Modern Concept Science and Environment – 8 243
d) Absorption
The epithelial cells lining the small intestine absorb nutrients from the digested food.
e) Excretion
Epithelial tissue in the kidney excretes waste products from the body and reabsorbs
the required materials during urine formation. Sweat is also excreted from the body
through the epithelial cells present in the sweat glands.
f) Diffusion
Epithelium promotes the diffusion of gases, liquids and nutrients. Because they form
the thin lining of the walls of capillaries,lungs, etc.
g) Cleaning
Ciliated epithelium helps to remove dust particles and foreign bodies which have
entered into the air passages like nose.
h) Reduces Friction
The smooth and tightly-interlocking epithelial cells are present in the inner lining of the
blood vessel. They reduce friction between the blood and the walls of the blood vessels.
Types of epithelial tissue
On the basis of specialized shape, size and functions, epithelial tissues are again classified into
different groups. They are:
a) Squamous or pavement epithelium b) Cubical epithelium
c) Columnar epithelium d) Glandular epithelium
e) Stratified epithelium f) Sensory epithelium
a) Squamous or pavement epithelium
The single-layered, thin epithelial tissue which has cells Nucleus
with centrally placed nucleus is called pavement epithelium Cytoplasm
or squamous epithelium. The cells of this tissue appear Cell membrane
thin, flat, polygonal and plate like structure. This tissue
seems like a mosaic floor or pavement. Squamous cells are Squamous epithelium
horizontally flattened. They have elliptical nuclei. These
cells are arranged edge to edge and form thin covering.
Location: Pavement epithelium makes the lining of cavities such as the mouth, blood
vessels, heart, lungs, etc. It is also found on the outer layers of the skin.
Functions: Squamous epitheliums are responsible for protection, covering, diffusion
and to reduce friction.
b) Cuboidal epithelium
The single-layered, epithelial tissue which has Cytoplasm
cubical cells with similar dimensions is called Nucleus
cubical epithelium. Cubical epithelium is formed Basement membrane
from the cells having roughly cuboidal shape.
Each cell of the cubical epithelium has a spherical Cuboidal epithelium
nucleus in its centre. The cells of this tissue are
attached with their lateral surfaces.
244 Cell and Tissue
Location : Cubical epithelium is found in the glands and ducts of glands. They are
also found in the lining of the kidney tubules. Cubical epithelium also constitutes the
germinal epithelium to produce egg cells in the female ovary and the sperm cells in the
male testes.
Function : The main functions of the cubical epithelium are excretion, secretion,
covering, protection and germination of the eggs and sperms.
c) Columnar epithelium
The single-layered, epithelial tissue which has column-shaped Columnar epithelium
elongated cells is called columnar epithelium. There are two types
of columnar epithelium. They are simple columnar epithelium and
ciliated columnar epithelium. Columnar epithelial cells occur in one
or more layers. The nuclei of the columnar epithelium are elongated
and are usually located near the base of the cells.
FACT WITH REASON
Columnar epithelium is also a sensory epithelium. Give reason.
Some columnar cells are specialized for getting stimuli. They have sensory receptors.They are present
in nose, ears, taste buds, tongue, etc. Therefore, columnar epithelium is also a sensory epithelium.
Location : Columnar epithelium forms the lining of the stomach, intestines, salivary
glands, urinogenital glands and their ducts. Some Memory Tips
columnar cells are specialized for sensory reception. The columnar epithelium which
So, they are present in nose, ears, taste buds of the has fine hair-like outgrowths
tongue, etc. Ciliated epithelium is usually found in called cilia on their free surfaces is
the air passages like in nose, uterus, fallopian tubes of called ciliated epithelium.
the females, etc.
Function : The functions of the columnar epithelium are protection, secretion, absorption,
cleaning, excretion, sensation, etc. This tissue secretes mucus which keeps the surface smooth.
d) Glandular epithelium Cilia
The columnar epithelium with goblet cells is called
glandular epithelium. Goblet cells are unicellular Mucus
glands which are found between the columnar
epithelial cells. Often columnar and cuboidal epithelial Goblet cell
cells become specialized for glandular cells.
Location Glandular epithelium is located in various Nucleus
endocrine and exocrine glands.
Glandular epithelium
Function
The main function of the glandular epithelium is to secrete certain substances such as
enzymes, hormones, milk, mucus, sweat, wax, saliva, etc.
Modern Concept Science and Environment – 8 245
FACT WITH REASON
Glandular epithelium is also called secretary epithelium, why?
The main function of the glandular epithelium is to secrete certain substances such as enzymes, hormones,
milk, mucus, sweat, wax, saliva, etc. So, glandular epithelium is also called secretary epithelium.
e) Stratified epithelium or compound epithelium
The epithelium which is composed of several layers of cells to
withstand from wear and tear is called compound or stratified
epithelium. Stratified epithelium is present in the outer and
inner linings of the body which have to withstand wear and
tear. In this tissue, the top cells are flat and scaly which may or
may not be keratinised. The mammalian skin is an example of
dry and keratinized stratified epithelium.
Stratified epithelium
Location : The inner lining of the mouth cavity is an example of
a non-keratinised, stratified epithelium.
Function : The main function of the stratified epithelium is covering and protection.
f) Sensory epithelium
The modified form of columnar epithelium Axons
which consists of elongated cells with sensory
hairs on their free surface is called sensory Cribriform
epithelium. Like glandular epithelium, plate
sensory epithelium is a modified form of
columnar epithelium. It consists of elongated Olfactory
cells with sensory hairs on their free ends. sensory
These cells are specialized to receive the neurons
stimuli form the surrounding. Dendrite
Mucous layer Cilia Basal
cells
Sensory epithelium
Location : Retina of eye, olfactory epithelial tissue of nose, etc. contain sensory
epithelium.
Function : It receives stimulus for its organ.
ACTIVITY 1
1. Go to the a meat shop and take a flap of skin of a hen.
2. Scrap the skin of the hen and keep it on a glass slide.
3. Add a drop of iodine on it.
4. Place the glass slide under the microscope and observe it.
5. What do you see? What type of epithelial cell is it? Give logic to your answer and show it to your teacher.
17.4 Plant Tissue
Tissues that are found in the body of plants are called plant tissue. On the basis of location and
function, plant tissues can be divided into following two types. They are:
a) Meristematic tissue b) Permanent tissue
246 Cell and Tissue
Meristematic tissue
The simple and undifferentiated plant tissue which has actively dividing cells is called
meristematic tissue. Meristematic tissues are found in the growing regions of a plant.
Continuous division of these cells helps in increasing the length and girth of the plant. The
main function of the meristematic tissue is to form a number of new cells.
Features of the meristematic tissue
The cells of meristematic tissues have the following features:
i) The cells of a meristematic tissue are similar in structure withthin cell wall.
ii) The cells of the meristematic tissues may be spherical, oval, polygonal or
rectangular in shape.
iii) The cells of a meristematic tissue are compactly arranged and do not contain any
intercellular space between them.
iv) Each meristematic cell contains dense cytoplasm with a single large nucleus.
v) The meristematic cells contain few vacuoles or no vacuoles at all.
According to the position, meristematic tissues are divided into three types. They are:
i) Apical meristem ii) Lateral meristem
iii) Intercalary meristem Apical
i) Apical meristem meristem
The meristematic tissue which is present at the tip Lateral
of root, stem and branches is called apical meristem. meristem
Apical meristem is also found at the tip of leaves. It
helps in the elongation of the roots, stem, branches Intercalary
and leaves. This is called primary growth. meristem
FACT WITH REASON
Pants with its tip cut do not achieve normal growth in its height, why?
The tip of a plant is consists apical meristem. It is responsible for the axial growth of a plant. So, a plant
does not grow when its apical meristem is cut.
ii) Lateral meristems
The meristematic tissue which is present along the side of the root and stem is called
lateral meristem. It is responsible for increasing the girth of a plant. This is called
secondary growth.
Differences between apical meristem and lateral meristem.
SN Apical meristem SN Lateral meristem
1 These are situated at the growing tip of 1 These are found beneath the bark (cork
the roots and stems. cambium) and in vascular bundles of
dicot roots and stems (cambium).
2 It brings about the elongation of the 2 It increases the diameter and girth of root
root and stem. and stem.
Modern Concept Science and Environment – 8 247
iii) Intercalary meristems
The meristematic tissue which is present at the base of leaf, fruit, internode, etc. is called
intercalary meristem. It is responsible for increasing the length of petiole, internodes, etc.
Note : You will study Permanent tissue in higher classes.
ACTIVITY 2
1. Take a grass and wash with water.
2. Cut its tip and put on a glass slide.
3. Add one drop of saffranine and keep some glycerol over it.
4. Put a cover slide over the glass slide and observe under a microscope.
5. Draw the meristematic cells you observed under the microscope and explain their structure and
arrangement.
17.5 Interrelationship between Cell, Tissue and Organ in Human Body
Cell
Each and every living thing has cells. A unicellular Cells Tissues Organ
organism consists of only one cell whereas multicellular
organisms contain many cells. Cell is the basic structural Muscle
tissue cell
and functional unit of life. They perform many
important functions without which we would not be Nerve cell
able to continue living activities. While breathing, the
cells exchange the deoxygenated air with oxygenated Epithelial
air. The cells produce enzymes that help in the digestion cell
of food. There are no other smaller components than Connective
the cell which perform all those important functions. cell
That is why the cell is the “fundamental unit of life.” Interrelationship between cell, tissue and organ
Tissue
A unicellular organism performs all the living activities such as respiration, digestion,
excretion, reproduction, etc. within a single cell. But in case of multicellular organisms, there
are separate groups of cells which are responsible for various activities. The body of the
multicellular organisms contains several different types of cells, such as blood cells, nerve
cells, muscle cells, etc. The group of large number of specialized cells with a common origin,
similar structure and function is called tissue. Four major types of tissue in human body are
epithelial tissue, connective tissue, muscular tissue and nerve tissue. Organs, for the specific
function of the body are formed through the combination of these tissues.
Organ
Organ is a group tissues working together for a particular function. An organ is a part of the
body which has characteristics function, shape and structure. It is specialized for a particular
physiologic function. For example, the stomach contains epithelial tissue, muscular tissue,
nerve tissue and connective tissue. Stomach has the specific physiologic function for breaking
down of food. Similarly, lung is involved for the exchange of gases, kidneys are involved for
the purification of blood, heart is involved for the blood circulation, etc. All the organs work
accordingly to keep the whole body functioning well.
248 Cell and Tissue
System Respiratory system Circulatory system Digestive system
Heart
Nervous system Nasal passage Blood Stomach
Brain Trachea vessels Liver
Lungs Gall
Spinal bladder
cord Large
intestine
Peripheral Small
nerves intestine
Excretory system Muscular system Skeletal system Integumentary system
Cartilage Hair
Kidneys Skin
Urinary Skeletal Bones
bladder muscles Joints Nails
Tendons
Immune system Endocrine system Epididymis Reproductive system
Thymus Pituitary Testes Mammary
Lymph gland glands
nodes Thyroid Ovaries
Spleen gland Uterus
Pancreas
Lymphatic Adrenal
vessels glands
Testes
Ovaries
A system is a group of specialized organs working together to achieve a major physiological
function. There are eleven systems in human body. All these system combine to form a
complete human body. For example, the mouth, oesophagus, stomach, small intestine, large
intestine, etc. are the organs of the digestive system. The digestive system is an organ system
responsible for breaking down of the foods into nutrients. These nutrients are transported
through the bloodstream. Similarly, heart and blood vessels make circulatory system which
is responsible for the circulation of the blood. Thus, there is a close relationship among cells,
tissues and organs. It can be summarized as:
Modern Concept Science and Environment – 8 249
Cells + Cells Tissue
Tissue + Tissue Organ
Organ + Organ System
The various systems, major organs and their tissues along with their main functions in human
body are summarized in the table below:
S.N Systems Major organs Types of tissues Functions
1. Integumentary Skin, Hair and Stratified To cover and protect the
epithelium body
System Nails
2. Skeletal System Bones and cartilage Connective tissues Production of blood
cells, body support, body
movement, protection for
internal organs, etc.
3. Muscular Various types of Voluntary and Body movement, facial
System muscles and skin involuntary expression, contraction and
muscles, relaxation of the heart, etc.
connective tissues,
cardiac muscles
4. Excretory Kidneys, ureters, Pavement and To excrete waste products
System urinary bladder, cubical epithelium from the body
urethra, skin, liver,
lungs
5. Glandular Different kinds Glandular To produce different kinds
System of endocrine and epithelium of hormones, enzymes, etc.
exocrine glands
6. Nervous Brain, spinal cord, Nerve tissue To receive and conduct the
System nerves, sensory sensory functions.
structures, etc.
7. Respiratory Nose, wind pipe, Pavement and To exchange oxygen and
System trachea, lungs,
bronchi, alveoli, cubical epithelium carbon dioxide
diaphragm, etc.
8. Circulatory Heart, blood, Pavement To transport nutrients
System arteries, veins, epithelium, and oxygen to the cells,
capillaries smooth and transport of wastes away
cardiac muscle, from the cells
connective tissue
9. Digestive Mouth, stomach, Columnar Digestion, absorption and
System intestine, liver, gall epithelium, elimination
bladder, pancreas involuntary
muscle
250 Cell and Tissue
10. Reproductive Ovaries, testes, Cubical epithelium Sexual reproduction
System vagina, penis, etc. and columnar
epithelium
11. Immune and Lymph, lymph Lymphatic tissue To defend the body against
Lymphatic nodes, thymus, infection and cancer,
system spleen, lymphatic supports circulatory
vessels system by returning
fluid from tissues to the
circulatory system
ANSWER WRITING SKILL
1. Where are epithelial tissues found?
Ans: Epithelial tissues are found in the internal and external covering of the body or body organs.
2. Name the largest organ of the human body.
Ans: Liver is the largest organ of the human body.
3. Cell is called the structural and functional unit of life, why?
Ans: Cell is called the structural and functional unit of life because the structure, shape and size of an
organism depends upon the number and organization of cells. Cell is called the functional unit of
life because all the metabolic activities performed by the body are the outcome of cellular activities.
4. Blood is called a tissue, why?
Ans: Blood is called a tissue because it consists of specialized groups of cells having a common origin
which perform a similar function.
5. Write any two differences between simple epithelium and compound epithelium.
Ans: Differences between simple epithelium and compound epithelium are:
S.N. Simple epithelium S.N. Compound epithelium
1 It consists of epithelial cells in a 1 It consists of epithelial cells in more
single layer. than one layer.
2 They are involved in secretion and 2 They are involved in covering and
absorption. protection.
6. Write down any four characteristics of epithelial tissue.
Ans: The characteristics of epithelial tissue are:
i. Epithelial tissue is found in the outer and inner covering of the body or body organs.
ii. The cells of the epithelial tissue are attached to the basement membrane.
iii. Epithelial tissues do not contain blood vessel.
iv. The cells of the epithelial tissue do not have intercellular substances. A
7. Observe the given diagram and answer the following questions. B
i) Name the meristems A, B and C.
Ans: A is apical meristem, B intercalary meristem and C is lateral meristem.
ii) Write down the function of A, B and C. C
Ans: A increases height of the plant, B increases internode and C increases girth of the plant.
Modern Concept Science and Environment – 8 251
iii) What happens if A is cut out?
Ans: If A is cut out, the height of the plant will not increase.
8. What is the relation among cell, tissue, organ and system?
Ans: Cell is the basic unit of life. A group of similar cells working together for a particular function is
called tissue. A group of tissues specialized for a particular function is called organ. Different
organs performing a related function make a system. One system has one specific function. The
group of systems such as respiratory system, digestive system, reproductive system, skeletal
system, muscular system, nervous system, etc. working together make a living body.
STEPS EXERCISE
STEP 1
1. Fill in the blanks with appropriate words.
a) ………………is the fundamental unit of life.
b) Epithelial cells in the sweat gland secretes ……………
c) …………… meristem is found at the apex of stem.
d) The epithelial tissue that secretes hormone is called…………tissue.
e) Plant tissues are divided into ………… tissue and ………… tissues.
2. Write True for the correct and False for the incorrect statements.
a) Tissue is the structural and functional unit of life.
b) The tissue on inside of cheeks is an example of columnar epithelium.
c) The mammalian skin is an example of keratinized epithelium.
d) Lateral meristem is found at the tip of roots and shoot.
e) Meristematic cells help to grow plants.
STEP 2
3. Answer the following questions in one word.
a) Name the device that is used to observe cells.
b) Which cells have cell wall?
c) Where are epithelial tissues found?
d) Which plant tissue has ability of cell division?
e) Name the tissue that is found in apex of plant.
4. Write any two differences between:
a) Cell and tissue
b) Tissue and organ
c) Ciliated epithelium and simple columnar epithelium
d) Meristematic tissue and permanent tissue
252 Cell and Tissue
e) Apical meristem and intercalary meristem
f) Epithelium and meristem
5. Give reasons.
a) Cell is the structural and functional unit of life.
b) Plants with its tip cut do not achieve normal growth in its height.
c) Glandular epitheliums are secretary epithelium.
d) Columnar epitheliums are sensory epithelium.
e) Blood is called a connective tissue.
6. Identify the types of epithelial tissues shown in the given figure.
a) b) c)
STEP 3
7. Answer the following questions.
a) Define cell, tissue and organ.
b) Write down the name of different tissues present in animal body.
c) What are epithelial tissues? Name four different types of epithelial tissues.
d) List out the major functions of the epithelial tissues.
e) Write down the location of the following epithelial tissues.
i) Pavement epithelium ii) Columnar epithelium
iii) Cubical epithelium iv) Stratified epithelium
v) Glandular epithelium vi) Sensory epithelium
f) Write down the function of the following epithelial tissues.
i) Pavement epithelium ii) Columnar epithelium
iii) Cubical epithelium iv) Stratified epithelium
v) Glandular epitheliums vi) Sensory epithelium
g) What is meristematic tissue? Write down the function of meristematic tissue.
h) Explain how cells, tissues, organs and systems are interrelated.
i) Draw the well labeled diagram for the followings:
i) Pavement epithelium ii) Columnar epithelium
iii) Cubical epithelium iv) Glandular epitheliums
v) Sensory epithelium vi) Location of meristematic tissue in plants.
UNIT Estimated teaching periods Theory MPordaecrtnicCaolncept Science and Environment – 8 253
10 2
18
Life Processes
Syllabus issued by CDC Human heart
Introduction to life process
Reproduction and its types
Various methods of asexual reproduction
Sexual reproduction in animals and plants
Blood circulatory system in human body
Blood circulation in human body
Photosynthesis and experiment based on it
LEARNING OBJECTIVES
At the end of this unit, students will be able to:
explain asexual and sexual reproduction that occurs in plants and animals.
introduce blood circulatory system in human body and explain the process of blood circulation.
introduce photosynthesis in plants and the experiments based on it.
Key terms and terminologies of the unit
1. Life processes : Those activities which are carried out by living organisms and essential to continue
life on the earth are called life processes.
2. Reproduction : The biological process in which living organisms produce their own kind by asexual
or sexual method is called reproduction.
3. Asexual reproduction : The type of reproduction which takes place without the fusion of a male gamete and
a female gamete is called asexual reproduction.
4. Fission : Fission is a method of asexual reproduction in which single parent body divides
itself into two or more daughter organisms.
5. Binary fission : The method of asexual reproduction in which a unicellular organism divides into
two daughter organisms is called binary fission.
6. Multiple fission : The method of asexual reproduction in which a unicellular organism divides into
more than two daughter organisms is called multiple fission.
7. Budding : The method of asexual reproduction in which new offspring is reproduced by means
of a small outgrowth or bud is called budding.
8. Fragmentation : Fragmentation is a method of asexual reproduction in which a new organism grows
from the fragmented or broken part of the parent organism.
9. Regeneration : Regeneration is a method of asexual reproduction in which organism regains its
lost parts or new organism is produced from the broken part of the parent organism.
10. Sporulation : Sporulation is a method of asexual reproduction which takes place by means of spores.
254 Life Processes
11. Vegetative propagation : Vegetative propagation is a method of asexual reproduction in which
new plants are produced by means of vegetative parts of the plants like
root, stem or leaf.
12. Sexual reproduction : The method of reproduction in which a male gamete and a female gamete
fuse together to give a new offspring is called sexual reproduction.
13. Gametes : Gametes are the haploid sex cells which are involved in sexual
reproduction.
14. Unisexual organism : Those organisms which have only one kind of sex organ (either male or
female) are called unisexual organisms.
15. Bisexual organisms : Those organisms which have both sex organs (male and female) in the
same body are called bisexual organisms.
16. Fertilization : Fertilization is a process of union of a male gamete and a female gamete to
form a zygote.
17. Internal fertilization : If the fusion of a male gamete and a female gamete takes place inside
the body of female, it is called internal fertilization.
18. External fertilization : If the fusion of a male gamete and a female gamete takes place outside
the body of female, it is called external fertilization.
19. Circulatory system : The organ system in human body which supplies food, oxygen,
hormone, etc. to the different parts of the body and carries away
metabolic wastes to the site of excretion with the help of blood is called
circulatory system.
20. Blood : Blood is a heterogeneous, red-coloured, viscous liquid connective
tissue that is made up of 55% plasma and 45% blood cells.
21. Plasma : Plasma is a yellow coloured semi-transparent liquid present in the blood.
22. Red blood cells (RBCs) : Red blood cells (RBCs) are red coloured, biconcave, enucleated
structures floating freely in the blood.
23. White blood corpuscles (WBCs) : White blood corpuscles (WBCs) are irregular blood cells which have
nucleus and other cell organelles.
24. Platelets : Platelets are non-nucleated, irregular, colourless, round or oval blood
cells found freely suspended in the blood plasma.
25. Blood vessels : The elastic tubes or pipes through which blood flows are called blood vessels.
26. Arteries : Arteries are thick-walled blood vessels that carry blood away from the heart.
27. Veins : Veins are the thin-walled blood vessels that carry deoxygenated blood
towards the heart.
28. Capillaries : Capillaries are hair-like, extremely narrow and thin-walled blood vessels.
29. Pulmonary circulation : The type of circulation in which blood flows from right ventricle to the
lungs and then to the left auricle is called pulmonary circulation.
30. Systemic circulation : The circulation of blood from the left ventricle to the right auricle of the
heart through body tissues (except lungs) is called systemic circulation.
31. Blood pressure : The force by which blood pushes the wall of the arteries when the left
ventricle contracts and relaxes is known as blood pressure.
32. Heart beat : A heart beat is a continuous rhythmic beat throughout the life which is
produced due to complete contraction and relaxation of the heart muscle.
Modern Concept Science and Environment – 8 255
33. Arterial pulse : The repetitive jerk felt at the major arteries of the body due to the pumping action of the
heart is known as the arterial pulse.
34. Photosynthesis : Photosynthesis is a process in which green plants and certain micro-organisms prepare
their own food in presence of chlorophyll by using carbon dioxide and water as raw
materials and sunlight as a sources of energy.
18.1 Introduction
It is very easy to differentiate living beings and non-living beings. This is because living
beings show various living activities such as respiration, nutrition, circulation, movement,
excretion, reproduction, etc. These activities are very essential to survive for a living being.
Plants do not show visible living activities as like that in animals. Therefore, those activities
which are carried out by living organisms and essential to continue life on the earth are called
life processes. Living beings cannot survive in absence of these life processes.
18.2 Reproduction
No organism survives forever because each and every living organism is mortal. All species
come to the nature, remain alive for a limited period of time and then die. But, why is the
population of living organisms increasing day by day? Was the number of organisms in the
present same as in the past? The simple answer of this question is no. Living organisms continue
their generation by producing their own kind. This is called reproduction. Thus, the biological
process in which living organisms produce their own kind by asexual or sexual method is
called reproduction. Most of the living organisms have higher tendency of reproduction. Due
to this reason, they grow in number increasing the population over a short period of time.
FACT WITH REASON
The number of organisms in the past was not same as the present, why?
The number of organisms in the past was not the same as the present because the reproductive
capacity of all organisms is higher in favourable environment condition. As a result, the population is
increasing day by day.
Types of reproduction in organisms
Reproduction in organisms occurs either through their vegetative parts or by involving male
and female gametes. So, on the basis of above fact, reproduction in plants and animals occurs
by two methods. They are:
a) Asexual reproduction
b) Sexual reproduction
Asexual Reproduction
The type of reproduction which takes place without the fusion of a male gamete and a female
gamete is called asexual reproduction. Asexual reproduction involves only one parent and
256 Life Processes
mostly occurs in lower plants and animals. The offspring produced from asexual reproduction
are completely identical to their parents. Organisms that undergo asexual reproduction are
amoeba, hydra, planeria, mushroom, potato, onion, ginger, bryophyllum, spirogyra, rose, etc.
In unicellular organisms, asexual reproduction occurs through the whole body whereas in
multicellular organisms, the parts of the body like stem, roots, leaves, branches, etc. involve
in reproduction.
Methods of asexual reproduction
Some of the major methods of asexual reproduction in plants and animals are given below:
a) Fission Memory Tips
b) Budding The word fission is derived from
c) Sporulation L atin word ‘fissio’ means to split.
d) Fragmentation or Regeneration So, in fission single parent body
e) Vegetative propagation divides into two or more daughter
a) Fission offspring.
In fission single organism divides into two or more.Thus, fission is a method of asexual
reproduction in which single parent body divides itself into two or more daughter
organisms. It occurs in unicellular organisms like amoeba, paramecium, euglena,
plasmodium, bacteria, etc. Depending on the number of resulting offspring, there are
two kinds of fissions. They are binary fission and multiple fission.
FACT WITH REASON
An amoeba never gets old, why?
An amoeba never gets old because it lives for sometimes and then itself divides by fission to form
young amoeba again.
i) Binary fission : The method of asexual reproduction in which a unicellular
organism divides into two daughter organisms is called binary fission. Binary
fission generally occurs in the favourable conditions of food, habitat, temperature,
pH value, etc. Binary fission is common in unicellular plants like bacteria, diatoms,
etc. and animals like amoeba, paramecium, plasmodium, euglena, etc.
Parent cell Nucleus divides Cytoplasm divides
Daughter cells
Binary fission of amoeba
ii) Multiple fission : In this reproduction, the number of offspring produced is more
than two. Thus, the method of asexual reproduction in which a unicellular
Modern Concept Science and Environment – 8 257
organism divides into more than two daughter organisms is called multiple
fission. During multiple fission, the resulting daughter cells are protected by a
thick covering called the cyst. The cyst prevents the immature release of cells into
the harsh environment. Memory Tips
In multiple fission, the parent nucleus divides Plasmodium divides repeatedly
into many fragments. Each fragment is in the blood by means of multiple
surrounded by cytoplasm followed by the fission causing malaria. Similarly
formation of cell membrane to form multiple amoeba divides by multiple fission
cells. When favourable conditions of food, causing dysentery.
habitat, temperature, pH value, etc. return, the
cyst ruptures to release the cells into the environment. In this way many offspring
from the single parent are formed. Examples: amoeba, paramecium, plasmodium,
chlamydomonas, bacteria, etc.
Daughter nuclei
Cyst Daughter
Parent cell plasmodia
Multiple fission
b) Budding Memory Tips
In some organisms like hydra, yeast, etc. a small bud 1. The word budding is derived
like structure appears in the body of parent. This from middle English budde
bud grows in size, collects the cellular materials and means pod of seed.
becomes matured. After the bud becomes matured, 2. Yeast is a unicellular fungi and
it detaches from the parent body to become a new hydra is a multicellular animal
individual. Thus, the method of asexual reproduction which show budding.
in which new offspring is reproduced by means of a
small outgrowth or bud is called budding. During budding, the body of parent and the
offspring are of unequal size. Examples: yeast, hydra, porifera, etc.
Bud grows Bud separates
Bud
Budding of hydra
258 Life Processes
ACTIVITY 1
OBJECTIVE: To show that yeast converts glucose into ethyl alcohol and carbon dioxide.
Take a packet of yeast, a small plastic water bottle, a cup, warm water, some sugar and a small balloon.
Fill the cup with a small amount of warm water and add few spoons of sugar. Stir it to make a solution.
Put water into the plastic bottle. Pour yeast and sugar solution into water bottle. Then, gently swirl the
bottle about a couple of times. Finally, place the mouth of a highly stretchable balloon onto the neck of
the bottle and leave it for about 20 to 30 minutes. You will observe that the balloon starts inflating. Why
does it happen? Which gas is present in the balloon?
The balloon inflates because the yeast present the bottle feeds on sugar and converts sugar into ethyl
alcohol and carbon dioxide. Due to the carbon dioxide gas, the balloon gets inflated.
c) Sporulation
Sporulation is a method of asexual reproduction which takes place by means of spores.
Spores are the asexual microscopic structures. They are capable of germination into
new organism under favourable conditions. The spores are present in the spore sac
called sporangium. Spores sac bursts open on maturity and releases spores to germinate
into new organisms.
sporangium sporangial wall
spores
columella
mycelium
(a) (b)
Sporulation of mucor
FACT WITH REASON
Why are spores asexual structures?
Spores are asexual structures because they are formed from the spore mother cell as a result of mitosis
cell division without the fusion of a male gamete and a female gamete.
ACTIVITY 2
OBJECTIVE : To observe sporulation in mucor.
1. Take a slice of bread and a small plastic container.
2. Sprinkle few drops of water on the bread and keep in the container.
3. Seal the container with the lid and tape it around.
4. After about 3-4 days observe the growth of mucoron the bread.
5. When mucor grows, it produces spores.These spores might be harmful to human beings. They
might cause allergies, cough, skin rashes, respiratory problems, etc. So, do not expose them in air.
Throw the plastic container after doing this activity.
Modern Concept Science and Environment – 8 259
d) Fragmentation or regeneration Memory Tips
Fragmentation and regeneration are similar terms but Sometimes, we happen to cut or
generally fragmentation is used for plants and wound. This cut or wound repairs
regeneration is used for animals. after certain interval of time. So, it
i) Fragmentation : Fragmentation is a method of is a type of regeneration.
asexual reproduction in which a new organism
grows from the fragmented or broken part of
the parent organism. In fragmentation, a
multicellular parent organism breaks down into Fragmentation of spirogyra
two or more pieces. Later on, each piece of the
organism develops into a complete organism.
Spirogyra, marchantia, some mosses, etc.
reproduce by means of fragmentation.
ii) Regeneration : Regeneration is a method of
asexual reproduction in which organism regains
its lost parts or new organism is produced from
the broken part of the parent organism. For
example, when a planarian is cut into pieces,
after few weeks, these cut parts regenerate into
fully living planarian. Other examples of animals
which show regeneration are tapeworm, hydra,
sponge, starfish, earthworm, etc.
FACT WITH REASON Regeneration of Planeria
A planaria does not die on cutting into two halves, why?
A planaria does not die on cutting into two halves because the cells of planeria are capable of
regeneration. Therefore, these two halves grow fully into new planeria.
e) Vegetative propagation
Vegetative propagation is a method of asexual reproduction in which new plants are
produced by means of vegetative parts of the plants like root, stem or leaf. Vegetative
propagation may be natural or artificial. In natural vegetative reproduction, a small bud
grows on the vegetative parts of the plant like root, stem or leaf. On maturity, the bud
detaches form the parent body and develops into a new plant. Similarly, the artificial
method of vegetative propagation involves new techniques like cutting, grafting,
layering, tissue culture, etc. to grow new plants.
FACT WITH REASON
Vegetative propagation cannot be done from all vegetative parts of the plant, why?
Vegetative propagation cannot be done from all vegetative parts of the plant because all parts of plant
cannot produce bud. So, only those parts of plants can do vegetative propagation which is capable of
producing bud.
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i) Vegetative propagation by roots : The method of asexual reproduction in
which new plants are produced by means of roots of plants is called vegetative
propagation by roots. For examples: dahlia, sweet potato, mint, gladiolus, etc.
Vegetative propagation by roots
FACT WITH REASON
The diseased part of the plant should not be used for vegetative propagation, why?
The diseased part of the plant should not be used for vegetative propagation because the offspring
produced through vegetative propagation are identical to their parent. They also carry the parental
characters. If the diseased part of the plant is used in vegetative propagation, the new offspring may
be affected by the same disease.
ii) Vegetative propagation by stem : The method of asexual reproduction in
which new plants are produced by means of stem of plants is called vegetative
propagation by stem. Examples of some plants which grow by means of stem are
given below:
1. Bulb of onion and tulip
2. Corm of ginger and gladiolus
3. Rhizome of sugarcane
4. Tuber of potato
5. Runner of airplane plant
main root scale leaf Node
New plant Intermode
eye Node
scale leaf bud
disc
root
Vegetative propagation by stem
FACT WITH REASON
Planting the sugarcane by cutting the stem is an asexual reproduction, why?
As no male and female gametes are involved during the cutting process, the planting the sugarcane by
cutting the stem is an asexual reproduction.
Modern Concept Science and Environment – 8 261
ACTIVITY 3
OBJECTIVE : To observe vegetative propagation in sugarcane stem.
1. Take a mature sugarcane stem containing buds in the nodes.
2. Cut the stem into pieces in the way that each piece should have node.
3. Plant these pieces of sugarcane in the soil and supply water for about 12-15 days.
4. After about 12-15 days, the sugarcane nodes germinate into new sugarcane plants.
c) Vegetative propagation by leaf : The method of asexual reproduction in which
new plants are produced by means of leaf of the plants is called vegetative
propagation by leaf. Examples: begonia, bryophyllum, etc.
New plantlets
New plantlet
Leaf of Bryophyllum Leaf of Begonia
Vegetative propagation by leaf
Significance of asexual reproduction or vegetative propagation
i) Asexual reproduction needs only one parent.
ii) It is useful to transfer the good qualities of plants.
iii) It is very effective for the plants which do not produce viable seeds.
iv) It is easier, cheaper and faster method of reproduction.
v) Plants obtained from vegetative propagation produce flower, fruits and seeds early
than those produced form seeds.
FACT WITH REASON
Vegetative propagation is beneficial for farmers. Give reason.
Vegetative propagation is beneficial for farmers because vegetative propagation produces flowers,
fruits and seeds sooner than those from sexual reproduction. Vegetative propagation is very effective
for the plants which do not produce viable seeds. Vegetative propagation is easier, cheaper and faster
method of reproduction.
Sexual reproduction
The method of reproduction in which a male gamete and a female gamete fuse together to
give a new offspring is called sexual reproduction. Sexual reproduction is a complex process.
It needs both male and female parents. Generally, higher animals and plants involve sexual
reproduction. In the life cycle of these higher animals and plants, the diploid phase (2n) is
very long and represent by the main body. Similarly, the haploid phase (n) is very short and
represents by the gametes.
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Gametes Memory Tips
Gametes are the haploid sex cells which are involved in Sperm is called a male gamete
sexual reproduction. The male gamete is called sperm and ovum or egg is called a female
for animals and pollen grain for plants. Similarly, the gamete. Male gametes are motile
female gamete is called egg or ovum for both plants and more in number but female
and animals. gametes are non-motile and very
less in number.
Differences between male gamete and female gamete
S.N. Male gamate S.N. Female gamate
1 The haploid male sex cell is called male 1 The haploid female sex cell is called
gamete. It is also called sperm (for female gamete. It is also called egg or
animals) and pollen grain (for plant). ovum for both plants and animals.
2 It is produced form the testes in 2 It is produced form the ovary in
animals and from anther in plants. animals and from anther in plants.
3 Male gametes are smaller in size, more 3 Female gametes are bigger in size,
in number and motile in nature. very less in number and non-motile
in nature.
Sperms (male gametes) Eggs (female gametes)
Gametes
Unisexual and bisexual organisms
Most of the organisms have male and female sex organs in Memory Tips
the separate bodies. They are called unisexual or dioecious Pumpkin, papaya, etc. are
organisms. Examples: humans, birds, reptiles, etc. Thus, unisexual plants. Similarly,
those organisms which have only one kind of sex organ mustard, pea, mango, etc. are
(either male or female) are called unisexual organism. bisexual plants.
Similarly, some organisms have both male and female sex
organs in the same body. They are called bisexual, monoecious or hermaphrodite organisms.
Examples: earthworm, tapeworm, starfish, leech, etc. Thus, those organisms which have both
sex organs (male and female) in the same body are called bisexual organisms.
Sexual reproduction in flowering plants
In flowering plants, the flower is a main reproductive organ. It is a colourful and the most
attractive part of the plant. A complete flower has four whorls. They are calyx, corolla,
androecium and gynoecium. Androecium is a male reproductive part whereas gynoecium is
a female reproductive part.
When flower becomes mature, androecium releases pollen grains form its anther. These
pollen grains reach to the stigma of the flower by various agents called pollination. After
pollination, the male gamete reaches to the ovary to fuse with ovum. It is called fertilization.
Modern Concept Science and Environment – 8 263
Thus, fertilization is a process of union of a male gamete and a female gamete to form a
zygote. The male and female gametes are haploid (n), so the zygote formed after their fusion
is diploid (2n) in nature. After fertilization, the ovary turns into fruit and the fertilized ovule
becomes a seed. The diploid zygote divides mitotically and develops into a baby plant called
an embryo. After getting favourable conditions like heat, light, water, etc. the seed germinates
into a new plant. In this way, sexual reproduction in a flowering plant takes place.
anther stigma pistil
filament style
ovary
petal
receptacle
sepal pedicel
Structure of flower
Sexual reproduction in animals Memory Tips
Sexual reproduction is an effective method of reproduction Formation of sperms is called
in most of the multicellular animals and in some unicellular spermatogenesis and formation
animals. It is the most common method of reproduction in of eggs is called oogenesis. The
vertebrates and also found in lower invertebrates. In this spermatogenesis and oogenesis
type of reproduction, the fusion of a male gamete (sperm) together called gametogenesis.
with a female gamete (ovum) takes place inside Haploid sperm
or outside of the female body. In male, the testes
produce sperms and in female, the ovaries produce
eggs. Sperms are formed from the sperm mother cell
through a process called spermatogenesis. Similarly,
the eggs are formed from the egg mother cell through
a process called oogenesis. Haploid egg Diploid zygote
During sexual reproduction, the haploid sperm
and the haploid egg fuse together to form a diploid Gamete and zygote
zygote called fertilization. The diploid zygote divides
mitotically and forms an embryo. The embryo finally develops into a young animal.
Internal fertilization and external fertilization
On the basis of location, fertilization is of two types. They are internal fertilization and external
fertilization.
a) Internal fertilization
In internal fertilization, the male releases his sperms into the body of the female. If
fusion of a male gamete and a female gamete takes place inside the body of female, it is
called internal fertilization. Internal fertilization is common in mammals, aves, reptiles,
insects, etc.
264 Life Processes
b) External fertilization
In external fertilization, male and female release their gametes out in open environment.
If fusion of a male gamete and a female gamete takes place outside the body of female,
it is called external fertilization. It is common in pisces and amphibian. External
fertilization usually takes place in water. The female lays hundreds of eggs in water
and male secretes millions of sperms over the eggs. Thus, the fusion of sperms and eggs
takes place in water. Likewise, the eggs too hatch outside.
FACT WITH REASON
In a pond, a female frog lays hundreds of eggs at a time but the numbers of survival frogs are very less. Why?
The eggs of frogs are not covered with the shell as in birds. So, they are very delicate. They dry due to
sunlight and also eaten by others. It makes very difficult to survive. Therefore, In a pond, a female frog
lays hundreds of eggs at a time but the numbers of survival frogs are very less.
Significance of sexual reproduction
i) Sexual reproduction helps to give continuity to the generation.
ii) It brings out genetic variation and leads to evolution.
iii) Sexual reproduction produces disease resistance offspring.
iv) The offspring obtained from sexual reproduction have more adaptability.
Differences between asexual and sexual reproduction.
S.N. Asexual reproduction S.N. Sexual reproduction
1 Asexual reproduction takes place 1 Sexual reproduction takes place due
without the fusion of a male gamete to the fusion of a male gamete and a
and a female gamete. female gamete.
2 In asexual reproduction, only one 2 In sexual reproduction, both male
parent is involved. and female parents are involved.
3 It is most common in primitive 3 It is most common in developed
animals and plants. animals and plants.
FACT WITH REASON
Why is zygote a diploid structure?
Zygote is formed by the union of a haploid male gamete and a haploid female gamete. Combination of
a male and female gametes finally gives to a diploid zygote.
Fertilization is only possible in sexual reproduction, why?
The fusion of a male gamete and a female gamete takes place only in sexual reproduction. The gametes
are not produced in asexual method.
Planting of sugarcane by cutting the stem is an asexual reproduction, why?
As no male and female gametes are involved during the cutting process, the planting of sugarcane by
cutting the stem is an asexual reproduction.
Modern Concept Science and Environment – 8 265
18.3 Human Blood Circulatory System
The organ system in human body which supplies food, oxygen, hormone, etc. to the different
parts of the body and carries away metabolic wastes to the site of excretion with the help
of blood is called circulatory system. The blood circulatory system is also responsible for
maintaining constant body temperature, chemical composition, pH value, etc.
The blood circulatory system consists of three main parts. They are blood, blood vessel and
heart. The heart is a main pumping organ of the blood circulatory system. The arteries, veins
and capillaries are the pathway through which the blood flows. Similarly, the blood is a main
medium to circulate various materials throughout the body.
Functions of the circulatory system
i) Blood circulatory system transports oxygen, nutrients, hormones, medicines, etc. to the
various parts of the body.
ii) It carries away different kinds of metabolic wastes to the site of excretion.
iii) It regulates the constant body temperature.
iv) It balances chemical composition, pH value, water, minerals, etc. in the body.
18.4 Blood
Blood is a red-coloured viscous liquid connective tissue that is made up of 55% plasma and
45% blood cells. It continuously circulates throughout the body and never stops. The colour
of blood is blackish red, scarlet (dark reddish orange) or blue depending upon its type. In
an adult, the total volume of blood is about 5.5 litres in average. The total volume of blood
depends upon the water content in it. Blood is slightly heavier than pure water. Its specific
gravity or relative density is 1.05 to 1.06. It is slightly alkaline in nature with pH value 7.3 to 7.6.
Composition of blood
Blood is a heterogeneous fluid. It is composed of two main components. They are 55% Blood
plasma and 45% blood corpuscles. Blood corpuscles are of three types. They are red blood
corpuscles (RBC), white blood corpuscles (WBC), platelets.
Blood
RBC
Plasma Blood Platelets
corpuscles WBC
Plasma
Red blood White blood Platelets Composition of blood
corpuscles corpuscles
266 Life Processes
Blood plasma
Plasma is a yellow coloured semi-transparent liquid present in the blood. It forms about 55%
of the total volume of blood. It contains about 90% water, 8% proteins and 2% respiratory
gases, nutrients, hormones, minerals, salts, carbohydrates, antibodies and other chemicals.
Without blood corpuscles, plasma looks yellow coloured.
Function of Plasma
There are many functions of plasma. Some of the major functions are listed below.
i) Plasma transports, digested food, minerals, hormones, antibiotics, water, etc. to
different parts of the body.
ii) It transports waste products to the site of excretion.
iii) It maintains constant body temperature.
iv) It maintains water, chemical composition and pH value of the blood.
v) It contains fibrinogen which plays an important role in blood clotting.
Blood corpuscles or cells
Blood corpuscles occupy about 45% of the total volume of the blood.
There are three kinds of blood corpuscles in the blood. They are red
blood cells, white blood cells and platelets.
a) Red Blood cell (RBC) or Erythrocytes
Red blood cells (RBCs) are red coloured, biconcave, enucleated
structures floating freely in the blood. They carry a red pigment
at their centre called haemoglobin. The matured RBCs do not
have a nucleus except in camels. The whole blood Memory Tips
appears coloured because there are millions of RBCs
that contain a red pigment called haemoglobin. 1. The haemoglobin that
A single haemoglobin molecule is made up of 4% carries oxygen is known as
haemin (iron) and 96% globin (protein). The function oxyhaemoglobin.
of RBC is to transport oxygen to all parts of the body 2. The haemoglobin that carries
and to collect carbon dioxide to excrete out into the carbon dioxide is called
lungs. There are 50 lakhs to 55 lakhs RBCs in 1 mm3 deoxyhemoglobin.
of blood. In every second, about 20 lakhs RBCs are 3. Carboxyhemoglobin is the
formed and the same number is destroyed. When haemoglobin that carries
RBCs die, their iron content present in haemoglobin carbon-monoxide (CO). CO is a
is reused by the liver to make a chemical called poisonous gas. If CO binds with
bilirubin. RBCs are formed in the bone marrow of the haemoglobin, one suffers from
bones such as vertebrae, ribs, skull, ribs, etc. and die a condition known as carbon
in the liver and spleen. In an adult man the number monoxide poisoning.
of RBCs ranges from 50 lakhs to 55 lakhs and in an
adult woman it ranges from 45 lakhs to 50 lakhs in 4. Anaemia is a condition which is
per cubic millimetre blood. Their average life span is caused due to the lack of RBCs
about 120 days. or haemoglobin in the blood.
Modern Concept Science and Environment – 8 267
Function of RBCs
The main functions of red blood cells (RBCs) are:
i) Transport of oxygen: RBCs are oxygen carriers from lungs to tissues. The
haemoglobin in the RBCs in lungs binds oxygen to form oxyhaemoglobin. Within
the lungs the blood gets oxygenated.
ii) Transport of carbon dioxide: RBCs carry carbon dioxide from tissues to lungs. In
tissues, oxyhaemoglobin in the RBCs releases oxygen and changes into
deoxyhaemoglobin. Within the tissues the blood gets deoxygenated. When carbon
dioxide produced from respiration in cells of different tissues binds to haemoglobin,
carbaminohaemoglobin is formed. Memory Tips
b) White blood cells (WBC) or Leucocyte 1. Leukaemia, or blood cancer is
White blood corpuscles (WBCs) are irregular blood a condition in which a person
cells which have nucleus and other cell organelles. has excess number of WBCs in
They show amoeboid movement (a crawling type of their body.
movement got by pushing out cell cytoplasm in the 2. Leukopenia is a condition in
form of pseudopodia) in the blood plasma. They do not which a person has reduced
contain haemoglobin. Leucocytes are produced by the number of WBCs in their body.
stem cells in the red bone marrow and lymph nodes. 3. WBCs have irregular shaped
Similarly, they are destroyed in the liver, spleen and at nucleus.
a site of infection. There are about 6000-10000 WBCs in 4. The collection of dead WBCs,
1 mm3 of blood. Their life span is about two weeks or tissues, cells or other chemicals
15 days. In fact, the life span of WBC is not fixed as they inside the tissues or skin is
may die anytime while fighting with the pathogens. called pus.
Neutrophil Eosinophil Basophil Lymphocyte Monocyte
Various types of leucocytes (WBCs)
Function of WBCs
The main function of WBCs is to kill microorganism present in the blood. They also
engulf the foreign particles and digest them. Sometimes, WBCs cannot digest bacteria
or virus or foreign particles. Due to which they explode and die. If significant numbers
of WBCs are died, we suffer from different diseases.
c) Platelets or Thrombocytes
Platelets are non-nucleated, irregular, colourless,
round or oval blood cells found freely suspended
in the blood plasma. They are non-nucleated and
irregular structures. In 1 mm3 of blood, there are
about 2 to 4 lakh of platelets. Their life span is 2
to 3 days. They are produce in bone marrow and
destroyed in spleen.
Plateletes
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Memory Tips
1. WBCs are the largest blood cells with nucleus whereas platelets are the smallest without nucleus.
2. Thrombocytopenia is a condition in which a person has less number of thrombocytes, or platelets,
in the blood.
3. Haemophilia is a genetic disorder that impairs the body’s ability to make blood clots. If a person is
suffering from haemophilia, bleeding occurs from the cuts and wounds for longer time.
Function of platelets
The main function of platelets is to stop bleeding by clumping and clotting blood vessel
injuries. So, they prevent the loss of blood.
ACTIVITY 1
OBJECTIVE : To observe blood clotting and blood film under the microscope.
1. Wash your hands with soap and water.
2. Take a clean and sterilized lancet and prick your finger to extract few drops of blood.
3. Keep few drops of blood in a petri dish and observe the time taken for the blood clotting.
4. Similarly, keep few drops of blood in a slide, spread it using another slide uniformly and
leave it to dry.
5. Add some Leishman stain on the blood sample. Then, observe the blood cells under a
compound microscope.
FACT WITH REASON
Why is blood red in colour?
Blood is red coloured due to the presence of red pigment called haemoglobin.
Blood without RBCs has light yellow colour, why?
In absence of RBCs, blood has only WBCs, platelets and blood plasma. The blood plasma comprises
about 55% of the total blood. It is transparent yellow liquid. Therefore, blood without WBCs has light
yellow colour.
WBCs are called the soldiers of our body, why?
WBCs defend the body from disease causing agents. They kill or control the pathogens or foreign
matterials. Therefore, WBCs are called the soldiers of our body.
A person suffering from anaemia feels tired on walking a short distance, why?
The circulatory system of the anaemia person cannot transport sufficient amount of oxygen to his/
her muscles due to the lack of red blood cells or haemoglobin. As a result muscle cells cannot release
sufficient amount of energy for continuous walking. Hence, a person suffering from anaemia feels
tired on walking a short distance.
Functions of Blood
The basic function of the blood is to transport gases (oxygen and carbon dioxide), nutrients
and waste materials to the desired locations. But, the blood also performs variety of other
functions which are mentioned below:
Modern Concept Science and Environment – 8 269
a) Transportation
Blood transports essential materials like water, nutrients, hormones and oxygen to the
tissues. It also transports waste substances like urea, carbon dioxide, etc. to the site of
excretion.
b) Protection
Blood fights against germs and toxic materials. As a result, it protects body from various
diseases.
c) Regulation
Blood maintains body temperature. It regulates amount ot water in the body. It regulates
different chemicals like salt, sodium, potassium, calcium, acidity, alkalinity, etc.
18.5 Heart
The heart is the centre of the circulatory system. It is conical shaped hollow muscular organ.
The size of the heart is approximately the size of the fist of owner. It measures about 12 cm in
length and 9 cm in breadth. The average weight of the heart is about 300 grams in adult. The
detailed structure of the heart can be studied in two headings. They are:
External morphology of heart
The heart is a three-dimensional Superior vena cava Aorta
conical shaped muscular organ.
Its morphology can be best Pulmonary veins Pulmonary artery
studied by having either a model Pulmonary veins
or an actual heart from a dead
animal. It is a pumping organ of Left auricle
the body that makes the blood
flow through the arteries. It is Right auricle
located between two lungs, in Right ventricle Left ventricle
the centre of the chest. The two-
third part of the heart is located
towards the left. It is covered by a Inferior vena cava Pericardium
double layered membrane called
pericardium. Thus, the double
layered membranous structure External structure of heart
that covers the heart is called the pericardium. The two layers of the pericardium are close to
each other forming a gap called pericardial cavity. The pericardial cavity contains a fluid in it.
Thus, the lubricating fluid present in the pericardial cavity is called thepericardial fluid. The
pericardial fluid makes the heart beat smooth and also prevents the heart from the mechanical
shock. The heart has hair-like blood vessels seen externally. These blood vessels are called
coronary blood vessels. They carry blood towards and away from its own tissues. Coronary
blood vessels are of two types. They are coronary artery and coronary vein. Coronary arteries
carry oxygenated blood to the heart tissues and coronary veins collect deoxygenated blood to
the heart.
270 Life Processes
Internal morphology or anatomy of the heart
The heart is a four chambered Superior vena cava
organ. The upper two chambers Aorta
are called auricles and the Pulmonary artery Pulmonary artery
lower two chambers are called Pulmonary veins
ventricles. Inside the normal Left auricle
heart, the blood flows only Right auricle Pulmonary valve
from top to bottom but not Pulmonary veins
from bottom to top. The auricles Aortic valve
Bicuspid/mitral valve
Left ventricle
pump the blood to the ventricles. Tricuspid valve Septum
Ventricles are more muscular Right ventricle Cardiac muscle
than auricles because they have Inferior vena cava
to pump blood to the lungs and
other parts of the body at high Internal structure of heart
pressure. But, auricles have to pump blood only to the ventricles. Similarly, the left ventricle is
more muscular than the right ventricle because the left ventricle has to pump blood to all parts
of the body at longer distance while the right ventricle has to pump the blood to the lungs
at shorter distance. The two auricles are separated from each other by a septum called inter-
auricular septum. Similarly, the two ventricles are separated from each other by a septum
called inter-ventricular septum.
Differences between auricles and ventricles.
S.N. Auricles S.N. Ventricles
1 Auricles are the upper two chambers 1 Ventricles are the lower two chambers
of the heart. of the heart.
2 They are relatively thin walled. 2 They are relatively thick walled.
3 Auricles receive blood from inferior 3 Ventricles receive blood from the
venacava, superior venacava, coronary auricles.
sinus and pulmonary veins.
4 Auricles open into ventricles. 4 Ventricles open into arteries.
5 Auricle pump blood to the ventricles. 5 Ventricles pump blood to the lungs
and all parts of the body.
Valves in the heart
For one-way flow of the blood, there are four valves present inside the heart. The short
description of these valves is given below:
a) Tricuspid valve: The valve between the right auricle and right ventricle is called
tricuspid valve (tricuspid means three flaps).
b) Bicuspid valve or mitral valve: The valve present between left auricle and the left
ventricle is called bicuspid valve.
Modern Concept Science and Environment – 8 271
c) Pulmonary valve: The valve present between
pulmonary artery and right ventricle is known Tricuspic valve Posterior Bicuspic
as pulmonary valve. valve
d) Aortic valve : The valve present between aorta
and the left ventricle is known as the aortic Right Left
valve. side of side of
heart heart
In a normal healthy person, the flow of blood in the Aortic valve Pulmonary
heart is always unidirectional. It flows from right Anterior valve
auricle → right ventricle → pulmonary arteries →
lungs → pulmonary veins left auricle → left ventricle Valves of heart
→ aorta → body parts. The blood circulation is maintained by the pumping action of the heart.
FACT WITH REASON
Fluid is filled in the space between pericardial membranes, why?
Fluid is filled in the space between pericardial membranes because it makes the heart beat smoot, decreases
friction between the moving parts of the heart and protects the heart from the mechanical shock.
Valves are present between auricle and ventricles. Give reason.
To allow the unidirectional blood flow from auricles to the ventricles and to prevent the back flow of
the blood valves are present between auricles and ventricles.
Right auricle is larger than the left auricle. Give reason.
The right auricle has to collect large volume of deoxygenated blood from all parts of the body but
left auricle has to collect comparatively less volume of the oxygenated blood from the lungs. So, right
auricle is larger than the left auricle.
Pulmonary vein does not have valves, why?
Pulmonary vein transports oxygenated blood from the lungs to the heart. Presence of valves in them
might cause some amount of blood to remain stagnant in the lungs which might be fatal. So, pulmonary
vein does not have valves.
18.6 Blood Vessels
The elastic tubes and pipes through which blood flows are called blood vessels. Blood vessels
vary in shape, size, diameter and functions. Some blood vessels carry oxygenated blood while
others carry deoxygenated blood. On the basis of structure and function, there are three types
of blood vessels. They are:
a) Arteries Tunica interna
Tunica media
Arteries are thick-walled blood vessels that carry
blood away from the heart. They start from the left Tunica externa
ventricle of the heart as aorta and then branch out.
They carry oxygenated blood (except pulmonary Artery
artery which arises from right ventricle and carries
deoxygenated blood). They have thick wall to
overcome high pressure. Arteries are usually deep
272 Life Processes
seated in the body. It is because loss of blood from the arteries is very dangerous during
cuts and wounds as blood oozes out at high pressure and clotting becomes difficult.
FACT WITH REASON
Why are arteries thick walled?
Arteries are thick walled to overcome the high pressure and high speed of the oxygenated blood which
is directly pumped by the heart.
Why do arteries have narrower lumen?
Arteries have narrower lumen to increase the blood pressure. This sufficient blood pressure helps to
transport blood to the different parts of the body.
Pulmonary artery carries deoxygenated blood but is still called an artery, why?
Pulmonary artery carries deoxygenated blood but is still called an artery because artery is a blood
vessel that carries blood away from the heart. Pulmonary artery also carries the blood away from the
heart to the lungs. Therefore, it is still called an artery even it carries deoxygenated blood.
Why do arteries have no valves?
Arteries have no valves because valves prevent the backflow of the blood but there is no chance of
back flow of blood in arteries as heart directly pumps the blood into the arteries at higher pressure.
Blood loss from the arteries is dangerous. Give reason.
Blood loss from the arteries is dangerous because:
i) Arteries carry oxygenated blood and loss of oxygenated blood causes death of cells in the vital
organs.
ii) It is difficult for an artery to form blood clots after it is punctured.
Why is the arterial blood not drawn during normal blood donation?
Arterial blood is not drawn during blood donations because:
i) Loss of arterial blood directly hampers the amount of oxygenated blood supply to the vital organs.
ii) The deoxygenated blood transfused to the recipient is easily oxygenated by the lungs.
b) Veins
Veins are the thin-walled blood vessels that carry Tunica interna
deoxygenatedblood towards the heart (except
pulmonary vein which carries oxygenated Tunica media
blood from lungs to the left auricle). Veins start Tunica externa
from the different parts of the body as venules. Valve
These venules are formed by the union of many
capillaries. All the veins of the body finally unite
to form either superior venacava or inferior
venacava. These large veins (venacava) pour Vein
blood into the right auricle. Veins have semi-
lunar valves in them that allow one-way flow of blood. In veins, blood flows against
gravity at low pressure. So, the valves at regular intervals prevent the back flow of the
blood. Veins are superficial in position. They have a wider lumen than arteries through
which deoxygenated blood flows easily at low speed and under low pressure.
Modern Concept Science and Environment – 8 273
FACT WITH REASON
Why are veins thin walled?
In veins, blood flows at low speed and under low pressure. Due to which extra thickness in the wall of
the veins is not necessary.
Veins have wider lumen, why?
Veins have wider lumen to flow the large volume of the deoxygenated blood at low speed and under
low pressure.
Why do veins have valves at regular intervals?
In veins, deoxygenated blood flows at low speed and under low pressure. From the lower parts of the
body blood also flows against the gravity. In these conditions, there may have chance of back flow of the
blood. Hence, to prevent the backflow of the blood, veins are provided with valves at regular intervals.
Capillaries
Capillaries are hair-like, extremely narrow and thin-walled blood vessels. They are present
everywhere in the body. Half of the capillaries transport oxygenated blood to the body while
other half collects deoxygenated blood from there. They are the connection between arterioles
and venules. They are microscopic with one cell layer thick. They are the actual site of exchange
of nutrients, toxic waste and gases (O2 and CO2).
Arteriole Venule
Artery
Tunica interna Capillary network
Structure of a capillary Capillaries and their network
Capillaries
Differences between arteries and veins.
S.N. Arteries S.N. Veins
1 Arteries carry blood away from the 1 Veins carry blood towards the heart
heart to the tissues. from the tissues.
2 The blood in arteries flows at high 2 The blood in veins flows at low speed
pressure and under high speed. and under low pressure.
3 They have thick and strong wall. 3 They have thin and weak wall.
4 They do not have valves (except in 4 They have valves (except in superior
aorta). venacava, inferior venacava and
pulmonary vein).
274 Life Processes
5 They usually carry oxygenated blood 5 They usually carry deoxygenated blood
except pulmonary artery. except pulmonary vein.
6 They are located deep in the tissues. 6 They are located superficially in the tissues.
7 They have narrow lumen. 7 They have wider lumen.
FACT WITH REASON
Why are capillaries extremely thin-walled?
Capillaries are extremely thin-walled because the thin wall allows the capillaries to exchange oxygen,
carbon dioxide, nutrients, toxic waste, etc. in the cellular level.
18.7 Blood Circulaltion
The heart of the vertebrates (except Pisces) follows the double circulation because the blood
flows through the heart twice to flow the oxygenated blood once in the body. The double
circulation of the blood occurs through two ways.
Blood circulation in human body
a) Pulmonary circulation Memory Tips
The type of circulation in which blood flows from right Blood circulation in human is
ventricle to the lungs and then to the left auricle is called called double circulation because
pulmonary circulation. Pulmonary circulation starts from the blood is transported to the heart
the right ventricle and pumps deoxygenated blood to the twice: once from all parts of the
lungs through the pulmonary artery. In the lungs, the
blood becomes oxygenated by exchanging carbon dioxide body and second from the lungs.
Modern Concept Science and Environment – 8 275
with oxygen. This process is called blood purification. After oxygenation, the lungs transport
oxygenated blood through the pulmonary veins back to the left auricle.
Right ventricle Pulmonary artery
Lungs
Left auricle Pulmonary veins
b) Systemic circulation Pulmonary circulation
The circulation of blood from the left ventricle to the right auricle of the heart through body
tissues (except lungs) is called systemic circulation. Systemic circulation starts from the left
ventricle. When left ventricle contracts, the oxygenated blood passes to the aorta, arteries,
arterioles and finally to the capillaries. In the tissues, the capillaries exchange nutrition, oxygen,
hormones,with metabolic wastes of the tissues like carbon dioxide, toxic materials, etc. Now,
the blood becomes impure. This impure blood passes to the venules, veins, venacavae and
finally to the right auricle of the heart. This is a complete systemic circulation.
Left ventricle Aorta Arteries
Right auricle Arterioles
Vena cavae Capillaries
Veins Venules Capillaries Tissues and cells
Systemic circulation
18.7 Blood Pressure (BP)
The force by which blood pushes the wall of the arteries when the left ventricle contracts and
relaxes is known as blood pressure. This pressure is measured in the mercury column. The
blood pressure of a person changes with the factors like age, sex, time of the day, stress, exercise,
work, emotions, disease, fear, etc. Blood pressure is measured by a sphygmomanometer.
18.8 Heart Beat Healthy heart beat representation
A heart beat is a continuous rhythmic beat throughout the life
which is produced due to complete contraction and relaxation of
the heart muscle. A normal healthy person has 60-72 times heart
beats in one minute.
276 Life Processes
Arterial pulse
The repetitive jerk felt at the major arteries of the body due to the pumping action of the heart
is known as the arterial pulse. In a normal healthy person, the arterial pulse is equal to the
heart beat i.e. 60-72 times per minute. The major arteries where the pulse can be felt are radial
artery (wrist), common carotid artery (neck) and temporal artery (temporal lobe of head).
18.9 Photosynthesis
Photosynthesis is a process in which green plants
and certain micro-organisms prepare their own Sunlight Glucose to the
food in presence of chlorophyll by using carbon plant body
dioxide and water as raw materials and sunlight
as a sources of energy. In photosynthesis green
plants and certain microorganisms transform
light energy into chemical energy. During Oxygen to the environment Carbon dioxide Water and minerals
photosynthesis, green plants capture sunlight as Photosynthesis
a source of energy. This energy is used to convert water and carbon into oxygen and energy-
rich organic compound called glucose. Photosynthesis takes place in green plants, euglena
and certain bacteria.
The overall chemical reaction involved in photosynthesis is given below :
6CO2 + 6H2O Light energy, chlorophyll C6H12O6 + 6O2
Oxygen
Carbon dioxide Water Starch
Glucose formed as a product of photosynthesis is used by plants. The special plant tissue
called phloem transports food materials to different parts of the plant. Excess glucose is stored
as starch and also converted into plant biomass. All animals are directly or indirectly depend
upon plants for their food. Oxygen is the by-product of photosynthesis. It is taken by living
organisms and release carbon dioxide in the atmosphere.
ACTIVITY 2
OBJECTIVE : To show that starch is present in the green leaves
REQUIREMENT: Beaker, fresh green leaf, petri dish, distilled
water, ethanol (90%), iodine, forceps, burner and dropper
METHODS :
1. Take a fresh green leaf and boil it in the beaker Boiling leaf in Petri dish with
for about 2 minutes. Boiling removes the hard Fresh green leaf alcohol iodine solution Leaf turns
blue-black
and water proof covering of the leaf.
2. Take out the leaf using forceps and again boil it for about one minute in 90% ethanol solution.
3. Boiling in ethanol removes chlorophyll from leaf.
4. Take out the leaf and put it in a petri dish.
5. Wash the leaf with distilled water and add some drops of iodine on the leaf surface.
OBSERVATION: Leaf turns into blue-black in colour. This is because the starch reacts with iodine to
form blue-black colour.
CONCLUSION: This experiment proves that green leaves contain starch in them.
Modern Concept Science and Environment – 8 277
FACT WITH REASON
Leaves are called the kitchen of the plant, why?
Leaves are called the kitchen of the plants because they prepare food in presence of carbon dioxide,
water and sunlight.
Animals do not exist if there are no plants, why?
Animals depend upon plants for their food. So, animals do not exist if there are no plants.
Requirements of photosynthesis
a) Chlorophyll : Plants can synthesize food but animals cannot because plants have chlorophyll
in them while animals do not. Chlorophyll is found in the chloroplast of the plant cell. It is
a green pigment. Chlorophyll absorbs sunlight that is essential for photosynthesis.
b) Sunlight : Sunlight provides energy source to convert carbon dioxide and water into
glucose. The amount of sunlight required by plants varies according to plants. Some
plants need longer sunshine hours while some need shorter or shading. Chlorophyll
absorbs sunlight for photosynthesis.
ACTIVITY 3
OBJECTIVE : To show that sunlight is necessary for photosynthesis.
REQUIREMENT: A potted plant, black or opaque paper, clip
METHODS :
1. Bring a potted plant in the laboratory and keep it in dark for 2-3
days.
2. After 2-3days, cover some portion of the leaf with black paper and
clip it.
3. Expose the plant into the sunlight for about 8 hours.
4. Pluck the leaf and remove the black paper.
5. Conduct starch test.
OBSERVATION: The exposed portion of the leaf shows blue-black colour in iodine solution. But, no blue-
black colour is seen in the covered portion of the leaf. This indicates that exposed surface of the leaf
takes part in photosynthesis and covered surface does not.
CONCLUSION: This experiment shows that sunlight is essential for photosynthesis.
c) Carbon dioxide : Carbon dioxide is essential for photosynthesis. The outer layer of the
plant tissue is called epidermis which has tiny openings called stomata. Stomata are
the breathing organ of plants. During photosynthesis, plants take carbon dioxide from
the atmosphere and release oxygen as a by-product. But during respiration, plants take
oxygen and release carbon dioxide. Carbon dioxide released by living organisms is the
source of raw material for photosynthesis. Thus, plants maintain the balance of carbon
dioxide and oxygen in atmosphere.
278 Life Processes
ACTIVITY 4
OBJECTIVE: To show that carbon dioxide is required for photosynthesis.
REQUIREMENT: Potassium hydroxide solution, potted plant, bottle or plastic bag, a rubber, etc.
METHODS :
1. Bring a potted plant in the laboratory and Potted plant
keep it in dark for 2-3 days.
2. After 2-3days, take a transparent bottle or Cork Starch present
a polythene bag and keep some potassium (Blue-black)
hydroxide solution in it. Bottle Starch absent
(Pale yellow)
3. Adjust one or two leaves inside the bottle KOH solution
or polythene bag containing potassium Wooden black
hydroxide solution.
4. Potassium hydroxide solution in the bottle or bag absorbs carbon dioxide.
5. Tie the mouth of bottle or bag air tight and keep the plant in sunlight for about 8 hours.
6. Take a leaf from inside the bottle or bag and another leaf from outside the bottle or bag.
7. Conduct starch test for both of the leaves.
OBSERVATION: No blue-black colour appears in the leaf kept in the bottle or bag. But, blue-black colour
appears in the leaf taken from the outside.
CONCLUSION: This experiment shows that carbon dioxide is necessary for photosynthesis.
FACT WITH REASON
Why is potassium hydroxide solution used in the experiment to show that plants need carbon dioxide
for photosynthesis?
Potassium hydroxide absorbs carbon dioxide and no carbon dioxide will be available for
photosynthesis. So, to make a carbon dioxide free environment, potassium hydroxide solution is used
in the experiment to show that plants need carbon dioxide for photosynthesis.
d) Water : Water is another important raw material for photosynthesis. Hydrogen present in
water is used to make carbohydrate. Plants absorb water and different kinds of minerals
through the root hairs. The special tissue of plants called xylem transport water and
minerals from roots to leaves. Plants need more water in hot and warm climate because
they lose most of the water through evaporation and transpiration.
ACTIVITY 5
OBJECTIVE: To show that oxygen gas is produced during photosynthesis.
REQUIREMENT: Twigs of hydrilla, large test tube, beaker, water oxygen gas
glass funnel, water, sodium bicarbonate, matchbox, etc. test tube gas bubbles
METHODS : beaker water
1. Put twigs of hydrilla in a beaker and cover them funnel Hydrilla plant
inside an inverted funnel.
2. Fill the beaker with water and add a pinch of (a) Before (b) After
sodium bicarbonate as a source of carbon dioxide.
Modern Concept Science and Environment – 8 279
3. Fill the test tube with water and invert it gently over the funnel stem as shown in the figure.
4. Air should not enter inside the test tube while inverting it over the stem of the funnel.
5. Keep the apparatus in the sunlight for a few hours.
OBSERVATION: After few hours gas bubbles are seen in the test tube. Gas starts to displace the water
downward in the test tube.
TEST OF GAS: After enough collection of the gas, we lift up the test tube and insert a burning matchstick
inside the inverted test tube with gas immediately. Matchstick burns more rapidly inside the test tube
than in ordinary air.
CONCLUSION: This experiment shows that oxygen gas is produced during photosynthesis.
ANSWER WRITING SKILL
1. What is asexual reproduction? Write down the different methods of asexual reproduction.
Ans: The type of reproduction which takes place without the fusion of a male gamete and a female
gamete is called asexual reproduction. Some of the major methods of asexual reproduction in
plants and animals are given below:
i) Fission ii) Budding iii) Sporulation
iv) Fragmentation or Regeneration v) Vegetative propagation
2. Define regeneration and fragmentation.
Ans: Regeneration is a method of asexual reproduction in which organism regains its lost parts or new
organism is produced from the broken part of the parent organism. It mainly occurs in animals.
Fragmentation is a method of asexual reproduction in which a new organism grows from the
fragmented or broken part of the parent organism. It mainly occurs in plants.
3. Define fertilization. What do we get after fertilization?
Ans: The fusion of a male gamete with a female gamete is called fertilization. After fertilization we get
zygote which develops into embryo.
4. How many valves are present in the human heart? Name with position.
Ans: There are four valves in the human heart. Their names and position are given below:
S.N. Name of the valve Position
1 Tricuspid valve It is present between right auricle and right ventricle.
2 Bicuspid valve It is present between left auricle and left ventricle.
3 Aortic valve It is present between left ventricle and aorta
4 Pulmonary valve It is present between right ventricle and pulmonary artery.
5. Name the artery that carries deoxygenated blood and the vein carries oxygenated blood.
Ans: Pulmonary artery carries deoxygenated blood from right ventricle to the lungs. Similarly, pulmonary
vein carries oxygenated blood from lungs to the left auricle.
280 Life Processes
6. Write any two differences between internal fertilization and external fertilization.
Ans: The differences between internal and external fertilization are given below.
S.N. Internal Fertilization S.N. External Fertilization
1 In this fertilization, fusion of sperm and egg 1 In this fertilization, fusion of sperm and
takes place inside the body of the female. egg takes place outside the body of female.
2 The eggs are laid after fertilization. 2 The eggs are laid before fertilization.
7. Write down the importance of asexual reproduction.
Ans: The importance of asexual reproduction are:
i) Asexual reproduction needs only one parent.
ii) It is useful to transfer the good qualities of plants.
iii) It is very effective for the plants which do not produce viable seeds.
iv) It is easier, cheaper and faster method of reproduction.
8. Describe an experiment to show that light is essential for photosynthesis.
Ans: Objective : To show that sunlight is necessary for photosynthesis
Materials required : A potted plant, black or opaque paper, clip
Procedure: Bring a potted plant in the laboratory and keep it in dark
for 2-3 days. After 2-3days, cover some portion of the leaf with a black
paper and clip it. Expose the plant into the sunlight for about 8 hours.
Pluck the leaf and remove the black paper. Conduct starch test.
Observations: The exposed portion of the leaf shows blue-black
colour in iodine solution. But, no blue-black colour is seen in the
covered portion of the leaf. This indicates that exposed surface of the
leaf takes part in photosynthesis and covered surface does not.
Conclusion : This experiment shows that sunlight is essential for photosynthesis.
STEPS EXERCISE
STEP 1
1. Fill in the blanks with appropriate words.
a) The process of asexual reproduction in which a parent cell divides into two
identical cells is called …….........
b) Yeast is reproduced by ……………
c) The fertilization that takes place inside the body of female organism is called
…………… fertilization.
d) …………… is an iron compound which absorbs oxygen.
e) …………… artery carries deoxygenated blood.
f) ……..…...... blood cells have nucleus.
g) Starch turns ………………. colour in iodine solution.
Modern Concept Science and Environment – 8 281
2. Write True for the correct and False for the incorrect statements.
a) Multiple fission occurs in plasmodium parasite.
b) Bread mould propagates through spores.
c) Tuber of potato is an example of vegetation propagation by root.
d) A sperm cell is diploid (2n).
e) Pulmonary vein carries oxygenated blood.
f) Systematic circulation of blood involves lungs.
g) Iodine test helps to test the presence of starch in the leaf of a plant.
STEP 2
3. Answer the following questions in one word.
a) What is the male reproductive part of a flower?
b) Which type of reproduction does not involve gametes?
c) How do yeast and hydra generally reproduce?
d) Name the blood vessel that carries blood away from heart.
e) How much percentage of plasma is in blood?
4. Write any two differences between:
a) Sexual reproduction and asexual reproduction
b) Binary fission and multiple fission
c) Auricles and ventricles
d) Unisexual animals and bisexual animals
e) Pulmonary artery and pulmonary vein
f) Arteries and veins
g) RBCs and WBCs
h) Internal fertilization and external fertilization
5. Give reasons.
a) Farmers prefer vegetative propagation than seed reproduction.
b) Pumpkin flower is called a unisexual flower.
c) Earthworm is called a hermaphrodite organism.
d) Iron tablets are given to a pregnant women.
e) Leaf is called the kitchen of a plant.
f) Potassium hydroxide solution is used in experiment to show plants need carbon
dioxide for photosynthesis?
g) Valves are present in the veins?
6. Identify the type of asexual reproduction shown in the given diagrams:
Daughter
plasmodia
a) b) c) d)
282 Life Processes
e) f) g) h)
STEP 3
7. Answer the following questions
a) What is life process? List three advantages of asexual reproduction.
b) Define fission, sporulation and vegetative propagation.
c) Define asexual reproduction and list its types.
d) What are the major parts of the circulatory system?
e) What is haemoglobin? Describe plasma in short.
f) Write down the major function of plasma, RBC, WBC and platelets.
g) Describe internal structure of human heart briefly with a labelled diagram.
h) What is circulatory system? Name the valves with their locations.
i) What is heart beat? Define arterial pulse.
j) What do you mean by systolic and diastolic blood pressure?
k) What are capillaries? Write down their function.
l) Describe blood circulation in human body.
m) Draw a labelled diagram of human heart.
n) What is blood pressure?
o) What is pericardial fluid? Write its functions.
p) What is photosynthesis? Write the requirements for photosynthesis?
q) Name any two organisms that show the following mode of asexual reproduction:
i) Binary fission ii) Multiple fission
iii) Budding iv) Regeneration
v) Fragmentation vi) Sporulation
vii) Vegetative propagation by stem
viii) Vegetative propagation by roots
r) Describe an experiment to show that leaves contain starch in them.
s) Show experimentally that carbon dioxide is required for photosynthesis.
t) With a labelled diagram describe an experiment to show that oxygen is released
during photosynthesis.
u) Show that green plants need sunlight for photosynthesis.
8. Diagram based questions.
a) Name the types of blood vessels shown below.
a) b) c)
UNIT Estimated teaching periods Theory MPordaecrtnicCaolncept Science and Environment – 8 283
6 1
19
Structure of the Earth
Syllabus issued by CDC Earth
Introduction to minerals
Characteristics and uses of minerals
Some important minerals found in Nepal (iron, copper, lead, zinc, limestone and graphite).
Process of soil formation
Composition of soil and soil profile
Erosion and deposition
Conservation of soil
LEARNING OBJECTIVES
At the end of this unit, students will be able to:
define minerals and explain physical properties and advantages of minerals.
give general introduction to major minerals found in Nepal (iron, copper, lead, zinc, limestone
and graphite).
explain the process of soil formation and make soil profile.
describe soil erosion and deposition and explain the method of soil conservation.
Key terms and terminologies of the unit
1. Rocks : Rocks are the hard and solid materials that are formed from the combination of
one or more inorganic materials.
2. Mineral : A mineral is a naturally occurring inorganic substance that is made up of metals,
non-metals and their compounds.
3. Metallic minerals : The minerals that contain significant amount of metals are called metallic minerals.
4. Non-metallic minerals : The minerals that do not contain significant amount of metals are called non-
metallic minerals.
5. Ores : Ores are those minerals from which usable or commercial metal can be extracted
in a profitable amount.
6. Fuel minerals : The minerals that are used as fuels are called fuel minerals.
7. Soil : Soil is a mixture of different kinds of organic and inorganic substances like humus,
minerals, water, sand, clay, dead animals and plants, etc.
8. Soil formation : Soil is formed by the weathering of parent rocks by various methods.
9. Soil composition : Soil is composed of organic materials, inorganic materials, air and water.
284 Structure of the Earth
10. Humus : Humus is a dark-brown organic matter which is derived from the dead and decomposed
parts of plants and animals or their waste products.
11. Soil profile : The vertical arrangement of various layers of soil down from the surface of the soil is
called soil profile.
12. Erosion : Erosion is a process of carrying away of humus, soil particles, sediments, rock fragments,
etc. from one place to another by the agents like air, water, storm, flood, landslide,
hurricane, etc.
13. Deposition : Deposition is a process of accumulation of the eroded materials away from the place of
erosion.
14. Soil erosion : The removal of top fertile soil by various agents like air, water, wind, river, glaciers,
hurricane, cyclone, etc. is called soil erosion.
15. Soil deposition : Soil deposition is a process of accumulation of the eroded soil away from the place of
erosion.
16. Deforestation : The cutting down of trees on a large scale is called deforestation.
19.1 Introduction
Our earth is composed of different materials like air, water, Memory Tips
soil, rocks, etc. Two third of the earth surface is covered with 1. Rock is made up of inorganic
water and remaining one third is covered with land. Land materials while soil is made
surface is composed of soil and rocks. Soil is the uppermost up of organic and inorganic
loose material that covers the earth’s surface and supports materials.
life. Soil is composed of organic and inorganic substances
like humus, minerals, sand particles, etc. Rocks are present 2. Talc is the softest material and
on the earth’s surface in different shape, size, colour, weight diamond is the hardest mineral
and density. They are made from different inorganic one.
substances. Thus, rocks are the hard and solid materials that
are formed from the combination of one or more inorganic materials like rock salt, mica, lead,
granite, slate, limestone, sandstone, etc.
19.2 Minerals
A mineral is a naturally occurring inorganic substance that is made up of metals, non-metals
and their compounds. The earth’s crust (except small proportion of organic material) is made
up of minerals. Some minerals consist of single element such as gold, silver, diamond (carbon),
sulphur, etc. Similarly some minerals consist of two or more elements like silica, copper pyrite,
horn silver, bauxite, etc. More than two thousands minerals have been identified till today.
Mostly these minerals contain inorganic compounds made by various combinations of the
eight elements (O, Si, Al, Fe, Ca, Na, K, and Mg). Some minerals contain large amount of
metals called ores. Thus, ores are those minerals from which usable or commercial metal can
be extracted in a profitable amount. Haematitie, bauxite, copper pyrites, argentite, etc. are
some examples of ores. Minerals are the non-renewable sources of energy.
Minerals are of three types. They are metallic minerals, non-metallic minerals and fuel
minerals.
Modern Concept Science and Environment – 8 285
Lead Mica
Rock salt
Granite Limestone Sandstone
Some minerals
FACT WITH REASON
Rust is a mineral but magnetite is an ore. Give reason.
Rust is a mineral because it contains very less amount of metal (Fe) which cannot be extracted. But
magnetite is an ore because it contains higher percentage of metal in it.
Metallic minerals
The minerals that contain significant amount of metals are called metallic minerals. However,
the minerals from which metals can be obtained profitably are called ores. Ores contain less
amount of impurities and higher amount of metals. Metallic minerals are the compounds
of metals. For example: iron oxide, aluminium oxide, copper pyrites, limestone, dolomite,
etc. Haematitie, magnetite, limonite, etc. are ores of iron, bauxite is an ore of aluminium and
copper pyrites is an ore of copper similarly, argentite is an ore of silver. From these ores we
can obtain metals easily and profitably.
Haematite ore Magnetite ore Cuprite ore Chalcopyrite ore Argentite ore
Metallic minerals
Non-metallic minerals
The minerals that do not contain significant amount of metals are called non-metallic minerals.
Most of the non-metallic minerals are metallic compounds while some are non-metallic
compounds. Non-metallic minerals cannot be used to extract metals. They are mostly used
for manufacturing cement, fertilizers, pesticides, gems and other decorative items. Examples
of non-metallic minerals are granite, slate, sulphur, silica, feldspar, quartz, obsidian, etc.
Sulphur Coal Slate Granite
Non-metallic minerals
286 Structure of the Earth
FACT WITH REASON
Non-metallic minerals cannot be used to extract metals, why?
Non-metallic minerals cannot be used to extract metals because they contain very less amount of
metals. For example: granite, silica, feldspar, quartz, etc.
Granite is a non-metallic mineral, why?
Granite is a non-metallic mineral because metal cannot be extracted from it.
Differences between metallic minerals and non metallic minerals
SN Metallic mineral SN Non-metallic mineral
1 The minerals that contain 1 The minerals that do not contain
significant amount of metals are significant amount of metals are called
called metallic minerals. non-metallic minerals.
2 Metallic minerals are simply 2 Most of the non-metallic minerals are
metallic compounds. metallic compounds while some are also
non-metallic compounds.
Fuel minerals
The minerals that are used as fuels are called fuel minerals. Coal, petroleum, natural gas, etc.
are some examples of fuel minerals. They are formed from the partial decomposition of the
organic materials under the earth’s crust for millions of years. Fuel minerals are also called
fossil fuels.
Petrol Coal Natural gas
FACT WITH REASON
Coal is called a fuel mineral. Give reason.
Coal is called a fuel mineral because it is a naturally occurring mineral that can be used as a fuel.
Characteristics of Minerals
i) Minerals are natural substances.
ii) All mineral are solid (except some fuel minerals) in natural state.
iii) The hardness of minerals differs from each other.
iv) All minerals have their own chemical composition.
v) Minerals have crystalline structure.
vi) Metallic minerals show metallic lustre.
Modern Concept Science and Environment – 8 287
Uses of minerals
i) Minerals are the major sources of metals.
ii) Many minerals are used for making jewelleries and decorative items.
iii) Some of them are used as fuels. Examples: coal, petrol, natural gas, etc.
iv) Calcite minerals are used for making construction materials, medicine and toothpaste.
v) Silica is used for manufacturing glass, semiconductors, electronic devices, etc.
vi) Talc is used as a baby powder, cosmetics material, etc.
vii) Feldspar is used in ceramics and porcelain.
viii) Gypsum is used for making wall board and plaster of Paris.
19.3 Important Minerals Found in Nepal
Mineral is one of the important materials for the industrial development. It has important
role for the development of a nation. Different kinds of industries like iron industry, steel
industry, cement industry, etc. depend upon minerals. In this unit we will discuss about some
important minerals found in Nepal.
a) Iron (Fe)
Iron is a grey coloured hard and strong metal. It is a main metal which is used in infrastructure
development and manufacturing of heavy machinery equipment. It is used for making arms,
agricultural tools, vehicles, etc. Iron is also used for making household utensils, rods, cables,
buildings, bridges, etc. Magnetite and haematite are the main ores of iron found in Nepal.
These ore are found in different districts of Nepal. For examples: Phulchoki (Lalitpur), Thoshe
(Ramechhap), Labdi Khola (Tanahun), Jeekhabang (Chitwan), Dhuwakot (Parbat), Purchaundi
(Baitadi), Khanigaun (Bajhang), etc.
b) Copper (Cu)
Copper is a reddish-brown, hard and strong metal. It is an important metal which is mainly
used in electrical appliances, telecommunications equipment, crafts, alloys, utensils, and other
household items. In the past, many people in hilly area were used to extract copper by using
traditional methods. The most common copper ore found in Nepal is chalcopyrite. In Nepal,
copper deposits are found in Kalitar (Makwanpur), Dhusa (Dhadhing), Wapsa (Solukhumbu),
Bamangaun (Dadeldhura), Khandeshori or Marma (Darchula), Kurule (Udayapur), Bhut
Khola (Tanahun), Pandav Khani (Baglung), etc.
c) Zinc (Zn)
Zinc is a bluish-white, hard, strong and lustrous metal. It is used for galvanizing iron. It is
also used for making dry cells, soldering, dyeing, glue making, alloying etc. Zinc sulphide
is a main ore of zinc found in Nepal. In Nepal, zinc deposits are found in Ganesh Himal
area (Rasuwa), Phakuwa (Sankhuwasabha), Labang- Khairang, Baraghare and Damar
(Makwanpur), Pangum (Solukhumbu), Salimar valley (Mugu/ Humla), Phulchoki (Lalitpur),
Sisha Khani and Kandebas (Baglung), etc.
288 Structure of the Earth
d) Lead (Pb)
Lead is a soft, malleable, bluish-white and heavy metal. It is used to make lead sheets, pipes,
bullets, alloys, pigments, dyeing and printing process, insecticide, medicine, etc. Galena is
the major ore of lead found in Nepal. Lead occurs in association with zinc. In Nepal, lead
deposits are found in the same places of zinc deposits. Examples: Ganesh Himal (Rasuwa),
Phakuwa (Sankhuwasabha), Labang- Khairang, Baraghare and Damar (Makwanpur),
Pangum (Solukhumbu), Salimar valley (Mugu/ Humla), Phulchoki (Lalitpur), etc.
e) Limestone
Limestone is one of the most exploited mineral of Nepal. Over 1.3 billion metric tons of
cement grade limestone deposits are already known from the Lesser Himalayan region of
Nepal. Cement and lime industries are based on limestone.The major limestone deposits in
Nepal are Sindhali (Udaypur), Bhainse and Okhare (Makwanpur), Chhovar (Kathmandu),
Jogimara (Dhading), Ropla, Dang, etc. Due to rapid development activities such as
construction of roads, bridges, dams, irrigation channels, housing complexes, multi-storeys
buildings, etc. the demand of cement is increasing day by day. This is a main reason why
cement industries have evolved in Nepal than any other industries.
f) Graphite
Graphite is a soft, greyish-black and non-metallic mineral which is mostly found in
metamorphic rock. It is found in different parts of Nepal like Ilam, Dhankuta, Sankhusabha,
Nuwakot, Sindhupalchok, Dadeldhura, etc. It is mainly used in lead pencils, crucibles,
paints, lubricants, electrodes, etc.
Differences between iron and graphite.
SN Iron SN Graphite
1 Iron is a metal. 1 Graphite is a non-metal.
2 Itisusedformakingarms,agricultural 2 It is mainly used in lead pencils,
tools, vehicles, household utensils, crucibles, paints, lubricants, electrodes,
rods, cables, buildings, bridges, etc. etc.
19.4 Soil
Soil is a mixture of different kinds of organic and inorganic
substances like humus, minerals, water, sand, clay, dead animals
and plants, etc. It is the topmost layer of the earth’s crust. It contains
life supporting substances and supports life on the earth. Most part
of the earth’s surface (except rocky ground and ice covered areas)
is covered with soil. Soil contains various nutrients that support
life. The existence of different soil organisms like ants, earthworms, Soil
bacteria, fungi, insects, etc. is possible in soil. Some vertebrates like
rats, rabbit, snakes, porcupine, etc. live in burrows under the soil. Similarly, growth of plants
is only possible in soil. Plants absorb water and minerals from the soil for photosynthesis.
Modern Concept Science and Environment – 8 289
FACT WITH REASON
Soil is called life supporting medium, why?
Soil contains different kinds of life supporting medium like humus, minerals, air, water, sand, clay,
micro-organisms, etc. So, it is called life supporting medium.
Formation of soil
Soil is formed by the weathering of parent rocks by various methods. The sun, wind, water,
glaciers, etc. are responsible for weathering of rocks into soil. Formation of soil is very slow
process. It takes millions of years for formation of soil. Some common methods of weathering
of rocks are briefly explained below:
a) Water: Pores and cracks are present in the big rocks. Water enters into these pores and
cracks. At low temperature, water freezes into ice. Ice has more volume than water. So,
it exerts pressure on the rocks. Similarly, when water melts, it releases pressure. This
activity expands and contracts rocks. As a result, rocks weather and forms soil in long
time. Memory Tips
b) Heat: Continuous heating and cooling cause expansion The weathering of rocks into soil
and contraction of rocks. Over a long period of time, by means of biological factors like
the rocks break down into smaller fragments. These animals, plants, bacteria, fungi,
fragments finally form soil particles. etc. is called biological weathering.
c) Humidity: Many rocks swell in humid air and shrink in dry air. The swelling and
shrinking activity break down the rocks into fragments. These fragments finally form
soil particles.
d) Tides of sea and ocean: Tides of sea and ocean grind the rocks from their bank. Rivers
also erode their channel and make them deeper. Similarly, the current of river water
also carry small fragments of rocks along with them. In the course of their movement,
these fragments hit each other and break down into smaller particles. Rivers finally
deposit soil in their bank and channel.
e) Plants: Plants like lichens grow in rocks. Their growth, death and decay release organic
acid. In long run, these organic acids decay the rocks into soil. Similarly, roots of trees
go deeper into the ground. Sometimes, they may enter into the cracks of the rocks and
grow. When they grow, they exert pressure inside the rocks and break down into
fragments. Finally, these fragments form soil.
f) Glaciers movement: Glaciers movement through Memory Tips
the rocky mountains weather rocks into soil. When
glaciers move, they carry rocks and soil fragments The weathering of rocks into soil
by means of physical factors like
in them. In the course of their movement, the rock air, water, heat, humidity, etc. is
fragments further grind into fine soil particles. called physical weathering.
290 Structure of the Earth
Composition of soil Memory Tips
Soil is composed of organic materials, inorganic materials, 1. Soil consists of 45% minerals,
air and water. An ideal soil is supposed to be 25% water, 25% air & 5%
composed of 45% minerals, 25% water, 25% air, and organic matter
5% organic matter. In reality, the percentage of these 2. Approximately 10% of the
four components varies place to place.
world’s carbon dioxide
The inorganic material of the soil is composed of pebbles, emissions is stored in soil.
sand, silt, clay and other minerals. Similarly, the organic 3. It takes 500 years to produce
matter of the soil is composed of dead and decayed organisms just under an inch of topsoil,
or their parts. It is generally called humus. Thus, humus is a
dark-brown organic matter which is derived from the dead this is the most productive
and decomposed parts of plants and animals or their waste layer of soil.
products. Humus improves water-holding capacity of the soil. It also adds different nutrients,
and makes the soil fertile. Soil also contains different kinds of soil organisms like bacteria,
fungi, earthworms, etc. They help to make soil light, porous and fertile.
The components of soil differ according to the place. There are various layers of the soil.
The topmost layer of the soil is called humus. The second layer of soil contains humus, soil
organisms, roots of plants, etc. The third layer of soil contains different kinds of inorganic
minerals like iron, zinc, magnesium, aluminium, cobalt, etc.
FACT WITH REASON
The top layer of soil contains various nutrients in it, why?
The top layer of the soil contains various nutrients in it because it receives these nutrients from the
dead and decayed organic materials.
ACTIVITY 1
OBJECTIVE: To observe different layers of the soil. Water
1. Take a transparent glass bottle or a jar.
2. Collect some amount of soil from the garden or field and keep it in the bottle Clay
Silt
or jar. Sand
3. Add water in the bottle. Keep in mind that water should make solution easily. Bed rock
4. Stir the mixture for about 2 minutes and leave it without disturbing.
5. Observe the solution after an hour.
6. You can see that the soil is arranged in different visible layers like humus,
clay, silt, sand and pebbles.
Soil profile
Soil profile is a physical and chemical description of soil which is arranged in different
layers (called horizons). It shows the layers from the surface to the depth where soil forming
processes are no longer evident. Thus, the vertical arrangement of various layers of soil down
from the surface of the soil is called soil profile. Different layers of soil can be studied after
digging a trench vertically down at a place. A soil profile contains various layers like top-soil,
sub-soil and bed rocks.
Modern Concept Science and Environment – 8 291
A typical soil profile includes the following horizons. Vegetation
Top soil (Horizon A)
a) A horizon : The uppermost dark layer which is
rich of humus is called top soil or A-horizon. It Sub-soil (Horizon B)
is also called an organic layer. It is light, soft and
porous. It holds enough water. Various kinds of Horizon C
soil organisms like bacteria, fungi, earthworms, etc. Bed rock
are present in this layer. From this layer, roots of
plants can absorb water and minerals. The amount
of humus and minerals is not same in all top soil.
b) B horizon: This layer is present below the top soil.
It is hard, compact and rich in soluble minerals. It Soil profile
does not contain more organic matter like in top soil. Roots of plants can reach up to this
layer. Substances leached from overlying horizons accumulate in this horizon.
c) C horizon: It is a layer made up of large pieces of bed rocks such as granite, basalt,
quartzite, sandstone, limestone, etc. Small cracks are partially or totally filled with soil
material and roots of big plants.
19.5 Erosion and Deposition
Erosion is a process of carrying away. It can be done by air, water, wind, river, glaciers,
hurricane, cyclone, etc. It is also cause by human beings. Thus, erosion is a process of carrying
away of humus, soil particles, sediments, rock fragments, etc. from one place to another by
the agents like air, water, storm, flood, landslide, hurricane, etc. After erosion, it is necessary
to sediment the eroded materials away from the site of erosion. It is called deposition. Erosion
and deposition occur side by side. It means erosion is always followed by deposition. Thus,
deposition is a process of accumulation of the eroded materials away from the place of erosion.
Soil erosion
The top layer of the soil can be carried away from its natural place due to different natural
agents like air, water, wind, river, glaciers, hurricane, cyclone, etc. It is a serious problem in
the agricultural land. Due to various human activities, the rate of soil erosion is increasing day
by day. After soil erosion, the fertile land becomes unfertile. Thus, the removal of top fertile
soil by various agents like air, water, wind, river, glaciers, hurricane, cyclone, etc. is called
soil erosion. After soil erosion, it is necessary to sediment the eroded soil away from the site
of erosion. It is called soil deposition. Soil erosion and soil deposition occur side by side. It
means soil erosion is always followed by soil deposition. Thus, soil deposition is a process of
accumulation of the eroded soil away from the place of erosion. Soil erosion mainly occurs by
the natural process but these natural processes are induced by various human activities. Some
of the major causes of soil erosions are given below:
292 Structure of the Earth
Causes of soil erosion
a) Deforestation
The cutting down of trees on a large scale is called
deforestation. After deforestation, the forest exposed
to wind and rainfall. Absence of plants makes the soil
loose and prone for erosion. Therefore, rainfall easily
washes the top layer of the land that contains loose
organic materials.
FACT WITH REASON Deforestation
Deforestation is an important cause of soil erosion. How?
Deforestation results dry lands, irregular rainfall, extreme weather and wind. As a result soil erosion
is more possible after deforestation.
b) Overgrazing Over grazing
Grazing of pastures, grassland and forest by livestock
beyond the capacity of renewal of vegetation is called
overgrazing. Absence of vegetation in land makes the
soil dry and loose. Such soil is easily washed away by
wind, floods and landslide.
c) Improper farming
The traditional method of farming on hills and mountain
makes the soil weak and prone. Such practice exposed
the soil to wind, water and sunlight. As a result, the
fertile soil is easily washed by wind and rainfall.
Effects of Soil erosion and deposition
i) After soil erosion, the soil becomes infertile and hence Improper farming
production of crops decreases.
ii) After soil erosion, the soil does not support vegetation for longer time.
iii) Soil erosion causes landslides and flood.
iv) Deposition of soil into reservoir decreases the life of the reservoir.
v) Deposition of soil, silt, sand, etc. destroys crops and vegetation.
vi) Deposition of soil, silt, sand, etc. changes the chemical composition of the soil.
vii) Both erosion and deposition of soil changes the structure of land.
FACT WITH REASON
Terai region of Nepal is more fertile than mountain and Himalayan region, why?
The fertile soil of mountain and Himalaya region is washed out every year by rain. This eroded soil is
carried out by flood and deposited in the Terai region. Thus, Terai region of Nepal is more fertile than
mountain and Himalayan region.
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Science book class 8
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