Ncert solution biology class 12 Reproduction in Flowering Plants chapter 2

 Ncert solution biology class 12 Reproduction in Flowering Plants chapter 2

Question 1: Name the parts of an angiosperm flower in which development of male and female gametophytes take place.

Solution 1: Development of male gametophyte (micro-gametogenesis) occurs in pollen sac of anther up to 2-celled stage. The female gametophyte develops (megagametogenesis) in the nucellus of 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?

Solution 2: Differences between microsporogenesis and megasporogenesis are as follows-

Microsporogenesis Megasporogenesis
1 The process of formation and differentiation of pollen grains from microspore mother cells by meiosis is known is micro-sporogenesis. The process of formation and differentiation of megaspores form megaspore mother cells by meiosis is known as megasporogenesis.
2 Pollen grains are produced in the anther which is a broader knob like fertile part of the stamen. Ovules (which are the future seeds) are formed in the ovary.
3 All the four pollen grains that are formed from microspore mother cell are functional. Only one out of the four megaspores is functional.

Each microspore mother cell and megaspore mother cell contain two sets of chromosomes and are therefore diploid megaspore mother cell and microspore mother cell enlarges and undergo meiosis to produce, four haploid cell called megaspores and microspores respectively. The chromosome number is reduced by half and therefore megaspores and microspores are haploid.

Microsporogenesis and megasporogenesis give rise to pollen grains and embryo sac respectively. Pollen grain is the male gamet
A typical angiospermic ovule is a small structure which is formed in the ovary. Ovule first develops as a projection on the placenta and composed of multilayered cellular tissue called the nucellus. The hypodermal cell of die nucellus enlarges and transformed into megaspore mother cell.
This cell undergoes meiosis to produce four haploid cells only one of which develops and forms embryo sac (female gametophyte). An ovule may be surrounded by one or two protective layers called integuments, leaving a small opening at one end termed as micropyle which acts as passage for the entry of the pollen tube into the ovule. Thus, a typical ovule consists of a fully developed embryo sac with the nucellus and integuments. male gametophyte and embryo sac represents the female gametophyte.

Question 3: Arrange the following terms in-the correct developmental sequence : Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes.

Solution 3:Sporogenous tissue – pollen mother cell – microspore tetrad – pollen grains – male gametes.

Question 4: With a neat, labeled diagram, describe the parts of a typical angiosperm ovule.

A typical angiospermic ovule is a small structure which is formed in the ovary. Ovule first develops as a projection on the placenta and composed of multilayered cellular tissue called the nucellus. The hypodermal cell of die nucellus enlarges and transformed into megaspore mother cell.

Question 5: What is meant by monosporic development of female gametophyte?

Solution 5: In many flowering plants, only one out of the four megaspores enlarges and develops into female gametophyte or embryo sac. The other three megaspores degenerate. This type of embryo sac formation is called as monosporic type development.

Question 6: With a neat diagram explain the 7-celled, 8-nucleate nature of the female gametophyte.

Embryo sac (or female gametophyte) is formed by three successive mitotic divisions that take place in the nucleus of megaspore. The nucleus of the functional megaspore divides meiotically to form two nuclei which move to the opposite poles, forming the 2-nucleate embryo sac.
Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleate stages of the embryo sac. After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte or embryo sac. Six of the eight nuclei are grouped together at micropylar and chalazal end and form the egg apparatus and antipodals respectively. The large central left over with two polar nuclei. Thus, a typical female gametophyte consists of 7 cells with 8 nucleus.

Question 7: What are chasmogamous flowers? Can cross-pollination occur in cleistogamous flowers? Give reasons for your answer.

Solution 7:
Chasmogamous flowers or open flowers in which anther and stigma are exposed for pollination. Cross-pollination cannot occur in cleistogamous flowers. These flowers remain closed thus causing only self-pollination. In cleistogamous flowers, anthers dehisce inside the closed flowers. So the pollen grains come in contact with stigma. Thus there is no chance of cross-pollination, e.g., Oxalis, Viola.

Question 8: Mention two strategies evolved to prevent self-pollination in flowers.

Solution 8:
Continued self-pollination decreases the vigour and vitality of a particular race. Thus, flowering plants have developed many devices to discourage self-pollination and to encourage cross-pollination.
Dichogamy and self-sterility are two most common devices that ensure cross-pollination. Dichogamy- Maturation of anther and stigma at different times in a bisexual flower prevent self-pollination. Self-sterility (or self-incompatibility) – Due to the presence of self-sterile gene in some flowers, pollen grains do not germinate on the stigma of that flowers. e.g., – tobacco, potato.

Question 9: What is self-incompatibility? Why does self-pollination not lead to seed formation in self- incompatible species?

Solution 9: When the pollen grains of an anther do not germinate on the stigma of the same flower, then such a flower is called self-sterile or incompatible and such condition is known as self- incompatibility or self-sterility. The transference of pollen grains shed from the anther to the stigma of the pistil is called pollination.
This transference initiate the process of seed formation. Self-pollination is the transfer of pollen grain shed from the anther to stigma of pistil in the same flower. But in some flower self-pollination does not lead to the formation of seed formation because of the presence of same sterile gene on pistil and pollen grain.

Question 10: What is bagging technique? How is it useful in a plant breeding programme?

Solution 10: It is the covering of emasculated flowers (removal of anthers in bud condition from a bisexual flower by a bag of butter paper of polythene in their bud condition i.e., before anthesis) to prevent contamination of its stigmas with unwanted pollens. When the stigmas of emasculated flowers mature the bags are removed, stigmas are dusted with pollen grains of desired male plants by means of a presterilized brush and flowers are rebagged till fruit develop. This technique is mainly used in artificial hybridization. Plant breeders often use this technique to prevent the contamination of stigma of the flowers from unwanted pollen grains.

Question 11: What b triple fusion? Where and how does it take place? Name the nuclei involved in triple fusion.

Solution 11: Fusion of second male gamete with die two polar nuclei located in the central cell to form the triploid primary endosperm nucleus (PEN) is called triple fusion or vegetative fertilization.

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