What traumatic event does Zitkala-Sa describe at the school?

The forcible cutting of her long hair

Why was the cutting of her hair so humiliating to Zitkala-Sa?

Among her people, shingled hair was worn by cowards and mourners

What is the ploidy of the primary endosperm nucleus and why?

It is triploid (3n) because one haploid male gamete fuses with the central cell containing two haploid polar nuclei during triple fusion.

Define double fertilisation.

It is the fusion of one male gamete with the egg cell (syngamy) and the second male gamete with the central cell (triple fusion), a phenomenon unique to angiosperms.

What is the function of the tapetum in the anther?

The tapetum is the innermost wall layer of the microsporangium that nourishes the developing pollen grains and provides materials for the pollen wall (sporopollenin).

Name the cells present in a typical mature embryo sac.

One egg cell, two synergids, three antipodal cells and one central cell with two polar nuclei (7 cells, 8 nuclei).

What is sporopollenin and why is it significant?

Sporopollenin is the highly resistant material forming the exine of pollen, resistant to high temperature, acids and enzymes, making pollen well preserved as fossils.

Differentiate between autogamy and xenogamy.

Autogamy is self-pollination within the same flower, while xenogamy is cross-pollination involving transfer of pollen to the stigma of a genetically different flower.

What is the role of synergids in fertilisation?

Synergids contain the filiform apparatus that guides the entry of the pollen tube into the embryo sac toward the egg apparatus.

What is parthenocarpy?

It is the development of fruit without fertilisation, producing seedless fruits such as in banana.

How does self-incompatibility promote cross-pollination?

It is a genetic mechanism that prevents pollen of a flower from fertilising its own ovules by inhibiting pollen germination or pollen tube growth.

What develops into the seed coat and what into the embryo?

The integuments of the ovule develop into the seed coat, while the zygote (formed from egg and male gamete) develops into the embryo.

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Chapter 1: Sexual Reproduction in Flowering Plants — Class 12 Biology

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Chapter 1: Sexual Reproduction in Flowering Plants

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What is the ploidy of the primary endosperm nucleus in angiosperms?

Summary

This chapter examines how flowering plants reproduce sexually through the flower, the reproductive structure of angiosperms. The androecium produces microspores in the anther through microsporogenesis, yielding pollen grains that carry the male gametophyte. The gynoecium, with ovary, style and stigma, develops ovules in which a megaspore mother cell undergoes megasporogenesis to form the embryo sac (female gametophyte), typically an 8-nucleate, 7-celled structure with an egg, two synergids, three antipodals and a central cell with two polar nuclei. Pollination transfers pollen to the stigma and may be self (autogamy, geitonogamy) or cross (xenogamy), aided by wind, water, insects and other agents, with floral devices like dichogamy and self-incompatibility promoting outcrossing. After pollination the pollen tube grows through the style to the embryo sac, where double fertilisation occurs: one male gamete fuses with the egg (syngamy) forming the zygote, and the other fuses with the central cell forming the triploid primary endosperm nucleus. The zygote develops into an embryo, the ovule into a seed and the ovary into fruit. The chapter also covers apomixis, polyembryony and pollen-pistil interaction, linking these to plant breeding and crop improvement.

Flower structure and pre-fertilisation eventsMicrosporogenesis and pollen grainMegasporogenesis and embryo sacPollination and outbreeding devicesDouble fertilisationPost-fertilisation: seed and fruit, apomixis

Key terms

Microsporogenesis

Formation of haploid microspores (pollen grains) from a diploid microspore mother cell through meiosis in the anther.

Embryo sac

The female gametophyte of angiosperms, typically a 7-celled, 8-nucleate structure formed within the ovule.

Double fertilisation

The fusion of one male gamete with the egg (syngamy) and another with the central cell (triple fusion), unique to angiosperms.

Pollination

Transfer of pollen grains from the anther to the stigma, either within a flower or between flowers.

Endosperm

Triploid nutritive tissue formed from the primary endosperm nucleus that nourishes the developing embryo.

Apomixis

Production of seeds without fertilisation, a form of asexual reproduction mimicking sexual reproduction.

Important questions

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Formation of haploid microspores (pollen grains) from a diploid microspore mother cell through meiosis in the anther.

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Practice quiz · Sexual Reproduction in Flowering Plants

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