Structures for Reproduction in Animals

Key Concepts

• Reproduction
• Oviparous animals
• Viviparous animals
• Structure of an egg
• Life-cycle of chicken
• Life-cycle of frog
• Life-cycle of cockroach
• Life-cycle of butterfly

Introduction: 

We know that structure is a part of the body of an organism. Animals have different structures that help them to grow, survive and reproduce in their environment. Reproduction is an essential process that takes place in all organisms.  

We might have seen a bird feeding its babies or a dog playing with its puppies, or a monkey carrying its young one. Have you wondered why there is a similarity between these animals and their babies? 

We can see that the animals and their babies have similar characteristics and features. Both animals and their young ones have the same pattern of hair, skin, tail, etc. 

All living things reproduce so that they can replace their old and dying forms. They will disappear from the Earth if they fail to reproduce. For example: If dogs do not reproduce, they will not be seen in future after some time.  

So, reproduction is an important process for every animal to continue its race. 

Explanation: 

Like any other living organism, animals are born, grow, give birth to their own kinds, get old and die.  

Reproduction is the mechanism by which animals produce more animals of their own kind. It is essential for the continuation of life on the Earth. It ensures that an animal produces a young one just like itself, generation after generation. 

Animals mainly reproduce by two methods: 

1. By laying eggs 

2. By giving birth to young ones 

1. Animals that lay eggs: 

Some animals reproduce by laying eggs. These animals are called oviparous animals. Examples of oviparous animals include fishes, frogs, snakes, lizards, insects and birds. 

The majority of the animals reproduce by laying eggs. The eggs are deposited in a safe place like a nest, burrows, holes, etc. The young bird will only develop at the proper temperature. This happens only when a bird sits on them for several days. 

So, after the eggs are laid, one of the parents, usually the mother, sits on their eggs to keep it warm. This is called incubation. 

After a certain amount of time, the egg gets matured, and the young one hatches out. 

Structure of an egg: 

All eggs are covered by a protective covering called the shell. Shell is made up of calcium carbonate. It is porous and allows the transfer of gases. 

The shell consists of the yolk and the albumin. The yolk is the yellow part, and albumin is the white part. Albumin is rich in protein that is necessary for the development of growing birds. It protects the embryo and provides water and protein to it. 

The yolk contains high amount of fats, vitamins and minerals, which is the food for the growing embryo. It contains the developing baby called embryo at the top. The newborn bird does not have feathers when it hatches from the egg. So, the bird feeds their young ones till their feather develops. 

Life cycle of birds: 

Birds make nests to lay eggs and raise their young ones. Within the egg, the embryo passes through several stages of development. 

To keep the egg warm, the mother usually sits on it. The egg hatches into a baby bird.  

Parent birds feed and protect their young ones until they are able to care for themselves. The young bird grows into an adult.  

All the developmental stages, right from the embryo to a mature adult, make up a complete cycle. This cycle is called the life cycle of an animal. 

Frogs: 

Frogs also lay eggs. A female frog can lay hundreds of eggs at a time. Each of the black dots in the picture given below counts for an egg. Unlike the chicken, they lay eggs in an aquatic environment like a lake or a pond. These large clusters of eggs are called spawns.  

Within a few days, the egg hatches into tadpoles. Initially, the tadpoles have a tail and no legs; they swim in the water and look like fish. After a few weeks, the tadpole starts growing legs, and the tail starts to disappear. It also starts to form a frog-like face. 

The young four-legged frog resembles more like an adult frog. Their gills disappear completely, and their lungs start to develop and enlarge. The last stage is the fully developed adult frog. 

Insects: 

All insects lay eggs. Many of them go through various stages before they become adults. For example, cockroaches pass through three stages in their life cycle. The first stage is the egg.  

The baby cockroach that hatches out from the egg is called a nymph. It resembles the adult cockroach, except that it does not have wings. The nymph sheds its skin several times and changes into an adult. This is called molting. Molting can be defined as the process of shedding off the outer covering of the body.  

Like cockroaches, grasshoppers, locusts, and termites also go through these three stages. 

Butterfly: 

Unlike cockroaches, butterflies and moths go through four stages of the life cycle. Female butterflies lay their eggs in clusters, usually on the underside of leaves. The eggs hatch into tiny worm-like young ones, also known as the larvae. The larva of a butterfly is called a caterpillar. 

The caterpillar eats leaves and grows quickly. It then forms a shell called a chrysalis around its body. This stage is called the pupal stage. Inside the chrysalis, the caterpillar gradually changes its shape. An adult butterfly finally emerges out of the chrysalis. 

This change occurring in the form, structure, or function of an organism in the process of its growth or development is called metamorphosis. 

Other egg-laying animals: 

Fishes lay eggs in water. The female fish lay thousands of eggs at a time, scattering them in water, where the male fish fertilizes them. The baby fishes hatch out from the developed eggs. But a lot of the eggs and baby fishes are eaten by other fishes.  

Snakes lay eggs in the soil or inside holes in the ground. Turtles bury their eggs in the sand. 

Crocodiles lay their eggs in shallow pits dug into sandy riverbanks. The mother protects the eggs by covering them with sand and guarding them. When the babies hatch, the mother digs them out. Sometimes, she carries them in her mouth or on her back. 

2. Animals that give birth: 

Animals like lions, tigers, horses, cows and humans give birth to babies. Such animals are called viviparous animals. These animals are highly evolved and have a more complex method of reproduction. 

The babies are developed inside the mother’s womb, where they stay for many weeks or months before being born. After birth, the newborns are small, weak and helpless. They are not even able to walk. After their birth, they feed on their mother’s milk till they learn to feed on their own. Such animals that feed their babies with their milk are called mammals. 

Mammals are highly evolved animals with very well developed brains. Their bodies are covered in hair. The majority of mammals are found on land and breathe through their lungs. 

Whales and dolphins are also mammals since they give birth to their young ones but are aquatic. Although a bat is a bird, it gives birth to young ones.