Question

Zygote is formed by the process of
A. Anisogamy
B. Isogamy
C. Oogamy
D. Syngamy

Answer 1

Hint: Fertilization involves a series of events and the final step of this process is fusion of gametes. In plants, pollination is the first step before fertilization and in animals transfer of gametes take place before fertilization.

Complete Answer:
Asexual and Sexual reproduction are two modes of reproduction process. Sexual reproduction is biparental and thus mixing of gametes takes place.
This type involves three stages
1. Pre-fertilisation events
- This stage involves formation of gametes.
- In animals, male gametes are sperms while female gametes are ova.
- In plants, the male gametes are pollen while female gametes are eggs.

2. Fertilisation events
- This involves fusion of gametes also known as syngamy.
- Fertilisation and syngamy are different but often used synonymously.
- Fertilisation involves a series of processes that ultimately result in fusion whereas the act of fusion is syngamy.
- The result of fusion is zygote.

3. Post-fertilisation events
- This involves growth and development of zygote to form embryos and further foetus (in animals) or seeds (in plants).

Option A : Anisogamy means the gametes are of different sizes (Aniso means different and gamy means gametes) Example : In humans, sperms are of small size while ovum are of larger size.
Option B : Isogamy means the gametes are of same size (Iso means same and gamy is gametes). Example : Chlamydomonas
Option C : Oogamy is a type of Anisogamy in which the ovum is larger in size than the male gametes and hence is non motile as seen in humans (oo means ovum and gamy means gametes)

Hence the answer is Syngamy (Syn means fusion and gamy means gametes) i.e. Option D.

Note: Zygote (zygo means to join) is considered to be the vital link of sexual reproduction. This zygote undergoes a series of developments to form embryos. Oscar and Richard explained animal zygote for the first time.