1. Photosynthesis: Alternative Pathways
The environment in which an organism lives can impact the organism’s ability to carry out photosynthesis.
C4 plants (sugar cane and corn) – during hot days, Calvin Cycle occurs in different types of cells (location) to minimize water loss.
CAM plants (desert and marsh plants) – in dry or saline environments, Calvin Cycle occurs at a different time.
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2. What do we think of when we think of respiration?
Cellular Respiration
What do we think of when we think of respiration?

3. Where does this occur?

4. oxygen required (aerobic)
Three Stages
Glycolysis – no oxygen required (anaerobic)
Krebs Cycle
Electron Transport
oxygen required (aerobic)
What does anaerobic mean?

5. Glycolysis Glucose is broken down in the cytoplasm through glycolysis.
Net yield: two molecules of ATP, two molecules of NADH, two molecules of pyruvate

6. G3P

7. Three Stages
Glycolysis
Krebs Cycle
Electron Transport

8. Krebs Cycle
Pyruvate (from glycolysis) is broken down into carbon dioxide (CO2) through a series of reactions.
In the presence of oxygen (aerobic)
Basic steps:
Pyruvate reacts with coenzyme A (CoA) to form acetyl CoA.
Carbon Dioxide is released
NAD+ is converted to NADH
Acetyl CoA moves to the mitochondrial matrix.

9. Krebs Cycle - continued
Acetyl CoA combines with a 4-carbon compound to form a 6-carbon compound called citric acid.
Citric acid is broken down in a series of steps releasing the following molecules:
2 CO2
1 ATP
3 NADH
1 FADH2 – similar to NADH
Ends with four carbon compound
Cycle continues with the production of a new acetyl CoA and turns again because there are two molecules of pyruvate.
Keep in mind that with two molecules of pyruvate being formed, the cycle goes through two turns!

10. Citric Acid

11. look out for these again!
Krebs Cycle – Net Yield
Keep in mind some of these are produced “pre- cycle”
6 CO2
2 ATP
8 NADH
2 FADH2
look out for these again!

12. Three Stages
Glycolysis
Krebs Cycle
Electron Transport

14. Electron Transport The stage where the most ATP is produced – 32!
High energy electrons and hydrogen ions from NADH and FADH2 are put to work.
Electrons move along membrane from one protein to another.
This release of electrons also causes NADH and FADH2 to lose a proton (H+)
These protons are pumped into intermembrane space from the mitochondrial matrix

15. Electron Transport - continued
The protons (H+) then diffuse back down their concentration gradient through ATP synthase
This flow of protons causes the formation of ATP
Oxygen is the final electron acceptor to form H2O
Some prokaryotes also go through aerobic respiration (utilizing their cell membrane)
Cellular Respiration Net Yield: 36 ATP

17. Anaerobic Respiration
Done by many prokaryotes, and on occasion by eukaryotes.
A pathway by the name of fermentation follows glycolysis in anaerobic respiration.
Produces limited ATP
Replenishes NAD+ (see next slide)
Lactic Acid Fermentation – muscles!
Alcohol Fermentation – yeast and bacteria.
Some cells may function for a short time when oxygen levels are low.
What would be the problem in solely relying on glycolysis? (Have ppt up, go back to slide) NAD+ runs out!

18. Lactic Acid Fermentation Alcohol Fermentation
Key step – replenishing of NAD+