Question

Plants which disregard the requirement of a definite day length for flowering are called
A) Short day plants
B) Long day plants
C) Day-neutral plants
D) Long-short day plants

Answer 1

Photoperiodism is the physiological reaction of organisms to the length of night or a dark period. It is a developmental response. It occurs both in plants and animals.

Complete Answer:
Photoperiodism is the developmental response of an organism to relative length of light and dark period. Flowering plants use a photoreceptor protein like phytochrome to sense photoperiod.
According to the response, plants are classified into three groups

1. Short day plants: These plants flower when the night period is longer. They cannot flower under short nights.
   E.g. Rice, Jower.
2. Long day plants: These plants flower when the night length is critical. These plants flower when the length of the day is longer like in late spring or early summer.
   E.g. Pea, wheat.
3. Day neutral plants: The flowering of these plants are independent of photoperiodism. Day- neutral plants initiate flowering after attaining overall developmental stage.
   Ex. cucumber, roses.

Thus the correct answer is (c). Flowering in day neutral plants are independent of photoperiods.

Note: Flowering plants have photoreceptors which are dependent on photoperiod. Day-neutral plants do not depend on photoperiods. They flower after attaining maturation age.