Chapter 27, Problem 1STP

Summary Introduction

Introduction:

Anthophytes are flowering plants. They have distinctive life cycles and like all plants they also exhibit alternation of generations. The development of male and female gametophyte begins in an undeveloped flower. Anthophytes are heterosporous- pistils produce megaspores and stamens produce microspores.

Correct answer :

The correct answer is option B. ovule

Explanation/justification for the correct answer:

Option B. ovule − A specialized cell in the ovule of a pistil’s ovary undergoes meiosis to produce four megaspores. Out of these four megaspores, three disintegrate and disappear. The nucleus of functional megaspore undergoes mitosis. Mitosis continues several times till there is one large cell with eight nuclei. Two nuclei migrate to the center and membranes form around other six nuclei. The result is three nuclei at each end of the cell and two nuclei called polar nuclei in the center. One of three nuclei towards the micropyle becomes the egg. Since the eggs develop in the ovule of the ovary, so this is the correct option.

Explanation for incorrect answer:

Option A. anther −Anther is the male reproductive part of a flower. It produces male gametophyte or pollen grain and not egg which is a part of female gametophyte. Hence this is not the correct option.

Option C. seed − Seed is formed as a result of fertilization of egg and male sperm nuclei. After fertilization, ovule develops into seed and ovary develops into fruit. Hence this is not the correct option.

Option D. stigma − Stigma is the receptacle which receives the pollen grains during pollination. It does not produce egg. Hence this is not the correct option.

Answer to Problem 1STP

Correct answer :

The correct answer is option B. ovule

Explanation of Solution

Explanation/justification for the correct answer:

Option B. ovule − A specialized cell in the ovule of a pistil’s ovary undergoes meiosis to produce four megaspores. Out of these four megaspores, three disintegrate and disappear. The nucleus of functional megaspore undergoes mitosis. Mitosis continues several times till there is one large cell with eight nuclei. Two nuclei migrate to the center and membranes form around other six nuclei. The result is three nuclei at each end of the cell and two nuclei called polar nuclei in the center. One of three nuclei towards the micropyle becomes the egg. Since the eggs develop in the ovule of the ovary, so this is the correct option.

Explanation for incorrect answer:

Option A. anther −Anther is the male reproductive part of a flower. It produces male gametophyte or pollen grain and not egg which is a part of female gametophyte. Hence this is not the correct option.

Option C. seed − Seed is formed as a result of fertilization of egg and male sperm nuclei. After fertilization, ovule develops into seed and ovary develops into fruit. Hence this is not the correct option.

Option D. stigma − Stigma is the receptacle which receives the pollen grains during pollination. It does not produce egg. Hence this is not the correct option.