Absorption spectra and action spectra

Overview

Wavelengths at which chlorophyll b absorbs most strongly and shape of the action spectrum for a green plant.

What you need to know

Answer each one before you reveal it.

Questions from this subtopic

Each one with the model answer underneath.

1. 1

   What does an absorption spectrum show?

   Model answer

   An absorption spectrum is a graph of the proportion of light absorbed by a pigment plotted against the wavelength of that light.

2. 2

   What does an action spectrum show?

   Model answer

   An action spectrum is a graph of the rate of photosynthesis plotted against the wavelength of light supplied.

3. 3

   State the two regions of the spectrum in which chlorophyll a absorbs most strongly.

   Model answer

   Chlorophyll a has peaks of absorption in the blue-violet region at about 430 nm and in the red region at about 662 nm.

4. 4

   State the wavelengths at which chlorophyll b absorbs most strongly.

   Model answer

   Chlorophyll b peaks at about 453 nm in the blue region and about 642 nm in the red region.

5. 5

   Over which part of the spectrum do the carotenoids absorb?

   Model answer

   Carotene and xanthophyll absorb in the blue and blue-green region, roughly between 400 and 500 nm.

6. 6

   Which wavelengths are absorbed least by the photosynthetic pigments?

   Model answer

   Green light of roughly 500 to 560 nm is absorbed least and is largely reflected or transmitted.

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