etc. Chloroplasts
make plant green and help in Vacuole
photosynthesis Chromoplasts Nuclear
Membrane
make flower and some other
parts colourful. It helps to
attract insects for pollination. Necleus
Colourful flowers are
attractive, ornamental and Cytoplasm
economically useful. Nuceleolus
Leucoplasts generally found
in roots and other parts of the plant where light do not reach. It helps for storing food
materials such as carbohydrates, protein etc.
154 Blooming Science & Environment Book 6
Animal Cell
An animal cell is generally oval or spherical in shape. The main components of an
animal cell are described below:
Cell membrane: The animal cell is bounded by cell-membrane. It is made of
protein and lipids. It is porous, thin and invisible. It is very delicate. It holds the cell
together and plays an important part in controlling what passes into and out of it.
Cell membrane protects the internal structures of the cell and different organelles
of the cytoplasm. It maintains the shape of the cell. It acts as selective permeable
membrane and transports the substances like sugar, sodium etc.
Cytoplasm: The substance which surrounds the nucleus is called cytoplasm. It is
bounded peripherally by the cell membrane. It has similar structures and functions
as in the plant cell. The cytoplasm produces energy, makes things and stores food.
Many chemical reactions take place inside it.
Vacuoles: Unlike the plants cells, animal cells have small vacuoles. These occur in
the form of globular structures inside cytoplasm. Each vacuole is surrounded by a
cytoplasmic membrane. The vacuole contains a sugary liquid called cell-sap. Some
animal cells do not contain vacuoles.
Nucleus: Nucleus of the Cell membrance
cell is centrally located. Mitochondrion
It consists of a fluid Centriole
celled nucleoplasm inside it.
There are chromosomes. The
chromosomes carry the genetic N ecleolus
materials through genes. The Nucleus
size of the nucleus is different Nuclear
in different cells. The shape of Membrane
nucleus vary as well. It may
be circular, oval, elongated Cytoplasm
etc. Nucleus is the main organ
which controls all the functions
besides transmission of heredity information and reproduction. The other structures
and functions are almost similar to the nucleus of the plant cell.
Centrosome: This is the characteristics feature of animal cell. It consists of centrioles
and centrospheres. It helps in cell division.
Unicellular Organism
Some living beings are made up of single cell. All the life activities are carried by a
single cell in them. These living beings are called unicellular organism or protozoans.
Amoeba, paramecium, easlena, plasmodium, etc are unicellular organisms.
Blooming Science & Environment Book 6 155
Amoeba is an unicellular organism. Amoeba cannot be seen by our naked eyes. We
have to use microscope to see amoeba.
D Pseudopodium Scan for practical experiment
visit: csp.codes/c6e21
Multicellular Organism
Many living beings are made up of two or more than two cells. Such living beings
are called multicellular organism. Earthworm, rabbit, human beings are multicellular
organisms.
Hydra Earthworm Bird Snake
Differences between Unicellular Organism and Multicellular Organism
Unicellular Organisms Multicellular Organisms
1. These living-beings are made up of 1. These living-beings are made up of
only a single cell. many cells.
2. Amoeba is an unicellular organism. 2. Human being is a multicellular
organism.
3. They can be seen only by microscope. 3. They can be seen with naked eyes.
Functions of Cell
1. Cells are fundamental, structural and functional units of all living beings.
2. Cells control different activities of living beings such as movement, growth,
respiration, etc.
156 Blooming Science & Environment Book 6
3. The reactions that take place in the cytoplasm continue life.
4. Chromosomes are responsible for transmission of all the genetic instruction to
new cells.
5. Because of nucleus the cell division, reproduction and growth are possible.
Differences between Plant and Animal Cell
Plant Cell Animal Cell
1. It is surrounded by a cell wall in 1. It has only an outer cell membrane.
addition to the cell-membrane. There is no cell wall.
2. It usually has one or two large 2. Vacuoles are either absent, or they are
vacuoles. very small.
3. Plastids are present in plant cell. 3. Plastids are absent.
4. Centrosome is absent. 4. Centrosome is present.
Main Points to Remember
1. All living beings are made up of cells.
2. Cells are the fundamental units of life.
3. Cell membrane covers the interior part of animal cell.
4. Cell membrane protects the interior part of the cell.
5. The cell wall is the outer most part of the plant cell.
6. The cell wall protects the cells in it.
7. There is protoplasm in the cell.
8. There is round and oval shaped nucleus in protoplasm.
9. Nucleus controls the metabolic activities within the cell.
10. Vacuoles are also present in the protoplasm.
11. Vacuoles are small in animal cells but large in plant cells.
12. Some cells have fixed shape while some have irregular shape.
PRO J ECTWORK
To prepare the model of plant cell or animal cell.
Collect some locally avaiable materials like plywood, threads of different colour,
styrotfoam, coloured beans, glue stick, seeds of different plants,etc according to
your need. Make a model of animal cell or plant cell which you like and submit the
project work to your teacher.
Blooming Science & Environment Book 6 157
Exercises
1. Fill in the blanks:
a. All living beings are made up of …………………………
b. A large empty space in plant cell is ……………………..
c. ………………… controls the metabolic activities in the cell.
d. A type of …………………… is found inside the cell.
e. ……………………. is the largest cell in the human body.
2. Write true and false against each of the following statements:
a. Cells are found in all living beings.
b. Cell membrane is not found in animal cell.
c. All cells can be seen by naked eyes.
d. All cells have the same type of shape.
e. All living beings have same number of cells.
3. Answer the following questions:
a. What is the body of living beings made up of?
b. Draw and label the plant cell as is seen under compound microscope.
c. List out main cell organelles of animal cell.
d. What are the importance of a cell?
e. What is the important part inside the cell?
f. What is the main function of nucleus?
g. What are unicellular organism?
h. Motorbike is not a living thing, why?
i. Distinguish between animal and plant cell.
j. Draw an animal cell and label it.
k. Vacuoles in plant cells are bigger, why?
158 Blooming Science & Environment Book 6
4. Match the following:
Cell plant cell
Large vacuole amoeba
Liquid brain of cell
Unicellular organism protoplasm
Nucleus cytoplasm
5. Choose the correct one:
a. What is the centre point of cell?
i. Protoplasm ii. Vacuole
iii. Cell membrane iv. Nucleus
b. What is the function of cell membrane?
i. Protection of a cell ii. Balance of water in cell
iii. Protection of the cell content
iv. Changing shape of a cell membrane
c. By why is an amoeba called unicellular organism?
i. for having only a single cell
ii. due to the absence of cell membrane
iii. due to the presence of only one nucleus
iv. due to very small size
d. Who discovered Cell?
i. Charles Darwin ii. Robert Hooke
iii. Robert Brown iv. None of above
e. What is cell wall made up of?
i. Living-beings ii. Non-living thing
iii. Both of a & b iv. None of above
6. Draw the diagram of the following and label their parts.
a. Plant cell b. Amoeba
7. Differentiate between:
a. Cell wall and cell membrane b. Unicellular and mu lticellular organism
c. Plant and animal cell. d. Cell organells and cell inclusions.
Blooming Science & Environment Book 6 159
8. Study the diagram and answer the questions that follows.
a. Label A, B, C and D in the given figure. A
B
b. Which cell is shown in the given
figure? Give two important reasons E C
c. What is ‘E’ if it is found only in
plant cell? Write down its important
function.
d. Write down the main function of A, D
B, C and D.
Glossary
Regard : think or consider
Bounded : surrounded, having a boundary
Rigidity : hardness, inflexibility
Fluid : liquid
Stain : make clear or visible
Sap : plant liquid
160 Blooming Science & Environment Book 6
16Chapter Life Process in Plants
Learning Outcome Estimated Periods: 10 + 2
On the completion of this unit, students will be able to:
describe the functions of roots, and leaves of flowering plants
distinguish between tap root and fibrous roots.
explain in short about structure and function of shoot system.
explain in short about structure and function of leaf.
explain and demonstrate absorption, transportation and transpiration
process in plants.
A. Parts of Flowering Plant
There are different kinds of plants found on the earth. Some grow in water and other
grown on land. The size of the plants may vary from unicellular microscopic to big trees.
The plants like maize, rice, wheat, mustard, vegetables, etc. are grown in the field for
food value. Many other plants are also found around us.
Activity Flower
Pull out the flowering plant
carefully in such a way that no Fruit
Stem
part of it gets injured. Why is force
Leaf
necessary to pull it out? Gently wash Shoot
the underground part of the plant. system Bud
How does the underground part
differ from the aerial part? Observe
it. Make a list of all the differences in Node
your copy.
Scan for practical experiment
Root Main root
system Secondary
root
visit: csp.codes/c6e22
On the basis of division of labour, all the flowering plants can be divided into two
systems: The root system and the shoot system.
Blooming Science & Environment Book 6 161
The Root System Region of maturation
The part of the plant that grows Root hairs Root hair
downward into the soil by the network region
of roots is called the root system. The
root system extends to a very shorter Region of
distance. It does not bear any nodes, elongation
leaves and buds.
Growing Root cap
point
Parts of a typical toot
Regions of a typical root
A typical root has these five parts of regions.
1. Root cap: It is a cap like structure that covers the delicate growing point or tip
of the root. It protects the growing point from the friction of the soil particles.
2. Growing point: It lies protected below the root cap. It produces new cells for
the root cap and the basal region of the root. Therefore, it helps for the growth
of the root.
3. Region of elongation: It lies behind the growing point. This region helps to
increase the length of the root. It also helps to absorb water and mineral salts
from the soil.
4. Root hairs region: This region gives rise to minute hair like outgrowths called
root hairs. The root hairs help to absorb water and minerals from the soil.
5. Region of maturation: It forms the main part of the root and lies just above
the root hair region. This region bears lateral branches to form a network of
roots into the soil. The function of this region is to hold the plant firmly in the
soil.
Types of Roots
There are two types of the root system. They are tap root system and fibrous root
system.
a. Tap root system
The root that arises from the radicle of the Primary root
seed is called the tap root system. It grows Seconday root
vertically downward as main root. This main Tertairy root
root is called primary root. It lives throughout Root cap
the life of the plant. The primary root is
thick at its base and gradually tapers towards
its apex. The primary root produces many
lateral branches called secondary roots. The
secondary roots in turn give tertiary roots.
162 Blooming Science & Environment Book 6
The tap root system is also called primary root system. It is found in the
dicotyledonous plants like pea, sunflower, gram, mustard, radish, turnip, carrot,
etc.
Primary root
Primary root
Carrot Turnip Mustard root
b. Fibrous root system
In some plants, the primary root is short-lived. It is soon replaced by thin
clusters or roots that arise from the base of the stem. Such a root system is
called fibrous root system. This root system does not have main root. These
roots are usually spread in a larger area rather than growing deep into the
soil. The fibrous root system is found in monocotyledonous plants like maize,
wheat, paddy, onion, grass, etc.
Fibrous root Root of maize Adventitious root
Differences between Tap Root System and Fibrous Root System
Tap Root system Fibrous Root system
1. Tap root develops directly from the 1. Fibrous root grows from base of the
radicle. stem of the plant except the radicle.
2. The primary root continues growing 2. The fibrous root ceases to grow after
throughout the life. a certain time.
3. They usually grow deep in the soil 3. They may be both usually aerial or
rather than spreading in larger area. underground. They are spread in a
larger area rather than growing deep.
4. They give rise to fine lateral roots. 4. They form a cluster of roots.
Note: On the basis of origin of roots, they are two types: true roots and
adventitious roots. True roots are those roots which are arised from the radicle
of the seeds. Tap roots and fibrous roots are the examples of such roots.
Adventitious roots are those which are arised from any part of the stem other than
radicle of the seeds.
Blooming Science & Environment Book 6 163
Activity
To observe tap root and fibrous root.
Materials required: A plate, cotton, some seeds of pea and wheat, water.
Method:
1. Take some wet cotton in a plate.
2. Put some seeds of pea and wheat on it and keep it in a warm place.
3. Water it if necessary.
Germination of Fibrious root of
pea seed wheat
After a few days, you will see roots growing from each of the seeds. Observe the
root of the both types of the seeds. Draw a well labelled diagram of each kind of the
roots.
Functions of the Root System
The main functions of the roots are as follows:
1. It absorbs water and dissolved mineral salts from the soil.
2. It provides anchorage to the plant by helping it to hold the soil firmly.
3. It helps to conduct the absorbed materials up to the stem.
4. In some plants like radish, carrot, turnip, etc the roots store the food.
In some floating or submerged plants either the root system is poorly developed or
totally absent. In these plants, the roots neither help to anchor nor absorb water and
minerals from the soil.
The Shoot System
The part of the plants that grows above the soil is shoot system. It is the aerial system,
usually grown above the soil. It grows from the plumule of the embryo of a seed. It
consists of main stem, branches, leaves, buds, flowers and fruits with seeds.
One the basis of their functions, the shoot of a plant can be classified into two groups:
Vegetative part and reproductive part.
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1. Vegetative part
It consists of stem, branches and leaves. It takes part in the growth and
development of plant body and preparation of food. In some cases, it takes
part in asexual reproduction also.
2. Reproductive part
The flowers and fruits are known as the reproductive parts because they take part in the
formation of seeds. When the seeds get suitable environment, they germinate into new
plants.
Mango tree Rose bush Maize plant
Stem
The stem grows up from the soil. It grows or leaf
bends towards the light. Stem is differentiated fruit
into nodes and internodes which may not be flower
distinct in some cases. The place, where a leaf or a
branch is attached to the stem is called node. The steam
length of the stem between two successive nodes
is called internode. The stem bears three types of root
buds. They are, terminal buds, auxillary buds and
floral buds. A terminal bud is present at the tip of
the stem or a branch, which helps to increase the
height of the plant. The bud present at the angle
between a leaf and the stem or its branch is called
auxillary bud. This gives rise to a new branch.
The floral bud, which grows into a flower, may
be terminal or auxillary in position.The aerial stem of most of the plants is erect as
in pine, mango, corn, etc. But in some plants such as pea, bean, grapes, bitter guard,
etc., the stem cannot stand erect. They climb up with the help of a support.
In some other plants such as watermelon and pumpkin, the aerial stem creeps along
the ground because their stem is not strong enough to become erect. They grow in a
horizontal direction over the surface of the soil.
Blooming Science & Environment Book 6 165
Creeper-pumpkin Climber-bean Erect-sugarcane
Functions of Stem
The main functions of the stem are as follows:
1. Stem helps plants to stand erect.
2. Stem transports water and miniral salts from roots to the leaves and prepared
food from leaves to other parts.
3. In some plants like potato, ginger, onion, etc.stem stores the food.
4. In some plants like cactus, opuntia, etc. the stem prepares the food by the process
of photosynthesis.
Differences between Root and Stem
Root Stem
1. It develops from the radicle. 1. It develops from the plumule.
2. It is brownish or whitish in colour. 2. It is often green in colour.
3. It does not bear leaves and buds. 3. It bears leaves and buds.
4. Root cap is found at the tip of the root. 4. There is no cap present at the apex.
5. It does not have nodes and internodes. 5. It has nodes and internodes.
Leaf
Leaves are the food making parts of plants. Their shape, size
and structure may vary from plant to plant. Mostly, leaves are
expanded and flattened in form. In some cases they are needle-
like or scale-like as in pines or nearly cylindrical as in onion. Peepal leaf
Leaves arise from the nodes as a lateral outgrowth of the stem
or a branch. They are green in colour due to the presence of green pigments called
chlorophyll.
Leaves are arranged on the stem in different manners. The arrangement of leaves on
the stem may be alternate, opposite or whorled.
166 Blooming Science & Environment Book 6
Scan for practical experiment
Alternate Opposite Whorled visit: csp.codes/c6e23
Structure of a leaf
A typical leaf consists of leaf base, petiole and leaf blade.
a. Leaf base apex
margin
It is the lowermost part of the leaf. It is veins blade
the part attached to the node of the stem. midrib
The leaf base may be in the form of
expanded sheath (monocotyledonous petiole
plants) or of two lateral outgrowths stipule
called stipules (dicotyledonous plants). base
b. Petiole Parts of typical leaf
Petiole is a stalk of the leaf by which it is attached to the stem. It lifts the leaf
blade above the stem in order to provide it maximum exposure to the sunlight.
When petiole is absent in a leaf, it is said to be sessile leaf otherwise it is called
petiolate.
c. Leaf-blade
It is also called lamina. It is a thin, flattened, expanded green part. It has two
surfaces: upper surface and lower surface. The green pigment, i.e. the chlorophyll
is found in the leaf blade for preparing food. The leaf blade bears many tiny pores
on the leaf surface called stomata. Through stomata, exchange of gases takes
place between the leaf and atmosphere during respiration and photosynthesis. The
leaf blade is supported and nourished by a number of thin veins and veinlets. A
prominent vein present in the middle of the leaf blade runs from its base to the
apex called mid rib. It gives out numerous veins and in turn veintlets.
Venation in Leaves
The arrangement of veins and the veinlets of lamina is called venation. There are two
types of venation. They are reticulate vanation and parallel venation.
Blooming Science & Environment Book 6 167
Reticulate Venation
When veins and veinlets are irregularly distributed without Reticulate
a definite pattern in the lamina forming a network, then it is
called reticulate venation. This type of venation is often found
in dicotyledonous plants.
Parallel Venation
When the veins run parallel or roughly parallel to one another
in the lamina, it is called parallel venation. In this, the veintlets
do not form network in the leaf. Most of the monocotyledonous Parallel venation
plants have parallel venation.
Functions of leaves
The main functions of the leaves are as follows:
1. The chlorophyll of the leaves helps the plants to make food in the presence of
the sunlight. This process is called photosynthesis.
2. The stomata of the leaves help in the exchange of gases during photosynthesis
and respiration.
3. The excess of water in the plants evaporates through the stomata. This process
is called transpiration.
4. Leaves protect the auxillary and terminal buds from mechanical injury.
Main Points to Remember
1. All flowering plants have two systems: The root system and the shoot system.
2. There are two types of root: tap root and fibrous root.
3. Roots absorb water and numerals and fix the plant in the soil.
4. Stem keeps the plants straight and helps to transport water and minerals to the
soil.
5. Stem with its branches and leaves are called the shoot.
6. The chief function of leaves is to prepare food.
7. The arrangement of leaves on the stem may be alternate, opposite or whorled.
8. A typical leaf consists of leaf base, petiole and leaf blade.
9. Leaves are greatly in their size, form and venation.
10. The arrangement of veins and veinlets in the leaf is called venation.
PRO J ECTWORK
Collect the roots of dubo, onion, radish, bean and mustard. Find out the differences
between them. Then preserve them dry for your herbarium collection.
168 Blooming Science & Environment Book 6
Exercises
1. State whether the following statements are ‘True’ or ‘False’:
a. The root sometimes stores surplus food.
b. The main function of stem is to fix the plant to the soil.
c. The colour of root and stem is same.
d. Veins and veinlets are not arranged in the lamina of a leaf.
e. Rice has fibrous root system.
2. Draw a flowering plant and label its different parts.
3. Write the functions of radicle and plumule.
4. Give reason:
a. Leaf can be considered as the food factory of the plants.
b. A pea plant has tendrills.
c. The potato which is used as vegetable is stem
d. The water-melon cannot stand erect.
e. The leaves of gram have reticulate venation.
5. Answer the following questions:
a. Name any four plants which bear tap root.
b. Name any four plants that bear fibrous root.
c. What are the functions of the root?
d. Draw a well-labelled diagram of a peepal leaf.
e. What are the differences between the stem and the root?
f. What are the functions of the leaves?
g. What is meant by venation? Classify it.
h. What are the functions of the stem?
i. Differentiate between tap root and fibrous root.
j. What do you mean by the root system and the shoot system?
k. Name two types of venation.
Blooming Science & Environment Book 6 169
6. Study the given figure and answer these questions. C
a. Name A, B and C. B
b. Write the function of B.
c. Which part of it absorbs water from the soil? A
d. Which part of it takes part in reproduction?
Glossary
Delicate : soft
Embryo : The structure that develops from the fertilized egg prior to
germination.
Synthesis : Manufacture of chemical compounds from simple compounds.
Persist : To continue to exist.
Tapers : to become gradually narrower.
Apex : Tip of the plant’s parts.
Dicotyledonous : Having two seed leaves in the seeds.
Monocotyledonous : Having one seed leaf in the seeds.
Vitally : Extremely, in an essential way.
Nourished : To keep living things alive and healthy with food.
170 Blooming Science & Environment Book 6
B. Plant Physiology
The study of all the life process of plants which involves the study of the functions of
various plant organs and tissues is called plant physiology. In this topic we will study about
reproductions, transpiration, photosynthesis, respiration, absorption and transportation of
nutrients as the physiological activities of plants.
Absorption
Water is absorbed due to activities
going on in roots. Absorption of water
occurs with the help of energy in the
form of ATP, which is released due to Water
metabolic activities of root cells such vapour
as respiration. Absorption takes place
against concentration gradient even when
the concentration of cell sap is lower than
that of soil, water, roots, stems and leaves.
However, mainly the water is absorbed
by roots. The area of young roots where Xylem
most absorption takes place is the root
hair zone. The root hairs are delicate
structures which get continuously
replaced by new ones at an average rate of 100 millions per day. The root hairs lack
cuticle and provide a large surface area. They are extensions of the epidermal cells.
They have sticky walls by which they adhere tightly to soil particles. As the root
hairs are extremely thin and large in number, they provide enormous surface area for
absorption. They take in water from the intervening spaces mainly by osmosis.Water
is absorbed due to activities going on in roots.
Passive absorption is by osmosis
Passive absorption takes place along the concentration gradient when the concentration
of cell sap is higher than that of soil water. Water is absorbed when transpiration
rate is high or soil is dry. Due to high transpiration rate, water deficit is created in
transpiring cells. Rapid transpiration removes water and reduces turgor pressure in
living cells of root. The suction force thus developed is transmitted to root by xylem.
It pulls water from surrounding root cells to make up water deficit.
Reproduction in Plant
We have seen that number of plants can be formed from a single plant. How is it
possible? It is reproduction, by which any living being multiplies its number.
The life process in which living beings multiply their number is called reproduction.
Reproduction is done by two methods. They are asexual reproduction and sexual
reproduction.
Blooming Science & Environment Book 6 171
Activity
To show a sexual reproduction in plants.
Materials required: a sharp knife, rose plant and flower pot.
a piece of rose stem A forming bud A new plant
Method
1. Take a rose plant.
2. Cut a piece of old stem of it about 6 inches long.
3. Put it partially in the soil in a wooden box or flower pot.
4. Water it daily for about fifteen days.
Observe the growth seen on its stem. Is their any growth? If you water it for some
more days, it will change in the form of new plant of rose. This is an example of
asexual reproduction.
Activity
To show germination of seeds.(sexual reproduction)
Materials required: Pea seeds, water, plate, cotton
Method
1. Take some pea seeds.
2. Place them between the water soaked cotton.
3. Leave the apparatus for 2-4 days.
Observe the change occurred in the seed. If you put them in soil, they will grow in the
form of new plants. It is an example of sexual reproduction.
Thus, if a plant forms new plants by its seeds, that is sexual reproduction.
172 Blooming Science & Environment Book 6
Seeds are formed in fruits. Seeds and fruits are formed from flowers. Therefore,
flowers have very important role in sexual reproduction in plants.
Flowers have androecium and gynoecium as reproductive organs. Androecium
are male reproductive organs which form pollen grains. Gynoecium are female
reproductive organs which form ovules. The transformation of pollen grains from
anther of androecium to stigma of gynoecium is called pollination. After pollination
fertilization takes place which forms seeds for sexual reproduction.
Transpiration
The plant root absorbs water and minerals from the soil. Only a small amount of the
absorbed water is used to manufacture Carbohydrates (glucose) as food. The rest
amount of the absorbed water is lost from the aerial parts of plants (mostly from
leaves) in the form of water vapour. The loss of water in the form of the water vapour
from the surface of aerial parts of the plant is called transpiration.
All the aerial parts like stem, leaves, etc., of a plant transpire water. But, most of
the transpiration takes place from the leaves. The surface of the plant leaves has
a number of minute pores called stomata. They are mostly found on the leaves. A
stoma consists of a minute pore surrounded by two guard cells. The opening and
closing of the stoma helps to allow water vapour to escape out in the atmosphere
Stomata
Leaf Leaf cell and stomata
Activity Water droplets
To show transpiration process Bell jar
Materials required: A potted plant, a bell jar, Plant
polythene bag, big glass plate, Polythene bag
Method Flower pot
1. Take a small well-watered potted plant.
2. Cover the flower pot and its soil with
polythene bag.
3. Place the potted plant on a glass plate and cover it with a dry bell jar.
4. Make the apparatus air tight.
5. Leave the apparatus undisturbed for few hours.
Observe the inner layer of the bell jar after 5-6 hours. You will see droplets of water at
the inner surface of the jar. They are transpired from the potted plant.
Blooming Science & Environment Book 6 173
Photosynthesis
All the leaving things need food in sufficient amount. They need food to get energy
for the growth and repair of their bodies. Different living organism has different
methods of obtaining their food. All the green plants can prepare their own food
in their leaves with water and carbon dioxide in the presence of the sunlight. This
process is called the photosynthesis.
Thus, photosynthesis can be defined as the process in which the green plants
synthesize carbohydrates from carbon dioxide and water using the energy of the
sunlight.
This process takes place in the green cells of plants. The overall equation representing
photosynthesis is:
Carbon dioxide + water sunlight Carbohydrate+ oxygen
Chlorophyll
6CO2 + 6H2O C6H12O6 + 6O2
In this process of photosynthesis, the following points can be noted.
a) Carbon dioxide and water are the raw materials for the photosynthesis.
b) Carbon dioxide is absorbed from the air through stomata.
c) Water is absorbed from the soil by root hairs and conducted to the leaves by
stem.
d) The reaction requires energy which is fulfilled by the sunlight.
e) The green pigment, chlorophyll traps the light of the sun.
f) Simple sugar and oxygen are the end products of the photosynthesis.
The presence of starch in any thing can be tested with the help of a few drops of
iodine solution. A drop of iodine turns into blue-black in colour when dropped in
starch. It is called starch iodine-test or starch test.
Activity
Strach Test
Materials required: Two potted plants X and Y, two beakers, water, alcohol, iodine,
tray, tripod stand, spirit lamp, wire guaze.
Method:
1. Take two healthy potted plants namely X and Y.
2. Place X in sunlight and Y in a dark room for 2-3 days.
3. Pluck one leaf from each of the plants, X and Y.
4. Boil both of the leaves first in water and then in alcohol.
174 Blooming Science & Environment Book 6
Strach Test
Materials required: Two potted plants X and Y, two beakers, water, alcohol, iodine,
tray, tripod stand, spirit lamp, wire guaze.
Method:
1. Take two healthy potted plants namely X and Y.
2. Place X in sunlight and Y in a dark room for 2-3 days.
3. Pluck one leaf from each of the plants, X and Y.
4. Boil both of the leaves first in water and then in alcohol.
Boiling Boiling Hot water
water Alchohol Iodine drop
white tile
5. Wash them with cold water. Now, the green colour of the leaves is totally
bleached.
6. Place the leaves in a tray and add a few drops of iodine solution on both of the
leaves.
Observe what happens to the colour of the leaves. You will notice that leaf of plant X
turns into blue black but the leaf of plant Y does not turn into blue black. From this
activity, it is also proved that sunlight is necessary for the plants to prepare food.
Transportation of Nutrients
Plants prepare their food in leaves by the Transportation of water mineral
process of photosynthesis. The leaves (xylem) and food (phoem)
need water for photosynthesis. Similarly
the prepared food is required by different
parts of plants to survive. To supply the
materials in different parts, plants have
conducting tissues. There are two types of
such tissues, xylem and the phloem. Xylem
conducts water and minerals from root to
the leaves to manufacture food. Phloem
transports the prepared food from leaves to
the different parts of the plant. In this way,
the raw materials, like water and minerals,
and prepared food are transported up to the
respective parts of plants.
Blooming Science & Environment Book 6 175
Activity
To show transportation in plants.
Materials required: a twig with white rose, beaker, water,
red ink
Method:
1. Place some drops of red ink in a glass tumbler filled
with water.
2. Place the rose twig in the water.
3. Leave the flower for about two hours.
4. Observe in the petals of rose. Draw your conclusions and write
Main Points to Remember
1. Absorption is a life process in which plants absorb water and minerals from
soil with the help of xylem.
2. Asexual and sexual are two methods of reproduction.
3. Asexual reproduction is done without fertilization.
4. Sexual reproduction is done by fertilization.
5. Roots of plants normally grow in soil.
6. The loss of water in the form of water vapour from the surface of the aerial
parts of plants is called transpiration.
7. Photosynthesis is defined as the process in which green plants synthesis
carbohydrates from carbon dioxide and water using the energy of the sunlight.
8. Carbon dioxide and water are the raw materials to manufacture during the
photosynthesis.
9. Xylem and phloem are the conducting tissues.
10. The process of removing of green colour of pigment of any parts of the plant is
called bleaching.
PRO J ECTWORK
Make a collection of those plants which do not reproduce by sexual method.
Preserve them by dry or wet method whatever is possible.
Exercises
1. Fill in the blanks.
a) A mustard plant, reproduces by ............................... method .
b) The process of multiplying the number of plant is called ................
176 Blooming Science & Environment Book 6
c) The green pigment which helps leaves to manufacture food is known as
................................
d) The food taking mechanism is called....................
e) The plants absorb oxygen and throw carbon dioxide through ....................
f) ...............................and phloem are the ..........................tissues.
2. Answer the following questions.
a) Define absorption.
b) What is reproduction?
c) Mention the types of reproduction.
d) Describe in short about sexual reproduction in plants.
e) What do you mean by stomata? What are their functions?
f) What is chlorophyll?
g) Define photosynthesis. Write its equation.
h) What do you mean by plant physiology?
i) Define transpiration.
j) Describe an activity to demonstrate transpiration.
k) List the raw materials needed to prepare food by plants during the
photosynthesis.
l) Give an experiment to show that sunlight is necessary for photosynthesis.
m) Name the conducting tissues.
n) Why is internal transport necessary in plants ?
o) What do you mean by transportation of nutrients in plants?
p) What is bleaching?
3. Sketch the figure of stomata.
4. Give an experiment with necessary diagrams showing that plants
prepare starch.
Glossary
Stoma : Singular form of stomata.
Guard Cells : Bean shaped cells found around a stoma.
Starch : Atype of carbohydrate prepared by plants during photosynthesis
Bleaching : The process of removing colour.
Translocate : To transport from one place to another place.
Absorption : to draw inside
Pollination : process of transferring pollen grains from anther to stigma.
Fertilization : fusion of male and female a gamete.
Blooming Science & Environment Book 6 177
17Chapter Structure of The Earth
Learning Outcome Estimated Periods: 5+1
On the completion of this unit, students will be able to:
describe the internal and external structure of Earth.
describe various parts of land surfaces like mountain, plain, valley, plateaue,
etc.
describe various parts of water surface like ocean, sea, river, lake, etc.
Scientists believe that the Earth started as a huge ball of burning gases about 4,600
million years ago. After many years, the Earth began to cool. When it had cooled
enough, it began to harden slightly and became smaller (contracted). The earth is
our home planet. It is not completely round. It is somewhat flat at the two poles and
bulges out at the equator. The diameter of the earth at the poles is 12,713 km and at
the equator is 12,756 km.
There are seven large continuous landmasses which are called continents. They are
Asia, Europe, Africa, North America, South America, Australia and Antarctica.
According to a German Geologist, Alfred Wagener, about two hundred million years
ago, there was only one landmass of the earth. It was Pangaea. Then the Pangaea
divided into two landmasses: Laurasia and Gondwana. Present North America and
Eurasia (Europe and Asia) were emerged from Laurasia while South America, Africa,
Australia and Antarctica are formed from Gondwana land.
Earth is surrounded by the atmosphere. The earth rotates on its own axis and revolves
around the sun. The earth completes one rotation on its axis in 24 hours and one
revolution around the sun in about 365 days (one year).
Mountains, valleys, flat lands, etc. are found on the surface of the earth. Two third
part of the earth is covered by water and one third part is land. Earth is surrounded
by a layer of air, which is known as the atmosphere. The depth of the sea ranges from
about 4,000 meters to 11,000 meters. The top of Mount Everest (the highest peak in
the world) is about 8,848 meters above sea level.
Internal Structure of the Earth
The internal structure of the earth has four different layesr. They are crust, mantle,
outer core and innercore
1. Crust: The outermost layer of the earth is the crust. Its thickness ranges from
5km to 50km. It is made up of solid rocks.
178 Blooming Science & Environment Book 6
2. Mantle: Below the crust is Atmosphere Ocean Continental
the mantle. Its thickness is Crust crust crust
about 2900 km. It is made Mantle Lithosphere
up of liquid materials called Upper Mantlecontimues down to
magma. Magma comes out mentle outer core
in the form of lava when it Asthenosphere
breaks through weak parts (part of mantle)
in the crust of the earth. It
is made up of hard silicate Outer
and minirals like iron and core
magnesium. temperature
varies from 750o-2500oC Outer core of
molten metal
Solid metal
inner code
3. Outer Core: This lies
between the mantle and the
inner core. Its thickness is
about 2,100 km. It is also
made up of liquid materials. Heavier metals like iron, cobalt and nickel are
found in this layer. Its temperature ranges from 2500oc to 3000oc.
4. Inner Core: This is the central portion of the earth. It is about 1,300km in
thickness. It is made up of solid materials. Due to very high pressure the
materials are found in solid state. Its temperature ranges from 3000oc to 5000oc.
External Structure of the Earth
The outer part of the earth is made up of soil, water, rocks and air. The earth is divided
into three different parts. They are lithosphere, hydrosphere and atmosphere. The
land part of the earth is called lithosphere. There are various forms of land on the earth’s
surface like mountains, hills, plains, valleys, plataeus, etc. The water part of the earth’s
surface is called hyddrosphere. There are various forms of water like oceans, seas,
river, lakes, ponds, streams, etc. The earth is surrounded by a layer of air called
atmosphere. About two-thirds of the earth is covered by water and about one-third of its
surface is covered by land.
The various forms of land and water present on the earth are describe below:
Mountains
Mountains are a part of the land. Any raised part of the land
higher than 300 metres is known as a mountain. The highest
peak of the world is Mount Everest, which is always covered
with snow.
Mountains are made up of rocks. The outer portion of a
mountain consists of soil. The soil is suitable for plant
growth. In rocky mountains, due to the lack of soil, plant Mountains
growth is not possible. When the mountain is lower in
height, it is called hill. Most of the hills in Nepal are covered with jungles.
Blooming Science & Environment Book 6 179
Mountains are of three types:
1. Fold mountains:
Most of the mountains are fold mountains. The crust
of the earth folds in a length and rises up to form
a fold mountains. Horizontal quakes are the main
causes of the formation of fold mountains.
2. Block mountains:
Due to vertical quakes, block mountains are formed.
Such quakes push a part of the land upward and
the land next to it goes down. Due to this, a valley
is formed. The portion of the land that is raised is
called a block mountains.
3. Volcanic mountains:
The molten mass (lava) comes out from the earth’s
crust due to volcanic eruptions. This lava settles at
the mouth of the volcano. When the molten lava
cools off, it becomes solid, forming a mountain.
This is known as a volcanic mountain.
Advantages of mountains
Mountains are very useful to us. Some of the advantages of the mountains are as
mentioned below:
1. The snow found on the high peaks of the mountains is the origin of rivers.
2. Mountains are important for tourism.
3. Mountains are rich in minerals.
4. Mountains are used as political and geographical borders.
5. Mountains help to rain.
Plain
The plane land that is about 200 meters above sea level Plain
is known as the plain. Most of the plain lands are fertile.
Some plains are formed due to erosion by the wind and
rain. Such plains are usually not fertile. Fertile plain
lands are formed by the deposition of organic humus-rich
substances; soil that is carried by rivers. Thus plains are
formed due to the erosion and the deposition of organic
substances. Some fertile plain lands were formed due to
the deposition of materials in lakes. Kathmandu valley
is one of the best examples, because it has this type of plain land.
180 Blooming Science & Environment Book 6
Pene plain is formed due to the erosion of mountains. It is infertile because the
fertile soil is washed away from there. Alluvial plain is formed by the deposition
of alluvial soil brought by river water. It is the most fertile plain. Deltaic plain is
formed at the junction of two or more rivers by the deposition of the sand transported
by the river water. Lake plain is formed by the deposition of materials (sediments)
in lakes.
Valley and Plateau
Valley and plateau are some other geographical structures that are usually found on
the mountains. The flat surfaces found above 200m from the seal level form valleys
and plateaus.
Valley is the flat land surrounded by the hills having sources of water like rivers
and lakes. It is formed by the deposition of fertile soil. Dense population is found in
valleys because it has fertile soil and sources of water. Kathmandu valley (the capital
of our country), Pokhara valley and Dang valley are some examples.
Valley Plateau
Plateau is also found at height but it has table like plain land and has no rivers.
It has infertile land therefore population is not dense here. Plateaus are formed by
the volcanic eruption and by the erosion on mountains. They are also formed by
the forces exerted by the motion of landmasses (as the block mountain is formed).
The roof of the world, Pamir of Tibet, is an example. A plateau may or may not be
surrounded by hills.
Ocean
The huge masses of water that cover the earth are called oceans. The oceans are very
deep. Many kinds of marine animals live in them. Animals that live in water are
called marine animals. We can also see big ships sailing on the oceans.
The water portion of the earth is divided into the following oceans:
1. The Pacific Ocean
2. The Atlantic Ocean
3. The Indian Ocean
Blooming Science & Environment Book 6 181
4. The Arctic Ocean
5. The Antarctic Ocean (also called the Southern Ocean).
The Pacific is the largest and deepest of the oceans.
The Atlantic and Indian oceans are the second and
third largest. The Antarctic is the next followed by
the Arctic Ocean, which is the smallest of all. The
Antarctic and the Arctic oceans are frozen on the
surface for most of the time in year.
Sea
Parts of the oceans, particularly when enclosed by land is called sea. The Arabian sea
and the South China Sea are examples.
There are also huge bodies of water totally enclosed by land on all four sides. These
are also called seas. Examples are the Mediterranean Sea, the Black Sea and the
Caspian Sea.
Which is the biggest animal on the earth?
The biggest animal on the earth is the blue whale. It lives in the sea. The weight of
one blue whale can be as much as the weight of thirty adult elephants.
Rivers
A river begins as a stream of water. It rises from lake
or spring in the high mountains. It is small and narrow
near its source or beginning. As it moves on, it grows
bigger in size. It flows into the sea or big river. Our
country has many rivers. Some of them are very big
and others are small. All of them flow from the north
to the south.
A river passes through three stages. Its first stage is in the mountains and hills. Here,
the rivers flow fast because of steep slopes. So, it erodes (washes away) the riverbed.
At this stage, the river is not very wide but it is deep.
The second stage of a river is in the plains. At this stage, the river widens because of
plain land. It also flows more slowly than in the mountains. Due to the slope of land
wind is bent.
This stage of river is very useful to us. Canals can be built to irrigate the fields. The
river can be used to produce electricity. We can play on the riverbanks. Rivers also
help transportation of people and goods.
The last stage of river is the sea. As the river moves very slowly at this stage it
deposits all the soil (silt) it has carried from mountains and plains. The deposit of silt
is called delta. Because of delta, river branches flow into the sea. These branches are
called tributaries.
182 Blooming Science & Environment Book 6
Lakes
You must have seen a lake. When a large body of
water is surrounded by land it is called a lake. If
you have not seen a lake you can go to Pokhara
and see once, from where you can see beautiful
mountains like Mt. Annapurna, Mt. Dhaulagri and
Mt. Machhapuchhre.
These mountains are covered with snow. You can see the reflection of these
mountains in the Fewa lake. Pokhara is a very popular tourist spot because of its
scenic beauty.
There are some famous lakes in Pokhara such as Fewa, Rupa and Begnas. Mahendra
lake is the biggest lake in Nepal. It is also called Rara Lake. It is in Mugu district
of Karnali zone.
As it moves towards the plains it becomes bigger because many streams join in. It
also forms waterfalls and rapids at this stage.
During the rainy season rainwater flows into the lake filling it water and making it
much bigger in size.
In summer the hot sun often dries up the water. Small lakes into marshes. Bigger
lakes, however, do not lose their water. Lakes in mountains are very beautiful. They
are charming spots for tourist. Some lakes give rise to rivers that flow down to the
plains.
Main Points to Remember
1. About two-third part of the earth is covered with water.
2. There are 5 layers of atmosphere. They are troposhere, stratosphere, mesosphere,
thermosphere and exosphere.
3. Asia, Europe, Africa, North America, South America, Australia and Antarctica
are the seven continents of the earth.
4. Diameter of the earth at the poles is 12,713 km and at the equator is 12,756 km.
5. The earth has plains, valleys, plateaus, mountains, lakes, rivers and oceans.
6. Depth of the oceans ranges from 4,000 m to 11,000 m.
7. Height of land varies from the sea level upto 8,848m.
8. Plain is the flat surface of the earth which is found between sea level and 200m
height.
9. Pene plain, alluvial plain, lake plain and delta plain are the main types of the
plain.
10. The steep earth’s surface found above 200m high from the sea level is the
mountain.
11. The mountains lower in height are called hills.
12. Fold mountain, block mountain and volcanic mountain are the main types of
mountain.
Blooming Science & Environment Book 6 183
13. Mountains are advantageous to us.
14. Valley is a flat surface formed by the deposition at height. It is surrounded by
hills.
15. Plateau is a table like flat surface, which is found at height and has no rivers.
16. Rivers, lakes, oceans and seas are different sources of water on the earth.
PRO J ECTWORK
Make a clay model to show internal structure of the Earth. Colour the various
layers with different colours and show to your teacher.
Exercises
1. Fill in the blanks.
a. ……………………. mountains are formed due to horizontal quakes on
the earth’s surface.
b. …………………….. is formed by the deposition of soil carried by rivers.
c. The diameter of the earth at the poles is ………………… and at the
equator is ………………………….
d. …………………….. part of the earth is covered by water and
………………. part is land.
e. Plainsareformeddueto………………………..and………………………..
f. ………………………. continuously break down to form soil.
g. Plains that are formed due to erosion by wind or rain are not …………………
2. Are the following statements True (T) or False (F)? Write down.
a. Soil from a mountain is more fertile than from a valley.
b. The thickness of the earth’s crust is about 2900 km.
c. All rocks are hard and solid.
d. Due to great pressure, igneous rock is changed into metamorphic rock.
e. Due to vertical quakes, fold mountains are formed.
f. Fertile plain land is formed due to the deposition of organic, humus-rich
substances.
g. There are 5 layers of the earth’s surface.
3. Match the following:
Plateau formed by horizontal force on the crust
Valley mountain of lower height
Hill formed by vertical force on the crust
Fold mountain table-like plain
Block mountain always surrounded by hills
184 Blooming Science & Environment Book 6
4. Answer the following questions:
a. Write 4 sentences about history of the earth.
b. What are the layers of the earth? Name them with thickness.
c. The polar diameter and the equatorial diameter of the earth are different.
Why?
d. What is the depth of the oceans?
g. What type of mountain is the Himalayan range of Nepal?
h. What is atmosphere?
i. What is plain? Mention its major types.
j. What are hills and mountains? List the major types of mountain.
k. What are valleys and plateaus?
l. How is a fold mountain formed? Also draw its figure.
m. How is a block mountain formed?
n. How do volcanic mountains form?
o. How are mountains advantageous to us?
p. Name any five lakes of Nepal.
5. Give reasons:
a. Most of the plains have fertile soil.
b. Population is dense in valleys but not in plateaus.
c. Volcanic mountains have no fertile soil.
6. Write two differences for each:
a. Valley and plateau b. Fold mountain and volcanic mountain
c. Fold mountain and block mountain
7. Define:
a. Plain b. Hills c. Sea d. Lake e. Ocean
Glossary
Erosion : Removal of rock particles from any place.
Deposition : Collection of eroded particles.
Infertile : unable to give good crop yielding.
Alluvial soil : fine black soil having more humus.
Steep : Having vertical slopes.
Extreme : Very strong.
Erupt : Explode
Lava : Magma coming out at the earth’s surface.
Cinder : The dust formed from the sprayed lava.
Volcanic bombs : Big rock masses come out from a volcano.
Accumulation : Collection.
Blooming Science & Environment Book 6 185
18Chapter Weather and Climate
Learning Outcome Estimated Periods: 6+2
On the completion of this unit, students will be able to:
explain weather and its type.
discuss elements of weather and climate.
describe the measuring process on weather factors.
describe about importance of water.
describe and demonstrate water cycle.
Weather
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. Thus, the condition of
the sun, temperature, wind, pressure etc of particular place for short time duration is
called weather.
The atmospheric conditions of a particular place for a particular time is
weather. The weather of a day is different at different time and it is different in
different places even at same time also. The weather varies time to time and place
to place. The waether for a long period of time is climate. Climate is determined by
measuring the average of wheather for long period of time. The average atmospheric
conditions of a particular place over a long period of time is called climate.
Rainy climate
186 Blooming Science & Environment Book 6
Meteorology deals with weather and climatology deals with climate. Nowadays
meteorological services are used by many people like farmers to plan their work and
sailors to protect themselves from typhoon. Similarly, modern air crafts, military
operations, geographical expeditions, even important games and outings are often
taken due to the consideration of meteorological reports. Therefore, fair knowledge
of weather is not only useful but also essential.
Factors of Weather and Climate
The following are the major elements of the weather and climate on the basis of which
climatic data, maps and charts are prepared. The elements that affect of weather and
climate are as follows.
1. Rainfall 2. Pressure 3. Temperature
4. Humidity 5. Wind 6. Cloud
Rainfall
When clouds come in contact with cold air, they cool and changes in
the form of water droplets. The tiny droplets of water combine together
to form larger drops, they cannot suspend in the atmosphere and fall in
the form of rain.
Rainfall is measured with a metallic instrument called rain gauge. It
is made of a copper cylinder with a metal funnel of 5 inch diameter. Rain gauze
It leads into a smaller copper container or a glass bottle. The gauge
should be placed at least one foot above the ground and the instrument should be
sited well away from tall buildings, tall trees and other objects which would shelter
it. The measurement of rainfall is done by removing the funnel and pouring the rain
water into a graduated cylinder of 1/2 inch diameter.
The rain gauge must be examined every day. The daily records of the rainfall will be
added at the end of the month to find the total rainfall of the month. The total rainfall
of each month is again added at the end of the year to find the annual rainfall.
Pressure
Air exerts a pressure on the surface of the earth. It is called
atmospheric pressure. The pressure varies from place to place and
from time to time. Pressure can be measured accurately by using a
barometer.
A mercury barometer is made of a one metre long glass tube. Its one Barometer
end is opened and other is closed. It is adjusted upside down into a
container containing mercury. The glass tube has mercury column,
the height of which varies according to the change in the pressure of air.
At the sea level, the pressure of the air is 76 cm or 760 mm. It is termed as 760 mm
of Hg. The pressure lowers with height. Nowadays, aneroid barometer is also used,
which measures the pressure more accurately. Any liquid is not used in it.
Blooming Science & Environment Book 6 187
Temperature
The degree of hotness or coldness is called temperature. In meteorology, the
temperature of air is measured by using a simple thermometer. A simple thermometer
is made of a glass tube having a bulb of mercury or alcohol at its one end. It has a
scale engraved on it. This instrument is based on the principle that liquid expands
on heating. Degree Celsius/degree Centigrade (ºC) and degree Fahrenheit (ºF) are
common units for measuring temperature.
Thermometer
Maximum-minimum thermometer is used to record the
maximum-minimum temperature of a day. It is made
of a U-shaped glass tube having two bulbs at its two
ends. It is partially filled with mercury and the ends are
filled with alcohol as shown in the figure. The bulb A
is completely filled but the bulb B has a vacuum. Each
limb of the tube is supplied with a steel pointer just above
the mercury level. Scales are made on the limbs.
When the temperature of air increases, the alcohol in
bulb A expands and the mercury is pushed, which lifts
the pointer for the maximum temperature. When the Maximum and minimum
temperature of the air decreases, the alcohol in bulb A thermometer
contracts and the mercury is pulled towards it. Therefore,
the other pointer is lifted for the minimum temperature. Next morning, the pointers
are adjusted again just above the mercury level by using a magnet.
Humidity
Humidity is the measure of moisture content of the
atmosphere. The actual amount of water vapour present
in the unit volume of the air is called absolute humidity.
It is expressed in gram of water vapour per cubic metre.
In meteorology, the relative humidity is used, which is
the ratio of the actual amount of the water vapour in the
air to the total amount of the water the air can hold at a
given temperature. It is expressed in percentage. Warm
air has more humidity than cold air.
The relative humidity is measured by using a Hygrometer
hygrometer. It is also known as dry and wet thermometer.
Hygrometer is a pair of simple thermometers. The bulb of one of them is placed in
water or wicked with water. It is called wet thermometer. The bulb of the other
thermometer is left in air. It is called dry thermometer. The difference of readings
188 Blooming Science & Environment Book 6
between these two thermometers is used to calculate relative humidity. When the
both thermometers show the same readings, it is said that the relative humidity is
100%.
Wind
Air in motion is called wind. It has both speed and direction.
It cannot be seen but experienced only. Sometimes the
wind may take the form of storm.
The direction of the wind is measured by using wind
vanes and the speed is measured by using an anemometer.
Winds are named according to the direction they blow. An Anemometer
east wind is one that blows from east to west and a south
wind is one that blows from south to north. Wind vanes
have fixed indicators for direction and a rotator indicator,
which indicates the direction of the wind.
An anemometer consists of 3 or 4 semicircular cups which
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.
Forecasting of Weather
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
clouds in the sky. Meteorologists use such photographs for the forecasting of the
weather.
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.
Blooming Science & Environment Book 6 189
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. In general, we
observe four different types of weather like hot, cold, rainy and stormy.
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 perform an activity.
Activity Smoke Cool air
Convection Current Hot air
Make a rectangular box with
the two projected holes on the Candle Glass box
upperside as shown in the figure.
The front side is made of glass.
Put a candle or lamp just below Movement of air (Convectional current)
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.
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 Hot air
with the help of a stick and thread so that Cool air
it looks like a balance. See that they are
Hot air molecules move up
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.
190 Blooming Science & Environment Book 6
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.
Land breeze and sea breeze are the results of this phenomena.
Water Cycle
The rotation of water from land surface to the atmosphere and back to land is called
water cycle.
Water cycle in nature is the consequence of change of states of water. The heat of the
sun causes evaporation of water from seas, river, lakes, ponds etc. The water vapours
go up in the atmosphere and form clouds. These clouds move through long distances.
When the cloud cools, it condenses and pours as rain. When it rains, water comes
to the earth’s surface. Rain water fills up the ponds and the lakes on the earth. Some
rainwater goes into the ground. Snow on the Himalayas melts and flows down the
rivers. Some rainwater and streams also join the rivers. The rivers carry the water
to sea. Water which goes into the ground may come out as springs. Again the whole
process of evaporation and condensation continues in nature. This makes the water
cycle possible. The water cycle keeps the balance of water in nature.
Condensation
Precipitation
Evapotranspiration
Evaporation
Blooming Science & Environment Book 6 191
Main Points to Remember
1. Weather constitutes direction of the sun, direction of wind, water vapour in the
air, temperature, etc.
2. The sun, air and water are some of the important elements of the weather.
3. Hot air moves up and the space is occupied by the cool air. Thus setup air
currents are called convectional current.
4. 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.
5. 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.
6. Meteorology is the study of the weather.
7. Weather is determined by sunlight, cloud, rain and many other factors.
8. Movement of air is wind, when it blows faster it is storm.
9. Rain gauze is used to measure rainfall in a day.v
10. Barometer is used to measure atmospheric pressure.
11. Hygrometer is used to measure relative humidity.
12 Anemometer is used to measure speed and direction of wind.
13. Maximum and minimum thermometer is used to measure maximum and
minimum temperature of a day.
14. Weather is forecasted by the help of information collected from the instruments
installed in weather stations.
15. The continuous process of changing surface water into work vapour and water
vapour into rain and surface water is called water cycle.
PRO J ECTWORK
Visit a nearby meteorological station if possible and notedown the records of
various observation shown by different equipments. Draw some equipments used
to measure various weather factors in meteorological station.
Exercises
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 used to measure ........................ and ........................
temperature is called maximum and minimum thermometer.
192 Blooming Science & Environment Book 6
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 these questions.
a. What is weather? Define meteorology?
b. How can you determine that the weather is being changed?
c. Why does air move? Explain with the help of a figure.
d. Give an experiment that shows the movement of air.
e. Give an experiment to show that hot air is lighter.
f. How do the clouds form?
g. How does the rainfall take place?
h. Give an experiment to show the formation of cloud and rain.
i. What is a rain gauze? How do you measure the rainfall in a day?
j. What is meant by humidity? What is the instrument used to measure
humidity?
k. Name the instruments used to determine weather conditions.
l. What is relative humidity?
m. Define land breeze and sea breeze.
3. Write short notes on:
a. Anemometer b. Hygrometer c. Rain Guage
d. Barometer e. Maximum and Minimum thermometer
Glossary
Abundant : Existing in large quantities.
Germs : Small living things that can cause diseases.
Frost : Weather condition in which the temperature drops below 0 ºC.
So that a thin white layer of ice is formed on the ground.
Hydroelectricity : The electricity produced by using the power of water.
Irrigation : The process of supplying water to grow crops.
Degrade : To make something or become worse especially in quality.
Contaminate : To make substance or place no longer pure by adding a
substance that is dangerous.
Blooming Science & Environment Book 6 193
19Chapter The Earth and Space
Learning Outcome Estimated Periods: 5+1
On the completion of this unit, students will be able to:
introduce solar system and list out its members.
compare the sizes and distance of the earth, moon and sun.
describe the conditions and causes of solar and lunar eclipse.
describe the eclipses with the help of diagram.
Astronomy is the study of stars, planets and all the other objects in the space that
make up the universe. The universe is a vast space in which the sun, the stars, the
planets and their satellites, meteors, meteorites and everything else exist.
The Earth and its Motion
The planet on which we live is
the earth. The earth has suitable
environment for living beings. It is
the third planet from the sun and has
a satellite called moon. The earth
moves in two ways. It moves on its
axis called diurnal motion. Its one
complete round on its axis is called
rotation. The duration of one rotation
is about 24 hours. Rotation of the
earth causes day and night. Due to the rotation, the part of the earth which receives
the sun’s light, experiences day. The part of the earth which is not receiving the
sunlight experiences night.
The earth also moves in its orbit, called annual motion. One complete round of the
earth in its orbit is called revolution. The revolution of the earth is responsible for the
change in season and variation of the length of days and nights.
In E1 condition, the northern E1 E2
hemisphere is tilted towards the sun.
In this situation maximum parts of E4 E3
this hemisphere receives the direct
sunlight for longer period. Therefore, Fig: Change in season.
this region has long hot days and short
nights.
IthneEn2oarnthderEn4 conditions, equal part of
and southern hemisphere
194 Blooming Science & Environment Book 6
receive sun’s rays for equal period. Due to it, in these two situations, the earth has
equal duration of days and nights.
hInemEi3spchoenrdeitrieocne,ivtehse northern hemisphere is tilted against the sun. The northern
bent rays of the sun for short period. Therefore, this region has
short cold days and long nights.
Solar System
The sun with other heavenly
bodies such as eight planets,
satellites, asteroids, comets,
meteors, dust particles scattered
between the planets etc. which
revolve around the sun form a
solar system. The sun is a star. It is
the centre of the solar system. The The solar system
planet and all the other members
of the solar system revolve around the sun in closed orbits. The earth is one of the
planets of the solar system.
The Sun Scan for practical experiment
The sun is a star around which the earth and other planets
revolve. It is the largest body in our solar system with a
diameter of about 13,82,400 km. The volume of the sun is
about 12,99,370 times the volume of the earth. Still it is a
medium sized star of average brightness in the Milky way
galaxy. It appears to be larger and bright in the sky because it
is nearer to the earth. It is at a distance of 1.5x107 km from the visit: csp.codes/c6e24
Earth. Light with the velocity of 3x108 m/s takes nearly 8 minutes and 20 seconds to
reach the earth from the sun.
The sun is the mass of hot gases. The sun’s mass makes up 99.8 percent of the
mass of the entire solar system. Its mass is 2x1030 kg, which is about 3,32,946 times
greater than the mass of the earth. The surface temperature of the sun is 5500oC and
the core temperature is about 15,000,000oC.
The Planets
The planets are dark, solid or gaseous bodies that revolve round the sun in closed
elliptical paths called orbits. Planets have no light of their own. Most of them appear
to shine only because they reflect light that they receive from the sun. Since the
planets are much nearer than the stars, they appear to be big and do not twinkle at
night. Planets revolve round the sun from west to east. So the relative positions of
the planets keep changing day by day. There are eight planets including the earth.
These planets in the order of increasing distances from the sun are; Mercury, Venus,
Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Out of eight planets of the solar
Blooming Science & Environment Book 6 195
system, five planets Mercury, Venus, Mars, Jupiter and Saturn can be seen from the
earth without the use of telescope and other can be seen with telescope. Some facts
on different planets :
1. The larger planet Jupiter
2. The smallest planet Mercury
3. Planet nearest to the sun Mercury
4. Planet farthest to the sun Neptune
5. Planet nearest to the earth Venus
6. The brightest planet Venus
7. Planet with maximum number of satellites Jupiter
8. The coldest planet Neptune
9. Heaviest planet Jupiter
10. The blue planet Earth
11. The red planet Mars
12. Earth’s sister planet Venus
All planets possess these similar characters
1. They all revolve round the sun in the same direction moving westward across
the sky as seen from the earth.
2. Each planet rotates also on the axis that looks anti-clockwise from the earth’s
North Pole. On these planets, the sun rises in the east and sets in the west.
3. All are non-luminous.
These are the fundamental similarities and they differ greatly in sizes, orbits,
rotation period, revolution period and of the physical characteristics which is
reflected in table given below.
Planets Distance from Diameter Revolution Rotation No of
the sun (in 106 (km) time earth time satellites
Mercury day/year (moon)
Venus km) 4880 88d 59d 0
Earth 57.6 12104 225d 243d 0
Mars 108 12756 365.25d 24hr 1
Jupiter 150 6720 687d 24hr 37mm 2
Saturn 225.6 1,40,800 9hr 55mm
Uranus 1,20,585 12y 10hr 14mm 62
Neptune 768 51,200 29.5y 17hr 14mm 53
1600 48,000 84y 16hr 27
2870 164y 13
4480
Solar system compare data (Source: IAU, WGPSN)
196 Blooming Science & Environment Book 6
oNlaorteSy:sTtehme CploamneptasrcaltoivseesDt atotat he sun move around(stohueirrceo:rbIAitVs f(aWstGerPtShNan) those
farther away.
Differences between Stars and Planets
Stars Planets
1. Stars have their own light and emit 1. Planets have no light of their own. They
continuously. They twinkle at night. shine on light received from the sun.
They do not twinkle at night.
2. They are big masses of extremely hot 2. They are solid masses made of rocks
gas. They are very far away from the and minerals. They are smaller than
earth. the stars and are nearer to the earth.
3. They revolve around the galactic 3. They revolve around the sun from
center and appear to be moving from west to east.
east to west.
4. They are uncountable. 4. They are eight in number.
The Moon
The moon is the closest heavenly body from the earth. It revolves around the earth.
So it is the natural satellite of the earth. Like planets, the moon has no light of its
own. It is visible to us on account of reflection of light from its surface. Its diameter
is 3476 km. It is about 3,82,400 km away from the earth. It revolves once around the
1
earth in 27 3 days and it take about same duration to complete its one rotation.
Revolution of moon around the earth
Comparative study of the sun, the earth and the moon
1. Moon is the natural satellite of the earth. It has no light of its own. Moon takes
1
27 3 days to revolve around the earth.
2. The diameter of the earth is about 4 times more than that of the moon. The diameter
of the sun is about 110 times more than that of the earth.
Blooming Science & Environment Book 6 197
The following chart shows some facts about the moon, the earth and the sun in
short.
S.N. Name of Mean Mean Temperature Remarks
masses Diameter distance from
(Km) earth (Km)
5500oC at surface Source of
1. Sun 1392000 1.5 x 108 and 15000000oC at energy for the
centre earth
2. Earth 12735 - Average 22oC Planet’s day =
24hr Planet’s
year = 365.25
days
3. Moon 3476 386000 About 130oCat day Satellite’s day
and -120oC at night = 27.33 days
Shadow
The rectilinear propagation of light is responsible for formation of shadow. When an
opaque object is placed in front of sources of light, a shadow is formed.
Shadow differs in shape and size
The shape and size of shadow depends upon where the sources of light and obstacles
are placed.
Types of Shadow
An area of darkness is formed on a surface when an object intercepts the light falling
on the surface from a source. If the source has an appreciable size the shadow has
two distinct regions; one of full-shadow, called the umbral, the other of partial called
penumbra.
The shadow at the middle is darker than the one arround it. The darker region is
umbra. No light rays can reach the umbra region. Around the umbra is the lighter
part of the shadow called as penumbra. Greater is the distance between the opaque
objects and the screen, larger the shadow is formed on the screen.
Umbra and Penumbra
198 Blooming Science & Environment Book 6
Take a blank page of your exercise book as a screen facing towards the pane of
window. Now place a pencil or pen in between the screen and the window in such a
way that it casts shadow. You will get a dark shadow called the umbra and light shadow
around the umbra called penumbra. If penumbra is not clear, increase the distance
between the screen and the pencil. The umbra and penumbra play a vital role for the
eclipse to be occurred.
Usually the umbra causes total eclipse in which the whole heavenly body is obstructed
and penumbra causes partial eclipse in which only a part of the body is obstructed.
Solar Eclipse
When the moon passes directly between the earth and the sun, it obstructs the sun. It
casts a shadow on the earth. From the region of shadow some or total part of the sun is
not seen. It is called solar eclipse.
When an observer is in A i.e. in umbral region of the earth, he/she experiences total
solar eclipse. If the observer is in B or C he/she experiences partial eclipse. Usually
partial solar eclipse occurs frequently and total solar eclipse repeats after 360 years at
any particular place. Total solar eclipse stays maximum for 8 minutes only. Total solar
eclipse is very important for scientists because they can study about corona of the sun
in this condition.
Solar eclipse occurs on new moon. It begins from western part and escapes from the
eastern part of the sun. Solar eclipse stays for short period because during it the moon
and the earth are in opposite motion and area of the moon’s shadow is less.
If the moon lies farthest from the earth in its orbit, the umbra form an opposite cone
and the bright part of the sun is seen as a ring called annular eclipse. It is very rare and
repeats after a thousand of years only.
Lunar Eclipse
When the earth passes directly between the sun and the moon, it obstructs light of the sun.
The earth casts its shadow on the moon and the moon darkens partially or completely. It
is called lunar eclipse.
If the whole moon is in penumbral region, a penumbral eclipse is occurred in which
whole the moon is seen fainter. When it is partially in umbra, partial lunar eclipse is
Blooming Science & Environment Book 6 199
occurred and when completely covered with umbra, total lunar eclipse is occurred. In
given diagram lunar eclipse begins from ‘m1’ condition which is penumbral. In ‘m1’
and ‘m3’ condition partial lunar eclipse occurs and total lunar eclipse is experienced in
‘m2’ condition again. The moon escapes from eclipse after ‘m3’ condition. Total lunar
stays for 1 hour and 40 minutes. During total lunar eclipse, the moon does not darken
completely, it is because the atmosphere of the earth through which the rays of the sun
refract towards the moon and the moon appears coppery red. Annular lunar eclipse never
occurs.
Lunar eclipse occurs on full moon only and it begins from the eastern region of the moon.
The illustration shows that the eastern region of the moon enters first in the shadow of
the earth. (As the moon revolves eastward). Lunar eclipse stays longer than solar eclipse
because in this condition the moon and the earth are moving in the same direction and
the shadow of the earth has more area than that of the moon.
Why do eclipses not occur every full moon and new moon
On every new moon and full moon, eclipse do not occur because of the inclination of the
planes of the moon’s orbit and the earth’s orbit. The inclination is of 5.15o to 5.5o. Due to
it in most of the new moons and full moons the position of moon is found little bit high
or low from the plane of the earth’s orbit.
In this condition shadow of any heavenly mass does not cast on the other. But sometimes
when the planes of the moon’s orbit and the earth’s orbit coincide, shadow of one mass
casts on the other causing eclipse. The sun is eclipsed when the moon comes between
it and the earth. The moon is eclipsed when it passes into the shadow cast by the earth.
200 Blooming Science & Environment Book 6
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