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Honors Biology
Cellular Energetics Homework
Molecules
1. Define ATP, and draw and label its structure.
2. What is NAD+ used for?
Glycolysis
3. Describe glycolysis. Where do the reactions occur? What molecule do you start with?
What do you end with? What other products do you get out of the reaction?
Krebs Cycle
4. The Krebs cycle uses what is left of the glucose molecule broken in glycolysis. It occurs
in the mitochondria. The transfer of pyruvate (the 3-carbon sugar) into the
mitochondria is actually important to cell respiration. What happens to pyruvate as it
crosses the mitochondrial membrane? Aside from acetyl-CoA, what other molecules
result from this reaction?
5. Describe in general terms what happens in the Krebs cycle. The two carbons that are
left from pyruvate enter. What happens to them? What are the products you get from
the cycle?
6. Why is it important that the Krebs cycle be a cycle? In other words, why do you start
with oxaloacetate, and end up with oxaloacetate?
7. There are two purposes of the Krebs cycle. One is for cell energetics—to produce ATP.
What is the other? How is the Krebs cycle run differently to accomplish this second
goal?
Electron Transport Chain
8. Describe the electron transport chain. How many ATP are produced from one
NADHH+? From one FADH2? What does oxygen do?
9. How does the F1F0 ATPase work? How many protons must pass through it to make one
ATP?
10. You have discovered life on Mars. You become instantly world famous and insanely
rich. You perform some fundamental biochemical research on this life, and discover it
has a different cellular respiration process than life on Earth. This earns you the Nobel
Prize and the deep respect of your scientific peers. You die incredibly successful, rich,
and fulfilled.
The Martian’s respiration cycle produces the following molecules:
46 NADHH+, 14 FADH2
Its ATPase needs three protons to pass through in order to make one ATP.
How many ATP will it make, assuming that everything else works the same as
terrestrial life?
11. The miniature candy bars you get on Halloween contain about 2.3 x 10 22 (23 000 000
000 000 000 000 000) glucose molecules. How many ATP would you get from eating
just one?
12. A chemical reaction creates 7 NADHH+. How many ATP will this produce?
You get 17 FADH2 from a different reaction. How many ATP would this create?
Fermentation
13. What is fermentation? What are two chemicals produced by fermentation? Which one
is created by humans?
14. Why does your body perform fermentation when there is no oxygen present?
15. If someone dies from suffocation, the medical examiner can often determine this by
examining the pH of the blood. Blood pH is normally about 7.4 (slightly basic). After
someone is deprived of oxygen for long periods, their blood becomes acidic, a medical
condition called acidosis.
This occurs for two reasons: First, CO2 builds up the blood. When CO2 dissolves in
water, it forms an acid called carbonic acid.
What is the second reason? Think fermentation…
Photosynthesis
16. Give the balanced chemical formula for photosynthesis. How is it related to cellular
respiration?
17. What is the purpose of the light reactions? The Calvin Cycle (dark reactions)?
Light Reactions
18. Compare the light reactions of photosynthesis to the electron transport chain in
mitochondria. Think about where they are located, what parts they share, and what
parts are different.
19. PSII (photosystem II) requires light and water to function. Describe what each is used
for.
Dark Reactions
20. The role of the dark reaction is to create glucose. Why do plants, who receive so much
energy from the light reactions, need glucose?
21. The dark reactions require three chemicals to create glucose. Provide them.
This question is optional, and will not be graded. For serious students who want to think a little
more deeply:
22. When a glucose molecule is broken down in the mitochondria of plants, 36 ATP are
produced. When a glucose molecule is created in photosynthesis, it takes the
equivalent of over 50 ATP to create. Why is it so much more expensive to make
glucose?