Question

what is photoperiod ??

Answer 1

Photoperiodism is the physiological reaction of organisms to the length of day or night. It occurs in plants and animals. Photoperiodism can also be defined as the developmental responses of plants to the relative lengths of light and dark periods.

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Answer 2

NCERT based Answer for Class 11 Biology Students

Photoperiodism:  

 Ability of plant to detect and respond to length of daily period of light is called photoperiodism.

 It is observed that some plants require exposure of light for a period longer than the critical period for flowering (long day plants) whereas some require less than critical period (short day plants). Some other plants flower, irrespective of the duration of light exposure (neutral or intermediate day plants).

 It can also be said that the length of darkness must exceed a critical dark period for short day plants to flower while the period of darkness must be shorter than a critical dark period for long day plants to flower.

 Short day plants are Cosmos, dahlia, Chrysanthemum, rice etc. These plants are grown in winter season.

 Long day plants are wheat, barley, sugar beet, larkspur etc. These plants are grown in summer season.

 Neutral plants are Tobacco, cucumber, sunflower, tomato.

 It is believed that a hormonal substance called florigen is responsible for flowering.

 Site of perception of light/dark duration is the leaves. Florigen is synthesised in leaves when plants are exposed to inductive photoperiod.

 The hormone is translocated from leaves to apical meristem for inducing flowering by conversion of vegetative meristem into reproductive meristem.

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