Photosystem 1, in higher plants, converts light into chemical energy. Energy, in
ID: 1062638 • Letter: P
Question
Photosystem 1, in higher plants, converts light into chemical energy. Energy, in the form of photons, is absorbed by a chlorophyll complex, P700 , which donates an electron to A . The electron is passed down an electron-transport chain, at the end of which NADP+ is reduced. The reduction potentials of P700+ , A , and NADP+ , at pH7.0 and 25C are 0.490 V , -0.900 V , and -0.350 V , respectively.
1. Calculate, at pH7.0 and 25C , of the reaction
P700+AP700++A .
Express your answer to four significant figures and include the appropriate units.
2.
At pH7.0 and 25C find rG in kJmol1 for the reaction
NADP++H2(g)NADPH+H+ .
Express your answer using two significant figures and include the appropriate units.
Explanation / Answer
1. Calculate, at pH7.0 and 25C , of the reaction
P700+AP700++A
E0 P700+ = 0.490 V
A = -0.900 V
NADP+ = -0.350 V
NADP++H2(g)NADPH + H+ E0 = 0.350 V
½ O2 + 2H+ + 2e ---à 2 H2O E0 = 0.900V
of the reaction = 1.250 V
Express your answer to four significant figures and include the appropriate units.
2.
At pH7.0 and 25C find rG in kJmol1 for the reaction
NADP++H2(g)NADPH+H+ .
rG0 = -n F E0
F is Faraday constant = 96.5KJ/mol
Plugging all the value in equation
rG0 = - 2 x 96.5 KJ/mol x 1.25 V = -241.25KJ/mol
Answer using two significant figures and include the appropriate units.
= -241.25KJ/mol