Question

Why do most amphibians lay their eggs in water?
A) Eggs absorb water and swell to several times their original volume
B) Eggs will dry up and die
C) Eggs do not have a soft skin or a hard shell
D) All of the above

Answer 1

Hint: Amphibians reproduce sexually, with either internal or external fertilisation depending on the species. However, all amphibians characteristically lay their eggs in water or very moist environments.

Complete answer:
In water, through a process of imbibition, the eggs swell up to several times their original volume. This increases the mass and slipperiness of the jelly layer as well, helping protect the eggs from predation. The jelly may also keep the eggs warmer than the surrounding water. Option A is correct.

Amphibian eggs, unlike those of reptiles, birds and mammals, are not amniotic. The eggs are therefore in danger of drying out if they lie on land. Laying the eggs in water prevents drying out, and many amphibian species add a second level of protection by covering their eggs with a jelly-like substance. Option B is correct.

Amphibian eggs also do have a hard shell or a leathery membrane to protect them. Being in water keeps the eggs physically safer as well. Option C is correct.
As all the options are correct, the correct answer id option D, all of the above.
Frogs mate sexually, but fertilisation is external. Male grogs release sperm into the water through the amplexus, while the female releases eggs into the water through oviposition. Fertilisation then takes place in the water. Frogs ignore their eggs completely after mating.

Hence the correct answer is OPTION(D)

Note: Though almost all amphibians lay their eggs in water, there are some species like the Pristimantis genus of frogs which lay they legs on land. When these eggs hatch, they directly hatch as little frogs, bypassing the tadpole stage.