Vertebrates: Animals that have a spine or backbone.
Invertebrates: Animals that have do not have a spine or backbone.
Vertebrates are divided into five groups :
The most visible characteristic of mammals is that they have hair on their bodies. They are warm-blooded creatures. They have lungs and they breathe in oxygen through their nose and breathe out carbon dioxide.
Mammals give birth to young ones just like themselves, only smaller in size. Their life cycle has only two stages—the baby and the adult. Mammals feed their young ones with their own milk.
Mammals live on land (cows, deer, horse, etc.), underground (rats, moles, etc.) and in water (whale, dolphins, etc.). Bats are the only mammals that can fly.
Mammals can be herbivores, carnivores or omnivores. Animals that eat grass are called herbivores. Animals that eat flesh are called carnivores. Animals that eat both grass and flesh are called omnivores.
A bird is a warm-blooded animal. All birds have feathers. Most birds can fly though some like the penguin, ostrich and kiwi cannot. They have a set of wings which enable them to fly. Their feathers keep them warm in the cold weather. They have two legs with sharp claws that help them to walk, perch on branches and catch their prey. Birds have lungs for breathing.
Birds lay eggs. The eggs have a hard shell that protects the embryo (the unborn baby) bird inside. The embryo gets nourishment from the yolk of the egg. Small holes in the eggshell allow it to breathe. The mother bird sits on the egg till it hatches. The young bird is like the adult but smaller.
Some birds build nests in trees and in nooks and corners of houses. Some birds like ducks, swans, geese, etc., live on land and in water.
Some birds like hawks, eagles, vultures and falcons are carnivores. They eat rabbits, rats and dead animals. They have sharp beaks and claws to help them catch their prey.
Some birds like bulbul, sparrow and hen are omnivores and they eat grains along with worms, small insects, etc. Pigeons and doves are herbivores and eat only seeds.
Fish are animals that live in water. They have scales on their bodies that protect them. The shape of their bodies helps them to swim easily. The fins of a fish help it to control its movements and balance its body.
The fish breathe with the help of gills. The gills absorb the oxygen dissolved in the water and release carbon dioxide.
Fish lay a large number of eggs at one time. The eggs of fish do not have shells. These eggs hatch into small fry (young of a fish) that look just like the parent but smaller.
Fish live in water. Some fish are freshwater fish and live in rivers and streams. Some are seawater fish and are found in seas and oceans.
Most fish eat the plants that grow in or under the water. Some eat the insects and smaller animals and fish in the water. Others eat both plants and animals.
Cold-blooded animals like snakes, turtles, lizards, etc., that crawl on the ground with their four legs are called reptiles. They creep and crawl. They have hard scales on their bodies. They breathe through their lungs.
Reptiles can live on land and in water. Limbs of reptiles are made to suit their habitat, for example, turtles have flipper-like limbs to help them swim. Snakes have no legs but they move by wriggling their body from side to side in S-shaped waves.
Reptiles also lay eggs on land, in the sand or on leaves, etc. Their eggs have hard shells so that they do not break as these do not have the cushion of a nest. Baby reptiles have the same features as their parents but are only smaller.
Reptiles such as tortoise are herbivores and eat plants. Snakes, lizards, crocodiles, etc., eat other animals like frogs, rats, moles, etc.
Amphibians are cold-blooded animals with smooth, moist skins. Frogs, toads, newts and salamander are amphibians.
Amphibians can live on land and in water. They have body parts to adapt to their habitat. For example, frogs have strong and long hind legs for hopping on land. But they also have webbed feet with which they can swim easily.
To understand the life cycle of amphibians, we can study the life cycle of a frog. The female frog lays many eggs at a time. They are jelly-like with a small black centre. This black spot becomes the tadpole. A tadpole has no legs and looks like a fish. It cannot survive on land and lives only in water. After some time, its legs begin to grow. When the legs grow, the tail starts disappearing. The baby frog looks less like a fish and more like a frog now. A full-grown frog has no tail. It lives on land and in water.
Amphibians are primarily carnivorous. They eat insects and worms found on land and in water. They have long sticky tongues with which they catch their prey.
The invertebrates are divided into seven groups. The largest group of invertebrates is called arthropods which includes insects and spiders.
Insects are the largest number of animals found on the Earth. Insects are grouped together because they have some common characteristics like :
Their body is made of three parts: the head, the thorax and the abdomen.
They have three pairs of jointed legs,
They have compound eyes.
They have breathing tubes for breathing.
Most insects have feelers or antennae that help them to feel their way. Some insects have wings and can fly. Other insects crawl with the help of their legs.
Insects are found everywhere. Beetles and ants live in soil. Bees, ants and butterflies are found on trees and plants. Many insects like mosquitoes, dragonflies, etc., are found in ponds. Mosquitoes, fleas, lice and leeches are parasites. Parasites drink the blood of other animals to survive.
Different types of insects have different life cycles. One life cycle that is amazing and unique is that of butterfly. Female butterflies lay eggs on leaves of plants. A larva comes out of the egg. The larva of a butterfly is called a caterpillar. It feeds on leaves of plants. After some time, the larva spins a cocoon (a covering) around itself. It then changes into a pupa. The pupa does not eat. When the pupa comes out of the cocoon it has changed into a butterfly.
Different insects eat different things. Some eat only plants, some eat other insects and some feed on both. Bees feed on nectar from the plants.