1. Phytochrome has 2 forms Red-absorbing phytochrome
Far red absorbing phytochrome
Interconverted
Two forms of the same compound
Total amount same Pr
Pfr Pr
Pfr

2. In red light Pfr Pr Pfr Pr absorbs red light, changes to Pfr form.
Pfr doesn’t absorb red light, stays the same.

3. In far red light Pr Pr Pfr
Pr doesn’t absorb far red light, stays the same.
Pfr absorbs far red light, changes to Pr form.

4. Sunlight
Mostly red
A little far red

5. In sunlight In sunlight most P gets converted to Pfr form. Pr Pfr Pfr

6. Start of night Most P in Pfr form. Pr Pfr Pfr Pr Pfr Pr Pfr Pfr Pr Pfr

7. In the dark Pfr form changes gradually to Pr form. Pfr Pr Pfr Pr Pfr

8. After a short night Pfr still left. Pfr Pr Pfr Pr Pfr Pr Pfr Pfr Pfr

9. Later in the night More Pfr changes to Pr. Pfr Pr Pr Pfr Pfr Pfr Pr

10. After a long night All the Pfr is gone. Pr Pfr Pr Pr Pfr Pfr Pr Pr Pr

11. Day dawns Most P gets converted to Pfr form again. Pr Pfr Pfr Pr Pfr