Important Questions on Sexual Reproduction in Flowering plants
Question 1.
What is meant by monosporic development of female gametophyte? Solution
Since only one of the (four) megaspores formed by a megaspore mother cell, develops into the embryo sac, the type of development is described as monosporic development.
Question 2. Differentiate between:
(a) Hypocotyls and epicotyls Solution
Hypocotyl
Epicotyls
Hypocotyls is the region of embryonal axis between the radicle and the point of attachment of cotyledons.
Epicotyl is the region of embryonal axis between the plumule and the point of attachment of cotyledons.
Filiform apparatus refers to the special cellular thickening in the synergids, toward micropylar tips.
Question 6. How is it possible in oxalis and viola plants to produce assured seed- sets even in the absence of pollinators?
Or
Pea flowers produce assured seed- sets. Give a reason. Solution
Oxalis and viola or pea produce cleistogamous flowers, in which anthers and stigma lie close to each other; when the anthers dehisce in the flower buds, the pollen grains fall on the stigma and fertilization is affected leading to assured seed- set.
Question 7.
Name the part of the flower, which the tassels of the corn cab represent. Solution
Styles and stigmas
Question 8. Why do corn cobs have long tassels? Solution
The long tassels of corn cob are the styles and stigmas; they are meant to easily trap the air- borne pollen grains.
Question 9.
How are the pollen grains protected from wetting by water, in case of hydrophily?
Or
How do the pollen grains of vallisneria protect themselves? Solution
Pollen grains of vallisneria are protected from wetting by the mucilaginous covering.
Question 10.
Name the seeds that have retained their viability for thousands of years? Solution
Lupinus arcticus and Phoenix dactylifera
Question 11. Name two parasitic species of plants that produce many minute seeds in a fruit. Solution
Orobanche and striga
Question 12.
Differentiate between the two cells enclosed in a mature male gametophyte of an angiosperm. Solution
Question 13.
Not all hydrophytes are pollinated by water. Justify by giving two examples. Solution
Those hydrophytes whose flowers emerge above the surface of water, are pollinated by insects or wind, e.g. Water hyacinth and water lily are pollinated by insects.
Question 14.
How is pollination affected in sea grasses? Solution
In sea grasses, the female flowers remain submerged in water.
The pollen grains are released inside the water.
Pollen grains are long and ribbon- like; they are carried passively by water.
Some of them reach the stigma and achieve pollination.
Question 15.
Explain the mutually rewarding relationship between yucca plant and a species of moth. Solution
The plant Yucca and the moth, both of them cannot complete their life cycles without each other.
The moth deposits its eggs in the locule of the ovary; during this the flower gets pollinated by the moth.
The larvae of the moth come out of the eggs, when the seeds start developing; some of the seeds are eaten by the larvae.
Question 16.
Name the product of fertilization that forms the kernel of coconut. How does the kernel differ from coconut water? Solution
Primary endosperm cell forms the kernel of coconut. Difference: The kernel of coconut is the cellular endosperm, while the coconut water is the free- nuclear endosperm.
Question 17.
How is parthenocarpy different from parthenogenesis? Give an example of each. Solution
Question 18.
Why are some seeds of citrus referred to as polyembryonic? How are they formed?
Or
if you squeeze a seed of orange, you might observe May embryos of different sizes. How is it possible? Explain. Solution
It is a case of polyembryony, the phenomenon of occurrence of more than one embryo in a seed.
It is possible in the following ways:
Some of the nucellar cells surrounding the embryo sac start dividing produce into the embryo sac and develop into embryos.
Synergids of the embryo sac divide and form embryos.
Question 19.
Name and explain the mechanism by which seeds from hybrid plants are developed that are able to retain the desired hybrid character in the progeny . Solution
Apomixis is the mechanism.
It refers to the form of asexual reproduction that mimics sexual reproduction and seeds are formed without fertilization.
If the hybrid seeds are made into apomictic seeds, there will be no segregation of the hybrid characters in the progeny plants and they will be maintained for a number of generations.
Question 20.
What will be the advantage of making the hybrids into apomicts? Why? Solution
In general, the hybrid characters segregate in every generation and are not maintained.
The production of hybrid seed is costly and is too expensive for the farmers.
If the hybrids are made into apomicts, there will be no segregation of the hybrid/ desirable characters in the progeny plants and seeds can be collected from the plants generation after generation and used for raising the new plants.
Question 21. How are cleistogamous and chasmogamous flowers different from each other? Give an example for each. Solution
Question 22.
Describe the endosperm development in coconut.
Why is tender coconut considered a healthy source of nutrition?
How are pea seeds different from castor seeds with respect to endosperm?
The primary endosperm nucleus of the primary endosperm cell undergoes repeated mitotic divisions, to give rise to a number of free nuclei; at this stage, the endosperm is called free nuclear endosperm.
Subsequently, cell wall formation starts from the periphery and the endosperm becomes cellular.
The water in the tender coconut represents the nuclear endosperm, while the white kernel represents the cellular endosperm.
Since the endosperm cells are rich in stored food materials, it is a healthy source of nutrition.
Pea seeds are non-endospermic, while castor seeds are endospermic.
Question 23.
A flower of a tomato plant following the process of sexual reproduction produces 240 viable seeds. Answer the following questions giving reasons.
What is the minimum number of pollen grains that must have been involved in the pollination of its pistil?
What would have been the minimum number of ovules present in the ovary?
How many megaspore mother cells are involved?
What is the minimum number of microspore mother cells involved in the above case?
240 pollen grains; each ovule requires one pollen grain for fertilization.
240 ovules; each ovule becomes a seed and 240 ovules become 240 seeds.
240 megaspore mother cells; though each megaspore mother cell forms four megaspores by meiosis, only one megaspore forms the female gametophyte in an ovule.
60 microspore mother cells; each microspore mother cell undergoes meiosis to form four microspores, each of which forms a pollen grain.
480 male gametes; each ovule requires two male gametes for fertilization (double fertilization).
Question 24. Give reason why?
Most zygotes in angiosperms divide only after a certain amount of endosperm is formed.
Groundnut seeds are exalbuminous and castor seeds are albuminous.
Micropyle remains as a small pore in the seed coat of a seed.
Integuments of an ovule harden and the water content is highly reduced, as the seed matures.
The zygote starts dividing only after a certain amount of endosperm is formed as an adaptation to provide assured nutrition to the developing embryo; hence we can say it remains dormant for some time.
In groundnut, the developing embryo utilizes the endosperm completely; there is no residual endosperm is not completely used so the seed is exalbuminous
In castor; the endosperm is not completely used up by the developing embryo; there is some amount of endosperm left in the seeds and hence the seeds are albuminous.
The integuments encircle the ovule except at the tip, leaving a small opening, called micropyle.
As the integuments harden as the seed coat the micropyle remains as a small opening or pore in the seed coat.
The micropyle facilitates the entry of water and oxygen into the seed during germination.
The integuments harden as a seed coat to protect the embryo.
The moisture content is reduced and the seed becomes dry(with only 10-15% of moisture by mass), so that the general metabolic activity of the seed decreases and the seed can enter a state of inactivity, called dormancy, to tide over the unfavorable conditions.
Since the thalamus (a part other than the ovary) contributes to fruit formation, these fruits are not true fruits; they are called false fruits.
Question 25. Explain the role of tapetum in the formation of pollen-grain wall? Solution
Tapetum provides nourishment to the developing pollen-grains.
Its cells produce various enzymes, hormones, amino acids, and other nutritious material, which are essential for the development of pollen grains.
It secretes sporopollenin, which is required for the formation of exine of the pollen grains.
