The proteinaceous pigment that acts as the center of activities concerned with light is:

When the dark period of short-day plants is interrupted by a brief exposure of light,then the plant:

Assertion: Dark period plays a more important part in flowering than the light period.
Reason: Flowering occurs in short-day plants if the dark period is interrupted by a light break.

Some plants require exposure to light for a period exceeding a well-defined critical duration. These plants are known as:

Photoperiodism was first observed in

The response of different organisms to the environmental rhythms of light and darkness is called