Organisms and their Structure

Different living things live in different places: in ponds and rivers, in fields and forests, in hot deserts and on cold mountains. Each has a body that suits its own place.

A fish lives in water. A rat lives in a hole. Birds fly in the air. Each of them has special body parts for this. A fish has fins and gills. A rat has sharp claws to dig. A bird has wings. Because of these parts, each one can live easily where it lives.

Every living thing gets what it needs from its surroundings: food, water, air and a safe place to live. Over a very long time, living things have come to have the right body parts, the right ways of working inside their bodies, and the right habits for their own home.

The ability of a living thing to live well in its surroundings is called adaptation. A body part or habit that helps it live there is an adaptive feature (or adaptation characteristic). Because of these features, living things can grow and live easily in their own surroundings.

Adaptive characteristics of terrestrial animals

Animals that live on land are terrestrial animals. Their bodies are built in many different ways. Let’s look at some.

Animals that run fast and hunt, such as the dog, the cat, the tiger, the bear and the jackal (syal), have broad paws with strong claws. (Questions may call the toes phalanges, the name of the small bones in fingers and toes.) The paws help them run and grip the ground. The claws help them catch and hold their prey.

Animals that run fast have long, strong legs and strong muscles. A horse, a deer and a leopard are good examples.

Animals of cold places. Animals of the Himalaya and other cold places are covered with thick fur or long hair. Air trapped between the hairs keeps the cold out and the body’s heat in, like a thick woolen jacket. The yak, the snow leopard and the polar bear have thick fur. A polar bear also has a thick layer of fat under its skin.

Animals of hot places. Animals that live in hot places have thin fur, or very little hair. A rhinoceros (gaida) and an elephant have almost none. Thin fur lets the heat leave their bodies.

Animals of deserts. A desert is hot and dry, with very little water. Desert animals have thick, dry skin, which lets very little water escape from their bodies. The camel is the best known desert animal:

• Its hump stores fat, not water. When there is no food for a long time, the camel uses this fat for energy.
• It can drink a huge amount of water at once: more than 100 liters in about ten minutes.
• It loses very little water: it sweats very little, and its droppings are very dry.
• It has long eyelashes and can close its nostrils, to keep out blowing sand. Its broad, padded feet don’t sink into the sand.

Animals that climb trees. Monkeys and squirrels climb trees. Climbing animals have strong chest and arm muscles. A monkey’s fingers and toes are long and can wrap round a branch to hold it tightly. Many monkeys also use their tail to balance.

A wall lizard (mausuli) can walk on walls and even on the ceiling. The pads under its toes are covered with tiny hairs (bristles), much too small to see. Each one touches the wall very closely and holds on a little. Millions of them together hold the lizard up. A wall lizard can also drop its tail when an enemy catches it, and run away. Later, a new tail grows.

Birds

Birds are built to fly. Their wings carry them through the air, and their bones are light and hollow, so their body is light. Feathers make the wings broad and smooth.

Birds have different beaks for different jobs. Some beaks pick up grains; some catch insects; some eat fruit. A woodpecker’s beak is long, strong and pointed like a chisel: it drills holes in tree trunks to find insects. A duck’s beak is flat, to pick food out of water and soft mud.

Animals that live in holes

Some animals live in holes in the ground. Some dig their own holes; others live in holes dug by other animals. Rats and rabbits dig their own holes. They have a pointed, strong snout and sharp claws to dig with. A snake has no legs to dig, so it lives in holes made by other animals, such as rats.

Adaptive characteristics of aquatic animals

Animals that live in water are aquatic animals. The fish is the best example.

Aquatic animals usually have a streamlined body: pointed at the front, wide in the middle and narrow at the back, like a boat. Water flows smoothly over it, so swimming is easy. The outside of the body is slimy and slippery, and it is covered with scales. Fins push the fish along and steer it. Many aquatic animals breathe (respire) through gills, which take the oxygen that is dissolved in the water. The body temperature of a fish changes with the temperature of the water around it.

Not every water animal has gills, though. A crocodile, a turtle and a dolphin live in water but breathe air with lungs. They must come up to the surface to breathe.

Adaptive characteristics of terrestrial plants

Plants, like animals, live in water or on land. Their shape and size depend on where they grow.

Plants that grow on land are terrestrial plants. Their roots are well developed, much more than the roots of water plants: they hold the plant in the soil and reach for water. Their stems are hard and strong, to hold the plant up in the air. Plants of different places on land have different features.

Plants of hot, wet places grow tall, with hard, strong stems. A coconut palm has no branches at all, just a crown of big leaves gathered at the top. Mango and rubber trees also grow tall in hot places.

Plants of dry places must save water.

• Their leaves are small and thick, or turned into spines (thorns), so they lose very little water.
• Their stems are thick and green, and store water. In a cactus, the green stem makes the food.
• Their skin is thick and waxy, and their roots go deep or spread wide to find water.

Cactus (siudi) and aloe vera (ghiukumari) are plants of this kind.

Plants of shady places. Where very little sunlight falls, on a forest floor, on a shady wall or by a stream, small plants grow. Many of them never flower: ferns and mosses are examples.

Plants of the Himalaya and snowy places have thin, needle-shaped leaves, and the tree is cone-shaped: wide at the bottom and pointed at the top. Snow slides off its sloping branches instead of piling up and breaking them. Needle leaves lose little water and are not hurt by the cold. Pine (salla) and juniper (dhupi) are trees of this kind.

Climbers. Some plants have weak stems that can’t stand up by themselves. They climb up other plants or supports to reach the light. A cucumber and a sponge gourd (ghiraula) climb with tendrils: thin coils that wind round a support. A bean plant climbs by twining its whole stem round a stick.

Adaptive characteristics of aquatic plants

Plants that live in water are aquatic plants. Some float on the water; some live under the water (submerged); some have their roots in the mud and their leaves on the surface.

• Roots: water plants have water all round them, so their roots are small and not well developed. Algae have no roots at all. Floating plants have fine, hair-like roots that hang in the water and keep them balanced, like the keel of a boat.
• Stems: their stems are soft and flexible. Flowing water bends them, but doesn’t break them.
• Floating: many have air spaces inside. A water hyacinth (jalkumbhi) floats because its leaf stalks are swollen and spongy, full of air.
• Leaves: a lotus has broad, round leaves that float on the water, while its roots stay in the mud at the bottom. The leaves are waxy, so rainwater rolls off them. Plants that live under water, like hydrilla, have small, thin leaves.

So the roots, stems and leaves of each plant suit the place where it lives.

1. Fill in the blanks with the right word

gills, adaptation, flexible, strong, water, air

2. Choose the correct answer

3. Write the differences

4. Write one job of each of these body parts of animals

5. Draw these animals and plants

6. How does each beak help the bird?

7. Answer these questions

Every animal needs energy to live. It gets energy from food: it eats food, digests it, and uses the energy from it to carry out its life processes, such as moving, breathing and growing.

Animals eat many kinds of food. Cows and buffaloes eat grass, plants and grains. A tiger eats the flesh of other animals. A cat eats rats, but also milk and rice. Eagles and vultures tear and eat flesh. A crow eats fruits, grains and the flesh of animals. Animals get their food from different places and in different ways, so their body parts are built differently.

By what they eat, animals are sorted into three groups: herbivores, carnivores and omnivores.

a. Herbivores

Animals that eat only plants, grains and fruits are herbivores. The cow, buffalo, deer, rabbit, rhinoceros and elephant are herbivores.

• They have broad, flat grinding teeth to chew grass, grains and pulses. Their front teeth cut and bite off plants.
• They have a long alimentary canal (food pipe and intestines). Plants are hard to digest, so the food must spend a long time in the body.
• Cows, buffaloes, goats and deer chew the cud: they swallow grass quickly, then bring it back up into the mouth and chew it again at rest.

b. Carnivores

Animals that eat the flesh of other animals are carnivores. The tiger, leopard, vulture and eagle are carnivores.

• A tiger and a leopard have long, sharp, pointed teeth to grip their prey and kill it with a bite, and sharp cheek teeth to cut meat.
• They have sharp, strong claws on their feet to catch and hold prey.
• An eagle catches birds and small animals with its claws (talons), and tears their flesh with its hooked beak.
• A vulture tears the flesh of dead animals with its long, hooked beak.
• Carnivores have a shorter alimentary canal than herbivores, because meat is easier to digest.

c. Omnivores

Animals that eat both plants and animals are omnivores. The bear, the dog, the crow and human beings are omnivores. They have teeth of all kinds: some to bite and tear meat, and some broad, flat ones to chew grains and pulses.

1. Sort these animals into herbivores, carnivores and omnivores

2. Look at the teeth and sort the animals

3. Answer these questions

Run your fingers down the middle of your back. The row of knobs you feel is your backbone, or vertebral column. It is made of many small bones, the vertebrae, joined in a chain. It holds up the body’s weight, lets the body bend, and protects the spinal cord inside it.

Animals that have a vertebral column are called vertebrates. Humans, monkeys, cows, buffaloes, hens and other birds, fish, frogs and snakes are vertebrates. Some vertebrates live in water, some on land, and some in both.

Animals without a backbone are invertebrates: insects, worms, snails, spiders. You will meet them in Grade 7.

Vertebrates are sorted into two groups by whether their body temperature changes with their surroundings or stays the same.

A. Cold-blooded animals

Animals whose body temperature changes with the temperature of their surroundings are cold-blooded animals, or poikilothermic animals. Fish, frogs, lizards, tortoises, crocodiles, snakes and wall lizards are cold-blooded.

On a cold morning, a cold-blooded animal is cold and slow. It basks in the sun to warm up. In the heat of the day it hides in the shade. Some cold-blooded animals sleep through the winter, hidden in a safe place, to escape the severe cold: this is hibernation.

B. Warm-blooded animals

Animals whose body temperature stays the same whatever the temperature of their surroundings are warm-blooded animals, or homeothermic animals. Humans, cows, buffaloes, tigers, rhinoceroses and all birds are warm-blooded.

A healthy person’s body temperature is about 37 °C (98.6 °F), in summer and in winter. A warm-blooded animal makes its own heat from its food. When it is cold, it shivers and its fur or feathers fluff up; when it is hot, it sweats or pants to lose heat.

The five classes of vertebrates

Vertebrates are divided into five classes by how their bodies are built and their other features.

1. Pisces (fish): all kinds of fish.
2. Amphibia (amphibians): frog, toad, salamander.
3. Reptilia (reptiles): lizard, crocodile, snake, tortoise.
4. Aves (birds): hen, pigeon, danphe and all other birds.
5. Mammalia (mammals): human, bat, whale, cow.

1. Pisces (fish)

All fish belong to this class. Their body is streamlined. Their features:

• i.Their body is slender, usually flat from side to side, and covered with scales.
• ii.They live in water.
• iii.They swim with the help of fins.
• iv.They breathe through gills, on both sides of the head.
• v.Their heart has two chambers.
• vi.Most fish lay eggs in water, and the eggs are fertilized outside the body (external fertilization).

Examples: asla (snow trout), rohu, seahorse.

2. Amphibia (amphibians)

Amphibians live both on land and in water, which is why they are called amphibians (“both lives”). Their life begins in water. Their features:

• i.Their skin is moist, slimy and slippery, with no scales.
• ii.Their heart has three chambers.
• iii.They have four limbs.
• iv.Young ones (tadpoles) breathe through gills. Adults breathe through their skin in water and through lungs (and skin) on land.
• v.They lay eggs in water, and in frogs and toads the eggs are fertilized outside the body.

Examples: frog, toad, salamander.

3. Reptilia (reptiles)

Most reptiles crawl on the ground (the name comes from the Latin for “to creep”). Most live on land; some live in water. Their features:

• i.Their skin is dry and covered with hard scales.
• ii.Most have a heart with three chambers. (A crocodile’s has four.)
• iii.They breathe through lungs.
• iv.They lay eggs on land, with a tough shell.
• v.They move by crawling.

Examples: snake, crocodile, tortoise, garden lizard (chheparo), wall lizard (mausuli).

4. Aves (birds)

All birds belong to this class. Their features:

• i.Their body is covered with feathers (soft, fluffy down feathers underneath and smooth feathers on top).
• ii.They have a pair of wings, a pair of legs and a beak. Their front limbs have become wings.
• iii.They breathe through lungs.
• iv.Their heart has four chambers.
• v.Their bones are light and hollow.
• vi.They lay eggs with a hard shell, and the eggs are fertilized inside the body (internal fertilization).

Examples: pigeon, duck, hen, danphe, peacock, crow.

5. Mammalia (mammals)

Humans belong to this class. Most mammals live on land, some live in water, and some fly: the whale and the dolphin live in water, and the bat flies. Their features:

• i.Their body is covered with hair (fur).
• ii.They give birth to young ones and feed them milk (suckle them).
• iii.They breathe through lungs.
• iv.Their heart has four chambers.
• v.Most have a pair of external ears (ear flaps, the pinnae).

Examples: human, bat, whale, cow, buffalo.

1. Fill in the blanks with the right word

homeothermic, vertebral column, light, poikilothermic, three, gills

2. Choose the correct answer

3. Match the columns

4. Answer these questions

There are many kinds of plants on Earth. Some are tiny; some are huge trees. Some are so small that you can see them only with a microscope. Some plants have flowers; others never do.

a. Non-flowering plants

Non-flowering plants never have flowers at any time of their life. Some can be seen only with a microscope; others are of middle size. They are simpler plants. They are also called cryptogams. Instead of seeds, most of them make tiny spores, too small to see, which grow into new plants.

Algae

Simple green plants whose body can’t be divided into root, stem and leaf are algae (one is an alga). They have chlorophyll, so they make their own food. They live in water and in damp places. Some can be seen only with a microscope. Examples: Spirogyra, Chlamydomonas.

Fungi

Simple living things whose body can’t be divided into root, stem and leaf, and that have no chlorophyll, are fungi (one is a fungus). Without chlorophyll, they can’t make their own food: they take it from dead and rotting things, or from other living things. Examples: mushroom, yeast (used to make bread dough rise) and mold (Mucor), the fluff on old bread.

Bryophytes

Green plants that grow on moist ground, with fine, hair-like threads called rhizoids to hold them to the ground, are bryophytes (Bryophyta). They have chlorophyll and make their own food, but they have no real roots and no flowers. Examples: moss, Marchantia.

Pteridophytes (ferns)

Ferns are a group of non-flowering plants called pteridophytes (Pteridophyta). Unlike mosses, they have real roots, stems and leaves, and tubes inside to carry water. But they have no flowers and no seeds: they make spores. They grow in cool, damp, shady places. Examples: fern (uniu), niguro.

b. Flowering plants

The flower is the most beautiful part of a plant. Many kinds of flowering plants grow around us, at home and at school. Seeds form from flowers, and new plants grow from the seeds. Plants that make seeds are called phanerogams. Plants with real flowers, whose seeds are inside a fruit, are angiosperms.

Most flowering plants make seeds. Look inside a seed: the seed leaves inside it are called cotyledons.

• Some plants have one cotyledon in each seed. They are monocotyledonous plants, or monocots. Their leaves are usually long and narrow with veins running side by side, and they have a bunch of thin, fibrous roots. Examples: rice, wheat, maize, bamboo, onion.
• Some plants have two cotyledons in each seed. They are dicotyledonous plants, or dicots. Their leaves are usually broad, with a net of veins, and they have one main root, a taproot. Examples: mustard, gram, pea, bean, pumpkin, apple, orange.

Some seed plants have no real flowers and no fruits. Their seeds lie naked, on the scales of a cone. Their leaves are usually like needles. These plants are gymnosperms. Examples: pine (salla), cycas, juniper (dhupi).

The roots, stems and leaves of flowering and non-flowering plants are built very differently. The main differences:

1. Fill in the blanks with the right word

phanerogams, rhizoids, root, chlorophyll, cryptogams, food

2. Answer these questions