Download Ch. 9 – Cellular Respiration Why does the energy stored in different

Ch. 9 – Cellular Respiration
1. Why does the energy stored in different foods, (carbohydrates, proteins, lipids) differ amongst the types of
food?
The energy stored in each of the macromolecules varies because their chemical structures, and therefore their
energy-storing bonds, differ.
2. Define “cellular respiration” and write out the full equation for the process.
Cellular Respiration is the process by which cells take in food energy and convert it to cellular energy in the form
of ATP. C6H12O6 + 6O2  6CO2 + 6H2O + 36-38 ATP
3. What is “oxygen’s” role in cellular respiration? Why is it so important?
Oxygen is the final electron acceptor in the ETC. It’s important because without O2 present in the mitochondrial
matrix our cells would be unable to attract electrons and remove H+ ions from the electron carriers NADH and
FADH2. When oxidized these molecules can be reused in the CR process, if not, their limited quantities run out
and ETC and Kreb’s shuts down.
4. What is the unique relationship between photosynthesis and cellular respiration? Write out the equations if you
need a little help, look at them closely.
The equations are exact opposites of each other. What one uses for reactants the other produces so they feed
each other.
5. Briefly describe what happens during the process of “glycolysis”. Where does it occur inside the cell?
In Glycolysis, a single molecule of glucose is broken down to 2 pyruvate molecules using an invested 2 ATP in the
cytoplasm of cells. Along this process of oxidation, 2 electron carriers (NAD+) are able to attract a H+ ion and 2
high energy electrons a piece and 4 ATP are produced for a net total of 2 ATP.
6. Briefly describe what happens during the process of the “Kreb’s Cycle”. Where does it occur inside the cell?
In the Kreb’s Cycle, each molecule of Pyruvate are first converted to Acetyl CoA by removing a Carbon atom (CO2
released) and adding a coenzyme A molecule to the structure. In the matrix of the mitochondria there are
recycled 4 carbon molecules (oxaloacetate) that are combined with the 2 carbon Acetyl CoA by removing the
CoA. This new molecule is called Citric Acid. As it proceeds to be oxidized into the oxaloacetate molecule 2
more CO2 molecules are released along with the collection of several electron carriers that will later be used in
the ETC.
7. Briefly describe what happens during the “electron transport chain”. Where does it occur inside the cell?
In the ETC, the electron carriers, NADH and FADH2 that were produced in Glycolysis and Kreb’s are now going to
drop off their high energy electrons and H+ ions onto the mitochondrial membrane. Once there, the energy of
the electrons, with help from electron carrier proteins, will pump the H+ ions against their concentration
gradient out into the intermembrane space, thereby setting up an electrochemical gradient. As the electrons
lose their energy they are combined with loose H+ ions and ½ O2 molecule to form H2O. The H+ ions out in the
intermembrane space are now sitting on some potential energy. Once they reach the ATP synthase enzyme in
the mitochondrial membrane they will be allowed to travel passively down their gradient. This energy will spin
the enzymes structure and perform the process of chemiosmosis (ADP + P  ATP) producing the large majority
of the cellular energy of CR (32-34 ATP).
8. How do some organisms produce energy when oxygen is not available? What is this process called?
Some organisms, including humans, will use a process similar to glycolysis called fermentation. This process
uses fewer steps, does not require O2, and happens at a faster rate. The down side is that the electron carriers
need to get rid of their H+ ions and high energy electrons so other molecules will be used besides O2 as an
electron acceptor. Sometimes the products that are produced are beneficial or harmful to those organisms or
the surrounding environment.
9. Do humans ever need to produce energy in certain body cells when oxygen is not available? Give an example of
when this occurs?
Yes, Lactic Acid Fermentation in skeletal muscles. When muscle cells are void of O2 during intense activities they
will rely upon Glycolysis (LAF) to produce small amounts of energy very quickly to alleviate the immediate need.
However, it can only last for just under a minute or so.
10. What are some ways in which fermentation can be used to produce products that we use on a daily basis?
We use bacteria to produce breads, cheeses, spirits, etc… in food production. We also use bacteria to break
down harmful products that come from industrial uses so we do not pollute our environment.
11. Why would an athlete breathe heavily after a 400 meter race? Explain.
O2 levels would be so low that your muscle cells would go into a phase called oxygen recovery, also known as
oxygen debt. Your body adapts by increasing the respiratory and heart rates to accommodate low levels.