Chapter 1: Sexual Reproduction in Flowering Plants

Q11Written answer

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

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Ans: Triple fusion is a process by which male gamete fuses with two polar nuclei within the embryo sac of Flowering Plants. The events taking place in triple fusion are:

The pollen grain germinates by getting dusted on the stigma and giving rise to a pollen tube that enters the ovule.
The pollen tube passes into one of the synergids and releases two male gametes one of which fuses with the egg nucleus and forms a zygote.
The other gamete fuses with the two polar nuclei located in the central cell and forms a triploid endosperm nucleus.

Q12Written answer

Why do you think the zygote is dormant for some time in a fertilized ovule?

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Ans: Zygotes become embryos after resting for a while. Until some amount of endosperm forms, most zygotes remain dormant. Developing embryos need this nutrition to grow and develop properly.

Q13Multiple choice

Differentiate between:

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Correct option: A

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Ans:

(a) Hypocotyl and Epicotyl;

Epicotyl	Hypocotyl
This is the part of the embryonal axis between plumule and cotyledon nodes.	The area between the cotyledonary node and radicle forms part of the embryonal axis.
When epicotyl 2 elongates during hypogeal germination, the soil retains the cotyledons.	Hypocotyls extend so that cotyledons emerge from the soil during epigeal germination.
Epicotyls have plumules at their terminal ends.	Hypocotyls have radicals at their terminal ends.

(b) Coleoptile and Coleorhiza;

Coleoptile	Coleorhiza
A foliar structure called the coleoptile surrounds the epicotyl and a leaf primordium.	Roots and their caps are enclosed in a sheath called a coleorhiza.
It protects the plumule during emergence from soil.	For the first leaf to appear, there is an opening at the end of the coleoptile. The coleorhiza is a solid structure.
Plumules are protected from the soil when they emerge from soil.	Radicles are not protected when they pass through the soil.
It grows much beyond the grain	After emergence from grain, it stops growing
Coleoptile after emergence from soil	Coleorhiza does not come out of the soil.
Germination occurs when the seed becomes green and begins to photosynthesize.	It remains nongreen

(c) Integument and Testa;

Integument	Testa
The ovule is covered by this membrane.	In other words, it is the outer covering of a seed.
There are two or three layers, and it is thin.	It is layered and quite thick.
Live cells make up its structure.	Cells in it are no longer alive.
There are no sclereids.	Sclereids are found in abundance in cells.
The ovule produces it at the chalazal end.	The ovule outer integument is the source of the ovule structure.
The integument is pre fertilised.	Structures that develop postfertilization are called testa

(d) Perisperm and Pericarp.

Perisperm	Pericarp
It serves as the nucleus of the seed.	From the ovary wall develops a covering for the fruit.
Seeds contain it.	It is a component of fruit.
Usually, it is dry.	There is no moisture or flesh in it.
Many times, seeds do not function properly.	Protection and nutrition are also provided by this covering.
Seeds without perisperm are rare.	Every fruit contains this.

Q14Written answer

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

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Ans: True fruit is an ovary that has ripened botanically. Often called false fruits, these are fruits in which the thalamus, floral parts, and ovary are present. Apple is derived from the thalamus and is hence called a false fruit. Mainly the fleshy thalamus of apples can be eaten—the ovaries from a parthenocarpic fruit after or without fertilisation.

Q15Written answer

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

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Ans: The stem of a flower bud is systematically excised to remove the anthers and stamens before they die. In order to minimize self-pollination, this is done. Hybridization by artificial means includes emasculation. This method is used by plant breeders to prevent the pollination of adjacent flowers and pollinate stigmas with pollen of the desired variety.

Q16Written answer

If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?

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Ans: The fruit of the parthenocarpy is seedless. The ovary does not fertilize them before they develop. A few seedless fruits are of great economic importance, such as banana, grape, orange, pineapple, guava, watermelon, and lemon. In fruits with edible seeds or seeds (e.g., pomegranates), parthenocarpy is not selected.

Q17Written answer

Explain the role of tapetum in the formation of pollen-grain walls.

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Ans: Microsporangia are surrounded by a thin layer called the tapetum. Multinucleated and polyploidy tapetal cells make up the tissue. Pollen grains develop as a result of them. Ubisch bodies are found in these cells and contribute to the ornamentation of the microspores and pollen grains. Sporopollenin is a substance produced by the Ubisch bodies of the tapetal cells. This substance is present on the exine layer of pollen grains. A spiny appearance is attributed to the exine of pollen grains due to the presence of this compound.

Q18Written answer

What is apomixis and what is its importance?

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Ans: The asexual reproduction process of apomixis results in seeds without fertilization, such as in certain species of Asteraceae and Grasses. The hybrid seed industry relies on this method. Increasing productivity is the leading reason for cultivating hybrids. However, the main problem is the need to grow hybrid seeds annually since seeds from hybrid plants do not preserve hybrid characteristics for long periods because of the segregation of characters. By introducing apomixis into hybrid seeds, this can be avoided. As a result, scientists are seeking genes associated with apomixis.

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