Rock Eaters ■ 95travel into any organelle. The sensor relays information stating that
it has lodged itself in a compartment of the mitochondrion, where
there is a concentration gradient of hydrogen ions (H+) and levels
of ATP production are high. From what you know about cellular
respiration in mitochondria, where is the sensor lodged?(a) inner mitochondrial membrane(b) mitochondrial matrix(c) chloroplast stroma(d) cell cytoplasm(e) plasma membraneLeveling Up
(^15) What do you think? What would happen if a virus destroyed all
photosynthetic organisms on Earth?
(^16) Write Now biology: calorie-burning fat Your friend has e-mailed
you a link (see below) to a New York Times article on “brown” fat.
He has been trying to lose weight and wants to know whether you
think it would be a good idea for him to spend more time in the cold,
rather than continuing to exercise regularly. He is also interested
that the article mentions ephedrine’s ability to stimulate brown
fat, and he asks if you think he should begin to take ephedrine
supplements. Compose an reply to your friend addressing the
following points (using one to two paragraphs for each one).
[Note: You may need to do further reading to answer (b) and (c).]
a. Explain in detail how brown fat burns calories when someone is
chilled.
b. Explain how ephedrine affects metabolism and what its possible
side effects are.
c. Contrast (a) and (b) with the effect of exercise on metabolism,
both in the short term and in the longer term by increasing
muscle mass.
d. In your final paragraph, advise your friend as to whether he
should begin spending time in the cold to increase weight loss or
take ephedrine supplements, and whether he should continue to
exercise regularly. Justify your opinion with data and logic.
To research your answer, begin with the following New York Times
article, published on April 8, 2009: “Calorie-Burning Fat? Studies
Say You Have It” (http://www.nytimes.com/2009/04/09/health/
research/09fat.html). Consult and reference at least two additional
sources in your answer.
(^17) Is it science? Wouldn’t it be amazing if humans could
manufacture their own food through photosynthesis like plants
do? Use Internet research to determine whether this idea is real
science or science fiction. Is there evidence that animals can use
the sun’s energy directly and/or perform photosynthesis in nature?
In the lab? If so, how would that capability affect life as we know it?
(d) ATP is accumulating in muscle cells, causing a burning
sensation.
(e) Without adequate oxygen, muscle cells are fermenting pyruvate
into lactic acid.
(^11) The graph presented here depicts the activation energy, or
the amount of energy needed for a reaction to proceed, with and
without an enzyme.
Reactants
Products
Progress of the reaction
Energy
Course of
reaction
without
enzyme
Course of
reaction
with
enzyme
a. Which reaction requires more energy to proceed—the one with
or without an enzyme? How do you know?
b. Is this reaction anabolic or catabolic? How do you know?
Tr y Something New
(^12) In 2012, an Illinois man was killed by cyanide poisoning after he
won a million dollars in the lottery. Cyanide is a lethal poison because
it interferes with the electron transport chain in mitochondria. What
effect would cyanide have on cellular respiration?
(a) Glycolysis, the Krebs cycle, and oxidative phosphorylation
would all be inhibited.
(b) The Krebs cycle would be inhibited, but oxidative
phosphorylation would not.
(c) Oxidative phosphorylation would be inhibited.
(d) Glycolysis, the Krebs cycle, and oxidative phosphorylation
would all be stimulated.
(^13) Plants in the genus Ephedra have been harvested for their active
substance ephedrine for centuries. Ephedrine is used to reduce
the symptoms of bronchitis and asthma, as a stimulant and study
aid, and as an appetite suppressant. It is also the main ingredient
in the illegal production of methamphetamine. Since 2006, the
sale of ephedrine and related substances has been limited and
monitored in the United States. One effect of ingesting ephedrine is
greatly increased metabolism, which has been known to kill users of
ephedrine. How might an increased metabolic rate cause death?
(^14) You have been transported into the future, where a
nanosensor can be inserted into a living cell and subsequently
For more, visit digital.wwnorton.com/bionow2 for access to:
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