Classification of Living Beings

Plants and animals come in every shape and size. An ant is tiny. An elephant is huge. Moss is small. A peepal tree is very large.

To sort animals, start with one simple question: does it have a backbone? The backbone is the long row of bones down the middle of the back. It runs from the neck to the tail.

• Animals without a backbone: earthworm, crab, centipede, spider, fly, ant, snail and starfish.
• Animals with a backbone: fish, frog, lizard, snake, chicken, pigeon, dog, cat, cow and human.

Plants can be sorted with one question too: does it make flowers? So plants fall into two big groups: flowering plants and non-flowering plants.

All these animals have a backbone. Animals with a backbone are called vertebrates.

But vertebrates are not all alike.

• A fish lives in water. Its bones are thin and sharp, like thorns.
• A frog or a toad lives both in water and on land.
• Snakes, crocodiles and turtles crawl.
• A danphe or a pigeon is covered with feathers. It flies with its wings.
• Cows, goats and humans live on land. Their babies are born looking like them.

Their bodies are built differently. They breathe in different ways. Some lay eggs. Others give birth to babies.

These riddles name the five groups of vertebrates. Each group has its own clues:

1. Pisces (fish): live only in water.
2. Amphibians: live both in water and on land.
3. Reptiles: crawl, with a rough, scaly skin.
4. Aves (birds): covered with feathers, and fly.
5. Mammals: give birth to babies, and feed them milk.

1. Pisces (fish)

Rohu, seahorses and every other fish belong to this group, small or large. Fish can live only in water.

What all fish have

• Most fish have a body covered with scales.
• Their body is streamlined: smooth and pointed at the front, so it slips through water easily.
• They swim with fins.
• They breathe with gills, on the two sides of the head.
• They lay eggs in water.

2. Amphibians

Frogs and toads belong to the group called amphibians. They can live both in water and on land. (Amphibian means “living two lives”.)

What all amphibians have

• Their skin is moist and smooth, without scales.
• The body has a head and a trunk, with no neck between them. There are two pairs of legs.
• They walk, jump and crawl with their legs.
• They lay eggs in water. A tadpole hatches from each egg. It grows up in the water.
• They breathe in different ways at different times:
  • A tadpole breathes with gills.
  • A grown frog in water breathes through its moist skin.
  • On land, it breathes mainly with its lungs. Its skin helps too.

3. Reptiles

Snakes, lizards, crocodiles and turtles are in the group called reptiles. Most reptiles live on land. Some, like crocodiles and many turtles, live in water too.

What all reptiles have

• The body is covered with dry, hard scales.
• The body has a head, a neck, a trunk and a tail.
• Most have two pairs of legs. Snakes have no legs.
• They breathe with lungs.
• They lay eggs on land. The eggs have a tough shell.

4. Aves (birds)

Chickens, pigeons, sparrows, crows, cuckoos, ducks, hawks and ostriches are birds. Most birds live on land and can fly. Some, like ducks, live on water too. The bird group is called Aves.

What all birds have

• The body is covered with feathers.
• The body is streamlined, shaped like a boat. Air flows past it easily.
• The body has a head with a beak, a neck, a trunk and a tail.
• Birds have a beak, but no teeth.
• Their bones are light. Many are hollow, with air spaces inside, like a honeycomb.
• They have one pair of legs and one pair of wings. The feet are for walking, running, perching, swimming and catching prey. The wings are for flying.
• They breathe with lungs.
• They have air sacs: thin bags of air inside the body, joined to the lungs.
• They lay eggs with a hard shell. They sit on the eggs to keep them warm until they hatch.

5. Mammals

Humans, dogs, cows, tigers, elephants, rats, cats, deer, rhinoceroses, dolphins, whales and bats are mammals. Mammal mothers give birth to babies and feed them milk. Most mammals live on land. Bats can fly. Whales and dolphins live in water.

What all mammals have

• The body is covered with fur or hair.
• The body has a head, a neck, a trunk and two pairs of legs. Most have a tail too.
• They breathe with lungs.
• Most mammals give birth to babies. This is called being viviparous. The mothers feed the babies milk (breastfeed them).

1. True or false?

2. Fill in the blanks

breastfeeds, fins, gills, vertebrates, crawls, swim

3. Match the body covering with the animal

4. Choose the correct answer

5. Answer these questions

Words to know

• Adult: a fully grown living thing.
• Backbone: a long row of bones down the middle of the back, from the neck to the tail.

Some parts of a plant are under the soil. The rest are above it.

• The part under the soil is the root system.
• The part above the soil is the shoot system.

Root system

The root is the part of a plant that usually stays under the soil. Roots are mostly white, cream or gray. There are two main kinds of root system.

1. Tap root system
A mustard plant has a tap root.

• One thick main root grows straight down into the soil. It is also called the primary root.
• The deeper it goes, the thinner it gets.
• Many smaller roots grow out from its sides. These are the secondary roots.
• Even finer roots grow out of the secondary roots.

Dicot plants, like mustard, gram and mango, have a tap root.

2. Fibrous root system
An onion has fibrous roots.

• Many thin roots grow from one place, at the bottom of the stem.
• They are all about the same thickness.
• Smaller roots grow out of them.

Monocot plants, like onion, maize and rice, have fibrous roots. (You will meet dicots and monocots later in this unit.)

What roots do

1. Roots grip the soil. They hold the plant firmly in the ground, so wind and rain can’t knock it over.
2. Roots take in water and minerals (nutrients) from the soil for the plant.
3. Some roots store food. Radish, carrot, turnip and sweet potato are roots full of stored food.

Shoot system

The parts of a plant above the soil are the stem, branches, leaves, buds, flowers and fruits. Together they are the shoot system: every part of the plant except the root.

The stem is the part of the plant joined to the root, above the ground. It is thick near the root and gets thinner towards the top.

• The stems of many monocots, like wheat, rice and bamboo, are hollow.
• The stems of dicots, like mustard and mango, are solid.

Branches grow out of the stem. Leaves, buds, flowers and fruits grow on the branches. Some plants, like maize and banana, have no branches.

The place on a stem where a leaf or a branch grows out is called a node. The part of the stem between two nodes is an internode. In monocots, like bamboo and sugarcane, the nodes are easy to see, as rings round the stem. In dicots, they are not so clear.

What the stem does

1. The stem holds up the branches, leaves, buds, flowers and fruits, so the leaves get sunlight.
2. Water and minerals taken in by the roots go up through the stem to the leaves.
3. Food made in the leaves goes through the stem to every part of the plant.

Leaf

Parts of a leaf
Leaves come in many shapes. But a leaf usually has three parts:

• the leaf base: the part where the leaf is joined to the stem or twig;
• the petiole: the stalk, between the leaf base and the lamina;
• the lamina: the broad, flat part of the leaf.

A thick vein runs from the petiole to the tip of the lamina. It is the midrib.

• In the leaves of peepal, radish and pumpkin, many small veins branch out from the midrib and join up like a net. These are net veins (also called reticulate veins).
• In the leaves of maize, banana and bamboo, the veins run side by side, from the base to the tip. These are parallel veins.

Leaves are green because they have chlorophyll. Leaves also let gases in and out:

• To breathe (respiration), a plant takes in oxygen and gives out carbon dioxide, just as we do. It does this all the time, by day and by night.
• To make food, a plant takes in carbon dioxide and gives out oxygen. It does this only in light.

What leaves do

1. Green leaves make food for the plant.
2. Leaves take in oxygen for respiration, and give out carbon dioxide.
3. When they make food, leaves take in carbon dioxide and give out oxygen.
4. Leaves give out the plant’s extra water, as water vapor. This is called transpiration.

Flower

Flowers come in many kinds. But a flower usually has four parts, in rings, one inside the other: the calyx, the corolla, the androecium and the gynoecium.

1. Calyx
The calyx is the outermost part of the flower. It is made of small, green, leaf-like parts called sepals. When the flower is still a bud, the sepals cover it and keep it safe.

2. Corolla
The corolla is the second part, inside the calyx. It is made of petals. Different flowers have petals of different shapes, numbers and colors. Bright colors and a sweet smell attract bees, butterflies and birds. People love them too.

3. Androecium
The androecium is the third part, inside the corolla. It is the male part of the flower. It is made of stamens. Each stamen is a thin stalk with a little bag on top. The bags are full of a fine yellow dust called pollen. Pollen is needed to make seeds. Carrying pollen to the gynoecium is called pollination.

4. Gynoecium
The gynoecium is in the very middle of the flower, inside the androecium. It is the female part. It is made of one or more carpels. A gynoecium has three parts: a swollen part at the bottom, a thin tube in the middle, and a round, sticky tip on top that catches pollen. The seeds form in the swollen part, which grows into the fruit.

All four parts sit on the swollen top of the flower’s stalk, called the thalamus. The stalk under it is the pedicel.

Fruit and seed

After flowering, a plant makes fruits. Fruits come in all shapes and sizes. Inside a fruit are one or more seeds. Most new plants grow from seeds.

Inside a seed there is food for the baby plant. It is stored in cotyledons, the seed leaves. By the number of cotyledons in their seeds, flowering plants are sorted into two groups: monocotyledons and dicotyledons.

Moss, ferns and mushrooms make no flowers. Onions, maize and bananas are flowering plants.

Flowering plants are not all alike either. Their roots, stems, leaves, flowers, fruits and seeds differ. That is why they look so different. Flowering plants make fruits from their flowers, with seeds inside.

Flowering plants are sorted into two groups, monocotyledons (monocots) and dicotyledons (dicots), by four clues:

• the number of cotyledons in the seed;
• the kind of leaf veins;
• the kind of stem;
• the kind of roots.

Seed

Look at some maize grains, and at some gram that has been soaked and has sprouted. How are they different?

• Seeds with one cotyledon: rice, wheat, maize, barley, coconut, banana and pineapple. These plants are monocotyledons.
• Seeds with two cotyledons: gram, pea, beans and mustard. These plants are dicotyledons.

1. True or false?

2. Fill in the table

hollow, dicotyledonous, fibrous roots, solid stem, reticulate veins, parallel veins, monocotyledonous, tap root

3. Match the parts of a flower with their names

4. Name the parts of the leaf

5. Choose the correct answer

6. Read the table and answer

7. Answer these questions