Photosynthesis: Capturing Energy

Copyright © 2005 Brooks/Cole — Thomson Learning

Biology, Seventh Edition Solomon • Berg • Martin

Chapter 8

Photosynthesis: Photosynthesis: Capturing EnergyCapturing Energy


Biology, Seventh Edition CHAPTER 8 Photosynthesis: Capturing Energy

• Light• Composed of photons

• Visible light small portion of electromagnetic spectrum• All energy travels as waves• Shorter wavelengths have more

energy than longer wavelengths



Electromagneticspectrum



• Chloroplasts• Organelles enclosed by a double

membrane• Site of photosynthesis• Located mainly within mesophyll cells

inside leaf



Site of photosynthesis



• Chlorophyll• Main photosynthetic pigment• Chlorophyll a, chlorophyll b,

carotenoids, and other photosynthetic pigments are components of thylakoid membranes of chloroplasts



• Photosynthesis is redox process• Light energy captured and converted

to carbohydrates• Hydrogens from water reduce carbon• Oxygen derived from water becomes

oxidized



• Two phases of photosynthesis• Light-dependent

–In thylakoids–Electrons energized by light generate

ATP and NADPH

• Carbon fixation–In stroma–Compounds generated in phase one

provide energy for formation of carbohydrate



Overview of photosynthesis



• Photosystems I and II• Two types of photosynthetic units

involved in photosynthesis• Each photosystem includes

–Chlorophyll molecules–Multiple antenna complexes

• Photosystem I reaction center–P700 has absorption peak at 700 nm

• Photosystem II reaction center–P680 has absorption peak at 680 nm



Photosystem



• Noncyclic electron transport• ATP and NADPH formed • Electrons energized by absorption of

light and pass through electron transport chain to NADP+

• Series of redox reactions• Electrons given up by P680 are

replaced by electrons from photolysis of H2O



Noncyclic electron transport



• Cyclic electron transport• Electrons from photosystem I

returned to photosystem I• ATP produced by chemiosmosis• No NADPH or O2 generated





• ATP synthesis and electron transport• Electrons move down electron

transport chain• Protons (H+) move from stroma to

thylakoid lumen, creating proton gradient

• Greater concentration of H+ lowers the pH



Accumulation of protons in thylakoid lumen



Electron transport and chemiosmosis



• Carbon fixation• Energy of ATP and NADPH used in

formation of organic molecules from CO2

12 NADPH + 18 ATP + 6 CO2 →C6H12O6 + 12 NADP + + 18 ADP + 18 Pi + 6 H2O



• Three phases of Calvin cycle• CO2 uptake• Carbon reduction• RuBP regeneration



Calvin cycle



Summary of photosynthesis



C3 and C4 plant structure compared



Summaryof the C4

pathway

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Photosynthesis: Capturing Energy