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Chapter 34: Problem 47

Chlorophyll is a photosynthetic molecule common in green plants. On a per- unit-wavelength basis, its ability to absorb visible light has two peaks, at \(430 \mathrm{nm}\) and \(662 \mathrm{nm}\). (a) Find the corresponding photon energies. (b) Use these peak wavelengths to explain why plants are green.

Short Answer

Expert verified
The corresponding photon energies for the two peaks of chlorophyll absorption (at 430 nm and 662 nm) can be computed by using the Planck-Einstein relation. Plants appear green because chlorophyll mainly absorbs light in the blue and red regions of the spectrum, but reflects light in the green region.

Step by step solution

01

Wavelength to Energy Conversion

The energy of a photon is computed using the formula: \[E=h\nu=h(c/\lambda)\], where \(h=6.626 \times 10^{-34} \mathrm{J} \cdot \mathrm{s}\) is the Planck constant, \(c=3.00 \times 10^{8}\) m/s is the speed of light and \(\lambda\) is the wavelength in meters. First convert the given wavelengths from nm to meters and then use the formula to get the energy for the photons related to \(430 \mathrm{nm}\) and \(662 \mathrm{nm}\).
02

Spectral Absorption and Color Perception

The color an observer perceives from an object is the light that is reflected from or transmitted through that object. In the case of plants, chlorophyll absorbs light most efficiently at the blue (430 nm) and red (662 nm) regions of the spectrum. This light is used in the photosynthesis process. Green light (around 500-570 nm) however is not absorbed efficiently and is thus reflected, making plants appear green.

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