Introduction
Classification means sorting out things into groups on the basis of similarities and differences among them. Figure shows three groups of objects. In each group, things are put together on the basis of some similarities among them. For example, all the things of group
(a) are made of metals. The things of group
(b) are books and those of group
(c) are fruits.
In this unit, we will study different groups of living things aand compare their characteristics.
Classification of Living Things
There are millions of living organisms in our world. Scientists have grouped them on the basis of similarities in their characteristics. Grouping of living organisms on the basis of similarities and differences in their characteristics is called classification of living things.
Classification of living things is essential for making their study easier. During classification, scientists examine the characteristics of an unfamiliar organism and find its proper group. They also suggest name for the organism for its identification.
You Need To Know
The bodies of all the living things are made up of very small units called cells.
The organisms whose bodies consist of single cell are called unicellular organisms.
The organisms whose bodies are made up of more than one cells are called multicellular organisms.
The Five Kingdom System of Classification
Now-a-days, scientists classify living things into five main groups called kingdoms. These kingdoms are named as monera, protista, fungi, animalia and plantae. Examples of living things that belong to these kingdoms are as under:
Kingdom |
Example |
| Monera ............ |
Bacteria |
|
Protista ............ |
Algae |
|
Fungi ............ |
Yeast, mushrooms, etc... |
|
Animalia ............ |
Animals |
| Plantae ............ | Plants |
Bacteria
Bacteria are unicellular organisms. They are found everywhere on the Earth. Some bacteria can make their food but others live in and get food from the bodies of other organisms or dead bodies. Most bacteria cause diseases in animals and plants.
Algae
Algae are unicellular, colonial and multicellular organisms. They are found in ponds, lakes, sea, etc. They have chlorophyll and make their own food by photosynthesis. Chlamydomonas, Volvox and Spirogyra are the examples of algae.
Fungi
Fungi are found as unicellular, multicellular or filamentous forms. All fungi lack chlorophyll and cannot prepare their own food. They absorb food from their surroundings.
Yeasts, Rhizopus and Mushrooms, etc., are included in kingdom Fungi. Yeasts are microscopic fungi. Rhizopus (black bread mould) grow on moist bread and fruits. Mushrooms (umbrella like fungi) appear on dumps of debris and heaps of dung.
Animals
Animals are a major group of multicellular organisms. They cannot prepare their own food. They depend on plants and other animals for their food.
Plants
Plants are photosynthetic, multicellular organisms. We will learn about their further classification under section
Classification and Characteristics of Animals
Animals are classified into two main groups, i.e. vertebrates and invertebrates.
Vertebrates
Vertebrates are animals which have a backbone.
Activity
Feel the back of your body with your fingers.
Do you have a backbone?
Are you a vertebrate or an invertebrate?
There are about 47,000 different kinds of vertebrates on the Earth. Vertebrates are further divided into five classes (groups), ie, fishes, amphibians, reptiles, birds and mammals.
Mammals
Human beings, cows, goats, horses, tigers, cats, rabbits, etc., belong to a group of vertebrates called mammals. Mammals have hair or fur on their bodies. Babies of the mammals are fed on the mother’s milk. The young ones in mammals generally develop inside the mother’s body.
For Your Information about mammals
The quantity of hair or fur on the bodies of mammals depends upon the climate of their environment. Polar bear lives in very cold climate; hence, it has a thick coat of fur. Elephant lives in hot climate, so it does not need a thick covering of hair or fur.
Whale and dolphin are mammals. Blue whale is the world’s largest animal. It is about 35 metres long and nearly 120 tonnes in weight. Indus blind dolphin or ‘susu’ is a river dolphin of Pakistan not found anywhere else in the world.
Human, monkey, gorilla and chimpanzee are intelligent mammals. They have highly developed brain. Bat is a flying mammal.
Activity
Make alist of birds that you see in your surroundings.
Examine their beaks.
Why different birds have beaks of different shapes?
Birds
Sparrows, crows, parrots, doves, robins, hens and pigeons, etc., belong to the group of vertebrates called birds. Birds have feathers, wings and beaks. They have hollow bones and air sacs, which make their bodies very light. Some birds like kiwi and ostrich cannot fly and are known as running birds. Birds lay eggs with shells. Eggs hatch into baby birds.
For Your Information
Owl is a bird with big eyes. Kiwi and ostrich are running birds. Duck is a swimming bird. Penguin is a bird that lives on ice. Woodpecker is a bird that makes holes in trees.
Hummingbird is the smallest bird in the world. Eagle lives in tall trees or on cliffs. It often builds nest near lake or river, so that it can dive down to catch fish for its food. Hawk is a bird of prey.
Reptiles
Lizards, snakes, tortoises, crocodiles, alligators, etc., belong to a group of vertebrates called reptiles. Reptiles have dry, thick and scaly skin which covers and protects their bodies. They reproduce by laying eggs on land. Their eggs have thick leathery shells which prevent them from getting dry. Most reptiles have four limbs but snakes lack limbs.
For Your Information
Dinosaurs were the biggest reptiles in ancient times. They do not exist anymore.
Amphibians
Toad, frog, salamander, etc., belong to a group of vertebrates called amphibians. They have four limbs. Amphibians can live in water as well as on land. They breathe through lungs or skin. They usually have loose and wet skin. Most of them spend their adult life on land and return to water to lay eggs. Amphibian eggs look like beads in jelly. These are soft and do not have hard shells.
For Your Information
In winter, amphibians bury themselves in the mud and sleep for a long time to keep themselves safe from cold climate.
Fishes
There are over 25,000 different kinds of fishes found all over the world. They live in water. They have streamlined bodies well suited to swim fast in water.
Fishes have fins and tail which help them to swim. They have stiff scales on their skin for protection. They have gills to breathe in water. Most of the fishes reproduce by laying eggs.
Activity
Mark (L) for the animals which breathe through a pair of lungs and (G) for the animals which breathe through gills.
Sheep
Sparrow
Shark
Lizard
Invertebrates
Animals which do not have backbone are called invertebrates. There are different kinds of invertebrates found on the Earth. Insects, snails, starfish and worms are the examples of invertebrates.
Insects
Insects are well known invertebrates with jointed legs. They have segmented bodies. Ant, butterfly, bee, cockroach, etc., are the examples of insects. Every insect has three parts of its body: head, thorax and abdomen. Insects have six legs (three pairs). They have hard skeleton on the outside of their body. Outer skeleton provides support to their bodies.
Worms
Worms are invertebrates with soft bodies having no limbs. Most of them have elongated, snake-like bodies.
Earthworm and tapeworm are the worms whose bodies are divided into many segments.
Flatworm and roundworm are the worms without segmented bodies.
For Your Information
Some worms live in the bodies of higher animals getting food.
For Your Information
Starfish and sea anemone are the examples of marine invertebrates.
Classification and Characteristics of Plants
Plants are mainly classified as flowering plants and non-flowering plants.
Flowering Plants
The plants that bear flowers are called flowering plants. Flowers are their reproductive organs. The leaves in their flowers are called floral leaves.
The outer green coloured floral leaves of a flower are called sepals. Inside the sepals, there are colourful leaves which are called petals.
Flowering plants develop seeds in their fruits.
Do you Know?
There is a young plant in every seed of flowering plants called embryo. Embryo bears one or two seed leaves called cotyledons. Cotyledons often store food which is used by the young embryo. Seeds of grasses have only one cotyledon.
Non-Flowering Plants
The plants which do not bear flowers are called non-flowering plants. Conifers, ferns, mosses and liverworts, etc., are the examples of non-flowering plants. Conifers have needle-like leaves. They reproduce by seeds developed in their cones. Leaves of ferns are divided into leaflets. Ferns reproduce by spores developed on the underside of their leaves. Mosses and liverworts have simple stem and tiny leaves. They reproduce by spores developed in their capsules.
There is a young plant in every seed of flowering plants called embryo. Embryo bears one or two seed leaves called cotyledons. Cotyledons often store food which is used by the young embryo. Seeds of grasses have only one cotyledon.
Monocot Plants
Flowering plants whose seeds have only one cotyledon are called monocot plants. Examples are oat, wheat, rice, etc. Their leaves have veins which run parallel to each other. Floral leaves are usually three or multiples of three.
Dicot Plants
Flowering plants like rose, pea, bean, etc., have two cotyledons in their seeds. They are called dicot plants. Their leaf veins are in the form of a network. Floral leaves are usually four or five or their multiple.
Activity
Soak some pea seeds in water for one day.
Remove their outer covering and observe the cotyledons inside.
How many cotyledons are there?
Activity
You have studied the differences between monocot and dicot plants. Considering the characteristics of plants, tick the relevant box.