Flower Arrangements

SEXUAL REPRODUCTION IN FLOWERING PLANTS

EXERCISE SOLUTIONS

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

Ans: Development of male and female gametophytes takes place in anther and ovary, respectively.

 

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.

Meiosis occurs during micro and megasporogenesis.

Microspores (Pollen grains) are formed at the end of microsporogenesis and female gametophytes (embryo sacs) are formed at the end of megasporogenesis.

Question 3: Arrange the following terms in the correct developmental sequence:

Pollen grain, sporogenous tissue, microspore tetrad, pollen mother cell, male gametes

Ans: 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 4: With a neat, labelled diagram, describe the parts of a typical angiosperm ovule.

Ans:

  • The ovule is a small structure attached to the placenta by means of a stalk called funicle.

  • The junction between an ovule and a funicle is called hilum. Sometimes, the funicle extends beyond the hilum to form a ridge called raphae.

  • The ovule is surrounded by one or two protective envelopes called integuments.

  • Integument encircles the ovule entirely except at the tip, resulting in a small opening called micropyle.

  • The basal part of an ovule opposite to micropyle is called chalaza.

  • The cells with high or abundant reserve food material enclosed within integument is called nucellus.

  • The female gametophyte located within the nucellus is called an embryo sac.

Ovule.png

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

Ans: The female gametophyte or the embryo sac develops from a single functional megaspore. This is known as monosporic development of the female gametophyte. In most flowering plants, a single megaspore mother cell present at the micropylar pole of the nucellus region of the ovule undergoes meiosis to produce four haploid megaspores. Later, out of these four megaspores, only one functional megaspore develops into the female gametophyte, while the remaining three degenerates.

 

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

Ans:

  • 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.