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Vocabulary and quiz questions over cellular respiration and fermentation.

Proton-Motive Force

The potential energy stored in the form of an electrochemical gradient, generated by the pumping of hydrogen ions across biological membranes during chemiosmosis.

ATP Synthase

Copies of a protein complex found in the inner membrane of the mitrochondrion that make ATP from ADP and inorganic phosphate.

Oxidative Phosphorylation

The production of ATP using energy derived from the redox reactions of an electron transport chain.

Citric Acid Cycle

A chemical cycle involving eight steps that completes the metabolic breakdown of glucose molecules by oxidizing a derivative of pyruvate to carbon dioxide; occurs within the mitochondrion; the second major stage in cellular respiration.

Oxidizing Agent

The electron acceptor in a redox reaction.

Reducing Agent

The electron donor in a redox reaction.

Cellular Respiration

Process that releases energy by breaking down glucose and other food molecules in the presence of oxygen

Aerobic Respiration

Respiration in which oxygen is consumed and glucose is broken down entirely; water, carbon dioxide, and large amounts of ATP are the final products

Summary equation for cellular respiration.

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy

Redox Reactions

A chemical reaction involving the transfer of one or more electrons from one reactant to another; also called oxidation-reduction reaction.


A reaction involving the loss of electrons by an element.


A reaction involving the gain of electrons by an element.


(nicotinamide adenine dinucleotide) an organic molecule that serves as an electron carrier by being oxidized to NAD+ and reduced to NADH

Electron Transport Chain (ETC)

A sequence of electron carrier molecules (membrane proteins) that shuttle electrons during the redox reactions that release energy used to make ATP.


Catabolism of glucose or other monosaccharides to pyruvate and 2 molecules of ATP in the absence of oxygen or 34 molecules of ATP in the presence of oxygen.

Substrate-Level Phosphorylation

The formation of ATP by directly transferring a phosphate group to ADP from an intermediate substrate in catabolism.

Acetyl CoA

Acetyl coenzyme A; the entry compound for the citric acid cycle in cellular respiration, formed from a fragment of pyruvate attached to a coenzyme.


A partial degradation of sugars that occurs without the use of oxygen


An iron-containing protein, a component of electron transport chains in mitochondria and chloroplasts.


An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis.

Alcohol Fermentation

The conversion of pyruvate to carbon dioxide and ethyl alcohol.

Lactic Acid Fermentation

Glycolysis is followed by the breakdown of the 3 carbon pyruvate into 2 lactic acid molecules with no release of carbon dioxide.

Obligate Anaerobes

An organism that only carries out fermentation or anaerobic respiration. Such organisms cannot use oxygen and in fact may be poisoned by it.

Facultative Anaerobes

An organism that makes ATP by aerobic respiration if oxygen is present but that switches to fermentation under anaerobic conditions.

Beta Oxidation

A metabolic sequence that breaks fatty acids down to two-carbon fragments which enter the Krebs cycle as acetyl CoA.

When an individual is exercising heavily and when the muscle becomes oxygen-deprived, muscle cells convert pyruvate to lactate. What happens to the lactate in skeletal muscle cells?

It is taken to the liver and converted back to pyruvate.

In vertebrate animals, brown fat tissue's color is due to abundant blood vesses and paillaries. White fat tissue, on the other hand, is specialized for fat storage and contains relatively few blood vessels or capillaries. Brown fat cells have a specialized protein that dissipates the proton-motive force across the mitochondrial membranes. What might the function of the brown fat tissue be?

To regulate temperature by converting most of the energy from NADH oxidation to heat.

What is the term for metabolic pathways that release stored energy by breaking down complex molecules.

Catabolic pathways.

Which process in eukaryotic cells will proceed normally whether O₂ is present or absent?


In addition to ATP, what are the end products of glycolysis?

NADH and pyruvate.

Why is glycolysis described as having an investment phase and a payoff phase?

It uses stored ATP and then forms a net increase in ATP.

During cellular respiration, acetyl CoA accumulates in which location?

Mitochondrial matrix.

How many carbon atoms are fed into the citric acid cycle as a result of the oxidation of one molecule per pyruvate?


During aerobic respiration, electrons travel downhill in what sequence?

food → citric acid cycle → electron transport chain → oxygen

In cellular respiration, the energy for most ATP synthesis is supplied by

a proton gradient across a membrane.

In chemiosmosis phosphorylation, what is the most diret source of energy that is used to convert ADP + Pi to ATP?

Energy released from movement of protons through ATP synthase, down the electrochemical gradient.

What naturally occurs regardless of whether or not O₂ is present?


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