4th Class Science Reproduction in Animals Reproduction in Animals

     Reproduction in Animals

Like any other living thing, animals are born, grow, give birth to their own kinds, get old and die. The ability to produce more of their own kind is known as reproduction. Reproduction is very essential for the continuation of a species or a group of animal. It ensures the continuation of similar kind of individuals (animals) generation after generation. Animals have mainly two different ways of reproduction. Animals, which give birth to their young one, the baby develops inside the body of the mother. Second group of animals are those which lays eggs, baby hatches out from the egg. Now let us understand these two ways of reproduction in detail.

                                 Reproduction    

         Egg Laying Animals

Many of the animals reproduce by laying eggs. The eggs are laid in a safe place like nest, borrows, holes etc. Either of the parents sit on the egg to keep it warm. After a fixed period of time the egg gets matured and the young one hatches out. In the centre of the egg, is a yellow portion called yolk. It contains the developing baby called embryo. Yolk is rich in fats, vitamins and minerals which is the food for the growing embryo.

             Hen’s Egg

Yolk is surrounded by a white jelly like substances called albumen. It is rich in protein. Albumen protects the embryo and provides water to it. These substances are protected all together in a thin protective shell called the egg shell. The embryo develops into a chick.

         Birds

All birds reproduce by laying eggs. Birds build nests to lay eggs and to raise their young ones. Within the egg, embryo goes through various developmental stages. Mostly the mother sits on the egg to keep it warm. The baby bird hatches out. The parent birds feed and protect the young bird until they can look after themselves. The baby bird grows into an adult. All the stages of development from the embryo to a mature adult make up a complete cycle. This cycle is called life cycle of an animal.

       Frog

Female frog lays hundreds of eggs at a time in a lake or pound. These large clusters of eggs are called spawns. Tiny tadpoles hatch out of the egg. They swim in water and look like fishes. A tadpole starts to grow legs after a few weeks. Tadpole's tails becomes shorter and shorter and finally disappear, and they develop into an adult frog.

                 Life cycle of Frog

Tadpole undergoes several change (as we have seen), before it becomes an adult. This process is called Metamorphosis.

       Insects

All insects lays eggs. Many of them go through several stages before growing into adults. Let us look at the life cycle of cockroaches. The baby cockroach that hatches out from the egg look like an adult but has no wings. This is called nymph. It sheds its skin several times before developing into an adult. Shedding of old skin is called moulting. Grasshoppers, locusts and termites also go through the same stages of development.

    Life cycle of Cockroach     

         Butterfly

Butterfly and moths go through 4 stages in their life cycle before becoming an adult. Life cycle of butterfly also shows metamorphosis. The female butterfly lays eggs in a cluster on the back part of a leaf. The eggs hatch into young ones called larva. The larva of a butterfly is called caterpillar. Caterpillar eats leaves and grows. It forms a shell called cocoon around the body. This stage is called pupa. The adult butterfly finally comes out of the pupa.

 Life cycle of Butterfly     

       Fishes

Fishes lay thousands of eggs in water. Baby fishes hatch out of the eggs. The eggs and the baby fishes are eaten by other fishes.     

            Life cycle of Fish    

         Turtles

Turtles and tortoises dig holes in the sand and lay their eggs there. They cover them with the sand and leave them to hatch. Young ones hatch out and move to the nearest water.

         Crocodiles

Mother crocodile digs shallow pits in sandy river banks to lay eggs. Then they cover the eggs with the sand and guard them. When the babies hatch, it digs away the sand and sets them free.

         Animals that Give Birth to Babies

Highly evolved animals have developed a much complex process of reproduction. Here the babies develop in the mother's womb. They stay in the mother's womb for fixed period of time. The baby born looks like his/her parents. When the babies are born they are weak and helpless. Mother takes proper care of her babies and protects them from all odds till they can look after themselves well and lead their life independently. The mother feeds her babies with her own milk. Such animals which give birth to their babies and feed them their own milk is called mammals. They are highly evolved animals, with very well developed brains. They have hairs on their body. Most mammals live on land and breathe through lungs. Whale and dolphins are aquatic mammals. Examples horse, dear, man, cat dog, elephant etc.

          Leopard with her Cub      

Turtles have been inhabiting our planet for more than 150 million years.

Green Turtles can stay under water for up to five hours with the air of one breath in their lungs.

Green Turtles can reduce their heart rate to a minimum of one pulse per nine minutes when diving.

An elephant can smell water three miles away.

Classification of Animals: Animals are broadly classified into invertebrates and vertebrates.

Habitat of Animals: Environment in which an animal lives.

Food of Animals: Things eaten by animals to get energy and nutrition.

Adaptation for Protection: The process of protecting oneself from enemy.

Reproduction: Process by which new young one are produced.