Oasis Science and Technology 9

Mushroom Yeast Bread mould

Fig. 17.20

Fungi cannot prepare their own food due to the absence of chlorophyll. They get their food
from dead and decaying organic matter. So, they are called saprophytes. However, some fungi
are parasites of plants and animals.

Characteristics of fungi

1. Fungi contain eukaryotic cells which may contain more than one nucleus.

2. The plant body is a thallus, i.e. without root, stem and leaves.

3. Their cell wall is made of fungus cellulose, i.e. mixture of chitin and cellulose.

4. They do not have chlorophyll.

5. Their body is made of hyphae, i.e. long filaments or mycelia.

6. They may be unicellular (yeast) or multicellular (mushroom).

7. They reproduce asexually by budding, fragmentation and sporulation.

Economic importance of fungi

Useful effects of fungi
1. Fungi act on dead bodies and decompose them. Thus, they help to increase the fertility

of soil and recycle materials in the environment.
2. Some fungi, i.e. edible mushrooms are valuable food sources for human beings.
3. Some fungi like yeast are used in wine industries and bakeries.
4. Some fungi like penicillin are used as antibiotics.
Harmful effects of fungi
1. Fungi attack tissue of plants and animals and cause diseases.
2. Fungi infect humans and cause diseases like skin infection, vaginal yeast infection, etc.
3. Many fungi attack food grains and vegetables and spoil them.

BIOLOGY Oasis School Science - 9 293

Differences between Bacteria and Fungi

S.N. Bacteria S.N. Fungi
1. They have prokaryotic cell. They have eukaryotic cell.
2. They are unicellular.
They may be unicellular or
3. Nuclear membrane is absent. multicellular.

4. They have autotrophic and Nuclear membrane is present.
heterotrophic nutrition.
They have heterotrophic nutrition.

Control Measures of Fungi
Following measures can be adopted to control fungi and fungal diseases:
1. Preserving food items like milk, meat, fish, fruits, vegetables, etc. in refrigerator
2. Using fungicides to kill fungi
3. Using sugar to control growth of fungi
4. Personal cleanliness to control growth of fungi
5. Using salts to control the growth of fungi on fruits and vegetables

Activity 4

To grow and observe fungi on bread
• Take a piece of bread and leave it in a moist place for 3-4 days.
• Observe the bread after 4 days.
• What do you observe? Can you see the growth of white cottony mass?
• Prepare a slide and observe the cottony mass under the compound microscope.
• Draw a neat and labelled figure after your observation.

17.10 Viruses Fig. 17.21 Flu virus

Viruses are the smallest and possibly the most primitive,
acellular, non-protoplasmic bodies. The word virus has been
derived from a Latin word venom which means poison or
poisonous fluid. Viruses are much smaller than bacteria, and
can be detected only under the electron microscope. The size
of viruses ranges from 25 nanometers (nm) to 250 nanometers
[1nm = 10-9m]. On an average, viruses are about 50 times smaller
than bacteria.

In 1886 AD, Meyer first described the viral disease of tobacco
and called it 'tobacco mosaic'. All viruses are totally parasitic
and behave like living organisms inside the living host cell,
while they are quite inactive and seem to be dead out of the host

294 Oasis School Science - 9 BIOLOGY

cell. Therefore, viruses are placed on the boundary of the living world and non-living world.

Viruses have different shapes like spherical, cylindrical, hexagonal, etc. Viruses do not have
cellular structure, i.e. they do not have cell membrane or cell organelles. They are simply
made of nucleic acid (either DNA or RNA) which remains surrounded by coat of proteins (a
thin film of protein). Viruses can exist outside the living cell for a long period of time but they
cannot reproduce outside the living cell. Since viruses can reproduce only inside the living cell
of the host, they are called obligatory parasites.

Living properties of Viruses

i. Viruses contain genetic material, i.e. either DNA or RNA.

ii. Viruses can reproduce in a large number and they transmit hereditary
characteristics to their offspring.

iii. Viruses infect living organisms and cause various diseases.

Non-living properties of Viruses

i. They do not have a cellular structure.

ii. They do not perform metabolic activities.

iii. Viruses can be crystallized like non-living things.

iv. They become inert and cannot reproduce outside the living cell.

Viruses - The agents of diseases

Viruses cause a wide range of diseases among living organisms. A few hundred plant diseases
caused by viruses have been recorded so far. For example, mosaic disease of tobacco, cabbage,
cauliflower, mustard, etc; black ring spot of cabbage, leaf roll of tomato, etc. Similarly, disease
caused by viruses in human beings include AIDS, polio, mumps, common cold, rabies,
measles, chicken pox, swine flu, etc.

Classification of viruses [On the basis of host]

On the basis of types of host, viruses are of three types:

i. Plant Viruses: The viruses that attack plants are

called plant viruses. For example, Tobacco Mosaic

Virus (TMV). Most of the plant viruses contain

RNA as a genetic material. TMV is a rod-shaped

RNA virus that attacks leaves of tobacco. An

American scientist Stanley first isolated TMV in

the form of crystals in 1935 AD.

ii. Animal Viruses: The viruses that attack Fig.17.22 Structure of TMV

animal tissues are called animal viruses. For

example, Retro virus (HIV), Rhabdo virus, Paramyxo virus, Rhino virus, etc.

BIOLOGY Oasis School Science - 9 295

iii. Bacteriophages: The viruses that attack bacteria and Capsid
destroy their nuclear material are called bacteriophages Head
[phagein - to eat]. Actually, bacteriophages are the feeder DNA
or eater of bacteria. For example, T2 phage, T4 phage, etc. Tail
The body of a bacteriophage virus is differentiated into
Tail
two parts, i.e. head and tail. The head is hexagonal in fibres

shape which contains a contractile protein coat called Fig. 17.23 Bacteriophage virus

capsid. The cylindrical tail contains end plate and

tail fibres.

Activity 5

• Prepare a model of bacteriophage virus and tobacco mosaic virus. Label the main
parts and write down their main features.

Differences between Bacteria and Viruses

S.N. Bacteria S.N. Viruses
1.
Bacteria are very small in size. They 1. Viruses are smaller than bacteria. They
2. can be seen under a compound can be seen only under an electron
3. microscope. microscope.

4. Bacteria show metabolic activities. 2. Viruses do not show metabolic activities.

Bacteria are living cellular 3. Viruses are acellular particles. However,
organisms. they show living properties inside the
host.
A bacterial cell is surrounded by a 4.
distinct cell wall. Cell wall is absent in viruses.

Classification of Viruses [On the basis of genetic material]
On the basis of presence of genetic material, viruses are of two types:

i. DNA Virus: The virus containing DNA as the genetic material is called DNA virus.
Examples: Bacteriophage virus, Small pox virus, Adeno virus, etc.

ii. RNA Virus: The virus containing RNA as the genetic material is called RNA virus.
Examples: Retro virus, Polio virus, Rhabdo virus, Rhino virus, etc.

Modes of transmission of Viruses
Viruses are transmitted by either of the following modes:
i. direct contact with the infected organism or the materials used by the patient
ii. through the medium of air, water and food

296 Oasis School Science - 9 BIOLOGY

iii. by means of mouthparts, legs of flies, animal bite, etc.

iv. by means of droplets during coughing, sneezing, laughing, talking, etc.

v. from infected mother to her unborn/newly born child

vi. through seeds, soil, vectors, etc.

vii. through vegetative propagation

Control Measures of Viruses or Viral Diseases

i. The infected parts of plants should be burnt.

ii. The seeds of plants infected with viruses should not be used.

iii. Viral diseases in human beings can be prevented by immunization.

iv. The patient suffering from viral diseases should be isolated.

v. The use of personal materials of the patient should be avoided.

17.11 Protozoa

Protozoa includes unicelluar and microscopic animals. They can be seen only under the
compound microscope. They cause various diseases in human beings like amoebiasis,
giardiasis, African sleeping sickness, leishmaniasis, trichomoniasis, toxoplasmosis, malaria,
babesiosis, etc.
Amoeba, paramecium, euglena, etc. are some free-living protozoans. They do not cause any
disease in human beings. But some species of amoeba like Entamoeba histolytica, Entamoeba
gingivalis, etc. infect human beings. Some other examples of parasitic protozoa are Plasmodium,
Trichomonas, Trypanosoma, Toxoplasma, Giardia, Leishmania, etc.

Parasitic protozoans can transmit from one person to another by direct contact, sexual contact
with the infected partner, through contaminated foods and drinks, insect bite like mosquito
bite, etc.

The transmission of parasitic protozoa can be controlled by avoiding direct contact and sexual
contact with the infected partner, avoiding mosquito bite, drinking pure water, etc.

Plasmodium Leishmania Trypanosoma Trichomonas Giardia
Fig. 17.24

BIOLOGY Oasis School Science - 9 297

SUMMARY

• Adaptation is the ability of an organism to change over a period of time for better
adjustment with the environment.

• Plants and animals possess several structural and functional features which
enable them to survive and breed in their habitat.

• There are mainly three types of adaptations, viz. aquatic adaptation, terrestrial
adaptation and aerial adaptation.

• Aquatic plants are adapted to stay and grow in water. They have weak root
system and flexible stem.

• Most of the aquatic plants are covered with waxy substance to prevent them
from decaying.

• Mesophytes have well-developed root system and shoot system.

• Xerophytic plants show various adaptations to conserve water and to absorb
maximum amount of water from the soil.

• Aquatic animals show adaptations for buoyancy in water and against decaying.
They have streamlined and slippery body.

• Terrestrial animals may be walkers, runners, burrowers, climbers, diggers, fliers,
etc. Their body structure is modified according to their habit and habitat.

• Birds have a streamlined body. Their fore limbs are modified into wings for
flight. They have light weight body.

• Bacteria (singular-bacterium) are the smallest and most widespread
single-celled plant organisms.

• Fungi are non-green thallophytes without chlorophyll. Their mode of nutrition
may be saprophytic or parasitic.

• Viruses are the smallest and possibly the most primitive, acellular, non-
protoplasmic bodies which cause various diseases in plants and animals.

• Protozoa includes unicellular and microscopic animals which are generally
found in water.

• Parasitic protozoa cause various diseases in human beings, like malaria, African
sleeping sickness, trichomoniasis, giardiasis, etc.

298 Oasis School Science - 9 BIOLOGY

Exercise

Group-A
1. What is adaptation? What do you mean by adaptational characteristics?
2. Write any two adaptational characteristics of the plant given in the figure.

3. Write any two adaptational characteristics of aquatic plants.
4. Write any two adaptational characteristics of the animal shown in the given figure on the

basis of habitat. Name a mammal which can survive on the desert.

5. Write any two adaptational characteristics of the plants found in mountain region.
6. Write any two adaptational characteristics of
the animal shown in the given figure.
7. Write any two characteristics of the animals that live in dry climate.
8. Write any two adaptational characteristics of the plant shown in the figure.

9. Write any two adaptational characteristics of a polar bear on the basis of habitat. Name
any two animals having climbing capacity.

10. Write any two adaptational characteristics of terrestrial plants. Name a bird having long
and strong beak.

11. Write any two characteristics of the
animals given in the figure.

BIOLOGY Oasis School Science - 9 299

12. Write any two adaptational characteristics of water lily.
13. Write any two adaptational characteristics of the animals found in Himalayan region.

Name any one aquatic mammal having streamlined body for adaptation.
14. What is called the ability of adjustment of organisms in the existing environment?
15. Write any two adaptational characteristics of Aloe vera.
16. Write any two adaptational characteristics developed in arboreal animals.
17. Write any two adaptational characteristics of the animal given in the figure.

18. `What is bacteriology?
19. Where are bacteria found?
20. Write down the size of bacteria.
21. How many types of bacteria are there? What are they?
22. Name any five human diseases caused by bacteria.
23. What are fungi? Where are they found?
24. Write any two characteristics of fungi.
25. What is mycology?
26. How do fungi reproduce?
27. Name the fungi which is used for making bread.
28. What are viruses? Where are they found?
29. Write any two characteristics of viruses.
30. Name the scientist who isolated TMV from tobacco leaves for the first time .
31. What is the size of viruses?
32. How many types of viruses are there? What are they?
33. What is bacteriophage virus?
34. What are the main methods of virus transmission?
35. Name any four human diseases caused by viruses.
36. Name any five human diseases caused by protozoa.

Group-B
1. Differentiate between aquatic plants and terrestrial plants in any two points.
2. The stem of aquatic plants is covered with waxy substance, why?

300 Oasis School Science - 9 BIOLOGY

3. Write any two differences between hydrophytes and xerophytes on the basis of
adaptation.

4. The stem of desert plants is thick and fleshy. Give reason.
5. Differentiate between aquatic animals and aerial animals on the basis of adaptation.
6. House wall lizard can climb easily on the walls but a rat cannot, why?
7. The beak of a duck is flat and broad, why?
8. Write any two differences between bacteria and viruses.
9. Why are viruses called obligatory parasites?
10. Bacteria are both useful and harmful for living beings. Justify this statement.
11. Viruses are called living beings as well as non-living things, why?

Group-C
11. What is the importance of adaptation for living beings? Write any two adaptational

characteristics of the plants found in mountainous region.

12. How does spoon-shaped beak of a duck help in adaptation? Describe in brief. Write any
two control measures of viruses.

13. Body structure and colour of animals help them in adaptation. Justify this statement
with an example.

14. Write any three importance of bacteria.

15. Write any three harmful activities of fungi.

Group-D

11. Write any two adaptational characteristics of a camel required to live in a desert. Write
any two differences between leaves of submerged plants and freely floating plants on the
basis of adaptation.

12. Water storage pouch is found in desert animals, why? Write any two differences between
aquatic and terrestrial animals on the basis of adaptation.

13. How do long legs of a crane help in adaptation? Birds have light but strong bones.
Describe this statement on the basis of adaptation.

14. What is bacteriophage virus? Draw its labeled figure. Differentiate between leg of a cow
and leg of a tiger on the basis of adaptation.

15. Describe the structure of bacteriophage virus with a neat and labelled figure.

BIOLOGY Oasis School Science - 9 301

UNIT 18 Estimated teaching periods

Theory 13

Practical 4

System

Robert Hooke

Objectives

After completing the study of this unit, students will be able to:
• introduce cell, tissue, organ and system and explain interrelation among

them.
• explain the types and location of plant tissues.
• explain human skeletal system.
• list the bones of human skeleton and classify them.
• introduce digestive system and explain it.
• introduce respiratory and excretory system and explain their importance.

18.1 Introduction

All living organisms are composed of microscopic units called cells. These cells are called
building blocks of life. A cell is defined as the basic, structural and functional unit of life
capable of independent existence. A cell has a complete set of parts neatly arranged in a mass
of cytoplasm surrounded by a membrane that appears a tiny compartment. Therefore, the cell
is also called basic unit of life. A cell is made up of the life giving substance called protoplasm.

302 Oasis School Science - 9 18.1 Compound microscope
BIOLOGY

Cell was discovered by Robert Hooke in 1665 AD. He observed a thin slice of cork under his
self-built microscope and found that the cork piece had numerous compartments connected together
in a honey-comb like structure. He named these compartments as cells (L., cella – compartments).

The body of multicellular organisms is made up of a large number of cells. There are different
groups of cells that perform different functions. A group of cells having a common origin and
performing similar function is called a tissue. Each tissue comprises of cells that originate from
common parent cells and has a characteristic shape, size and arrangement. A tissue can be
defined as a group of cells having a common origin which are more or less alike in shape, size
and function. Epithelial tissue, muscular tissue, blood, meristematic tissue, xylem, phloem,
etc. are some examples of tissues. The microscopic study of tissues and their functions is called
histology. Plants and animals contain different kinds of tissues.

An organ is a part of an animal or a plant having a characteristic function, shape and structure.
Eyes, heart, lungs, stomach, kidneys, etc. are examples of some organs of animals. Similarly,
root, stem, leaves, flowers, etc. are organs of plants. Several organs may function together
which is called an organ system. So a body is a collection of systems, organs, tissues and cells.

18.2 Relation Among Cells, Tissues, Organs and Systems

Cell is the basic, structural and functional unit of life. The body of all living organisms is made
up of cells. A unicellular organism consists of only one cell whereas multicellular organisms
contain many cells. The single cell of unicellular organisms can perform various activities
like respiration, excretion, reproduction, digestion, etc. But in case of multicellular organisms,
there are separate groups of cells responsible for different functions. Such group of cells is
called tissue. The cells of a tissue show similar pattern of growth and development. In the
developed organisms, there are many functions being carried out by various tissues in the
group. Such group of tissues that performs a particular function is called an organ. In the body
of an organism, a set of organs act together to perform a certain function. Such a group of
organs is called system. Examples: digestive system, circulatory system, etc. Various systems
act together and form a complete organism. Thus, there exists a close relationship among cells,
tissues, organs and systems.

Cell + Cell → Tissue
Tissue + Tissue → Organ
Organ + Organ → System

Various systems, organs and tissues of human body and their functions are given in the
table below:

S.N. Systems Organs Tissues Functions
1. Digestive system Digestion and
Mouth, stomach, Columnar absorption
2. Respiratory system liver, pancreas, epithelium,
intestine involuntary muscle To exchange oxygen
and carbon dioxide
Nose, wind pipe, Pavement and
lungs cubical epithelium

BIOLOGY Oasis School Science - 9 303

3 Circulatory system Heart, blood, blood Pavement To supply food and

vessels epithelium, cardiac oxygen, fight against

muscle, smooth infection

muscle, connective

tissue

4. Excretory system Kidney, liver, ureter, Pavement and To excrete waste

urinary bladder cubical epithelium materials

5. Muscular system Various types of Skeletal, smooth To help in movement
muscles and cardiac muscle of body parts, to give
shape

6. Skeletal system Bones and cartilage Connective tissue To give internal

framework, to help
in locomotion

7. Reproductive Testes, ovaries Cubical and Sexual reproduction

system vagina, penis, etc. columnar

epithelium

8. Nervous system Brain, spinal cord Nervous tissue Sensory

and nerves

9. Endocrine system Endocrine glands Glandular To bring out

epithelium harmonious

development of

body

18.3 Plant Tissue

On the basis of location and function, plant tissues can be divided into following two types:

A. Meristematic tissue Apical
B. Permanent tissue meristem

A. Meristematic tissue

Meristematic tissue is made up of simple Lateral
undifferentiated cells which continue to divide meristem
actively to produce new cells. The meristematic
cells are thin-walled cells and are in active state of Intercalary
mitosis. meristem

The meristematic cells are compactly packed Fig. 18.2 L.S. of a shoot showing
without leaving intercellular spaces. The cells are
meristematic tissue
small with a distinct nucleus and dense cytoplasm

without vacuoles.

On the basis of location, meristematic tissues are of three types:

i. Apical meristem

ii. Lateral meristem

iii. Intercalary meristem
i. Apical meristem
The meristematic tissue present at the tips of root, stem and their branches is called

apical meristem. It is responsible for axial growth of the plant.

304 Oasis School Science - 9 BIOLOGY

ii. Lateral meristem
The meristematic tissue located along the side of the stem and root is called lateral

meristem. It is responsible for increasing the girth of the plant.
iii. Intercalary meristem
The meristematic tissue located at the base of leaf and fruit is called intercalary

meristem. It increases the length of internodes.

B. Permanent tissue

Permanent tissue is a group of cells that do not have power of cell division. These cells
have specialized permanent shape to perform some fixed functions. The cells may be
either living or dead and thin-walled or thick-walled. Permanent tissues are developed
from apical or lateral or intercalary meristem.

There are three types of permanent tissues found in plants. They are:

a. Simple permanent tissue

b. Complex permanent tissue

c. Special permanent tissue

a. Simple permanent tissue

This type of tissue consists of structurally similar cells forming a uniform mass
and is responsible for a common function. This tissue is further sub-divided into:

i. Parenchyma

ii. Collenchyma

iii. Sclerenchyma

i. Parenchyma

Parenchyma consists of thin-walled living cells which may be oval, spherical,
polygonal, irregular or elongated. In this tissue, cells contain a distinct nucleus
and vacuole. The cells are loosely arranged forming intercellular spaces.
Parenchyma containing chloroplast is called chlorenchyma which is responsible
for photosynthesis.

Parenchyma having air spaces between the cells is called aerenchyma.

Nucleus Cell wall
Cell wall Nucleus
Cytoplasm

(a) Cytoplasm

(b)

Fig. 18.3 Parenchyma (a) in T.S. (b) in L.S.

BIOLOGY Oasis School Science - 9 305

Functions
1. To conduct food and water
2. Protection of underlying parts
3. To manufacture and store food
4. To keep the plant in turgid condition

5. To help in exchange of gases, absorption of water and minerals

ii. Collenchyma

Collenchyma consists of elongated and thick-
walled living cells. In these cells, corners are
thickened due to the deposition of extra cellulose
and pectin at the edges of the cells.

The cells are mostly circular, elongated, oval Fig. 18.4 Collenchyma
or polygonal. Intercellular spaces may or may
not be present. The cells may also contain
chloroplasts.

Location

Collenchyma is found below the epidermis of stem, petiole, pedicel of leaves of dicots, etc.

Functions

1. Collenchyma provides flexibility, elasticity and mechanical support to the plant body.

2. Collenchyma having chlorophyll helps in photosynthesis.

iii Sclerenchyma fibres stone cell

Sclerenchyma consists of very long, narrow and any

thick-walled dead cells with very little or without

cytoplasm. The cell wall is thickened due to the cross section lumen (c)
deposition of cellulose or lignin or both. At maturity, (b)
the cells become dead which cannot elongate.

Location

Sclerenchyma is found in all the hard parts of plants canal solereids
like seed coat, shells of nuts, fibres, flesh of fruits, etc.

Function

Sclerenchyma is responsible for providing mechanical (a) longitudinal
Fig.18.5 Sclerenchyma (a) in L.S.
support and hardness to the concerned part of plant.
(b) in T.S. (c) single fibre magnified

b. Complex permanent tissue

The permanent tissue having various types of cells working together for
performing different but closely related functions is called complex permanent
tissue. This tissue consists of vascular bundles and is responsible for transportation
of materials into various parts of plant. So this tissue is also called vascular or
conduction tissue. It is of two types, viz. xylem tissue and phloem tissue.

306 Oasis School Science - 9 BIOLOGY

i. Xylem

Xylem or wood is a conducting tissue
having four different types of cells. They
are trachieds, vessels, wood fibre and
wood parenchyma. Wood parenchyma
only is the living structure.

Location

Xylem is found in internal parts of root, stem and (d)
leaves of pteridophytes and flowering plants.
(a) (b) (a) Trachieds
Functions (b) Vessels
Xylem is responsible for: (c) Xylem fibres
(c) (d) Xylem parenchyma
1. conduction of water and minerals from
root to the leaves. Fig. 18.6 Components of xylem tissue

2. providing mechanical support and strength to the plant.

3. storage of food and water.

ii. Phloem Sieve plate
Sieve tubes
Phloem is another conduction tissue Sieve tubes
made up of four types of cells. They
are sieve tube, companion cells, (a) Phloem parenchyma (c) Sieve tubes
phloem parenchyma and phloem and companion
fibre. Phloem fibre is the only non- Companion cells (c) cells in L.S.
living structure in phloem tissue. (b) Sieve tubes

Location

Phloem is found in roots, stem and
leaves of plant.

Functions Fig.18.7 Components of phloem tissue

Phloem is responsible for:

1. conduction of prepared food from leaves to various parts of plant.

2. storage of food.

3. mechanical support to the plant.
Differences between Xylem and Phloem

S.N. Xylem S.N. Phloem

1. It is made up of dead cells except xy- 1. It is made up of living cells except
lem parenchyma. phloem fibres.

2. It is responsible for conduction of wa- 2. It is responsible for conduction of
ter and minerals from roots to leaves prepared food from leaves to various
and providing mechanical support. parts of the plant.

3. It is made up of tracheids, vessels, xy- 3. It is made up of sieve tube, companion
lem parenchyma and xylem fibres. cells, phloem parenchyma and
phloem fibres.

BIOLOGY Oasis School Science - 9 307

Activity 1

To observe plant tissue under the compound microscope.
• Take a young stem of cucumber.
• Prepare a transverse section of the stem.
• Prepare a temporary slide and observe it under the compound microscope.
• Draw a neat and labeled figure.

c. Special permanent tissue

It is the modified permanent tissue containing excretory and secretory structures
in the form of glands, ducts, cells, etc. It is mainly of two types:

i. Glandular tissue and ii. Laticiferous tissue

i. Glandular tissue: Glandular tissue secretes various substances like oils, mucilage,
resin, gum, etc. It is found in plants like pine, tobacco, tulsi, pudina, leaves of
orange, lemon, citrus, etc. and in insectivorous plants.

ii. Laticiferous tissue: Laticiferous tissue secretes latex, i.e. milky or yellow or watery
juice. Such tissue is found in plants like Papaya, Banyan, Opium, Calotropis,
Argemone, Euphorbia, etc. It acts as storage tissue or as reservoir of waste products.

18.4 Skeletal System in Human Body

The bony framework of human body is made up of 206 bones of various shapes and sizes.
These bones are joined together to form the skeleton. The skeleton is the general framework
of the body formed by the combination of bones. This framework of bones encloses all the
internal organs giving support, strength and shape to the body. The bones appear like non-
living things but they are made up of living cells. They contain blood vessels and nerves.

The bones of the skeleton are organized into a skeletal system. This system is made up of
bones, joints and connective tissues which support, help in movement and protect the body.
Besides bones, there are three main types of connective tissues in the skeletal system. They are
tendons, ligaments and cartilage. Tendons are tough and inelastic tissues that attach muscles
to the bones. Ligaments are strong and elastic bands of connective tissues that hold two or
more bones together at joints. Similarly, cartilage is an elastic and tough skeletal tissue located
wherever two or more bones come together. It cushions the bones and prevents them from
rubbing together. Small pads of cartilage are found between the vertebrae. These cartilage
pads act as shock absorbers.

18.5 Functions of Skeleton

i. Skeleton gives a definite shape and support to the body.
ii. It provides surfaces for the attachment of muscles.

iii. It protects the delicate organs of our body by forming cavities or sockets. The skull
protects the brain. The rib cage protects the heart and lungs. The vertebral column
protects the spinal cord.

308 Oasis School Science - 9 BIOLOGY

iv. Skeleton helps in the movement of body parts and locomotion.

v. Bones of skeleton contain bone marrow which produces blood corpuscles.

The human skeleton consists of the skull, the backbone, the ribs and the breastbone. There are
two pairs of limbs which are attached to two pairs of girdles. Some bones are long and strong,
some are short and curved whereas some are small and irregular. Most of the short bones are
solid but many of the long bones are hollow.

Cranium

Clavicle Facial region
Humerus Cervical vertebrae

Lumbar vertebrae Sternum
Pelvis Ribs

Femur Radius
Ulna
Carpals
Metacarpals

Phalanges

Patella

Tibia
Fibula

Phalanges Tarsals
Metatarsals

Fig. 18.8 Human skeleton (Anterior view)

18.6 Types of Skeleton

On the basis of location, the bones of skeletal system can be divided into two groups:

A. Axial skeleton
B. Appendicular skeleton

BIOLOGY Oasis School Science - 9 309

A. Axial skeleton

The skeleton formed by the bones of skull, ribcage and vertebral column is called axial
skeleton. This skeleton constitutes the axis or central bony core. The bones of axial
skeleton are further sub-divided into following groups:

i. The skull

The skull is composed of 22 flat and curved bones, joined closely together. The bones of
the skull can be divided into two groups, viz. cranial bones and facial bones.

a. Cranial bones

The upper roof of the skull is made up of eight flat bones interlocked together by
forming a hard bony box called cranium. The cranium protects the most important organ
of our body, the brain. The bones of cranium are connected together at suture. Many
perforations are present in bones through which nerves and blood vessels pass. The
names and number of cranial bones are given below:

S.N. Name Number

1. Frontal bone 1
2. Parietal bone 2
3. Temporal bone 2
4. Occipital bone 1
5. Sphenoid bone 1
6. Ethmoid bone 1
8 bones
Total

Frontal bone Suture
Parietal bone

Sphenoid bone Temporal bone
Nasal bone Occipital bone
Zygomatic bone
Ethmoid bone

Maxilla

Mandible

Fig: 18.9 Human skull

1. Frontal bone: This bone forms the forehead, orbital cavities and the nasal cavity. Frontal
bone is connected with the parietal, zygomatic, nasal, lacrimal, sphenoid and ethmoid
bones.

2. Parietal bone: Two parietal bones form the roof and sides of the cranium. Parietal bones
are connected to the frontal, temporal and occipital bones.

310 Oasis School Science - 9 BIOLOGY

3. Temporal bone: Two temporal bones are located at the base and on either side of the
skull. Temporal bones combine with lower jaw and form a movable joint, which is the
only movable joint of the skull.

4. Occipital bone: This bone is located at the back of the skull and forms its posterior base.
It forms a hinge joint with the atlas, i.e. the first bone of vertebral column. This bone is
connected with the parietal, temporal and sphenoid bones.

5. Sphenoid bone: This bone is located at the base of the skull in front of the temporal
bone. When viewed from above, sphenoid bone appears as a wing-spread bat. This bone
is connected with the frontal, parietal and temporal bones.

6. Ethmoid bone: This bone forms the anterior base of the cranium, orbital cavities and
roof of the nose.

b. Facial bones

There are 14 pieces of flat and irregular facial bones. The names and number of facial
bones are given below:

S.N. Name Number Parietal bone
1. Mandible (lower jaw) 1 Frontal bone
2. Maxilla (upper jaw) 2
3. Nasal bones 2 Temporal bone
4. Zygomatic bones 2 Lacrimal bone
5. Palatine bones 2 Nasal bone
6. Lacrimal bones 2 Vomer
7. Vomer 1 Maxilla
8. Inferior nasal conchae 2
14 bones Mandible
Total
Fig: 18.10

1. Mandible: This bone is located at the base of mouth cavity. It is the only movable bone
of the skull. It forms the lower jaw.

2. Maxilla: Upper jaw is formed by the combination of two bones called maxilla. They form
the roof of the mouth cavity.

3. Nasal bones: Two small long and flat nasal bones form the bridge of the nose.

4. Zygomatic bones: Two zygomatic bones form the upper part of both cheeks below the eyes.

5. Palatine bones: The posterior part of the hard palate is made up of two palatine bones.
6. Lacrimal bones: Two lacrimal bones are located at the innermost corner of eyes near the

lacrimal glands.

7. Vomer: This bone is located at the base of the nose. It looks like the blade of spade.
8. Inferior nasal conchae: These bones are located on both sides of nasal pores, i.e. nostrils.

BIOLOGY Oasis School Science - 9 311

c. Larynx
Hyoid bone: This bone is located in the neck region below the mandible and above

the larynx. It is a horse-shoe shaped bone.

d. Ear ossicles or Auditory ossicles
Three small bones are present in each of the middle ears called ear ossicles. These

bones are malleus (hammer shaped), incus (anvil shaped) and stapes (stirrup
shaped). These bones are not connected directly with the skeletal system.

Malleus Incus Stapes
Fig. 18.11 Ear ossicles

ii. The vertebral column

The vertebral column or backbone consists of 33 small and irregular bones called
vertebrae. Each bone of the vertebral column is called vertebra. The vertebral
column is attached to the base of the skull. It forms the central supporting rod
or bony pillar for the skeleton. Each vertebra has a hole in it. Bones of vertebral
column collectively form a canal called neural canal through which spinal cord
passes. Thus, the backbone protects the delicate spinal cord. The backbone forms
the axis of the trunk. It provides attachment to the head, shoulder girdle, rib cage
and pelvic girdle. The names and number of bones present in the vertebral column
are given below:

S.N. Name Number
1. Cervical vertebrae 7
2. Thoracic vertebrae 12
3. Lumbar vertebrae 5
4. Sacral vertebrae 5 (fused into 1 in adults)
5. Coccyx 4 (fused into 1 in adults)
33 bones
Total

1. Cervical vertebrae: There are seven cervical vertebrae in the neck region. The first and
second vertebrae of this group are called atlas and axis respectively. The atlas articulates
with skull whereas the axis combines with atlas and third vertebra and forms the pivot
joint. The joint helps in the movement of head from side to side.

2. Thoracic vertebrae: There are twelve pieces of bones present in the thoracic region. The
bones of each pair of rib are connected to each thoracic vertebra.

312 Oasis School Science - 9 BIOLOGY

3. Lumbar vertebrae: The five bones of waist region form the lumbar vertebrae. This is the
group of vertebrae having maximum movement. These bones are big and heavy. They
can withstand heavy weight.

4. Sacral vertebrae: It contains five pieces of bones during infancy but in adult stage all
bones of this region fuse to form a single bone called sacrum.

5. Coccyx: It is also called a tail bone. It is made up of four pieces of bones but in adult those
bones fuse together forming a small triangular bone.

iii. The rib cage

Rib cage is made up of 25 pieces of bones. It consists of twelve pairs of thin, flat and
curved bones called the ribs. The ribs are joined to the backbone at the back and the
sternum (breast bone) in the front. The first seven pairs of ribs are called true ribs. They
are directly connected to the sternum. The eighth, ninth and the tenth pairs of ribs are
indirectly connected to the sternum via the seventh pair of ribs. So, they are called false
ribs. Similarly, the 11th and 12th pairs of ribs are short and not connected to the sternum.
So, they are called floating ribs.



Sternum

Ribs

Fig. 18.12 Thoracic cage or rib cage

The rib cage protects the heart and lungs. It also protects the parts of the stomach and
kidneys. It connects upper limbs with axial skeleton. The names and number of bones
present in the rib cage are given below:

S.N. Name Number
1. Sternum 1
2. True ribs 7 pairs
3. False ribs 3 pairs
4. Floating ribs 2 pairs
25 bones
Total

B. Appendicular skeleton

The skeleton formed by the bones of the shoulder girdle with the bones of upper limbs
and the pelvic girdle with the bones of lower limbs is called appendicular skeleton.
Bones of appendicular skeleton are attached to the right and left sides of the axial
skeleton. Appendicular skeleton helps in voluntary movement of the body and body
parts, production of blood cells and protection of vital body parts.

BIOLOGY Oasis School Science - 9 313

i. Shoulder girdle and bones of upper limbs Clavicle
Scapula
Shoulder girdle
Humerus
It is made up of four pieces of bones. Shoulder girdle
supports the bones of upper limbs. This girdle can be
divided into two halves and each half contains two
bones, viz. scapula and clavicle.

Scapula is a triangular flat bone located at the back of Ulna

the rib cage. This bone is also called shoulder blade. It Radius
is connected to the ribs and backbone with the help of

muscles. Scapula articulates with humerus and clavicle. Carpals

Metacarpals

Clavicle is a bow-shaped bone which is attached to Phalanges

the scapula and sternum. Clavicle is connected to the Fig. 18.13 Bones of shoulder girdle
scapula by a strong ligament. and upper limb

Bones of upper limbs

Humerus: It is the largest bone of human hand and the second largest bone of human
body. This bone is connected to the scapula forming ball and socket joint whereas it
articulates with radius and ulna forming the hinge joint.

Radius and ulna: The portion of hand between elbow and wrist consists of two bones,
viz. radius and ulna. The radius lies towards the thumb side and ulna lies towards the
side of little finger. Radius and ulna articulate with carpals forming the wrist joint and
with humerus forming the elbow joint.

Carpals: Wrist contains eight small bones called carpals. These bones are closely fitted
together by ligaments. Carpals are arranged in two rows with four pieces of bones in
each wrist. Carpals are connected anteriorly with metacarpals and posteriorly with
radius and ulna.

Metacarpals: Each palm contains five metacarpals. They are attached to the phalanges
and carpals.

Phalanges: Each hand contains fourteen phalanges in five fingers. Each finger consists
of three phalanges except the thumb which contains only two bones. Phalanges are
connected to metacarpals with ligaments.

S.N. Name No. on either side No. on both sides
A. Shoulder girdle
1. Scapula 1 1 + 1 =2
2. Clavicle 1

B. Bones of upper limbs 1+1=2
3 Humerus 1 1+1=2

314 Oasis School Science - 9 BIOLOGY

4 Radius 1 1+1=2
5 Ulna 1 1+1=2
6 Carpals 8 8 + 8 = 16
7 Metacarpals 5 5 + 5 = 10
8 Phalanges 14 14 + 14 = 28

Total 32 Grand total : 64 bones

ii. Pelvic girdle and bones of lower limbs

Pelvic girdle: Pelvic girdle is made up of two innominate bones. Each innominate bone
is formed by the fusion of three bones, i.e. ileum, ischium and pubis. Innominate bone is
also called hipbone.

This bone contains a cup-like depression called socket which articulates with the round
head of femur. Two hip bones form a space called pelvis. In comparison to men, the
pelvis of women is lighter, rounded and more spacious which provides space for foetus
during pregnancy.

Female Male

Fig. 18.14 Pelvis of female and male

Bones of lower limbs

Femur: Femur is also called thigh bone. It is the longest and strongest bone of the human
body. One end of this bone articulates with hipbone and another end with tibia and
patella. The femur is spongy inside and supports the body weight.

Tibia and fibula: The shank or calf consists of two bones called tibia and fibula. Tibia
is a thick and strong bone of the shank which supports the body weight. Upper end of
this bone articulates with femur and patella whereas lower end with fibula and tarsals.
Fibula is an outer, thin and weak bone of the shank. The upper end of fibula articulates
with the tibia and the lower end with tibia and tarsals.

Patella: It is a flat triangular bone which forms knee cap. This bone is associated with the
knee joint.

Tarsals: The posterior part of each foot consists of seven pieces of bones called tarsals.
Tarsal bones are also called ankle bones. Tarsals articulate with metatarsals and tibia-
fibula. Tarsals are round in shape and arranged in three rows.

Metatarsals: Each foot consists of five metatarsals. They are straight and long. Metatarsals
articulate with tarsals and phalanges.

Phalanges: There are fourteen phalanges in five toes. Each toe contains three pieces of
bones except great toe which contains only two pieces of bones.

BIOLOGY Oasis School Science - 9 315

S.N. Name No. on either side No. on both sides
A. Pelvic girdle
1 1+1=2
1. Innominate bone
1 1+1=2
B Bones of lower limbs 1 1+1=2
2. Femur 1 1+1=2
3. Patella 1 1 + 1 =2
4. Tibia 7 7 + 7 = 14
5. Fibula 5 5 + 5 = 10
6. Tarsals 14 14 + 14 = 28
7. Metatarsals 31 Grand total : 62 bones
8. Phalanges

Total

Activity 2

• Feel the bones in your body starting from the head. Feel the bones on your face, neck,
shoulders, arms, legs and chest, fingers, toes, etc.

• Try to guess the shape and size of each bone. Are there any parts of your body that
do not have bones?

18.7 Human Nutrition and Digestive System

Food is necessary to obtain energy to do work and for the growth of a body. The process by
which living beings obtain and use food is called nutrition. The process of nutrition in human
beings involves five different steps. They are: ingestion, digestion, absorption, assimilation
and egestion.

• Ingestion : The process of taking in food is called ingestion.

• Digestion : Digestion is the process in which the complex food taken in is changed into
simple and absorbable form by the action of various enzymes.

• Absorption : The process of taking in digested food by the body is called absorption.

·• Assimilation : The absorbed food material is utilized by the body to release energy. This
process is called assimilation.

• Egestion : The process by which undigested and insoluble food material is eliminated
from the body is called egestion.

Cells cannot absorb food in the form eaten by an organism. So the complex food is broken into
a simple absorbable form. This process is called digestion. The system formed by alimentary

316 Oasis School Science - 9 BIOLOGY

canal and digestive glands is called digestive system. This system is responsible for ingestion,
digestion, absorption and egestion of food.

Fig. 18.15 Human digestive system

Alimentary Canal and Digestive Glands

The human alimentary canal is a muscular tube which starts from the mouth and
terminates at the anus. This canal includes mouth, buccal cavity, pharynx, food pipe
(oesophagus), stomach, small intestine, large intestine and anus.

The alimentary canal is associated with some glands called digestive glands. They are: salivary
glands, gastric glands, liver, pancreas and intestinal glands.

The mouth forms the entry of alimentary canal. It is guarded by two lips with the help of
which mouth is opened and closed. The mouth contains three pairs of salivary glands. One
parotid gland is present beneath each ear. Similarly, one pair of salivary gland lies below the
tongue and another pair is found in the inner side of the lower jaw. Salivary glands secrete
saliva which contains an enzyme called ptyalin.

Tongue is a soft muscular structure present in the mouth. It helps in chewing food. Mouth
opens behind into a muscular tube called oesophagus or food pipe. It connects pharynx to the
stomach.

Stomach is a large muscular bag-like structure. The part of stomach which is connected to the
oesophagus is called cardiac part and the part which is connected to the duodenum is called
pyloric part. The inner wall of the stomach contains gastric glands which secrete enzymes and
hydrochloric acid.

Stomach is connected to a highly coiled narrow tube like structure called small intestine. It

BIOLOGY Oasis School Science - 9 317

can be divided into three regions, viz. duodenum, jejunum and ileum. Duodenum is a
C - shaped part which is connected to the stomach. It is 30 cm long. It is 30 cm long. Jejunum
is the middle part which is 2.5m long whereas ileum is the posterior part of small intestine
which is connected to the large intestine. The ileum is about 3 m long and is connected. The
wall of the small intestine contains numerous finger-like projections called villi which help to
absorb the digested food. The inner wall of small intestine secretes intestinal juice which
contains various enzymes.

Posteriorly, small intestine is connected with large intestine.

The large intestine can be divided into five major parts. They

are: caecum, ascending colon, transverse colon, descending

colon and rectum. A small blind projection called vermiform

appendix is present at the junction of small intestine and large

intestine. It is a vestigial part and has no role in digestion. The

large intestine is shorter than the small intestine; however, its

diameter is more than that of the small intestine. Large intestine Fig. 18.16 Large intestine
does not produce any enzyme and no absorption of food takes

place here. But water is absorbed by the large intestine from the

undigested food. Rectum is the hind part of large intestine which is connected to the anus.

Process of digestion of food

Food is chewed in the mouth with the help of teeth and mixed with saliva. The saliva softens
the food in mouth. The saliva contains an enzyme called ptyalin or salivary amylase which
acts on starch and converts it into maltose. After chewing, the food is swallowed into the
pharynx. Then the food moves to the stomach through oesophagus.

The muscles of stomach wall contract rhythmically, crushing and mixing the food with gastric
juice. This juice contains two enzymes – pepsin and renin. It also contains hydrochloric acid
which kills microbes present in the food. Pepsin acts upon proteins and converts them into
smaller protein molecules called peptones. Similarly, renin changes milk protein (caesin) into
insoluble curd.

After two to four hours of meal, the food moves into the duodenum in the form of a thick
paste (i.e. chyme) where bile juice from the liver mixes with the food. Bile juice does not
contain any enzyme. However, it helps to digest fat. It also provides an alkaline medium
in the duodenum for the action of enzymes of the pancreatic juice. Pancreatic juice contains
three enzymes – trypsin, amylase and lipase. Trypsin acts on proteins and converts them into
peptones. Similarly, amylase converts starch into maltose and lipase acts on fats and changes
them into fatty acid and glycerol.

From the duodenum, the food moves to ileum where it is acted upon by erepsin, maltase,
sucrase and lactase. Erepsin acts upon peptones and peptides to convert them into amino
acids (simple proteins). Maltase acts upon maltose and converts it into glucose. Sucrase acts
upon sucrose and converts it into glucose and fructose. Similarly, lactase acts upon lactose and
converts it into glucose and galactose. In this way, digestion of proteins, fats and carbohydrates
completes in small intestine.

318 Oasis School Science - 9 BIOLOGY

The inner surface of small intestine contains finger-like projections called villi
(singular - villus). They increase the surface area for absorption of digested food. The digested
food passes through the thin walls of blood vessels and enters the blood stream. This process
is called absorption.

All food cannot be digested and the undigested food passes into the large intestine where
absorption of water takes place. The undigested food forms faeces which move to the rectum
and is passed out of the body through the anus. This process is called egestion.

Digestion Chart

Parts of Digestive Secretion Enzyme Food acted Food converted into
alimentary glands upon

canal

Mouth Salivary Saliva Ptyalin Starch Maltose
glands

Gastric juice Pepsin Protein Peptones

Stomach

Renin Milk Insoluble curd
protein (Paracaesin)
Gastric (Caesin)
glands

Hydrochloric No enzyme Provides acid environment to pepsin
acid and kills bacteria

Liver Bile juice No enzyme Divides fat globules into tiny
droplets to be acted upon by lipase

Pancreas Pancreatic Trypsin Proteins Peptides
juice and
Amylase peptones Maltose
Small intestine Lipase Starch Fatty acid and glycerol
Fats

Intestinal Intestinal juice Erepsin Peptides Amino acids
glands Maltase Maltose Glucose

Lactase Lactose Glucose and galactose

Sucrase Sucrose Glucose and fructose

BIOLOGY Oasis School Science - 9 319

Importance of digestive system

i) Digestive system converts complex food material into simple form which can be absorbed
by body.

ii) It helps to absorb digested food into blood.

iii) It helps to excrete undigested waste products.

18.8 Respiratory System in Human Body

Life is a result of various metabolic activities that take place in a living body without
interruption. Living organisms need energy to perform various physical and metabolic
activities. We eat food to obtain energy. After digestion, the food is absorbed by our body. Thus
absorbed food is oxidized in mitochondria of the cells and energy is released. This process is
called respiration. In this process, water and carbon dioxide are produced as by-products.
Respiration occurs in each and every living cell. Oxygen is essential for respiration. Living
organisms obtain oxygen through breathing. Respiration is the process of releasing energy by
breaking down food in the presence of oxygen.

The system made of nasal cavity, pharynx, larynx, trachea, bronchi and lungs which helps
in exchange of gases is called respiratory system. The respiratory system in human beings
includes nose, nostrils, nasal cavity, pharynx, larynx, trachea, bronchi, bronchioles and lungs.

Nose
Nose is an external organ of respiratory system. It consists of two nostrils. The nasal cavity
consists of two tubular structures separated by a cartilaginous septum. The inner surface of
the nasal passage is lined by ciliated epithelium, mucous secreting cells and hair which check
the entry of microbes and dust particles. Air enters the body and comes out through nasal
passage.

Nasal cavity Pharynx
Mouth cavity Larynx
Trachea
Bronchus
Bronchiole Heart
Right lung Left lung
Diaphragm

Fig. 18.17 Respiratory system

320 Oasis School Science - 9 BIOLOGY

Pharynx

The pharynx is situated at the back of the mouth. It connects nose and throat. From the nasal
cavity, the air moves into the pharynx which is a common area to both digestive and respiratory
tracts. The pharynx opens into the larynx which leads to the trachea. It is also connected to the
esophagus or food pipe. A cartilaginous flap called epiglottis guards the entrance to trachea.
When we swallow some food or drink, the epiglottis covers the trachea to prevent food or
water from entering the respiratory tract.

Larynx

The larynx or voice box or Adam's apple is a cartilaginous box-like structure, located at tracheal
opening. It is hollow form inside. When we swallow some food material, the larynx moves up
and down allowing safe passage of food or air. Larynx also contains vocal cords which vibrate
and produce sound while speaking.

Trachea or wind-pipe

Trachea or windpipe is a tube that extends into thoracic cavity. Its length is about 11 cm and
diameter is about 2.5 cm. It lies on the ventral surface of the esophagus. It consists of C-shaped
cartilaginous rings.

Bronchi and bronchioles

At its lower end the trachea divides into two branches called bronchi (singular-bronchus). The
right bronchus is divided into three bronchi which extend separately into three lobes of the
right lung. Similarly, the left bronchus is divided into two bronchi penetrating into the two
lobes of the left lung.

Within the lung, each bronchus is divided many times into bronchioles which are about 0.5
mm in diameter. There are about 700 million alveoli present in lungs. Alveoli are the actual
sites of respiratory exchange. So they are called functional unit of lungs. Each alveolus has a
dense layer of capillaries on its outside. The exchange of gases occurs in these capillaries.

Lungs

The lungs are a pair of highly elastic, hollow, bag-like structures situated in the thoracic cavity,
along with the heart. The broad lower surface of the lungs rests on a sheet of muscle called
the diaphragm which forms the floor of the thoracic cavity. The right lung is larger than the left
one. The right lung is divided into three lobes whereas the left lung has two lobes. Numerous
bronchioles, alveoli, arteries, veins and capillaries are found inside lungs. About 700 million
alveoli are found in both lungs of adult human being. The lungs are surrounded by a narrow
space called pleural cavity which is fixed by two membranes called pleural membranes. These
membranes secrete an oily substance called pleural fluid which occupies pleural cavity. This fluid
acts as a lubricant to reduce friction between the lungs and the thoracic wall during breathing.

Mechanism of Breathing

Breathing involves two steps, viz. inhalation or inspiration and exhalation or expiration.
We normally breathe about 18-20 times per minute. The depth and frequency of breathing
increases during and immediately after physical exercise (about 20-25 times per minute).

BIOLOGY Oasis School Science - 9 321

Inhalation is an active energy-requiring process involving contraction of diaphragm and inter
coastal muscles. This produces a forward and backward movement of ribcage. This process
straightens and contracts the diaphragm. This results in an increase in the volume of the
thoracic cavity and is followed by an increase in the volume of lung. As the lungs expand,
the air pressure in them reduces and so air rushes into them from the atmosphere through air
passage.

Exhalation or breathing out is brought about by relaxation of the inter-coastal muscles and
diaphragm. The ribs return to their original position and the diaphragm becomes dome-
shaped. Both these movements reduce the thoracic cavity volume and the lungs return to
their original size. The air rushes out of the lungs due to the increase in pressure above that of
the atmosphere inside the lungs.

The concentration of oxygen in lung alveoli is higher than that in the de-oxygenated blood in
capillaries. This difference causes oxygen to diffuse from the alveoli into the lung capillaries
since diffusion continues so long as the molecules concerned are unequally distributed. The
blood contained in the capillaries has high concentration of carbon dioxide which it has
absorbed from body tissues. Therefore, carbon dioxide diffuses out form blood capillaries into
the alveoli.

Internal Respiration

Internal respiration involves the oxidation of food (glucose) to release energy. In this process,
water and carbon dioxide are formed as by–products. Various enzymes help in this process.

Glucose + Oxygen Enzymes Energy + Water + Carbon dioxide

C6H12O6 + 6 O2 Enzymes Energy + 6 H2O + 6 CO2

Internal respiration takes place in mitochondria of a cell. So, this process is also called cellular
respiration. The energy released is stored in the form of ATP (Adenosine Triphosphate)
molecules. Thus released energy is utilized to operate various life activities.

Differences between External Respiration and Internal Respiration

S.N. External Respiration S.N. Internal Respiration

1. It involves inhaling of oxygen and 1. It involves oxidation of food into
exhaling of carbon dioxide. energy, water and carbon dioxide.

2. It takes place outside the cell. 2. It takes place inside the cell.

3. No energy is released in this process. 3. Energy is released in this process.

Importance of respiratory system
(i) It supplies oxygen required to the body.
(ii) It helps to exhale carbon dioxide gas.
(iii) It helps to release energy required to perform various metabolic activities of the body.

322 Oasis School Science - 9 BIOLOGY

18.9 Excretory system

Various metabolic activities take place in all living organisms. Those activities are chemical
reactions. Various products are formed due to these reactions. Some of these products may be
poisonous or toxic to the organisms if allowed to accumulate inside the body. All organisms
contain special organs to remove waste materials. The process of removing waste materials,
formed as a result of chemical reactions in the body, is called excretion. The system which is
responsible for excretion is called excretory system. This system consists of a set of excretory
organs. The main excretory organs are kidneys and lungs.

Human beings have well developed urinary system which is responsible for eliminating urea.
This system is made up of a pair of kidneys, ureter, urinary bladder and urethra. Kidneys
are bean-shaped organs present on either side of the backbone. They convert urea into urine.
Ureter leads out from each kidney which carries urine from kidneys to a pouch-like urinary
bladder. It has a tubular structure called urethra through which urine is eliminated from the
body.



Kidneys Cortex Renal artery
Medulla Renal vein
Ureter
Ureter
Urinary bladder
Urethra

Figure 18.18 (a) Urinary system Fig. 18.18 (b) Detailed structure of kidney

Besides urinary system there are various organs that help in excretion of various waste
materials. These organs are lungs, liver, large intestine and skin.

Lungs
During cellular respiration, carbon dioxide and water are formed as by–products, carbon
dioxide and excess water are eliminated in the air exhaled by the lungs through nose.

Liver
Liver produces bile pigments from the haemoglobin of broken RBCs. It also converts toxic
ammonia produced by the body cells into urea. Urea is then carried to the kidneys through
blood circulation, from where it is eliminated.

Large Intestine
Our body cannot digest all food particles eaten by us. The undigested food particles are
eliminated out by large intestine through the rectum and anus.

Skin
Skin excretes urea, salts, excess of water and other waste materials in the form of sweat.
These waste materials are carried away by blood from various body parts to sweat glands
in the skin.

BIOLOGY Oasis School Science - 9 323

Importance of Excretory system

i) Excretory system helps to remove waste products like urea, uric acid, etc. in the form
of urine.

ii) Excretory system helps to transport waste materials released during metabolic activities
to the excretory organs for removal from the body.

iii) Kidneys play an important role in excretion of waste products. They excrete waste
products in the form of urine.

SUMMARY

• A cell is defined as the basic, structural and functional unit of life capable of
independent existence.

• A group of cells having a common origin and performing similar function is
called a tissue.

• The microscopic study of tissues and their functions is called histology.

• An organ is a part of an animal or a plant having a characteristic function, shape
and structure.

• Permanent tissue is a group of cells that do not have power of cell division.

• The skeleton is the general framework of the body formed by the combination of
bones.

• The human skeleton consists of the skull, the backbone, the ribs and the breastbone.
There are two pairs of limbs which are attached to two pairs of girdles.

• Bones of vertebral column collectively form a canal called neural canal through
which spinal cord passes.

• The rib cage protects the heart and lungs. It also protects the parts of the stomach
and kidneys. It connects upper limbs with axial skeleton.

• The skeleton formed by the bones of the shoulder girdle with the bones of upper limbs
and the pelvic girdle with the bones of lower limbs is called appendicular skeleton.

• The process by which living beings obtain and use food is called nutrition.

• The digested food passes through the thin walls of blood vessels and enters the
blood stream. This process is called absorption.

• The system made of nasal cavity, pharynx, larynx, trachea, bronchi and lungs
which helps in exchange of gases is called respiratory system. The respiratory
system in human beings includes nose, nostrils, nasal cavity, pharynx, larynx,
trachea, bronchi, bronchioles and lungs.

• The process of removing waste materials, formed as a result of chemical reactions
in the body, is called excretion. The system which is responsible for excretion is
called excretory system. This system consists of a set of excretory organs. The
main excretory organs are kidneys and lungs.

• Human beings have well developed urinary system which is responsible for
eliminating urea. This system is made up of a pair of kidneys, ureter, urinary
bladder and urethra.

324 Oasis School Science - 9 BIOLOGY

Exercise

Group-A

1. What is a cell? What is it made of?

2. Name two types of tissues found in plants.

3. What is meristermatic tissue? What are its types?

4. What is apical meristem? Write down its function.

5. Where is lateral meristem located? Write its function.

6. What is permanent tissue? What are its types?

7. Write any two characteristics of permanent tissue.

8. What is parenchyma?

9. What are complex tissues?

10. Write two functions of each xylem and phloem tissue.

11. What is special tissue? Write its major functions.

12. What is skeletal system?

13. How many bones are found in human skeleton?

14. What is axial skeleton? How many bones form axial skeleton?

15. Write any two functions of skeletal system.

16. Write any two functions of human skull.

17. Where is palatine bone located?

18. Name the bones of skull which are not found in pair.

19. Define tendon and ligament.

20. What is synovial fluid? Where is it located?

21. What is the major function of synovial fluid? Write.

22. What is pelvis? Write down its function.

23. Which part of the human body are following bones found?

i) vomer ii) temporal bone iii) femur iv) radius v) atlas vi) carpal

vii) patella viii) occipital ix) tarsal

24. Name the bones found in human internal ear.

25. Name the longest bone of human body and write the major function of the bones of ver-
tebral column.

26. Name the following bones:

i) Bone that connects ribs together ii) Bone of the forehead

iii) Bone of larynx iv) Bone that connects skull to the backbone

v) Bone of the finger vi) Bone of the palm

BIOLOGY Oasis School Science - 9 325

27. What is pelvic girdle? Write down the names of bones found in it.
28. Write down the number of bones found in the given body parts:
i) Skull ii) Coccyx iii) Sacral vertebrae iv) Cervical vertebrae
29. How many groups the bones of human body can be divided on the basis of shape? Write.
30. What is meant by human nutrition?
31. What is digestive system?
32. What is respiratory system?
33. What is excretory system?
34. What is the function of kidney?

Group-B
1. `Why is cell called the basic unit of life?

2. Write any two differences between tissue and organ.

3. The growth of a plant stops if its apex is cut, why?

4. Differentiate between parenchyma and sclerenchyma.

5. A plant dies if its phloem tissue is removed, why?

6. Write any two differences between simple tissue and complex tissue

7. Differentiate between xylem and phloem in any two points.

8. The pelvic girdle of women is wider than that of men, why?

9. The bone kept in hydrochloric acid becomes soft, why?

10. Differentiate between axial skeleton and appendicular skeleton.
Group-C

1. What is the relationship among cell, tissue, organ and system in a living body? Describe
in brief.

2. What is skull? How many bones are found in the skull? Write down any two functions
of human skull.

3. What is synovial fluid? Where is it located? What is the major function of synovial fluid?
Write?

4. What is excretory system? Name the organs that takes part in this system. Write the
major functions of special tissue.

5. Write down the names and number of bones found in human lower limb.

6. Describe the mechanism of breathing.

326 Oasis School Science - 9 BIOLOGY

Group-D
1. Write any two characteristics of each parenchyma and scelerenchyma with figures.
2. Label the bones A, B, C and D shown in the given figure. Differentiate between xylem

and phloem in any two points.

AE

F
BG

H
C
D

3. What would happen if there were no skeleton in human body? Draw a neat and labelled
figure of digestive system.

4. Write down the names and number of bones found in the lower limb of human skeleton.
5. Write down the importance of respiratory system. Draw a neat and labelled figure of

respiratory system.

BIOLOGY Oasis School Science - 9 327

UNIT 19 Estimated teaching periods

Theory 2

Practical 0

SENSE ORGANS Human eye

Objectives

After completing the study of this unit, students will be able to:

• explain the structure of sense organs of human body and describe their
functions.

19.1 Introduction

All living organisms are sensitive. They respond to physical and chemical changes in their
environment. All environmental changes, external and internal, are known as senses or
stimuli (singular–stimulus). The special organs of the body which detect the changes in the
environment are called sense organs. The major sense organs and their receptors are as follows:

1. Eyes (organs of sight) or photoreceptors

2. Ears (organs of hearing and equilibrium) or statoacoustic receptors

3. Nose (organ of smell) or olfactoreceptors

4. Tongue (organ of taste) or gustatoreceptors

5. Skin (organ of touch) or tangoreceptors

19.2 Terminology

• Stimulus : A physical or chemical event that affects an organism and excites
its receptors is called stimulus. Examples: mechanical stimuli
(touch and pressure), chemical stimuli (smell and taste); and
thermal stimuli (heat and cold).

• Sensation : A general state of awareness of stimulus is called sensation.

• Receptors : Receptors are the special cells that receive stimulus from the
environment. They are found in sense organs.

• Photoreceptors : The receptors that respond to light are called photoreceptors,
e.g. rods and cones in eye.

• Chemoreceptors : The receptors that respond to chemicals are called
chemoreceptors, e.g. taste buds.

• Thermoreceptors : The receptors that respond to heat or change in temperature are

328 Oasis School Science - 9 BIOLOGY

called thermoreceptors, e.g. nerve fibres in skin.

• Mechanoreceptors : The receptors that respond to touch are called mechanoreceptors,
e.g. nerve fibres around hair.

19.3 Eyes: Organs of Sight

The sense of sight is due to stimulation of the eyes. Vision or sense of sight is the most important
of all body senses.

External morphology

Humans have two eyes located in orbital cavities on the front side of the head. Each eye is a
hollow, spherical organ which measures about 2.5 cm in diameter. Each eye ball can be rotated
with the help of distinct muscles. Each muscle is attached at one end to the eyeball and at the
other to the orbit.

The frontal exposed part of the eyeball is Ciliary Sclerotic layer
called cornea. Movable upper and lower muscle Choroid
eyelids are folds of skin and muscle lined Retina
by conjunctiva. Eyelids can close the Iris
eyes, when required, and protect them Aqueous Yellow spot
from dust particles and excessive light. humour Blind spot
The upper eye-lid is more movable than Optic nerve
the lower one. The stiff hairs of eyelashes Pupil
present on the free edges of eyelids and Cornea Vitreous humour
Eye lens

Conjuctiva
Suspensory

ligament

eyebrows guard the eyes against foreign Fig.19.1 Morphology of human eye

particles, rain, sweat and glare (a very

bright unpleasant light). The nictitating membrane in human eye is vestigial and represented

by a pink semilunar mass.

Glands

Lacrimal glands or tear glands are a group of glands that produce and pour tears. A lacrimal
gland is situated at the upper side of each orbit towards its outer corner. It secretes a slightly
saline and antiseptic fluid, the tears. Blinking spreads this fluid over the surface of eye and
serves as a lubricant. It cleans the front surface of eye by washing away dust particles. It
keeps the eye moist, soft, clean and free from bacteria. Tears kill the germs and also help in
communicating emotions.

Internal morphology

A vertical section of eyeball reveals that it is hollow from within. Its wall is made up of three
layers of tissues in close contact—an outermost sclerotic or sclera, middle choroids and the
innermost retina.

vestigial /veˈstɪdʒɪəl/ - remaining as the last small part of sth that used to exist Oasis School Science - 9 329
BIOLOGY

A. Sclerotic layer

It is the outermost covering layer of eyeball made up of dense connective tissue fibres. It
provides strength to the wall. It can be divided into two regions – the posterior portion
called sclera, and the anterior portion called cornea.

The sclera is an opaque white coat of dense fibrous tissue which covers the entire eyeball
except iris. It gives shape to the eyeball and also protects the inner parts.

The anterior exposed part of sclerotic bulges out slightly and forms a transparent cornea.
Its outer surface is intimately covered with a thin transparent, epidermal layer called
conjunctiva. It is supplied with free nerve endings and blood capillaries and is connected
with the epidermis lining of eyelids.

Note: The surface of the eye is exposed to various external influences like infections and
allergic reactions. Sometimes the conjunctiva turns red due to viral infection called
conjunctivitis.

B. Choroid

It is the middle layer of eyeball made up of a thin layer of connective tissue. It is heavily
pigmented and richly vascular. Its dark pigmentation absorbs light rays reducing internal
reflections that might blur the image.

The choroid lines only the posterior region of sclera. Anteriorly, near the junction of
sclera and cornea, the choroid enlarges to form ciliary body. It contains ciliary muscles
and projects into vascular folds called ciliary processes, which secretes the aqueous
humour.

In front of the ciliary body, the choroid becomes widely separated from cornea, forming
the iris. It is visible from outside as an opaque brown disc, perforated in the centre by a
round hole called pupil. The iris contains two sets of smooth muscles, circular and radial.
The pigmented iris prevents the light from entering the eye except through the pupil.
The pupil can be constricted or dilated due to the action of iris muscles. The size of pupil
regulates the amount of light entering the eye.

Lens

A crystalline, solid and biconvex lens is present just behind the pupil. The lens divides
the eyeball into two chambers. The lens is made up of concentrically arranged layers of
transparent fibres enclosed within a thin transparent lens capsule. The lens is held in
position by suspensory ligaments which attach it to ciliary body. The thickness of the
lens is controlled by the contraction and relaxation of the ciliary muscles so that the
image is formed on the retina. If the objects are nearer, the lens becomes thick and if the
objects are farther, the lens becomes thin.

Chambers

The iris, lens and the suspensory ligaments divide the internal cavity of the eye into two
unequal chambers, viz. aqueous chamber and vitreous chamber.

The aqueous chamber lies in between the lens and cornea. It is a smaller chamber filled
with a clear, thin, lymph-like watery fluid called aqueous humour. It keeps the lens moist
and protects it from mechanical shock.

330 Oasis School Science - 9 BIOLOGY

The vitreous chamber lies in between the lens and retina. It is a larger chamber filled with
a gelatinous secretion called vitreous humour. It prevents the eyeball from collapsing
and helps to support the retina.

C. Retina

Retina is the innermost transparent layer sensitive to light. It consists of an outer
non-nervous pigmented layer and the inner nervous layer containing two types of
photosensitive cells – rods and cones. Retina is connected to the optic nerve.

Rods are more sensitive to light of low intensity and are suitable for night vision. They
do not respond to colour. Cones are sensitive to light of high intensity (bright light) and
are more suited for day vision. Cones produce a sharp image with fine details. They are
responsible for colour vision. Colour perception in mammals is confined to man and
primates only.

The distribution of rods and cones within the retina is not uniform. Rods are more
concentrated towards periphery whereas cones are more concentrated towards the centre.

Yellow spot – the area of best vision

It is a spot located in the centre at the back of the eye. It contains a maximum number
of photosensitive cells, the cones. The yellow spot is the region of colour vision and the
brightest vision.

Blind spot -- the area of no vision

It is the spot of retina just below the yellow spot. In this spot, retinal cells are not present
so no image is formed here. Blind spot is the spot of no vision.

Working mechanism of human eye

The light rays coming from the object enter the eye through cornea and then pass
through the pupil. The eye-lens refracts the light rays and forms a real, inverted and
highly diminished image on the retina. When the light rays fall on the sensory cells, i.e.
rods and cones, they get activated and generate electric signals. Those signals are sent
to the brain by optic nerves. The brain intercepts the signals and renders the erect and
correct image of the object.

Aqueous Iris Lens Vitreous chamber
chamber Cornea
Retina
Inverted image
of object

Object Pupil
Liquid
Optical nerve
Ligaments Jelly
Cilliary muscle

Fig.19.2 Working mechanism of human eye


BIOLOGY Oasis School Science - 9 331

Dim light vision and night blindness

In dim light, a maximum amount of rhodopsin is present in the rods. On coming out of
a dark cinema hall in bright day light, one feels dazzled until the level of rhodopsin is
reduced in the rods. Conversely, one cannot see properly when going from a bright light
to a dark room until the level of rhodopsin has increased in the rods.

Night blindness is a condition in which there is difficulty in seeing in dim light. This is
because of the non-production of rhodopsin pigment in the rods as only rods function in
dim light. It is most often caused by deficiency of vitamin A. Vitamin A is first converted
into retinene and then into rhodopsin. Therefore, deficiency of vitamin A in the body
may result in night blindness. It can be cured by having a diet rich in vitamin A.

Colour vision and colour blindness

The exact nature of colour vision is not understood. It is known that cones of retina are
stimulated by very strong light and they distinguish colours. The light sensitive pigment
of cones is iodopsin.

Colour blindness is the condition in which a person is unable to distinguish between red
and green colours. This is a genetic disorder. It cannot be treated life long.

Activity 1 19.3 (a) Pupil of the eye becomes
larger in dim light.
To observe the effect of light on the size of pupil
• Make a group of four friends and observe the size of 19.3 (b) Pupil of the eye becomes
smaller in bright light.
pupil of each other.

• Now, ask any two friends to stay in bright light for
ten minutes and remaining friends to stay in a dark
room for the same time.

• Return to your class room and observe the size of pu-
pil of each other.

• What change in the size of pupil can you notice?

• Prepare a short report and discuss in your class.

Care of the eyes
i. We should wash our eyes regularly with clean water.
ii. We should not work in dim light or very bright light which tires the eyes.
iii. We should not read in a moving vehicle which strains our eyes.
iv. We should not rub our eyes with a dirty towel or dirty hands which may cause

infection. We should not use anyone else's towel or handkerchief.

19.4 Ears: Organs of Hearing and Equilibrium

The senses of hearing and equilibrium are associated with a pair of ears. Humans have two
ears, one on either side of the head in temporal region. Human ear consists of a miniature
receiver, an amplifier and a signal processing system. The human ear can be divided into

332 Oasis School Science - 9 BIOLOGY

three regions – external ear, middle ear and inner ear. All these three parts are concerned with
hearing, but only the internal ear is concerned with equilibrium or balancing.

A. External ear

The external ear, also known as pinna, is the visible, oval and skin covered cartilaginous
projection from the side of the head. It surrounds the opening of tubular passage called
auditory canal. It leads into the skull terminating at a cone-shaped delicate membrane
called tympanic membrane or eardrum.

The auditory canal, fine hairs, oil and wax prevent dust particles and small creatures
from entering and damaging the delicate ear drum.

B. Middle ear

The middle ear is a small air-filled cavity which is enclosed in a bony chamber. It is
separated from the external ear by the eardrum and from the inner ear by a thin bony
partition having oval window and round window.

The middle ear contains a chain of three small bones called ear ossicles or auditory
ossicles. These bones are malleus (hammer-shaped), incus (anvil-shaped) and stapes
(stirrup-shaped). The handle of malleus is attached to the inner surface of the eardrum
and its opposite end is connected with the incus. The incus is articulated with the head
of the stapes. The flat part of stapes fits into the oval window.

Ear Ossicles Semicircular
Malleus Incus Stapes canals

Vestibular
nerve

Tympanic Tympanic cavity Cochlea Cochlear nerve

membrane Eustachian tube

Pinna (outer ear) External auditory canal

Fig. 19.4 External and internal details of human ear

The anterior wall of the middle ear contains an opening that leads directly into the
Eustachian tube. It connects the middle ear with the throat. Its opening into throat
normally remains closed, but when we swallow or yawn, it opens so that air can pass
from pharynx into the middle ear cavity which equalizes the air pressure on both sides
of the eardrum. This prevents distortion of eardrum by a pressure differential on the two
sides.

If one climbs a high mountain, or goes up a long steep hill in a car or rapidly gains
height in an aircraft, the atmospheric pressure is suddenly reduced outside the eardrum.
Similarly, if one goes down into a mine or goes for scuba diving, this pressure is increased.

BIOLOGY Oasis School Science - 9 333

During such occasions, chewing of sweets helps to equalize air pressure on both sides of
the eardrum via Eustachian tube.

C. Inner ear

The inner ear is the essential and delicate structure containing sensory cells. It is also
called membranous labyrinth. It has two main parts, viz. cochlea and semicircular canals.

Cochlea is a hollow, spiral-shaped conical chamber which resembles a snail's shell. It
consists of a bony spiral canal that makes about 2.75 turns around a central bony core. Its
inner spiral cavity contains three parallel canals filled with endolymph.

The middle canal contains an organ of hearing called organ of corti. It contains a series of
nerve cells and hair cells which join the auditory nerve and help in auditory sensation.

The inner ear also contains three semicircular canals which are arranged at right angles
to each other in three different planes – one horizontal and two vertical. These canals are
filled with a fluid called endolymph. One end of each canal enlarges to form an ampulla.
The ampulla contains sensory cells which help in balancing the body while moving. The
nerve fibres arise from these cells which join the auditory nerve.

There is a short vestibule that connects cochlea and semicircular canals. It contains two
small sacs – the sacculus and utriculus. They also contain tiny hair cells which help in
static balance of the body while at rest.

Mechanism of hearing

The pinna collects and amplifies sound waves which then pass through auditory canal to
the eardrum. Sound waves strike the eardrum and produce vibrations in the thin stretched
membrane called eardrum. The eustachian tube equalizes air pressure on either side of the
eardrum which allows a free vibration. The vibration reaches ear ossicles in the middle ear.
The lever-like action of malleus and incus magnifies the vibration of stapes and the vibrating
stapes transmit vibrations to the membrane of the oval window. Vibrations from oval window
transmit to cochlea which leads to vibration of fluid in the cochlear canals. This vibration
triggers the movement of hair cells of organ of corti in cochlea.

Auricle Incus Scala Scala
vestibuli tympani
Malleus
External auditory canal Owivnadlow

Cochlea

Tympanic membrane Stapes Organ of Corti
(Ear drum)
Sound waves Round window
Basilar membrane

Outer ear Middle ear Inner ear

Fig.19.5 Mechanism of hearing

The movement of hair cells is converted into a nerve signal which is transmitted to the brain
via auditory nerve. As a result, we hear the sound.

334 Oasis School Science - 9 BIOLOGY

Mechanism of balancing

The sensory hair cells in semicircular canals are concerned with dynamic equilibrium, i.e.
balance of the body while it is in motion. Similarly, sensory cells in utriculus and sacculus are
concerned with static balance with respect to gravity.

The movement of fluid inside semicircular canals triggers hair cells in them. This sensation
passes to nerve cells and then to the brain. The three canals are at right angles to each other so
that the brain can detect even the slightest tilting in any direction.

Movement stimulates hair
cells, which sends a signal
through the sensory nerve

Cupula

Hair cell

Head stationary Sensory
nerve

Head moving

Fig.19.6 Mechanism of balancing the body

Care of the ears

i. We should not clean our ears with a matchstick or hairpin which may injure the
eardrum inside.

ii. We should use a clean towel to dry our ears.
iii. We should not let the water enter the ears.
iv. We should visit a doctor in case of earache.

Reasonable fact-1

When one rotates for 2 to 4, times, he/she feels dizziness. Why?

The semicircular canals help to balance the position of body with respect to gravity.
When one rotates for 2 to 4 times, the fluid inside semicircular canals spins which
creates strong shock in the cerebellum. Due to this, the cerebellum cannot work
properly and the person feels dizziness.

Reasonable fact-2

Why does a person feel difficulty in hearing when the eardrum gets ruptured? Give reason.

Eardrum is the part of ear which receives and transmits the sound to the brain
through cochlea. If it is damaged, it receives less sound which cannot pass into the
brain to hear properly. Due to this reason, a person feel signals difficulty in hearing
when the eardrum gets ruptured.

BIOLOGY Oasis School Science - 9 335

19.5 Nose: Organ of Smell

The sensation of smell is due to the stimulation Frontal sinus Superior turbinate
of olfactory cells present in the nasal epithelium. Sphenoid sinus

The receptors of smell or olfactory sense are

located in the epithelial cells of nasal cavity. The

olfactory cells have hair-like projections, called

olfactory hairs. Those hairs react to odours in

the air and then stimulate olfactory cells. The Nasal vestibule

substances to be smelled are dissolved in the Eustachian tube

mucous secretion of the nose. The olfactory Fig. 19.7 Internal details of nose with smell receptors
cells generate electric signals (impulses). Those

impulses are transmitted to the brain by the olfactory nerves. As a result, sensation of smell

can be received.

The sensation of smell is felt very quickly and only a minute quantity of a substance needs
to be present in air for it to be smelled. The sense of smell is fatigued very fast. If we smell
something repeatedly, after sometime we become accustomed to the smell and we no longer
sense its smell.

Care of the nose
i. We should keep our nostrils clean by blowing our nose gently.
ii. The hairs inside the nose keep out dust in the air. So, we should breathe through

our nose.

iii. We should inhale steam to clear a blocked nose.

19.6 Tongue: Organ of Taste Bitter
Taste buds
The sensation of taste is due to the stimulation of
gustatory cells present in the tongue. Tongue is Sour
a soft, large, mobile and muscular organ located
on the floor of the buccal cavity. Its undersurface Salty
remains attached to buccal floor except for the free Sweet
rounded anterior end. The dorsal surface of the
tongue is marked by a median groove. Numerous Fig.19.8 Various sites of tastes in tongue
papillae containing taste buds are present on the
dorsal surface of the tongue.

The taste buds are oval bodies having three types
of cells – supporting cells, gustatory cells and
basal cells. Each gustatory cell contains a hair-like
process which projects outside through an opening
in taste bud called the taste pore. The substance in
solution form enters these pores and stimulates the
sensory hair.

The taste buds are found in small knob-like elevation on the tongue called papillae. These
papillae give the rough appearance to the upper surface of the tongue.

336 Oasis School Science - 9 BIOLOGY

There are basically four primary taste

sensations in humans. These tastes are – sweet, Taste pore

salty, sour and bitter. All other sensations are Epithelium

combination of these four tastes. Sensory cells
Supporting cells
Each of the four taste sensations is located in
a special region of the tongue. The tip of the
tongue is sensitive to sweet and salty tastes,

the sides are sensitive to sour taste and the

posterior part of the tongue is sensitive to bitter Nerve
taste.
Fig. 19.9 Structure of a taste bud

Flavour is a combination of taste and smell, in

which both senses, i.e. gustatory and olfactory

receptors are stimulated at the same time. Therefore, we cannot receive proper taste of food

when we suffer from common cold.

Activity 2

• Bring an apple, a boiled potato, an onion, a knife and a scarf.

• Cut the apple, potato and onion into pieces. Cover your friend's eyes with the scarf.
Make him/her hold the nose.

• Feed each of these to your friend. Give the onion last as its strong taste might spoil
other tastes. Can your friend tell you what he/she is being fed?

• Now, ask your friend to try each food again. As he/she tastes, hold another type of
food under his/her nose at the same time. Does the smell make the taste different?
Smell has a role in our sense of taste. Without a sense of smell, the apple, potato and
onion would taste much the same.

• Discuss this in your class and prepare a short report.

19.7 Skin: Organ of Touch

The sensation of touch, temperature Hair
and pain are due to the stimulation of
tangoreceptors present in the skin. Skin Epidermis
is the outermost covering layer of human
body. The skin consists of two layers, viz. Dermis Sebaceous gland
epidermis (the outer lifeless layer) and
dermis (the inner living layer). Sweat gland Nerve
Blood Root of hair
The epidermis is the outermost layer of
skin formed of stratified epithelium. It is vessels
the lifeless tissue without blood vessels.
It is the tough and protective layer of Fig.19.10 Detailed structure of human skin
skin.

BIOLOGY Oasis School Science - 9 337

The dermis is the inner thick layer of connective tissue made up of elastic fibres. It is the living
layer of skin and rich in blood vessels. The blood vessels in the dermis play a role in regulating
body temperature. Dermis contains nerve fibres, sensory cells, hair follicles, sweat glands,
sebaceous glands, etc.

Skin protects the underlying organs against mechanical injuries. It regulates the body
temperature and prevents the excessive loss of water. The skin is richly supplied with
cutaneous sensory receptors. Those receptors help in sensing touch, pain, pressure, heat, etc.

Care of skin

i. We should wash our skin regularly with soap and water.

ii. We should wear clean and comfortable clothes to allow the fresh air during
summer.

iii. A cut or scratch on the skin should be treated with antiseptic to stop the growth of
microbes.

SUMMARY

• Sense organs are the special organs in the body which detect the changes in the
environment, e.g. eyes, ears, nose, etc.

• Receptors are the cells present in the sense organs that receive stimulus from the
environment, e.g. photoreceptors, chemoreceptors, etc.

• There are five major sense organs in human body, viz. eyes, ears, nose, tongue
and skin. These sense organs are sensitive to sight, sound, smell, taste and touch
respectively.

• Eyes are the sense organs responsible for receiving the sensation of vision.

• The eyeball has three layers – sclerotic, choroids and retina.

• The retina of the eye contains photosensitive cells called rods (sensitive to dim
light) and cones (sensitive to bright light and colour vision).

• Ears are the sense organs responsible for hearing and balancing.

• The human ear can be divided into external ear, middle ear and inner ear.

• Nose is the organ of smell which receives the sensation of smell with the help of
olfactory cells present in the nasal epithelium.

• Tongue is the sense organ responsible for sensation of taste.

• Human tongue contains many taste buds having taste cells.

• Human tongue can detect four types of tastes – sweet, salty, sour and bitter.

• The skin is richly supplied with cutaneous sensory receptors which help in
sensing touch, pain, pressure, heat, etc.

338 Oasis School Science - 9 BIOLOGY

Exercise

Group-A
1. What are sense organs?
2. Write down the function of:
i) Pupil ii) Lens iii) Retina iv) Ciliary muscle v) Cornea
3. Name any two layers that form the wall of eye.
4. What is aqueous humour? Write down its function.
5. What is vitreous humour? Write down its function.
6. Write down the functions of iris and optic nerve
7. What do you mean by the window of a human eye?
8. What is conjunctiva? Write down its function.
9. What is colour blindness? Write down its cause.
10. Write down the function of:
i) semi-circular canals ii) auditory canal iii) eardrum iv) cochlea
11. Name the parts of tongue that perceive the given tastes:
i) sour ii) bitter iii) sweet iv) salty
12. Where is Eustachian tube located? Write down its function.
13. Name the three bones present in middle ear.
14. What is the function of nose? Write.
15. What are olfactory nerve and optic nerve?
16. In which condition does the ear drum rupture?
17. What are taste buds?
18. What are different types of taste buds found in human tongue? Write with a figure.
19. What is cochlea? Write down its function.
20. Name the sense organ that balances our body.

Group-B
1. Differentiate between aqueous humour and vitreous humour.
2. Eyes and ears are called sense organs, why?
3. Write any two differences between rods and cones.
4. The pupil of eye becomes small when we see in bright light, why?
5. Differentiate between optic nerve and auditory nerve.
6. When we enter a cinema hall at once from a bright place, nothing can be seen

immediately, why?

BIOLOGY Oasis School Science - 9 339

7. Differentiate between olfactory nerve and optic nerve.

8. A person feels dizziness after rotating 2-4 rounds, why?

9. Chocolate is chewed while travelling by aeroplane, why?

10. Sweet taste is felt earlier than the bitter taste, why?

11. We cannot see properly when we come out in a bright place from a dark room. Give
reason.

Group-C

1. Write down the functions of iris and optic nerve. Describe in brief the working mechanism
of human ear.

2. What is eardrum? Write down its function. Describe in brief the balancing mechanism of
human ear.

3. Write down the safety and protective measures of skin. In which condition does the ear
drum rupture?

4. What is cochlea? Write down its function. How many semi-circular canals are present in
human ear? Write down their functions.

5. Describe in brief the importance of sense organs in human body.

Group-D

1. Draw neat and labelled diagram showing internal structure of human ear. Differentiate
between photoreceptors and chemoreceptors.

2. Draw neat and labeled figure showing the internal structure of human eye.

3. Describe the structure of human tongue with a neat and labelled figure.

4. Describe the structure and working mechanism of skin with a neat and labelled figure.

340 Oasis School Science - 9 BIOLOGY

UNIT 20 Estimated teaching periods

Theory 2

Practical 0

EVOLUTION Jean B. de Lamarck

Objectives

After completing the study of this unit, students will be able to:
• discuss the evidences of organic evolution.
• explain the theories of organic evolution.

20.1 Introduction

Evolution (L., evolvere – to unroll) means the descent of a new form of organism from the pre-
existing one. It is a gradual change, which is going on very slowly and for millions of years,
which we can only imagine. Thus, the entire process of change includes events which have
neither recognizable beginning nor end in time or space.

Evolution is a kind of gradual formation of new organisms from the pre-existing primitive
organisms through slow and steady changes. It is the progressive development of simple
organism to the complex organism over a long period of time. Thus, evolution can be defined
as the sequence of gradual changes which take place in the primitive organisms over millions
of years in which new species are evolved. Once life came into existence, it became continuous,
progressing and changing through successive generations and finally gave rise to present
forms of organisms over a long period of time. Evolution is proceeding even now and will
continue in the future as well. It is a naturally occurring, slow, continuous and irreversible
process of change.

20.2 Evolution of Life

According to scientists, life originated on the earth about 600 million years ago in the form of
marine algae and primitive vertebrates. Gradually, the earth cooled and there was spontaneous
generation of life – how and exactly when, we are not in a position to say with any degree of
certainty. Life must have originated more than 2000 million years ago in an even simpler form,
possibly in the form of aquatic bacteria. All living organisms on the earth which we see today
have evolved from some or the other simple ancestors that lived on this earth in the past.
Regarding the evolution of organisms on the earth, scientists have two views (hypotheses)
which are as follows:

1. Special creation by God

2. Organic evolution

BIOLOGY Oasis School Science - 9 341

1. Special creation by God

According to this hypothesis, all the species of plants and animals were created by
God. Some earlier scientists believed that all living organisms present on the earth were
created by God in the beginning in their present forms. This hypothesis is not accepted
nowadays due to the lack of evidences.

2. Organic evolution

According to the theory of organic evolution, unicellular organisms evolved into
simple multicellular organisms like invertebrates, which in turn evolved into advanced
multicellular vertebrates like fish. The fishes evolved into amphibians which gradually
evolved into reptiles from which birds and mammals have evolved. The term 'organic
evolution' was proposed by Charles Darwin, which means that the present complex life
has evolved from an earlier simpler form of life by gradual changes.

Organic evolution is a very slow process and a human life-time or even all the human
history is too short to witness it. According to this theory, new species are formed from old
ones. Evolution thus clearly shows that there is a profound and continous modification
going on in the forms of life from generation to generation over a long period of time. It
shows how things have become. What are they? How are things changing? According
to the evolution, there is no break in the chain of life and everything has originated
from something of the past. The idea of the evolution, called the theory of evolution, is
generally accepted but in its principle it is still an imperfect synthesis.

20.3 Evidences in Favour of Organic Evolution

Various biological studies tell us that since their origin, living organisms have been undergoing
changes in their organization to evolve into complex forms. A number of common features
of various kinds of organisms provide evidence in favour of evolution. Evidences obtained
from various studies reinforce the view that the living organisms have evolved from common
ancestors. The major evidences that support the theory of organic evolution are mentioned
below:

1. Evidences from the study of fossils

2. Evidences from comparative morphology and anatomy

3. Embryological evidences

4. Evidences from the study of vestigial organs

5. Evidences from bridge organisms or connecting links

6. Evidences from distribution of organisms

1. Evidences from the study of fossils

Fossils are the petrified remains of ancient plants and animals or impressions left by them
in rocks. A fossil is thus a relic of the past life – plant or animal – dug out of the earth's
crust and the study of fossils is called paleontology. Fossils found in the sedimentary rocks
provide direct and most reliable evidences for evolution. Rocks formed in strata in successive
geological periods of the earth have been found to bear particular types of fossils.

petrify /ˈpetrɪfaɪ/ - to change into a substance like stone

342 Oasis School Science - 9 BIOLOGY