1. Photosynthesis
Chapter 10

2. Autotroph vs. Heterotroph
Autotrophs
“self-feeders”
Produce organic materials from CO2 and other inorganic materials
Also known as producers
Heterotrophs
Cannot produce their own food
Eat other organisms
Also known as consumers

3. Chloroplasts & Gas Exchange
Site of photosynthesis
Pigment = chlorophyll
Located in the mesophyll cells of plant leaves
Has a double membrane
Contains thylakoids, grana, and stroma
Gases are exchanged through the stomata of leaves

4. 6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2
Photosynthesis
Purpose – to convert light energy into chemical energy stored in sugars or other organic compounds
Anabolic pathway
Occurs in the chloroplasts of plant cells
6 CO2 + 6 H2O + light energy  C6H12O6 + 6 O2

5. Oxidizing Agent in Photosynthesis
Coenzyme NADP+
Accepts electrons and hydrogen ions from water
Transports them to the Calvin cycle
Reduced to NADPH by accepting 2 electrons and 1 hydrogen proton

6. Stages of Photosynthesis
Light Reactions
“photo” part of photosynthesis
Uses solar power to generate ATP and NADPH
Occurs on the thylakoid membrane
Calvin Cycle
“synthesis” part of photosynthesis
Produces organic sugars (G3P) through carbon fixation
Occurs in the stroma

7. Photosystems Overview
Photosystems are located in the thylakoid membranes of chloroplasts
Contain all of the pigment molecules that harvest light energy
Contain a reaction-center complex with a pair of chlorophyll a molecules

8. 1. Light Reactions Requires light energy (photons)
Photons excite electrons on pigments
3 types of pigments: chlorophyll a and b and carotenoids
Uses 2 photosystems: Photosystem II (PS II) and Photosystem I (PS I)
PS II and PS I are connected by an electron transport chain which generates ATP through chemiosmosis (this whole process is called photophosphorylation)
Electrons are ultimately passed on to NADP+

9. 4 7 2 8 3 5 1 6

11. A Closer Look At ATP Production

12. 2. Calvin Cycle 3 molecules of CO2 are “fixed” to produce 1 net G3P
So by using 6 CO2 molecules you are producing 2 G3P molecules
Déjà vu moment (aka: blow your mind moment)
G3P molecules are the first molecules formed during glycolysis when glucose splits in half (each G3P is then further processed to get the pyruvate molecules)
Therefore, by uniting two G3P molecules, you get GLUCOSE! THE ULTIMATE PRODUCT OF PHOTOSYNTHESIS

13. 2. Calvin Cycle Overview of Phases: Carbon Fixation
3 CO2 enter the cycle and each is attached to a RuBP (a 5-C sugar molecule) by an enzyme called rubisco
Each “fixed” RuBP immediately splits in half creating 6 new molecules
Reduction
ATP adds a phosphate to each of the 6 molecule
NADPH adds electrons to reduce each of the 6 molecules
Produces 6 G3P molecules of which 1 is released for use
Regeneration
ATP is used to rearrange the 5 remaining G3P molecules back into the 3 starting RuBP molecules
Requires 9 ATP and 6 NADPH to make one usable G3P

14. This cycle happens twice to utilize all 6 CO2 molecules in the photosynthesis equationb c f d e

15. Carbon Fixation Problem
Photorespiration
On hot/dry days the stomata close which decreases the amount of CO2 intake and increases the amount of O2 retained in the leaves
This may cause O2 to be added to the Calvin cycle instead of CO2 (RuBP will accept it)
Doesn’t produce G3P and consumes ATP
The final product (a 2-Carbon sugar) is rearranged and broken down by peroxisomes and mitochondria releasing CO2 (respiration)
Would be fine if it also produced ATP, but it doesn’t
Normal for C3 plants such as rice, wheat, soybeans

16. Alternative Carbon Fixation Methods (to reduce photorespiration)
C4 Photosynthesis
C4 Plants such as corn and sugarcane
Contain 2 types of photosynthetic cells: bundle sheath cells and mesophyll cells
Use an enzyme called PEP carboxylase to add CO2 to PEP, producing a 4-C sugar in the mesophyll cells
PEP carboxylase can not bind to O2
4-C sugar is sent to bundle-sheath cells where it releases CO2 for the Calvin cycle
Minimizes photorespiration and enhances sugar production

17. Alternative Carbon Fixation Methods (to reduce photorespiration)
CAM
Succulent plants such as cacti and pineapple
Live in dry/arid areas and open their stomata at night instead of during the day
Crassulacean acid metabolism – take the CO2 and carbon fix it into a variety of organic acids at night
During the day when the light reactions are occurring, the organic acids release CO2 for the Calvin cycle