How Does the Human Reproduce?
Humans reproduce with the help of their reproductive organs; males and females have different kinds of organs which help in producing offspring by fusion of the male and female gametes forming a zygote. The zygote is then developed into a new similar species and the kind of reproduction in human beings is sexual reproduction. Similarly, other animals reproduce to continue their species in generations to come and undergo various methods of aswxual as well as sexual reproduction methods.
In this article, we will cover the topics of reproduction in animals for class 8 students.
Modes of Reproduction in Animals
There are two different modes of reproduction in animals:
1. Sexual Reproduction
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In this type of reproduction, males and females have different reproductive organs. For example, talking about reproduction in human beings, testes are the organs which produce gametes and female reproductive organs are ovaries that produce female gametes called ova or eggs. The fusion of this sperm and ovum is called fertilization that results in the formation of zygote.
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Further, the zygote divides continuously to generate a ball of cells that are divided into groups. These groups of cells develop into different tissues and organs giving rise to a full body. The developing structure is called embryo that entails all features of the parent gametes. This embryo continues development in the uterus and gives rise to the body parts including face, ear, head, hands, nose, toes, legs and many others. This stage of embryonic development is called foetus; when the development of foetus is complete, the baby is ready to be born. This is the process of reproduction in human beings.
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Animals that give birth to young ones are known as viviparous animals. Fertilization is internal in this type and the embryo receives nutrition from their mother. The zygote development takes entirely inside the mother. The survival chances are higher as the young ones are protected well inside the mother. Mostly, reproduction in mammals takes place this way and they give birth to young ones. Examples include tiger, cats, dogs, humans, cow, sheep, etc.
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Another kind of animals that reproduce sexually but they lay eggs are called oviparous animals. Here, fertilization can be either internal or external and the embryo receives nutrients from the egg yolk. There is no or very little development of embryos inside the mother’s body. The chances of the young ones are fewer as the eggs are laid in the open environment. Examples are birds (except bats) and lizards.
2. Asexual Reproduction
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It is one of the types of animal reproduction, only a single parent is responsible for producing offspring. Examples are Hydra and Amoeba.
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In hydra, budding is the name of asexual reproduction where new individuals develop from the buds.
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In Amoeba, a nucleus is divided into two nuclei to form new individuals and the process of this asexual reproduction is called binary fission.
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Some other kinds of asexual reproduction include fragentation, regeneration and parthenogenesis. Fragmentation leads to breaking of the body of an organism into multiple pieces and these pieces develop and grow into an individual offspring. Planarians undergo fragmentation through accidental damage by predators or also as a natural form of reproduction. It is also seen in sea stars where the broken arm grows into a complete organism. Regeneration is the modified form of fragmentation that occurs mostly in Echinoderms. It is such that when a part of an organism’s detach from the body, such as the arm, it grows into a new individual. Parthenogenesis is a kind of asexual reproduction where an egg develops without fertilization. Examples of parthenogenesis organisms include ants, bees, wasps, etc. It is also observed in a few vertebrates like dragons, blacktop sharks and hammerhead sharks.
Besides sexual and asexual reproduction which are natural processes, the modern science techniques are applied to produce exact copies of a cell, also leading to a complete organism. This method is called cloning and animal cloning was performed for the first time by Ian Wilmut and his colleagues in Scotland. The animal which was cloned was a sheep named Dolly in the year 1996.