Stigma: The Uppermost Part of the Gynoecium that Traps Pollen

The correct answer to the question is option 'B', Stigma. The stigma is the uppermost part of the gynoecium, which is the female reproductive part of a flower. It plays a crucial role in the process of pollination, specifically in the capture and recognition of pollen.

Explanation:

1. Structure of the Gynoecium:

The gynoecium is the collective term for all the female reproductive organs of a flower. It is made up of three main parts:

- Ovary: The ovary is the enlarged basal part of the gynoecium. It contains one or more ovules, which are responsible for the development of seeds after fertilization.
- Style: The style is a slender, elongated structure that connects the ovary to the stigma. It provides support and allows the pollen tube to grow during fertilization.
- Stigma: The stigma is the uppermost part of the gynoecium. It is located at the top of the style and serves as a landing platform for pollen during pollination.

2. Function of the Stigma:

The stigma plays a crucial role in the pollination process. Its main functions include:

- Pollen Capture: The stigma is designed to capture pollen grains from visiting pollinators, such as bees, butterflies, or birds. It is often sticky or covered in specialized cells called papillae, which help trap the pollen grains.

- Pollen Recognition: After capturing the pollen, the stigma plays a role in recognizing and accepting compatible pollen. It has specific receptors that can detect and differentiate between pollen grains of different species or individuals.

- Pollen Germination: Once the pollen has been recognized as compatible, it germinates on the stigma. The pollen grain forms a pollen tube, which grows down through the style towards the ovary. This tube serves as the conduit for the male gametes to reach the ovules for fertilization.

Conclusion:

The stigma, as the uppermost part of the gynoecium, is responsible for capturing and recognizing pollen during the process of pollination. Its sticky or specialized surface helps trap pollen grains, and it also plays a role in determining the compatibility of the pollen. The stigma is a vital component of the female reproductive system in flowers, ensuring successful fertilization and seed development.