Internal vs External Fertilization

In sexual reproduction, a male sperm must fuse with a female egg (ovum) to form a zygote. This process is called fertilization. Based on where this fusion happens, it is classified as Internal or External fertilization.

Question (Click to Flip)

Differentiate between internal and external fertilization.

Answer

Internal fertilization occurs inside the female's body, providing high protection to the offspring, requiring fewer eggs (e.g., humans). External fertilization occurs outside in water, offering no protection, requiring the release of thousands of eggs (e.g., frogs).

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Key Facts

Internal Fertilization: Happens inside the body. Safe. Mammals, Birds.

External Fertilization: Happens outside in water. Risky. Frogs, Fish.

Why thousands of eggs? External fertilizers lay thousands of eggs because predators and harsh environments will destroy most of them before they hatch.

1. Internal Fertilization

Definition: The fusion of the male and female gametes takes place inside the body of the female.
Process: The male transfers sperms directly into the female reproductive tract.
Survival Rate: Very high. The developing embryo is protected inside the mother's body or inside a tough-shelled egg.
Gamete Production: Fewer eggs are produced (e.g., humans produce 1 egg per month) because the chances of successful fertilization are high.
Examples: Humans, Dogs, Cows, Birds, Reptiles.

2. External Fertilization

Definition: The fusion of male and female gametes takes place outside the body of the female (usually in water).
Process: The female releases hundreds of eggs into the water, and the male simultaneously releases sperm over them.
Survival Rate: Very low. The eggs and zygotes are exposed to water currents, temperature changes, and predators.
Gamete Production: Millions of eggs and sperms are released at once to ensure at least a few survive and fertilize.
Examples: Frogs, Toads, Starfish, and most Fish.

Summary Table

Feature	Internal Fertilization	External Fertilization
Location of fusion	Inside female's body	Outside (in water)
Protection	High	Low (vulnerable to predators)
Number of Eggs	Few	Thousands/Millions
Examples	Mammals, Birds	Frogs, Fish

Questions and Answers

Differentiate between internal and external fertilization.+

Where does fertilization occur in a frog?+

In frogs, fertilization is external. It occurs outside the body, in a pond or stream water.

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