Which organ in a flower is responsible for producing pollen grains?

The organ in a flower responsible for producing pollen grains is the anther. The anther is a part of the stamen, which is the male reproductive structure of the flower. Pollen grains are formed within the anther through a process called microgametogenesis, where diploid microspore mother cells undergo meiosis to produce haploid microspores. These microspores then develop into pollen grains.

In contrast, the stigma, style, and ovary are parts of the pistil, which is the female reproductive structure of the flower. The stigma serves as the landing platform for pollen during pollination, the style is the elongated part that connects the stigma to the ovary, and the ovary contains the ovules, which develop into seeds after fertilization. Each of these parts plays a crucial role in the reproductive process but is not involved in the production of pollen grains.