A carpel is the female reproductive part of a flower, the structure that produces seeds. If you've ever looked closely at a flower, you might have noticed a bottle-shaped part in the center: that's often the carpel, or a group of carpels together, sometimes called the pistil.

The carpel has three main sections. At the bottom sits the ovary, which contains tiny structures called ovules that will become seeds if the flower gets pollinated. Rising from the ovary is a narrow tube called the style, and at the top of the style sits the stigma, which has a sticky surface designed to catch pollen grains. When pollen from another flower lands on the stigma, it travels down the style to fertilize the ovules in the ovary, and seeds begin to develop.

Some flowers have just one carpel, while others have several carpels fused together or arranged separately. That tomato you slice for a sandwich grew from a flower's ovary: after pollination, the carpel's ovary swelled and ripened into a fruit, protecting the seeds inside. The same process creates apples, peppers, cucumbers, and countless other fruits and vegetables.