Cellular Respiration In photosynthesis, light energy is stored in the bonds of glucose molecules in the chloroplasts of plant cells (or other autotrophs). In photosynthesis, light energy is stored in the bonds of glucose molecules in the chloroplasts of plant cells (or other autotrophs). In respiration, energy is released from the glucose molecules so the cells of organisms can use it for basic cell functions. In respiration, energy is released from the glucose molecules so the cells of organisms can use it for basic cell functions.

Compare: CO2 + H2O --- light energy --  C6H12O6 + O2 C6H12O6 + O  CO2 + H2O + energy (3811 calories of energy to be exact)

The breakdown of glucose: I Glycolysis Takes place in the cytoplasm Glucose is broken in half forming two 3 carbon molecules of pyruvic acid Requires 2 ATP molecules to get the process started Produces 4 ATP (net gain of 2 ATP) NAD+ accepts high energy electrons, forms NADH Cells can produce thousands of ATP in milliseconds Process does not require oxygen

After glycolysis, pyruvic acid can follow one of two paths: When oxygen is NOT present... When oxygen is NOT present... Anaerobic pathways called fermentation Anaerobic pathways called fermentation Either alcoholic or lactic acid fermentation Either alcoholic or lactic acid fermentation When oxygen IS present… When oxygen IS present… Aerobic pathway called cellular respiration Aerobic pathway called cellular respiration Consists of the Krebs Cycle and Electron Transport chain Consists of the Krebs Cycle and Electron Transport chain

II Fermentation (anaerobic) Alcoholic fermentation: Yeasts…wine, beer, bread Produces ethyl alcohol and CO2 (waste products) + ATP from glycolysis Regenerates NAD+ so it can be used again in glycolysis Lactic acid fermentation: When the body cannot supply enough O2 for the aerobic pathway…burning sensation in muscles Regenerates NAD+ so it can be used again in glycolysis Lactic acid (waste product) + ATP from glycolysis Bacteria produce cheese, yogurt, sour cream, pickles, sauerkraut

III Cellular respiration (aerobic) Krebs Cycle (citric acid cycle) Pyruvic acid enters mitochondria Produces CO2 as waste product 1 molecule of ADP  ATP 4 NAD+  NADH 1 FAD  FADH2 NADH and FADH2 carry high energy electrons Electron Transport Chain High energy electrons passed from carrier to carrier Their energy is used to convert ADP to ATP Once the electrons have lost most of their energy, they are accepted by H+ and O2, forming water

Cellular Respiration (cont) From 1 glucose molecule: Glycolysis  2 ATP Krebs Cycle and Electron Transport  34 ATP Total for Cellular Respiration  36 ATP (compared to only 2 ATP in the anaerobic pathway) You recover 38 % of the energy in each glucose molecule. The rest is lost as heat energy.