Photosynthesis • Process by which plants use light energy to make food. • A reduction process that makes complex organic molecules from simple molecules.
Ps General Equation 6 CO2 + 6 H2O ---> C6H12O6 + 6 O2 Requires: Chlorophyll Light
Early Question • Does the Oxygen in sugar come from the CO2 or from the H2O ? • Model: CO2 + 2 H2O ----> CH2O + O2
Proof • Used 18O as a tracer. CO2 + 2 H2O ----> CH2O + O2 CO2 + 2 H2O ----> CH2O + O2 Both experiments confirm that water is split. • O2 is a waste product of Ps that altered life on earth.
Ps: a redox process • Hydrogens are added to Carbons. • Water is a source for the Hydrogens. • Complex covalent bonds are made.
Ps • Has two chemical reactions: 1. Light Reaction 2. Dark Reaction Names are from “light” as a requirement, not where or when they occur.
Light • A form of electromagnetic radiation. • Visible light has the right energy for use in Ps.
Too Hot Too Cold JustRight
Action Spectrum • Not all colors are useable to the same degree for Ps. • Red and Blue light - absorbed and used in Ps. • Green light - reflected or transmitted.
Comment • In oceans, red light is lost or filtered out early because it has lower energy. • Only blue light which has higher energy can reach the lower depths.
Result • Many deep ocean fish are bright red in color. • Why? • They can’t be seen because there is no red light to reflect their color.
Photosynthesis Pigments 1. Chlorophylls 2. Accessory Pigments
Chlorophylls • Has CHON and Mg. • Several types possible. • Molecule has a lipophilic tail that allows it to dissolve into membranes. • Contains Mg in a reaction center.
Accessory Pigments • Absorb light energy and transfer it to chlorophyll. • Ex: Carotene (orange). Xanthophyll (yellow)
Fall Leaf Colors • Chlorophyll breaks down. • N and Mg salvaged and moved into the stem for next year. • Accessory pigments remain behind, giving the various fall leaf colors.
Chloroplast Structure • Double outer membrane. • Inner membrane folded and stacked into grana. • Stroma - liquid that surrounds the thylakoid membranes.
Photosystems • Collection of pigments that serve as a light trap. • Made of chlorophyll and the accessory pigments. • Two types known: PSI, PSII
Cyclic Photophosphorylation • Uses PSI only. • Produces ATP. • Requires light.
Noncyclic Photophsphorylation • Uses PSI and PSII. • Splits water, releasing H+, a pair of e-, and O2. • Produces ATP and NADPH. (e- carrier similar to NADH)
Light Reaction • Same thing as Noncyclic Photophsphorylation. • Location - grana of the chloroplast. • Function - to split water and produce ATP and NADPH.
Light Water ADP + Pi NADP+ O2 ATP NADPH Light Reaction Requirements Products
Chemiosmosis Model • The chloroplast produces ATP in the same manner as the mitochondria in Rs. • Light energy is used to pump H+ across a membrane. • When the H+ diffuses back, ATP is generated.
Chemiosmosis • H+ are pumped into the thylakoid space. • ATP and NADPH are made when the H+ diffuse into the stroma.
Comment • There can be a 3 pH unit difference between the thylakoid space and the stroma.
Dark Reactions • How plants actually makes food (carbohydrates). • Don't require light directly to run. • Also known as the Calvin cycle or C3 Ps.
Dark Reaction • Function - to use ATP and NADPH to build food from CO2 • Location - stroma of the chloroplast.
Rubisco • Ribulose BisPhosphate Carboxylase. • Enzyme that adds CO2 to an acceptor molecule. • Most important enzyme on earth.
6 CO2 18 ATP 12 NADPH C6H12O6 18 ADP + 18 Pi 12 NADP+ C3 Ps Requirements Products