Botany and Plant Science

Gymnosperms are having a haploid endosperm. But, angiosperms have a triploid endosperm due to the double fertilization. The pollen grain is the haploid in nature. Therefore, in gymnosperms, the pollen grains and the megaspores are the haploids. The functional megaspores from the embryo sac. The endosperm is formed prior to the fertilization and hence it is haploid.

Germ pore is the pore in the outer wall of a pollen grain through which the germ tube or pollen tube makes its exit on germination. When this fusion happens, the zygote is produced. The germ pore also releases the extra nucleus which results in the formation of triploid endosperm.

Sporopollenin is a major component of the tough outer walls called as exine walls of plant spores and pollen grains. It is chemically very stable and usually well preserved in soils and sediments. The chemical composition of sporopollenin is not exactly known due to its unusual chemical stability and resistance to degradation by enzymes and string chemical reagents.

Pollen sacs are located in the anther. It is the structure where pollen are produced. Angiosperms have 4 pollen sac in anther. 

Sporopollenin is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from (for example) lake sediments to provide useful information to palynologists about plant and fungal populations in the past. The chemical composition of sporopollenin is not exactly known, due to its unusual chemical stability and resistance to degradation by enzymes and strong chemical reagents. Analyses have revealed a mixture of biopolymers, containing mainly long chain fatty acids, phenylpropanoids, phenolics and traces of carotenoids. Tracer experiments have shown that phenylalanine is a major precursor, but other carbon sources also contribute. It is likely that sporopollenin derives from several precursors that are chemically cross-linked to form a rigid structure.

Stamen is the male reproductive organ that consists of long slender filament and broad knob like anther; each anther lobes of anther contains two long and cylindrical microsporangia. Since, stamen bear microsporangia in anther lobes, they are also called as microsporophylls. Option A is incorrect. Gynoecium represents the megasporophyll as it carries megasporangia, i.e., the ovule, at basal part of pistil. Option B is incorrect. Megaspore represents the first cell of embryo sac/female gametophyte; depending upon the number of megaspores involved in development of female gametophyte, single/two/three successive mitotic division form eight nucleate-seven celled female gametophyte. Option C is incorrect. Pollen grain is the first cell of male gametophyte that divides mitotically to form small generative cell and large tube/vegetative cell. Pollen with small generative and large vegetative or with one vegetative cell and two male gametes is known as mature male gametophyte.

The pollen grain is the immature male gametophyte that precociously develops into mature male gametophyte through micro gametogenesis. Meiosis in microspore mother cell forms four haploid microspores which are initially covered with a common wall of callose ($\beta$ 1,3-glucan).  Microspore matures into pollen grain which is a uni-nucleate cell with the two-layered cell wall. The exine is the outer covering of pollen grain which is highly sculptured with sporopollenin; a chemically inert polymer of carotenoid ester which is highly resistant to degradation by any enzyme, as known so far.  It can withstand extremes of temperature and desiccation. Cutin is an insoluble heterogenous lipid-polymer of long chain substituted aliphatic acids which are main constituent of cuticles and serves as the waterproof substance to reduce water loss; it does not withstand extremes of temperatures and is not present in exine. Suberin is a waterproofing waxy substance which restricts the water movement to reduce the risk of embolism caused by wear and tear damage to leaf/petiole. It is not a constituent of exine. Thus, the correct answer is option C. 

Pollen grain is a uninucleate cell with two layered cell wall. Exine is the outer covering of pollen grain which is highly sculptured with sporopollenin; a chemically inert polymer of carotenoid ester which is highly resistant to degradation by any enzyme, as known so far. Option C is correct. 

Pollen grain is an immature male gametophyte as it has two cells out of which one develops into two male gametes after pollination. The generative cell of pollen undergoes mitosis to form two male gametes. So, pollen is a immature or partially developed male gametophyte. Correct answer is D.

Micropyle is a small opening in the surface of an ovule.

In the Pinus, winged pollen grains exist. It is an outgrowth of exine on the two lateral sides to make the wings of pollen. It is the characteristic feature, only in Pinus. In Pinus, some surface tissues of the ovuliferous scale are still attached to the seed. Thus forming a membranous wing.

Thus the correct answer is Exine.

The correct option is B.

Sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments.

Plastids are found in almost all cells of the plant body either in the form of colorless plastids or colored plastids or proplastids.