CBSE · Class 12 · Biology · Chapter 1

Sexual Reproduction in Flowering Plants — Formula Sheet

Board Formulas

10 formulas

1.Ploidy of Embryo Sac Cells★
$Egg = n, Synergids = n, Antipodals = n, Central cell = n + n = 2 n$
All cells of the female gametophyte are haploid; the central cell has two polar nuclei that later fuse.
2.Double Fertilisation (Syngamy)★
$n (sperm) + n (egg) \to 2 n (zygote)$
One male gamete fuses with the egg to form a diploid zygote.
3.Triple Fusion★
$n (sperm) + n (polar) + n (polar) \to 3 n (PEN)$
The Primary Endosperm Nucleus (PEN) is triploid and develops into the endosperm.
4.Microsporogenesis Output
$1 MMC (2 n) meiosis 4 microspores (n) \to 4 pollen grains$
One microspore mother cell (pollen mother cell) gives four haploid pollen grains arranged as a tetrad.
5.Megasporogenesis Output★
$1 MMC (2 n) meiosis 4 megaspores (n); 3 degenerate, 1 functional$
Only the chalazal (functional) megaspore survives and forms the embryo sac (monosporic development).
6.Polygonum-type Embryo Sac
$Functional megaspore 3 mitoses 8 nuclei \to 7 cells$
Cell breakdown: 1 egg + 2 synergids (egg apparatus) + 3 antipodals + 1 central cell (with 2 polar nuclei).
7.Ploidy Ledger of the Seed★
$Embryo = 2 n, Endosperm = 3 n, Seed coat = 2 n, Perisperm (nucellus) = 2 n$
Seed coat and perisperm are of maternal (sporophytic) origin; only endosperm is triploid.
8.Pollen Grain Composition
$Mature pollen = 1 vegetative cell + 1 generative cell (n each)$
2-celled at shedding in most species; 3-celled when the generative cell has already divided to give two male gametes.
9.Exine Composition
$Exine = sporopollenin (highly resistant biopolymer)$
Sporopollenin resists high temperature, strong acids/alkalis and enzymes — the reason pollen fossilises so well.
10.Apomixis and Polyembryony
$Apomixis: seed without fertilisation; Polyembryony: many embryos in one seed$
Apomictic seeds are genetically identical to the mother — useful in hybrid seed technology.