Question

The action spectrum of photosynthesis shows a high light absorption for violet/blue and orange/red and low absorption for green/yellow. If we were to set up an experiment where narrow bands of unicoloured light were shown on an aquatic plant such as Hydrilla, and we counted the number of bubbles of oxygen produced as an indicator of photosynthetic rate, how would the graph appear?

• A. Just like the action spectrum with peaks at violet/blue and orange/red and a trough at yellow/green
• B. Exactly inverted from the action spectrum with a peak for yellow/green
• C. Perfectly flat because many wavelengths are used by chlorophyll
• D. A descending line because ultra-violet has more energy than infra-red

Answer 1

Answer: (A)

Just like the action spectrum with peaks at violet/blue and orange/red and a trough at yellow/green

Through the photosynthetic process plants take up carbon dioxide and evolve oxygen. The whole process is principally dependent on light, O2, temperature and water supply from the surrounding environment. The efficiency of photosynthesis with monochromatic (uni-colored) light as a function of the wavelength of light is known as the action spectrum of photosynthesis. The absorption of light by the pigments is termed as an absorption spectrum, which varies from pigment to pigment. For photochemical reactions involving a single pigment, the action spectrum has the same general shape as the absorption spectrum of the pigment.

So, the correct option is 'Just like the action spectrum with peaks at violet/blue and orange/red and a trough at yellow/green'.