KEY to Questions for Neil 9e, Overview (p. 163) and 9.1 (pp. 164-168)
1. Cellular respiration… [statements taken from section 9.1]
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breaks fuel down, generating ATP and waste products (water and carbon dioxide)
is how the chimpanzee in fig. 9.1 obtains energy for its cells when it eats plants
is how cells harvest the chemical energy stored in organic molecules
is the reaction of organic molecules and oxygen to form carbon dioxide, water ATP, and heat energy
is a synonym for aerobic respiration
is similar, in principle, to the combustion of gasoline in a car engine after oxygen is mixed with the fuel
is: C6H12O6 + 6O2  6CO2 + 6H2O + energy
is exergonic, releasing 686 kcal/mol of glucose decomposed
is a redox reaction: glucose is oxidized, while oxygen is reduced
transfers electrons to a lower energy state, liberating energy
consists of many steps, each one catalyzed by an enzyme, so that the energy released is harnessed efficiently
is electrons traveling “downhill” - from glucose, to NAD+, to the electron transport chain, to O2 (to form water)
is 3 stages: glycolysis, pyruvate oxidation and the citric acid cycle, and oxidative phosphorylation (fig. 9.6)
is catabolic
takes place in the cytosol and the mitochondria
yields about 32 molecules of ATP for every molecule of glucose degraded
2. Cellular respiration is an oxidation-reduction reaction because glucose loses electrons (and protons), while
oxygen gains electrons (and protons). Remember, a hydrogen atom is one electron and one proton. I like the
acronym, “LEO GER:” Lose Electrons Oxidized, Gain Electrons Reduced.
3. NAD+ is a temporary holding container for electrons and protons (a.k.a. hydrogens). When it is carrying 2
electrons and one proton, NAD+ becomes NADH. When it delivers them to the electron transport chain (so they can
be “cashed in” for ATP), NADH becomes NAD+ again.
4. We need to eat nutritious food to obtain niacin, an essential nutrient. This means that niacin is not a molecule we
can make from scratch. Niacin is used to manufacture NAD+/NADH, which help transfer the energy in food to useful
cellular energy. With sufficient cellular energy, we can mount a strong immune response, repair wounds, have cell
division when we need it, and so on. Without sufficient cellular energy, we are likely to become sick. (In fact, lack of
niacin is the cause of a condition known as pellagra.)
5. The efficiency of cellular respiration is calculated by dividing the energy in 32 ATP by the energy in 1 glucose.
Efficiency of respiration = [32 x (- 7.3 kcal/mol) / - 686 kcal/mol ] x 100
= [- 233.6 kcal/mol] / - 686 kcal/mol] x 100
= 0.34 x 100
= 34%, with 56% of glucose energy lost as heat.
If, as stated on p. 150, the actual free energy change for ATP hydrolysis is closer to -13 kcal/mol, then:
= [-416 kcal/mol / -686 kcal/mol] x 100
= 0.61 x 100
= 61%, with 39% of glucose energy lost as heat
For comparison, the efficiency of an incandescent light bulb is 5%, a car engine, 25%, and a small electric motor, 63%.
[Source: www.carolinacurriculum.com]