CBSE Class 10 Answered

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

Many plants use a photoreceptor protein, such as phytochrome or cryptochrome, to detect seasonal changes in day length.

Flowering is an important example of photoperiodism in plants.

Broadly, flowering plants can be classified as long day plants, short day plants, or day neutral plants.

Short day plants will be induced to flower only when the day-length is below a certain critical length. If the critical day-length is exceeded, the plant remains in a vegetative state. The night is longer than a critical length. These plants generally flower in late summer or fall. For eg. chrysanthemums.

Long day plants will be induced to flower only when the critical day-length is exceeded. Until the day-length exceeds the critical length, vegetative growth continues. The night is shorter than a critical length. These plants generally flower in the spring or early summer. Eg. - spinach.

3. Day neutral plants will flower under any day-length. They do not initiate flowering based on photoperiodism and can flower regardless of the night length. For eg. - Tomato, rose.

Other than flowering, the growth of stems or roots during certain seasons, or the loss of leaves are also cases  of photoperiodism in plants.