In deep shade the photosynthetically active photon flux is of the full-sunlight value of

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Molecular machines, transport and bioenergetics · Molecular machines, transport and bioenergetics

Forces, Machines and Signals, Ch Proton gradients, ATP synthesis and photosynthesis

Problem

In deep shade the photosynthetically active photon flux is 1%1\% of the full-sunlight value of 1.2×1021 photons m−2 s−11.2\times10^{21}\,\mathrm{photons\,m^{-2}\,s^{-1}}. A chlorophyll aa molecule has absorption cross-section σ=3.8×10−20 m2\sigma = 3.8\times10^{-20}\,\mathrm{m^2} at its peak. ((a)) Calculate the absorption rate of one chlorophyll in this shade. ((b)) A reaction centre turns over at 100 s−1100\,\mathrm{s^{-1}}. Calculate the number of chlorophylls needed in its antenna to supply this rate.

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