1. Cellular Respiration - Harvesting Chemical Energy
Add anything with *** to your handout
Cellular respiration – breaking down food to make ATP using oxygen as a final electron acceptor
*** Gas exchange done in lungs functions to maintain levels of gas in your body due to this process (take in/use oxygen and make/release carbon dioxide)

2. Cellular Respiration - Harvesting Chemical Energy
Plants and animals both use products of photosynthesis (glucose) for metabolic fuel.
*** So plants have mitochondria too. Remember that photosynthesis is merely an autotrophs way of getting food.
Heterotrophs: must take in energy from outside sources, cannot make their own e.g. animals
When we take in glucose (or other carbs), proteins, and fats-these foods don’t come to us the way our cells can use them. We must break them down to make ATP.

3. Cellular Respiration Overview
Transformation of chemical energy in food into chemical energy cells can use: ATP
These reactions proceed the same way in plants and animals. Process is called cellular respiration
Overall Reaction:
C6H12O6 + 6O2 → 6CO2 + 6H2O
*** Notice that this is the exact opposite of photosynthesis
Why do we need this process (or why don’t we just break down our food all at once?)

4. Draw and label this picture on your handout

5. Cellular Respiration Stages
Stage 1: Glycolysis
Series of reactions which break the 6-carbon glucose molecule down into two 3-carbon molecules called pyruvate in the cytoplasm
*** Process is an ancient one-all organisms from simple bacteria to humans perform it the same way
Notice this occurs in the cytoplasm so mitochondria are not required (so bacteria can do it)
Yields 2 ATP and 2 NADH molecules for every one glucose molecule broken down, BUT *** For eukaryotic organisms, the main purpose of this stage is to break down glucose to pyruvate
*** NADH is electron carrier like NADPH in photosynthesis (think P for photosynthesis to differentiate the 2)
After this point, life diverges into two forms and two pathways.
Anaerobic cellular respiration (aka fermentation)
Aerobic cellular respiration

7. ***(Whole slide) Anaerobic Cellular Respiration
Some organisms thrive in environments with little or no oxygen
Marshes, bogs, gut of animals, sewage treatment ponds
No oxygen used = anaerobic
All prokaryotic organisms do only this level of cellular respiration as they do not have mitochondria for the next 2 steps
Results in no more ATP, final steps in these pathways serve ONLY to regenerate NAD+ so it can return to pick up more electrons and hydrogens in glycolysis.
End products are ethanol and CO2 (single cell fungi (yeast) in beer/bread) or lactic acid (muscle cells)
Why wouldn’t every species want to use this type of respiration?

8. Aerobic Cellular Respiration
Oxygen required=aerobic
2 more sets of reactions which occur in a specialized structure within the cell called the mitochondria
1. Kreb’s Cycle (Citric Acid Cycle)
2. Electron Transport Chain

10. Step 2 of Cellular Respiration: Citric Acid Cycle (*** Kreb’s Cycle)
Completes the breakdown of glucose
Takes the pyruvate (3-carbons) and breaks it down, the carbon and oxygen atoms end up in CO2 and H2O
*** Occurs in mitochondrial matrix
Hydrogens and electrons are stripped and loaded onto NAD+ and FAD to produce NADH and FADH2
*** FADH2 also an electron carrier
** Production of only 2 more ATP so main purpose of this stage is to produce electrons carriers (NADH and FADH2) for next stage

12. 3RD Step of Cellular Respiration: Oxidative Phosphorylation (
3RD Step of Cellular Respiration: Oxidative Phosphorylation (** Production of ATP in first 2 stages called “substrate” level b/c doesn’t use oxygen)
Electron carriers loaded with electrons and protons from the Kreb’s cycle move to this chain-like a series of steps (staircase). (What are these “electron carriers”?)
*** As electrons drop down stairs, energy released to pump H+ ions into the INTERMEMRANE SPACE.
This is called the Electronic Transport Chain and is similar to the ETC used in chloroplasts for photosynthesis.
These H+ ions flow back into the MITOCHONDRIAL MATRIX through the ATP Synthetase (remember chemiosmosis) to create a total of 32 or 34 ATP
Oxygen waits at bottom of staircase, picks up electrons and protons and in doing so becomes water.
This is the reason why breathe harder and faster whenever we are exercising. Also the reason why you can see moisture when you breathe on a window.

13. Why oxygen?
***Oxygen is the most electronegative (what did this word mean) element in living organisms.
This means that the electrons can “fall” through more molecules releasing more kinetic energy.
Combining hydrogen to oxygen at the end of the ETC makes water (which is why you can see moisture if you breathe on glass).

14. Electron Transport Chain and Chemiosmosis Similarities and differences for mitochondria and chloroplasts

16. Energy Tally 36 ATP for aerobic vs. 2 ATP for anaerobic
Glycolysis ATP
Kreb’s ATP
Electron Transport 32 ATP
36 ATP
Anaerobic organisms can’t be too energetic but are important for global recycling of carbon

18. Glucose (carbs) are not the only macromolecule that can be used in cellular respiration. Proteins and fats can also be broken down for energy as well.