Question

Why does the zygote begin to divide only after the division of Primary endosperm cell (PEC)?

Answer 1

Formation of zygote and PEC

The zygote and PEC are formed, during the process of double fertilisation, in the following manner:-

• Zygote formation- One male gamete fertilises the egg to form a diploid zygote.
• Triple fusion- Another male gamete fuses with the two haploid polar nuclei (present in the central cell) to form a triploid primary endosperm nucleus.This is called triple fusion. After triple fusion, the central cell is called the primary endosperm cell (PEC).

The PEC divides repeatedly to form the endosperm tissue, which is a food storing tissue.

Role of endosperm

The zygote requires a lot of energy for the purpose of cell division. Only after the zygote receives nutrition can it divide. This nutrition is supplied by the food storing tissue i.e. the endosperm.
Therefore, the zygote can divide only after the division of the PEC.
The endosperm can be consumed completely during maturation of seed or remain in the mature seed and can be utilised in germination of seed.