Question 1

Name the parts of an angiosperm flower in which development of male and female gametophyte take place.

Accepted Answer

In an angiosperm flower, the male gametophyte develops in the anther, specifically in the pollen sacs where microspores develop into pollen grains. The female gametophyte develops in the ovule, specifically within the nucellus where the megaspore develops into the embryo sac. — The male gametophyte (pollen grain) originates from microspores formed in the anther. The female gametophyte (embryo sac) develops from the megaspore inside the ovule.

Question 2

Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structures formed at the end of these two events.

Accepted Answer

Microsporogenesis is the process of formation of microspores from microspore mother cells (pollen mother cells) in the anther, whereas megasporogenesis is the formation of megaspores from the megaspore mother cell in the ovule. Both processes involve meiosis (reduction division). At the end of microsporogenesis, a tetrad of haploid microspores is formed, which develop into pollen grains (male gametophyte). At the end of megasporogenesis, typically four haploid megaspores are formed, but usually only one functional megaspore survives and develops into the female gametophyte (embryo sac). — Both microsporogenesis and megasporogenesis involve meiosis to reduce the chromosome number from diploid to haploid. Microsporogenesis produces microspores (male spores), while megasporogenesis produces megaspores (female spores). The structures formed are microspore tetrads and megaspore(s), respectively.

Question 3

Arrange the following terms in the correct developmental sequence: Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Accepted Answer

The correct developmental sequence is: Sporogenous tissue → Pollen mother cell → Microspore tetrad → Pollen grain → Male gametes.
Explanation:
- Sporogenous tissue differentiates into pollen mother cells.
- Pollen mother cells undergo meiosis to form microspore tetrads.
- Microspores develop into pollen grains (male gametophyte).
- Pollen grains produce male gametes (sperm cells) by mitosis. — This sequence follows the developmental stages from diploid sporogenous tissue to haploid male gametes through meiosis and mitosis.

Question 4

With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Accepted Answer

A typical angiosperm ovule consists of the following parts:
1. Funiculus: A stalk that attaches the ovule to the placenta.
2. Hilum: The point of attachment of the ovule to the funiculus.
3. Integuments: One or two protective layers surrounding the nucellus, leaving a small opening called micropyle.
4. Micropyle: The opening through which the pollen tube enters.
5. Nucellus: The central tissue containing the embryo sac (female gametophyte).
6. Embryo sac: The female gametophyte inside the nucellus.

[Diagram should show all these parts clearly labelled.]

Explanation:
The integuments protect the nucellus and embryo sac. The micropyle allows entry of the pollen tube. The funiculus connects the ovule to the ovary wall. — The ovule structure is essential for fertilization and seed development. The labelled diagram helps to visualize the spatial arrangement of these parts.

Question 5

What is meant by monosporic development of female gametophyte?

Accepted Answer

Monosporic development of female gametophyte means that the embryo sac (female gametophyte) develops from a single functional megaspore out of the four megaspores formed after meiosis during megasporogenesis. The other three megaspores degenerate, and only one megaspore undergoes mitotic divisions to form the embryo sac. — This is the most common type of development in angiosperms, where only one megaspore contributes to the formation of the female gametophyte.

Question 6

With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.

Accepted Answer

The female gametophyte (embryo sac) in angiosperms is typically 7-celled and 8-nucleate.

Explanation:
- It develops from one functional megaspore which undergoes three rounds of mitotic division to form eight nuclei.
- These eight nuclei are arranged as follows:
  * Three antipodal cells at the chalazal end (3 nuclei, 3 cells).
  * Two polar nuclei in the central cell (2 nuclei, 1 cell).
  * One egg cell and two synergids at the micropylar end (3 nuclei, 3 cells).

Thus, total cells = 7 (3 antipodals + 1 central cell + 1 egg cell + 2 synergids) and total nuclei = 8 (including the two polar nuclei in the central cell).

[Diagram should show the arrangement of these cells and nuclei clearly labelled.]

This structure is important for fertilization and subsequent development of the embryo and endosperm. — The 7-celled, 8-nucleate structure is characteristic of the Polygonum type of embryo sac development, the most common type in angiosperms.

Question 7

What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Accepted Answer

Chasmogamous flowers are flowers that open up at maturity, exposing their stamens and pistils, thus allowing pollination by external agents like wind or insects.

Cleistogamous flowers are flowers that do not open at all and remain closed. Cross-pollination generally does not occur in cleistogamous flowers because the flower remains closed, preventing pollen from other flowers from reaching the stigma. Pollination in cleistogamous flowers is usually self-pollination.

Therefore, cross-pollination is not possible in cleistogamous flowers due to their closed nature, which restricts pollen transfer from other flowers. — Chasmogamous flowers facilitate cross-pollination by opening, while cleistogamous flowers promote self-pollination by remaining closed.

Question 8

Mention two strategies evolved to prevent self-pollination in flowers.

Accepted Answer

Two strategies to prevent self-pollination in flowers are:
1. Dichogamy: Temporal separation of maturation of stamens and pistils, e.g., in sunflower.
2. Herkogamy: Spatial separation of anthers and stigma, e.g., in mustard.

Other strategies include self-incompatibility and production of unisexual flowers. — These mechanisms reduce the chances of pollen from the same flower fertilizing the ovules, promoting genetic diversity through cross-pollination.

Question 9

What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?

Accepted Answer

Self-incompatibility is a genetic mechanism in flowering plants that prevents self-pollination and promotes cross-pollination by rejecting pollen from the same plant or genetically similar plants.

In self-incompatible species, when pollen from the same plant lands on the stigma, the pollen tube growth is inhibited or the pollen fails to fertilize the ovule, thus preventing seed formation.

This mechanism ensures genetic diversity by avoiding inbreeding and promoting outcrossing. — Self-incompatibility involves recognition and rejection of self-pollen at the stigma or style, preventing fertilization and seed development from self-pollination.

Question 10

What is bagging technique? How is it useful in a plant breeding programme?

Accepted Answer

Bagging technique involves covering the flowers with a bag (usually made of paper or cloth) to prevent unwanted pollen from reaching the stigma. This technique is used to control pollination.

In plant breeding programmes, bagging is useful to ensure controlled pollination, either self-pollination or cross-pollination with selected pollen, thus producing desired hybrids or pure lines. — By preventing contamination from unwanted pollen, bagging helps breeders maintain genetic purity and achieve specific breeding objectives.

Question 11

What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

Accepted Answer

Triple fusion is the fusion of one male gamete nucleus with two polar nuclei in the central cell of the embryo sac, resulting in the formation of a triploid (3n) primary endosperm nucleus.

It takes place in the embryo sac (female gametophyte) after one male gamete fertilizes the egg cell (syngamy). The other male gamete fuses with the two polar nuclei located in the central cell.

The nuclei involved are:
- One male gamete nucleus
- Two polar nuclei

This event leads to the formation of endosperm, which nourishes the developing embryo. — Triple fusion is a unique feature of angiosperm fertilization and is essential for endosperm development.

Question 12

Why do you think the zygote is dormant for sometime in a fertilised ovule?

Accepted Answer

The zygote remains dormant for some time in a fertilised ovule to allow the endosperm to develop and provide nourishment. This dormancy ensures that the embryo develops only when sufficient nutrients are available for its growth. — The delay in zygote development coordinates embryo growth with endosperm formation, optimizing seed development.

Question 13

Differentiate between:
(a) hypocotyl and epicotyl;
(b) coleoptile and coleorrhiza;
(c) integument and testa;
(d) perisperm and pericarp.

Accepted Answer

(a) Hypocotyl vs Epicotyl:
- Hypocotyl is the part of the embryo axis below the cotyledons and above the radicle.
- Epicotyl is the part of the embryo axis above the cotyledons and below the plumule.

(b) Coleoptile vs Coleorrhiza:
- Coleoptile is a protective sheath covering the young shoot in monocot embryos.
- Coleorrhiza is a protective sheath covering the young root (radicle) in monocot embryos.

(c) Integument vs Testa:
- Integuments are the protective layers surrounding the nucellus in the ovule.
- Testa is the outer seed coat formed from the integuments after fertilization.

(d) Perisperm vs Pericarp:
- Perisperm is nutritive tissue derived from the nucellus in some seeds.
- Pericarp is the fruit wall developed from the ovary wall after fertilization. — These pairs represent different parts of seed and fruit anatomy with distinct origins and functions.

Question 14

Why is apple called a false fruit? Which part(s) of the flower forms the fruit?

Accepted Answer

Apple is called a false fruit because the edible part is not derived from the ovary but from the thalamus (receptacle) of the flower. The actual fruit develops from the ovary inside the apple and forms the core containing seeds.

Thus, the thalamus forms the fleshy edible part, while the ovary forms the core. — False fruits develop from floral parts other than the ovary, unlike true fruits which develop solely from the ovary.

Question 15

What is meant by emasculation? When and why does a plant breeder employ this technique?

Accepted Answer

Emasculation is the removal of anthers from a bisexual flower before they mature and release pollen to prevent self-pollination.

Plant breeders employ emasculation during hybridization to ensure controlled cross-pollination by preventing self-pollination and allowing pollen from the desired male parent to fertilize the female parent. — This technique is essential in producing hybrids with desired traits by controlling the source of pollen.

extinction. Reproduction becomes a vital process without

extinction. Reproduction becomes a vital process without — Study Notes

Introduction to Reproduction

1.1 Flower – A Fascinating Organ of Angiosperms

1.2 Pre-fertilisation: Structures and Events

Practice Questions — extinction. Reproduction becomes a vital process without

All 13 Chapters in Biology