Question

Match the items in Column A with those in Column B.

Column A	Column B
(a) Generative nucleus	(i) Pollen tube
(b) Germ pore	(ii) Endosperm nucleus
(c) Exine	(iii) Testa
(d) Secondary nucleus	(iv) Fertilization
(e) Integuments	(v) Male nuclei
(f) Egg nucleus	(vi) Rough

Accepted Answer

(a)-(v)

The pollen grains are the microscopic male reproductive cells found in the anther lobes. The mature pollen grain is a two-celled structure that consists of an outer thick exine and an inner thin intine. The exine is very thin at one or more places, giving the appearance of a pore called a germ pore. When the two-celled (generative cell and vegetative cell) pollen grains reach the stigma, the nucleus of the generative cell divides into two male gametes, or male nuclei. The intine forms the pollen tube on germination.

(b)-(i)

The pollen grains are uni-nucleate with two-layered cell wall microspores. The outer layer is called the exine. The inner layer is thin and made up of cellulose called the intine. At one or more places, the exine is very thin or missing at some points, giving the appearance of a pore called the germ pore.

(c)-(vi)

The pollen grains contain male nuclei, which remain protected by an outer layer called exine. The outer layer is tough and often has spinous outgrowth. It is made up of a complex substance called sporopollenin. The inner layer is called the intine.

(d)-(ii)

The ovary is the basal swollen part of the pistil. Each ovary contains one or more ovules. The functional megaspore divides by three successive divisions to form an eight-nucleated embryo sac. The three cells arranged at the micropyle end consist of a middle egg apparatus and two synergids. The other three are called the antipodal cells, arranged at the chalazal end. The two nuclei serve as secondary nuclei and fuse with the male nucleus. This leads to the formation of triploid endosperm, which provides nutrition to the developing embryo.

(e)-(iii)

The ovary holds the tiny haploid female gametes called the ovules. Each ovule consists of a parenchymatous tissue called the nucellus, with one or two protective coverings called integuments. The integuments surround the nucellus all around except at the apex, leaving a narrow passage called a micropyle. The ovary turns into a fruit, ovules turn into seeds, and the integuments form the testa and tegmen, called the seed coat.

(f)-(iv)

The anther contains pollen grains. The pollen grains undergo mitosis and produce a vegetative cell and a generative cell. At this stage, the dehiscence of an anther takes place, and the pollen grains land on the stigma. The generative cell further divides to form two male gametes. The intine of pollen grains now germinates through the germ pore and forms the pollen tube. The pollen tube carrying the two male gametes reaches the ovule through a micropyle. Out of two male gametes, one fuses with the egg cell and forms a zygote. This process is called "true fertilisation." The other fuses with the two secondary nuclei of the ovule and forms endosperm. This is called triple fusion.

H S Vishnoi Solutions for Exercise 3: REVIEW QUESTIONS

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