Which of the following statements is true about external and internal fertilization? a. internal fertilization doesn't require sexual intercourse. b. all animals that lay eggs use external fertilization. c. external fertilization doesn't require sexual intercourse. d. all animals that lay eggs use internal fertilization.

The answer is C.  External fertilization doesn't require sexual intercourse.

Explanation:

Fertilization is the process by which haploid gametes, sperm and egg, unite to produce a genetically distinct individual.

Fertilization in most of the animals is similar to that in humans. Animals also produce gametes for fusion. But the fusion of gametes may take place inside or outside the body. Based on this, fertilization is of two types – internal and external fertilization.

Internal fertilization

In sexual reproduction, the male inserts the sperms into the female reproductive tract to fuse with the egg. If the fusion takes place within the female parent, it is called internal fertilization.  

External fertilization

When the fusion of sperm and egg takes place outside the female parent, it is called external fertilization. Only a minority of organisms exhibit this type of gamete fusion. For example, fish, frogs, etc. Here the female parent deposits her eggs in a place and later, the male parent ejects his sperms over them, then fusion takes place.

Gametes that fuse externally has to face many challenges. Since eggs and sperms are deposited in the external environment, the chances of fusion are very less. Predators may eat eggs and the zygote that is formed. To compensate this loss, organisms like fish and frogs lay hundreds of eggs at a time.