Describe the four main parts, or whorls, of a flower.

Flower is the reproductive organ of an angiosperm. Angiosperms reproduce sexually with the help of flowers. Flowers also help in attracting pollinators for pollination by producing nectar as a reward for the pollinators. A flower in general has four whorl components: calyx, corolla, gynoecium and androecium.

The calyx and corolla are the non-reproductive parts of the flower. They are called the accessory parts of the flower, that performs different functions.

• The flower's outer whorl is called the calyx. It is made up of sepals, which are tiny leaves located at the base of flowers. Calyx provides protection to the flower while it is in bud stage and they perform photosynthesis as well.
• The second whorl of the flower is called corolla, that is made up of petals. Petals are vividly coloured and scented to attract pollinators.

The gynoecium(carpel) and androecium(stamen) are reproductive parts of the flowers that is involved in the reproduction process.

• The carpel is the flower's fourth whorl, and it is found in the centre. The carpels house the pistil, the female reproductive component of the flower. It includes the ovary, style, and stigma. The egg, or ovule, is found in the ovary. After fertilisation the ovary becomes the fruit and the ovules become the seed, which are guarded and enclosed by the fruit. The stigma is supported at the tip of the ovary by a vertical structure called the style. Pollen that has been dispersed, sticks to the stigma and travels down the style to the ovary.
• The male reproductive part of the flower is the stamen, and makes up the third whorl of the flower. It consists of an anther and a slender stalk supporting the anther, called filament. Pollen grains, which contain the male gametes are produced and stored in the anther.