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This chapter is a favourite for NEET questions on ploidy, counting and sequence: how many nuclei in an embryo sac, what is the ploidy of the endosperm, how many meiotic divisions make a given number of seeds. The facts are all in NCERT, but they are spread over several sections. This post follows the story from flower to seed, then works through the numbers.
What does the syllabus include?
The NEET (UG) 2026 syllabus lists flower structure, development of male and female gametophytes, pollination, outbreeding devices, pollen-pistil interaction, double fertilisation, development of endosperm and embryo, seed and fruit formation, and apomixis, parthenocarpy and polyembryony. These are covered in NCERT's Class 12 chapter on sexual reproduction in flowering plants. Check the syllabus for your exam year when it is notified.
How is the male gametophyte formed?
Inside the anther, each microspore mother cell (pollen mother cell) undergoes meiosis to form a microspore tetrad of four haploid cells. Each microspore matures into a pollen grain with a large vegetative cell and a small generative cell. NCERT notes that in over 60 per cent of angiosperms, pollen is shed at this 2-celled stage. In the rest, the generative cell divides by mitosis into two male gametes before shedding (the 3-celled stage).
How is the embryo sac formed?
In the ovule, the megaspore mother cell (MMC) undergoes meiosis to form four megaspores. In most flowering plants one is functional and three degenerate (monosporic development). The functional megaspore's nucleus then divides by mitosis three times, giving 2, then 4, then 8 nuclei, without cell walls at first.
The mature embryo sac is 8-nucleate but 7-celled:
Egg apparatus at the micropylar end: two synergids and one egg cell. The synergids carry the filiform apparatus, which guides the pollen tube.
Three antipodals at the chalazal end.
One large central cell with two polar nuclei.
What is double fertilisation?
The pollen tube enters the ovule through the micropyle and then one of the synergids, where it releases two male gametes.
Syngamy: one male gamete fuses with the egg, giving a diploid zygote.
Triple fusion: the other fuses with the two polar nuclei, giving a triploid primary endosperm nucleus (PEN).
NCERT calls the two fusions together double fertilisation, "an event unique to flowering plants".
What happens after fertilisation?
Endosperm develops before the embryo, to feed it. In the most common type, the PEN first divides into free nuclei and then becomes cellular. NCERT's example: tender coconut water is free-nuclear endosperm, and the white kernel is cellular endosperm.
Embryo: the zygote forms a proembryo, then globular, heart-shaped and mature embryos. Monocot embryos have one cotyledon, called the scutellum in grasses.
Seeds: non-albuminous seeds have no endosperm left (pea, groundnut); albuminous seeds keep some (wheat, maize, barley, castor). In black pepper and beet, remnants of the nucellus persist as perisperm. Mature seeds dry to about 10 to 15 per cent moisture by mass.
Special cases: apomixis gives seeds without fertilisation, and polyembryony is more than one embryo in a seed.
Worked example: ploidy and meiosis counts
A flowering plant has 2n = 24. Give the chromosome number of each cell.
Nucellus, MMC, microspore mother cell, integuments: diploid, 24.
Megaspore, egg, synergids, antipodals, each polar nucleus: haploid, 12.
Microspore, pollen vegetative cell, generative cell, male gametes: 12.
Zygote and embryo: 12 + 12 = 24.
PEN and endosperm: 12 + 12 + 12 = 36.
Seed coat (from integuments) and fruit wall (from ovary): 24.
How many meiotic divisions are needed to produce 100 seeds? Assume each seed comes from one fertilised ovule.
Each ovule needs one embryo sac, and each embryo sac comes from one MMC meiosis: 100 meioses.
Each ovule needs one pollen grain, because one pollen tube carries both male gametes. One microspore mother cell meiosis gives four pollen grains, so 100 pollen grains need 100 ÷ 4 = 25 meioses.
Total: 100 + 25 = 125 meiotic divisions.
How many mitotic divisions turn the functional megaspore into an 8-nucleate embryo sac? Three: 1 to 2, 2 to 4, 4 to 8.
Which mistakes cost the most marks?
Calling the embryo sac 8-celled. It has 8 nuclei but 7 cells, because the two polar nuclei share the central cell.
Giving the endosperm as 2n or n. In flowering plants it is triploid. (In gymnosperms the nutritive tissue is the haploid female gametophyte, a different structure.)
Saying the pollen tube enters the egg. It enters a synergid.
Forgetting that one pollen grain serves one ovule when counting meioses.
Mixing up albuminous and non-albuminous examples. Pea and groundnut have no endosperm left; castor and cereals keep it.
A practice routine
Rereading this chapter feels productive but is a weak strategy. A review of ten study techniques by Dunlosky and colleagues (2013) gave high utility ratings to practice testing and distributed practice. Roediger and Karpicke (2006) found that practising recall beat restudying on tests two days and a week later.
Draw the embryo sac from memory with all seven cells labelled, then check against NCERT Figure 1.8.
Ploidy drill: pick a new 2n (say 14 or 20) and list the chromosome number of twelve structures.
Counting drill: three "how many meioses for N seeds" questions with different N.
Connect chapters: compare plant groups in our guide to the plant kingdom, and flower parts in morphology of flowering plants.
If triple fusion or free-nuclear endosperm is still hard to picture, the Fermi Concept Library covers every concept in physics, chemistry, biology, mathematics and computing, each with its own lesson, so you can see the idea step by step.
Today, write out the ploidy of every structure in the worked example for a plant with 2n = 16, without looking.
