If the somatic cell of a plant has 36 chromosomes, what will be the chromosome number in the endosperm?

Angiosperms uniquely undergo double fertilisation. One sperm fertilises the egg (zygote = 2n = embryo). Second sperm fuses with 2 polar nuclei = triploid primary endosperm nucleus (3n) = endosperm. This simultaneous formation ensures food reserves are produced only when an embryo is present.

Key rule: Endosperm = 3n = 3/2 × 2n. If 2n=10 → 3n=15. If 2n=14 → 3n=21. If 2n=36 → 3n=54. If 2n=48 → 3n=72. Egg = n. Zygote = 2n. Male gametophyte (pollen) = n. Generative cell divides → 2 sperm cells (n each).

Helobial (most monocots): first division asymmetric. Nuclear (most dicots): free nuclear divisions before cellularisation. Cellular (rare, Orchidaceae): each division followed by wall formation. Endosperm function: nutrition for developing embryo and germinating seedling.

Gymnosperms: NO double fertilisation. Endosperm = female gametophyte = haploid (n). Angiosperms: double fertilisation → triploid (3n) endosperm. This is a key distinguishing feature used in classification.

A pollen tube delivers two male gametes into the embryo sac, and both fuse — which is why the event is called double fertilisation and is unique to angiosperms. One gamete fuses with the egg to form the diploid zygote, which becomes the embryo. The other fuses with the two polar nuclei to form the triploid primary endosperm nucleus, which develops into the endosperm. The second fusion involves three nuclei, so it is specifically called triple fusion.

The endosperm is 3n because it comes from one haploid male gamete plus two haploid polar nuclei. The embryo is 2n from the ordinary single fusion. The seed coat, however, develops from the integuments, which were maternal tissue all along and took no part in fertilisation — so it is 2n and purely maternal. This is why seeds from one plant look alike regardless of which plant supplied the pollen.

A seed is albuminous when the endosperm persists to maturity, as in castor, coconut and cereals, and non-albuminous when it is fully consumed by the developing embryo, as in pea and groundnut. Apomixis is a separate route entirely: a seed forms without fertilisation, so the offspring is a genetic clone of the mother. This matters commercially because it would let hybrid vigour be preserved across generations rather than lost after the first.