Biology · Plant Kingdom · NEET
Start with the big plant (Pinus tree) = diploid (2n) sporophyte. It makes two kinds of cones. In the male cone, microsporophylls carry microsporangia; inside them, microspore mother cells do meiosis to make haploid microspores. Each microspore becomes a pollen grain (the tiny male gametophyte). In the female cone, the ovule holds the megasporangium (nucellus); a megaspore mother cell does meiosis, and one megaspore survives and grows into the female gametophyte, which forms archegonia (each with an egg). Wind carries pollen to the ovule. A pollen tube grows and carries the male gamete to the egg. Fertilisation makes a 2n zygote, which grows into an embryo. The whole ovule now becomes a SEED. Because no ovary wall covers it, the seed is naked.
YES, gymnosperms DO form a pollen tube. This is a very common NEET trap. Wind first carries the pollen grain to the mouth of the ovule. Then the pollen grain grows a pollen tube that carries the male gametes down to the archegonia and releases them near the egg. So both statements are true: wind does the long-distance travel, and a pollen tube does the final short delivery. Do NOT think 'no pollen tube' just because pollination is by wind.
The male gametophyte is the pollen grain, which develops from a microspore. In Pinus it is winged (two air bladders) so wind can carry it. The female gametophyte develops from the megaspore inside the ovule and bears the archegonia (each holding an egg). Key point for NEET: neither gametophyte is free-living. Both are very reduced and stay inside the sporangia/ovule on the parent sporophyte (2026 NEET tested exactly this).
'Gymnosperm' means gymnos = naked, sperma = seed. The ovules sit exposed on the megasporophyll, with NO ovary wall around them, both before and after fertilisation. Since there is no ovary, there is no fruit, so the seed that forms stays uncovered on the cone. In angiosperms the ovule is inside an ovary that becomes a fruit, so their seeds are enclosed, not naked. This one difference is the most tested gymnosperm fact in NEET.
The dominant phase is the DIPLOID (2n) sporophyte, i.e. the big Pinus/Cycas plant itself. The gametophytes (pollen grain and female gametophyte) are haploid (n) but tiny and dependent. This is the same pattern as angiosperms and opposite to bryophytes (where the haploid gametophyte dominates). Remember: in all seed plants (gymnosperms + angiosperms), the sporophyte rules and the gametophyte is reduced.
Meiosis happens twice, in the spore mother cells. (1) In the microsporangium, the microspore mother cell undergoes meiosis to give haploid microspores. (2) In the megasporangium (nucellus of the ovule), the megaspore mother cell undergoes meiosis; usually one of the four cells becomes the functional megaspore. So meiosis makes the spores (spores are haploid), and the gametes are then made by mitosis inside the gametophytes. This is called sporic meiosis.
Assertion A: In gymnosperms the pollen grains are released from the microsporangium and carried by air currents. Reason R: Air currents carry the pollen grains to the mouth of the archegonia where the gametes are discharged and pollen tube is not formed.
Statement I: In gymnosperms, the male and female gametophytes remain within the sporangia. Statement II: In gymnosperms, seeds are not covered.
Winged pollen grains are present in
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Heterosporous. They make two kinds of spores: small microspores (which form the male gametophyte/pollen) and large megaspores (which form the female gametophyte). Homosporous would mean only one kind of spore, which is wrong for gymnosperms.
No. Unlike bryophytes and pteridophytes, gymnosperms do not need water for fertilisation. Wind carries the pollen and a pollen tube delivers the male gamete, so water is not required. This is one advantage of the seed habit.
No. Gymnosperms have cones (strobili), not flowers, and the seeds are naked because there is no ovary and therefore no fruit. Flowers and fruits with enclosed seeds are features of angiosperms.
The ovule becomes the seed after fertilisation. The zygote grows into the embryo, the female gametophyte tissue stores food, and the outer layers harden into the seed coat. The seed sits exposed on the megasporophyll, so it is called a naked seed.
