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|Chapter||2. Sexual Reproduction In Flowering Plants|
|Category||NCERT Solutions for Class 12|
Our NCERT Solutions for Class 12 Biology is a great resource for students preparing for boards or competitive exams, such as the NEET. These Biology Class 12 Solutions are made by expert faculties, keeping the latest curriculum in mind. Besides helping students with understanding the concepts of Biology, these solutions are also helpful in writing accurate answers that are vital to score full marks in examinations. On this page, we have given the Class 12 Biology Chapter 2: Sexual Reproduction In Flowering Plants Solutions.
NCERT Solutions for Class 12 Biology Chapter 2
Sexual Reproduction In Flowering Plants Solutions
Q1) Name the parts of an angiosperm flower in which development of male and female gametophyte take place.
Answer) The male gametophyte or the pollen grain develops inside the pollen chamber of the anther, whereas the female gametophyte (also known as the embryo sac) develops inside the nucellus of the ovule from the functional megaspore.
Q2) 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.
|It is the process of the formation of microspore tetrads from a microspore mother cell through meiosis.||It is the process of the formation of the four megaspores from a megaspore mother cell in the region of the nucellus through meiosis|
|It occurs inside the pollen sac of the anther.||It occurs inside the ovule.|
|Pollens are produced by microsporogenesis.||Embryo sacs are produced by megasporgenesis.|
|The arrangement of microspores is tetrahedral.||The arrangement of megaspores is linear.|
Meiotic cell division occurs during megasporogenesis and microsporogenesis. It is also known as reductional division that leads to the production of haploid gametes.
The structures formed at the end of these events are:
- Microsporogenesis – Pollen grain
- Megasporogenesis – Embryo sac
Q3) Arrange the following terms in the correct developmental sequence:
Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes
Answer) The correct development sequence is as follows:
Sporogenous tissue – pollen mother cell – microspore tetrad – Pollen grain – male gamet
During the development of microsporangium, each cell of the sporogenous tissue acts as a pollen mother cell and gives rise to a microspore tetrad, containing four haploid microspores by the process of meiosis (microsporogenesis). As the anther matures, these microspores dissociate and develop into pollen grains. The pollen grains mature and give rise to male gametes.
Q4) With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.
Answer) An ovule is a female megasporangium where the formation of megaspores takes place.
The various parts of an ovule are:
- Funiculus – It is a stalk-like structure which represents the point of attachment of the ovule to the placenta of the ovary.
- Hilum – It is the point where the body of the ovule is attached to the funiculus.
- Integuments –They are the outer layers surrounding the ovule that provide protection to the developing embryo.
- Micropyle – It is a narrow pore formed by the projection of integuments. It marks the point where the pollen tube enters the ovule at the time of fertilization.
- Nucellus – It is a mass of the parenchymatous tissue surrounded by the integuments from the outside. The nucellus provides nutrition to the developing embryo. The embryo sac is located inside the nucellus.
- Chalazal – It is the based swollen part of the nucellus from where the integuments originate.
Q5) What is meant by monosporic development of female gametophyte?
Answer) Monosporic development is the development of female gametophyte from one functional megaspore. In angiosperms, a single diploid mother megaspore undergoes meiotic division to form four megaspores (haploid). Only one out of the four megaspores is functional that forms a female gametophyte, while the rest of the three degenerate.
Q6) With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
The female gametophyte (embryo sac) develops from a single functional megaspore. This megaspore undergoes three successive mitotic divisions to form eight nucleate embryo sacs.
The first mitotic division in the megaspore forms two nuclei. One nucleus moves towards the micropylar end while the other nucleus moves towards the chalazal end. Then, these nuclei divide at their respective ends and re-divide to form eight nucleate stages. As a result, there are four nuclei each at both the ends i.e., at the micropylar and the chalazal end in the embryo sac. At the micropylar end, out of the four nuclei only three differentiate into two synergids and one egg cell. Together they are known as the egg apparatus. Similarly, at the chalazal end, three out of four nuclei differentiates as antipodal cells. The remaining two cells (of the micropylar and the chalazal end) move towards the centre and are known as the polar nuclei, which are situated in a large central cell. Hence, at maturity, the female gametophyte appears as a 7-celled structure, though it has 8 nucleate.
Q7) What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Answer) Chasmogamous flowers are the flowers that have open petals such that the reproductive organs are exposed to allow cross-pollination.Cleistogamous flowers are small, closed flowers with unexposed reproductive organs. Therefore, they cannot undergo cross-pollination. However, they undergo self-pollination since the stigma and anther are present near each other.
Q8) Mention two strategies evolved to prevent self-pollination in flowers.
Answer) Self-pollination involves the transfer of pollen from the stamen to the pistil of the same flower. Two strategies that have evolved to prevent self-pollination in flowers are as follows:
- In certain plants, the stigma of the flower hasthecapability to prevent the germination of pollen grains and hence, prevent the growth of the pollen tube. It is a genetic mechanism to prevent self-pollination called self- incompatibility. Incompatibility may be between individuals of the same species or between individuals of different species. Thus, incompatibility prevents breeding.
- In some plants, the gynoecium matures before the androecium or vice-versa. This phenomenon is known as protogyny or protandry respectively. This prevents the pollen from coming in contact with the stigma of the same flower.
Q9) What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Answer) Self-incompatibility refers to a genetically controlled mechanism that prevents self-pollination and promote cross-pollination in flowers. Self-pollination cannot lead to the formation of seeds in a self-incompatible species. This happens because the pollens are unable to fertilize the ovules that would develop into an embryo and hence form seeds.
Q10) What is bagging technique? How is it useful in a plant breeding programme?
ANswer) Various artificial hybridization techniques (under various crop improvement programmes) involve the removal of the anther from bisexual flowers without affecting the female reproductive part (pistil) through the process of emasculation. Then, these emasculated flowers are wrapped in bags to prevent pollination by unwanted pollen grains. This process is called bagging.
This technique is an important part of the plant breeding programme as it ensures that pollen grains of only desirable plants are used for fertilization of the stigma to develop the desired plant variety.
Q11) What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Answer) Triple fusion occurs when a male gamete fuses with two polar nuclei within the embryo sac of flowering plants. The following events take place in triple fusion:
- The pollen grains get dusted on stigma and germinate giving rise to a pollen tube that enters the ovule.
- The pollen tube passes into one of the synergids and release two male gametes.
- One out of the two gametes 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.
The nuclei involved in triple fusion are:
- A male gamete nucleus
- Two polar nuclei
Q12) Why do you think the zygote is dormant for sometime in a fertilized ovule?
Answer) The zygote is formed by the fusion of the male gamete with the nucleus of the egg cell. The zygote remains dormant for some time and waits for the endosperm to form, which develops from the primary endosperm cell resulting from triple fusion. The endosperm provides food for the growing embryo and after the formation of the endosperm, further development of the embryo from the zygote starts.
Q13) Differentiate between:
(a) Epicotyl and hypocotyl
(b) Coleoptile and coleorrhiza
(c) Integument and testa
(d) Perisperm and pericarp
a) Differences between Epicotyl and hypocotyl:
|Terminates at the plumule.||Terminates at the coteladonary node.|
|Starts from coteladonary node.||Starts from the radicle.|
b) Differences between Coleoptile and Coleorrhiza
|It is a protective sheath.||It is an undifferentiated sheath.|
|Comes out of the soil.||Remains inside the soil.|
c) Integument and testa
|Covers the ovule.||Outer covering of seed.|
|Pre-fertilized structure.||Post fertilized structure.|
d) Perisperm and pericarp
|Part of a seed.||Part of a fruit.|
|Non-functional in seed.||Protects the fruit and helps in nutrition and dispersal.|
Q14) Why is apple called a false fruit? Which part(s) of the flower forms the fruit?
Answer) Fruits derived from the ovary and other accessory floral parts are called false fruits. On the contrary, true fruits are those fruits which develop from the ovary, but do not consist of the thalamus or any other floral part. In an apple, the fleshy receptacle forms the main edible part. Hence, it is a false fruit.
Q15) What is meant by emasculation? When and why does a plant breeder employ this technique?
Answer) Emasculation refers to the removal of stamens from bisexual flowers done before the maturation of anther in order to avoid self-pollination in the flowers. This technique is employed when the breeder wants plants of desired characteristics. The flowers are bagged even before the anther mature. When the anther matures, the pollen grains are shed on the covered stigma and are allowed to pollinate with the flowers of the desired characteristics.
Q16) If one can induce parthenocarpy through the application of growth substances, which fruits would you select to induce parthenocarpy and why?
Answer) Parthenocarpy is the process of developing fruits without involving the process of fertilization or seed formation. Therefore, the seedless varieties of economically important fruits such as orange, lemon, water melon etc. are produced using this technique. This technique involves inducing fruit formation by the application of plant growth hormones such as auxins.
Q17) Explain the role of tapetum in the formation pollen-grain wall.
Tapetum is the internal layer of microsporangium and plays an important role in the formation of pollen grain wall. It provides nutrition to the maturing pollen grains. Various amino acids, enzymes, and hormones are produced by tapetum cells that are essential for the maturation of pollen grains. Tapetum also forms the exine layer of pollen grains.
Q18) What is apomixis and what is its importance?
Answer) Apomixis is the mechanism of seed production without involving the process of meiosis and syngamy. It plays an important role in hybrid seed production. The method of producing hybrid seeds by cultivation is very expensive for farmers. Also, by sowing hybrid seeds, it is difficult to maintain hybrid characters as characters segregate during meiosis. Apomixis prevents the loss of specific characters in the hybrid. Also, it is a cost-effective method for producing seeds.
That’s it. These were the solutions of NCERT Class 12 Biology Chapter 2 – Sexual Reproduction In Flowering Plants. Our team hopes that you have found these solutions helpful for you. If you have any doubt related to this chapter then feel free to comment your doubts below. Our team will try their best to help you with your doubts.