Chapter 6: Reproduction in Animals
Modes of Reproduction
Reproduction is a fundamental biological process by which new individual organisms – "offspring" – are produced from their "parents". It is essential for the continuation of a species. There are two main modes of reproduction in animals.
1. Sexual Reproduction
Reproduction resulting from the fusion of male and female gametes. It involves two parents and introduces genetic variation in the offspring. Most animals, including humans, reproduce sexually.
2. Asexual Reproduction
Reproduction in which a single parent is involved, and the offspring are genetically identical to the parent. It is common in very small animals like Hydra and Amoeba.
Sexual Reproduction
This process involves the production of male gametes (sperms) and female gametes (ova or eggs) and their subsequent fusion.
Human Reproductive System
- Male Reproductive Organs: Include a pair of testes, sperm ducts, and a penis. The testes produce the male gametes called sperms.
- Female Reproductive Organs: Include a pair of ovaries, oviducts (fallopian tubes), and the uterus. The ovaries produce the female gametes called ova (eggs).
Fertilization
The fusion of a sperm and an ovum is called fertilization. The fertilized egg is called a zygote, which is the first cell of a new individual.
- Internal Fertilization: Fertilization which takes place inside the female body. Occurs in many animals including humans, cows, dogs, and hens.
- External Fertilization: Fertilization which takes place outside the female body. It is very common in aquatic animals such as fish, starfish, and frogs.
Development of Embryo
The zygote divides repeatedly to form a ball of cells, which develops into an embryo. The embryo gets embedded in the wall of the uterus for further development. The stage of the embryo in which all the body parts can be identified is called a foetus.
Viviparous and Oviparous Animals
Viviparous Animals
Animals which give birth to young ones are called viviparous animals.
Examples: Human beings, cows, dogs.
Oviparous Animals
Animals which lay eggs are called oviparous animals.
Examples: Hens, frogs, lizards, butterflies.
Young Ones to Adults: Metamorphosis
The transformation of the larva into an adult through drastic changes is called metamorphosis. For example, a tadpole undergoes metamorphosis to become an adult frog. Similarly, the caterpillar or pupa of a silkworm transforms into an adult moth.
Asexual Reproduction
1. Budding
In organisms like Hydra, a bulge called a 'bud' develops on the parent's body. This bud grows and develops into a new individual, which then detaches from the parent.
2. Binary Fission
In microscopic organisms like Amoeba, reproduction occurs by the division of the nucleus into two nuclei, followed by the division of its body into two. Each part receives a nucleus and becomes a new Amoeba.
The Story of Dolly, the Clone: Cloning is the production of an exact copy of a cell, any other living part, or a complete organism. Dolly was the first mammal to be cloned, born on 5th July 1996. The clone was created by Ian Wilmut and his colleagues at the Roslin Institute in Scotland.
Frequently Asked Questions (FAQ)
What is a zygote?
A zygote is the single cell formed by the fusion of a male gamete (sperm) and a female gamete (egg) during fertilization. It is the beginning of a new organism.
What is the difference between internal and external fertilization?
Internal fertilization is the fusion of gametes inside the female's body (e.g., humans), while external fertilization is their fusion outside the body, typically in water (e.g., frogs).
What is metamorphosis?
It is a biological process involving a profound transformation from a larval stage to an adult stage, seen in insects and amphibians like frogs.
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