One of the key differences between slow- and fast-twitch muscles is whether they require _____ when making ATP for energy.
Some microorganisms that live around hydrothermal vents in the deep ocean use inorganic energy sources and compounds to produce their own food. Therefore, these organisms are considered to be _____.
autotrophs; Autotrophs are organisms that produce their own food.
The function of cellular respiration is to __________.
extract usable energy from glucose; The most prevalent and efficient energy-yielding pathway is cellular respiration, in which oxygen is consumed as a reactant, along with the organic fuel (frequently glucose).
If humans did not breathe in O2, we would not __________.
make enough ATP to meet our energy requirements; The electron transport chain accepts electrons from the breakdown products of glycolysis and the citric acid cycle, and it passes these electrons from one molecule to another until they are passed (along with two hydrogen ions) to oxygen to form water.
An electron carrier acts as an energy-storage molecule when it is _____ (for example, _____)
reduced ... NADH; The most versatile electron acceptor in cellular respiration is NAD+, which gains electrons and is thereby reduced to NADH.
A molecule is oxidized when it __________.
loses an electron
Which one of the following best describes the electron transport chain?
Electrons pass from one carrier to another, releasing a little energy at each step. ... NADH and FADH2 deliver electrons from the breakdown products of glycolysis and the citric acid cycle to the electron transport chain, which passes these electrons from one molecule to another, releasing a small amount of energy at each step.
Which one of the following serves primarily as a hydrogen-atom-carrier molecule in cells?
NAD; Like FAD, NAD+ accepts hydrogen ions that have been stripped from glucose and delivers them to the electron transport chain.
During the reaction C6H12O6 + 6 O2 → 6 CO2 + 6 H2O, _________.
oxygen becomes reduced
In cellular respiration, _____ is oxidized and _____ is reduced.
glucose ... oxygen; In cellular respiration, electrons and hydrogen are removed from glucose and added to oxygen.
During respiration in a eukaryotic cell, reactions of glycolysis occur __________.
in the cytosol; Glycolysis occurs in the cytosol.
During respiration in a eukaryotic cell, reactions of the citric acid cycle occur in __________.
the fluid within the mitochondrion; The citric acid cycle, which takes place in mitochondria, completes the degradation of glucose.
Most of the electrons released from glucose by cell respiration __________.
are bound to NAD+ to be sent through electron transport; Most of the electrons released from the glucose are picked up by NAD+ and sent through the electron transport chain.
Immediately after completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of _____.
NADH; Each NADH yields ATP once the electrons are delivered to the electron transport chain.
In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive oxygen. The mice were closely monitored, and in a few minutes radioactive oxygen atoms showed up in _____.
carbon dioxide; The oxidation of glucose involves the release of CO2.
What is the name of the process in which glucose is converted to pyruvic acid?
glycolysis; Glycolysis, or the splitting of sugar, splits a 6-carbon glucose into two 3-carbon pyruvic acid molecules.
In preparing pyruvic acid to enter the citric acid cycle, which of the following steps occurs?
A compound called coenzyme A binds to acetic acid.; Coenzyme A binds to acetic acid before entering the citric acid cycle.
When pyruvic acid is converted to acetyl CoA __________.
CO2 and NADH are formed; Pyruvic acid loses a carbon dioxide molecule, which diffuses out of the cell. The remaining two-carbon fragment is oxidized while NAD+ is reduced to NADH.
Most of the NADH that delivers electrons to the electron transport chain comes from _____.
the citric acid cycle; Both NADH and FADH2 are produced during the citric acid cycle.
Why is the citric acid cycle called a cycle?
The two-carbon acetic acid binds to a four-carbon molecule that is restored at the end of the cycle to be used again in the citric acid cycle.; The cycling referred to is that of the resynthesis of the four-carbon compound.
The major (but not sole) energy accomplishment of the citric acid cycle is the __________.
formation of NADH and FADH2; Each turn of the citric acid cycle releases carbon dioxide, forms 1 ATP, and passes electrons to 3 NAD+ and 1 FAD.
The energy given up by electrons as they move through the electron transport chain is used to __________.
pump H+ through a membrane; Many of the electron transport molecules in the mitochondrion pump hydrogen ions across the inner mitochondrial membrane when they pass an electron along the chain.
The ATP synthase in a human cell gets energy for making ATP directly from __________.
the flow of H+ through a membrane; As electrons move along the transport chain, hydrogen ions are pumped across the inner mitochondrial membrane.
In respiration, which one of the following is done during the electron transport chain phase?
carry electrons; As its name states, the electron transport chain transports electrons.
Which part of the breakdown of glucose requires molecular oxygen (O2)?
the electron transport chain; The electron transport chain accepts electrons from the breakdown products of glycolysis and the citric acid cycle, and it passes these electrons from one molecule to another until they are passed (along with two hydrogen ions) to oxygen to form water.
During aerobic respiration, molecular oxygen (O2) is used __________.
at the end of the electron transport chain to accept electrons and form H2O; O2 is the final electron acceptor.
Which one of the following is the source of the energy that pumps hydrogen ions across the inner mitochondrial membrane?
electrons; Energy from the flow of electrons along the electron transport chain is used to pump hydrogen ions across the inner mitochondrial membrane.
When a poison such as rotenone blocks the electron transport chain, glycolysis and the citric acid cycle soon grind to a halt as well, because __________.
they run out of NAD+ and FAD; Oxygen moves freely across cell membranes. It does not reach toxic concentrations unless an oxygen-enriched gas is being breathed.
In the citric acid cycle, the energy production per glucose molecule is __________.
2 ATP, 6 NADH, 2 FADH2; Then the NADH and FADH2 go through the electron transport chain.
Most of the ATP produced in cellular respiration comes from __________.
the flow of electrons across the inner mitochondrial membrane
Sports physiologists at an Olympic training center wanted to monitor athletes to determine at what point their muscles were functioning anaerobically. They could do this by checking for a buildup of _____.
lactic acid;In humans, muscle cells switch to lactic acid fermentation after becoming anaerobic.
In glycolysis in the absence of oxygen, cells need a way to regenerate which compound?
NAD+; The NAD+ needs to be regenerated, which is why ethyl alcohol or lactic acid is formed.
A.V. Hill did his lactic acid experiments on frog muscles. This means that Hill was working under the premise that frog muscle __________.
undergoes the same lactic acid fermentation as human muscle cells; If frog muscle did not naturally undergo lactic acid fermentation, it would not have been a good choice for studying the effects of lactic acid on muscle.
Fermentation is essentially glycolysis plus an extra step in which pyruvic acid is reduced to form lactic acid or alcohol and carbon dioxide. This last step __________.
enables the cell to recycle NAD+; Normally, the reduced NADH delivers its electrons to the electron transport chain, enabling NAD+ to be recycled to glycolysis.
How much ATP can a cell make from one glucose molecule in the presence of carbon monoxide?
2 ATP; That is what you could obtain in the absence of carbon monoxide and an abundance of oxygen.
A chemist has discovered a drug that blocks an enzyme that catalyzes some of the reactions of glycolysis. He wants to use the drug to kill bacteria in people with infections. However, he cannot do this because __________.
human cells also perform glycolysis; the drug might also poison them; The chemist's drug could have a devastating effect on human cells.
Of the metabolic pathways listed below, the only pathway found in almost all organisms is __________.
glycolysis; Ancient prokaryotes probably used glycolysis to make ATP long before oxygen was present in Earth's atmosphere.