Question

According to the graph, which wavelengths of light drive the highest rates of photosynthesis?

Short answer

According to the graph, the wavelengths 430 to 460nm in the blue range and the 630 -670 nm in the red range drive the highest photosynthesis rate.

Step-by-step solution

Photosynthetic pigments and light absorption

The function of chlorophyll is to absorb energy from light required for photosynthesis. Chlorophyll a is the principal light-harvesting pigment found in all photosynthetic organisms.

Light harvesting is also aided by accessory pigments found in higher plants such as chlorophyll b and carotenoids.

Absorption spectra and action spectra

Absorption spectra refer to a spectrum of colors ranging from red to violet, where red has the longest wavelength. It helps define the wavelengths that are absorbed by chloroplasts.

The absorption spectra of extracted chlorophyll and carotenoids (accessory pigments) exhibit that chlorophyll a and b absorb light in the blue and red regions. Carotenoids absorb light in the blue and green wavelengths.

An action spectrum describes the effectiveness with which specific wavelengths induce a photochemical reaction. Thus, an action spectrum describes the wavelengths that drive photosynthesis.

Wavelength most effective for photosynthesis

Engelmann studied the absorption and action spectra and experimented to determine the wavelengths of light that are most effective for driving photosynthesis.

The absorption spectra showed three curves that represent the light best absorbed by the three types of pigments. The action spectra showed how the rate of photosynthesis depends on the different wavelengths of light.

From the graph, it can be inferred that chlorophyll absorbs maximum light in the blue range (430 to 460 nm) and red range (630 to 670nm).

It is observed more wavelengths of light can be absorbed by these pigments together than chlorophylls alone. This is because it can increase the range of light employed in light reactions as part of photosystems' light-harvesting complexes.

Thus, the blue and red range of light is most effective for photosynthesis.