Biology Sexual Reproduction in Flowering Plants Chapter 2 – Exercise : NCERT solutions of Biology chapter 2 exercises. We mentioned all important questions below check them, Or you can just directly download question paper. But you will get solutions in this page only. So you can book mark this page and you will find it easily.
Q.1 Name the parts of an angiosperm flower in which development of male and female gamete take place.
Male gamete develops in microspore inside the pollen grains released from anther. Female gamete develops from megaspore inside the ovule.
Q.2 Differentiate between microsporogenesis and megasporogenesis. Which type of cell division occurs during these events? Name the structure formed at the end of these two events.
Ans. Microsporogenesis occurs inside the pollen sacs of the anthers. During this process meiosis occurs in microspore mother cells resulting in the formation of microspores.
Megasporogenesis occurs inside the ovule where one of the sporogenous cell of nucleus acts as megaspore mother cell. During this process, meiosis occurs resulting in the formation of megaspore.
Q.3 Arrange the following terms in a correct developmental sequence:
Pollen grains, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.
Ans. The correct sequence is sporogenous tissue, pollen mother cell, microspore tetrad, pollen grain and male gamete.
Q.4 With a neat labeled diagram, describe the parts of a typical angiosperm ovule.
Ans. 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.
Q.5 What is meant by monosporic development of female gametophyte?
Ans. When the female gametophyte (embryo sac) develops from a single megaspore, it is called monosporic development. Usually, in most angiosperms, the megaspore mother cell divides by meiosis to form four haploid megaspores arranged in a linear fashion. The three, situated towards micropyle, digenerate and one remains functional which develops into female gametophyte.
Q.6 With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.
The female gametophyte of plants is formed from a single functional megaspore with the help of four unequal mitotic divisions. These mitotic divisions give rise to 8 nuclei. Later, these nuclei assemble into 7 cells. To both chalazal and micropylar end three cells each move. The three cells at chalaza are called antipodal cells while those at micropylar end constitute egg apparatus. The egg apparatus includes two larger cells called synergid while the egg is the smallest cell that acts as a female gamete. Two nuclei migrate to the centre and together they form a single cell called the central cell. This central cell consists of two nuclei called polar nuclei. Thus, the mature embryo sac possesses 7 cells ( 3 antipodal cells, 2 synergid cells, 1 egg cell and 1 central cell) and 8 nuclei ( 3 of antipodal cell, 2 of synergid cells, 1 of egg cell and 2 of central cell).
Q.7 What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.
Ans. Chasmogamous flowers are similar to flowers of other species with exposed anthers and stigma. Cleistogamous flowers never open to ensure self-pollination. They remain closed so that cross pollination does not occur.
Q.8 Mention two strategies evolved to prevent self-pollination in flowers.
Ans. Cross-pollinating flowers develop the following strategies to prevent self-pollination:
- Protogyny (when gynoecium matures earlier than androecium) or Protandry (when androecium matures and shed pollen before maturation of gynoecium).
- Self incompatibility
Q.9 What is self-incompatibility? Why does self-pollination not lead to seed formation in self-incompatible species?
Ans. Self-incompatibility is a genetic mechanism in which pollen are prevented from fertilizing the ovules by inhibiting pollen germination or pollen tube growth in the pistil. Self-pollination does not lead to seed formation in self-incompatible species due of interaction between the chemicals of the pollen and stigma.
Q.10 What is bagging technique? How is it useful in a plant breeding programme?
Ans. Bagging technique refers to covering of emasculated flowers with the help of butter paper or plastic bags to avoid contamination of stigma of these flowers to undesired pollens. This technique is used during artificial hybridisation experiments. This technique is useful in breeding programmes because it prevents contamination of stigma with unwanted pollens. So, through this technique, we can allow the breeding of species according to our need and obtain superior species.
Q.11 What is triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.
Ans. Fusion of male gamete with secondary nucleus inside the embryosac (female gametophyte) of angiosperms is called triple fusion. It involves fusion of one male gamete nucleus and two polar nuclei.
Q.12 Why do you think the zygote is dormant for sometime in a fertilized ovule?
Ans. 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.
Q.13 Differentiate between: (a) Hypocotyl and epicotyl; (b) Coleoptile and coleorrhiza; (c) Integument and testa; (d) Perisperm and pericarp.
Ans. (a) Hypocotyl is the part of embryonic axis between radicle and cotyledonary node while epicotyl forms the part of embryonic axis between plumule and cotyledonary node.
(b) Coleoptile is a protective covering that surrounds part of epicotyl (the immature shoot). Coleorrhiza is an undifferentiated sheath of monocot seed that covers the radicle and the root cap.
(c) Integuments are outer cell layers surrounding the megasporangium of an ovule and form seed coat after double fertilization while testa represents the outer layer of seed coat and develops from outer integument of ovule.
(d) The presistent nucellus present in some seeds is called as perisperm. The fruit wall is pericarp and develops from ovarian wall.
Q.14 Why is the apple called a false fruit? Which part/s of the flower forms the fruit?
Ans. The fruit, derived from ovary of a flower not associated with any noncarpellary part, is called a true fruit, whereas, the fruit derived from the ovary along with other accessory floral parts, is called a false fruit. The apple is called false fruit because the main edible part is the fleshy receptacle.
Q.15 What is meant by emasculation? When and why does a plant breeder employ this technique?
Ans. The process of removal of anthers from the flower with the help of forceps without affecting the female reproductive parts is called emasculation.
This technique is used by plant breeders to allow suggestive breeding between plants in order to produce plants with desired seeds. Hence, it can be used to prevent self-pollination or prevent cross-pollination according to the need of the breeder.
Q.16 If one can induce parthenocarpy through the application of growth substances, which fruits you would select to induce parthenocarpy and why?
Ans. The fruits formed as a result of parthenocarpy are generally seedless. Hence, for parthenocarpy, we can select fruits which have a lot of seeds in them. Such fruits include Orange, lemon, watermelon, guava, etc. So we can select watermelon to induce parthenocarpy because by this method we can have seedless watermelons.
Q.17 Explain the role of tapetum in the pollen-grain wall formation.
Ans. During microsporogenesis, the cells of tapetum provide various enzymes, hormones, amino acids and other nutritive materials to the dividing microsporocytes. The main functions of tapetum are –
(a) Transportation of nutrients into anther locule at the time of meiosis in spore mother cells
(b) Secretion of enzymes and hormones
(c) Production of Ubisch bodies which are coated with sporopollenin to cause thickening of exine
(d) Secretion of an oily material (pollenkitt) over outerside of mature pollen
(e) Secretion of special proteins for pollen to recognise compatibility
Q.18 What is apomixes and what is its importance?
Ans. The process of development of seeds from diploid cells of nucellus tissue without the process of fertilisation is called apomixis. This process is a form of asexual reproduction that mimics sexual reproduction. Apomixis is very commonly seen in grasses.
Importance of apomixis
- Apomixis is used by horticulturists to produce hybrid seeds.
- Apomixis leads to the formation of infection-free embryos.
- Apomixis can be used to produce multiple embryos at a time.
- Apomictic embryos are genetically similar to their parent plants. For this reason, they can be used in order to conserve specific characters in crop plants.