Cellular Respiration



Cellular Respiration

Cellular Respiration—the process by which cells break down food molecules to produce ATP under aerobic conditions.

3 stages of cellular respiration

• glycolysis

• citric acid cycle (a.k.a. Krebs cycle ( Hans Krebs)

• electron transport chain

Glycolysis—an anaerobic process (does not use oxygen).

Occurs in the cytoplasm

➢ Glucose is broken down into 3-carbon molecules called pyruvic acid.

➢ Produces only 2 ATP net. (4 are made but two are used up.)

Krebs cycle—an aerobic process (requires oxygen).

➢ Occurs in mitochondria

➢ Pyruvic acid is broken down and combined with other molecules.

➢ Carbon dioxide (CO2) is released.

➢ Produces only 2 ATP, plus NADH and FADH2 (other energy containing molecules.)

Electron transport chain—an aerobic process

➢ Occurs in mitochondria (*cell membrane in prokaryotes)

➢ NADH and FADH2 from the Krebs cycle go through a “chain” of reactions and combine hydrogen and oxygen to form water (H2O).

➢ Produces 32 ATP.

Fermentation—a process that can produce 2 ATP under anaerobic conditions (without oxygen.)

In animal muscles, fermentation makes lactic acid.

In some simple organisms (like yeast and bacteria), fermentation makes CO2 and alcohol.

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