Ncert Solutions Class 12 Biology Chapter 1 – Download Free PDF

Adda 247 provides NCERT Solutions for Class 12 Biology Chapter 1 which is for the students who want to go ahead in life and achieve great marks in their examinations. The NCERT Solutions for class 12 Chapter 1 are provided by the teachers who are experts in their subjects. The solutions are set according to the rules formulated by the NCERT class 12 biology and in a language that can be understood by every student. By reading the solutions students can build up a strong base easily.

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NCERT Solutions for Class 12 Biology Chapter 1 – Sexual Reproduction in Flowering Plants

The chapter provides information about Sexual reproduction in flowering plants. Events that take place before fertilization are termed as Pre-fertilization events. The following events would occur before actual fertilization takes place in a plant: Gametogenesis-Development of male & female reproductive structures. Formation of male & female gametes. Gamete transfer-Bringing together male & female gamete. Pollination occurs in plants to facilitate gamete transfer.

Features of the NCERT Solutions for Class 12 Biology Chapter 1

 NCERT Solutions of class 12 have been answered based on the important information on the question.

• The columns are used wherever necessary.
• Solutions are solved point-wise and accurately answered point-to-point.

Ncert Solutions Class 12 Biology Chapter 1 Questions Answers

Question 1. Name the parts of an angiosperm flower in which the 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.

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.

Answer:

Type of cell division during microsporogenesis and megasporogenesis meiosis.

Structure formed — (a) Due to microsporogenesis. Microspores (pollen grains) are formed which lead to development of male gametophyte.(b) Due to megasporogenesis. Megaspores are formed. Out of them one megaspore leads to development of female gametophyte (embryo sac).

Question 3. Arrange the following terms in 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 gamete

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.

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

Answer:  Megaspore is the first cell of the female gametophyte. Depending upon the number of megaspores the development of female gametophyte is termed as monosporic, bisporic or tetrasporic. Monosporic development starts with meiosis in megaspore mother cell to form a dyad and then tetrad of megaspores. Out of four, one is functional that undergoes the three simultaneous divisions to form 2-, 4- and finally 8-nucleate and 7-celled embryo sac.

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

Answer: There are two types of flowers present in plants namely Oxalis and Viola − chasmogamous and cleistogamous flowers.

Chasmogamous flowers have exposed anthers and stigmata similar to the flowers of other species.

Cross-pollination cannot occur in cleistogamous flowers. This is because cleistogamous flowers never open at all. Also, the anther and the stigma lie close to each other in these flowers. Hence, only self-pollination is possible in these flowers.

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

Answer:    The strategies evolved to prevent self-pollination in flowers are:

1) Dichogamy- The maturation of anthers and stigma at different time in a bi-sexual flower which prevents self-pollination.

2) Self-incompatibility: The pollen grains of a flower are not capable of completing growth on the stigma of the same flower.

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

Answer: Self incompatibility is also called self-sterility. It is the natural inability to prevent self-pollination in which pollen grains from the same flower is unable to fertilize ovules of same flower or plant.

It happens due to several complex mechanisms. These could be saprophytic or gametophytic incompatibility. Prevent of pollen germination, retardation of growth, reorientation of pollen tube, failure of nuclear fusion could be one of the reason.

Question 10. What is bagging technique? How is it helpful in a plant breeding programme?

Answer:

i)In the flowers with both anther and stigma, the anther is removed before maturation carefully using forceps.

ii)The flower is then covered with a bag made up of butter paper.

iii)The covering of emasculated flowers with a bag of suitable size, generally made up of butter paper, to prevent contamination of its stigma with unwanted pollens is called bagging technique.

1. iv) When the stigma matures, the pollens from desired flower are dusted on the stigma with the help of pre-sterilized brush and the flower is re-bagged until the fruit is developed.
2. v) This technique is called artificial hybridization. Plant breeders often use this method to prevent the contamination of stigma of flowers from unwanted pollens. This technique is also helpful is developing the plant of desired variety.

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

Answer: Triple fusion is the fusion of the male gamete with two polar nuclei inside the embryo sac of the angiosperm.

This process of fusion takes place inside the embryo sac.

When pollen grains fall on the stigma, they germinate and give rise to the pollen tube that passes through the style and enters into the ovule. After this, the pollen tube enters one of synergids and releases two male gametes there. Out of the two male gametes, one gamete fuses with the nucleus of the egg cell and forms the zygote (syngamy). The other male gamete fuses with the two polar nuclei present in the central cell to form a triploid primary endosperm nucleus. Since this process involves the fusion of three haploid nuclei, it is known as triple fusion. It results in the formation of the endosperm.

One male gamete nucleus and two polar nuclei are involved in this process.

Question 12. Why do you think zygote is dormant for sometime in a fertilized ovule?

Answer:  Further development of zygote into embryo and subsequent development of embryo need food resources. The food is provided by endosperm. Hence, endosperm needs to develop to ensure development of embryo. Hence, zygote remains dormant for some time till endosperm develops

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