Pollen Grain Structure and Sporopollenin

Pollen grains are tiny structures that contain the male gametophyte in seed plants. They have a tough protective wall that helps them survive in various environmental conditions.

The pollen grain wall is typically composed of two main layers:

• Exine: This is the outer layer.
• Intine: This is the inner layer, lying just inside the exine.

Let's look at the components mentioned in the options:

• Exine: The exine is primarily made up of a highly resistant substance called sporopollenin. Sporopollenin is one of the most resistant biological polymers known. It can withstand high temperatures, strong acids, and bases, and it is not degraded by enzymes. This makes the exine very durable, allowing pollen grains to be well-preserved in fossils.
• Pollen cytoplasm: This is the living content within the pollen grain, enclosed by the intine. It contains organelles, stored food reserves, and the generative and tube cells (in a two-celled pollen grain) or the two male gametes and tube nucleus (in a three-celled pollen grain). It does not contain sporopollenin.
• Tapetum: This is a nutritive tissue layer surrounding the developing pollen grains within the anther. It provides nourishment to the microspores as they develop into pollen grains and also contributes substances (including precursors for sporopollenin synthesis) to the pollen wall, but it is not a part of the mature pollen grain itself.
• Intine: The intine is the inner layer of the pollen wall. It is mainly composed of cellulose and pectin. Unlike the exine, it is not made of sporopollenin.

Therefore, the part of the pollen grain that contains sporopollenin is the exine.