Photoperiodism refers to the induction of flowering in plants in response to photoperiods. Phytochromes are the blue green pigments that sense the light and dark periods. Phytochorome exists in two interchangeable forms that are regulated by ratio of red to far-red light. Exposure of Pr form of phytochrome to red light converts it into Pfr form which is physiologically active form and restore the flowering process.
I think the correct answer among the choices listed above is option B. For photoperiodism to occur, a plant must use a phytochrome. This is a pigment that plants use to detect light. It is sensitive to light in the red region. Hope this answers the question.
The answer is C because the rest of the answer choices are all physical reactions. In your stomach, food is chemically broken down by different substances.
