Living organisms are open systems that exchange energy with their surroundings.
Correct Answer
True
True. Organisms take in energy, for example as food or sunlight, and release energy, for example as heat. Because they constantly exchange energy with their environment, they are open systems.
Category: Energy and Thermodynamics
Question 2
According to the second law of thermodynamics, energy transfers are perfectly efficient, with no energy lost as heat.
Correct Answer
False
False. The second law states that no energy transfer is completely efficient, so some energy is always lost as heat that cells cannot use. This is why organisms need a steady supply of energy.
Category: Energy and Thermodynamics
Question 3
Entropy is a measure of the disorder of a system.
Correct Answer
True
True. Entropy describes disorder, and higher entropy means more disorder and less energy available for work. Living things are highly ordered, so they must use energy constantly to keep their entropy low.
Category: Energy and Thermodynamics
Question 4
Endergonic reactions release free energy and occur spontaneously.
Correct Answer
False
False. Endergonic reactions have a positive change in free energy, so they absorb energy and are not spontaneous. Exergonic reactions are the ones that release free energy and occur spontaneously.
Category: Energy and Thermodynamics
Question 5
Even an exergonic reaction needs a small input of activation energy to get started.
Correct Answer
True
True. All reactions, including those that release energy overall, need activation energy to begin breaking bonds in the reactants. Enzymes speed reactions by lowering this energy barrier.
Category: Enzymes
Question 6
An enzyme changes the overall free energy difference between the reactants and products of the reaction it speeds up.
Correct Answer
False
False. An enzyme lowers only the activation energy and leaves the overall free energy change of the reaction the same. A reaction that is endergonic without the enzyme is still endergonic with it.
Category: Enzymes
Question 7
Extreme heat or an extreme pH can denature an enzyme, changing its shape so that it no longer works.
Correct Answer
True
True. An enzyme's activity depends on its three-dimensional shape, especially the shape of its active site. Excess heat, extreme pH or very high salt can unfold the protein, and a denatured enzyme loses its function.
Category: Enzymes
Question 8
A noncompetitive inhibitor works by binding directly to the enzyme's active site.
Correct Answer
False
False. A noncompetitive, or allosteric, inhibitor binds to a site away from the active site and changes the enzyme's shape so that the substrate binds poorly. Inhibitors that bind the active site itself are competitive inhibitors.
Category: Enzymes
Question 9
Mature mammalian red blood cells rely on glycolysis as their only source of ATP.
Correct Answer
True
True. Mature mammalian red blood cells have no mitochondria, so they cannot carry out the citric acid cycle or oxidative phosphorylation. If glycolysis stopped, these cells would run out of ATP and die.
Category: Glycolysis
Question 10
Glycolysis occurs only in eukaryotic cells.
Correct Answer
False
False. Glycolysis takes place in the cytoplasm of most prokaryotic cells as well as all eukaryotic cells. Its wide distribution suggests it is one of the most ancient metabolic pathways.
Category: Glycolysis
Question 11
The first half of glycolysis uses energy from ATP to prepare the six-carbon sugar for splitting.
Correct Answer
True
True. Early in glycolysis the cell invests ATP to add phosphate groups to the sugar, which makes it unstable enough to split into two three-carbon molecules. The second half then produces ATP and NADH.
Category: Glycolysis
Question 12
Carbon dioxide is released when pyruvate is converted to acetyl CoA.
Correct Answer
True
True. As each pyruvate enters the mitochondrion, one carbon is removed and released as carbon dioxide, leaving a two-carbon acetyl group. That group is attached to coenzyme A and enters the citric acid cycle.
Category: Citric Acid Cycle
Question 13
Each turn of the citric acid cycle releases six molecules of carbon dioxide.
Correct Answer
False
False. Each turn of the citric acid cycle releases two molecules of carbon dioxide. Since one glucose yields two acetyl groups, the cycle releases four carbon dioxide per glucose, and the step that forms acetyl CoA releases the other two.
Category: Citric Acid Cycle
Question 14
In prokaryotes, the electron transport chain is located in the plasma membrane.
Correct Answer
True
True. Prokaryotes have no mitochondria, so their electron transport chain complexes are embedded in the plasma membrane. In eukaryotes, the chain is found in the inner mitochondrial membrane.
Category: Electron Transport and ATP Synthesis
Question 15
The ATP-producing steps of glycolysis and the citric acid cycle make most of the ATP produced during aerobic breakdown of glucose.
Correct Answer
False
False. Most ATP from aerobic respiration is made by oxidative phosphorylation, in which hydrogen ions flowing through ATP synthase drive ATP production. Glycolysis and the citric acid cycle make only a small amount of ATP directly.
Category: Electron Transport and ATP Synthesis
Question 16
In lactic acid fermentation, pyruvate accepts electrons from NADH and becomes lactic acid.
Correct Answer
True
True. The enzyme lactate dehydrogenase transfers electrons from NADH to pyruvate, forming lactic acid and regenerating NAD+. This occurs in red blood cells, in muscle cells short of oxygen and in bacteria used to make yogurt.
Category: Fermentation
Question 17
Obligate anaerobes, such as Clostridium bacteria, require oxygen to survive.
Correct Answer
False
False. Obligate anaerobes live and grow only in the absence of molecular oxygen, which is toxic to them. Organisms that can use oxygen when it is present but survive without it are facultative anaerobes.
Category: Fermentation
Question 18
Facultative anaerobes can switch between aerobic respiration and fermentation depending on whether oxygen is available.
Correct Answer
True
True. Many prokaryotes, and also yeast, use aerobic respiration when oxygen is present and switch to fermentation when it is absent. Aerobic respiration yields far more ATP per glucose, so they use it when they can.
Category: Fermentation
Question 19
When triglycerides are broken down for energy, their glycerol enters metabolism at the citric acid cycle.
Correct Answer
False
False. Glycerol is phosphorylated and enters glycolysis. The fatty acid chains are the part of the triglyceride that is broken into two-carbon units that enter the citric acid cycle as acetyl CoA.
Category: Connected Pathways
Question 20
Triglycerides store about half as much energy per gram as carbohydrates do.
Correct Answer
False
False. Triglycerides store more than twice as much energy per gram as carbohydrates, which is why fat is the body's main form of long-term energy storage. Each triglyceride is made of a glycerol molecule bonded to three fatty acids.
Category: Connected Pathways