Correct Option
The correct option is (c) 2 and 3 only.
Explanation
Fertilisation is the fusion of sperm and egg. Based on where this fusion takes place, it is classified into two types: internal fertilisation (inside the female body) and external fertilisation (outside the female body). External fertilisation is most common in aquatic animals.
Statement-wise Analysis
- Statement 1 is Incorrect. Terrestrial mammals, such as cows, dogs, and humans, undergo internal fertilisation. In this process, the fusion of the egg and sperm occurs inside the body of the female. External fertilisation is characteristic of aquatic animals like fish and amphibians (e.g., frogs), not terrestrial mammals.
- Statement 2 is Correct. In external fertilisation, the female releases eggs into a fluid medium (usually water), and the male deposits sperms over them. This ensures that the gametes meet in the external environment. For example, during the rainy season, frogs move to ponds where the female lays hundreds of eggs in the water.
- Statement 3 is Correct. Unlike the eggs of birds or reptiles which are covered by a hard shell, the eggs of animals undergoing external fertilisation (like frogs) are delicate. A layer of jelly holds the eggs together and provides protection to the eggs while they float in the water.
Key Takeaway
External fertilisation involves the fusion of gametes outside the female body, typically in water, and is common in aquatic organisms like fish and amphibians, whereas terrestrial mammals utilize internal fertilisation.