Question

Fertilisation is defined as the process by which
A. a diploid spermatozoan unites with a haploid ovum to form a triploid zygote.
B. a haploid spermatozoa unites with a haploid ovum to form a diploid zygote.
C. a diploid spermatozoan unites with a diploid ovum to form a diploid zygote.
D. a diploid spermatozoan unites with a haploid ovum to form a diploid zygote.

Answer 1

Hint: Fertilisation is a process of fusion of haploid gametes which are egg and sperms to form the diploid zygote. The process of fusion of gametes is called syngamy.

Complete answer:
Fertilisation is a process of fusion of haploid gametes which are eggs and sperms to form the diploid zygote. The gametes have half the number of chromosomes of the organisms. Haploid( n number of chromosomes) spermatozoan means the haploid male gametes and haploid ovum is the female haploid gamete. So when these haploid spermatozoa and haploid ovum units fuse together by the process of fertilisation then it gives rise to diploid zygote. (2n number of chromosomes). Their fusion is a form of sexual reproduction and that involves fusion between the male and female.

So from the above explanation you can compare all the options now.
> Option A which is a diploid spermatozoan unites with a haploid ovum to form a triploid zygote. It's right that haploid spermatozoan and haploid ovum unites but it does not form triploid zygote. So, this option is incorrect.

> Option B which is a haploid spermatozoa unites with a haploid ovum to form a diploid zygote. This option is the correct one as haploid sperm and ovum unites and they form diploid zygote. Therefore, it is the correct option.

> Option C which is a diploid spermatozoan unites with a diploid ovum to form a diploid zygote. Diploid zygote is formed not by fusion of diploid spermatozoan but by fusion of haploid spermatozoa and haploid ovum. Therefore, this is also incorrect.

> Option D is a diploid spermatozoan that unites with a haploid ovum to form a diploid zygote. This option is also incorrect since both the spermatozoa and ovum are haploid which unites together to form diploid zygote.

Hence, the correct answer is option (B).

Note: Since in the fertilisation process, there is fusion of haploid spermatozoa unites with a haploid ovum to form a diploid zygote. Haploid means having a number of chromosomes and diploid means having 2n number of chromosomes.