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
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.
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.
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
It is one of the types of animal reproduction, only a single parent is responsible for producing offspring. Examples are Hydra and Amoeba.
In hydra, budding is the name of asexual reproduction where new individuals develop from the buds.
In Amoeba, a nucleus is divided into two nuclei to form new individuals and the process of this asexual reproduction is called binary fission.
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.
FAQs on Reproduction and Animals
1. What is reproduction in animals, and why is it essential for a species?
Reproduction is the fundamental biological process by which new individual organisms, or 'offspring', are produced from their 'parents'. It is essential for the continuation of a species, ensuring that life is passed on from one generation to the next and preventing the species from becoming extinct.
2. What are the two main types of reproduction found in the animal kingdom?
The two main types of reproduction in animals are:
- Sexual Reproduction: This involves the fusion of male and female gametes (sperm and egg) to form a zygote. It results in offspring that are genetically different from both parents. Humans, cows, and frogs reproduce sexually.
- Asexual Reproduction: This involves a single parent producing offspring that are genetically identical to itself. Examples include budding in Hydra and binary fission in Amoeba.
3. How does asexual reproduction work in animals like Hydra and Amoeba?
In some animals, asexual reproduction happens through simple mechanisms:
- Budding in Hydra: A small outgrowth, or 'bud', develops on the parent Hydra's body. This bud grows, develops a mouth and tentacles, and eventually detaches to become a new, independent individual.
- Binary Fission in Amoeba: A single-celled Amoeba reproduces by dividing its nucleus and then its cytoplasm into two equal halves. Each half grows into a new, separate Amoeba.
4. What are the primary male and female reproductive organs in humans?
In humans, the primary reproductive organs are responsible for producing gametes. The male reproductive organs are the testes, which produce sperm. The female reproductive organ is the ovary, which produces eggs or ova.
5. What is the difference between internal and external fertilisation?
The main difference lies in where the fusion of gametes occurs. Internal fertilisation is the fusion of the egg and sperm inside the female's body, as seen in humans, birds, and reptiles. In contrast, external fertilisation is the fusion of gametes outside the female's body, typically in an aquatic environment. This is common in animals like fish and frogs.
6. How can you tell the difference between viviparous and oviparous animals?
The difference is based on how they give birth to their young. Viviparous animals, like humans and dogs, give birth to live young ones that have developed inside the mother's body. Oviparous animals, like birds, frogs, and insects, lay eggs. The young ones develop inside the egg and hatch after a period of incubation.
7. What is metamorphosis, and can you explain it with the example of a frog?
Metamorphosis is the drastic transformation of an animal's body structure from a larval stage to an adult. In a frog, the life cycle starts as an egg, which hatches into a larva called a tadpole. The tadpole lives in water, breathes through gills, and has a tail. Through metamorphosis, it gradually loses its gills and tail, develops lungs and limbs, and transforms into an adult frog that can live on land.
8. What is a zygote and how does it develop into an embryo?
A zygote is the first cell of a new individual, formed immediately after the fusion of a male gamete (sperm) and a female gamete (egg) during fertilisation. This single cell then begins to divide repeatedly, forming a ball of cells. This ball of cells, called an embryo, embeds itself in the wall of the uterus for further development.
9. Why do animals like fish and frogs produce a massive number of eggs, whereas a hen lays only a few?
This is related to the type of fertilisation and survival chances. Fish and frogs practice external fertilisation, releasing their eggs and sperm into the water. Many of these eggs are lost to predators, water currents, and other environmental factors before they can be fertilised or hatch. Producing a huge number of eggs increases the probability that at least some will survive to become adults. A hen practices internal fertilisation, and the egg is protected by a hard shell, ensuring a much higher survival rate for each offspring.
10. Why is sexual reproduction generally considered more advantageous for a species' long-term survival than asexual reproduction?
Sexual reproduction is considered more advantageous because it creates genetic variation among offspring. Since the offspring inherit genes from two different parents, they have a unique combination of traits. This variation is crucial for the adaptation and evolution of a species, allowing it to better survive in changing environments or resist new diseases. In contrast, asexual reproduction produces genetically identical offspring, making the entire population vulnerable to the same threats.
