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. Page 233!

What do we think of when we think of respiration? Cellular Respiration What do we think of when we think of respiration?

Where does this occur?

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

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

G3P

Three Stages Glycolysis Krebs Cycle Electron Transport

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.

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!

Citric Acid

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!

Three Stages Glycolysis Krebs Cycle Electron Transport

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

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

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!

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