Sexual Reproduction in Flowering Plants Test - 68

Endosperm is a triploid tissue in angiosperms, because double fertilization results in the formation of a diploid zygote and a triploid endosperm. The female gametophyte or embryo sac has an egg nucleus and two polar nuclei. One sperm fertilizes the egg nucleus and forms the zygote, 2n. Another sperm joins the two polar nuclei forming the triploid (3n) nutritive tissue, called as the endosperm. 

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. 

Emasculation refers to the process of removal of anthers from the bisexual flowers. The removal of anthers is done without injuring the pistil. This process is carried out as a part of various plant hybridization techniques wherein plant breeders pollinate the bisexual flowers with pollen grains to get desired varieties. This process has no validity in the case of plants with unisexual flowers.

• A unisexual flower is a flower that contains three whorls such as petals, sepals, the male reproductive structure (stamen) or the female reproductive structure (pistil). 
• Autogamy is pollination by the transfer of pollen grains from the anther of a flower to the stigma of the same flower.
• Geitonogamy is the pollination by transfer of pollen grains from the anther of a flower to the stigma of another flower of the same plant.
• Thus, a unisexual flower cannot show autogamy but geitonogamy is possible.

Correct Answer- A

Gymnosperms have a haploid endosperm. Whereas angiosperms have a triploid endosperm as a result of double fertilization. 

Stamens of a flower are considered to be the male reproductive part of the plant which consists of two parts filaments which is a long slender stalk and anther is the bilobed structure where the formation of the male gamete (pollen grains) occur. Whereas Stigma where pollen lands and style which leads the path of pollen tube are the part of the female reproductive part.

• Staminate flower is the one in which androecium is present. Each unit of the androecium is called microsporophyll or stamen. 
• It is the male reproduc­tive organ of the flower. A stamen is made up of a stalk called the filament and anther which contains microsporangia.
  
  Hence, the correct option is A.

Small, bisexual, colorless flowers which do not secrete nectar and always remain close are called as cleistogamous flowers, their closed condition favors exclusive self-pollination. Example- Commelina, Cardamine.