Chapter 2: Sexual Reproduction in Flowering Plants

Ans: Correct option is c.  

Carpel and sepal are individual parts and make gynoecium and calyx respectively. The other two terms Androecium and corolla refer to an entire region containing gynoecium, androecium, corolla, and calyx. These, therefore, can be used for the floral whorls. These, respectively, are made by carpels, petals, and sepals.

Ans: Correct option is c.

Embryo sac is present in one ovule, while pollen grains are present in another. The female gametophyte is the embryo sac for which the ovule is the megasporangium i.e., it contains the female gametophyte or embryo sac. Similarly, the pollen grain being the male gametophyte resides in the microsporangium i.e., the anther. This establishes that what embryo sac is to ovulate, the pollen grain is to another in a flower.

Ans: Correct option is a.

As we go from outer to inner arrangement in a floral whorl on the thalamus of a flower, we encounter calyx, corolla, androecium, and gynoecium. The flower in angiosperms has four floral whorls namely, calyx, corolla, androecium, and gynoecium constituting it. The outermost whorls are the accessory or the helping whorls as they do not directly contribute to reproduction in the plant. The accessory whorls contain calyx and corolla. Female and male parts of the flower, which are directly involved in reproduction are gynoecium and androecium respectively. These are the inner whorls. Therefore, a correct arrangement would correspond to the one given in option a.

Ans: Correct option is d.

A pistillate flower is the one which contains pistils only and the staminate flower contains stamens only. Hence, a dicotyledonous plant which bears flowers but does not make fruits or seeds must be dioecious and have staminate flowers. Dioecious means that the plant has either pistils or stamens which is a requirement for a plant to not be able to produce seeds or fruits. However, a pistillate flower has a probability of getting fertilized by pollen grains received from some other flowers whereas a staminate flower will not be fertilized itself. Therefore, the option d forms the most suitable answer.

Ans: Correct option is d.

The wall layers of microsporangium of an anther are four in number, namely, epidermis, endothecium, middle layers, and tapetum. The tapetum is the innermost layer and the outer three layers protect and aid in disinfecting the anther. Among these three, the outermost layer is epidermis. The innermost layer i.e., the tapetum provides nutrition to the pollen grains. Therefore, the innermost and outermost layer of microsporangium wall in an anther are epidermis and tapetum.

Ans: Correct option is b.

Microsporogenesis is defined as the process of formation of microspores i.e., pollen grains. This process occurs inside the pollen sac or microsporangium by reduction division or meiosis. The microspore mother cells undergo reduction division to form microspores which then differentiate to form pollen grains. Therefore, the Ans is pollen grains as those are formed after meiosis.

Ans: Correct option is a.

The gynoecium in a flower is the female part of a flower which directly assists in plant reproduction in angiosperms. A gynoecium is made up of stigma, the apical portion which receives pollen; ovule the basal portion of the stalk or style; placenta lies in the central axis of the ovary, and embryo sac is the female gametophyte residing in ovule of a flower lying in ovule. Therefore, stigma, ovule, embryo sac, and placenta are the parts of a gynoecium of a flower.

Ans: Correct option is b.

Ovule is the part of gynoecium which contains the female gametophyte and where the fertilization in an angiosperm occurs. Going from the innermost part in an ovule, we see, egg nucleus, which is the female gamete; embryo sac, which is the female gametophyte; nucellus, which provides nourishment to the developing embryo after fertilization; and integument, which serves as a protection for the inner layers of an ovule. Therefore, the correct option is b.

Ans: Correct option is c.

A typical female gametophyte is an angiosperm i.e., an embryo sac consists of an egg apparatus which lies at the micropylar end of the ovule containing one egg cell and two synergids in it. At its center, there are two polar nuclei which fuse with sperm nuclei to form a triploid endosperm; a distinct characteristic of angiosperms. There are also three antipodal cells located at the chalazal end of the egg apparatus. The megaspore mother cells undergo reduction division which leads to formation of four megaspores. Out of these four, three megaspores degenerate and one functional megaspore is left behind which gives rise to an 8-nucleate female gametophyte through free nuclear division via three mitotic divisions. These 8 nuclei then get arranged in the female gametophyte to form antipodal cells, central nuclei, and egg apparatus. The two polar nuclei at the center join to form a binucleate cell making it a 7 celled gametophyte at the time of maturity. Therefore, option i and ii are the correct options. 

Ans: Correct option is c.

A chasmogamous flower is one in which the anther and stigma are exposed to the environment. Autogamy means pollination of a flower with a pollen grain from its own anther. For autogamy to occur in a chasmogamous flower, both the pollen grains and ovule containing egg have to reach the stage of maturation at the same time and they both should be located close to each other for pollination to occur easily. This ensures that when the mature pollen falls on the pistil and reaches a mature ovule, fertilization can occur without any delay to form a zygote. According to this theory, the most suitable option is c.