Questions: Sexual reproduction in flowering plants

Q1 Where do the two gametophytes of a flowering plant develop?

Answer (English): The male gametophyte, the pollen grain, develops inside the microsporangia of the anther, which is the upper part of the stamen. The female gametophyte, the embryo sac, develops inside the ovule, which lies in the ovary of the pistil. This question is asked as a one-mark identification, so the safe answer names the anther and the ovule rather than the stamen and the pistil.

Hinglish: Male gametophyte yaani pollen grain anther ke microsporangia mein banta hai, aur female gametophyte yaani embryo sac ovule ke andar. Anther stamen ka part hai aur ovule ovary ke andar hota hai, isliye exam mein anther aur ovule likhna zyada sahi hai.

Q2 Describe the structure of a typical stamen and a mature anther.

Answer (English): A stamen has a long slender filament and a terminal anther. The filament attaches to the thalamus or to a petal. The anther is usually bilobed and each lobe is divided into two theca, which makes the anther dithecous. A transverse section shows four microsporangia, two in each lobe, placed at the four corners. The microsporangia extend along the length of the anther, turn into pollen sacs and are packed with pollen grains. Each microsporangium has a wall of epidermis, endothecium, middle layers and tapetum around a central sporogenous tissue.

Hinglish: Stamen mein filament aur anther hote hain. Anther bilobed aur dithecous hota hai, aur transverse section mein chaar microsporangia dikhte hain, har lobe mein do. Anther wall ki chaar layers hoti hain, aur center mein sporogenous tissue hota hai. Ye description exam mein diagram ke saath likhne par poore marks milte hain.

Q3 What is microsporogenesis? Give the sequence of structures formed.

Answer (English): Microsporogenesis is the route from a pollen mother cell to four separate microspores, and meiosis drives it. Cells of the sporogenous tissue in a young anther take on the role of pollen mother cells. A meiotic division in one of them yields a tetrad of four haploid microspores. When the anther matures and dries, the tetrad breaks and the microspores separate. Each isolated microspore develops into a pollen grain. The sequence to write is sporogenous tissue, pollen mother cell, microspore tetrad, microspore and finally pollen grain.

Hinglish: Microsporogenesis mein pollen mother cell meiosis se chaar haploid microspores ka tetrad banata hai. Anther ke mature hone par tetrad toot jata hai aur har microspore pollen grain ban jata hai. Sequence yaad rakho: sporogenous tissue, PMC, tetrad, microspore, pollen grain.

Q4 Explain the structure of a mature pollen grain.

Answer (English): A mature pollen grain is roughly spherical and measures about 25 to 50 micrometres across. Its wall has two layers. The hard outer exine is made of sporopollenin and bears germ pores where the wall is thin. The inner intine is a thin continuous layer of cellulose and pectin. The cytoplasm contains two cells in most species: a large vegetative cell with food reserves and an irregular nucleus, and a small spindle-shaped generative cell. In about forty per cent of species the generative cell divides before shedding, so the pollen grain leaves the anther in the three-celled state carrying two male gametes. Pollen of rice and wheat loses viability within about thirty minutes, while some species stay viable for months or can be stored for years in liquid nitrogen.

Hinglish: Pollen grain ka bahari hissa exine hota hai jo sporopollenin se bana hota hai, aur andar patli intine hoti hai. Zyadatar species mein ek bada vegetative cell aur ek chhota generative cell hota hai; kuch species mein generative cell pehle divide hokar do male gametes de deta hai. Pollen ki viability rice aur wheat mein sirf 30 minute hoti hai, isliye pollen bank ke liye liquid nitrogen use hota hai.

Q5 Describe megasporogenesis and monosporic development.

Answer (English): Megasporogenesis is the meiotic route from a megaspore mother cell to four megaspores. The mother cell forms in the micropylar part of the nucellus, grows large and undergoes meiosis to yield four haploid megaspores. In most flowering plants one megaspore survives and the other three degenerate. The survivor develops into the embryo sac without any fusion, and because the whole female gametophyte comes from a single megaspore, the process is called monosporic development.

Hinglish: Megasporogenesis mein nucellus ki megaspore mother cell meiosis se chaar megaspores banati hai. Inme se sirf ek bachta hai aur baaki teen mar jaate hain. Bacha hua megaspore embryo sac banata hai, aur kyunki poora gametophyte ek hi megaspore se banta hai, isliye ise monosporic development kehte hain.

Q6 Why is the mature embryo sac called seven-celled and eight-nucleate?

Answer (English): The functional megaspore passes through three free nuclear mitotic divisions and reaches the eight-nucleate stage. Cell walls then form and organise the nuclei into cells. At the micropylar end, two synergids and one egg cell together make the egg apparatus. At the chalazal end are three antipodal cells. The remaining two nuclei, the polar nuclei, lie in the central cell. Counting gives seven cells, because the central cell contains two nuclei, and eight nuclei in all. The synergids carry the filiform apparatus that guides the pollen tube.

Hinglish: Aath nuclei saat cells mein bat jaate hain: micropylar end par do synergids aur ek egg, chalazal end par teen antipodals, aur beech mein ek central cell jisme do polar nuclei hoti hain. Isliye embryo sac 7-celled, 8-nucleate kehlata hai. Filiform apparatus synergids mein hota hai aur pollen tube ko rasta dikhata hai.

Q7 Distinguish autogamy, geitonogamy and xenogamy.

Answer (English): Autogamy keeps the pollen within one blossom: a grain moves from an anther to a stigma of that same flower. Geitonogamy takes pollen to a different blossom, but one that grows on the same individual plant. Xenogamy carries pollen to a blossom on another plant entirely. Autogamy is selfing in the strict sense. Geitonogamy needs an external agent and looks like cross-pollination, but genetically it is selfing because both flowers belong to the same plant. Xenogamy alone brings pollen with a different genetic constitution to the stigma.

Hinglish: Autogamy same flower mein pollination hai, geitonogamy same plant ke doosre flower mein, aur xenogamy doosre plant ke flower mein. Geitonogamy bahar se cross-pollination lagti hai par genetically selfing hi hai. Sirf xenogamy hi naye gene combinations laati hai.

Q8 What adaptations help wind-pollinated and water-pollinated flowers?

Answer (English): Wind-pollinated flowers make light, dry and non-sticky pollen that air currents can lift. Their stamens are well exposed, their stigmas are large and often feathery, and many flowers are packed into an inflorescence. They usually have one ovule per ovary and do not invest in colour or nectar. Water-pollinated flowers are rare, found in about thirty genera, mostly monocots. In Vallisneria the female flower reaches the water surface and pollen floats to it. In seagrasses the pollen is long and ribbon-like and is carried underwater. A mucilaginous covering protects pollen from wetting, and these flowers are also dull and nectar free.

Hinglish: Wind pollination mein pollen halka aur non-sticky hota hai, stamens bahar nikalte hain aur stigma feathery hota hai. Water pollination sirf kuch genera mein hoti hai, jaise Vallisneria aur Zostera; pollen ke chaaron taraf mucilage layer bachati hai. Dono tarah ke flowers mein colour aur nectar nahi hota kyunki koi animal unhe dekhne nahi aata.

Q9 What is double fertilisation? Name the two fusions and their products.

Answer (English): Double fertilisation is the occurrence of two fusion events in one embryo sac. The pollen tube enters a synergid and releases two male gametes. One fuses with the egg nucleus, which is syngamy, and the product is the diploid zygote. The other fuses with the two polar nuclei in the central cell, which is triple fusion, and the product is the triploid primary endosperm nucleus. The central cell becomes the primary endosperm cell. Double fertilisation is unique to flowering plants.

Hinglish: Double fertilisation mein do fusions hoti hain. Syngamy mein male gamete egg se milta hai aur 2n zygote banta hai. Triple fusion mein doosra male gamete do polar nuclei se milta hai aur 3n PEN banta hai. Ye process sirf angiosperms mein hota hai, aur central cell phir primary endosperm cell ban jaati hai.

Q10 How does a seed form, and what is apomixis?

Answer (English): After fertilisation the ovule becomes the seed and the ovary becomes the fruit. Integuments give the seed its coat. The zygote becomes the embryo, while the endosperm is built by the primary endosperm cell. Some seeds hold on to that endosperm, as wheat and castor do, and others spend it completely, as pea and groundnut do. Apomixis is the formation of seed without fertilisation. The embryo may arise from a diploid egg cell that skipped meiosis, or from nucellar cells that grow into the embryo sac, as in many Citrus and mango varieties. Apomictic seedlings are genetically identical to the parent, which is why apomixis is studied for hybrid seed production.

Hinglish: Fertilisation ke baad ovule seed aur ovary fruit ban jaati hai. Integuments seed coat bante hain, zygote embryo banata hai. Apomixis mein bina fertilisation seed banta hai, kabhi diploid egg se aur kabhi nucellar cells se. Iske offspring parent ke clone hote hain, isliye hybrid seed industry ke liye ye important hai.

That closes the ten questions. When you are ready, take the five-question quiz below to check the definitions that exams repeat most often: the number of microsporangia, the filiform apparatus, the ploidy of the endosperm nucleus and the apomixis examples. If any answer feels slow, go back to the concept page that covers it and read only that page again.