Question

In Red $\left(P_r\right)$ and Far-red $\left(P_{fr}\right)$ (given alternately) responses of plants, it is the

• A. First treatment that is effective
• B. Middle treatment that is effective
• C. Last treatment that is important
• D. Sum total of all treatments that counts

Answer 1

The correct option is C Last treatment that is important

Phytochromes are pigments present in plants that plays important role in various biological responses of plants like flowering. It is present in two forms, P${}_r$, inactive form and P${}_{fr}$, active form. When P${}_r$ is exposed to red light, it is converted to active form P${}_{fr}$. This active form then responses to various biological processes. When P${}_{fr}$ is exposed to far-red light, it is converted to P${}_r$. After the exposure to red light if it is immediately exposed to far-red light, the active form P${}_{fr}$ is converted back to P${}_r$ and plant will not flower. Similarly, after the exposure of far-red light if it is immediately exposed to red light, the plants will flower as P${}_r$ is again converted back to P${}_{fr}$. Hence, the last treatment which is given that is important.

Thus, the correct answer is option C.