Oasis Science and Technology 9

4. Maize plant Zea mays
5. Tiger Panthera tigris
6. Mango Mangifera indica

Rules of writing scientific names in Binomial System

1. The name of the genus is written first with its first letter in capital and the name of the
species is written after the generic name with its first letter in small.

2. The binomial should be printed in italics or underlined separately if handwritten. For
example, the scientific name of lion is Panthera leo or Panthera leo.

Genus

A genus is the group of closely related species resembling each other. For example, all true cats
like lion, tiger and domestic cat are kept in the same genus Panthera or Felis.

Species

A species is the group of closely related organisms which are almost identical in their anatomy,
physiology and behaviour and can interbreed to produce fertile offspring. Members of a
species also often resemble each other very closely in appearance. For example, all types of
human beings throughout the world are kept in same species sapiens. Thus, a species is the
group of similar organisms that are able to breed together and produce fertile offspring.

16.5 Categories of Classification

Classification of living organisms is done by arranging all organisms into various groups
or categories called taxa on the basis of their similarities or differences. First of all, living
organisms are split into kingdoms like Plant Kingdom or Animal Kingdom. Those kingdoms
are divided into a large number of smaller groups called phyla (singular-phylum). Then the
phyla are further divided into classes, classes into orders, orders into families, families into
genera and genera into various species.

Taxa Human being Potato
Kingdom Animalia Plantae
Phylum / Division Chordata Spermatophyta
Sub-phylum / Sub-division Vertebrata Angiospermae
Class Mammalia Dicotyledonae
Order Primates Polemoniales
Family Hominidae Solanaceae
Genus Homo Solanum
Species sapiens tuberosum

genus /ˈdʒiːnəs/ - the group of closely related species Oasis School Science - 9 243
BIOLOGY

16.6 Five Kingdom System of Classification

In previous classes you have studied two kingdom system of classification, viz. Plant kingdom
and Animal Kingdom. In this unit, you will study five kingdom system of classification of
living beings. The concept of Five Kingdom System of Classification was introduced by an
American Biologist Robert H. Whittaker in 1969 A.D.

Five Kingdom System of Classification is more appropriate and scientific
than two Kingdom System of Classification. It can be justified by following
facts:

i) Prokaryotes and eukaryotes are separated.

ii) Unicellular and multicellular organisms are separated.

iii) Green plants and non-green plants like algae and fungi are kept in Robert H. Whittaker
separate groups. Fig. 16.1

iv) This system of classification is related to evolution of organisms. So
it helps to get clear concept of life style of living beings.

According to the concept of 'Five Kingdom System of Classification', living beings are
classified as follows:

1. Kingdom Monera

This kingdom includes unicellular prokaryotic microscopic organisms. Their cell contains
DNA (Deoxyribonucleic Acid) as a nucleus. They may be autotrophs or parasites.

Examples: Bacteria, Azotobacter, Blue-green algae, etc.

Bacteria Azotobacter Blue-green algae

Fig. 16.2

2. Kingdom Protista

This kingdom includes eukaryotic
unicellular organisms. Their cells
contain well developed nucleus.

Examples: Amoeba, Paramecium,
Euglena, etc.

Amoeba Paramecium Euglena

Fig. 16.3

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3. Kingdom Fungi

This kingdom includes unicellular and multicellular non-green plants. Their body is
thalloid (without root, stem and leaf). They derive their food from dead and decaying
organic matter. Their mode of nutrition is either saprophytic or parasitic. They reserve
food in the form of glycogen. Their cell wall is made of the mixture of chitin and cellulose.

Examples: Mushroom, Yeast, Mucor, etc.

Mushroom Yeast Mucor

4. Kingdom Plantae Fig.16.4

This kingdom includes different types of non-flowering and flowering plants.
Characteristics of Plant Kingdom
i. They may be unicellular or multicellular.
ii. Their cells contain cell wall which is made up of cellulose.
iii. They prepare their own food by photosynthesis. So they are called autotrophs.
iv. They store food in the form of carbohydrates such as starch.
v. They appear green due to the presence of chlorophyll.
vi. They may be non-flowering or flowering.

Kingdom Plantae is divided into three divisions which are as follows:

a. Division Algae b. Division Bryophyta

c. Division Tracheophyta

a. Division Algae [L., alga–sea weed]

Division algae includes green thallophytes. Most algae are aquatic (both fresh water and
marine water) whereas some are found on moist land.
Characteristics

i. The plant body is a thallus which may be unicellular or multicellular.
ii. They usually contain green pigment, i.e. chlorophyll for photosynthesis. Some

algae contain red, brown, blue-green, yellow-green and purple pigments.

iii. They are autotrophic due to the presence of chlorophyll. Reserve food is
generally starch.

iv. The cell wall is made up of cellulose.
v. They reproduce asexually or sexually.

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Examples: Green algae (Spirogyra, Chlamydomonas, Volvox, Ulothrix, etc.), Blue-
green algae (Anabaena, Nostoc), Red algae (Batra), Brown algae (Laminaria), etc.

Spirogyra Chlamydomonas Ulothrix Volvox

Anabaena Nostoc Batra Lamnaria

Fig. 16.5 Some algae

Differences between Algae and Fungi

S.N. Algae S.N. Fungi

1 Chlorophyll is present. 1 Chlorophyll is absent.

2 The mode of nutrition is 2 The mode of nutrition is either

autotrophic. saprophytic or parasitic.

3 Cell wall is made up of cellulose. 3 Cell wall is made up of chitin and
cellulose.

4 Reserve food is starch (glucose). 4 Reserve food is glycogen.

b. Division Bryophyta [Gk., Bryon-a moss, a liverwort]
Bryophytes are a group of higher cryptogams. They grow on old damp walls, on

moist ground and on bark of trees; however, they need water for reproduction.
Therefore, bryophytes are also called amphibians of Plant Kingdom. The plant
body of bryophytes is more advanced and complicated than that of algae.

Characteristics

i. The plant body is multicellular which may be thalloid (in primitive forms like
liverworts) or leafy (in advanced forms like moss).

ii. True roots, stem and leaves are absent.

iii. In bryophytes, the main plant body is a gametophyte which bears sex organs.

iv. Gametophyte is attached to the substratum by means of hair-like outgrowths
called rhizoids, which absorb water and minerals from the soil.

vascular / ˈ v æ s k j ə l ə r / - of or containing veins or tubes that carry liquids around the bodies of plants/animals

246 Oasis School Science - 9 BIOLOGY

v. Vascular tissues, i.e. xylem and phloem are absent.
vi. They possess alternation of generations in their life cycle. Spores are produced by

sporophyte in a capsule and gametes are produced by gametophyte.

Examples: Marchantia (liverworts), Riccia, Moss, etc.

Marchantia Riccia Moss
Fig. 16.6 Some bryophytes

c. Division Tracheophyta

This division includes well developed plants having vascular tissues, i.e. xylem and
phloem tissues. Various types of pteridophytes, gymnosperms and angiosperms
are kept in this division.

Division Tracheophyta is further divided into three sub-divisions. They are as
follows:

i) Sub-division Pteridophyta

ii) Sub-division Gymnosperms

iii) Sub-division Angiosperms

Sub-division Pteridophyta

Sub-division pteridophyta includes the highest group of cryptogams, i.e. non-flowering
plants in which the plant body is differentiated into root, stem and leaves. Pteridophytes
are more advanced than bryophytes as the plant body contains vascular tissues, roots,
stem and leaves. Pteridophytes are mostly found in damp, cool and shady places.

Characteristics
i. The plant body can be differentiated into roots, stem (rhizome) and leaves.
ii. They have well developed vascular tissues, i.e. xylem and phloem tissues.
iii. Flowers and seeds are absent.
iv. The ventral surface of leaf contains numerous spots called sori (singular-sorus)

which produce spores and help in asexual reproduction.

v. Spore germinates and forms gametophyte which helps in sexual reproduction.
vi. Sex organs are multicellular. Alternation of generations is common in the life cycle.

Sporophyte is more advanced than gametophyte.

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Examples: Fern, Lycopodium, Equisetum (Horsetail), Selaginella (club moss), Marsilea, etc.

Fern Lycopodium Equisetum Selaginella Marsilea

Fig. 16. 7 Some pteridophytes

Differences between Bryophytes and Pteridophytes

S.N. Bryophytes S.N. Pteridophytes

1 The plant body may be thalloid with 1 The plant body is clearly differentiated

rhizoids or having rhizoids, stem into roots, stem and leaves.

(seta) and leaves.

2 Gametophyte is larger and more com- 2 Sporophyte is larger and more

plicated than sporophyte. complicated than gametophyte.

3 Vascular system is absent. 3 Vascular system is present.

Activity 1

• Visit a forest with your science teacher and observe various types of cryptogams.
• Collect some fungi, bryophytes and pteridophytes.
• Study their morphology and differentiate among them.
• Classify them with well labelled figures.

• Also, write at least two important features of each which helped you in deciding
the group in which the plant should be kept.

Sub-division Gymnosperms [Gk., gymno-naked, sperma-seed]

Sub-division Gymnosperms includes cone-bearing plants having naked seeds. These plants
grow in cold and dry places. The salient features of the plants belonging to this sub-division
are mentioned below:
i. Cones are present instead of true flowers. Male cones and female cones are separate.
ii. Seeds are not enclosed in fruit. They develop in the woody scales of cones.

iii. Needle-shaped leaves are present.
iv. There is no fruit due to the absence of ovary.
v. Pollination takes place with the help of air.

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Examples: Cycas, pine, cedar, fir, etc.

Cycas

Pine Cedar

Female cones of a pine tree Male cones of pine tree

Fig. 16.8 Some gymnosperms

Sub-division Angiosperms [Gk., angion - case, sperma - seed]
Sub-division Angiosperms includes well developed flowering plants having seeds enclosed
within fruit. These plants grow on land and in water. The salient features of the plants
belonging to this sub-division are mentioned below:
i. Well developed flowers are present. The reproductive organs are aggregated in a flower.

ii. Seeds are enclosed inside the fruit.
iii. The plant body is made of root, stem and leaves.
iv. Vascular system is present.
v. Flowers contain ovary and ovule which develop into fruit and seed.
vi. Pollination takes place with the help of air, water, insects, etc.

vii. Their stems may be hollow or woody.

Examples: Grass, banana, lotus, wheat, papaya, mustard, rice, maize, bamboo,
pea, orange, mango, soyabean, bean, pumpkin, etc.

On the basis of number of cotyledons in a seed, sub-division Angiosperms is further divided
into two classes, viz. Monocotyledons and Dicotyledons.

Class Monocotyledons (Monocot)

This class includes flowering plants having only one cotyledon in their seeds. They are found
in water and on land. The salient features of the plants belonging to this class are as follows:

i. The seed of these plants bears only one cotyledon.
ii. Fibrous or adventitious root system is present.
iii. Distinct nodes and internodes are present in the stem.
iv. Leaves are elongated having parallel venation.

BIOLOGY Oasis School Science - 9 249

v. The flowers are trimerous, i.e. having three petals or multiples of three.
vi. Vascular bundles are closed and scattered.
vii. They have hollow stem.

Examples: Bamboo, grass, maize, wheat, rice, barley, sugarcane, onion, lemna,
pistia, water hyacinth, banana, coconut, etc.

Maize Oats Rice Pistia Water hyacinth

Fig.16.9 Some monocot plants

Class Dicotyledons (Dicot)

This class includes well developed flowering plants having two cotyledons in their seeds. The
salient features of the plants belonging to this class are as follows:

i. The seeds of these plants contain two cotyledons.

ii. Leaves are broad having reticulate venation.

iii. Tap root system is present.

iv. The flowers are usually pentamerous, i.e. having five petals or multiples of five.

v. The vascular bundles are open and arranged in a ring.

vi. They have solid and strong
stem.

Examples: Pea, sunflower,
mango, rose, orange, neem,
bean, lettuce, mustard, gram,
soyabean, pumpkin, orange,
papaya, lotus, etc.

Mustard Rose Mango
Fig. 16.10 Some dicot plants

Activity 2

• Visit a park and observe various types of gymnosperms and angiosperms. Study
their external morphology and differentiate between them.

• Visit a crop field and collect some angiosperms. Study their external morphology
and separate them in terms of monocots and dicots.

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Differences between Gymnosperms and Angiosperms

S.N. Gymnosperms S.N. Angiosperms

1. Cones are present instead of true 1. Well developed flowers are present.
flowers.

2. Seeds are naked. 2. Seeds are enclosed inside the fruit.

3. Generally, leaves are elongated and 3. Generally, leaves are flat and broad.
pointed.

Differences between Dicot and Monocot

S.N. Dicot S.N. Monocot
1. A seed contains two cotyledons. 1. A seed contains only one cotyledon.
2. Tap root system is present. 2. Fibrous root system is present.
3. Leaves contain reticulate venation. 3. Leaves contain parallel venation.
4. Flowers are usually pentamerous. 4. Flowers are usually trimerous.
5. Distinct nodes and internodes are 5. Distinct nodes and internodes are
absent. present.

Activity 3

To observe root, stem and leaves of plants
• Uproot some small plants in your surroundings and observe their roots, stem and leaves.
• Collect leaves of some tall plants and observe them .
• Classify these plants in terms of monocot and dicot.
• Draw a neat and labelled figure of each and submit to your science teacher.

Kingdom Plantae

Division

Algae Bryophyta Tracheophyta
e.g. Spirogyra, e.g. Marchantia, Moss, etc. e.g. Fern, Cycas,
Chlamydomonas, etc. Bamboo, Mango, etc.

Sub-division

Pteridophyta Gymnosperms Angiosperms
e.g. Fern, Lycopodium, etc. e.g. Cycas, Pine, etc. e.g. Sugarcane, Pea, etc.

Class

Monocotyledon Dicotyledon
e.g. Paddy, Banana, etc. e.g. Mustard, Rose, etc.

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5. Kingdom Animalia
Kingdom Animalia includes different types of multicellular invertabrates and vertebrates.

Invertebrates

Invertebrates are the animals without a backbone or vertebral column inside the body. More
than 90% of all species of animals are invertebrates and they include sponges, coelenterates,
worms, insects, molluscs, echinoderms, etc.

Many invertebrates do not contain skeleton, however some invertebrates contain tough
skeleton called exoskeleton on the outer surface of their bodies.

Note: Invertebrates do not possess 'Notochord'. So, they are also called Non-chordates.

On the basis of structure and development, Invertebrates are divided into nine phyla
(singular--phylum).

Phylum 1. Porifera [Gk., porus—pore, ferre—to bear]

Phylum Porifera includes the primitive multicellular invertebrates having numerous pores in
their bodies. They are sedentary (attached to the substratum) mostly found in marine water
but some are found in fresh water. They are commonly known as sponges.

Characteristics
i. The shape of the body may be vase-like, sac-like, rounded or branched.
ii. The body contains numerous small pores called ostia (singular-ostium) that open

into a canal system and one or more large pores called oscula (singular-osculum).
iii. The body remains attached to the substratum with the help of basal disc.
iv. They are the simplest multicellular and diploblastic animals, i.e. body tissue

differentiates from two embryonic germ layers.
v. The body may be asymmetrical or radially symmetrical.

vi. Digestive tract, respiratory organs and excretory organs are absent.

vii. Breathing takes place through the body surface and excretion takes place through
osculum/oscula.

viii. They reproduce asexually by budding and regeneration and sexually by the
fusion of gametes.

Examples: Sycon, Spongilla, Euspongia, Leucosolenia, etc.

Sycon Spongilla Euspongia Leucosolenia

252 Oasis School Science - 9 Fig. 16.11 Some sponges

BIOLOGY

Phylum 2. Coelenterata or Cnidaria [Gk., koils—hollow, enteron--gut]

Phylum Coelenterata includes aquatic invertebrates having hollow body cavity called
coelenteron. This phylum includes hydras, sea anemones, jelly fishes and corals. Most of the
coelenterates are found in marine water while some are found in fresh water.

Characteristics
i. The body contains a hollow cavity called coelenteron where digestion of food takes

place.
ii. Mouth is present but anus is absent.
iii. Mouth remains surrounded by a ring of tentacles.
iv. Locomotion takes place with the help of tentacles.
v. Their body is diploblastic and radially symmetrical.
vi. Breathing takes place through the general body surface.
vii. They reproduce by both asexual and sexual methods.
Examples: Hydra, Jellyfish, Coral, Sea anemone, etc.

Hydra Jelly fish Coral Sea anemone

Fig.16.12 Some coelenterates

Phylum 3. Platyhelminthes [Gk., platys – flat, helmins – worm]

Phylum Platyhelminthes includes invertebrates having dorsoventrally flattened body. The
animals belonging to this phylum are commonly known as flatworms. Most of the flatworms
are endoparasites of animals whereas some are free living in moist soil. The body measures
from a few millimeters to a few centimeters in length.

Characteristics
i. The body is dorsoventrally flattened and bilaterally symmetrical.
ii. Suckers or hooks or both are present for attachment to the body of host.
iii. Digestive tract is incomplete. Mouth is present but anus is absent.
iv. They are first triploblastic animals, i.e. body tissue differentiates from three

embryonic germ layers.
v. They are hermaphrodite or bisexual animals, i.e. both male and female sex organs

occur in the same organism.
vi. Respiratory system and circulatory system are absent.

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vii. The body is soft, thin, leaf-like, tape-like or ribbon-like.
viii. Excretory system consists of protonephridia or flame cells.
ix. Nervous system is present.
x. Most of them reproduce by sexual method.
Examples: Tapeworm (Taenia), Liverfluke (Fasciola), Planaria, etc.

Tapeworm Liver fluke Planaria

Fig. 16.13 Some flatworms

Phylum4.NemathelminthesorAschelminthes[Gk.,ascus-abladder,helmins-worm]

Phylum Nemathelminthes includes unsegmented invertebrates having a round body. The
animals belonging to this phylum are commonly called nematodes or round worms. Most
of the nematodes live as parasites of plants and animals whereas some are free living in
soil or in water.

Characteristics
i. The body is round, slender, unsegmented, cylindrical and tapering at the

two ends.
ii. The body is triploblastic and bilaterally symmetrical.
iii. Body is covered with a tough and thick cuticle.
iv. The alimentary canal is complete, with a mouth and anus.
v. Respiratory and circulatory systems are absent.
vi. They are unisexual animals, i.e. sexes are separate. Males are smaller than females.
vii. Nervous system and reproductive system are present.

viii. They reproduce by sexual method.

Examples: Ascaris male female
(roundworm), Ascaris
Ancylostoma
(hookworm),
Wuchereria (filarial
worm), Enterobius
(pinworm), etc.

Ascaris Hookworm Wuchereria Enterobius

Fig. 16.14 Some roundworms

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Phylum 5. Annelida [L., annelus – ring, segmented worms]

Phylum Annelida includes invertebrate animals having numerous segmented rings in their
bodies. Earthworms, leeches and sandworms are kept in this phylum. The members of this
phylum are commonly called annelids. Their bodies appear as if made up of a series of rings.
Annelids may be free-living or parasitic. Most of them are aquatic (marine or fresh water)
while some are terrestrial found in moist soil.

Characteristics

i. The body is soft, elongated and cylindrical having numerous circular rings.
ii. The body is triploblastic, bilaterally symmetrical and metamerically segmented

(made up of a series of similar segments having similar pattern of organs).

iii. The body is covered with a thin cuticle.

iv. Locomotion takes place with the help of setae (e.g. earthworm), sucker (e.g. leech)
or parapodia (e.g. Nereis).

v. Alimentary canal is complete which extends from mouth to anus.
vi. Closed blood vascular system is present.

vii. Excretory and nervous systems are present.
viii. Sexes may be united (hermaphrodite) or separated (unisexual).

ix. They reproduce by sexual method.

Examples: Earthworm (Pheretima), Leech (Hirudinaria) Sandworm (Nereis), etc.

Earthworm Leech Nereis
Fig. 16.15 Some annelids

Phylum 6. Arthropoda [Gk., arthros – jointed, podos – foot]

Phylum Arthropoda includes invertebrate animals having jointed appendages (legs and
antennae). The members of this phylum are commonly known as arthropods. This is the largest
phylum of the animal kingdom. About 900,000 species of arthropods are known. Arthropods
are cosmopolitan in distribution. They are widely distributed on land and in water. They may
be free living, commensals or parasitic in nature.

Characteristics

i. The body is triploblastic and bilaterally symmetrical having jointed appendages.

ii. The segmented body can be differentiated into two regions – cephalothorax and
abdomen or three regions – head, thorax and abdomen.

iii. The head contains brain and sensory organs.
iv. The body is covered with a thick chitinious and jointed exoskeleton.
v. Locomotion takes place with the help of legs or wings or both.

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vi. Alimentary canal is complete.
vii. Breathing takes place through the general body surface, by gills, trachea or

book-lungs.
viii. Circulatory and excretory systems are present.
ix. Sexes are usually separate. They reproduce by sexual method.

Examples: Crab, Crayfish (prawn), Centipede, Millipede, Mosquito, Butterfly,
Grasshopper, Honeybee, Scorpion, Spider, Ant, etc.

Phylum Arthropoda is further divided into following four classes:

Class 1. Crustacea
i The body can be divided into cephalothorax and abdomen.
ii. Breathing takes place by means of gills.
iii. They are found in water.

Examples: Prawn (Crayfish), Crab, etc.

Prawn Crab
Fig. 16.16 Some crustaceans
Class 2. Myriopoda

i. Body is elongated and metamerically segmented.

ii. Each segment of the body contains one or two pairs of jointed legs.

iii. They are found on land.

iv. Breathing takes place with
the help of trachea.

Examples: Centipede, Millipede, etc.

Centipede Millipede

Class 3. Insecta Fig. 16.17 Some myriopods

i. The body can be divided into head, thorax and abdomen.

ii. Head contains mouthparts, compound eyes and antennae. Thorax contains two
pairs of wings and three pairs of jointed legs. Abdomen lacks appendages.

iii. Breathing takes place with the help of trachea.
iv. They are mostly terrestrial.

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Examples: Butterfly, Mosquito, Silverfish, Cockroach, Housefly, etc.

Mosquito Butterfly Silverfish

Fig. 16.18 Some insects

Class 4 : Arachnida

i. The body can be divided into cephalothorax and abdomen.
ii. Antennae and true jaws are absent.
iii. Four pairs of jointed legs are present.
iv. Breathing takes place with the help of tracheae or book-lungs.
v. They are terrestrial arthropods.

Examples: Spider, Scorpion, etc.

Scorpion Spider

Fig. 16.19 Some arachnids

Phylum 7. Mollusca [L., molluscus – soft]

Phylum Mollusca includes unsegmented invertebrates having soft and unsegmetned body
which is often covered by one or two hard shells. Most of the molluscs are aquatic (mostly
marine) and some are terrestrial.

Characteristics
i. The body is soft, unsegmented and generally protected by a hard shell made up of

calcium carbonate.
ii. The body can be divided into head, visceral mass and muscular foot.
iii. Locomotion takes place with the help of muscular foot or cephalic arms.
iv. Breathing takes place with the help of gills or lungs.
v. The body is triploblastic and bilaterally symmetrical.
vi. Digestive system, excretory system, blood vascular system, nervous system and

reproductive system are present.

vii. Sexes are generally separate. They reproduce by sexual method.



BIOLOGY Oasis School Science - 9 257

Examples: Snail, Slug, Pila, Unio, Octopus (devil fish), Sepia (cuttle fish), Squid, etc.

Snail Slug Pila

Octopus Sepia Squid

Fig. 16.20 Some molluscs

Phylum 8. Echinodermata [Gk., echinos-spiny, derma-skin]

Phylum echinodermata includes aquatic invertebrates having spiny skin. These are exclusively
marine animals and are largely bottom dwellers.

Characteristics
i. The body remains covered with spiny skin.
ii. Locomotion takes place with the help of tube feet.
iii. The body may be star shaped, globular or cylindrical.
iv. Distinct head is absent. Mouth is present on the ventral surface.
v. Water vascular system is present.
vi. The body is unsegmented, triploblastic and radially symmetrical.
vii. Sexes are separate. They can reproduce by regeneration.
Examples: Starfish, Sea urchin, Sea cucumber, Brittle star, etc.

Starfish Sea urchin Sea cucumber Brittle star

Fig. 16.21 Some echinoderms

Activity 4

• Collect some invertebrates from your surroundings and observe their structure
carefully.

• Classify them on the basis of their characteristics and write their salient features.

258 Oasis School Science - 9 BIOLOGY

Vertebrates are kept in phylum chordata.

Kingdom Animalia

Phylum 1. Porifera, e.g. Ameoeba, Paramecium, etc.
2. Coelenterata, e.g. Hydra, Coral, etc.
3. Platyhelminthes, e.g. Tapeworm, Liver fluke, etc.
4. Nemathelminthes, e.g. Ascaris, Pinworm, etc.
5. Annelida, e.g. Crab, Mosquito, etc.
6. Arthropoda, e.g. Crab, Mosquito, etc.
7. Mollusca, e.g. Snail, Octopus, etc.
8. Echinodermata, e.g. Starfish, Sea Anemone, etc.
9. Chordata

Sub-phylum

Hemichordata Urochordata Cephalochordata Vertebrata

e.g. Balanoglossus e.g. Herdmania e.g. Amphioxus Class

Pisces Amphibia Reptilia Aves Mammalia
e.g. Snake, e.g. Parrot, e.g. Elephant,
e.g. Shark, e.g. Frog, Lizard, etc. Crow, etc.
Labeo, etc. Toad, etc. Bat, etc.

16.7 Vertebrates

Vertebrates are the developed animals having backbone or vertebral column. Vertebrates are
more developed than invertebrates. Examples: Fish, Frog, Snake, Sparrow, Cow, etc.

16.8 Phylum Chordata

Phylum chordata includes advanced animals having notochord. They are triploblastic and
coelomate animals having bilaterally symmetrical body. The characteristics of the animals
belonging to the phylum chordata are given below:

i. Notochord is present throughout life or at some stages of the life history.
ii. Dorsal hollow nerve cord is present, lying just above the notochord.
iii. Post anal tail is present.
iv. They have a closed blood vascular system. Blood flows forward ventrally and backwards

dorsally.
v. They contain gills in embryonic stage.

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vi. The body is bilaterally symmetrical and triploblastic.
Examples: Balanoglossus, Herdmania, fish, frog, bat, monkey, etc.

Note: Notochord is a flexible rod like structure running along the dorsal surface of
chordata embryo ventral to the nerve cord. In vertebrates, the notochord is replaced
by vertebral column, i.e. backbone.

(a) Balanoglossus-A Hemichordate (b) Herdmania-A Urochordate (c) Amphioxus-A Cephalochordate

Fig.16.22 Some chordates

Phylum Chordata is divided into four sub-phyla. They are (i) Hemichordata (ii) Urochordata
(iii) Cephalochordata and (iv) Vertebratra. In this unit, you will study about sub-phylum
vertebrata only.

16.9 Sub-phylum Vertebrata

Sub-phylum vertebrata is the most familiar sub-phylum of chordates. The members of this
sub-phylum are commonly known as vertebrates. In vertebrates, bones or vertebrae develop
around the notochord and the nerve cord. They live on land and in water. The salient features
of the animals belonging to this sub-phylum are mentioned below:

i. In vertebrates, notochord is replaced by vertebral column, i.e. backbone.
ii. A tubular nerve cord is present in the dorsal side of the body which is differentiated into

brain and spinal cord.
iii. They breathe through gills or lungs.
iv. The body is well developed having head, trunk and paired fins or limbs.

Examples: Fish, frog, snake, crow, cow, dolphin, bat, horse, etc.
On the basis of structure and development, sub-phylum vertebrata is further divided into five
classes.

Class 1. Pisces
Class Pisces includes aquatic, cold-blooded vertebrates which are commonly known as fishes.
The characteristics of the animals belonging to this class are mentioned below:

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i. The body is streamlined or boat-shaped which remains covered with smooth, slippery
and waterproof scales.

ii. The body is differentiated into head, trunk and tail.
iii. Locomotion takes place with the help of fins and tail.
iv. Breathing takes place with the help of gills.
v. Heart is two-chambered.
vi. They are oviparous, i.e. egg laying and fertilization is external.

Examples: Shark (Scoliodon), Rohu (Labeo), Sea horse (Hippocampus), Katla (Catla), etc.

Sea horse Shark Rohu
Fig. 16.23 Some fishes

Class 2. Amphibia [Gk., amphi - double, bios - life]

Class Amphibia includes cold-blooded vertebrates leading two lives, i.e. on land and in water.
Amphibians form the first group of chordates adapted to live out of water and comprise first
tetrapod (four legged) land vertebrates. Most amphibians lay eggs in water where the eggs
develop into tadpoles. The tadpoles develop into adults after metamorphosis which can live in
water as well as on land. The characteristics of amphibians are mentioned below:

i. The body is divided into head and trunk. Neck is absent.
ii. The body remains covered with smooth or rough skin which is moist and rich in glands.
iii. Heart is three-chamberd.
iv. Two pairs of limbs are present. Claws are absent in toes or digits.

v. They breathe through skin in water and through lungs on land. However, tadpoles
breathe through gills.

vi. The tadpole, i.e. larval stage, is tailed and aquatic.
vii. They are oviparous and fertilization is external.

Examples: Frog (Rana), Toad (Bufo), Salamander (Salamandra), Tree frog (Hyla), Ichthyophis,
Ambystoma, etc.

Salamander Toad Frog Ichthyophis Ambystoma

Fig 16. 24 Some amphibians

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Class 3. Reptilia [Latin, repre - to crawl, creeping vertebrates]
Class Reptilia includes creeping or crawling cold-blooded vertebrates. The members of this
class can live solely on land and are very less dependent on water. Snakes, lizards, crocodiles,
etc. are kept in this class. The salient features of reptiles are given below:

i. The body remains covered with hard, dry and horny scales.

ii. The body can be divided into head, neck, trunk and tail.

iii. Heart is three-chambered but crocodiles have four-chambered heart.

iv. Two pairs of limbs with clawed digits are present. But limbs are absent in snakes and
some lizards.

v. Breathing takes place through lungs.
vi. They are oviparous and fertilization is internal.

Examples: Cobra (Naja), Garden lizard (Calotus), House wall lizard (Hemidactylus),
Gharial (Gavialis), Monitor lizard (Varanus), Ajgar (Python), Tortoise (Testudo), etc.

Wall lizard

Tortoise

Snake

Crocodile

Turtle

Fig 16.25 Some reptiles

Class 4. Aves [Latin, avis - bird]
Class Aves includes warm-blooded tetrapodous vertebrates with flight adaptations. Various
types of birds are kept in this class. The salient features of the animals belonging to this class
are mentioned below:

i. The streamlined body is covered with feathers which can be divided into head, neck,
trunk and tail.

ii. Fore limbs are modified in the form of wings.

iii. Teethless beak is present.

iv. Heart is four-chambered.

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v. They are warm-blooded animals.
vi. Breathing takes place with the help of lungs.
vii. They are oviparous and fertilization is internal.
Examples: Pigeon (Columba), Sparrow (Passer), Crow (Corvus), Owl (Bubo), Peacock

(Pavo), Vulture (Gypus), Parrot (Psittacula), Koel (Eudynamus), etc.

Cuckoo

Crow

Sparrow

Ostrich

Peacock

Pigeon

Fig. 16.26 Some birds

Class 5. Mammalia [Latin, mamma - breast]
Class Mammalia includes the most developed vertebrates which directly give birth to their
young ones and suckle them. However, two mammals, duck-billed platypus and spiny ant
eater lay eggs. All female mammals secrete milk on which their offspring feed. They live on
land and in water. The salient features of the mammals are given below:

i. Females have mammary glands, i.e. milk producing glands which secrete milk for the
nourishment of their young ones.

ii. Body is covered with hair. Sweat glands and oil glands are present in the skin.
iii. External ears (pinnae) are present.
iv. Heart is four-chambered.
v. They are viviparous and warm-blooded animals.
vi. Body can be divided into head, neck, trunk and tail.
vii. Two pairs of pentadactylus limbs are present. Digits contain nails, claws or hoofs.

viii. Breathing takes place with the help of lungs.

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Examples : Human, Whale, Bat, Dolphin, Dog, Cat, Cow, Squirrel, Rat, etc.

Rhinoceros Monkey
Bat
Dolphin

Duck-billed platypus Kangaroo

Squirrel
Fig. 16.27 Some mammals

16.10 Cold-blooded and Warm-blooded Animals

The animals whose body temperature changes according to the temperature of their
surroundings are called cold-blooded or poikilothermic animals. Fishes, amphibians and
reptiles are cold-blooded animals. These animals cannot tolerate extreme high and low
temperature and go for hibernation.
The animals whose body temperature remains constant and does not change according to the
temperature of their surroundings are called warm-blooded or homoiothermic animals. Aves
and mammals are warm-blooded animals. Generally, these animals do not go for hibernation.

Activity 5

• Study the structure of some birds and mammals in your locality and differentiate
between them. Also, classify them with two salient features of each.

16.11 Oviparous and Viviparous Animals

The animals that lay eggs are called oviparous animals and the animals that directly give birth
to their young ones are called viviparous animals. Fishes, amphibians, reptiles and birds are
oviparous whereas mammals are viviparous.

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16.12 Classification of Some Plants and Animals

1. Spirogyra
Kingdom : Plantae
Division : Algae
Type : Spirogyra

2. Marchantia

Kingdom : Plantae
: Bryophyta
Division : Marchantia

Type Plantae
3. Fern Tracheophyta
Gymnosperms
Kingdom : Plantae Cycas

Division : Tracheophyta Plantae
Tracheophyta
Sub-division : Pteridophyta Angiosperms
Dicotyldedon
Type : Fern Mustard

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Kingdom :
:
Division :
:
Sub-division

Type

5. Sugarcane

Kingdom : Plantae

Division : Tracheophyta

Sub-division : Angiosperms

Class : Monocotyledon

Type : Sugarcane

6. Mustard Kingdom :
Division :
Sub-division :
Class :
Type :


BIOLOGY

7. Sponge

Kingdom : Animalia

Phylum : Porifera

Type : Sponge

8. Liverfluke

Kingdom : Animalia
: Platyhelminthes
Phylum : Liverfluke

Type : Animalia
9. Butterfly : Echinodermata
: Starfish
Kingdom : Animalia
Animalia
Phylum : Arthropoda Chordata
Vertebrata
Type : Butterfly Amphibia
Bufo
10. Starfish Kingdom
Phylum
Type


11. Rohu : Animalia
Kingdom : Chordata
Phylum : Vertebrata
Sub-phylum : Pisces
Class : Rohu
Type

12. Bufo

Kingdom :
Phylum :
Sub-phylum :
Class :

Type :

13. Snake : Animalia
Kingdom : Chordata
Phylum : Vertebrata
Sub-phylum

Class : Reptilia
Type : Snake

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14. Parrot : Animalia
Kingdom : Chordata
Phylum : Vertebrata
Sub-phylum : Aves
Class : Parrot
Type
15. Bat

Kingdom : Animalia
Phylum : Chordata
Sub-phylum : Vertebrata
Class : Mammalia
Type : Bat

B. Mosquito

16.13 Introduction

Mosquitoes are two-winged flying insects that suck blood from humans and other animals.
Mosquitoes have a slender body, long jointed legs and needle shaped piercing and sucking
mouth parts. In most parts of the world, their biting is a considerable nuisance. More
importantly, they are carriers of a number of diseases, mostly in the tropics, causing illness
and death on a large scale.

There are about 3000 species of mosquito, of which about 100 are vectors of human diseases.
They transmit several tropical diseases including malaria, filariasis, dengue, Japanese
encephalitis and yellow fever. Anopheles, Culex, Aedes and Mansonia are the common genera of
mosquito distributed throughout the tropical countries.

16.14 Habit and Habitat

Mosquitoes are found in damp and marshy places in tropical and sub-tropical regions. They
are nocturnal in feeding habit but day time biting also occurs. Some species prefer biting at
certain hours, at dusk and dawn or in the middle of the night. Female mosquitoes feed on
the blood of man and animals and males suck the juice of flowers and fruits. Because of their
blood-sucking habit, the females are medically important as carriers of viral, bacterial and
protozoan infections. Adult mosquitoes fly well and can cover great distances. They are able
to fly without rest for 2-3 hours and easily cover 20-30 km in a night. The females become
aggressive after copulation and lay eggs in water, where the development of larvae and pupae
takes place.

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16.15 External Morphology

The body of a mosquito is small, soft, slender and covered with minute scales. It measures
about 3-4 mm in length and the body colour is grayish black.

Compound eye

Antenna Hind legs

Head Wing
Mouth parts Abdomen

Thorax

Fore leg Mid leg

Fig. 16.28 External morphology of a mosquito

The body of a mosquito can be divided into head, thorax and abdomen.

The head is small and almost spherical which is connected to the thorax by short neck. The
head bears a pair of kidney shaped compound eyes, jointed feathery antennae; and piercing
and sucking type of mouth parts.

The thorax is made up of very small prothorax, very large mesothorax with a single pair of
wings and a small metathorax. Each segment of thorax contains a pair of long jointed legs. The
wings are narrow, membranous and covered with scales. The metathorax bears a pair of small
drumstick-shaped structure, called the halters or balancers. Those balancers are rudimentary
hind wings, useless for flight and are supposed to produce characteristic sound.

The abdomen is slender and nine segmented. The anus is present on the eighth segment and
a genital pore is present on the ninth segment.

16.16 Life Cycle

Mosquitoes have four distinct stages in their life cycle – eggs, larvae, pupae and adults. They
show complete metamorphosis in their life cycle. The two sexes copulate during flight. The
male gets attracted to the female by her high-pitched whine. The females usually mate only
once but produce eggs at intervals throughout their life. In order to be able to do so, most
female mosquitoes require a blood-meal.

Eggs

Depending on the species, a female mosquito lays about 30 to 300 eggs at a time. The female
Culex mosquito lays nearly 200-400 eggs in a cluster in standing water of polluted ponds,

268 Oasis School Science - 9 BIOLOGY

ditches, marshes, etc. By her hind legs, she arranges the eggs. The eggs are white, cigar-shaped
and narrow, which are cemented together to form a small floating raft. An Anopheles lays
about 40-100 eggs in fresh water at a time. The eggs are boat-shaped having lateral air floats
and laid singly.

Larvae

On favourable condition, the eggs hatch within two to three days, and a small transparent
larva, measuring about 1 mm emerges out of an egg. Once hatched, the larvae do not grow
continuously but in four different stages (instars). The first instar measures about 1.5 mm in
length and the fourth about 8-10 mm. The aquatic larva of mosquito is popularly called the
wriggler as it swims actively in water with wriggling movements. The body of a larva can be
divided into three distinct parts, viz. head, thorax and abdomen.

The large head bears a pair of compound eyes, a pair of two jointed antennae and the chewing
type of mouth parts. The larvae are voracious feeders which feed on bacteria, yeast and small
aquatic organisms.

Adult Culex

Imago Eggs
emerging out of
puparium

Larva

Pupa

Fig. 16.29 Life cycle of Culex mosquito

The thorax is slightly broader than head, unsegmented and limbless. It contains three pairs of
lateral tufts of hairs.
The abdomen is nine-segmented and each segment bears lateral tufts of bristles. The dorsal
surface of 8th segment bears respiratory siphon and the 9th segment bears four tracheal gills.

When at rest, the larva of Culex hangs with its head downwards at an angle in water with
the tip of respiratory siphon projecting above the surface of the water. Similarly, the larva of
Anopheles remains parallel to the water surface. At the last moult, larva changes into a pupa.

BIOLOGY Oasis School Science - 9 269

compound eyes two spiracles 9th abdominal segment
tracheal gills
antenna
feeding brushes

head Larva vinral brush
thorax

respiratory trumpets

air float cephalothorax
antenna

compound eye

9th abdominal
segment

Eggs Pupa

racheal gifts
or paddles

Adult

Fig. 16.30 Life cycle of Anopheles

Pupae

On favourable condition, the larva changes into a comma-shaped pupa within a week. It is
commonly known as tumbler. Unlike most insect pupae, it is quite active. The pupa has an
unsegmented cephalothorax and nine-segmented abdomen. The ninth abdominal segment
bears a pair of large swimming paddles. The pupa clings to the surface film with its head
upwards. It respires through respiratory trumpets, located dorsally on thorax.

The pupa does not feed as there is no mouth and anus, but active changes of metamorphosis
are going on internally. Certain phagocytotic cells cause the histolysis of the larval organs and
at the same time certain cells carry out histogenesis by producing the organs of adult. This
stage lasts for 2-7 days depending on the environment.

Imago

After completing the metamorphosis, the pupa is transformed into a perfect adult mosquito
called imago. The imago emerges out by rupturing puparium which contains well-developed
wings and after a few moments flies away.

The complete life cycle, from egg to adult, takes from ten to several days depending on the
environment. The females live for one month or more and males live for about a week.

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Comparative study of life histories of Culex and Anopheles

S.N. Culex S.N. Anopheles

1. Eggs are laid vertically on the surface 1. Eggs are laid horizontally and singly on

of water in clusters forming rafts. the surface of water.

2. Eggs are cigar-shaped without lat- 2. Eggs are boat-shaped each with lateral air

eral air floats. floats.

3. Usually 200-400 eggs are laid in 3. Usually 40-100 eggs are laid in fresh and

dirty water near human habitation. clean water.

4. The larva of Culex is a bottom 4. The larva of Anopheles is a surface feeder.
feeder.

5. The larva has longer respiratory 5. The larva has shorter respiratory siphon.
siphon.

6. During the intake of air, the head of 6. During the intake of air, the head of larva

larva hangs downwards at an angle lies horizontally, parallel with the surface

with the surface of water. of water.

7. The pupa of Culex is colourles. 7. The pupa of Anopheles is green.

8. Respiratory trumpets of pupa are 8. Respiratory trumpets of pupa are shorter.
longer.

9. The body of adult Culex is well 9. The body of adult Anopheles is slender

built with stouter legs. with delicate legs.

10. At rest, the body of adult Culex lies 10. Adult Anopheles at rest, the body is in-

parallel to the surface. clined at an angle of 45° to the surface.

11. Adult Culex has wings of uniform 11. It has spotted wings and cannot fly for

colour and can fly for long. long.

12. Maxillary palpi are shorter than 12. Maxillary palpi are equal in length with

proboscis in female, but longer and the proboscis in both male and female.

pointed in male.

13. Female Culex transmits filarial 13. Female Anopheles transmits malarial

parasite. parasite.

16.17 Diseases Transmitted by Mosquitoes

S.N. Mosquitoes Diseases

1. Anopheles Malaria, lymphatic filariasis

2. Culex Lymphatic filariasis, Japanese encephalitis,
meningitis, etc.

3. Aedes Yellow fever, dengue, lymphatic filariasis

4. Mansonia Lymphatic filariasis

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16.18 Malaria

Malaria is a disease caused by Plasmodium (a protozoan parasite). This disease is widespread
in the tropics, sub-tropics and also in certain areas of temperate zones.

A healthy person acquires infection when a female Anopheles mosquito, containing infective
stages (sporozoites) of the parasite in its salivary glands, bites him/her for sucking blood.

At the onset of malaria fever, the patient suffers from shaking chills and sweating. As the chills
subside, the body temperature rises as high as 1060F. As the temperature lowers down, the
patient sweats profusely and finally becomes comfortable until the next attack, which takes
place at regular intervals of 48 hours.

In Nepal, the prevention and control of malaria is taken as a national problem and the anti-
malarial department of the government deals with it. Certain anti-malarial drugs, such as
Quinine, Paludrine and Daraprim are effective in keeping malaria away.

16.19 Mosquito Control

In order to prevent and control malaria and other diseases transmitted by mosquitoes, the
following methods for the destruction of mosquitoes must be adopted:

1. Destruction of adult mosquitoes

Adult mosquitoes can be most effectively combated in dwellings. Following methods
can be adopted to kill adult mosquitoes:

a. Direct killing by hands: The mosquitoes that approach or bite may be killed
directly by hands.

b. Fumigation: Mosquitoes can be killed or driven out of the house by fumigation.
Sulphur, pyrethrum, tar, camphor, etc. are burnt to produce poisonous fumes to
repel or kill mosquitoes.

c. Spraying: Mosquitoes can be killed inside house by spraying DDT, flit, pyrethrum,
etc. or by using mosquito bombs.

2. Elimination of mosquito breeding sites

The mosquito larvae and pupae develop in water. Therefore, elimination of breeding
sites is of primary importance. Stagnant water and swampy areas should be drained out.
If possible, the breeding grounds may be filled up with soil, sand or stones. The domestic
species of mosquitoes can largely be controlled by eliminating vessels that hold water
like buckets, tin-cans, old tyres, barrels, etc. The bushes and shrubs should be cleared off.
Open drains should be covered or made underground.

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3. Destruction of larvae and pupae of mosquitoes

It is easier and more convenient to kill aquatic larvae and pupae than winged adult of
mosquitoes. Wherever it is not possible to fill up or drain out swamps, lakes or ponds,
the larvae and pupae may be killed by covering or spraying the surface of water with
petroleum, paraffin oil, crude oil, kerosene, etc. Those substances produce a thin film of
oil on the surface so that the larvae and pupae die due to lack of breathing or suffocation.
The oil also enters the spiracles, blocks the tracheae, and poisons the body. Similarly,
chemical larvicides like DDT, BHC, dusts containing Paris green can be sprayed in larger
aquatic bodies to destroy mosquito larvae and pupae.

4. Biological control

Biological control is the best way of controlling mosquitoes. Larvicidal fishes like
sticklebacks, minnows (Gambusia), trout (Tilapia), Argentine pearlfish, carp, etc. should
be introduced in the ornamental fountains, ponds, lakes, ditches, canals, etc. Aquatic
nymphs and adult insects (like dragon flies) which are natural enemies of mosquitoes
should be introduced in the breeding sites to control the breeding of mosquitoes.

16.20 Prevention Against Mosquito Bites

i. Houses in the mosquito-affected areas should be made mosquito-proof by
screening doors, windows, ventilators, etc.

ii. While sleeping, mosquito nets should be used to keep away the mosquitoes.
iii. The exposed parts of the body can be protected by the application of repellants like

anti-mosquito creams, mustard oil, coconut oil, etc. or by using veils, boots, gloves, etc.

iv. We can also prevent mosquito bites by building houses on high grounds.

Activity 6
• Visit a nearby pond in the rainy season. Observe various stages of life cycle of the

mosquito. Study their structure by using a hand lens and draw a well labelled figure
of each of the stages.

BIOLOGY Oasis School Science - 9 273

SUMMARY

• Classification is the process of grouping the living organisms into various
groups and sub-groups on the basis of similarities and differences.

• Taxonomy or Systematic Biology is the branch of biological science which deals
with the identification, nomenclature and classification of living organisms.

• Binomial system of nomenclature is the scientific way of assigning two names
(i.e. first generic name and second specific name) to an organism.

• The great Swedish biologist Carolus Linnaeus (1707-1778 AD) is considered
as the father of taxonomy because he introduced the Binomial System of
Nomenclature in 1758 AD and a system of classification.

• A species is the group of closely related organisms having almost all similar
characters which can interbreed freely and produce fertile offspring.

• A genus is the group of closely related species.

• Algae are the most primitive autotrophic plants whose body cannot be divided
into roots, stem and leaves.

• Bryophytes are multicellular green plants having thalloid body with rhizoids or
the body with rhizoids, stem (seta) and leaves.

• Pteridophytes are the most developed non-flowering plants having feather-
shaped leaves. The plant body contains rhizoids (roots), stem, leaves and
vascular system.

• Gymnosperms are cone bearing plants having naked seeds.
• Angiosperms are well developed flowering plants having fruits and seeds.
• Monocots are flowering plants having only one cotyledon in their seeds.

• Dicots are flowering plants having two cotyledons in their seeds.

• Kingdom Protista includes unicellular, microscopic animals that live in water.
They are found in fresh water as well as marine water.

• Phylum Porifera includes the primitive multicellular invertebrates having
numerous pores in their bodies. They are commonly known as sponges.

• Phylum Coelenterata includes aquatic invertebrates having hollow body
cavity called coelenteron. For example, hydra, jellyfish, etc.

• Phylum Platyhelminthes includes invertebrate animals having dorsoventrally
flattened body. The animals belonging to this phylum are commonly known
as flatworms.

• Phylum Nemathelminthes includes unsegmented invertebrate animals
having a round body. For example, roundworm, hookworm, etc.

• Phylum Annelida includes invertebrate animals having numerous segmented
rings in their bodies. For example, leech, earthworm, etc.

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• Phylum Arthropoda includes invertebrate animals having jointed
appendages (legs and antennae). The members of this phylum are commonly
known as arthropods.

• Phylum Mollusca includes unsegmented invertebrates having soft body
which is often covered by one or two hard shells.

• Phylum Echinodermata includes exclusively marine invertebrates having
spiny skin.

• Chordates are advanced animals having notochord.

• Notochord is a flexible rod-like structure running along the dorsal surface of
chordata embryos ventral to the nerve cord. In vertebrates, the notochord is
replaced by vertebral column.

• Vertebrates are the most developed animals having vertebral column.

• The animals that lay eggs are called oviparous animals and the animals that
directly give birth to their young ones are called viviparous animals.

• The animals whose body temperature changes according to the temperature
of their surroundings are called cold-blooded or poikilothermic animals.

• The animals whose body temperature remains constant and does not vary
according to the temperature of their surroundings are called warm-blooded
or homoiothermic animals.

• Mosquitoes are two-winged flying insects that suck blood from humans and
other animals.

• Mosquitoes are carriers of a number of diseases like malaria, filariasis,
encephalitis, meningitis, yellow fever, etc., mostly in the tropics, causing
illness and death on a large scale.

• Mosquitoes are found in damp and marshy places in tropical and
sub-tropical countries.

• Both male and female mosquitoes feed on nectar and juices of plants. However,
female mosquito sucks vertebrate's blood especially for laying eggs.

• The body of mosquito is slender, which can be divided into head, thorax and
abdomen.

• The life cycle of mosquito shows complete metamorphosis. Egg, larva, pupa
and adult are the four stages of life cycle of mosquito.

• Eggs, larvae and pupae of mosquitoes are found in water whereas adults are
found in air.

• Female Anopheles mosquito transmits malaria from sick person to a healthy
person.

• The causative agent of malaria is Plasmodium (a protozoan parasite). It is
found in blood of infected person.

• Mosquitoes can be controlled by various methods. Among them, biological
method is the best way of controlling mosquitoes.

BIOLOGY Oasis School Science - 9 275

Exercise

Group-A
1. What is classification? Why are living beings classified?
2. What is binomial system of nomenclature?
3. Write down the scientific name of the following living beings.
i) Human being ii) Mustard plant iii) Rose iv) Frog
4. What do you mean by genus and species? Write.
5. Write any two characteristics of the living beings belonging to Kingdom Monera with

any two examples.
6. Write any two characteristics of the plants belonging to division algae with any four

examples.
7. Write any two characteristics of the organisms kept in Kingdom Protistia.
8. What types of plants are kept in the sub-division pteriodophyta? Write with examples.
9. What are autotrophic and heterotrophic plants?
10. Where are the following plants found? Write.
i) Spirogyra ii) Mushroom iii) Yeast iv) Liverwort v) Fern vi) Chlamydomonas
11. What do you mean by sporophyte and gametophyte?
13. What are rhizoids? Write down their function.
14. Write down the salient features of the plants belonging to division Gymnosperms with

any two examples.
15. What types of plants are kept in the division Angiosperms?
16. Mention any two characteristics of monocots and give any two examples of dicots.
17. Name the division of the plants having following features with one example of each.
i) Having cones instead of flowers
ii) Flowering, having primary roots and secondary roots
iii) Having naked seeds and needle-shaped leaves
iv) Having fibrous roots, flowering plants
v) Flowering plants, leaves having reticulate venation
vi) Having two cotyledons in a seed, with broad leaves
18. Which type of animals are called invertebrates? Give any two examples.
19. Which type of animals are kept in Kingdom Protista?
20. Which type of animals are kept in metazoa? Write any two examples.
21. Write any three characteristics of the animals belonging to phylum coenlenterata with

any two examples.

276 Oasis School Science - 9 BIOLOGY

22. Write any two functions of tentacles found in hydra.

23. What type of animals are called unisexual?

24. What type of animals are called hermaphrodite animals?

25. Name the locomotary organs of the following animals.

– Amoeba – Starfish

– Slug – Butterfly

– Cockroach – Hydra

– Leech – Paramecium

26. Write any two salient features of the animals belonging to phylum platyhelminthes.

27. Write down the characteristics of the animals belonging to phylum Annelida of the
Animal Kingdom.

28. Write any two characteristics of the animals belonging to phylum echinodermata with
any two examples.

29. Name any two animals that breathe through gills.

30. Name any two plants having rhizoids.

31. Name any two animals having mouth but no anus.

32. Name any three animals which move through tentacles.

33. Write down the characteristics of the animals belonging to the phylum Chordata with
any two examples.

34. Write any two salient features of the animals belonging to class Pisces with any three
examples.

35. Write down the characteristics of the animals belonging to class Aves with any two any
two examples.

36. What types of animals are called mammals? Write any two characteristics of these
animals.

37. Name the phylum and class of the animals having given features. Also, give an example
of each.

i) Breathe through gills, having scales
ii) Having external ears, give birth directly to young ones
iii) Having webbed feet, live on both land and in water
iv) Fly in air, lay eggs
v) Aerial, having mammary glands

vi) Having fins, cold-blooded

38. Classify mosquito and write down the habitat of mosquito.

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39. How many stages does mosquito complete its life cycle? Name them.
40. Name the stages in the life cycle of mosquito which are found in water.
41. What is the difference between the food of male and that of female mosquito?
42. Eggs of which mosquito are shown in the given figures:

i) ii)

43. What type of climate is suitable for mosquitoes? Write.
44. Which mosquito transmits malaria? Write.
45. Name the parasite that causes malaria.
46. Write down the major symptoms of malaria.
47. What is the function of siphon in the body of mosquito larva?
48. Which parasite causes filariasis?
49. Name the type of mosquito larva shown in the given figure? Name a disease transmitted

by the adult of this larva.

50. Differentiate between larva of Culex and that of Anopheles on the basis of feeding habit.
51. In how many days the life cycle of a mosquito completes normally?
52. How many days are required to develop a larva from an egg of mosquito on favourable

condition?
53. How many times does a mosquito larva change its skin?

Group-B
1. Why is Carolus Linnaeus called father of taxonomy?
2. Why are living beings classified? Give any two reasons.
3. Differentiate between geneus and species.
4. Write any two differences between cryptogams and phanerogams.
5. Volvox is called algae and mushroom is called fungus, why?
6. Write any two differences between thallophyta and pteridoplyta.
7. Why is fern called a pteridophyte? Give any two reasons.
8. Differentiate between gymnosperms and angiosperms.

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9. Maize is called a monocot and pea is called a dicot, why?

10. Differentiate between tapeworm and hookworm.

11. Write any two differences between starfish and fish.

12. Frog is called amphibian and snake is called reptile, why?

13. Differentiate between sea horse and horse.

14. Write any two differences between bat and bird.

15. Female mosquito is considered more harmful than male mosquito. Give reason.

16. Write any two differences between eggs of Culex and eggs of Anopheles.

17. Larvae of mosquito die when oil is sprayed on the surface of water containing mosquito
larvae, why?

18. Differentiate between larva of Culex and that of Anopheles mosquito.

19. We can control malaria by controlling mosquito. Give reason.

20. Differentiate between adult Culex and adult Anopheles mosquito.

Group-C

1. Write down the characteristics of the living beings belonging to kingdom Monera with
any two examples.

2. Write down the characteristics of the plants belonging to division bryophyta and write
any two examples.

3. Write down the salient features of the plants belonging to division Gymnosperms with
any two examples.

4. Name the phylum of the given animals. Also write a characteristic of each.

i) ii) iii)

5. What is the advantage of classification of living beings? Mention any three points.

6. How many times does a mosquito larva change its skin? How can you differentiate
between pupa of Culex and pupa of Anopheles mosquito on the basis of resting habit on
the surface of water?

7. How can we control mosquitoes biologically? What is the function of syphon in the body
of a mosquito larva?

9. How can we control mosquitoes by filling puddles? Explain.

10. Write any three methods to control mosquito larvae and pupae.

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Group-D

1. Classify the organisms shown in the figure and write any two characteristics of each.

i) ii)

2. Write any two differences between fish and frog on the basis of habitat and structure of
heart. Name the phylum of the animals having following features.
i) Having segmented body, hermaphrodite
ii) Moves with the help of tentacles, found in marine water
iii) Having sucker, flat and segmented body
iv) Soft body with a hard cover, having tentacles

3. What types of animals are called mammals? Write down three characteristics of these
animals.

4. Name the class of the animals having given features. Also, give an example of each.
i) Breathe through gills, having scales
ii) Having external ears, give birth directly to young ones
iii) Having webbed feet, live on both land and in water
iv) Fly in air, lay eggs

5. Draw a neat and labelled diagram showing the life cycle of an Anopheles mosquito.
6. Draw a neat diagram showing larva of each Culex mosquito.
7. Write a short note on mosquito control.

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UNIT 17 Estimated teaching periods

Theory 5

Practical 1

ADAPTATION Flying peacock
OF ORGANISMS

Objectives

After completing the study 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 oranisms (viruses, bacteria, fungi and protozoa)

and list human diseases caused by them.

17.1 Introduction

All living organisms have to be well-fitted to their environment for their existence. Any
characteristic that is advantageous to a particular organism which makes it better suited
to its environment is called adaptational characteristic. Adaptation can be defined as the
characteristics, i.e. structural and functional features of living organisms, which develop
over a period of time and enable them to survive and reproduce within their habitat. The
ability of adjustment of living organisms in their environment is called adaptation. In order
to live successfully in their habitat, living organisms have special characteristics which are called
adaptational characteristics, e.g. wings and feathers of birds, fins of fish, thorns of cactus, horns
of animals, etc. Living organisms change their body structure accordingly to exist in a particular
environment. Because of adaptation, organisms obtain food, shelter and protection in their habitat.

Adaptation includes structural, functional and behavioural modifications which make an
organism better fitted to survive, flourish and reproduce more successfully in a habitat.
Organisms that fail to adjust themselves to their surroundings are liable to disappear.

Living organisms live in diverse habitats, viz. aquatic habitat, terrestrial habitat and aerial habitat.
The organisms found in various habitats experience a variety of physical and climatic factors.

17.2 Adaptation in Plants

On the basis of quantity of water available in the habitat, plants can be grouped into three
types, viz. hydrophytes, mesophytes and xerophytes. Hydrophytes are the plants which grow
where water is available in abundance like pond, river, etc. Those plants which encounter
difficulty in acquiring water are called xerophytes. Mesophytes are the plants which require
moderate amount of water.

adaptation /ædæpˈteɪʃn/ - the process of changing sth to suit a new situation or a new environment

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17.3 Classification of Hydrophytes

Hydrophytes are the plants which live in water or aquatic habitat. They are mainly of following types:

a. Free floating: Some hydrophytes like Water hyacinth, Jussiaea, Pistia, Lemna, Wolffia,
etc. float freely on the water surface. They remain in contact with air and water but
not soil.

Water hyacinth Pistia Lemna Jussiaea Wolffia

Fig. 17.1 Free floating hydrophytes

b. Submerged floating: Some hydrophytes like Utricularia, Ceratophyllum, etc. remain in

contact only with water and are not rooted in the soil. Their stems are long and leaves are
small.

Ceratophyllum Utricularia

Fig. 17.2 Submerged floating hydrophytes

c. Rooted submerged: Some hydrophytes like Hydrilla, Vallisneria, Chara, etc. remain
completely submerged in water and rooted in soil. In Vallisneria, the stem is tuberous
with long, narrow and ribbon shaped leaves whereas in Hydrilla and Chara, the stem is
long with small leaves on nodes.

Hydrilla Vallisneria Chara
Fig. 17.3 Rooted submerged hydrophytes

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d. Rooted with freely floating leaves: In some hydrophytes like Nelumbo (Lotus), water
lily, Marsilea, Nymphaea, etc., the roots are fixed in the soil. They contain leaves with long
petioles which help them to float on the surface of water.

Waterlily Marselia Lotus

Fig. 17.4 Rooted hydrophytes with freely floating leaves

e. Rooted and emergent: In some hydrophytes that grow in shallow water like Ranunculus,
Sagittaria, Typha, etc., shoots are completely or partially exposed to air. Their root system
is fixed in the soil and remains under water.

Sagittaria Ranunculus Typha

Fig. 17.5 Rooted and emergent hydrophytes

17.4 Adaptational Characteristics of Hydrophytes

The plants that grow in water are called hydrophytes. Examples: Lotus, Lily, Hydrilla, etc.
Hydrophytes are adapted to stay and grow in water. They have adaptation for buoyancy in
water, against decaying and breaking. The different adaptational characteristics of hydrophytes
are mentioned below:

i. Due to the availability of plenty of water, hydrophytes have less developed and weak
root system.

ii. Roots are either absent, devoid of root caps or root hairs.

iii. The stem of freely floating hydrophytes like Lemna is reduced whereas in submerged
hydrophytes, the stem is flexible and spongy with a number of air spaces. The stems of
lotus and water lily contain large tunnels and holes for air that helps the rhizome to float.

iv. The leaves of submerged plants are thin, long, linear or ribbon-shaped (e.g. Hydrilla,
Vallisneria, Utricularia, etc.) or highly dissected ( e.g. Ceratophyllum, Ranunculus, etc.).
Floating leaves of water lily, lotus, etc. are large, flat, circular discs that stay afloat on
water surface. Their petioles are long, flexible and covered with mucilage. They also
contain air chambers.

buoyancy /ˈbɔɪənsi/ - able to float

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v. Most of the hydrophytes are covered with waxy substance which prevents them from

decaying in water. Reasonable fact-1

vi. Most of the hydrophytes have weak and The stem of aquatic plants is covered with waxy
flexible stem which helps them to bend substance, why?
easily without breakage.

vii. All hydrophytes contain a special tissue The stem of aquatic plants is covered
called aerenchyma which provides with waxy substance to prevent the stem
flexibility and buoyancy. from decaying due to exposure of water
for a long period of time.
viii. Mechanical tissues and water conducting

tissues are poorly developed. However,

phloem or food conducting tissues are well developed.

17.5 Mesophytes and their Adaptational Characteristics

The plants that grow in mesic habitat are called mesophytes. For example, mango, rose, crops,
sunflower, fruits, vegetables, etc. Mesic habitat is a terrestrial habitat where water is neither
in excess nor deficient such as cultivated land. Such habitat is suitable for growth of plants in
irrigated crop fields and tropical forests. The major adaptational characteristics of mesophytes
are given below:

Fig. 17.6 Climber of pumpkin

i. Mesophytes have well developed root system with root hairs.
ii. The stems are solid and freely branched.
iii. The leaves are generally large, broad, thin and variously shaped with numerous stomata.
iv. Mechanical tissues and conducting tissues are well developed.

v. Climber plants like pumpkin, cucumber, etc. contain hooks, tendrils, aerial roots, etc. for support.

17.6 Xerophytes and their Adaptational Characteristics

Xerophytes are the terrestrial plants that face scarcity of water and high temperature. The plants
that grow on desert or dry habitat are called xerophytes. Cactus, Aloe, Calotropis, Acacia,
Zizyphus, etc. are some examples of xerophytes. These plants show various adaptations to
conserve water and also to absorb maximum amount of water available in the soil. The major
adaptational characteristics of xerophytic plants are mentioned below:

tendril /ˈtendrəl/ - a thin curling stem that grows from a climbing plant

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Cactus Opuntia Aloe Zizyphus

Fig. 17.7 Some xerophytes

i. Xerophytic plants have well developed and extensive root system, which grows in search
of water.

ii. Desert plants that face prolonged phases of water scarcity and hot temperature contain
succulent organs (roots, stem and leaves). These organs serve as water storage organs.
They accumulate large amount of water during brief spell of rains. Such water-storing
spongy tissues may occur either in roots (e.g. Asparagus) or leaves (e.g. Aloe, Begonia,
Bryophyllum, etc.) or stem (e.g. Opuntia and other Cacti).

iii. In cactus, leaves are reduced to spines or scales. This helps in preventing loss of water.
The stem of cactus is fleshy and green which remains covered with spines.

iv. In xerophytic plants, stomata open only during night and remain closed during the day
to prevent the loss of water by reducing the rate of transpiration. The stomata are less in
number and are of sunken type.

v. Leaves of xerophytic plants are generally shiny and glazed to reflect light and heat.

vi The stem of xerophytic plants is spongy having water storage tissues which help to store water.

17.7 Adaptation in Animals

Like plants, animals also possess various structural and functional features which increase the
chances of their survival and help them fit in their habitats. Adaptations in animals are mainly
of following types:

a. Aquatic adaptations b. Terrestrial adaptations
c. Xeric adaptations d. Arboreal adaptations e. Aerial adaptations

a. Aquatic adaptation

Theanimalsthatliveinwaterarecalledaquatic

animals. Examples: fish, whale, dolphin, Reasonable fact-2
shark, octopus, etc. A large number of animals
live in water. They include both fresh water The body of fish is covered with smooth and
and marine water forms. Aquatic animals waterproof scales. Give reason.

mainly show adaptations for buoyancy The body of fish is covered with smooth

in water and against decaying. The major and waterproof scales to reduce water
adaptational characteristics of aquatic animals resistance while swimming in water.
are given below:

i. Body of most aquatic animals (e.g. fish) is streamlined, i.e. compressed laterally to
succulent /ˈʃʌkjʊlənt/ - having leaves and stems that are thick and contain a lot of water

BIOLOGY Oasis School Science - 9 285

reduce friction. Such body shape allows swift passage in water while swimming.

ii. Body remains covered with waterproof scales and mucus coat. Some animals
contain special coverings like shell, cuticle, waxy coating, etc. to protect the body
against decaying.

iii. Locomotion takes place with the help of fins in fishes, by webbed-feet in frog
and duck, and by flippers in whale. The tail fin acts as radar and helps to change
direction while swimming.

Fish Whale Duck Frog

Fig. 17.8 Swimming in water

iv. Breathing takes place with the help of gills. They are adapted to absorb dissolved
oxygen in water.

v. Air bladder or swim bladder is present in some fishes. It is filled with air and
maintains buoyancy.

b. Terrestrial adaptations

The animals that live on land are called terrestrial animals. They differ in habit and way
of living. They may be walkers, runners, climbers, burrowers, diggers, fliers, etc. Their
body structure is modified according to their nature and habitat. The major adaptational
characteristics of terrestrial animals are given below:

i. Terrestrial animals have different types of limbs and claws adapted for walking,
running, climbing, burrowing, etc. Pentadactyl animals (animals having five
digits) use their claws for walking and running. Limbs are long and strong in fast
running animals like horse, leopard, etc. In some animals like bear, baboon, the
entire palm or sole rests on the ground. Wrist and ankles are not raised from the
ground. The bones of wrist, palm, ankle and sole are raised from the ground in
cats, dogs, birds, etc. Some animals like donkey, horse, cow, sheep, rhinoceros,
buffalo, etc. walk and run on tips of digits covered with hoof (i.e. modified nail).
Some animals like cow, buffalo, sheep, etc. have bilobed hoof whereas horses, ass,
zebra, etc. have non-lobed hoof.

adhesive /ədˈhiːsɪv/ - a substance that makes things to stick together

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Rhinoceros Horse Waterbuffalo Monkey Zebra

Fig. 17.9 Some terrestrial animals

ii. Some animals like monkeys, baboon, etc. have climbing capacity. They climb on trees,
walls or cliffs for food, shelter and protection. They have modified bipedal limbs to hold
the branches of trees.

Fig. 17.10(a) House wall-lizard Fig. 17.10(b) Adhesive pads of house wall lizard

iii. Some animals like lizards contain adhesive pads on their digits which help them
to crawl on wall easily.

iv. Body muscles are well developed for walking and swift running in tiger, lion,
leopard, human, etc. and adapted for crawling in snakes, lizards, etc.

Lion Leopard Tiger

Fig. 17.11

v. In burrowing animals like mole, shrew, spiny anteater, the head is modified for burrowing
and digging. Their head and snout are tapering.

c. Xeric adaptations

The animals that live in desert or dry habitat are called desert animals. These animals
are adapted to withstand severe heat and water scarcity. The major adaptational
characteristics of desert animals are given below:
i. Desert animals adapt their bodies to prevent loss of water by perspiration. Animals
like snake, scorpion, spiders, etc. contain poison gland for protection.

arboreal /ɑːˈbɜːrɪəl - living in trees, relating to trees

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ii. The desert snakes, rats, etc. make deep burrows and remain inside them during
day time when the desert is hot and dry. These animals come out of hole during
night and become active.

iii. Camel is a very good example of a desert Hump
animal. It has a hump on its back to store
food in the form of fat. It uses the entire
food store while walking on hot sand. Its
large fleshy soles help it to walk on the hot
and slippery sand. Camel excretes only dry
faecal matter, highly concentrated urine
and perspires very little to conserve water.

Camel has long eyelashes and muscular nostrils Fig. 17. 12 Camel
adapted for protection from wind blown sand.
The body contains thick skin and water storage tissues.

d. Arboreal adaptations
Some land animals like flying lizards, tree frogs, monkeys, apes, etc. come to trees for

safety and shelter. Such animals are called arboreal animals. Their body is modified
according to their behaviour and habitat. They have patagium-like organs adapted for
gliding flight.

Flying squirrel Flying frog Spider monkey

Fig. 17.13 Some arboreal animals

e. Aerial adaptations

The animals that fly in air are called aerial animals. Different kinds of birds and bats are
well adapted for aerial mode of life. Aerial adaptation is also called volant adaptation.
The major adaptational characters of aerial animals are given below:

i. The body of birds is streamlined or boat shaped which offers least resistance to the
air during flight.

ii. Fore limbs are modified into wings for flight and hind limbs are shifted forward to
balance the body weight.

iii. Flight muscles or breast muscles are very strong to provide extra strength during
the flight.

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Beak

Feathers
Tail Wing

Claw

Fig. 17.14 Pigeon

iv. They have light-weight skeleton and toothless beak to reduce the body weight.
Bones also contain many air cavities.

v. The entire body of birds is invested with a close covering of feathers which are
light, elastic and waterproof.

vi. Forceps like beak is present for picking up foods and objects. Birds of prey like
hawk, vulture, owl, etc. have a sharp and curved bill for tearing meat. Duck has a
long and spoon-shaped flat beak that strains small plants and animals from water.
Woodpecker has a long and chisel-like bill adapted for boring into wood and to eat
insects. Crow has a multipurpose beak that helps to eat fruits, seeds, insects, etc.
Kingfisher has spear-like beak adapted for fishing.

Sparrow Crow Parrot Woodpecker

Eagle Owl Kingfisher Hummingbird

Fig. 17.15 Modification of beaks in various birds on the basis of adaptation

vii. Different types of birds have different types of feet according to their habit. They
are adapted for grasping, scratching, swimming, perching, running, climbing, etc.
Ducks and other swimming birds have paddle-like webbed feet. Vulture and other
birds of prey have large and curved claws adapted to grasp their prey. Pheasants

perc h /pɜ ːtʃ/ - to land and stay on a branch

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and other birds have nail-like toes adapted for scratching soil for food. Many fast run-
ning birds have feet with three toes for swift running. Woodpeckers have well devel-
oped hind toes adapted for climbing trees without falling backwards. Saras has long
hind limbs adapted for searching insects in crop fields.

Coot Mallard Hawk Woodpecker Grouse

Ostrich Parrot Jacana Crow

Fig. 17.16 Modification of claws and feet in various birds on the basis of adaptation

Activity 1

• Visit a nearby pond and collect some aquatic plants and animals. Observe their
adaptational characters and prepare a short report.

• Observe the adaptational characteristics of some animals in your locality. Draw a
conclusion from your observation.

17.8 Bacteria Fig. 18.17 Bacterium

Bacteria (singular-bacterium) are the smallest and most
widespread single-celled plant organisms. They were discovered
by Anton Van Leeuwenhoek in 1676 AD and the term bacteria
was coined by CG Ehrenberg in 1828 AD. Bacteria are the
simplest, most primitive and unicellular organisms. They are
found everywhere in air, water, soil, food, inside the bodies of
living beings, etc. Most bacteria are saprophytes but some are
autotrophs.

Characteristics of bacteria

1. They have prokaryotic cell.
2. They lack well developed nucleus and many cell organelles.
3. They have a cell wall.
4. They may live alone or in colonies.
5. They reproduce asexually by fission.
6. Most bacteria are immotile but some bacteria like bacilli and spirilla can move.
7. They show autotrophic as well as heterotrophic nutrition.

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8. Their size ranges between 0.5 to 5 micrometres.

9. Some bacteria can survive in ice and some in boiling water.

Types of bacteria

On the basis of shape, there are four types of bacteria.
i. Coccus or Spherical bacteria
ii. Bacillus or Rod-shaped bacteria
iii. Spirillum or Spiral bacteria

iv. Vibrio or Comma-shaped bacteria

i. Coccus or Spherical bacteria
Coccus (plural-cocci) or spherical-shaped bacteria are found in clusters like a bunch of

grapes or they may join end to end to from a long chain and some are found in pairs.
Examples: Staphylococci, Diplococci, Streptococci, etc.

Cocci bacteria Bacilli bacteria Spirillum Vibrio cholera

Fig. 17.18

ii. Bacillus or Rod-shaped bacteria
Bacillus (plural-bacilli) or rod-shaped bacteria may be present as single rod or in chains.

Examples: Escherichia coli, Bacillus anthracis, etc.

iii. Spirillum or Spiral-shaped bacteria

Sprillum (plural-spirilla) or spiral bacteria may have one or more flagella at the ends of
their bodies. Examples: Leptospira, Spirillum, etc.

iv. Vibrio or Comma-shaped bacteria

These bacteria are comma-shaped. In some bacteria, the body is curved and has only one

flagellum. Example : Vibrio cholera. DNA 2µm (microns)
Cytoplasm
Structure of bacteria Cell membrane

The structure of bacteria is very simple. It contains the Flagella
protoplast, i.e. living substance surrounded by a non-
living cell wall and a thin membrane called plasma
membrane.

The cell of bacteria does not contain membrane bound
cell organelles like mitochondria and chloroplasts.

Fig . 17.19 Structure of Escherichia coli bacterium

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There is a single molecule of DNA attatched to the cell membrane. Golgi complex and
plastids are also absent but ribosomes are present. Some bacteria contain flagella.

Economic importance of bacteria

Bacteria have both useful as well as harmful effects.

a. Useful effects of bacteria
1. Some bacteria like Rhizobium, Nitrobacter, Nitrosomonas, etc. regulate nitrogen cycle
and help to increase the fertility of soil.

2. Most bacteria act on dead bodies and decompose them which helps to recycle
materials in the environment.

3. In industries, bacteria are used in curding of milk, tanning of leather, production of
vinegar, cheese making, and processing of coffee, tobacco, etc.

4. Many bacteria are used for making medicines like antibiotics.

5. Many bacteria live in our intestine and help in digestion of cellulose.

b. Harmful effects of bacteria
1. Bacteria cause many harmful diseases in plants, animals and human beings. They
cause diseases in potato, maize, paddy, etc. and damage them. In humans, bacteria
cause diseases like typhoid, tuberculosis, leprosy, cholera, tetanus, pneumonia,
dysentery, etc.

2. They spoil milk, meat, vegetables and other food items.

3. Some bacteria cause food poisoning by releasing toxins into spoiled food.

4. Some bacteria like Pseudomonas, Micrococcus, etc. reduce the fertility of soil.

Control Measures of Bacterial Diseases

Bacterial diseases in plants and animals can be controlled by following methods.
1. Avoiding the seeds infected with bacteria
2. Using antibiotics in case of bacterial infection
3. Using antibacterial medicines to control infections
4. Isolating the organisms suffering from bacterial diseases

17.9 Fungi

Fungi are non-green thallophytes without chlorophyll. They are distributed throughout the
world. They grow in dark and moist places on the surface of dead and decaying organic
matter. Mushroom, yeast and moulds (Mucor, Rhizopus, etc.) are some examples of fungi.
Moulds can be observed as they grow on food, bread, leather, fruits, barks of trees, etc.

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