NEET Biology Plant Growth And Development Based Practice Questions & Answers with Viewers Discussion and Detailed Explanation

Answer: (d)

When continous red light is given the level of $P_r$ decreases as most of it is converted to $P_{fr}$ form. When the concentration of $P_r$ reaches below a critical value, it starts synthesis of more phytochromes in the Pr form so that there is an equilibrium between synthesis and destruction of $P_r$ form.