14. The leaves of xerophytes are reduced into thorns to reduce the loss of water through
transpiration.
15. The limbs of terrestrial animals are modified according to their habit and habitat.
They have long and strong legs adapted for walking, jumping, etc.
16. Birds are adapted for aerial mode of life. They have streamlined body adapted for
reducing air resistance while flying.
17. Desert animals (like camel) have special tissues adapted for storing water. They
have thick skin to prevent loss of water through perspiration.
18. Climbing animals like monkey have strong muscles and limbs with long digits
adapted for jumping, climbing and holding tree branches.
19. Bacteria are the most primitive, unicellular and microscopic plant organisms. They
are the simplest living organisms.
20. Some bacteria like Rhizobium increase the fertility of soil by regulating nitrogen
cycle.
21. Bacteria are used in tanning of leather, curding of milk, cheese making and
processing of tobacco, coffee, etc.
22. Viruses are sub-microscopic, obligatory parasites that cause various diseases in
plants and animals.
23. Viruses have different shapes like hexagonal, cylindrical, spherical, etc. The genetic material,
i.e. DNA or RNA of a virus remains surrounded by a coat of protein called capsid.
24. The virus that attacks bacteria is called bacteriophage virus. It consists of two parts,
i.e. head and tail.
25. Fungi are plants without chlorophyll. They may be unicellular (yeast) or multicellular
(mushroom).
26. Protozoa are the most primitive animals. They are unicellular and microscopic.
27. Some protozoa like Plasmodium, Entamoeba, Giardia, Leishmania, Toxoplasma,
etc. cause various diseases in animals.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Which of the given plants have well developed root system?
louts cactus
hydrilla onion
b. Which of the given animals has adhesive pads on digits?
garden lizard tiger
monkey house wall lizard
GREEN Science (Biology) Book-9 301
c. Which of the given animals has a hump on its back?
rhinoceros buffalo
yak camel
d. Which of the following is a viral disease?
amoebiasis toxoplasmosis
malaria rabies
2. Answer the following questions.
a. What is meant by adaptation? Why is it important for living beings?
b. Define adaptational characteristics with any five examples.
c. What are hydrophytes? Give any three examples.
d. Name three types of hydrophytes with any two examples of each.
e. Write any four adaptational characteristics of hydrophytes.
f. Write any four adaptational characteristics of aquatic animals.
g. How are fishes adapted in water? Write any three points.
h. Write down the major adaptational characteristics of terrestrial plants.
i. How do thick and fleshy leaves of Aloe vera help in adaptation?
j. Write down the major adaptational characteristics of terrestrial animals.
k. What are bacteria? Write down their importance.
l. How can we control bacterial diseases? Write any three measures to prevent
bacterial transmission.
m. What are fungi? Write down their importance.
n. Write down harmful activities and control measures of fungi.
o. What are viruses? Write down their types.
p. Write any five methods of transmission of viruses.
q. Write down the control measures of viruses.
r. What are protozoa ? Name any five diseases caused by protozoa.
3. Differentiate between
a. Hydrophytes and xerophytes
b. Aquatic animals and terrestrial animals
c. Bacteria and viruses
302 GREEN Science (Biology) Book-9
4. Give reason.
a. The body of fishes is streamlined.
b. The stem of aquatic plants is covered with waxy coat.
c. Camel has a hump on its back.
d. Viruses are called obligatory parasites.
5. Bacteria are both useful and harmful for human beings. Justify this statement.
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. What is adaptation?
2. Write any two adaptational characteristics of the plant given in
the figure.
3. What is bacteriology ?
4. Where are bacteria found ?
5. Name two fungi which cause food poisoning.
(Ans: Rhizopus, mucor)
6. Write down the size of bacteria.
7. What is mycology ?
8. What are fungi ? Where are they found?
9. Name two enzymes which are used for making alcohol.( Ans: Invertage and Zymase)
10. Write any two characteristics of viruses.
11. What are protozoa? Where are they found?
12. What is a bacteriophage virus?
13. What are viruses ? Where are they found?
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. The roots of terrestrial plants are more developed. Give reason. 2
15. Write any two differences between lotus plant and cactus plant on the basis of
adaptational features.
16. The body of desert animals is covered with thick skin. Why?
17. House wall lizard can climb easily on walls but a rat cannot. Give reason.
18. Write any two differences between bacteria and viruses.
19. Viruses are called living beings as well as non-living things. Give reason.
20. Write any two differences between viruses and fungi.
GREEN Science (Biology) Book-9 303
For Group ‘C’ (Application Type Questions) (3 Marks Each)
21. How does spoon-shaped beak and webbed feet of a duck help in adaptation? Describe
in brief with figure.
22. What is the importance of adaptation for living beings? Write any two adaptational
characteristics of the plants found in mountainous region.
23. Write any three harmful activities of fungi.
24. Body structure and colour of animals help them in adaptation." Justify this statement
with an example.
25. Write any three importance of bacteria.
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
26. How do long beak and long legs of a crane help in adaptation? "Birds have light but
strong bones.” Describe this statement on the basis of adaptation.
27. 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.
28. Water storage pouch is found in desert animals, why? Write any two differences
between aquatic and terrestrial animals on the basis of A
adaptation. B
29. What preventive measures can be adopted against bacterial C
and viral diseases?
30. Name the virus shown in the given figure and label the part
A, B and C. Differentiate between plants found on moist
places and plants found in desert in any two points.
31. Describe the structure of a bactriophage virus with a neat and labelled figure.
304 GREEN Science (Biology) Book-9
UNIT System
18
Weighting Distribution Theory : 5 Practical: 1
Before You Begin
The bodies of all living beings are made up of cells. Living beings
may be unicellular or multicellular. The unicellular organisms are
made up to only one cell, whereas multicellular organisms are made
up of so many cells. A cell is the basic, structural and functional unit
of life. In unicellular organisms, all the life processes occur within a
single cell. But multicellular organisms have various tissues, organs
and systems to carry out life processes. A tissue is a group of cells that
perform a certain function, e.g. blood, epithelial tissue, meristematic
tissue, xylem, phloem, etc. An organ is the group of tissues that
performs a certain function, e.g. eye, heart, kidney, flower, fruit, etc.
Similarly, the group of organs that perform a fixed function is called
a system, e.g. digestive system, circulatory system, etc. In a body,
there is a close relationship among cells, tissues, organs and systems.
In this unit, we will study about relation among cell, tissue, organ,
system and plant tissues in brief.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to: • Relation among cell, tissue,
i. introduce cell, tissue, organ and system and describe organ and system
interrelation among them. • Types of plant tissue
• Location of plant tissue
ii. state the types and location of plant tissues and • Skeletal system
explain them. • Digestive system
• Respiratory system
iii. discuss human skeletal system. • Excretory system
iv. name the bones of human skeleton and classify them.
v. introduce digestive system and explain it.
vi. describe respiratory and excretory system and
explain their importance.
Glossary: A dictionary of scientific/technical terms
cell : the basic, structural and function unit of life
tissue : the group of cell working together to perform a fixed function
xylem : the plant tissue that conducts, water and provides support to the plant
skeleton : the framework of a body made of bones
GREEN Science (Biology) Book-9 305
Interrelation among cell, tissue, organ and system
A cell is defined as the basic, structural functional unit of a life. A cell is made of life-
giving substance called cytoplasm which remains surrounded by cell membrane. Various
cell organelles and inclusions are found in a cell. A cell is capable of performing various
activities like respiration, digestion, excretion, reproduction, etc.
In multicellular organisms, a large number of cells work together to perform a certain
function. This group of cells is called tissue. A tissue can be defined as the group of cells
having a common origin and performing similar functions. In a tissue, the cells are more
or less alike in shape, size and performing the same function. Examples: epithelial tissue,
muscular tissue, blood, bones, meristematic tissue, etc. Plants and animals have different
types of tissues.
The group of tissues in animals or plants working together to perform a certain function
is called an organ. Eye, ear, nose, heart, lung, kidney, etc. are the organs of animals.
Similarly, flower, fruit, root, stem, leaf, etc. are the organs of plants. An organ has a
complex structure. The heart pumps blood to different parts of the body. The kidney
filters blood and throws waste products in the forms of urine. The liver is the organ in the
human body that performs various functions.
The group of organs working together to perform a specific function is called the system.
The circulatory system, respiratory system, urinary system, digestive system, etc. are
the examples of systems in the human body. There are nine system in human body. The
different organs work together in a system to perform a certain function. For example,
organs like nose, pharynx, wind pipe, lungs, etc. are found in the respiratory system.
Various systems and organs present in the system of our body are given below with their
functions:
S.N. System Organs Major functions
1. Skeletal system Bones and cartilage
To form internal framework of
2. Muscular system Various types of body, helps in locomotion
muscles
3. Digestive system Mouth, food pipe, To help in movement, to give
stomach, intestine shape
and glands
Digestion and absorption
4. Respiratory system Nose, larynx, lungs To help in exchange of oxygen
and carbon dioxide
5. Blood circulatory Heart and blood To circulate blood to different
system vessels body parts
6. Excretory system Kidney, liver, urinary To excrete various waste
bladder products
306 GREEN Science (Biology) Book-9
7. Glandular system Various endocrine To secrete hormones and
and exocrine glands enzymes
8. Nervous system Brain, spinal cord To control various activities of
and nerves body
9. Reproductive system Testes, ovaries, penis, To help in sexual reproduction
vagina
Interrelationship among Cells, Tissues, Organs and Systems in the
Human Body
In the human body, there is a close relationship between cells, tissues, organs and systems.
The smallest unit of a human body are cells. Cells of the same origin combine together
and form a tissue. So, a tissue consists of many cells. Different tissues work together and
form an organ to perform a specific function. Various organs work together to perform a
certain function. This group of organs is called the system. Various systems work together
and form a body. It shows that there is a close relationship among cells, tissues, organ and
systems in a body.
Cell + Cell → Tissue
Tissue + Tissue → Organ
Organ + Organ → System
System + System → Body
\ Cells + Tissues + Organs + Systems → Body
Plant tissue
There are two types of plant tissues on the basis of location and function. They are:
1. Meristematic tissue 2. Permanent tissue
1. Meristematic tissue Fig. Apical meristem
Lateral meristem
The plant tissue in which cells are undifferentiated 18.1
and divide actively is called the meristematic Intercalary
tissue. In this tissue, the cells are thin-walled and meristem
divide actively to from new cells. The cells of
this tissue are small with a distinct nucleus and Meristematic tissue
dense cytoplasm. The cells are compactly packed iii. Intercalary meristem
without intercellular spaces.
Meristematic tissues are of three types on the
basis of location. They are:
i. Apical meristem ii. Lateral meristem
GREEN Science (Biology) Book-9 307
i. Apical meristem
The meristematic tissue which is found in the tip of roots, stem and leaves is called the
apical meristem. It helps in an axial growth of plants.
ii. Lateral meristem
The meristematic tissue which is found along the side of stems and roots is called the
lateral meristem. It increases the girth (thickness) of the plant.
iii. Intercalary meristem
The meristematic tissue which is located at the base of a leaf and fruit is called the
intercalary meristem. It increases the length of internodes.
2. Permanent tissue
The plant tissue in which cells do not divide is called a permanent tissue. The cells present
in tissue may be living or dead. Similarly, their cell walls may be thick or thin.
On the basis of structure and function, permanent tissues are of three types. They are:
i. Simple tissue
ii. Complex tissue
iii. Special tissue
i. Simple tissue
The permanent tissue which is made up of similar type of cells to perform a common
function is called simple tissue. It is of three types.
a. Parenchyma
b. Collenchyma
c. Slerenchyma
a. Parenchyma
Simple permanent tissue having thin-walled
living cells is called parenchyma. This tissue
consits of intercellular space. In this tissue,
the shape of the cells a may be oval, spheircal
elongated etc.
Parenchyma is found in outer parts of root and Fig.
stem (cortex), mesophyll and inner parts of
stem.
The parenchyma having chlorophyll is called 18.2 Parenchyma
chlorenchyma. It helps in photosynthesis.
It also stores and distributes prepared food.
The parendyma containing air filled cells is called aerenchyma. It is mainly found in
308 GREEN Science (Biology) Book-9
hydrophytes. Aerenchyma helps hydrophytes to float in water, parenchyma also helps
plants to keep in turgid condition.
b. Collenchyma Fig. Fig. Collenchyma
Simple permanent tissue having elongated and thick-
walled cells is called collenchyma. The cells may or
may not contain intracellular space. The cells of this
tissue are thick-walled due to deposition of cellulose
and pectin. This tissue consists of living cells. The cells
of this tissue may contain chlorophyll.
Collenchyma is found below the epidermis of stem,
pedicel of leaves, etc. This tissue provides elasticity, 18.3
flexibility and mechanical support to the plant.
c. Sclerenchyma
Simple permanent tissue containing very long dead
cells having thick wall is called sclerenchyma. The
cells of this tissue are tapering at both ends.
Sclerenchyma is found in hard parts of plants. This
tissue provides mechanical support to the plant.
ii. Complex tissue 18.4
Sclerenchyma
Complex tissue is the permanent tissue having different types of cells working together to
perform closely related functions. This tissue is made up of living or deal cells. It consists
of vascular tissues to transport various substances from one part of plant to another.
Complex tissue is of two types.
They are as follows:
a. Xylem
b. Phloem
a. Xylem
The complex tissue made up of Fig. Xylem fibres Xylem
dead cells is called xylem tissue. vessles
This tissue consists of four Xylem Tracheids
types of cells. They are trachea, parenchyma
trachieds, wood fibre and wood 18.5 Xylem tissue
parenchyma. Out of four types
of cells, wood parenchyma GREEN Science (Biology) Book-9 309
consists of living cells.
Xylem tissue is found in hard parts of root, stem and leaves. Xylem tissue transports
water and minerals from root to the different parts of plants. It also provides mechanical
support to the plant and stores food.
ii. Phloem
Phloem is the complex tissue Parenchyma
made up of living cells. It also cells
consists of four types of cells.
They are sieve tube, companion Sieve tube
cells, phloem parenchyma and
phloem fibres. Out of four types Companion
of cells, only phloem parenchyma cell
consists of living cells.
Plasmodesmata
Phloem tissue is found in root,
stem and leaves of plants. It 18.6
stores and transports prepared Pholoem tissue
food from leaves to different Fig.
parts of plants. It also provides Fig.
mechanical support to the plant
body.
Differences between Xylem and phloem
Xylem Phloem
1. Most of the cells are dead. 1. Most of the cells are living.
2. It transports water and minerals for 2. It transports prepared food from leaves
photosynthesis. to different parts of plants.
3. It consists of trachea, trachieds, wood 3. It consists of sieve tube, companion
parenchyma and wood fibre. cells, phloem parenchyma and phloem
fibres.
3. Special tissue
The permanent tissue which is modified for excretion and secretion is called special tissue.
It is mainly of two types. They are :
i. Laticiferous tissue
ii. Glandular tissue
i. Laticiferous tissue 18.7
The special tissue that secretes latex, i.e. milky secretion is called Laticiferous plant
laticiferous tissue. It acts as storage tissue or as reservoir of waste tissue
products. This type of tissue is found in papaya, grapefruit,
banyan, opium, etc.
310 GREEN Science (Biology) Book-9
ii. Glandular tissue
The special tissue that secretes oil, mucilage, gum, resin, etc. is
called glandular tissue. It is found in pine, tulsi, citrus, lemon,
orange, pudina, etc.
Fig.
Skeletal System of Human Body Fig. 18.8
Laticiferous plant
The internal framework of Skull tissue
human body which is made
up of combination of bones Cervical vertebrate Sternum
is skeleton and the system Clavicle Humerus
formed by combination
of bones is called skeletal Ribs Ulna
system. Human body is Radius
made of 206 pieces of bones Spinal vertebra
of different shapes and sizes. Pelvis Phalanges
Bones are the hard part of
our body. They are made of Sacrum Fibula
living cells called osteocytes. Tibia
Bones become very hard due
to presence of calcium salts.
There is supply of blood Femur
vessels and nerves in Petalla
osteocytes. In this unit, we
will study about different
types of bones present in
human body and functions
of skeletal system.
There are different types of
bones in human skeleton. The Phalanges
bones may be long, short, flat
and irregular. Similarly, ear 18.9
ossicles are the small bones Skeletal system of human body
present in our body. The
bones of limbs are long and the bones of fingers and toes are short. The bones of skull and
thorax are flat, whereas the bones of vertebral column are irregular in shape.
GREEN Science (Biology) Book-9 311
The human skeleton can be divided into following two types:
1. Axial skeleton 2. Appendicular skeleton
1. Axial skeleton
If consists of bones of skull, vertebral column and thoracic cage. It forms the central bony
core of human skeleton.
Axial skeleton consists of three groups of bones. They are:
i. Skull ii. Vertebral column
iii. Rib cage or thoracic cage
i. Skull Fig. Frontal bone
The skull forms the bony Parietal bone
framework of head region. Sphenoid bone
It is made of 22 flat and Temporal bone
irregular bones. The Occipital bone
bones of skull can also be
divided into two regions, Ethmoid bone
viz. cranial bones and Mandible
facial bones.
18.10
Cranial bones Side view of human skull
Cranial bones from the upper roof of the skull called cranium. It looks like a round box
of bones. The cranium is formed by eight flat bones. The cranium protects the brain and
eyes. The bones of cranium are interlocked together by forming fixed joints.
Bones of cranium
Name No. of bones
1. Frontal bone 1
2. Parietal bone 2
3. Temporal bone 2
4. Occipital bone 1
5. Sphenoid bone 1
6. Ethmoid bone 1
Total 8
1. Frontal bone : The bone of fore head is called frontal bone. It forms fore head and roof
of eyes and nose.
2. Parietal bones: There are two parietal bones in the upper parts of cranium. One is
located on the right and another on left side of the brain.
312 GREEN Science (Biology) Book-9
3. Temporal bones : Two temporal bones are located at the base of the cranium, one on
either side.
4. Occipital bone : It is a single bone located at the back of the skull. It is connected to
the vertebral column.
5. Sphenoid bone : It is a single bone located in front of temporal bone.
6. Ethmoid bone: It is a single bone located between two eyes. It forms the base of the
brain and roof of the nose and eyes.
Facial bones
The facial region consists of 14 irregular and flat bones. Facial bones include the bones of
jaws, palate, ears, nose and cheek.
Frontal bone
Zygomatic bone Nasal bone
Mandible Maxilla
Fig.
18.11
Anterior view of human skull
Bones of facial region No. of bones
2
Name 1
1. Maxilla (upper jaw) 2
2. Mandible (lower jaw) 2
3. Zygomatic bones 2
4. Nasal bones 1
5. Lacrimal bones 2
6. Vomer 2
7. Palatine 14
8. Inferior nasal conchae
Total
1. Maxilla: The upper jaw is formed by combination of two bones called maxilla. It
forms the roof of the mouth cavity.
2. Mandible : It is a single bone which forms the lower jaw, i.e. base of the mouth cavity.
GREEN Science (Biology) Book-9 313
3. Zygomatic : Zygomatic bones form the upper part of cheeks below the eyes.
4. Nasal : Two flat nasal bones form the bridge of the nose.
5. Lacrimal : Two lacrimal bones are located at the corner of eyes.
6. Vomer : It forms the base of the nasal passage.
7. Palatine : Two palatine bones form the palate, i.e. roof of the mouth cavity.
8. Inferior nasal conchae : Two nasal conchae are located one on either side of nostril.
Ear ossicles
Each middle ear consists of three small bones called ear ossicles. They are malleus, incus
are stapes. Ear ossicles are also called auditory ossicles. Stapes is the smallest bone of the
human body.
Malleus
Stapes Auditory nerve
Incus
Cochlea
Fig.PinnaTympanic membrane
Fig. External auditory canal
18.12
Ear ossicles inside the ear
ii. Vertebral column Cervical (7)
Thoracic (12)
Vertebral column forms the bony pillar of the Lumbar (5)
trunk. It consists of 33 bones in children and 26
bones in adults. The bones of vertebral column
are irregular in shape. The backbone connects the
trunk with head and limbs. It protects the spinal
cord and forms the axis of the trunk.
18.13 Sacrum (5, fused)
Coccyx (4, fused)
Vertebral column of human
314 GREEN Science (Biology) Book-9
Bones of vertebral column No. of bones
7
Name 12
1. Cervical vertebrae 5
2. Thoracic vertebrae 5 (1 in adults)
3. Lumbar vertebrae 4 (1 in adults)
4. Sacral vertebrae 33 (26 in adults)
5. Coccyx
Total
1. Cervical vertebrae
It consists of seven irregular bones. The first and second bone of cervical vertebrae are
called atlas and axis respectively. Atlas is connected to the skull. Cervical vertebrae are
located in the neck region.
2. Thoracic vertebrae
In thoracic region, there are 12 thoracic vertebrae. It forms the upper back side of the
trunk. Twelve pairs of ribs are attached to the thoracic vertebrae.
3. Lumbar vertebrae
Lumbar vertebrae is formed by 5 irregular bones. It is found in the waist region. It is
found in the waist region. It consists of large, strong and irregular bones.
4. Sacral vertebrae
It is formed by combination of five irregular bones. In adults, these bones fuse and form
only one bone. It is located between the hip bones.
5. Coccyx
The bone of tail region, i.e. coccyx is formed by four small bones. In adults, four bones
fuse and form a single bone. It is located at the lowermost part of the vertebral column.
iii. Thoracic cage Superior thoracic aperture
Vertebral column
The thoracic cage is Mediastinun
formed by 25 flat and
irregular bones. There Right pleural cavity Left pleural cavity
are twelve pairs of Rib I
semi-circular ribs which
remain attached to the Manubrium of sternum
sternum at the front and
to the vertebrae at the Sternal angle
back. Thoracic cage is
also called a rib cage. The Ribs Body of sternum
thoracic cage protects
the heart, lungs, kidneys Fig. Xiphoid process
and upper portion of Inferior thoracic aperture
digestive system. Diaphragm
Thorax of human
18.14
GREEN Science (Biology) Book-9 315
Bones of thoracic cage
Name No. of bones
1. True ribs
2. False ribs 7 pairs = 14
3. Floating ribs 3 pairs = 6
4. Sternum 2 pairs = 4
Total 1
25
First seven pairs of ribs are connected directly to the sternum. So, they are called true
ribs. Eighth, ninth and tenth pairs of ribs are connected indirectly to the sternum. So, they
are called true ribs. Eighth, ninth and tenth pairs of ribs are connected to the sternum
indirectly. So, they are called false ribs and 11th and 12th pairs of ribs are not connected to
the sternum. They are floating freely in the muscle. So, they are called floating ribs.
Activity 1
Visit a nearly butcher's shop and ask a small piece of bone.
Now, press the bone and find whether it is hard or soft.
Take a beaker and immerse the lower half of the bone into dilute hydrochloric acid.
Leave it for 1 day.
Remove the bone from the acid with foreceps and wash is properly.
Now, press the portion of the bone immersed into the acid.
What do you feel? What can you conclude from this activity?
2. Appendicular skeleton
It consists of the bones of right and left side of axial skeleton. The bones of shoulder
girdle, upper limbs, are grouped in appendicular skeleton.
Appendicular skeleton can be divided into two parts, viz. upper part and lower part.
The upper part of appendicular skeleton consists of bones of shoulder girdle and upper
limbs. Similarly, the lower parts of appendicular skeleton consists of the bones of pelvic
girdle and lower limbs.
Shoulder girdle or pectoral girdle
Shoulder girdle is made up of two scapula and two clavicle. Scapula is a triangular flat
bone and clavicle is a bow-shaped bone. Clavicle is attached to scapula and sternum.
316 GREEN Science (Biology) Book-9
Clavicle
Scapula
Bones of upper limb Humerus
Elbow
Each upper limb consists of 30 pieces of bones. So both
upper limbs contain 60 pieces of bones. Radius
Thumb Ulna
Fig. Wrist
Phalanges
Bones of shoulder girdle or pectoral girdle 18.15
Name No. of bones (either side) No. of bones (both sides)
1. Scapula 1 2
2. Clavicle 1 2
Total 2 4
Bones of upper limbs
Name No. of bones (either side) No. of bones (both sides)
1. Humerus 1 2
2. Radius 1 2
3. Ulna 1 2
4. Carpals 8 16
5. Metacarpals 5 10
6. Phalanges 14 28
Total 30 60
Humerus : It connects scapula to radius and ulna. This is the longest bone of human hand.
Radius and Ulna : Radius and ulna are two bones found between the elbow and wrist.
Radius is located towards the thumb and ulna is located towards the little finger.
Carpals : The wrist of human hand is made of eight small bones. These are called carpals.
These bones are arranged in two rows. Each row consists of four bones.
Metacarpals : They form the palm of human hand. They are five in number. They are
connected to carpals and phalanges.
Phalanges : They are commonly known as finger bones. Five fingers contain 14 phalanges.
The thumb contains two bones and rest of the fingers contain three bones each. They are
connected to metacarpals.
GREEN Science (Biology) Book-9 317
Pelvic girdle Sacroiliac joints Iliac bone
The pelvic girdle is made of two Sacrum
large bones called hip bones or
innominate bones. The pelvic Coccyx
girdle of female is wider than
that of males. It provides space to Fig.
the growing foetus. Pelvic girdle Fig.
protects reproductive organs,
intestine, urinary bladder, etc.
18.16 Symphysis pubis
Pelvic girdle of human
Bones of lower limbs Femur
Each lower limb consists of 30 bones of different Patella
shape and size. Femur is the longest and strongest Tibia
bone of human body. Fibula
18.17 Tarsals
Metatarsals
Phalanges
Bones of lower limb of human
Name No. of bones (either side) No. of bones (both sides)
1. Femur 1 2
2. Patella 1 2
3. Tibia 1 2
4. Fibula 1 2
5. Tarsals 7 14
6. Metatarsals 5 10
7. Phalanges 14 28
Total 30 60
Femur : Femur is the longest and strongest bone of our body. It is commonly known as
thigh bone. It is connected to the knee and hip bone.
Patella : It is a small flat bone. It forms knee cap. It is a triangular bone of knee joint.
Tibia and fibula : They are two bones of shank region. Tibia is located at the side of big
toe and fibula is located at the side of small toe. Tibia is larger and stronger than fibula.
318 GREEN Science (Biology) Book-9
Tarsals : Seven bones are located at the posterior part of the foot. Theses bones are called
tarsals. They are commonly known as ankle bones. They are arranged in three rows.
Metatarsals : Five metatarsals are located between tarsals and phalanges. They are long
and straight.
Phalanges : Five toes of each foot contain 14 phalanges. The toes contain three bones each.
Functions of skeletal system
1. It forms the internal framework of the body.
2. It determines the shape and size of the body.
3. It protects vital organs like brain, spinal cord, heart, lungs, kidney, reproductive
organs. etc.
4. It provides attachment to muscles and helps in locomotion and movement of body
parts.
5. It stores calcium.
6. It helps to produce blood cells.
7. The cartilage present in larynx helps to produce sound.
Human Digestive system Fig. Mouth
Tongue
We need to eat food to get energy. Phargnx
The food that we eat should be
digested before it is supplied to Food pipe
different parts of the body. The
complex food is broken down into Liver
simple absorbable form by a group Stomach
of organs. This process is called
digestion. The system formed by Duodenum
digestive tract and digestive glands Small
which is responsible for digestion intestine
of food is called digestive system. Large
intestine
Human digestive system can Rectum
be divided into two parts, viz. Anus
alimentary canal and digestive
glands. Human digestive system
18.18 GREEN Science (Biology) Book-9 319
i. Alimentary canal
Alimentary canal begins from mouth and end in anus. It consists of mouth, food pipe,
stomach, small intestine, large intestine and anus. The diameter of alimentary canal
differs from organ to organ.
ii. Digestive glands
Various chemicals are required for digestion of food. These chemicals are called enzymes.
Different glands produce different types of enzymes. The glands involved in digestive
system are salivary glands liver (gall bladder), pancreas and intestinal glands.
Process of Digestion
Food is taken into mouth and chewed with the help of teeth. Salivary glands secrete
saliva which softens the food in mouth. The saliva contains an enzyme called salivary
amylase. This enzyme acts on starch and converts it into maltose. After chewing, the food
is swallowed into the pharynx which finally reaches the stomach through a food pipe
(oesophagus).
The wall of stomach secretes gastric juice which contains hydrochloric acid and two
enzymes, viz. pepsin and renin. The hydrochloric acid kills microbes present in the food.
In stomach, pepsin acts on proteins and converts them into peptones (smaller protein
molecules) renin acts on milk protein (casein) and changes into insoluble curd.
Nearly after two hours of meal, the food proceeds towards duodenum in the form of a
thick paste, i.e. chime. In duodenum, bile juice from the liver (gall bladder) and pancreatic
juice from the pancreas mix with the food. Bile juice does not contain any enzyme but it
helps to digest fat. The pancreatic juice contains three enzymes. They are trypsin, amylase
and lipase. Trypsin acts on proteins and converts them into peptones, amylase acts on
starch and changes it into maltose and lipase acts on fats and changes them into fatty acid
and glycerol.
After digestion in duodenum, the food slowly moves to the ileum where it is acted upon
by four enzymes; viz. erepsin, maltase, lactase and sucrase, produced by intestinal glands.
Erepsin acts on peptones and peptides and converts them into amino acids. Maltase acts
on maltose and converts it into glucose. Sucrase acts on sucrose and changes it into glucose
and fructose. Lactase acts on lactose and changes it into glucose and galactose. In this way,
proteins, fats and carbohydrates are digested in the small intestine with the help of various
enzymes. The digested food is absorbed by the thin walls of small intestine and mixed into
blood stream. This process is called absorption. After absorption, digested food is supplied
to various cells through blood circulation.
After digestion in small intestine, food proceeds towards large intestine where absorption
of water occurs. The undigested solid particles of food form faeces which moves towards
rectum and is passed away through the anus. This process is called digestion.
In this way, digestion of food takes place in the human body.
The digestion of food that occurs in different parts of alimentary canal is given below:
320 GREEN Science (Biology) Book-9
Part of Digestive Secretion Enzyme Food acted Food
alimentary glands upon changed
canal into
1. Mouth Salivary Saliva Salivary Starch Maltose
glands amylase
Pepsin Protein Peptones
Gastric Gastric juice Milk protein Insoluble
glands Renin
2. Stomach (casein) curd
Liver Bile juice No enzyme Helps to digest fat
Trypsin Proteins and Peptides
Amylase peptones
Lipase
3. Small Pancreas Pancreatic Starch Maltose
intestine juice
Fats Fatty acid
and glycerol
Intestinal Intestinal Erepsin Peptides Amino acids
glands juice Maltase Maltose
Lactase Lactose Glucose
Glucose and
galactose
Sucrase Sucrose Glucose and
fructose
Importance of digestive system
1. Digestive system acts on complex food material and changes into simple absorbable
from.
2. It absorbs nutrients required for the body.
3. It helps to remove undigested food particles.
GREEN Science (Biology) Book-9 321
Respiratory system
We need energy to live and to do work.
We get energy from the food that we eat.
So, we cannot do any work for a long Nose
time without having food. Therefore, we
eat food to obtain energy. After digestion, Wind pipe
the food is absorbed by our body and Lung
the absorbed food is transported to each
and every cell of our body. The food
gets oxidized in mitochondria of the cell
in the presence of oxygen. As a result,
energy is released. This process is called
respiration. So the process of releasing
energy by breaking down food in the Fig.
presence of oxygen in mitochondria is
called respiration. Oxygen gas is essential 18.19 Respiratory system of human beings
in atmosphere while breathing in.
Human respiratory system consists of various organs like nose, pharynx, laryx, windpipe
and lungs. A brief description of these organs is given below:
Nose
It is the outermost organ of respiratory system. It consists of two openings called nostrils.
The small hairs present in nasal passage help to filter dust particles. Nose helps in inhale
and exhale of air.
Pharynx
It connects nose and larynx. It acts as a passage for air and food. Wind pipe and food pipe
begin from the base of pharynx. Epiglotits is located at the mouth of windpipe. It closes
the opening of windpipe while swallowing food.
Larynx
It is also called voice box. It is made up of cartilage. Larynx has two folds which is called
vocal cord. It helps to produce sound. It helps to pass air towards windpipe or trachea.
Trachea or windpipe
It is a tubular structure made up of rings of cartilage. It begins from larynx. The lower
portion of trachea divides into two branches called bronchi. Those bronchi further divide
and form many branches and sub-branches. The sub-branches of bronchi are called
bronchioles. The bronchioles are connected to alveoli, i.e. air sacs present inside lungs.
Diffusion of oxygen in blood occurs inside alveoli present in the lungs.
Lungs
Human beings have two lungs inside the rib cage. They are large, elastic and hollow
structures having millions of air sacs called alveoli. The right lung consists of three
regions and left lung consists of two regions. Bronchi, bronchioles, alveoli, arteries, veins
322 GREEN Science (Biology) Book-9
and capillaries are found inside the lungs. Lungs are covered with a double layered
membrane called pleura. There is a fluid between two layers of pleura which protects the
lungs from mechanical injury.
While breathing, living beings take oxygen in and the oxygen reacts with glucose or
carbohydrate in mitochondria releasing energy, water and carbon dioxide gas. Living
beings perform life processes from the energy obtained during respiration.
Respiration occurs in two ways. They are external respiration and internal respiration.
External respiration or breathing is the Do You Know
process of inhaling air rich in oxygen and
exhaling air rich in carbon dioxide. No Internal respiration is also called cellular
energy is released in external respiration.
respiration as it occurs in cells. Animals
Internal respiration is the process of and plants breathe by different ways. They
oxidation of food in mitochondria of cells. have a variety of organs for breathing.
In this process, oxygen reacts with digested Plants breathe through stomata and
food and releases energy along with water animals breathe through body surface,
and carbon dioxide. The chemical reaction trachea, gills, skin or lungs.
of internal respiration is given below:
Glucose + Oxygen Enzyme Energy + Water + Carbon dioxide
C6 H12O6 + 6O2 Enzyme Energy + 6H2O + 6CO2
Importance of respiratory system
1. Respiratory provides oxygen essential for the body.
2. It helps to release waste products like carbon dioxide.
3. It affects the functioning of the brain.
4. It helps the brain to transmit electrochemical information.
5. It helps body to release energy essential to carry out various metabolic activities.
Excretory system
Human beings have well developed excretory system for removal of various waste
materials. The major organs in human body that help in excretion are given below:
Lungs
Lungs help in removal of carbon dioxide gas
produced during cellular oxidation or internal
respiration.
Fig.
18.20
Human lungs
GREEN Science (Biology) Book-9 323
Skin
Skin helps in removal of urea, uric acid, salts
and excess water in the form of sweat.
Fig.
18.21 Human skin
Kidneys
Kidneys help in removal of urea, uric acid, salt,
excess water, etc. in the form of urine.
18.22Fig. Fig. Human urinary system
Liver
Liver helps in removal of urea, ammonia, etc.
The waste materials produced by liver reach
the kidneys through blood circulation and are
excreted in the from of urine.
18.23 Human Liver
Large intestine
The undigested solid particles are removed by
large intestine through the rectum and anus.
In this way, excretion takes place in human
body by means of various organs.
Fig.
Importance of excretory system 18.24
1. It helps in removal of nitrogenous waste Human large intestine
products like urea, uric acid, etc. from the body in the form of urine.
324 GREEN Science (Biology) Book-9
2. It transports waste products produced in different parts of body to their sites for
excretion.
3. Kidneys help in exertion of waste products by forming urine and reabsorbs the
materials essential for the body.
4. Excretory system helps to remove metabolic wastes produced in cells during various
metabolic activities.
Key Concepts
1. A cell is made of life-giving substance called cytoplasm which remains surrounded
by cell membrane.
2. In multicellular organisms, a large number of cells work together to perform a
certain function. This group of cells is called tissue.
3. The group of tissues in animals or plants working together to perform a certain
function is called an organ.
4. The group of organs working together to perform a specific function is called the
system.
5. The plant tissue in which cells are undifferentiated and divide actively is called the
meristematic tissue.
6. The plant tissue in which cells do not divide is called a permanent tissue. The cells
present in tissue may be living or dead.
7. Simple permanent tissue having thin-walled living cells is called parenchyma. This
tissue consists of intercellular space.
8. Simple permanent tissue having elongated and thick-walled cells is called
collechyma.
9. Simple permanent tissue containing very long dead cells having thick wall is called
sclerenchyma.
10. Complex tissue is the permanent tissue having different types of cells working
together to perform closely related functions. This tissue is made up of living or
deal cells.
11. The permanent tissue which is modified for excretion and secretion is called special
tissue.
12. The internal framework of human body which is made up of combination of bones
is skeleton and the system formed by combination of bones is called skeletal system.
13. There are different types of bones in human skeleton. The bones many be long,
short, flat and irregular.
14. Vertebral column forms the bony pillar of the trunk. It consists of 33 bones in
children and 26 bones in adults.
15. The thoracic cage is formed by 25 flat and irregular bones.
16. The system formed by digestive tract and digestive glands which is responsible for
digestion of food is called digestive system.
17. After absorption, digested food is supplied to various cells through blood circulation.
18. Digestive system acts on complex food material and changes into simple absorbable
from.
19. The process of releasing energy by breaking down food in the presence of oxygen
in mitochondria is called respiration.
GREEN Science (Biology) Book-9 325
20. External respiration or breathing is the process of inhaling air rich in oxygen and
exhaling air rich in carbon dioxide.
21. Internal respiration is the process of oxidation of food in mitochondria of cells.
In this process, oxygen reacts with digested food and releases energy along with
water and carbon dioxide.
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. The group of cells working together to perform a certain function is called.........
organ tissue
system epithelium
b. Which of the given tissue is a simple tissue?
xylem phloem
parenchyma meristem
c. Which of the following bones is found in human skull?
patella parietal
carpal humerus
d. Which of the given organs is found in digestive system?
lung trachea
stomach kidney
e. Which of the given organs is the major organ of excretory system?
lung skin
kidney liver
2. Answer the following questions.
a. What are tissues and organs?
b. Write down the relation among cell, tissue, organ and system in human body.
c. What is meristematic tissue? Write its types.
d. What are permanent tissues? Write their types.
326 GREEN Science (Biology) Book-9
e. Write any two features of each parenchyma and sclerenchyma.
f. What xylem tissue? Write down the function of phloem tissue.
g. What is skeletal system?
h. Define axial and appendicular skeleton.
i. Write down the names and number of bones found in the lower limb.
j. What is pelvic girdle?
k. Draw a neat and labelled figure showing human digestive system.
l. Write down the significance of digestive system.
m. What is respiratory system?
n. Write down the mechanism of respiration in brief.
o. Write down the importance of respiratory system.
p. What is excretory system? Write down its importance.
3. Differentiate between:
a. Tissue and organ
b. Xylem and phloem
c. Parenchyma and sclerenchyma
d. Pectoral girdle and pelvic girdle
4. Give reason.
a. The bone kept in dilute hydrochloric acid becomes soft.
b. A plant does not grow if its tip is cut.
c. Digestive system is important for human body.
d. The pelvic girdle of female is wider than that of male.
5. Draw a neat figure showing human skull and label the main parts.
6. Draw a neat figure showing human respiratory system.
Grid-based Exercise 2 (1 Mark Each)
Group ‘A’ (Knowledge Type Questions)
1. What is a cell?
2. Name two types of tissues found in plants.
3. What is meristematic tissue ?
4. What is a permanent tissue ?
5. Write any two characteristics of permanent tissue.
6. What are complex tissues ?
7. What is skeletal system?
8. Name the bones of skull which are not found in pair.
GREEN Science (Biology) Book-9 327
9. Name the number of following bones found in the human body:
i. Patella ii. Ethmoid
iii. Metacarpals iv. Tarsals
10. What is meant by human nutrition ?
11. What is respiratory system ?
12. What is excretory system ?
13. What is pelvic girdle?
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. Cell is called the structural and functional unit of life, why?
15. A plant dies if its phloem tissue is removed, why ?
16. Differentiate between tissue and organ with examples.
17. The pelvic girdle of a woman is wider than of a man, why ? Give reason.
18. The bone kept in hydrochloric acid becomes soft, why ?
19. Write any two differences between xylem and phloem tissue.
20. Write any two differences between parenchyma and sclerendyma.
For Group ‘C’ (Application Type Questions) (3 Marks Each)
21. What is the relationship among cell, tissue, organ and system in a living body?
Describe in brief.
22. Write any three functions of skeletal system.
23. Write down the names and number of bones found in human lower limb.
24. Write down the importance of digestive system.
25. Write in brief the digestion of food that occurs in mouth, stomach, small intestine and
large intestine.
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
26. What would happen if there were no skeleton in human body? Draw a neat and
labelled figure of digestive system.
27. Write any two characteristics of each parenchyma and scelerenchyma with figures.
28. Write down the importance of respiratory system in human body. Draw a neat and
labelled figure of respiratory system. A
29. Bones of human lower limb are shown in the given figure. Name the C
bones A and B and write the type of joint C. Differentiate between axial B
skeleton and appendicular skeleton.
30. Draw a neat figure of human skull and label facial and cranial bones.
328 GREEN Science (Biology) Book-9
UNIT Sense Organs
19
Weighting Distribution Theory : 2 Practical: 0
Before You Begin
We see different types of things around us with the help of eyes. We
hear sound with the help of ear. We get smell of different things with
the help of nose. We get taste of different foods eaten with the help
of tongue. Similarly, we can feel hot, cold, hard, soft, etc. with the
help of skin. In our body, we have some special organs specialized to
get sensation of different stimuli. Eyes, ears, nose, tongue and skin
are five special organs of human body which respond to physical
and chemical changes in our surroundings. So they are called sense
organs. Sense organs can be defined as the special organs that receive
sensation of sight, hearing, smell, taste and touch. In this unit, we will
study about five sense organs of human body, viz. eyes, ears, nose,
tongue and skin.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce sense organs with examples. • Introduction to sense organs
ii. explain the structure of sense organs of human body • Types of sense organs,
and describe their functions. structure and working
mechanism
iii. state of methods of caring sense organs.
- Eyes
- Ears
- Nose
- Tongue
- Skin
Glossary: A dictionary of scientific/technical terms
sense organs : the special organs of a body having sense cells or receptors
sensation : a general state of awareness to a stimulus
receptors : special cells that receive stimulus from the environment
stimulus : a physical or chemical even to which living beings react
night blindness : a disorder in which a person cannot see clearly at night
GREEN Science (Biology) Book-9 329
Sense Organs
1. Eyes
Eyes are the most important sense organs of human body. We cannot see things around
us in the absence of eyes. Eyes are the sense organs that give us the sensation of sight or
vision.
Upper lacrimal punctum Upper eyelid
Pupil
Superior canaliculus Limbus
Lacrimal sac Iris
Sclera
Inferior canaliculus
Lower lacrimal punctum Lower eyelid
Fig. Nasolacrimal duct
19.1
External view of human eye
Human eye is located in the facial region in orbital cavity in the skull. It is found inside
lacrimal bones. Each eye is spherical in shape and hollow from inside which remains
filled with fluids called aqueous humour and vitreous humour.
The wall of eye consists of three different layers. They are
i Sclera
ii. Choroid
iii. Retina
A brief description of these three layers of eyes is given below:
i. Sclera
Sclera is the outermost layer of eye wall. It is white in colour. It is made of tough connective
tissue fibres. The anterior portion of sclera is transparent which is called cornea. The
cornea remains covered with an outer thin and transparent membrane called conjunctiva.
Sclera provides a fixed shape to the eye ball and also protects the inner parts of the eye.
330 GREEN Science (Biology) Book-9
Ciliary body Sclera
Suspensory ligament Choroid
Retina
Cornea
Iris Fovea centralis
Pupil Posterior pole
Anterior pole Optic nerve
Anterior segment Cathneednrtveraetiilnnaarotfery
(contains aqueous Optic dics
(blind spot)
humour)
Lens
Fig. Posterior segment
(contains vitreous
19.2
humour)
Internal Structure of eye ball
ii. Choroid
Choroid is the second layer of eye ball located between sclera and retina. It is made up
of connective tissues. It is richly supplied with blood vessels and black pigmentation.
The black pigmentation absorbs the radiation and hence prevents the reflection of
light. It also provides food and oxygen to the eye. In anterior portion, choroid forms
iris. The iris can contract and relax to control the size of the pupil. There is a hole at
the centre of the pupil. The rays of light enter the eye-ball through pupil.
iii. Retina
Retina is the third and inner layer of eye-wall. It is a transparent layer richly supplied
with nerve fibres and light sensitive cells. The image of the object forms in the retina.
The light sensitive cells present in retina are rods and cones.
Rods present in retina contain rhodopsin which helps to see in dim light or at night.
Similarly, the cones present in retina contain iodopsin which helps to see in bright
light or in day time. The defect in rods of eye causes a disease called night blindness.
In this disorder, a person can see during day time or in bright light but cannot see at
night or in dim light.
When there is defect in cones, a person suffers from colour blindness. In this disorder,
a person cannot distinguish colour. It is a genetic disease. Colour blindness is a sex-
linked disease which occurs only in males.
Human eye ball is made up of different parts. A brief description of these parts is
given below.
GREEN Science (Biology) Book-9 331
i. Eye lens
Human eye consists of a transparent biconvex lens. It is situated just behind the pupil,
and supported by suspensory ligaments and ciliary muscles. The thickness of the lens is
controlled by contraction and dilation of ciliary muscles. The lens is made of crystalline
living cells. The eye lens refracts the rays of light falling on it and forms a real, inverted
and diminished image on retina.
ii. Chambers
The eye lens divides the eye ball into two unequal chambers. They are aqueous chamber
and vitreous chamber. The small chamber of the eye located between eye lens and cornea
is called aqueous chamber. It remains filled with a transparent watery fluid called aqueous
humour. This fluid protects the eye from mechanical shock and keeps the eye ball moist.
Vitreous chamber is a large chamber located behind the eye less. It remains filled with
a thick fluid called vitreous humour. It provides spherical shape to the eye ball and
mechanical support to the retina.
iii. Cliary muscles
The choroid consists of a set of ciliary muscles in the anterior region. Ciliary muscles are
connected to suspensory ligaments and the suspensory ligaments support the eye lens.
The lens becomes thick and thin due to contraction and dilation of ciliary muscles. When
we see nearby objects, the eye lens becomes thick due to dilation of ciliary muscles. When
we see distant objects, the eye lens becomes thin due to contraction of ciliary muscles.
iv. Pupil
Pupil is the small hole located at the centre of the iris. It allows the rays of light to enter the
eyeball. The contraction and dilation of iris determine the size of the pupil. In dim light,
the pupil becomes larger due to contraction of iris and in bright light, the pupil becomes
smaller due to dilation of iris muscles.
v. Optic nerve
The nerve that carries signals (nerve impulses) from retina to the brain is called optic
nerve. It transmits the image formed in retina to the brain in the form of electric signals.
Working mechanism of human eye Fig.
The rays of light coming from an object 19.3
enter the eye through cornea, pupil and
strike the eye lens. Those rays are refracted Working mechanism of human eye
by the lens. As a result, a real, inverted and
diminished image of the object is formed
on the retina. Then the photosensitive
cells (rods and cones) present in the retina
generate nerve impulses. The optic nerve
sends those nerve impulses (electric
332 GREEN Science (Biology) Book-9
signals) to the brain. After processing by the brain, we see erect and correct image of the
object. In this way, eyes help us to see things in our surroundings.
Care and Hygiene of Human eye
In order to keep our eyes healthy, we should consume fruits and vegetables rich in vitamin
A such as yellow fruits and green vegetables. We should not work in too much bright
light or too much dim light. We should visit a doctor (eye specialist) in case of infection.
Similarly, we should not rub our eyes and put any medicine without doctor's prescription.
We should not read in moving vehicles. We should wash our eyes regularly with clean
and cold water. We should never wash our eyes with hot water.
2. Ears
Ears are the sense organs which help us to get the sensation of hearing. Humans have two
ears one is located in each temporal region. Ears also help to maintain body balance or
equilibrium.
Human ear can be divided into three distinct regions. They are as follows:
i. External ear
ii. Middle ear
iii. Internal ear
A brief description of three regions of human ear is given below:
Malleus
Stapes Auditory nerve
Incus
Cochlea
Fig. Tympanic membrane
External auditory canal
Pinna
Internal structure of human ear
19.4
i. External ear
It is the outer visible part of the ear. It has three parts. They are pinna, auditory canal and
ear drum. Pinna is the outermost visible part of the ear. It is made of cartilage. It is conical
in shape. The cartilage of the pinna remains covered with thin muscles and those muscles
are covered with skin. The lower portion of the pinna is made of fatty tissue.
GREEN Science (Biology) Book-9 333
The pinna surrounds the opening of auditory canal. The auditory canal is a tubular passage
through which sound waves enter the middle ear. The auditory canal is connected to the
ear drum. The ear drum is a cone-sheped delicate membrane which vibrates when sound
waves strike it. The opening of the auditory canal consists of fine hairs, wax and oily
substance. They prevent the entry of dust and small creature inside the ear. The ear drum
separates the external ear from the middle ear. Th ceruminous glands present in the skin
of auditory canal secrete ear wax whereas the sebaceous glands secrete oil which prevents
the ear canal form drying.
ii. Middle ear
The region of ear between external ear and internal ear is called middle ear. It is located
behind the ear drum or tympanic membrane. Actually, middle ear is a small air-filled
bony chamber which is separated from the internal ear by a bony partition. The bony
partition consists of oval window and round window. In anterior region, the middle ear
consists of an opening which leads to eustachian tube. The tube connects throat to the
middle ear. This tube helps to balance the air pressure between external ear and middle
ear. This tube opens while swallowing food and equalizes ear pressure on the both sides
of ear drum. Therefore, chocolate is chewed while travelling by aeroplane.
The middle ear consists of three small and irregular bones. These bones are called ear
ossicles. They are malleus, incus and stapes. The malleus is a hammer-shaped bone which
connects ear drum and incus. The incus is an anvil-shaped bone which connects malleus
to the stapes. Similarly, the stapes is a stirrup-shaped bone. It connects incus with the oval
window. The ear ossicles or auditory ossicles transmit the sound waves from ear drum to
the internal ear.
iii. Internal ear
Internal ear is the innermost Ear Vestibule Semicircular
part of the ear. It is located at ossicles canals
the middle of the temporal
Oval
window
bone. Internal ear is also called
labyrinth. The labyrinth can
be divided into two regions,
viz. bony labyrinth and
membranous labyrinth. Cochlea
The inner ear consists of
cochlea and semicircular Middle Eustachian
canals. The cavity of the ear tube
internal ear and semi- circular
canal is filled with a fluid Ear Round
called perilymph. The cochlea drum window
Fig.
is a spiral structure which
appears like the shell of snail. 19.5 Ear
The middle canal of cochlea drum
consists of organ of corti which
Detailed structure of middle ear and internal ear
is rich in nerve cells and sensory hair cells connected with auditory nerve.
334 GREEN Science (Biology) Book-9
There are three semi-circular canals in the inner ear arranged at right angles to each other.
Each semi-circular canal is filled with a fluid called endolymph. One end of each canal
consists of a swollen portion which is called ampulla. The ampulla consists of sensory hair
cells that help to maintain equilibrium or body balance. At the middle portion, there is a
short vestibule which connects cochlea and semicircular canals. The vestibule consists of
two small sacs. They are utriculus and sacculus. They are rich in sensory cells associated
with static balance of the body.
Mechanism of hearing
The sound waves coming from a source are collected by pinna and directed towards the
ear drum through auditory canal. When sound waves strike the ear drum, it produces
vibrations. Those vibrations are transmitted to the inner ear through ear ossicles. When
vibrations reach the inner ear through oval window. These vibrations finally reach the
cochlea through endolymph and stimulate the sensory hair cells. These sensory hair cells
produce nerve impulses and the impulses reach the brain with the help of auditory nerve.
The brain processes the impulses received. As a result, we near the sound.
Ossicles: Temporal bone
Stapes Semicircular ducts
Incus
Malleus Vestibular nerve
Sound Cochlear
waves nerve
Cochlea
Auricle
Eardrum
Fig. Auditory Tympanic Auditory
Earlobe canal cavity tube
19.6 Outer ear Middle ear Inner ear
Mechanism of hearing
Care and hygiene of ear
We should clean our ears regularly with clean water and soap. We should not insert
any hard and pointed object in the ear. We should not put medicine without doctor's
prescription. Mother should not let her milk to enter the ear of her baby while breast
feeding. We should consult a doctor in case of ear infection.
3. Tongue
Tongue is the sense organ which helps us to get the sensation of taste. It is a soft muscular
organ located in the mouth cavity. it is an important organ of digestive system. It also
helps us to speak.
GREEN Science (Biology) Book-9 335
The posterior part of the tongue is attached Fig. Large taste buds
to the hyoid bone of the neck region and Fig. Small taste buds
the sides of the tongue are attached to the Structure of tongue
bone of the chin but the anterior portion
of the tongue is mobile.
There are two surfaces on the tongue.
They are upper surface and lower surface.
The upper portion of the tongue if called
extrinsic muscle which is attached to root
(base) of the tongue and hyoid bone.
This muscle helps tongue to move up, in 19.7
and out. Similarly, the lower surface of
the tongue consists of intrinsic muscles.
These muscles help to change the shape of the tongue.
The upper surface of the tongue appears rough which consists of four types of taste buds.
These taste buds contain sensory cells. These sensory cells are attached to the gustatory
nerve. The taste buds or papillae are divided into three pairs. They are as follows:
i. Vallete papillae ii. Fungiform papillae iii. Filiform papillae
The papillae of the tongue help to receive the sensation of tastes. The upper surface of the
tongue consists of four types of taste buds. They detect sour, sweet, salty and bitter taste.
The taste buds that detect sweet and salty taste are located near the tip of the tongue. The
taste buds that detect sour taste are located at the side of the tongue and the taste buds
that detect the bitter taste are located at the back side of the tongue. Our tongue can detect
four different types of taste. Other taste sensations are the combination of different tastes.
Physiology of taste Palatine tonsil Bitter
When we eat food, a part of it Lingual tonsil Sour
dissolves into saliva and forms Foliate Salty
a solution. A part of the solution Sweet
enters the taste buds through taste papillae
pores. As a result, the sensory
hair cells present in taste buds get Circumvallate
stimulated and generate nerve papillae
impulses. Those nerve impulses are Filiform
transmuted to the brain with the papillae
help of gustatory nerve. The brain
processes the signal received and Fungiform
we get the sensation of taste. papillae
Human tongue performs two 19.8
different types of functions. They Taste buds in human tongue
are: sensory function and motor
function.
336 GREEN Science (Biology) Book-9
The sensory function of the tongue includes the process of getting four types of tastes, viz. sour,
sweet, salty and bitter. Similarly, the motor function includes masticating food, swallowing
food and speaking. We receive the sensation of sweet and salty taste earlier than the bitter
taste because the taste buds that detect bitter taste are located at the back side of the tongue
but the taste buds that detect sour and salty taste are located at the tip of the tongue.
Care and hygiene of tongue
We should keep our tongue clean. We should not drink very hot liquids. We should not
insert sharp and pointed objects in the mouth. We should eat juicy fruits. Similarly, we
should consult a doctor in case infection in tongue.
4. Nose Paranasal Paranasal
sinus sinus
Nose is the sense organ which Nasopharynx
helps to get the sensation of Nasal
smell. It also helps in breathing. cavity
Nose is located at the mid-
portion of the facial region. The Fig. Tongue Base of tongue
nose of human beings is less Fig. Floor of
sensitive than the nose of other mouth Posterior
animals. pharangeal wall
The human nose can be divided Oropharynx
into two parts, viz. outer part
and inner part. The outer part 19.9
of the nose consists of nasal
bones which are connected to Internal structure of human nose
maxilla and frontal bone.
The inner part of the nose Glabella Tear trough
mainly consists of nasal Naslon Supra alar crease
cavity. It is richly supplied Domes (tip defining points)
with sensory cells. The Nasal bridge Nostril
inner lining of the nasal Supratip break Philtrum
cavity consists of sensory
epithelium. It consists of Infratip break Tip defining point
numerous blood capillaries Nasolabial angle Soft tissue triangle
and olfactory cells.
Olfactory receptors are Nostril sill Columella
found in the upper portion Alarfacial groove
of the nasal epithelium.
Olfactory receptors are
connected to olfactory
nerve.
19.10
Structure of human nose
GREEN Science (Biology) Book-9 337
Mechanism of Smelling
The chemical substances having various odour enter the nasal epithelium through nasal
passage. These chemicals stimulate the olfactory cells present in the nasal epithelium. The
olfactory cells generate nerve impulses and we get the sensation of smell. The process of
getting sensation of smell is called olfaction.
The mucous membrane of the nasal epithelium swells up when we suffer from common
cold. The sensory cells present in nasal passage cannot work properly. Therefore, we do
not get the proper smell and taste of food while suffering from common cold.
Care and hygiene of nose
We should clean our nose early in the morning. We should not throw mucous forcefully.
We should not immerse the nose in water. We should not insert a sharp object and grains
in our nose. We should take steam bath while suffering from common cold.
5. Skin
Skin is the sense organ which gives the sensation of touch. In human body, skin forms the
outermost covering layer. The outer layer of skin is a lifeless layer which does not contain
blood vessels. It is a tough layer of skin. The inner layer of skin consists of nerves, blood
vessels, sweat glands, roots of hair, fat cells, sebaceous glands, etc.
Hair
Sebaceous gland
Sensory nerve ending
Epidermis
Nerve
Dermis
Subcutaneous tissue
Fig. Capillaries Arteriole
Fat, collagen, fibroblasts
Muscle
19.11 Sweat gland
Structure of human skin
Skin is the sense organ that gives us the sensation of touch, pain, temperature, etc. It
protects our body from external environment.
On the basis of structure, skin can be divided into two layers, they are
i. epidermis and
ii. dermis
338 GREEN Science (Biology) Book-9
Epidermis is the outer transparent layer made of stratified epithelium. It consists of numerous
pores through which excess water and waste products come out in the form of sweat.
The layer of skin that remains below the epidermis is called dermis. It is made of elastic
fibres. The dermis consists of nerve fibres, blood vessels, roots of hair, sweat glands,
sebaceous glands, fat cells, etc. A layer of fat is also found in the dermis. This layer keeps
our body warm. The layer of fat in the dermis is also called sub cutaneous fat. The amount
of sub-cutaneous fat is more in females than in males. The blood vessels present in dermis
helps to maintain body temperature.
The skin covers entire body and protects the body from external injury. It helps to regulate
body temperature by throwing excess heat through sweat. The skin absorbs fatty substances
and separates sweat from fat. It helps in excretion of waste products. It synthesizes vitamin
D by combination of solar radiation and ergosterol. The skin stores fat and water.
Care and hygiene of skin
We should clean our skin regularly with soap and water. We should use clean germ free
water and high quality toilet soap for bathing. We should protect skin from the contact of
very hot and very cold object. We should take nutritious diet and foods rich in vitamin A
and E to keep our skin healthy. We should protect our skin against insect bite.
Key Concepts
1. Eyes are the sense organs that give us the sensation of sight or vision.
2. Sclera is the outermost layer of eye wall. It is white in colour. It is made of tough
connective tissue fibres.
3. Choroid is the second layer of eye ball located between sclera and retina. It is made
up of connective tissues.
4. Retina is the third and inner layer of eye-wall. It is a transparent layer richly supplied
with nerve fibres and light sensitive cells.
5. The nerve that carries signals (nerve impulses) from retina to the brain is called
optic nerve.
6. There are three semi-circular canals in the inner ear arranged at right angles to each
other.
7 The papillae of the tongue help to receive the sensation of tastes. The upper surface
of the tongue consists of four types of taste buds. They detect sour, sweet, salty and
bitter taste.
8. Human tongue performs two different types of functions. They are: sensory
function and motor function.
9. Nose is the sense organ which helps to get the sensation of smell. It also helps in
breathing.
10. Skin is the sense organ which gives the sensation of touch. In human body, skin
forms the outermost covering layer.
11. The layer of skin that remains below the epidermis is called dermis. It is made of
elastic fibres.
12. The skin covers entire body and protects the body from external injury. It helps to
regulate body temperature by throwing excess heat through sweat.
GREEN Science (Biology) Book-9 339
Sequential General Exercise 1
1. Choose the best answer from the given alternatives.
a. Which of the given organs is not a sense organ?
eye ear nose heart
tongue
b. Which of the given organs contains auditory nerve? skin
eye
eye ear nose four
c. Optic nerve is found in ................
eye ear nose
d. Which of the given organs maintains body balance?
ear skin nose
e. Human tongue can detect ............. types of tastes.
one two three
2. Answer the following questions.
a. Define sense organs.
b. Name the sense organs present in human body.
c. Where are eyes located?
d. Describe the structure of human eye with a neat and labelled figure.
e. What is choroid? Write down the function of retina.
f. Draw a neat and labelled figure showing the structure of human ear.
g. Describe the working mechanism of human eye.
h. How can we get the sensation of hearing ? Describe in brief.
i. What are ear ossicles? Name them.
j. Write down the function of optic nerve and auditory nerve.
k. What are taste buds? Draw a neat and labelled figure showing taste sites of
human tongue.
l. Draw a neat and labelled figure showing the structure of nose.
m. How can we get the sensation of smell ? Write.
n. Write any two features of epidermis and dermis.
o. Write a short note on care and hygiene of
i. ears ii nose
iii. tongue iv. skin
340 GREEN Science (Biology) Book-9
3. Differentiate between:
a. Eyes and Ears
b. Optic nerve and Auditory nerve
c. Rods and Cones
d. Dermis and Epidermis
4. Give reason:
a. A person suffering from night blindness cannot see at night.
b. When we enter a dark room immediately from a bright place, nothing can be
seen clearly for a while.
c. When we rotate 2-4 rounds, we feel dizzy.
d. We do not get proper taste of food while suffering from common cold.
e. Chocolate is chewed while travelling by aeroplane.
5. Draw a neat and labelled figure showing the structure of skin.
Grid-based Exercise 2
Group ‘A’ (Knowledge Type Questions) (1 Mark Each)
1. What are sense organs ?
2. What is vitreous humour?
3. Write down the functions of iris and optic nerve.
4. What is conjunctiva ? Write down its function.
5. What do you mean by the window of a human eye ?
6. What is night blindness ? Write down its cause.
7. What is eardrum ? Write down its function.
8. In which condition does the ear drum rupture?
9. Where is eustachian tube located ? Write down its function.
10. What are taste buds?
11. What is cochlea? Write down its function.
12. How many semi-circular canals are present in human ear?
13. Name the sense organ that balances our body.
For Group ’B’ (Understanding Type Questions) (2 Marks Each)
14. Actual taste of food cannot be obtained while eating food by blocking the nose. Why?
15. Write any two differences between optic nerve and auditory nerve.
16. Why does the eye lens become thin when we see distant objects? Give reason.
17. Chocolate is chewed while travelling by aeroplane. Give reason.
18. Why does the capacity of olfaction decreases when one suffers from common cold?
Give reason.
GREEN Science (Biology) Book-9 341
19. Sweet and sour tastes can be felt earlier than the bitter taste. Give reason.
20. When one rotates 2-4 rounds, she/he feels dizziness. Why?
For Group ‘C’ (Application Type Questions) (3 Marks Each)
21. Describe in brief the importance of sense organs in human body.
22. Draw a neat and labelled diagram showing internal structure of human eye.
23. Describe the working mechanism of human ear. C
E
24. Name the sense organ shown in the
given diagram. Also, label the parts A, B, D
C, D, E and F with a function of each.
F
25. Write down the protective and safety B
measures of eyes.
A
For Group ‘D’ (Higher Abilities Type Questions) (4 Marks Each)
26. Draw a neat and labeled figure showing the internal structure of human eye. Write
down the safety and protective measures of skin.
C
27. Name the parts A, B and C in the given diagram B
of an eye and mention any one function each of B
and C. Describe the mechanism of vision in brief.
A
28. Draw a neat and labelled diagram showing
internal structure of human ear. Differentiate
between photoreceptors and chemoreceptors.
29. The pupil of an eye gets enlarged when a person moves towards dark. Why? Draw a
neat and labelled diagram showing various sites of taste in human tongue.
342 GREEN Science (Biology) Book-9
UNIT Evolution
20
Weighting Distribution Theory : 4 Practical: 0
Before You Begin
A variety of plants and animals are found around us. We can see
very simple plants like chalmydomonas, spirogyra, diatoms to
very large and well develop trees. Similarly, we can see very simple
and unicellular animals like amoeba, paramecium, euglena, etc. to
most developed animals like elephant, human beings, etc. All the
advanced organisms are the very simple organisms of the past. The
development of a complex organism from a primitive one is a very
slow process and takes millions of years. The process in which an
advanced organism develops form a simple and primitive organism is
called evolution. Actually, evolution is a sequence of gradual changes
in which advanced animals are formed from a primitive organisms
after millions of years. Evolution is a very slow but continuous process
of change. In this unit, we will study about evolution, evidences in
favour of organic evolution and theories of evolution in brief.
Learning Objectives Syllabus
After completing the study of this unit, students will be able to:
i. introduce evolution. • Introduction to evolution
ii. describe the evidences in favour of organic evolution.
iii. describe the theories of organic evolution. • Evidences in favour of
evolution
• Theories of evolution
- Lamarck's theory
- Darwin's theory
- Critisisms on Lamarck's
theory and Darwin's
theory
Glossary: A dictionary of scientific/technical terms
evolution : the sequence of gradual changes which takes place in organisms
homologous : having similar structure but different functions
analogous : having different structure but similar functions
vestigial : rudimentary or functionless
GREEN Science (Biology) Book-9 343
Evolution
The word evolution has been derived from the Latin word 'evolvere' which mean to unroll.
It means that a pre-existing primitive organism develops into an advanced form after
millions of years. The sequence of gradual changes in primitive organisms over millions
of years which forms a new species is called evolution. It is a very slow but continuous
process of change. It is a naturally occurring progressive process of change. Development
of human beings from the primates is an example of evolution. Similarly, development
of vertebrates from the invertebrates and development of flowering plants from the non-
flowering plants of the past are some more examples of evolution.
Scientists believe that life originated on the earth about 600 millions years ago in the
from of primitive and unicellular organism. Then the unicellular organism gradually
developed into multicellular organism. Different species of plants and animals evolved
from those simple and primitive organisms of the past. This process took millions of
years. According to the theory of organic evolution, unicellular plants developed into
multicellular plants. Similarly, non-flowering plants evolved into flowering plants.
Unicellular invertebrates and multicellular invertebrates developed into vertebrates like
fish. Then the fishes evolved into frogs and frogs evolved into reptiles. Finally, reptiles
evolved into birds and mammals.
Charles Darwin proposed the term evolution for the first time. He says that the present
complex life has been evolved from an earlier simple form of life by gradual changes over
a long period of time. Human life time or even entire history of human beings on the earth
is too short to observe the process of evolution. However, various kinds of organisms and
fossils provide evidences in favour of evolution.
Evidences in Favour of Organic Evolution
1. Evidences from the fossils
2. Evidences from the study of embryo
3. Evidences from comparative morphology and anatomy
4. Evidences from the study of bridge animals
5. Evidences from the study of vestigial organs
6. Evidences from the distribution
of organisms
1. Evidences from fossils Fig.
The dead remains or impressions of Fossil bird
plants and animals left in sedimentary
rocks are called fossils. We can collect
information about the ancient animals
and plants from the study of fossils. The
branch of science which deals with the
study of fossils is called palaeontotgy. 20.1
344 GREEN Science (Biology) Book-9
Fossils provide the most reliable evidence in favour of organic evolution. Fossils are found
in sedimentary rocks. When animals and plants die, their dead bodies are carried away
by rivers and streams which get deposited on the banks of river, coastal areas, etc. They
also get deposited at the bottom of big lakes and seas. This process occurs continuously
and many layers are formed. The upper layers exert pressure on lower layers. As a result,
sedimentary rocks are formed.
When we study the fossils present on sedimentary rocks, it is found that the lower layers of
rocks contain fossils of simple and primitive organisms. The middle layers of those rocks
contain fossils of developed as well as fossils of primitive animals. Similarly, the upper
layers of sedimentary rocks contain fossils of simple as well as developed organisms.
Similarly, There is a close relation between the fossils of upper layers and those of lower
layers. It proves that the advanced organisms of present day world might have evolved
from the primitive and simple organisms of the past. In this way, the evidences obtained
from the study of fossils support the theory of organic evolution.
2. Evidences form the study of embryo
An embryo is the very early stage of an organism. Shark Lizard Chicken Pig Human
It develops from a zygote due to cell division.
The branch of biology which deals with the
study the embryos is called embryology. The
embryos of different groups of vertebrates
look alike in early stage of their development.
We find many similarities among them and it
becomes difficult to distinguish among them.
For example, the embryos of fish, frog, reptile,
bird and mammal look identical in their early
stage of development. Later each embryo Fig.
develops into adult having different features
according to their parental characteristics. It
shows that the different types of animals and 20.2
plants of the present had been evolved from
simple and primitive organisms of the past. In Embryos of different types of
this way, evidences obtained from the study of vertebrates
embryos support the theory of organic evolution.
3. Evidences from comparative morphology and anatomy
There are many similarities and differences among different groups of organisms. For
example, fishes, frogs, reptiles, birds and mammals have many similarities though they
differ in structure and appearance. The evidences obtained from the study of homologous
and analogous organs also provide evidence in favour of organic evolution.
The fore limb of human being, fore limb of a horse, flipper of a whale, patagium of a bat,
etc. perform different functions but their basic structure is similar. These organs have
almost similar types of bones, muscles and blood vessels except minor differences. Such
type of organs are called homologous organs. It shows that all these organisms might
have been evolved from a common ancestor.
GREEN Science (Biology) Book-9 345
Humerus
Radius
Ulna
Carpals
Metacarpals
Fig. Phalanges Human Cat Whale Bat
Fig.
20.3
The wings of insects, patagium of a bat, Do You Know
feathers of birds, etc. perform similar function
but they differ in origin and structure. Such Homologous organs are those which
type of organs are called analogous organs. are different in functions but similar in
The study of anologous organs shows that structure and origin. Fore limb of human
though organisms differ in structure and being fore limb of a horse, fore limb of a
origin, they can modify their body parts cow, patagium of a bat, flipper of a whale,
according the their environment. etc.
In this way, the study of comparative
morphology and anatomy supports the theory of organic evolution.
4. Evidence from the study of bridge animals or connecting links
Those animals which show the characteristics of two different groups are called bridge
animals. For example, Archaeopteryx (a fossil bird of Jurassic period, duck-billed platypus,
echidna, lung fishes, etc. These organisms are also called connecting links because they
connect two different groups of organisms by showing some characteristics of lower
group and some characteristics of higher group.
20.4 Archaeopteryx Duck-billed platypus Echidna
Lung fish
Duck-billed platypus and echidna connect reptiles to the mammals. They lay eggs and
are cold-blooded like reptiles but they have mammary glands, pinnae and body hair like
mammals. Lung fishes connect pisces to amphibia. They have features of fishes but they
can breathe through lungs on land. Similarly, Archaeopteryx, connects reptiles and birds.
Like reptiles, it has teeth in jaw, and a long tail. Similarly, it has feathers and wings in the
body. These examples prove that higher groups of organisms might have evolved from
346 GREEN Science (Biology) Book-9
Fig.lower groups of organisms in the past. In this way, evidences obtained from the study of
Fig.bridge animals or connecting link support the theory of organic evolution.
5. Evidences from the study of vestigial organs
In human body, the organs like vermiform appendix, coccyx, body hair, nictitating
membrane of eye, articular muscles of ear are present but they do not perform any
function. However these organs are quite functional in other mammals. Such type of
organs are called vestigial organs.
Vermiform appendix is rudimentary and functionless in human beings but it is quite
functional in herbivores like cow, sheep, buffalo, goat, deer, rabbit, etc. It helps to digest
cellulose.
20.5 Vermiform appendix
Vermiform appendix of human
The articular muscles of human ear are rudimentary and functional in animals like cow,
buffalo, sheep, elephant, etc. These animals use articular muscles to rotate the pinna
(external ear) towards the direction of source of sound.
20.6
Vestigial ear muscle of
human
Similarly, the coccyx or tail bone is vestigial part in human beings but it is quite
functional in animals like cow, dog, cat, sheep, lion, tiger, etc.
GREEN Science (Biology) Book-9 347
CoccyxFig.
20.7Fig.
Coccyx of human
From these examples, it can be concluded that the animals having vestigial organs and the
animals in which those organs are quite functional might have evolved form a common
ancestor. In this way, the evidences obtained from the study of vestigial organs also
support the theory of organic evolution.
6. Evidences form the distribution of organisms
The earth is inhabited by different species of plants and animals. The species of plants and
animals that are found in a certain region may or may not be found in another region even
though both regions have the same climatic condition. For example, the elephant that is
found in Africa and India is not found in Brazil. When the members of the same species
migrate to the places having different climatic condition and remain there for many
generations, they develop new characteristics to adapt in their habitat. Environmental
variation also occurs in those organisms and they look different from their ancestors and
this process is called evolution. In this way, evidences obtained from the distribution of
organisms also support the theory or organic evolution.
Theories of Evolution
Various evidences suggest that evolution has taken place on the earth and it will be
continued in future as well. Various biologists and naturalists have been put forth many
theories to describe the evolution of organisms on the earth. Among them, we will discuss
Lamarck's theory and Darwin's theory of evolution with their criticisms.
1. Lamarck's theory of evolution 20.8
In 1809 AD, Jean Baptiste de Lamarck, a French scientist, Lamarck
proposed the general theory of evolution for the first time.
His theory is popularly known as Lamarck's theory of
evolution.
The Lamarcks' Theory of evolution can be described as
follows:
i. Effect of environment on organisms
ii. Use and disuse of organs
iii. Inheritance of acquired characteristics
348 GREEN Science (Biology) Book-9
i. Effect of environment on organisms
The structural characteristics of an organism change due to the effect of environment. When
an organism lives in a new environment, certain physical needs originate in the organism due
to changed mode of life. For example, the animals that live in cold places have thick fur in the
body to protect them form extreme cold. Similarly, the persons that live in Himalayan region
have more RBCs in the blood than those live in the Terai region. When new characteristics
develop in organisms due to effect of organisms, new species are evolved.
ii. Use and disuse of organs
According to Lamarck, which an organ is used, its size increases and when an organ is
not used for a long time, its size decreases gradually and finally disappears. A constant
use and disuse of organs determine the growth and development of an organ which leads
to modification of the organ. For example, an athlete develops strong muscles due to the
continuous use. Similarly, snakes lost their limbs due to disuse. This theory is known as
use and disuse of organs.
iii. Inheritance of acquired characteristics
Those characteristics which are obtained by an organism during its life time are
called acquired characteristics. Living organisms develop those characteristics due to
environmental effect and use and disuse of organs. According to Lamarck, acquired
characteristics are inherited by offspring form their parents. When acquired characteristics
are transmitted for several generations, new species of organisms are evolved.
According to Lamarck, long-necked giraffe evolved from a short-necked giraffe which
used to graze on the land. Due to scarcity of grass on land, giraffe tried to stretch its neck
to reach the leaves of tall plants. This habit of giraffe resulted in the development of long-
neck in giraffe. This process continued for several generations and finally species of long
necked giraffe evolved.
Short-necked Long-necked
giraffe giraffe
Fig.
20.9
Criticisms on Lamarckism
The major criticisms on Lamarck's theory of evolution are given below:
1. All the acquired characteristics of organisms are not inherited to the offspring.
2. According to Lamarck, new characteristics develop in the organisms according to
wish and need of organisms which is totally incorrect.
GREEN Science (Biology) Book-9 349
3. The change in structure of an organism due to use and disuse of organs is not observed
practically.
Darwin's Theory of evolution Fig.
Charles Darwin's theory of evolution is commonly known as
Darwinism. Charles Darwin was a famous English scientist.
He described the theory of evolution in his book"Origin of
new species by natural selection" which was published in
1859 AD. Darwin's Theory of evolution is also called theory
of natural selection. It can be described in following points.
1. Enormous fertility of organisms 20.10
2. Struggle for existence
Darwin
3. Variation and heredity
4. Natural selection
5. Origin of species
1. Enormous fertility of organisms
Every species have enormous capacity to produce a large number of organisms however
the population of organisms remains constant more or less in nature due to several
factors. The number of offspring produced is always more than the number of organism
that survive in nature. Struggle for food, space and mate among the members of the same
species are the key factors that control the population of a species in nature.
Charles Darwin took example of elephants, the slow breeder. Darwin calculated that a
pair of elephants would give about 19 million offspring in the duration of 750 years. But
this number of elephants is never found on the earth due to several factors.
2. Struggle for existence
Struggle for existence by an organism determines the survival of that organism in nature.
If all the offspring produced by organisms do not die, their number increases in an
uncontrolled manner. But the number of organisms remain more or less constant due to
competition among themselves, with other species or with the environment. This is called
struggle for existence. The struggle may be among the members of the same species. It
is called intraspecific struggle for existence. Similarly, the struggle may be among the
members of different species. It is called interspecific struggle for existence. Climatic
factors also affect the survival of organisms on the earth.
3. Variation and heredity
The structural differences which provide individuality among the numbers of the same
species is called variation. Similarly, the transmission of parental characteristics form one
generation to another is called heredity. Living organisms modify themselves according
to the environment. Those organisms which can adapt in the changing environment
survive and which cannot adapt in the changing environment will disappear.
350 GREEN Science (Biology) Book-9
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