Learning Objectives
- Understand the modes of reproduction in animals
- Learn about sexual reproduction and its stages
- Differentiate between viviparous and oviparous animals
- Understand asexual reproduction in animals
Key Concepts
Modes of Reproduction
Reproduction is the biological process by which organisms produce offspring to continue their species. Animals reproduce by two main methods: sexual reproduction and asexual reproduction.
Sexual Reproduction
Sexual reproduction involves the fusion of male and female gametes (sex cells).
Male reproductive organs: Testes produce male gametes called sperms. Sperm cells are tiny, have a head, middle piece, and a long tail for movement.
Female reproductive organs: Ovaries produce female gametes called ova (eggs). The egg cell is much larger than the sperm and is spherical.
Fertilisation
Fertilisation: The fusion of a sperm with an ovum to form a zygote. The zygote is the beginning of a new individual.
Internal fertilisation: Fusion occurs inside the female body. Examples: humans, cows, dogs, hens.
External fertilisation: Fusion occurs outside the female body, usually in water. Examples: frogs, fish, starfish.
Development of Embryo
The zygote divides repeatedly to form a ball of cells called an embryo. The embryo develops body parts and organs. When the embryo develops recognisable features, it is called a foetus.
Viviparous animals: Give birth to young ones directly. The embryo develops inside the mother's body. Examples: humans, cows, dogs, cats.
Oviparous animals: Lay eggs from which young ones hatch. The embryo develops inside the egg. Examples: hens, frogs, butterflies, fish.
Metamorphosis
Metamorphosis is the transformation of a larva into an adult through drastic changes in body form. Example: tadpole โ frog (develops legs, loses tail, develops lungs). Insects like butterflies also undergo metamorphosis: egg โ larva โ pupa โ adult.
Asexual Reproduction
In asexual reproduction, a single parent produces offspring without the fusion of gametes.
- Budding: A new organism develops as a bud on the parent's body, then detaches. Example: Hydra.
- Binary Fission: The parent organism splits into two identical daughter organisms. Example: Amoeba.
Cloning
Cloning produces an exact genetic copy of an organism. Dolly the sheep was the first cloned mammal (1996), created by Ian Wilmut.
Summary
Animals reproduce sexually (fusion of gametes) or asexually (budding, binary fission). Fertilisation can be internal or external. The zygote develops into an embryo and then a foetus. Viviparous animals give live birth; oviparous animals lay eggs. Some animals undergo metamorphosis during development.
Important Terms
- Gamete: Reproductive cell (sperm or ovum)
- Fertilisation: Fusion of sperm and ovum to form a zygote
- Zygote: The cell formed by fusion of male and female gametes
- Embryo: Early stage of development from the zygote
- Foetus: An embryo with well-developed body parts
- Viviparous: Animals that give birth to live young
- Oviparous: Animals that lay eggs
- Metamorphosis: Drastic change in body form during development
Quick Revision
- Sexual reproduction: male gamete (sperm) + female gamete (ovum) โ zygote
- Internal fertilisation: inside body (humans); External: outside body (frogs, fish)
- Zygote โ embryo โ foetus โ baby
- Viviparous = live birth; Oviparous = lay eggs
- Asexual: budding (Hydra), binary fission (Amoeba)
- Dolly = first cloned mammal (sheep, 1996)