Cellular Respiration

•People often think that cellular respiration means breathing because of the word respiration.

•Cellular respiration is not breathing but aerobic cellular respiration does require oxygen.

•In other words, humans can not do cellular respiration unless they breathe and this is what leads to the confusion.

•Cellular respiration is a process within the cell that releases the energy that was stored in chemical compounds(food).

•All living things require energy to maintain life.

•Both autotrophs ( producers) and heterotrophs ( consumers) need to release energy from their food.

•There are two kinds of cellular respiration

• aerobic respiration - uses oxygen

• anaerobic respiration which is called fermentation - does not use oxygen

•Both kinds of respiration start with glycolysis

•Glycolysis breaks a molecule of glucose into two molecules of pyruvic acid. This produces two molecules of ATP and two molecules of NADH

• ATP is a source of energy.

• The small amount of ATP made by glycolysis is enough to keep some very small organisms alive.

• Some bacteria and yeasts get all of their energy from glycolysis.

• Glycolysis does not use oxygen.

• Organisms that get all of their energy from glycolysis must also do fermentation.

• Fermentation does not produce any ATP or any other energy.

• The only purpose of fermentation is to change NADH back to NAD+ so that glycolysis doesn’t stop.

• Glycolysis requires NAD+.

•There are two kinds of fermentation:

•Yeast does alcoholic fermentation which produces alcohol and carbon dioxide( as well as NAD+)

•Bacteria do lactic acid fermentation which produces lactic acid( as well as NAD+)

yeast cells

• Lactic acid fermentation can be used to make a number of products:

• sour cream

• yogurt

• sauerkraut

• vinegar

• cheese

•Alcoholic fermentation is used in the making of bread and other baked goods, as well as alcoholic beverages

•Why are you not affected by alcohol when you eat bread?

•How does fermentation make bread rise?

•The alcohol evaporates when you bake the bread.

•The bread rises because of the bubbles of carbon dioxide produced by the yeast cells as they do fermentation.

•Larger multicellular organisms and even many unicellular organisms need more energy than the small amount produced by glycolysis.

•These organisms start with glycolysis but then they do aerobic cellular respiration.

•Aerobic respiration produces almost 20 times as much energy as glycolysis alone.

•Aerobic respiration requires oxygen.

•Where does aerobic respiration take place?

•In eukaryotic cells, aerobic respiration takes place in the mitochondria.

• Mitochondria is plural. Mitochondrion is singular.

Mitochondrion

•Like photosynthesis, aerobic respiration has two parts.

•Part one is the Krebs cycle ( also called the citric acid cycle)

•The Krebs cycle takes place in the mitochondrial matrix.

•The second part of aerobic respiration is the electron transport chain and chemiosmosis.

•The electron transport chain is in the inner mitochondrial membrane.

•Remember that aerobic respiration is preceded by glycolysis.

•Glycolysis takes place in the cytosol.

•Glycolysis changes each glucose molecule from photosynthesis into 2 molecules of pyruvic acid and also produces 2 molecules of ATP

•The pyruvic acid from glycolysis still contains most of the energy that was in the glucose.

•The pyruvic acid moves into the mitochondrial matrix and enters the Krebs cycle which produces 2 more molecules of ATP.

• The Krebs cycle releases carbon dioxide

•

•The Krebs cycle also produces some other chemicals called NADH and FADH2. These are used in the electron transport chain which is in the mitochondrial matrix.

•These chemicals supply the excited electrons that move along the chain just as chlorophyll did in the light reactions.

•It is the electron transport chain together with a process called chemiosmosis that makes most of the ATP. (34 molecules)

•ATP is the chemical energy that keeps our bodies working. Without energy everything would stop.

•Photosynthesis has an electron transport chain and then a cycle.

•Aerobic respiration has a cycle and then an electron transport chain.

Comparison with Photosynthesis

•In photosynthesis the Calvin cycle needs carbon dioxide which it takes from the atmosphere

•In aerobic respiration the Krebs cycle releases carbon dioxide which goes back to the atmosphere.

•In photosynthesis the electron transport chain splits water molecules and releases oxygen. The oxygen goes into the atmosphere.

•In aerobic respiration the electron transport chain takes oxygen which came from the atmosphere and combines it with hydrogen to make water.

• The equation for photosynthesis is:

• 6CO2 + 6H2O ----> C6H12O6 + 6O2

• The equation for aerobic respiration is:

• C6H12O6 + 6O2 ----> 6CO2 + 6H2O