Big Idea: Cellular respiration and fermentation harvest free energy from sugars to produce free energy carriers (ATP.) The energy in sugars drives metabolic pathways in cells. Photosynthesis and respiration are interdependent processes.

1. All living systems require a constant input of energy to maintain ordered systems

- What does this have to do with the 2nd Law of Thermodynamics?


2. Energy is used to maintain organization, grow, reproduce, and maintain body temperature (endotherms)

- What would happen if the amount of free energy in an organism changed?


3. Autotrophs and heterotrophs both capture free energy, just in different ways

4. Cellular respiration is the breakdown of glucose (C6H12O6) in the presence of oxygen (O2) to produce cellular energy - ATP

C6H12O6 + 6O2 → 6 CO2 + 6H2O + 36 ATP

Summary of Graphic

A. Glycolysis rearranges bonds in glucose, releasing ATP and producing pyruvate

B. Pyruvate moves to the mitochondria, where it is used in the Krebs Cycle

C. In the Krebs cycle, carbon dioxide is released and 2 ATP synthesized.

D. The Krebs cycle also produces NADH and FADH2 which are used in the electron transport chain

E. The electron transport chain produces 32 ATP (chemiosmosis)


The electron train uses hydrogen pumps and ATPase to generate ATP. Where have we seen this before?



At the end of ETC, electrons are donated to oxygen, which combines and forms water. This is why we need oxygen, without it, the ETC would not function.

cellular respiration

Anaerobic Respiration - without oxygen

Fermentation (anaerobic respiration)

In this process, the cell uses glycolysis to break up glucose (just as in aerobic respiration.) This reaction results in a byproduct called lactic acid. Fermentation produces less ATP than aerobic respiration.

Muscle cells will use this path during strenuous workouts where you accumulate and oxygen date. The lactic acid is what causes muscle soreness.

Fermentation of yeasts is used for the production of beers and wines.

Food for Thought

1. What is the purpose of cellular respiration?


2. Where does cellular respiration occur within the cell?


3. Why is oxygen necessary? What happens when oxygen is not available?


4. Comparing photosynthesis to respiration

a) Where does each occur?


b) What are the products of each?


c) Describe the role of ATPase in photosynthesis and cellular respiration.


5. Do plants have mitochondria and do they need to respire? How would you design an experiment to determine if plants exhibit cellular respiration?