Answers to the RI and UC questions
Reviewing Ideas
1. How are membranes involved in respiration?
Membranes are the site of the electron transport system in the mitochondria. Also, many
Krebs-cycle enzymes are membrane-bound. The plasma membrane serves a similar
function in prokaryotes.
2. Where in a cell does each part of cell respiration take place? Describe how the
location of each part of the process is different in bacteria an din more complex cells.
The cytosol is the site of glycolysis in both prokaryotic and eukaryotic cells. The
mitochondrion is the site of the Krebs cycle and the electron transport system in
eukaryotes, while the plasma membrane serves that function in bacteria.
4. What are the biological functions of these processes?
a. Cell respiration: breaks down food molecules in steps that allow the cell to
conserve the food’s energy in usable packets of ATP
b. glycolysis: produces stored energy in the form of ATP, NADH needed for ATP
synthesis, carbon skeletons for biosynthesis and pyruvate needed for
the Krebs cycle
c. Krebs cycle: forms ATP for energy, NADH an dFADH for ATP synthesis, and
carbon skeletons for biosynthesis.
d. electron transport chain: forms ATP for energy
5. Discuss the ways in which biosynthesis depends on cell respiration?
Biosynthesis depends on cellular respiration for energy in the form of ATP and for
carbon skeletons to be used as building blocks during biosynthetic reactions
6. How does the Krebs cycle depend on glycolysis? How does the electron transport
chain system depend on the Krebs cycle?
The Krebs cycle depends on glycolysis for a supply of pyruvate. The electron transport
system depends on the Krebs cycle for hydrogen atoms supplied in the form of NADH
and FADH2
Understanding Concepts
2. Why would you not expect to find mitochondria in anaerobic organisms?
Anaerobic organisms live by fermentation, which occurs in the cytosol. Mitochondria
provide the sites for the Krebs cycle and the electron transport system, which are not used
by bacteria
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6. Some cells contain no mitochondria at maturity. If these cells receive ample glucose,
could they use it for energy? Would they release carbon dioxide? Could these cells use
fat as a source of energy? Explain your answers.
Cells lacking mitochondria can use glucose to produce energy. Since they cannot carry
out the Krebs cycle or electron transport, they do not produce carbon dioxide. Such cells
could not use fat as a source of energy because fats enter respiration through the Krebs
cycle.
8. The complete oxidation of glucose to carbon dioxide produces about 686 kcal of free
energy. Oxidation of a molecule of glucose in a cell generates a maximum of 38
molecules of ATP. ATP provides about 7.3 kcal of energy. Calculate the efficiency of
the ATP energy yielded from the complete aerobic respiration of glucose. What happens
to the rest of the energy?
Using the values provided, the efficiency of aerobic respiration of glucose is about 40%.
The rest of the energy is converted to heat.