Suppose there were plants that had a high concentration of Chlorophyll b, but lacked chlorophyll a, would it carry out photosynthesis? Then why do plants have chlorophyll b and other accessory pigments?
No, plants lacking chlorophyll a would not carry out photosynthesis. Chlorophyll a is the chief pigment associated with photosynthesis. The wavelengths at which maximum absorption by chlorophyll a occurs (blue and red regions) show higher rates of photosynthesis. Without chlorophyll a, light energy cannot be properly utilized.
Plants have chlorophyll b and other accessory pigments (xanthophylls and carotenoids) for two main reasons. First, they absorb light at different wavelengths and transfer the energy to chlorophyll a, enabling a wider range of incoming light to be utilised for photosynthesis. Second, they protect chlorophyll a from photo-oxidation.
Explanation
The textbook clearly establishes chlorophyll a as the 'chief pigment associated with photosynthesis' based on the correlation between its absorption spectrum and the action spectrum of photosynthesis. Accessory pigments like chlorophyll b cannot independently drive photosynthesis - they function to transfer absorbed light energy to chlorophyll a. The two key functions of accessory pigments mentioned in the text are: (1) enabling utilization of a wider range of wavelengths, and (2) protecting chlorophyll a from photo-oxidation.
Solution Steps
Step 1: Identify that chlorophyll a is the chief photosynthetic pigment from the absorption and action spectrum correlation
Step 2: Explain that accessory pigments transfer energy to chlorophyll a, not directly drive photosynthesis
Step 3: List the two functions of accessory pigments - wider wavelength utilization and protection from photo-oxidation