1. Where we left off… Oxygen gas (released through stomata)
What are the products created by photosynthesis?
Oxygen gas (released through stomata)
* GLUCOSE * (C6H12O6)
These are created by autotrophs
(producers) from energy in sunlight
GLUCOSE = a form of energy that is storable and transportable
But NOT readily usable by cells
Another cellular process is required in order to transform energy stored in glucose into the energy currency that is usable by the cell…
ATP

3. Intro to: Respiration What does the word “respiration” mean to you?
What about “cellular respiration”?
Cellular Respiration – the process by which cells make ATP by breaking down organic compounds (glucose molecules)
Photosynthesis:
6 CO2 + 6 H2O + energy (sunlight) → C6H12O6 + 6 O2
Respiration:
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + energy (ATP)
Cellular Respiration is essentially the reverse of photosynthesis! … Just look at the formulas!
What types of organisms perform cellular respiration?
Animals?
Plants?
Both?

4. The Mitochondrion Internal Organization:
We referred to it as the “powerhouse” of the cell
The site of cellular respiration
One of three eukaryotic organelles surrounded by a double-membrane… what are the other two?
Internal Organization:
Cristae – Infoldings of the inner membrane
Matrix – Space within the inner membrane

5. Respiration Overview
There are two phases to the overall process of cellular respiration
GLYCOLYSIS (try to reason what this word means)
- Glyco = Sugar
- Lysis = Breakdown
RESPIRATION
- Anaerobic Respiration (Fermentation)
▪ Air (oxygen) is not needed/absent
- Aerobic Respiration
▪ Air (oxygen) is needed/available

6. Cleave (break up) glucose into two smaller molecules
The Cell’s Decision
Start with glucose
Cleave (break up) glucose into two smaller molecules
Decide whether or not oxygen is present
Carry out aerobic or anaerobic respiration
…to ferment, or not to ferment?

7. Glycolysis Glycolysis occurs in the cytoplasm
Another example of a biochemical
pathway, catalyzed by enzymes
Start with glucose
2 ATP’s are spent in the first step
*** 2 molecules of NAD+ are consumed ***
4 ATP’s are made in the fourth step
The end result of glycolysis is:
2 molecules of pyruvic acid (3-carbon)
Efficiency of glycolysis = 3.5 %
Glycolysis isn’t getting us as much “bang for our buck” as we could be getting out of one molecule of glucose

8. Anaerobic Respiration
Remember: after glycolysis, the cell must
make a decision about what to do next
When oxygen is NOT present in the cell, it chooses to carry out: anaerobic respiration (fermentation)
LACTIC ACID FERMENTATION
An enzyme converts pyruvic acid into lactic acid (3-carbon)
NO ATP IS MADE
*** NAD+ is created ***
ALCOHOLIC FERMENTATION
- Performed by a special set of enzymes in yeast
- CO2 is given off
- End product is ethyl alcohol (2-carbon)

9. Fermentation and You Lactic Acid Fermentation
Think about how your body is responding when you exercise
Muscles are working hard (using ATP)
You are breathing heavy (not getting enough O2)
THESE ARE PERFECT CONDITIONS FOR FERMENTATION
After a hard workout, why are your muscles sore?
ANSWER: Lactic acid has built up in the cytosol
Alcoholic Fermentation
This process is the basis of the beer and wine industry
Yeast cells are added to a fermentation mixture, and ethyl alcohol accumulates
Baking bread also depends on this type of fermentation

12. Aerobic Respiration
Anaerobic respiration is sufficient for most small, unicellular organisms
However, for organisms with higher energy requirements (like us), the low efficiency of glycolysis is not sufficient
Remember: after glycolysis, the cell must make a decision about what to do next
When oxygen is present in the cell, it chooses to carry out aerobic respiration
2 Main Steps
The Krebs (Citric Acid) Cycle
* Occurs in the matrix of the mitochondrion
Electron Transport Chain
* Occurs on the inner membrane of the mitochondrion

13. The Krebs Cycle The History of the Krebs Cycle
Pyruvic acid diffuses from the cytosol into the matrix of the mitochondria
It is then converted into a
2-carbon molecule called
Acetyl CoA in a simple reaction that creates and releases CO2
The History of the Krebs Cycle
Discovered by Hans Krebs, German biochemist ( )
Sometimes called the citric acid cycle

14. The Krebs Cycle OUTPUT:
1 molecule of Acetyl CoA is broken down by each turn of the cycle
Therefore, one glucose molecule causes two cycles
Therefore, one molecule of glucose yields…
6 molecules of NADH
2 molecules of FADH2
2 molecules of ATP
4 molecules of CO2
These molecules will be utilized in the next (and final) step of respiration:
THE ELECTRON TRANSPORT CHAIN
The Krebs Cycle

15. The Electron Transport Chain
Occurs on the inner mitochondrial membrane
NADH and FADH2 contain high energy electrons that are passed along a transport chain (similar to the chain in the light reactions of photosynthesis)
The energy they release is used to pump protons out of the matrix
Chemiosmosis: protons diffuse back into the matrix through the enzyme ATP synthase
Oxygen’s role = final electron acceptor
As electrons leave the transport chain, they are combined with oxygen and protons in order to form water…
O2 + 4e- + 4H+ → 2H2O

16. Energy Scorekeeping Yields 2 ATP per 1 glucose molecule
Glycolysis and Anaerobic Respiration
Yields 2 ATP per
1 glucose molecule
3.5% efficiency
Glycolysis and Aerobic respiration
Yields a total of 38 ATP per 1 glucose molecule
66% efficiency