Sporopollenin, a chemical substance is found in …………………………………
A. Endothecium of anther
B. Tapetum of anther
C. Intine of pollen grain
D. Exine of pollen grain

Hint: The male reproductive part of the plants produces pollen which is a powdery substance consisting of pollen grains. During pollination the pollen grains move from the stamens to the pistil of the flowering plant. In coniferous plants the pollen grains migrate from the male cone to the female cone. This process further leads to fertilization by formation of pollen tubes by the pollen grains which transfers the sperm to the ovule.

Complete answer:
The pollen grains are the male microgametophyte of the seed producing plants. The pollen grains produce male gametes or the sperm cells. Pollen grains are made up of two layered cell structures. The outer layer is called an exine and the internal layer is known as the intine. The pollen grains have a hard protein made up of a chemical or sporopollenin.

Sporopollenin is one of the most important biochemical polymers. It is known to protect the spores from desiccation which can be attributed to the chemical composition of sporopollenin. The chemical composition of sporopollenin shows that it is highly stable and resistant to degradation by enzymes and strong chemicals. They are a mixture of biopolymers containing long chains of fatty acids, phenylpropanoids, phenolics. Phenylalanine is one of the major precursors that are chemically cross linked to form the rigid structure of Sporopollenin.

It is also known to contain traces of carotenoids. The sporopollenin precursors are the tapetal cells surrounding the developing pollen grain and consist of a highly active secretory system. The secretory system contains lipophilic globules which are known to be the precursors of sporopollenin.

Hence, the correct answer is option (D).

Other options from the given question:
> Option A: The pollen grains during their development contain cells that line the lumen of the anther is known as the endothecium. It secrets materials that are important for the development and proper maturation of the pollen grains.

> Option B: Tapetum of anther is a specialized cell layer that is associated with the nutrition providing function to the anthers of the flowering plants. It provides nourishment to the developing anther and is the source of precursors for the pollen layer.

> Option C: Intine of pollen grain is the internal layer that lies towards the interior of the exine layer of the pollen grain. It covers the two types of cells present in the pollen grain which are the vegetative and reproductive cells.

Note: The pollen grain is the male microgametophyte which migrates to the female reproductive organ during reproduction. The pollen grain is made up of two layers which is the exine or the outer layer and the intine or the inner layer of the cell. The layer of the exine of the pollen grain is made up of a chemical known as the sporopollenin. It protects the pollen grain from desiccation and drying out.