IB Diploma Biology Practice Test

The stigma is the part of the female reproductive system where pollen lands during the process of fertilization. It is typically the top portion of the pistil, which is composed of the stigma, style, and ovary. The stigma is often sticky or feathery, which aids in capturing pollen grains that are transferred from the male anthers of the flower. Once pollen adheres to the stigma, it can germinate and grow a pollen tube down the style to reach the ovary, where fertilization of the ovules occurs. This role is crucial for sexual reproduction in flowering plants, making the stigma an essential component of the reproductive process. The other choices pertain to different parts of the flower. The style connects the stigma to the ovary but does not directly facilitate pollen landing; the ovary houses the ovules, which develop into seeds after fertilization; and the sepal protects the developing flower bud and is not involved in the pollination process. Understanding the specific roles of each of these parts helps clarify how the reproductive system of flowering plants functions as a whole.