Question

Exposure to monochromatic light i.e. wavelength greater than 680nm in red zone that cause reduction in yield is
(A). Red drop
(B). Emersons effect
(C). Enhancement effect
(D). Inversion effect
Choose the correct answer from the options given below:

• A. (A) and (D) only.
• B. (B), (C) and (D) only.
• C. (A), (B), (C) and (D).
• D. (A) and (B) only.

Hint:

To keep these straight:
- ______Red Drop (Emerson's 1st Effect):______ Sharp decline in quantum yield under far-red light ($>680\text{ nm}$) alone.
- ______Enhancement Effect (Emerson's 2nd Effect):______ Synergy when combining short red and far-red light together.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Photosynthesis is driven by light energy.
The quantum yield of photosynthesis (the number of $O_2$ molecules released per light quantum absorbed) remains relatively constant across most of the visible light spectrum.
However, research into light wavelengths revealed critical insights into the existence of two distinct photosystems.

Step 2: Detailed Explanation:
Robert Emerson and his colleagues exposed Chlorella cells to monochromatic light of different wavelengths.
They observed that when plants were exposed to monochromatic light of wavelengths greater than $680\text{ nm}$ (far-red light), there was a sudden, sharp, and dramatic decline in the quantum yield of photosynthesis.
Because this drop occurred at the far-red end of the red spectrum, it was named the ______"Red drop" (A)______.
This phenomenon is also historically referred to as the ______"Emerson's first effect" (B)______.
Emerson later discovered that if far-red light ($> 680\text{ nm}$) was supplemented simultaneously with shorter-wavelength red light ($< 680\text{ nm}$), the combined rate of photosynthesis was much higher than the sum of the two rates when administered individually.
This second phenomenon is called the ______Enhancement effect (C)______ (or Emerson's enhancement effect), which proved the cooperative existence of Photosystem I (PSI) and Photosystem II (PSII).
The question specifically asks about the *reduction in yield* under monochromatic light $>680\text{ nm}$, which represents the ______Red drop______ (A) and is the primary part of ______Emerson's effect______ (B).

Step 3: Final Answer:
The phenomena associated with the reduction in yield at wavelengths $>680\text{ nm}$ are (A) and (B) only, which corresponds to option (D).