Stigma

Definition

Stigma is the part of a flower's pistil that receives pollen during fertilization. It plays a crucial role in the reproductive process by capturing pollen grains, which are essential for the fertilization of ovules. The stigma's surface is often sticky or feathery, aiding in the effective collection of pollen from pollinators or the wind, connecting it to the overall structure and function of flowers as well as the process of pollination and fertilization.

5 Must Know Facts For Your Next Test

1. The stigma's surface can vary greatly between different flower species, with some having a smooth texture while others are covered in hairs or other structures to maximize pollen capture.
2. Stigmas can be adapted for specific pollinators; for example, some flowers have a structure that helps direct certain types of pollen to their stigmas based on shape or size.
3. In many plants, the stigma remains receptive for a limited time, which is often synchronized with the flowering period to ensure successful fertilization.
4. Once pollen lands on the stigma, it germinates and sends a pollen tube down through the style to reach the ovule in the ovary for fertilization.
5. Some plants have evolved mechanisms where their stigmas can reject incompatible pollen types, ensuring that only genetically suitable pollen can lead to fertilization.

Review Questions

• How does the structure of a stigma facilitate its role in pollination?
  • The structure of a stigma is designed to optimize its function in pollination. Its surface is often sticky or has specialized hairs that help capture pollen grains effectively when they land on it. This structural adaptation ensures that the stigma can efficiently collect pollen from various sources like insects or wind, thus enhancing the chances of successful fertilization.
• What adaptations might stigmas have developed to increase reproductive success in specific environments?
  • Stigmas may have developed unique adaptations depending on their specific environments and pollinators. For example, flowers that rely on specific insects might have stigmas shaped or positioned to accommodate those insects' anatomy, while others may have sticky surfaces to catch windborne pollen. These adaptations ensure that the flower maximizes its chances of successful pollination by aligning with its ecological niche and pollinator behavior.
• Evaluate the importance of stigma characteristics in relation to plant reproduction and biodiversity.
  • The characteristics of stigmas are vital for plant reproduction as they directly influence pollination success and genetic diversity. By having varied stigma shapes, sizes, and textures, plants can attract specific pollinators or increase compatibility with particular pollen types. This diversity not only aids in ensuring effective fertilization but also contributes to maintaining genetic variation within plant populations, which is crucial for resilience against environmental changes and diseases, ultimately supporting broader ecosystem health and biodiversity.

Related terms

Pistil:

The female reproductive part of a flower, consisting of the ovary, style, and stigma.

Pollination:

The transfer of pollen from the male anther to the female stigma, which can occur via various agents such as wind, water, or animals.

Ovule:

The structure within the ovary that develops into a seed after fertilization occurs.