Modern Concept Science and Technology 9

b) Bones are light in weight, air-filled, hollow and reduced. Such bones are known as
pneumatic bones.

c) Body temperature does not change with the change in the temperature of the
surroundings, i.e. they are warm-blooded animals.

d) Locomotion takes place with the help of wings (in air) and legs (on land). Legs have five
digits with claws (pentadactylated).

e) Breathing occurs with the help of lungs.

f) Heart is four chambered (two auricles and two ventricles).

g) Reproduction takes place by laying eggs i.e. they are oviparous. Sexes are separate.

h) Fertilization is internal.

Examples: parrot, sparrow, pigeon, crow, owl, vulture, eagle, etc.

Peacock Ostrich Sparrow Pigeon

FACT WITH REASON

Aves are called glorified reptiles, why?

Aves are called glorified reptiles because most of the characteristics of aves are similar to reptile which
suggests that aves are advanced form of reptiles.

Why do birds have hollow bones and streamlined body?

Birds have hollow bones that makes them light and the streamlined body helps to reduce friction with air,
so that birds can fly easily.

Class Mammalia: (Latin: 'mamma' - breast) Memory Tips

Mammals are the largest group of vertebrates on earth. There are three chief kinds of
They are the most intelligent and advanced creatures. Their mammals: monotremes, marsupials
chief characteristics are as follows: and placentals.
a. Monotremes are the egg-laying
a) Body is divided into head, neck, trunk and tail (if
present). Hairs are present on the body. They have mammals. e.g. platypus, echidna
externally projected ears called pinnae. (spiny ant eater), etc.
b. Marsupials are the mammals
b) Babies of all mammals suckle the milk of their mothers that carry their babies in a pouch.
after birth. e.g. kangaroo, koala bear, etc.
c. Placentals are the mammals that
c) Body temperature does not change with change in nourish babies in placenta before
the temperature of the surroundings, i.e. they are direct birth. e.g. human, cow, etc.
warm-blooded.

Modern Concept Science - 9 293

d) Locomotion mostly takes place with the help of two pairs of limbs (except in humans).
e) Breathing occurs with the help of lungs.
f) Heart is four chambered (two atria and two ventricles).
g) Brain has a distinct region called neocortex. Which is responsible for higher forms of

intelligence.
h) Reproduction takes place by giving birth to young ones directly except in monotremes.

Sexes are separate.
i) Fertilization is internal.
Examples: Human, blue whale, dolphin, bat, kangaroo, duck-billed platypus, etc.

Duck-billed platypus Squirrel Bat

Dolphin Kangaroo Monkey

Mosquito

Mosquitoes are six legged ectoparasites that live around us. They have wings which they flap
to produce a high frequency humming noise. Mosquitoes live in dark places like the ditches,
ponds, forests, tall grasses, house corners, under-beds, etc. They need water sources or moist
soil for laying eggs. Stagnant water, ponds, collected water, etc. are the common places where
they lay their eggs. They act as vectors and transmit diseases from infected person to a healthy
individual. Although they are the part of ecosystem, they cause irritation to humans and
animals by piercing, sucking blood, producing an awful noise and causing diseases.

Memory Tips

Culex Aedes Anopheles 1. Mosquito is a Spanish word for
‘little flies’. They don’t have teeth
but still they can suck blood by
using a long proboscis.

2. Mosquitoes are not seen much
in the winter season because
they hibernate to protect
themselves from cold.

294 Classification of Plants and Animals

Classification and Types of mosquito

Mosquito is an insect. Its systematic classification is given alongside.

Kingdom : Animalia About 3,500 species of mosquitoes have already been identified.
Phylum : Arthropoda Some main types of mosquitoes that have been problematic to
Class : Insecta Nepal and the world are the genus Culex, Anopheles, Aedes,
Mansonia and Culiseta.

Type : Mosquito Mosquito morphology

The body of the mosquito is just few millimetres long. Their body is divided into three
segments: head, thorax and abdomen.

Compound eye

Antenna Hind legs

Head Wing
Mouth parts Abdomen

Thorax

Fore leg Mid leg

External morphology of a mosquito Memory Tips

a) Head Only female mosquitoes bite us.
The head of a mosquito is a small organ in the frontal region

which is responsible for smell, sense, taste and hearing. It consists of the following parts:

i) A pair of compound eyes with small units called facets that help in vision. Each
facet creates an image of an object and sends to the brain.

ii) An occiput is a scaly region just behind the eyes.

iii) A pair of antennae directed forward with long hairy structure called flagellum
that senses smell, sound and vibrations.

iv) A multiple sectioned long proboscis for sucking blood, nectar of flowers and
piercing the skin of humans and animals exists.

v) A pair of short structure called palps present near the proboscis. They sense
several other complex odours like human sweat.

b) Thorax

The thorax is the part of the neck and the mid-body of the mosquito. The thorax is
connected to the head with the help of a short structure. It consists of two major parts:

i) Wings and halters: It has a pair of wings which helps them in flying. Mosquitoes
can fly dozens of kilometres without rest. The wings have dumb bell shaped

Modern Concept Science - 9 295

bristles called halters which help them in balancing and steering through the air.
While flying, they produce an unpleasant and irritating humming sound. But
this sound produced by the females attracts the males for sex as they sense sound
vibrations through their flagellum in antennae.

ii) Hind legs: The thorax has 3 pairs of jointed legs which can detect the sense of taste
and temperature. Because of this feature, they can detect the areas in human skin
with higher temperature (rich blood flow).

c) Abdomen

The abdomen is the posterior part of the mosquito. It contains stomach and the breathing
openings called spiracles. The spiracles help in taking oxygen and is carried to the body
through tubes called tracheae. The abdomen becomes enlarged when the female sucks
in enough blood. It is also the organ for the storage of eggs of female. It should be
noted that the male mosquitoes generally feed on starch and nectar of flowers. Only the
female feeds on the blood of animals.

The abdomen of both male and female mosquitoes has 10 segments altogether. But
some may have fused segments making the total number nine. The abdomen possesses
an opening for anus in the 8th segment and a genital pore on the 9th segment.

Life cycle of a mosquito

The male and the female mosquitoes copulate during their flight and the female lays eggs in
different water sources. The eggs turn into small larvae and then into pupa. The pupa leaves
the water source and flies when it becomes an adult. This process of life cycle occurs through
different distinct stages and is known as metamorphosis. The distinct stages in the life cycle of
mosquito are:

Larvae Egg

Egg Pupae Larvae
Adult
Adult Pupae

Life cycle of anopheles mosquito Life cycle of culex mosquito

a) Egg

The female mosquitoes produce around 30-300 eggs through sexual reproduction
depending on the species and the environment. The eggs are laid either as many single
units or groups that make rafts like structure. The eggs need water to hatch which
normally occurs in two or three days.

296 Classification of Plants and Animals

Anopheles Mosquito Culex Mosquito

Eggs
features

1. Number about 40-100 at a time. about 200-400 at a time.

2. Position They are laid separately and They are laid in rafts vertically on

horizontally on water. water.

3. Shape They are boat shaped. They are cigar shaped.

4. Habitat They are laid on clean water sources. They are laid on dirty water sources.

5. Air floats They have air floats for flotation Air floats are absent.

b) Larvae

When mosquito eggs hatch, the larvae come in water. They start swimming by twisting
and turning. Therefore, they are also called wrigglers or wigglers. These larvae
voraciously feed on organic matter, bacteria and other small microbes in water. Most of
the time, they hang from the surface of water to suck in air through their breathing tube
called siphon. When in danger, they quickly swim to the bottom of the pond or stagnant
water. The growth and development of the larvae occur through series of moulting
or ecdysis in which they shed their skin in order to expand and grow. These stages
are called instars. The larvae undergo four instars which takes about two weeks’ time
during which they shed their skin four times to turn into a pupa.

Anopheles Mosquito Culex Mosquito

Larva features

1. Siphon Respiratory siphon is shorter. Respiratory siphon is longer.

2. Feeding habit They are surface feeders. They are bottom feeders.

3. Position in water They remain parallel to water surface. They suspend at an angle.

The body of larva is mainly divided into three sections: head, thorax and abdomen.

i) Head of larva

The head of larva is an oval structure that projects from the thorax. It bears a pair of
compound eyes, a pair of antennae and the mouth parts. The antennae are not divided
into sections and contain long hairs on them.

ii) Thorax of larva

The thorax of a larva is an oval and hairy structure slightly broader than the head, with no
segments and legs. In the fourth instar, small wings and legs start to be seen in the thorax.

Modern Concept Science - 9 297

iii) Abdomen of larva
The abdomen of the mosquito larva consists of nine segments. On the 8th segment, there

is a respiratory siphon with pores called spiracles. The genitals are in the 9th segment.

FACT WITH REASON

The mosquito larvae are called wriggler, why?
After the eggs hatch and the mosquito larvae come in water, they start swimming by twisting and turning
(wriggling). Therefore, they are also called wrigglers.

c) Pupa

After the larva sheds its skin by ecdysis and comes out of it, a comma shaped pupa,
also called tumblers can be seen. Pupae do not feed as they possess no mouth parts.
They respire through hairs like structures called respiratory trumpets which emerge
out of water surface. Pupae remain suspended in the water surface with the help of two
hairs brushes present on their first segment. On the 9th segment, they have paddles for
swimming. Unlike the larva, the pupa has only two parts in the body: cephalothorax
(fused head and thorax) and abdomen. It remains enclosed in a transparent membrane
called puparium. Within 2-7 days, the pupa turns into an adult by the destruction of
some of its tissues and formation of new ones. This turns pupa into an adult mosquito.

Anopheles Mosquito Culex Mosquito

Pupa features

1. Head The head is small and oval. The head is large and oval.

2. Colour Its colour is green. It is colourless.
Trumets are short and broad. Trumpets are long and narrow.
3. Respiratory
trumets

d) Adult or Imago Memory Tips
At the adult stage, the wings, legs, antennae and the
1. A mosquito’s wings beat 300 to 600
mouth parts of the mosquito are fully developed times per second.
but tightly remain inside the pupal sheath called
the cuticle. The cuticle then ruptures and a fully 2. Adult mosquitoes usually mate
within a few days after emerging
grown mosquito climbs on the surface of water to from the pupal stage.
dry its wings. In a few minutes, the wings dry and 3. The male mosquito can easily find
spread out which enables the mosquito to fly. The the females for mating as the female

fully developed adult mosquito capable of flying is produces a high frequency sound

called an imago. The adult female mosquito requires which the males can sense.

blood meal in order to reproduce and lay eggs.

298 Classification of Plants and Animals

Anopheles Mosquito Culex Mosquito

Adult features

1. Wings The wings are spotty. The wings are transparent.
2. Legs
3. Palpi The adult legs are delicate. The legs are strong.

4. Rest position The palpi are equal in size to Palpi are shorter than the

5. Epidemiology proboscis. proboscis.

Body inclines at an angle of 45° Body remains parallel to the

with the horizontal. surface.

It transmits malaria parasites. It transmits encephalitis and
filarial parasites.

Diseases caused by mosquitoes

Mosquitoes suck human blood by piercing through the skin which is very painful. Ultimately,
they transmit different diseases from infected to a healthy individual by transmitting disease
pathogens. Some species of mosquitoes and the diseases they transmit are:

a) Anopheles: The anopheles mosquito transmits a parasite called Plasmodium which
causes malaria. It also transmits filarial worm and causes lymphatic filariasis or
elephantiasis (Hattipaaile)

b) Culex: The culex also transmits lymphatic filariasis, Japanese encephalitis, dengue and
also meningitis.

c) Aedes: The aedes mosquito transmits the viruses which cause dengue, yellow fever and
chikungunya. It also causes lymphatic filariasis in Asia.

FACT WITH REASON

Mosquito is a harmful insect, why?
Mosquito is harmful insect because it transfers life threatening diseases, its sound is annoying and its bite
is painful.

Malaria

Malaria is a mosquito-borne disease which is characterized by fever, headache, chill, vomiting,
seizures or even death. It is caused by a protozoan called Plasmodium vivax. The transmission
of malaria can be understood by these stages:

a) Asexual cycle in humans (secondary host): When a healthy host is bitten by Anopheles
mosquito bearing the Plasmodium cells which are in a stage called sporozoites, they
travel through the blood stream of that person into the liver. They multiply in thousands
of number in the liver cells and are ruptured which releases the Plasmodia finally into

Modern Concept Science - 9 299

the blood again. Then, they infect the RBCs of blood and also divide them by asexual
reproduction. The RBCs are then ruptured repeatedly because of which the person gets
chill, sweating, fever, anaemia or even death.
b) Sexual cycle in humans (secondary host): After many generations of division, the
formation of sexual cells called gametocytes occur which leads to the formation of
gametes later on in the mosquito’s body.
c) Sexual cycle in Anopheles (primary or definitive host): When an Anopheles mosquito
sucks the blood of a person infected by malaria, the Plasmodium gets sucked too. Then,
the gametocytes produce male and female Plasmodia by sexual reproduction and form
a zygote. The zygote multiples and forms many other cells in the intestine of Anopheles.
These cells then travel to the salivary gland and are ready to get transferred to other
hosts when bitten.

Control measures of mosquitoes

Mosquitoes can be controlled by the following methods:

a) Killing of eggs, larvae and pupa: Mosquitoes breed in the areas having stagnant or still
water e.g. in drains, ditches, ponds, containers, etc. The different stages like the eggs,
larvae and pupa can easily be killed as they cannot fly. We can kill these mosquitoes
using chemicals like kerosene, paraffin oil, DDT, BHC, Paris green dust, etc. Petroleum
liquids clog their respiratory siphons and suffocate them to death. Similarly, DDT, BHC
etc. poison the water and their bodies, however, they kill other organisms too.

FACT WITH REASON

How does the spraying of kerosene in stagnant water bodies controls population of mosquito?
Stagnant water is a breeding place of mosquitoes. Kerosene sprayed in stagnant water bodies floats on
water surface. It blocks the siphon of larva and trumpet of pupa and they die of suffocation. So, spraying of
kerosene in stagnant water bodies controls population of mosquito.

b) Disruption of breeding places: Most mosquitoes breed on water and moist soil that could
be flooded. Filling puddles nearby with soil, sand or concrete prevents mosquito breeding
in the residential areas. Damp and moist places should be dried out. If possible, people
should build their homes far away from rivers, ponds and marshy areas. Water holding
objects like the tin can, buckets, tyres, etc. should not be kept open in the rainy season.
Clearing drains, bushes and spreading DDT on them also decreases the mosquito number.

FACT WITH REASON

Why should we cover ditches nearby our home?
We should cover ditches nearby our home because mosquito lays eggs in stagnant water of ditches.

c) Killing of adult mosquitoes: The adult mosquitoes like to live in moist and damp places.
Spraying DDT, burning sulphur, mosquito repellents, baygon etc. can kill mosquitoes
directly. At least, the home and surroundings can be kept clean to discourage mosquito

300 Classification of Plants and Animals

breeding. They can be controlled by biological method too. Those places which cannot
be filled like the pond and lake can be turned into fish rearing places. Some fishes like
the carps, pearlfish, sticklebacks, gambusia etc. feed on mosquito larvae and other
young stages.

d) Self-protection: Protection from mosquitoes can be challenging. Despite worldwide
efforts, mosquito has been very successful in developing resistance against many
mosquito killing chemicals like DDT and some pyrethroids (chemical in mosquito nets).
So, it is best to stay protected in the individual level by staying away from mosquito bite
in the first place. Using mosquito repellents, using wire-nets in doors, windows and
ventilations, wearing full-sleeved shirts and pants, applying mosquito repellent creams
like odomos, mustard oil etc. can keep off mosquitoes from our homes.

ANSWER WRITING SKILL

1. What is binomial system of nomenclature?
Ans: The system in which an organism is given a name of two Latin words called generic and specific name

is called binomial system of nomenclature.
2. Write the scientific name of frog.
Ans: The scientific name of frog is Rana tigrina.
3. Write any two methods of controlling mosquitoes.
Ans: The two methods of controlling mosquitoes are:

i) By spilling kerosene or other chemicals over stagnant water.
ii) By killing the adult mosquitoes with insect repellants and killers.
4. Name any four classes of Arthropoda.
Ans: The four classes of Arthropoda are: Crustacea, Arachnida, Insecta and Myriopoda.
5. Write any two differences between algae and fungi.
Ans: The differences between algae and fungi is tabulated below:

S.N. Algae Fungi

1 They are autotrophic. They are heterotrophic.

2 Their cell wall is made up of chitin and cellulose. Their cell wall is made up of glycogen.

6. Why is owl an ave but bat a mammal?

Ans: Owl is an ave because it is oviparous and has no mammary glands in females. But bat is a mammal
because female bats have mammary glands to suckle milk to their babies.

7. Write in brief about cold and warm-blooded animals.

Ans: Cold-blooded animals are those animals which change their body temperature according to the
change in surroundings. They cannot keep their body temperature constant. They also usually go for
hibernation and aestivation to protect themselves from extreme weather. Warm-blooded animals, on
the other hand, cannot change their body temperature according to the surroundings. They keep their
body temperature constant. For humans, the constant body temperature is 37°C.

Modern Concept Science - 9 301

8. An animal lays eggs but is a mammal. Write any two other characteristics of that animal with its name.
Ans: The name of the animal is duck-billed platypus. The two other characteristics of platypus are:

i) Mother suckle milk to their babies.
ii) They spend most of their time in water.
9. What do reptiles and Pisces have in common? Write in three points.
Ans: The common features between reptiles and pisces are given below:
i) Both reptiles and Pisces are the classes of vertebrata.
ii) They have scales in their body.
iii) They are cold-blooded organisms.
10. Discuss the life cycle of a mosquito.
Ans: The life cycle of a mosquito completes in four different stages named egg, larva, pupa and adult as
described below:
i) Egg: The female mosquitoes produce around 30-300 eggs through sexual reproduction depending

on the species and the environment. The eggs are laid either as many single units or groups that
make rafts like structure. The eggs need water to hatch which occurs after two-three days.
ii) Larvae: After the eggs hatch, the larvae come out of them and start swimming by twisting and
turning (wriggling). These larvae voraciously feed on organic matter, bacteria and other small
microbes in water. Most of the time, they hang from the surface of water to suck in air through
their breathing tube called siphon. The larvae undergo four instars in about 2 weeks’ time during
which they shed their skin four times to turn into a pupa.
iii) Pupa: After the larva sheds its skin by ecdysis and comes out of it, a comma shaped pupa emerges
out. They do not feed as they possess no mouth parts. They respire through hairs like structures
called respiratory trumpets. Within 2-7 days, the pupa turns into an adult by the destruction of
some of its tissues and formation of new ones. This turns pupa into an adult mosquito.
iv) Adult or Imago: At the adult stage, the wings, legs, antennae and the mouth parts of the mosquito
are fully developed but tightly remain inside the pupal sheath. The cuticle then ruptures and a
fully grown mosquito climbs on the surface of water to dry its wings. In a few minutes time, the
wings dry and spread out which enables the mosquito to fly. The fully developed adult mosquito
capable of flying is called an imago.
Thus, the life cycle continues.

STEPS EXERCISE

STEP 1

1. Define taxonomy and taxon.
2. What is classification and nomenclature?
3. Write the meaning of genus and species.
4. Who introduced the five kingdom system?

302 Classification of Plants and Animals

5. Name the five kingdoms of the five kingdom system.
6. What is alternation of generation?
7. What are vascular bundles?
8. Define a tracheophyte.
9. Write the Greek etymological meaning of Tracheophyta.

10. Write the definition of reticulate and parallel venation.
11. What is a notochord?
12. Give any two examples of chordates.
13. What is a digestive tract?
14. Name two mammals that lay eggs.
15. Which mosquito causes malaria?
16. What is metamorphosis?
17. Write the meaning of an imago.

STEP 2

18. Write the rules for writing the scientific name.
19. Write any two differences between bryophyte and pteridophyte.
20. Are jellyfish and cuttlefish types of fish? Why/Why not?
21. Why is a frog called a cold-blooded animal?
22. How is the five kingdom system advantageous over the two kingdom system?
23. Why are dolphins and whales called mammals even they swim like fishes?
24. Write any two differences between monocot and dicot.
25. How are chordates and non-chordates different? Write in two points.
26. Write the meaning of diploblastic and triploblastic germ layers.
27. Give any two similarities between ant and spider.
28. Mention any two differences between spider and cockroach.
29. Why is water essential for the completion of a mosquito’s life cycle?

STEP 3

30. Mention any three characteristics of the following:
a) Algae
b) Gymnosperms
c) Angiosperms
d) Chordata

Modern Concept Science - 9 303

31. All vertebrates are chordates but all chordates are not vertebrates. Justify this statement.
32. Explain the structure of the head of a mosquito.
33. How does the mosquito pupa live in water? Describe.
34. Identify the following in the pictures and write short note about them.

a) b) c) d)

e) f) g) h)

35. Draw a well labelled diagram of the following:
a) Larva of anopheles and culex
b) Pupa of anopheles and culex
c) Adult of anopheles and culex
d) Monocot and dicot seeds

STEP 4

36. Describe the process of transmission of malaria in human.
37. Explain the life cycle of a mosquito in brief.
38. Make a table and compare monocot and dicot on the basis of root, leaf, stem and vascular

bundles.
39. Make a chart of the animal kingdom including the chordates and the non-chordates.
40. What are tracheophytes? Name the two sub-divisions of tracheophyta. Why are

gymnosperms and angiosperms called tracheophytes?

304 Classification of Plants and Animals

UNIT Estimated teaching periods Theory Practical
5 1
17
ADAPTATION

OF ORGANISMS

Syllabus issued by CDC Flying peacock

 Introduction to adaptation
 Aquatic adaptation in plants and animals
 Terrestrial adaptation in plants and animals
 Bacteria and fungi: importance, harmful effects and control measures
 Virus: classification, mode of transmission, harmful effects and control measures.
 Protozoa: introduction and diseases caused by them

LEARNING OBJECTIVES

At the end of this unit, students will be able to:
 enlist various types of aquatic and terrestrial organisms.
 describe the adaptational characteristics of plants and animals with examples.
 introduce some microscopic organisms (viruses, bacteria, fungi and protozoa) and list human

diseases caused by them.

Key terms and terminologies of the unit

1. Adaptation: Adaptation is the process by which organisms adjust themselves in the

environment in which they live.

2. Structural adaptation: The process of adaptation which involves change in body parts or organs

of individuals to adjust with the surroundings is called structural adaptation.

3. Camouflaging: The process of adapting the colour and texture of the body of organisms

to match the surroundings is known as camouflaging.

4. Behavioural adaptation: The process of adaptation which involves change in the behaviour of

individuals to adjust with the surroundings is called behavioural adaptation.

5. Physiological adaptation: The process of adaptation which involves change in biochemical

processes in the body of organisms is called physiological adaptation.

6. Prey and predator: A predator is an organism that naturally feeds on other organisms. The

organism on which the predator feeds is known as the prey.

7. Hydrophytes: The plants that grow in water and the swampy areas are known as

aquatic plants or hydrophytes.

8. Mesophytes: The plants that need moderate amount of water for survival are known as

mesophytes.

9. Arboreal animals: The animals that spend most of their time climbing on trees are known as

arboreal animals.

Modern Concept Science - 9 305

10. Aerial animals: Animals that fly from one place to other for food and shelter are known as
aerial animals.
11. Fossorial animals:
The animals that live underground in borrow and holes are known as
12. Xerophytes: fossorial animals
13. Aerenchyma:
14. Nocturnal animals: The plants that live in dry habitat and need less water are called xerophytes.

15. Diurnal animals: Aerenchyma are plant tissues that are filled with air and are buoyant.

Animals that are active during the night time are known as nocturnal
animals.

Animals which are active during the day and sleep at night are known as
diurnal animals.

Meaning of Adaptation

Every organism that we see around has the ability to cope with the environment it lives in.

This process of adjusting with the environment is called adaptation.
Memory Tips
Adaptation is the process by which organisms adjust

themselves in the environment in which they live. It is 1. Organisms that have better

not an easy task. We know that how much humans have adaptation features have more

to adjust during summer, winter, rains and floods. It is chance to survive than the

much more difficult for other organisms. If the earth had strongest ones.

been perfect without change, then every organism would 2. Adaptation results variation

have been more or less the same. But due to the change which is a cause of evolution.

in environment, organisms face different challenges like

temperature, food, habitat, survival from enemies and need for reproduction to live. It is to be

noted that those organisms which have the ability to adapt with the environment survive and

those which do not have the ability will be extinct.

FACT WITH REASON

Why is adaptation necessary?
Adaptation is necessary to survive in the surrounding environment and to be chosen by nature.
Why do chameleons change their body colour?
Chameleonschangetheirbodycolourtoadaptwiththesurroundingsforcatchingpreyandavoiding predators.

Aquatic adaptation

The adaptation of plants and animals in watery areas is known as aquatic adaptation. Living
in water can be dangerous in terms of food, hunting prey and protecting themselves from
predators. A short description of the aquatic plants and animals are given below:

Aquatic plants (Hydrophytes)

The plants that grow in water and the swampy areas are known as aquatic plants or hydrophytes.
These plants need to have special characteristics to adjust themselves in the water.

306 ADAPTATION

FACT WITH REASON

Aquatic plants have poorly developed root, why?
Aquatic plants have poorly developed root to avoid excess absorption of water because these plants grow
in water.
Aquatic plants have air sacs in aerenchymatous tissues, why?
Aquatic plants have air sacs in aerenchymatous tissues to make them spongy, light, buoyant and flexible.
Why do aquatic plants have thin, long, slender and ribbon shaped leaves?
Aquatic plants have thin, long, slender and ribbon shaped leaves to absorb large amount of sunlight for
photosynthesis.

Classification of Hydrophytes

a) Free floating hydrophytes
The hydrophytes that remain floating on the surface of water without attaching its roots
to the soil are known as free floating hydrophytes. For example, pistia, lemna, water
hyacinth, water lettuce, etc.

Water hyacinth Pistia Lemna Jussiaea Wolffia

b) Rooted free floating hydrophytes

The hydrophytes that remain floating on the surface of water by attaching their roots
inside the soil are known as rooted free floating hydrophytes. For example, lotus, water
lily, marsilea, etc.

Waterlily Marselia Lotus

FACT WITH REASON

Lotus has wider leaves and lots of stomata, why?

Lotus has wider leaves and lots of stomata because wider leaves help to float on water surface and numer-
ous stomata help to lose excess of water from body.

Modern Concept Science - 9 307

c) Submerged floating hydrophytes

The hydrophytes that remain under water without attaching their roots in the soil are
known as submerged hydrophtes. For example, Ceratophyllum, Utricularia, water
starwort, etc.

Ceratophyllum Utricularia

d) Rooted submerged hydrophytes

The hydrophytes that remain under water by attaching their roots in the soil are known
as rooted submerged hydrophytes. For example- hydrilla, chara, etc.

Hydrilla Vallisneria Chara

e) Rooted emergent or swampy hydrophytes

The hydrophytes that grow in swampy places and submerge their lower stem in water
are known as rooted emergent hydrophytes. For example, Reedmace, sagittaria, etc.

Sagittaria Ranunculus Typha

Adaptational characteristics of hydrophytes

Some important adaptational characteristics of hydrophytes are given below.

i) The root system of hydrophytes is poorly developed. They do not have root caps and root
hairs.

308 ADAPTATION

ii) The submerged hydrophytes have long, slender, spongy and flexible stems to move
easily in the direction of water current.

iii) The leaves are thin and small in case of submerged plants whereas in the free floating
plants, the leaves are large and broad with air spaces which make them lighter to float
on water.

iv) Their conducting tissues (xylem and phloem) are poorly developed.
v) Floating plants have aerenchymatous tissues which provide buoyancy to make them

easy to float.
vi) Hydrophytes are covered with waxy layer which prevents water from entering them

and protects the plants from decaying.

FACT WITH REASON

Submerged plants have very small leaves. Why?
Submerged plants have very small leaves to avoid damage due to current of moving water.
Aquatic plants have waxy coating in stem, root and leaf. Why?
Aquatic plants have waxy coating around it to prevent decaying. It blocks water and bacteria in it.

Aquatic and amphibian animals
An animal that lives in water is known as aquatic animal. For example, fish, shark, prawn
etc. There are both vertebrates and invertebrates aquatic animals. Prawn, starfish, sea urchin,
octopus etc. are invertebrate aquatic animals while dolphins, whales, etc. are vertebrates.
They complete their life cycle inside the water.
Adaptational characteristics of aquatic animals
The following are the major adaptational characters of the aquatic animals.

i) The body of aquatic animals is streamlined or boat-shaped so that they can swim easily
in water by reducing friction.

ii) The respiratory organs of aquatic animals are the pairs of gills. Dolphins and whale- like
sea mammals respire through lungs and they take in oxygen from the air.

iii) They have fins (e.g. fish) or flippers and paddles (e.g. whale) or webbed-legs (e.g. frog,
tortoise) for locomotion or swimming in water.

iv) Their body is covered with waterproof scales or cuticle to protect the body from decaying
due to the entry of water inside it.

v) They have a long tail which helps to change the direction while swimming.
vi) The aquatic animals are cold-blooded animals or poikilothermic animals i.e. they can

adjust their body temperature to live in water in all seasons.
vii) They have air sacs or air bladder in their body which makes their body light and easy

for them to swim inside the water.

Modern Concept Science - 9 309

Fish Whale Dolphin Frog

FACT WITH REASON

Fishes can live in water without decomposition, why?
Fishes can live in water without decomposition because of the presence of waxy coating of water-
proof scales on their bodies.
A fish can breathe under water. Give reason.
Fish can breathe under water because fish have gills that can absorb oxygen which is dissolved in water.
Whales repeatedly come out of the water, why?
Whales repeatedly come out of the water to breathe through the blowholes with the help of lungs.
Small fishes live in the oceans in large shoals. Why?
Small fishes live in the oceans in large shoals to defend against predators and confuse them as being larger.
Ducks have webbed feet, why?
Ducks have webbed feet which allows them to paddle and swim in the water more smoothly. When ducks
swim, the webbing catches the water and helps in pushing it behind the duck.

Mesic adaptation

The type of adaptation in areas of moderate water conditions is known as mesic adaptation.
Mesic plants (Mesophytes)
The plants that need moderate amount of water for survival are known as mesophytes. Some
of the mesophytes are: mango, pumpkin, banana, pea etc. Mesophytes grow in areas which
are neither too dry nor too wet. They are rooted in hard top soil and are adapted to search
water inside the soil with the help of their strong roots. The adaptational characteristics of
mesophytes are as follows:

i. Mesophytes includes basically herb, shrub and tree. They have well developed root
system with root hairs.

ii. In mesophytes, the stems are solid, hard with many branches.

iii. Generally, they have leaves with large size, broad, thin and variously shaped with
numerous stomata.

iv. Mechanical tissues and conducting tissues are well developed.

v. Weak and climber plants like cucumber, pumpkin, etc. have hooks, tendrils, aerial roots,
etc. They help in climbing up.

310 ADAPTATION

FACT WITH REASON

Why do mesophytes have developed root?
Mesophytes have developed root to collect enough water from land.
Why do climbers have tendrils?
Climbers have tendrils to climb high in trees or support so that these plants can collect sunlight.

Mesic animals
The animals that live in moderate water conditions are known as mesic animals. Depending
on their habitat, they are divided into various types:

a) Arboreal animals
The animals that spend most of their time climbing on trees are known as arboreal
animals. Some of the arboreal animals are monkey, squirrel, tree snake etc. Some of the
adaptational characteristics of arboreal animals are as follows:

i) Arboreal animals have sharp claws and nails for climbing the trees.
ii) Some of them like the lizards have sticky adhesive pads on their legs that enable

them to crawl vertically.

FACT WITH REASON

Lizards can walk easily on ceilings, why?
Lizards can walk easily on ceilings because lizards have adhesive pads on their legs which help to stick on
ceiling.

iii) Monkeys have a tail that can anchor the tree branches and also help in balancing.
Such kind of tail is called the prehensile tail. The prehensile tail act as a balancing
and anchoring organ.

iv) Flying squirrels have muscular folds of skin called patagium that joins their fore
limbs and hind limbs. The patagium helps them to remain in the air for a long
time during their gliding flight.

v) Claws are highly flexible which support the body whenever these animals apply
force to jump, hang or run.

vi) Tree snakes have strong muscles that can twist round a tree stem or branch to
support itself.

vii) The body size of arboreal animals are generally small which enables them to pass
through narrow branches.

FACT WITH REASON

The body of arboreal animals is flexible, why?
The body of arboreal animals is flexible which enables them to pass through narrow branches.

Modern Concept Science - 9 311

b) Aerial animals

Animals that fly from one place to other for habitat and food are known as aerial
animals. For example, pigeon, bat, butterfly, dragonfly etc. Some of the adaptational
characteristics of arboreal animals are as follows:

i) The bodies of aerial animals are streamlined. A streamlined body can move
swiftly in the air.

ii) The forelimbs of the aerial animals are modified into wings that help them to fly
in the air.

iii) The wings contain soft and hairy feathers that insulate heat and make the flying
smooth.

iv) The breast muscles of aerial animals are directly exposed to air current during
flight. So, they are strong enough to protect their internal organs.

v) The bones or skeleton are in reduced form. Heavy bones are not present. The
bones are lighter, hollow and filled with air called the pneumatic bones. The
pneumatic bones decrease the weight of an aerial animal and help it to fly with
lesser force applied.

FACT WITH REASON

Why do birds have pneumatic bones and strong flight muscle?

Birds have pneumatic bones that make bird light and strong flight muscles in wings help them to fly for
longer duration.

Why do birds have thick chest muscle?

Birds have thick chest muscles to prevent damage to internal organs while flying.

vi) In order to reduce weight, the teeth in the beaks Memory Tips

are absent. The beaks are modified according to Eagle can see their prey two miles

the feeding habit. away.

vii) The aerial animals have sharp claws with
pointed nails modified for different habitats and feeding habits. The claws help
in catching, climbing, flying, tearing, scratching etc.

Xeric adaptation

The word xeric means dry. Generally, xeric environment receives very less annual rainfall and
mostly remain dry throughout the year.

Xeric plants (Xerophytes)

The plants that live in dry habitat and need less water are called xerophytes. For example,
cactus, aloe vera, opuntia (prickly pear) etc. Some of the adaptational features of the xerophytes
are as follows:

i) They have a well-developed root system which is fixed very deeply in the soil to
absorb water from soil. There are a number of root hairs present in the roots.

ii) The leaves are reduced to thorns (in case of desert plants) and they are needle
shaped (in case of plants found in cold climate) to reduce transpiration and
prevent the leaves from decaying due to the snow respectively.

312 ADAPTATION

iii) The stems of desert plants are thick fleshy to store water.

iv) The leaves and stem have thick cuticle to reduce the loss of water.

v) The stomata are deep-seated which avoid the loss of water.

vi) The leaves of the plants found in cold climate are arranged in the shape of a cone
to drop the snow falling on them.

FACT WITH REASON

Xerophytes have highly developed and wide spread root and fleshy stem, why?
Xerophytes have highly developed and widespread roots to collect water whenever found and fleshy stem
helps to store water for longer time.
Desert plants have green stem with leaves reduced to thorns, why?
Desert plants have green stem for photosynthesis and leaves are reduced to thorns to reduce transpiration.

Cactus Opuntia Aloe Zizyphus

Some xerophytes

Xeric Animals (Desert animals)

Desert animals like the camel, lizard, desert snakes, Memory Tips skin
desert rats, scorpions etc. have the best adaptational
characteristics for surviving in dry environment. Some of Some of the desert animal’s
the characteristics are listed below: absorbs water vapour from air.

i) Camels in the desert face long term hunger, thirst and sand winds. They have
long eyelashes and muscular nostrils to protect themselves from sand winds.

ii) Similarly, they have a raised muscular hump that stores fat for further use. This is
why camels can walk longer without food.

iii) Camels can walk without difficulty in deserts as they have fleshy hoofs that are
flat, broad.

iv) They have long and strong legs that can hold their weights properly in sand.

v) Camels conserve water by passing the faeces and urine at low water concentration.

vi) Most of the desert animals get water from the succulent organs of desert plants,
blood and fluids of other animals and occasional rainfall.

vii) In the case of animals, most of the animals like the desert snakes, scorpions etc.
are venomous. They use their poisonous fluids to attack and defend themselves
from other organisms.

viii) Some desert animals like the desert viper and desert lizard can turn their skin
colour according to the colour of the sand. This makes them sit quiet; look for
their prey and also protect themselves from predators.

Modern Concept Science - 9 313

ix) Desert animals (desert fox, lizards etc.) often hide themselves in the holes during
hot daytime. They come out at the night time for catching their prey. So, most of
them are nocturnal in nature.

Camel Desert horned viper Scorpion

FACT WITH REASON

Camels can live easily in deserts, why?

Camels can live easily in desert because flat hooves help to walk, thick skin prevents loss of water, food is
stored in hump and they have very sensitive sense organs.

Micro-organisms and pathogens: bacteria, fungi, viruses and protozoa

Micro-organisms are very old microscopic creatures existing on the earth. They may belong to
any of these kingdoms: Monera, Protista, Fungi or Plantae. They are found everywhere: sand,
soil, air, water, human body, plant body etc. Some micro-organisms that we shall discuss in
this chapter are: bacteria, fungi, protists like protozoan and virus (although many biologists
do not consider virus as organisms).

Bacteria (sing. bacterium)

Bacteria are the simplest organisms that are found almost everywhere on earth. They were
discovered by biologist Antonie von Leeuwenhoek in 1676 A.D. A short history of scientists
and their contribution on study of bacteria are shown in the table below:

Date (A.D.) Scientist Discovery
1676
Anton von Leeuwenhock Discovered bacteria and
1838
1876 and 1864 named them animalcules

Christian Ehrenberg Coined the term bacteirum

Robert Koch and Louis Established that bacteria

Pasteur can cause diseases

Some of the characteristics of bacteria are as follows: Bacteria

i) They are the simplest unicellular prokaryotes i.e. Memory Tips

they do not have nucleus and membrane bound In five hours a single bacteria could
organelles. theoretically give rise to more than 1

ii) They are microscopic (size in micrometres) and billion offspring.
cannot be seen with naked eye.

iii) They have a cell wall around them.

iv) Some bacteria are autotrophic and others are heterotrophic.

314 ADAPTATION

v) Some can bear high temperature as high as boiling point of water and as low as freezing
point of ice.

vi) They are everywhere: in air, water, upper atmosphere, inside earth’s crust, volcanoes
and even in fires and fridges.

vii) They are of different shapes and sizes.

viii) They can cause pimples in skin, make our sweat stinky, cause tooth-decay or make us sick.

ix) They cause the decomposition of dead bodies and organisms.

x) Bacteria don’t need to be males and females for reproduction. They reproduce asexually
by fission (body division).

Types of bacteria

On the basis of their shapes, bacteria are categorised into four major types:

a) Coccus (spherical) : These bacteria are spherical in structure. They generally occur
in single form, pair, chain or cluster and are named accordingly as shown in the given
figure below. e.g., Streptococcus pneumoniae, Neisseria gonorrhoeae etc.

b) Bacillus (rod shaped) : They are rod-shaped or linear. They are both harmful and
non-harmful. Some of them live in the human gut. e.g. Salmonela typhi, Escherichia coli,
Shigella shiga etc.

c) Spirillum (spiral) : They are the bacteria which are spiral shaped. Some of them cause
stomach inflammation and ulcer. Some of them help in food digestion. e.g. Helicobacter
pylori, Treponema pallidum etc.

d) Vibrio (comma- shaped) : These are comma-shaped bacteria, e.g. Vibrio cholera, Vibrio
harveyi etc.

Cocci bacteria Bacilli bacteria Spirillum Vibrio cholera

Types of bacteria

Beneficial effects of bacteria

Bacteria are not always harmful to us. They are also extremely useful to us in many ways.
It is believed that the oxygen in the atmosphere that we breathe was firstly produced by the
bacteria. They are important in many ways as they perform the following tasks:

a) Production of oxygen : The autotrophic bacteria produce oxygen in different habitats
like the atmosphere, land, sea, oceans etc. and balance the exchange between carbon

and oxygen.

b) Feeding plants with nitrogen : Plants cannot take nitrogen gas through their roots.
The bacteria that are present in the air and soil simply convert the atmospheric nitrogen

Modern Concept Science - 9 315

into nitrates and nitrites (plants usable form). Thus, the plants become able to prepare
their food on which all living organisms depend on.

c) Production of different chemicals and food products : Bacteria are used to obtain
yoghurt, cheese, acetic acid, lactic acid, various amino acids by which proteins are
formed. The bacteria Streptococcus salivarius is used in cheese and yoghurt making. The
Lactobacillus and acidophilus convert milk to curd.

d) Extraction of antibiotics and medicines : Some bacteria types are especially used to prepare
antibiotics which in turn help to treat different forms of infections and diseases. Antibiotics
like streptomycin, erythromycin, chloromycetin, etc. are derived from the bacteria.

e) Removal of environmental pollutants : Some bacteria feed on oil spills in the ocean,
nuclear wastes, sewage etc. and help control environmental pollution.

f) Digestion of food : Bacteria like the bifidobacteria help in preventing diarrhoea, yeast
infection and indigestion. Escherichia coli helps to feed and digest the undigested sugars
and helps in the digestion of food.

g) Production of vitamins : Certain types of bacteria produce vitamins like vitamin B12
and vitamin K which are helpful in our body for metabolism and clotting of blood.

h) Decompostion of waste and dead matter : Bacteria directly feed on wastes and dead
organic matter. They then convert complex compounds into simpler compounds and
help in recycling dead organic matter.

FACT WITH REASON

People plant leguminous plants in field after interval of few years, why?
People plant leguminous plants in field after interval of few years because root nodules of such plants have
bacteria that changes atmospheric nitrogen into nitrogenous compounds. It increases fertility of soil.

Harmful effects of bacteria

Certain types of bacteria cause diseases in Disease Pathogen
animals, humans and plants. The harmful
effects of bacteria are as follows: 1. Cholera Vibrio cholerae

a) Some bacteria can cause infections and 2. Diphtheria Corynebacterium diphtheriae
diseases in throat, brain, spinal cord,
3. Gonorrhea Neisseria gonorrhoeae

4. Leprosy Mycobacterium leprae

5. Stomach ulcer Helicobacter pylori

lungs and they can be fatal. 6. Tuberclosis Mycobacterium tuberculosis

b) Bacteria can rot vegetables, meat, milk, 7. Pneumonia Streptococcus pneumonide
fruits, eggs and other organic products. 8. Typhoid Salmonella typhi

So, we cannot eat those foods that smell bad and which are kept for many days without

refrigeration. They might cause food poisoning and even cancer.

c) Bacteria can cause several diseases in plant parts affecting the growth of flower, fruits,
seeds, leaves, food making, productivity etc.

d) They can severely affect the person suffering from AIDS and cancer shortening their
lifetime.

316 ADAPTATION

e) Bacteria can cause several diseases in human like tuberculosis, leprosy, diarrhoea,
titanus, pneumonia, plague, meningitis, STDs like gonorrhea, syphilis, etc. Some human
bacterial diseases along with their causative agent are mentioned in the given table.

Control measures of bacteria

The harmful effects of bacteria can be controlled by the following methods:

a) In plants : Only healthy plant seeds should be sown. If the land has a history of infection,
we should use medicines.

b) In animals : Infected animals should be kept far from other animals and human. Most
bacterial diseases can be transmitted from an infected to healthy individual. Such
animals need to be administered with antibiotics.

c) In humans : Rules of personal hygiene should be followed. Rotten, odourous, stale,
open, uncooked, unwashed etc. foods should be avoided. Antibiotics should be used as
prescribed by doctor in correct dose during infection.

d) In environment : Organic foods, garbage, dung, hospital wastes, sewage, drain etc.
should be properly managed as they may transmit several bacterial diseases.

Fungi (sing. fungus)

Fungi are non-green organisms that mostly have filamentous bodies. They look like plants
because they are immobile and grow on soil. But, a fungus is very different from a plant. In
fact, fungi are not plants. Look at the following points why they are not plants:

a) Plants belong to plantae kingdom but fungi have a separate kingdom.

b) Plants are green and photosynthetic but fungi are non-green.

c) Most fungi have filamentous bodies that look like fibres while most plants do not have.

d) Plants have cell walls made up of cellulose but fungi have chitin in their cell walls similar
to that of insects.

e) Food storage occurs in the form of glycogen like that of animals. Plants, on the other
hand, store food in the form of starch.

Therefore, fungi are more closely related to animals than to plants.

Mushroom Yeast Bread mould

Fungi

Characteristics of fungi

a) Habitat : Most fungi are terrestrial but some are aquatic too.

b) Body : The body of fungi is both unicellular (e.g. yeast) and multicellular (e.g.

Modern Concept Science - 9 317

mushroom) but thallus in nature. The plant body is filamentous and has thread-like
branches called mycelium. The units of mycelium are called hyphae.
c) Nutrition : Fungi do not bear chlorophyll and are non-green. So, they are heterotrophic
in nature. Some are saprophytic while the rest are parasitic and symbiotic.
d) Food storage : The fungi store food in the form of glycogen.
e) Cell wall : The cell wall of fungus is made up of a modified carbohydrate called chitin.
f) Reproduction : They reproduce both by asexual and sexual methods.
Advantages of fungi
Fungi are an integral part of an ecosystem as decomposers. They have several advantages
which are listed below:

i) Fungi are the armies of nature. They feed on dead and decomposed organic matter and
recycle them.

ii) They decompose waste matter. They are the decomposers of the ecosystem which return
the nutrient values of organic wastes to the soil.

iii) They are of nutritious value. The fungus mushroom is used as food as it contains several
proteins, vitamins and minerals essential for our body. They help to prevent high
cholesterol, diabetes, high blood pressure and cancer.

iv) They help in liquor industry. The fungus yeast is used in fermentation of alcohol in
liquor industry and in bakeries.

v) They have medicinal value. Antibiotic called penicillin is extracted from the fungus
called penicillium.

vi) Fungi balance the biogeochemical cycles. They help to balance the carbon and nitrogen
cycles on the earth.

Disadvantages of fungi
i) Eating them can be fatal. Some poisonous mushrooms and other fungi like the Mucor,

Rhizopus, etc. have toxins which can cause food poisoning and even death.
ii) They cause infections in plants and animals. Fungus called Albugo can cause ‘white rust’

disease in plants. They cause the roots to die, leaves to wilt and wither and seedlings to
stop growing. They can infect human skin with ringworm (caused by fungus; not a worm).
iii) They rot fruits and vegetables and make them inedible.
iv) They can cause rashes under armpits and genitals and cause itchy sensation.
Control measures of fungi
Some species of fungi are parasitic and pathogenic too. They cause diseases in plant, animals
and human. Some of the control measures that we can adopt against fungal infection are:

i) Using certain products and chemicals like salt, oil, sugar, etc. which prevents growth of
fungi.

ii) Using fungicides we can kill and destroy fungal growth.
iii) We can refrigerate foods to prevent fungal attraction.

318 ADAPTATION

iv) Paying attention to personal hygiene and applying anti-fungal ointment we can control
fungal growth.

v) We can control fungal growth by storing pickles under hot sunlight and preventing in
damp places.

Virus (sing. virion) Capsid
Head
Viruses are microscopic pathogens which often cause diseases in DNA
human, animals and plants. Scientists consider them a borderline Tail
between living and non-living organisms. The word virus is derived
from Latin word “virion” meaning poison. The size of virus ranges Tail
from 25 nm to 250 nm. They contain genetic materials like RNA or DNA fibres
enclosed in a protein coat. They are not considered as a living organism
as they cannot reproduce independently but require a host cell. Virus Bacteriophage virus
multiply and reproduce only inside a host cell. For this reason, they are
called obligatory parasites.

FACT WITH REASON

Virus is called obligatory parasite, why?

Virus is called obligatory parasite because only inside the host cell these can replicate otherwise virus is
just like a non-living thing.

History of virus
The study of virus is known as virology. Adolf Mayer in 1886, discovered virus but did not

know its properties. Dmitri Ivanovski in 1892, studied virus. He discover TMV (tobacco mosais
virus). Wendel Stanley in 1935, crystallized virus.

Characteristics of virus
a) Viruses are considered as a borderline between living and non-living organisms.
Living characteristics of virus

i) Viruses contain DNA or RNA inside their structures like other living organisms.
ii) They can replicate and produce thousands of their copies inside living cell.
iii) They can infect living cells like the bacteria.
Non - living characteristics of virus
i) They do not respire, eat, excrete, and digest like the other living beings.
ii) They cannot reproduce outside the host cell.
iii) They do not have a cellular structure and cell organelles.
iv) They can be crystallized like the salt and sugar.
b) Viruses can divide and grow only inside the living host cell. So, they are known as
obligatory parasites.
c) Viruses are nanoscopic. Their size ranges from 25 nm to 250 nm.

Modern Concept Science - 9 319

d) They are host specific. Certain viruses attacking one type of organism or cell may not
affect the other.

e) Most viruses are pathogenic, i.e. they cause disease in living organisms.
Classification of virus

Viruses are of various types on the basis of host and genetic material in their structures. On the
basis of host cell they attack, viruses are of the following kinds:

a) Plant virus : The virus that infects the plant cells is known as the plant virus. For
example, tobacco mosaic virus (TMV), tomato bushy stunt virus (TBSV) etc. TMV was
the first discovered virus. It was first crystallized by Wendel Stanley in 1935 A.D.

b) Animal virus : The virus that infects animal cells is known as the animal virus. For
example, HIV, polio virus, rabdo virus that causes rabies etc. The first discovered animal
virus was foot and mouth disease virus (FMDV) discovered by Friedrich Loeffler and
Paul Frosch.

c) Bacteriophage : The virus that infects the bacteria is known as bacteriophage. Bacteria
are about 50 times bigger than viruses. So, these viruses can easily infect them. Those
viruses which infect cyanobacteria are known as cyanophage. Examples of bacteriophage
are: T3 phage, T4 phage, T7 phage, etc.

On the basis of genetic material present on them, viruses are of the following kinds:

a) DNA virus : The virus that contains DNA inside their protein coat as a genetic material
is known as DNA virus. They are less common. For example, adeno virus, bacteriophage,
small pox virus, herpes virus, etc.

b) RNA virus : The virus that has RNA inside their protein coat as a
genetic material is known as the RNA virus. It is more common
than the DNA virus. For example, polio virus, rabies virus, HIV, etc.

Mode of transmission of a virus

Viruses are transmitted in the following ways: HIV virus
a) Through vectors: insects, bugs, mosquitoes etc.

b) Through vehicles: utensils, clothes, handkerchief, etc.

c) Direct contact from an infected person to a healthy person or during vegetative
propagation in plants.

d) Through air, feces, water, soil, food and sexual contact.

e) Vertical transmission : from mother to her new born baby

f) Droplet infection : nasal discharges during talking, coughing, sneezing etc.

g) By animal bites : dog, cat, fox, etc.

h) Through soil, infected seeds, pollens, etc.

320 ADAPTATION

Control measures of viruses and viral diseases
In plants
a) Killing plant lice and small bugs that transmit viruses
b) Burning infected plant parts, seeds and flowers.
In animals
a) Immunization and vaccination.
b) Isolating infected animals
c) Killing or isolating rabid stray dogs and cats.

In humans
a) Immunization and vaccination

b) Avoiding materials used by viral patients, unsafe sex, tattoo piercing etc.

c) Wearing a mask.

FACT WITH REASON

Antibiotics do not work against virus. Why?
Antibiotics do not work against virus because virus do not respire, eat, excrete, and digest like the other
living beings.

Protozoa (sing. protozoan)

Protozoa are micro-organisms having eukaryotic cells. They do not have chlorophyll except
the euglena. They are both free living and parasitic. Some of them cause diseases in animals
and human beings. Some of the protozoan diseases are:

Disease Causative protozoan
Sleeping sickness Trypanosoma brucei
Trichomoniasis Trichomonas vaginalis
Malaria Plasmodium vivas. P. ovale, P. falciparum, etc.
Amoebiasis Entamoeba histolytica
Leishmaniasis Leishmanta donovant

Protozoa are carried to the host organism through several vectors like the mosquitoes, flies,
etc. and vehicles like the water, food, soil etc. Some of their characteristics are given below:

i) They are unicellular eukaryotic animals.
ii) They are both free living and parasitic.
iii) They have locomotory organs like pseudopodia ( in amoeba), cila (in paramecium),

flagella (in euglena), etc.
iv) Some of them like amoeba, plasmodium, giardia etc. cause diseases in humans.
v) All protozoa are heterotrophic except euglena which is both autotrophic and heterotrophic

Modern Concept Science - 9 321

Control measures of protozoan diseases
The protozoan diseases can be controlled in the following ways:
i) By avoiding contaminated food, water, drinks, (e.g. chatpate, paanipuri, street foods, etc).
ii) By following basic rules of personal hygiene and cleanliness.
iii) By disposing feces in safe place and keeping the toilet clean.
iv) By controlling mosquitoes and flies.
v) By not consuming stale, open and street foods.

ANSWER WRITING SKILL

1. What are free floating hydrophytes?

Ans: The hydrophytes that remain floating on the surface of water without attaching their roots to the soil are
known as free floating hydrophytes. For example, pistia, lemna, water hyacinth, water lettuce etc.

2. Mention any two names of xerophytes.

Ans: Xerophytes are cactus and aloe vera.

3. Name two animals which are suitably adapted to xeric environment.

Ans: Desert animals are desert fox and camel.

4. Write the full form of TMV.

Ans: The full form of TMV is tobacco mosaic virus.

5. Write any two differences between bacteria and viruses.

S.N. Bacteria S.N. Fungi

1 Bacteria are unicellular prokaryotes. 1 Fungi are both unicellular and
multicellular eukaryotes.

2 They may or may not be autotrophic. 2 They are heterotrophic.

6. Write in brief about the locomotion of whale and duck in water.

Ans: The locomotion of whale is swimming type. Whales swim with the help of flippers. They push the water
with flippers and move forward or jump out of the water. Likewise, ducks have webbed feet to swim in
water and walk on the ground. The webbed feet increase the cross sectional area which helps to push
back water and move forward easily.

7. Why are viruses called a borderline between living and non-living?

Ans: Viruses are called a borderline between living and non-living because they have characteristics of both
living and non-living beings. Some of their living characteristics are:

i) They can replicate from one to many.

ii) They can cause diseases.

iii) They have nucleic acids.

Likewise, some of their non-living characteristics are:
i) They can be crystallized.

ii) They do not eat and reproduce.

iii) They show no sign of life outside the host cell.

322 ADAPTATION

8. Milk turns into curd when kept overnight. What type of organisms mostly help in this process? Write
any two other disadvantages of such organisms.

Ans: The organisms that help milk turn into curd are bacteria. They do so by converting lactose in the milk
into lactic acid. The two disadvantages of bacteria are:
a) They can cause various diseases like T.B., cholera, pneumonia, etc.
b) They spoil organic foods, vegetables and fruits.

9. Classify the following organisms on the basis of their adaptive characteristics with their names:
a) Non-lobed hoof with strong muscles for running
Ans: Horse, terrestrial adaptation
b) Hump on back for food storage, large fleshy soles, concentrated fecal matter
Ans: Camel, xeric adaptation

10. Explain the following figures by relating them to the adaptational characteristics of the organisms that
they belong.

Ans: Camel walks easily on sand with the help of large fleshy soles. It has a hump on its back
for food storage. Camels can drink a lot of water at a time and live without next drink
for a long period. They have long eyelashes and muscular nostrils which prevent the
entry of sand.
Ducks swim in water with the help of webbed feet. Webbed feet are the feet in which
the toes or digits are fused with each other. They have strong hind legs along with
webbed feet which help them to paddle through water and walk on mud.
Cacti have many adaptational characteristics. They have well developed root system
to absorb water from the soil. Their succulent organs store water and thorns prevent
the loss of water. The stomata opens during the night time and remains closed during
the day.

STEPS EXERCISE

STEP 1

1. What is adaptation?

2. What is meant by structural and behavioural adaptation?

3. Define hydrophytes.

4. Name two floating hydrophytes.

5. Define mesophytes.

6. Write definition of the following:
a) Nocturnal animal b) Camouflaging c) Aerenchyma

7. Write the function of snakes’ hard scales.

8. What is a patagium?

9. What do you mean by prehensile tail?

Modern Concept Science - 9 323

10. Mention the meaning of pneumatic bones.

11. Is bacteriophage a bacterium or a virus?

12. Which pathogen causes sleeping sickness?

STEP 2

13. Write any two differences between:
a) Hydrophytes and xerophytes
b) Plantigrade and digitigrade motion
c) Aquatic snake and terrestrial snake

14. What is the function of a hump in camels?

15. Why are camels more adapted to desert than humans?

16. Why do chameleons change their colour?

17. Mention the reason why aquatic plants have air filled tissues.

18. How do ducks swim?

19. Why do whales repeatedly come on the surface of water?

20. Are bacteria useful to us? Write any two points for the support of your answer.

21. Which bacteria are comma and rod shaped?

22. Name any two bacterial diseases.

23. Why are virus called obligatory parasite?

STEP 3

24. Mention any three characteristics of: d) Xerophytes
a) Amphibians b) Mesophytes c) Aerial animals

25. How are camels adapted to hot desert? Write in brief.

26. List the adaptational features of birds.

27. Can a water hyacinth live on land? Why/Why not?

28. How does a dolphin find its prey?

29. How do bats find their prey at night?

STEP 4

30. What is a hydrophyte? Mention any three characteristics of hydrophytic stem.

31. Draw the sketches of the beaks and feet of various birds along with their functions.

32. Fish takes in oxygen from the water. Can we say that fish takes in oxygen from H2O
leaving hydrogen? Why/why not?

33. Write any two useful and harmful effects of bacteria.

324 ADAPTATION

UNIT Estimated teaching periods Theory Practical
13 4
18
System

Syllabus issued by CDC Robert Hooke

 Relation among cell, tissue, organ and system
 Plant tissues ( meristematic, permanent and complex)
 Skeletal system of human body
 Human nutrition
 Human respiratory system
 Human excretory sysem

LEARNING OBJECTIVES

At the end 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.

Key terms and terminologies of the unit

1. Meristematic tissue: Meristematic tissues are those tissues which constantly grow due to active cell division.

2. Permanent tissue: Permanent tissues are those tissues which are formed when the meristematic tissues
mature and lose their ability of cell division.

3. Mitosis: A type of cell division which occurs in somatic cells dividing a mother cell into two daughter cells.

4. Tannin: A brownish or yellowish substance extracted from some plants and is used in tea and
leather manufacturing is called tannin.

5. Resin: A sticky flammable substance produced from trees like pine, fir, etc. is called resin.

6. Skeletal system: The bones, joints and other tissues make up a system known as skeletal system.

7. Axial skeleton: The central part of skeletal system which forms the base or vertical axis is known as the
axial skeleton. It includes bones of head, chest, backbone, sternum and ribs.

8. Cranium: A hard bony cage made up of eight flat bones is called the cranium. In protects brain.

9. Suture: The regions where the cranial bones are attached to each other by a small connective
tissue is called the suture.

10. Ear ossicles: The middle ear consists of three small bones called the ear ossicles. They are malleus,
incus and stapes.

11. Ribcage: The ribcage is a cage-like structure made up of 12 pairs of bones attached to a single linear
bone in the chest known as the sternum or the breast bone.

Modern Concept Science - 9 325

12. True ribs: The ribs that are directly attached to the sternum are known as the true ribs.

13. False ribs: The three pairs of ribs are not attached directly to the sternum. They are called the false ribs.

14. Floating ribs: The last 2 pairs of ribs are free and not attached to the other ribs or the sternum are called

floating ribs.

15. Vertebral column: The vertebral column is a long and flexible bony structure present in the dorsal side of the body.

16. Spinal canal: There is a long central cavity inside the vertebral column that extends throughout the length

called the spinal canal

17. Atlas: The first and the topmost bone of the vertebral column is called the atlas (C1).

18. Axis: The second cervical vertebra (C2) is known as the axis.

19. Pectoral girdle: The upper extremity is the combination of the upper limbs and its bones of attachment

called the pectoral girdle.

20. Pelvic girdle: The lower extremity is the combination of the lower limbs and its bones of attachment is

called the pelvic girdle.

21. Digestive system: The system by which the human body converts complex compounds in the food into

simpler compounds that our body can utilize is known as the digestive system

22. Alimentary canal: The long tube that extends from mouth to the anus through which the food passes is known

as the alimentary canal or digestive tract or Gastrointestinal tract.

23. Villi: The finger-like projections in the small intestine that helps in the absorption of nutrients

from food are known as the villi.

24. Respiratory system: The respiratory system is the system of organs that helps us to inhale oxygen, break food,

release energy in the cells and excrete carbon dioxide out of the body.

25. Excretion: Excretion is the total process of getting rid of wasteful and toxic substances from the body.

Introduction

The body of an organism is not a single unit. It is made up of tiny units called cells. The
combination of each of these cells makes the whole structure of an organism. Cells are the
fundamental, structural and functional unit of an organism.

FACT WITH REASON

Cells are the fundamental, structural and functional units of an organism. Give reason.
A single cell is capable of performing all the functions that the body of an organism can perform e.g. nutri-
tion, respiration, reproduction, excretion etc. The combination of these cells make the whole structure of an
organism. So, cells are the fundamental, structural and functional unit of an organism.

Interrelationship between cells, Cells Tissues Organ
tissues, organs and system
Muscle
tissue cell

Without cells, no living organism would ever exist. In Nerve cell
general, cells are the building blocks of bodies of every

plant, animal and unicellular organisms. Cells having Epithelial
common origin and performing similar function are cell

called tissues. When tissues of similar origin and Connective
cell

function combine, they form organs. Organs then unite

Interrelationship between cell, tissue and organ

326 System

to form a system which carries out certain functions in the Memory Tips
body. The combination of systems forms the human body.
The adult body is made up of:
Some systems of human body along with their tissues and 100 trillion cells, 206 bones, 600
organs are shown in the table below: muscles, and 22 internal organs.

Body system Organs/parts Tissues Functions
Skeletal Bones and cartilages Connective tissue Protection and locomotion
Muscular Muscles fibres Muscular tissue Movement and circulation
Nervous Brain, nerves and Nervous tissue Co-ordination and control
Circulatory spinal cord
Heart, blood and Epithelial, Transportation and excreation
Reproductive blood vessels connective, of wastes
Respiratory cardiac tissue
Digestive Testes, ovaries, penis,
vagina, etc. Epithelial tissue Formation of sperm, egg and
Excretory Nose, trachea, lungs, helps in reproduction
etc.
Integumentary Mouth, food pipe, Epithelial tissue Release energy, take oxygen and
stomach, intestine, excrete carbon dioxide
Endocrine system liver, pancreas, etc.
Kidney, ureter, liver, Epithelial and Convert the food into
urinary bladder, gal muscular tissue absorbabale and useable form
bladder
Skin, hair and nails Epithelial tissue Throwing solid and liquid
wastes
Pituitary gland,
thyroid gland, Epithelial, Protection against germs and
pancreases, etc. muscular and temperature regulation
connective tissue
Water and mineral balance,
Epithelial tissue metabolism, heartbeat, sexual
development, etc.

Plant tissue

Some plants are unicellular and contain only a single cell without tissues. But in multicellular
vascular plants, tissues are differentiated into various types. A plant has two types of tissues
on the basis of location, developmental stage and function:

a) Meristematic tissue : tissues where the new cells are formed by division

b) Permanent tissue : tissues where the new cells are not Apical
formed but are matured meristem

Meristematic tissue Lateral
meristem
Meristematic tissues are those tissues which constantly
grow due to active cell division. They are found at the apex Intercalary
of leaves, roots and shoots. They are also called meristems. meristem
Meristems are responsible for making a plant part taller and

Meristematic tissue

Modern Concept Science - 9 327

longer i.e. they help in the increment of length. A type of cell division called mitosis constantly
makes this tissue grow in size. On the basis of location, there are three types of meristems:

a) Apical meristem
The meristematic tissues that are present at the tip of roots, shoots, stems and branches
are called apical meristems. They increase the vertical length or height of a plant body.
They are also called primary tissues.

FACT WITH REASON

Plants do not grow tall, if tip are cut, why?
Plants do not grow tall if tip of the plants are cut because tip of plants contains apical meristem which is
responsible for increase in height of a stem.

b) Lateral meristem
These tissues are present among the permanent tissues. They increase the girth, thickness
or horizontal size of plant. Some of them turn into vascular tissues and the outer layers
of stem after being developed. They are also called secondary tissues.

c) Intercalary meristem
These tissues are present in the nodes of leaves and fruits. They help to grow new parts
if cut or broken. They increase the length of internodes.

Permanent tissue
Permanent tissues are those tissues which are formed
when the meristematic tissues mature and lose their
ability of cell division. These tissues make up the
following parts of a mature plant:

a) Epidermis : outer layer
b) Cortex : tissues between epidermis and vascular

tissues present in stem and roots
c) Vascular tissues : xylem and phloem
d) Tissue fibres : supporting tissues
e) Pith : soft tissue at the centre of stem/trunk.
Types of permanent tissues
On the basis of origin and function, permanent tissues are:

a) Simple permanent tissue
b) Complex permanent tissue
c) Special permanent tissue
Simple permanent tissue
These tissues are derived from the meristematic tissues like that of all permanent tissues. They
contain only one type of cells and are thus structurally and functionally alike. Hence, they are
also called simple permanent tissues. They are further sub-divided into these types:

328 System

FACT WITH REASON

Permanent plant tissues do not grow, why?
Permanent plant tissues do not grow because they do not have the cells that can undergo division.

a) Parenchyma
Location : These permanent tissues are distributed in leaves, roots, branches etc.

They are present chiefly in cortex of stem and root, mesophyll of leaf, pulp or fruits,
endosperm of seed and packing fibres in xylem and phloem.

Structure : They are thin-walled oval, irregular, elongated, polygonal and round type
of cells. They have gaps within individual cells called intercellular spaces. The cells are
living and contain a nucleus and a vacuole. Some parenchymatous tissues containing
chlorophyll are able to prepare food and are called chlorenchyma. Similarly, some soft
and light tissues which are air filled are known as aerenchyma.

FACT WITH REASON

Some tissues of parenchyma are called chlorenchyma. Give reason.
Some tissues of parenchyma are called chlorenchyma because they contain chlorophyll that help in
photosynthesis.

Function: Their functions are as follows:
i) To protect the surrounding tissues
ii) To act as a support for xylem and phloem
iii) To help in manufacturing and storing food.
iv) To maintain the turgidity of the cells.
v) To help in breathing and absorption of water and minerals

Nucleus Cell wall
Cell wall Nucleus
Cytoplasm

(a) Cytoplasm

(b) Collenchyma

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

b) Collenchyma

Location: They are located in the epidermis of dicot stem,
petiole of leaves, mid-rib of dicot leaves etc.

Structure: These tissues have no intercellular spaces. They
contain some extra cellulose and pectin deposited in their cell
walls due to which they are different from the parenchyma.
They are elongated and thick-walled.

Modern Concept Science - 9 329

Function: Their functions are as follows:
i) To provide mechanical flexibility and strength to the plant
ii) Some of them bear chlorophyll which helps in food production
iii) To protect the leaves against the tearing effect of wind
iv) To allow the bending of various plant parts without breakage

FACT WITH REASON

Parenchyma is softer than collenchyma, why?
Parenchyma is softer than collenchyma because parenchyma has intercellular space which is not present
in collenchyma.

c) Sclerenchyma fibres stone cell

Location: These permanent tissues are located in the cross section lumen (c)
hard coats and shells of the plants like the seed coats, (b)
fruit flesh, nut shells, leaf veins, etc.
canal solereids
Structure: Sclerenchymatous tissues consist of
elongated, narrow and thick walled cells. They
contain dead cells with no cytoplasm. The cell walls
have deposition of a substance called lignin which is
the dusty or powdery part of the plant stem. They do
not have intercellular spaces.

Function: Their functions are as follows: (a) longitudinal
i) To give support and rigidity to the plant parts
ii) To provide elasticity during movement Sclerenchyma (a) in L.S. (b) in T.S.
(c) single fibre magnified

iii) To protect fruits and seeds

Complex permanent tissue

The complex permanent tissues are complex because they are made up of different types of
cells with different functions. The functional combination of different cells in this tissue helps
in the transportation of water and minerals along the plant body. The complex permanent
tissues are made up of two vascular tissues (xylem and phloem). They help in the transportation
of water, food and minerals throughout the plant body.

a) Xylem

b) Phloem

a) Xylem (Greek: 'Xulon' - wood) (d)

Location: They are present at the central whorls of (a) Trachieds
the stem and trunk. They contain dead cells except (b) Vessels
the xylem parenchyma. The walls of the xylem cells (c) Xylem fibres
are lignified which makes them strong and woody. (c) (d) Xylem parenchyma

Structure: The xylem tissue is made up of four

(a) (b)
Components of xylem tissue

330 System

different types of cells: Vessels or tracheae, Tracheid, Xylem parenchyma and Xylem
fibres.

Function: Their functions are as follows:

i) To provide mechanical strength to the plant Memory Tips
ii) To transport water and minerals from the
Out of four types of cells in xylem, three
roots to the leaves are dead cells (vessels, tracheids, xylem
iii) To help in food making process fibres) and only one type is of living cells
(xylem parenchyma).
FACT WITH REASON

If we cut the outer tissues of a plant stem, the upper part swells. why?

If we cut the outer tissues of a plant stem, the upper part swells because the outer phloem tissues are cut
which prevents the produced food materials from passing through the stem downwards to the roots. This
cutting process is known as girdling. Excessive girdling can kill a plant because the roots do not get food.

b) Phloem (Greek: 'phloos' - bark) Sieve plate

Location: Phloem tissues are present in the outer Sieve tubes
whorls of the plant stem. It also gives some mechanical Sieve tubes
support to the plant.

Structure: The phloem tissue is made up of four (a) Phloem parenchyma
different types of cells: Sieve tubes, Companion cells,
Phloem parenchyma and Phloem fibres.

Function: Their functions are as follows: Companion cells
i) To provide mechanical strength to the plant
(b) Sieve tubes (c)
ii) To transport the food prepared in the leaves to
all parts of the plant (c) Sieve tubes and companion cells in L.S.

Components of phloem tissue

iii) To provide the function of circulation Memory Tips

FACT WITH REASON Out of four types of cells in phloem, three

Xylem and phloem are called vascular bundle, why? are living cells (Seive tubes, Companion

Xylem and phloem are called vascular bundles because these cells, Phloem parenchyma) and only one
complex tissues in the plants help in the transportation of type is of dead cells (Phloem fibres).

water and minerals throughout the body.

Number of annular rings in trunk helps to know age of tree. Give reason.

Xylem tissue lives for one year and dies. New xylem tissues are formed around the old dead one, which

makes the number of rings over time. So it helps to know age of the tree.

Special permanent tissue

These are the modified forms of permanent tissues that secrete special excretory or functional
materials e.g. gum, resin, nectar, citrus juices, latex, oils, etc. These permanent tissues are of
two types:

Modern Concept Science - 9 331

a) Glandular tissue : These are the special permanent tissues which contain glands.
Glands are tissues that secrete a certain juice or enzyme material. They may contain a
single cell or a group of cells. They secrete substances like resin, oil, mucilage, tannin,
gum etc. They are found in tulsi, citrus fruits, pudina, tobacco, lemon, orange, etc. Most
insectivorous plants secrete juices from honey glands for trapping the insects. Some
glands are of digestive type and help to digest the food material.

b) Laticiferous tissue: They are thin walled and branched tissues which secrete a
yellowish milky juice known as latex. These tissues are common in papaya, opium,

calotropis etc. Plants bearing these tissues are called laticifers. The latex functions as the

liquid for food or waste material storage.

Introduction to skeletal system

The human body is designed to do various activities that require movement and strength. To
support the huge weight of the body, there are hard living tissues present inside the body known
as bones. The bones, joints and other tissues make up a system known as skeletal system. The
skeletal system is the strong and rigid structure and acts as a mechanical framework.

The whole skeletal system is composed of the following tissues:

Bones Memory Tips

Bones are the hard connective tissues that support the The adult human body has 206 bones
body weight. They are present inside the muscles. There in the skeleton.
are altogether four different kinds of bones: long bones (eg.

femur), short bones (wrist,ankle), flat bones (skull,scapula) and irregular bones (vertebrae).

Ligaments

Ligaments are the connective tissues that connect one bone to the other, e.g. suspensory

ligament of the eye, periodontal ligament etc. Clavicle Cranium
Humerus
Tendons Facial region
Cervical vertebrae
Tendons are the non-elastic and fibrous
connective tissues that attach the muscles to the Sternum
bones, e.g. biceps, triceps etc.

Cartilage Lumbar vertebrae Ribs
Pelvis
Cartilages are the soft and elastic connective tissues Radius
that are present in flexible parts of the body, e.g. in Ulna
vertebral column, ear, nose, windpipe etc. Carpals
Metacarpals
Functions of skeletal system
Phalanges
The skeletal system helps us in the following ways:
Femur

i) It acts as a bony framework that supports Patella
the weight of the body.
Tibia
ii) The skeleton stores the minerals like Ca, Fibula
Mg, P etc. which our body needs.
Phalanges Tarsals
iii) It attaches the muscles and help in Metatarsals
movement.
Human skeleton (Anterior view)

332 System

iv) The skeleton protects the vital organs like the heart, kidney, lungs, brain etc.
v) The skeletal system is the pathway for different nerves and blood vessels that carry

messages and nutrients to different parts of the body.

FACT WITH REASON

Bone dipped in an acid softens. Why?
A bone dipped in an acid softens because the acid dissolves the calcium present in the bone and weakens it.

Types of skeleton

The skeletal system of the human body is divided into two major parts: the axial skeleton (80
bones) and the appendicular skeleton (126 bones).

Axial Skeleton (80 bones)
The central part of skeletal system which forms the base or vertical axis is known as the axial
skeleton. It consists of 80 bones altogether. It is divided into four main parts: the skull, ribcage
(thorax), the ear ossicles and the vertebral column. The different parts of the axial skeleton are
given below:

a) The Skull (29 bones)

The skull is the hard and rigid bony structure that covers the brain and the face, above the
neck. It looks like a single bone but actually is the compact structure of bones attached to each
other at fracture like areas called sutures. The skull is composed of three types of bones: facial
bones, cranial bones and the hyoid bone.

Frontal bone Suture
Parietal bone

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

Maxilla

Mandible Parietal bone
Frontal bone
Human skull
Temporal bone
Facial bones (14 bones) Lacrimal bone
Nasal bone
The bones that form the anterior frontal part of the skull Vomer
are called the facial bones. Altogether 14 bones form the Maxilla
face. They can be named as follows:
Mandible
i) Mandible or the lower jaw (1): Mandible is the
only movable horse shoe like bone of the skull that Frontal skull
possesses the lower teeth. It connects the lower
teeth to the upper jaw or maxillae which contains
the upper teeth.

Modern Concept Science - 9 333

ii) Maxillae or the upper jaw (2) : Maxillae are immovable and are attached to the cheek
bone, nasal parts and the base of the eye. The movable parts of the skull are attached to
this bone.

iii) Zygomatic or the cheek bones( 2) : Zygomatic or the cheek bones are the two protruded
bones below both the eyes. They form the sideways of nasal cavity and the eye.

iv) Vomer (1)at the centre between the nostrils : Vomer is the central bone that partitions
the nasal cavities. It is one in number. It is attached to the upper nasal bones.

v) Nasal bones (2) between the eyes : The nasal bones form the structure of the upper nose.
They are two bones in the nose on which our spectacles rest.

vii) Inferior nasal conchae or turbinate bones (2) on the base of nostrils : These two bones
form the lateral base of nostrils present just above the upper teeth. It is located within
the nasal cavity.

viii) Palatine (2) below nasal bones : The two bones present in the posterior or back part of
upper hard palate are known as the palatine. These bones are present in the rear side of
the oral cavity.

iv) Lacrimal (2) near the lacrimal gland : They are the smallest bones of the face. These
small bones are present near the lacrimal gland at the middle of the eye socket.

Cranial bones (8 flat bones)

The top and back view of the brain is protected by a hard bony cage-like structure made up
of eight flat bones is called the cranium. The bones of the cranium are called the cranial bones.
The regions where the cranial bones are attached to each other by a small connective tissue
is called the suture. The cranium protects the brain against mechanical shock and injury. The
cranial bones are explained below:

a) Frontal bone (1): It is a single flat bone present at the upper forehead extending to the
upper part of the orbit and the upper nasal cavity.

b) Parietal bone (2): The parietal bones are two in number. They form the sides and top of
almost half of posterior cranium.

c) Temporal bone (2): These are the two bones on the two sides of the skull above and
behind our ears.

d) Occipital bone (1): On the lower back of the skull, a curved flat bone is present. It is
called the occipital bone. They are located just opposite to the eyes. One of the edges of
this bone consists of a hole through which the spinal cord passes. This hole is called the
foramen magnum.

e) Sphenoid bone (1): There is a complex bone behind the orbits present at the anterior side
of the temporal bone called the sphenoid bone. It looks like a winged bat with an eye. It
forms the base of the cranium, sides of the skull and eye sockets.

f) Ethmoid bone (1): A bone is present behind the nose and in front of the sphenoid bone
which forms the inner base of skull known as the ethmoid bone. The part of this bone is
seen through the orbits.

334 System

Hyoid bone (1)

A U-shaped or horseshoe like bone present in the upper part of larynx (in the neck) is known
as the hyoid bone. It is the part of the axial skeleton. It is an isolated bone. The back of the
tongue is attached to it.

The Ear ossicles [the malleus (2), the incus (2) and the stapes (2)]

There are three parts in the auditory system: the external, middle and the internal ear. The
middle ear consists of three small bones called the ear ossicles. There are three bones in the ear
ossicles: the malleus, the incus and the stapes.

Malleus Incus Stapes Memory Tips

Among the ear ossicles, the
stapes are the smallest bone in
human skeletal system.

Ear ossicles

b) The bones of the thoracic walls (the rib cage and the vertebral column)

The thoracic cavity is the region in the chest enclosed by the bones of the thoracic walls. The
thoracic walls have a cage like structure of ribs called the rib cage. It is formed due to the
attachment of the long curved ribs by the sternum (breast bone) in the chest and the vertebral
column in the back. Therefore, it is made up of three kinds of bones: the ribs, the sternum or
the breast bone and the vertebral column. The important organs: heart and the lungs stay safe
inside the thoracic cavity.

The ribcage (25 bones): sternum (breast bone) and the ribs

The ribcage is a cage-like structure made up of 12 pairs of bones attached to a single linear
bone in the chest known as the sternum or the breast bone. The ribs are arranged in a semi-
circular fashion starting from the sternum and ending in the backbone. On the basis of their
attachment in the sternum, there are three types of ribs:

i) True ribs (1st to 7th pairs): The ribs that are directly Sternum
attached to the sternum are known as the true ribs. Ribs
The first seven pairs of ribs are directly attached to the
sternum and are known as true ribs.

ii) False ribs (8th, 9th and 10th pairs): Similarly, the next three Thoracic cage or rib cage
pairs are not attached directly to the sternum and thus
are called the false ribs. They are attached to the 7th ribs
directly.

iii) Floating ribs (11th and 12th pairs): The last 2 pairs of ribs

Modern Concept Science - 9 335

are free and not attached to the other ribs or the sternum. Therefore, they are known as
floating ribs.
The ribs form the space in the thorax known as the thoracic cavity which encloses vital
body organs like the heart, lungs, liver and important blood vessels.
The vertebral column or backbone or spine (26 bones)
The vertebral column is a long and flexible bony structure present in the dorsal side of the body.
In infants, it consists of 33 small and irregular bones called the vertebrae. The 33 vertebrae get
fused to 26 vertebrae in adults. There is a long central cavity inside the vertebral column that
extends throughout the length called the spinal canal. The backbone and the spinal canal hold
the spinal cord safely and protect it against mechanical injury. The entire weight of the body
is supported by the backbone. This curved structure has mainly five regions. The vertebrae
present in these five regions are named accordingly:

Cervical (7)

Thoracic (12)

Lumbar (5)

Sacrum (5, fused)
Coccyx (4, fused)

Vertebral column

i) Cervical vertebrae (7 neck bones: C1-C7): The cervical vertebrae are the first seven
irregular bones present on the neck of the vertebral column. This region is known as the
cervical region. The first and the topmost bone of the vertebral column is called the atlas
(C1). The second vertebra (C2) is known as the axis. The atlas supports the skull and
helps in the ‘yes’ movement of the head. Similarly, the axis acts as a pivot for movement
for atlas and helps in the ‘no’ movement of the head. Both the atlas and axis along with
other cervical vertebrae help in the rotation of the head.

ii) Thoracic vertebrae (12 upper back bones: T1-T12): The thoracic vertebrae are 12 in
number that anchor the ribs in place. They form the major part of the thoracic region.
They are the bones of the upper back of the spine.

336 System

iii) Lumbar vertebrae (5 lower back bones:L1-L5):The five lumber vertebrae are little
modified to attach to strong back muscles as they help in back movement. They are
the largest and the strongest among the movable bones of the spine. The strain in these
vertebrae may often cause lower back pain.

iv) Sacral vertebrae (5 fused to 1 butt bone): In infants, the sacral vertebrae are five in
number. But in adults these five vertebrae fuse to form a single bone known as the
sacrum. It is slightly projected outward in females for increasing the size of pelvic
cavity. The large pelvic area helps in holding a baby during pregnancy and delivery. It
is somewhat triangular in shape.

v) Coccygeal vertebrae (4 fused to 1 tail bone): It is the bone present at the lower end of the
spine. In infants, four small vertebrae are present while in adults the four get fused to
form a single bone called the coccyx or the tail bone.

FACT WITH REASON

Cartilage is present in-between two vertebrae, why?
Cartilage is present in-between two vertebrae to reduce friction and allow easy movement of joint.

The Appendicular Skeleton: (126 bones) Clavicle
Scapula
The appendicular skeleton is the group of bones that are
attached on the right and the left end of the axial skeleton. Humerus
Altogether, there are 126 bones. They are divided into two
parts: the upper extremity (64 bones) and the lower extremity
(62 bones).

Bones of the upper extremity (64 bones) Ulna
Radius
The Upper extremity is the combination of the upper limbs
and its bone of attachment called the pectoral girdle.

Pectoral or shoulder girdle (4 bones) Carpals
The pectoral or the shoulder girdle consists of four bones Metacarpals

altogether. Out of these four bones, two are clavicle and the Phalanges

rest two are the scapula one on each girdle.

Bones of shoulder girdle and upper limb

The clavicle or the collar bone(1 bone on each side) is a bow-

shaped bone of the shoulder girdle that attaches to the sternum and the scapula.

The scapula or the shoulder blade (1 bone on each side) is the flat posterior bone of the shoulder
girdle that attaches to the ribcage. There are about 20 muscles attached to the scapula.

The upper limb (30 bones on each side)

The upper limb consists of a long humerus, radius and ulna, carpal, meta-carpal and the
phalanges. Altogether, there are 30 bones on each limb. The names of the bones are given below:

i) Humerus (1 bone) or upper arm bone: The humerus is the longest and largest bone of
the upper limb that extends from the shoulder to elbow. At the scapula, the upper end

Modern Concept Science - 9 337

of humerus is connected by a ball and socket joint which enables the movement of the
upper arm in almost all directions. Similarly, the lower end is connected to the radius
and ulna by a hinge joint. This reduces the movement of the elbow at an angle more
than 180 degrees.

ii) Radius and Ulna (1 each bone on either side of the forearm): The radius and the ulna are
the two bones originating from the elbow and ending in the hands on each arm. They
collectively provide flexibility to the forearm. The ulna is strongly joint at the humerus.
Similarly, the biceps muscles are attached to the radius.

iii) Carpels (group of 8 bones one each wrist): The carpels are the eight small individually
movable bones present in the wrist. They help in the dynamic movement of the hands.
They are present between the meta-carpels and the radius-ulna. Ligaments connect
them and help in their movement.

iv) Meta-carpals (group of 5 bones on hand): The five round bones of palm connected on
one side to carpels and the other side to the fingers is known as the meta-carpals.

v) Phalanges (14 finger bones 3 on each finger except the thumb which has 2): Phalanges
are the small finger bones. Each finger has three phalanges except for the thumb which
has only two. There are three types of phalanges:

– Proximal phalanges (attached to the metacarpals): one on each finger

– Intermediate phalanges (phalanges in the middle of the fingers): one on each
finger except the thumb

– Distal phalanges (at the edges of the fingers): one on each finger

Bones of the lower extremity (62 bones)

The lower extremity is the combination of the lower limbs and its bone of attachment is called
the pelvic girdle.

Pelvic girdle (2 bones)

The pelvic or the hip girdle consists of two

innominate or hip bones. The hip bones

along with two coxal bones and the sacrum,

are collectively called the pelvis. The hip

bone is the fusion of the three bones together:

ileum, ischium and the pubis. All these three Female Male
bones meet at a depression where the femur
Pelvis of female and male

articulates. This depression is known as the acetabulum. The acetabulum is the concave

depression in the meeting point of three fused hip bones at which the thigh bone articulates.

Pelvic girdle of female is wider and lighter than that of male.

FACT WITH REASON

The pelvic girdle of female is wider and lighter than that of male, why?

The pelvic girdle of the female is wider and lighter than that of male for assistance in delivery and pregnancy.
It provides a large space for the development of the baby. etc.

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The lower limb (30 bones on each leg): Memory Tips

The lower limb consists of a long and strong femur, tibia and The femur is the longest, largest and
fibula, tarsal, meta-tarsal and the phalanges. Altogether, there the strongest bone of the human
are 30 bones on each limb. The names of the bones are given body. It can hold as much as 30 times
below: the body weight if tested alone.

i) Femur or the thigh bone (single longest bone on each leg): Femur Hip
extends from the acetabulum of the hipbone to the knee cap. It is bone
hollow inside and contains a cavity called the medullary cavity. The
medullary cavity contains the bone marrow.

ii) Patella (1 on each leg): The patella or the knee cap is the flexible flat Femur
bone that can slide sideways in the knee. It is a part of the knee joint.
The patella helps the tendons to move the femur easily.

iii) Tibia and fibula (1 tibia and 1 fibula on each leg): The tibia or the Patella
shin bone is the strong bone of the lower leg that supports the Tibia
maximum body weight while the fibula does not directly hold the
body’s weight. The tibia is larger and stronger than the fibula. It is
articulated with femur and foot on opposite sides. The fibula or the
calf bone ensures extra support for the lower leg.

iv) Tarsals or the ankle bones (7 bones on each leg): The tarsals or the Fibula
ankle bones are the group of seven bones present at the feet. Out
of the seven bones, the largest bone called the calcaneus holds the
maximum body weight in the heel of the feet.

v) Metatarsals or the foot bones (5 on each leg): The metatarsals are Tarsals
five in number present in the feet. They connect the tarsals to the
phalanges. They balance the body weight while standing and Metatarsals
walking. Phalanges

vi) Phalanges or toe bones (14 on each leg): The phalanges are the lowermost bones of the
appendicular skeleton. They are 14 in number. Each toe has three phalanges except for
the big toe which has only two phalanges.

Summary of the skeletal system:
Total bones of the skeletal system

Axial skeleton – 80 bones Appendicular skeleton – 126 bones
Skull – 29 bones Upper extremity – 64 bones

Cranial bones – 8 bones Pectoral girdle - 4 bones
Frontal – 1 bone Scapula – 1+1=2 bones
Parietal – 2 bones Clavicle – 1+1=2 bones
Temporal – 2 bones
Occipital – 1 bone Forelimbs – 30+30=60 bones
Sphenoid – 1 bones Humerus – 1+1=2 bones
Ethmoid – 1 bone Radius – 1+1=2 bones
Ulna – 1+1=2 bones

Modern Concept Science - 9 339

Facial bones – 14 bones Carpals – 8+8=16 bones

Mandible – 1 bone Metacarpals – 5+5=10 bones

Maxillae – 2 bones Phalanges – 14+14=28 bones

Zygomatic – 2 bones Lower extremity – 62 bones

Nasal – 2 bones Pelvic girdle – 2 hipbones

Palatine – 2 bones Hipbone is the fusion of -

Vomer – 1 bone Ilium

Lacrimal – 2 bones Ischium

Inferior nasal conchae – 2 bones Pubis

Hyoid – 1 bone Lower limbs – 30+30=60 bones

Ear ossicles – 6 bones Femur – 1+1=2 bones

Malleus – 2 bones Knee cap or patella – 1+1=2 bones

Incus – 2 bones Tibia – 1+1=2 bones

Stapes – 2 bones Fibula – 1+1=2 bones
Vertebral column – 26 bones Tarsals – 7+7=14 bones
Metatarsals – 5+5=10 bones
Cervical – 7 bones Phalanges – 14+14=28 bones
Thoracic – 12 bones

Lumbar – 5 bones

Sacral – 1 bone

Coccygeal – 1 bone

Sternum – 1 bone

Ribs – 24 bones

true ribs – 14 bones

False ribs – 6 bones

Floating ribs – 4 bones

80 axial + 126 appendicular = Total bones = 206

The Digestive system and Digestion

(Human Nutrition)

The human body is a biological machine. It needs
energy to work. The energy is provided by the food
that we eat. But the food that we eat contains complex
compounds that our cells cannot use. They have to
be divided into simpler form and rearranged to get
essential elements that our body needs. This function
is carried out by a system known as the digestive
system. The system by which the human body
converts complex compounds in the food into simpler
compounds that our body can utilise is known as the
digestive system.

The Digestive process

The journey of food starts from the mouth and ends Human digestive system
in anus. The long tube that extends from mouth to the

340 System

anus through which the food passes is known as the alimentary canal or digestive tract or
Gastrointestinal tract. The organs of the gastrointestinal tract are explained in short below:

a) Mouth and Oral cavity
The food that we eat first enters into our mouth and reaches the buccal or oral cavity.
It is then broken down into smaller pieces with the help of teeth and tongue. This
process is called mastication. A group of three pairs of glands called the salivary glands
are present in the oral cavity. They secrete a digestive juice called saliva. The ptyalin
contains about 99.5% water and the rest 0.5% enzymes like amylase. It converts the
complex carbohydrate present in the food into maltose. Thus, it becomes clear that the
first step of digestion of food starts from the oral cavity.

FACT WITH REASON

Food should be properly chewed before swallowing, why?
Food should be properly chewed before swallowing because it makes easy the process of digestion by con-
verting it into simpler form and also converts starch into maltose.
Bread becomes sweeter if it is chewed for a longer time. Why?
Bread becomes sweeter if it is chewed for a longer time because amylase of saliva converts carbo-
hydrate into maltose.

b) Pharynx
The food is then passed into the pharynx by a coordinated action of neck muscles and
epiglottis. The epiglottis is the hanging cartilage at the rear end of oral cavity that pushes
food towards the oesophagus preventing it from moving into the wind pipe. The moist
food particles that pass from the mouth to pharynx and oesophagus is called bolus.

c) Oesophagus or food pipe
Once the food enters into the oesophagus, its movement cannot be controlled by our
will and the whole process after that remains involuntary. The involuntary movement
by which food moves downward the alimentary canal is called peristalsis.

d) Stomach
The peristalsis causes the food to land in a pouch-like organ of storage called stomach.
The stomach has two parts for food movement: cardiac part towards the oesophagus
and pyloric part towards the duodenum. The digestion of food continues here by the
action of three chemicals:

i) Hydrochloric acid : HCl makes the food acidic and kills the germs.
ii) Pepsin : It converts the protein into peptides.
iii) Chymosin or Rennin : It converts the milk into thicker curd like material.
After about 2-4 hours of eating, the food becomes ready for further digestion and moves
on towards the small intestine.

e) Small intestine
The yellowish thick curd like food that passes from the stomach to the small intestine is
called the chime. The small intestine is a narrow but a long tube that extends from the

Modern Concept Science - 9 341

pyloric part of the stomach to the large intestine. It is about 6m long and is divided into
three major parts:

i) The duodenum (25 cm long): The duodenum is present towards the pyloric part
of the stomach. Here, the chyme from the stomach is treated with about 600-
1000 ml bile juice secreted from the liver each day and also the pancreatic juice
secreted from the pancreas. The bile juice does not contain enzyme but helps to
neutralise acid and emulsify fat. The pancreatic juice contains three enzymes:
trypsin, amylase and lipase.

Trypsin: trypsin converts the proteins into peptones.

Amylase: amylase acts on starch to form maltose.

Lipase: lipase converts fats into fatty acid and glycerol.

The essentials nutrients like the iron, calcium, etc. are absorbed in the duodenum
wall. The finger-like projections in the small intestine that helps in the absorption
of nutrients from food are known as the villi. The villi contain tiny cells called
microvilli that absorb nutrients from food.

ii) The jejunum (2 m long): Most of the absorption of nutrients and digested chemicals
take place in jejunum. Then the food moves towards the ileum.

iii) The ileum (3 m long): The remaining digestion and absorption of food takes place
in the ileum. It is the longest part of the small intestine. In the ileum, the intestinal
juices named erepsin, maltase, sucrase and lactase are secreted.

Erepsin : The erepsin converts peptones and peptides into amino acids that is
used to form protein.

Maltase : The maltase acts on maltose and converts it into glucose.

Sucrase : The sucrase converts the sucrose into glucose and fructose.

Lactase : The lactase acts on lactose and converts it into glucose and galactose.

f) Large intestine

About 90% of the nutrients are absorbed in the small intestine. Only water along with

some minerals are absorbed in the large intestine. The large intestine is divided into

many sections through which the remaining undigested mass moves. The sections

are: cesium, ascending colon, transverse colon, Memory Tips

descending colon, sigmoid colon, rectum and anus. Most of the water is absorbed in
The large intestine is filled with good bacteria which large intestine.
feed on undigested food and thus aid in digestion.

g) Rectum and Anus

The remaining undigested mass now called feces are passed through a straight muscular
tube called rectum. When the feces accumulate more in the large intestine, we pass them
voluntarily out through the lower end opening of the alimentary canal called anus. This
process is called defecation.

The whole digestive action can be pointed out in the following steps:

i) Ingestion of food: The process of taking food inside the mouth and buccal cavity
is called ingestion.

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