Reproduction in Animals
Concept: Meaning of Reproduction
What is Reproduction?
Reproduction is the process by which living beings produce young ones of their own kind called offspring.Animals are divided into two categories based on their modes of reproduction—
- Viviparous animals: Animals that give birth to young ones. Examples: Dog, cat, horse, leopard, lion, zebra, elephant, man, etc.
- Oviparous animals: Animals that reproduce by laying eggs. Examples: Frog, snake, hen, duck, butterfly, shark, etc.
- These animals give birth to young ones.
- Viviparous animals are further divided into mammals and marsupials based on their characteristic features.
Features of viviparous animals:
- The body of viviparous animals is covered with hair.
- They use their lungs for breathing.
- Viviparous animals are complex organisms with well-developed brains.
- The process of reproduction includes a gestation period during which the babies develop inside their mothers’ womb for a specific period of time.
- Once the offspring are born, they are nurtured by their mothers till they become independent to survive.
- Both marsupials and mammals have mammary glands to feed milk to their young ones.
Examples : Mammals—Tiger, deer, monkey, rat, goat, sheep, etc.; Marsupials—Kangaroo, koala, opossum, etc.
- Animals that reproduce by laying eggs are called egg-laying or oviparous animals.
Features of oviparous animals:
- The young ones grow inside the eggs of these animals.
- The embryo gets nourishment from the yolk and the albumen that help in its growth and development.
- The eggs are protected from the predators and provided the warmth of the body or the sun till the embryo matures, the egg hatches and the young ones come out.
Examples : Insects, birds, reptiles, fishes and amphibians lay eggs for reproduction.
Let us now look at how some common oviparous animals reproduce.
Reproduction in birds:
- All birds lay eggs.
- The birds build nests to lay eggs and sit on them to keep them warm.
- It takes 21 days for a chick to hatch.
- The parents feed and take care of their young ones till they are strong to fly.
Reproduction in fishes:
- A fish lays thousands of eggs at a time in the water.
- All these eggs released by a fish in the water is collectively called a spawn.
- Only a few hundred eggs mature into tiny baby fishes; the rest are eaten by bigger fishes.
- Fish eggs do not have shells but have a jelly-like protective covering.• Fish eggs do not have shells but have a jelly-like protective covering.
Reproduction in reptiles:
- The animals which creep on the ground are called reptiles.
- Reptiles like snakes, turtles, crocodiles lay eggs in the holes of the ground.
- Shells of reptile eggs are leathery and elastic-like, and for this reason, the eggs do not break when they are laid on the ground.
- The eggs get warmth from the sun.
- After laying the eggs, some mothers go away and never return and leave the eggs to hatch on their own. Therefore, many of these eggs are eaten by other animals.
Parts of an Egg:
Eggs are laid by oviparous animals. An egg after fertilisation contains the zygote that develops inside it and comes out as a young one once the egg hatches.
The parts of an egg are described below—
- The outer oval-shaped overing of the egg is called shell.
- It is white in colour and is made up of calcium carbonate.
- The eggshell is porous and helps in the exchange of gases.
- These membranes are located immediately below the shell.
- The egg membranes protect the contents of the shell from bacterial growth and help in moisture retention.
- It is the transparent part that surrounds the egg yolk.
- It constitutes over 50% of the total liquid weight of an egg.
- The function of albumen is to provide nutrition (protein and fats) to the developing embryo for proper growth and development.
- It also protects the growing embryo from external injury.
- It is the yellow part located at the centre of an egg.
- The embryo develops within the yolk.
- It is rich in fats that are consumed by the embryo while growing.
- The small white spot on the yolk where the genetic material is located is called the germinal disc.
- Chalaza is the membranous structure that attaches the yolk to the end of the eggshell.
- It keeps the position of the yolk intact as it is necessary for the developing embryo.
Gestation period: The time for which a developing baby remains inside the womb of its mother. It varies from animal to animal.
Mammary glands: The glands present in female mammals responsible for production of milk to nourish the young ones.
Embryo: A developing animal, found in either a mother’s womb or an egg.
Fertilisation: A process in reproduction that involves the union of male and female reproductive cells.
Zygote:It is a fertilised egg cell that forms due to the union of male and female reproductive cells. It is a single cell and, over a certain period, gets divided into multiple cells.
Genetic material: Any material of plants and animals that carries genetic (related to genes, i.e., related to inheritance of traits) information which is passed through generations.
Did You Know?
- The gestation period of elephants is around two years.
- A female sea horse lays eggs in the pouch of a male sea horse, who takes care of the developing eggs and release the babies in water once they hatch out of eggs.
- Blue whales and dolphins are one of a kind as they are aquatic organisms but are mammals.