Cellular RespirationCellular Respiration

In photosynthesis, light In photosynthesis, light energy is stored in the energy is stored in the bonds of glucose bonds of glucose molecules in the molecules in the chloroplasts of plant chloroplasts of plant cells (or other cells (or other autotrophs).autotrophs).

In respiration, energy is In respiration, energy is released from the released from the glucose molecules so glucose molecules so the cells of organisms the cells of organisms can use it for basic cell can use it for basic cell functions.functions.

Compare:

CO2 + H2O --- light energy -- C6H12O6 + O2

C6H12O6 + O2 ---- 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 After glycolysis, pyruvic acid can follow one of two paths:paths:

When oxygen is NOT When oxygen is NOT present...present...

Anaerobic pathways Anaerobic pathways called fermentationcalled fermentation

Either alcoholic or lactic Either alcoholic or lactic acid fermentationacid fermentation

When oxygen IS When oxygen IS present…present…

Aerobic pathway called Aerobic pathway called cellular respirationcellular respiration

Consists of the Krebs Consists of the Krebs Cycle and Electron Cycle and Electron Transport chainTransport 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 andElectron Transport 34 ATP

Total for Cellular Respiration 36 ATP

(compared to only 2 ATPin the anaerobic pathway)

You recover 38 % of the energy in each glucose molecule.The rest is lost as heat energy.