CBSE Class 10 Answered

Photoperiodism is the developmental responses of plants to the relative lengths of the light and dark periods.

Phototropism is a phenomenon where the growth of a plant is determined by the direction of the light source. Growth towards a light source is a positive phototropism, while growth away from light is called negative phototropism.

In phototropism, the direction of the plant growth is influenced. There is no direction involved in photoperiodism.

Phototropism is enabled by auxins.  Phototropism in plants is regulated by receptors such as phototropins,  phytochromes, cryptochromes etc.

Several hormones are involved in photoperiodism. Many flowering plants use a photoreceptor protein, such as phytochrome or cryptochrome, to sense seasonal changes in day length.