Chapter 9: Cellular Respiration and Fermentation

Which term describes the degree to which an element attracts electrons?

Electronegativity

In glycolysis, ATP molecules are produced by _____.

substrate-level phosphorylation A phosphate group is transferred from glyceraldehyde phosphate to ADP.

The proximate (immediate) source of energy for oxidative phosphorylation is _____.

kinetic energy that is released as hydrogen ions diffuse down their concentration gradient Concentration gradients are a form of potential energy.

Which of these is NOT a product of glycolysis?

FADH2 FADH2 is a product of the citric acid cycle

Which of the following statements is true of the bonds in a water molecule?

Oxygen holds electrons more tightly than hydrogen does, and the net charge is zero. The oxygen and hydrogen atoms in water have partial charges, but the molecule has a net charge of zero.

In glycolysis, the carbon-containing compound that functions as the electron donor is ____.

glucose

In the process of cellular respiration, what is consumed and what is produced?

glucose is consumed and carbon dioxide is produced The carbon in glucose is oxidized to carbon dioxide during cellular respiration.

How many NADH are produced by glycolysis?

2

In glycolysis there is a net gain of _____ ATP.

2 It takes 2 ATP to produce 4 ATP.

Which of the following statements is not true of most cellular redox reactions?

A hydrogen atom is transferred to the atom that loses an electron. A hydrogen atom (proton, or H+) is often transferred to the atom that gains an electron.

The structure that phosphorylates ADP is ____.

ATP synthase

Gaseous hydrogen burns in the presence of oxygen to form water: 2H2 + O2 → 2H2 O + energy Which molecule is oxidized and what kind of bond is formed?

Hydrogen, polar. Hydrogen loses electrons to oxygen, which is more electronegative and thus pulls the electrons closer to itself in the water molecule.

Under anaerobic conditions (a lack of oxygen), the conversion of pyruvate to acetyl CoA stops. Which of these statements is the correct explanation for this observation?

In the absence of oxygen, electron transport stops. NADH is no longer converted to NAD+, which is needed for the first three stages of cellular respiration. NAD+ couples oxidative phosphorylation to acetyl CoA formation. The NAD+ needed to oxidize pyruvate to acetyl CoA is produced during electron transport. Without O2, electron transport stops, and the oxidation of pyruvate to acetyl CoA also stops because of the lack of NAD+.

____ is the compound that functions as the electron acceptor in glycolysis

NAD+

The reduced form of the electron acceptor in glycolysis is ____.

NADH

During electron transport, energy from _____ is used to pump hydrogen ions into the _____.

NADH and FADH2 ... intermembrane space The energy released as electrons, which have been donated by NADH and FADH2, is passed along the electron transport chain and used to pump hydrogen ions into the intermembrane space.

In cellular respiration, a series of molecules forming an electron transport chain alternately accepts and then donates electrons. What is the advantage of such an electron transport chain?

The advantage of an electron transport chain is that a small amount of energy is released with the transfer of an electron between each pair of intermediates. As the electrons "fall" down the electron transport chain, the energy released is used to actively transport protons into the inner-membrane space. Read about the respiratory electron transport chain.

Which one of the following statements about the redox reactions of the electron transport chain is correct?

The redox reactions of the electron transport chain are directly coupled to the movement of protons across a membrane. The reduction and oxidation of electron carriers in the electron transport chain provide the energy to move protons across a membrane, against the chemical gradient of protons.

Which of the following is true of the energy levels of electrons in shells?

Valence electrons have a higher energy level than those in other filled shells. The negatively charged electrons of an atom are attracted to the positively charged nucleus. It takes work to move a given electron farther away from the nucleus, so the more distant an electron is from the nucleus, the greater its potential energy. The valence electrons, located in the outermost electron shell (the valence shell), have the highest energy level.

Which of these is NOT a product of the citric acid cycle?

acetyl CoA Acetyl CoA enters the citric acid cycle.

Which of these enters the citric acid cycle?

acetyl CoA Acetyl CoA is a reactant in the citric acid cycle.

A glucose molecule is completely broken down to carbon dioxide and water in glycolysis and the citric acid cycle, but together these two processes yield only a few molecules of ATP. What happens to most of the energy that the cell obtains from the oxidation of glucose?

it is stored in NADH and FADH2 The electrons obtained from the oxidation of glucose are temporarily stored in NADH and FADH2. The energy derived from the oxidation of NADH and FADH2 is used to drive the electron transport chain and chemiosmotic synthesis of ATP.

In cellular respiration, most ATP molecules are produced by _____.

oxidative phosphorylation This process utilizes energy released by electron transport.

When a compound donates (loses) electrons, that compound becomes ____. Such a compound is often referred to as an electron donor.

oxidized

The final electron acceptor of cellular respiration is _____.

oxygen Oxygen is combined with electrons and hydrogen to form water.

Once the electron donor in glycolysis gives up its electrons, it is oxidized to a compound called ____.

pyruvate

Among the products of glycolysis, which compounds contain energy that can be used by other biological reactions?

pyruvate, ATP, and NADH ATP is the main product of cellular respiration that contains energy that can be used by other cellular processes. Some ATP is made in glycolysis. In addition, the NADH and pyruvate produced in glycolysis are used in subsequent steps of cellular respiration to make even more ATP.

When a compound accepts (gains) electrons, that compound becomes ____. Such a compound is often referred to as an electron acceptor.

reduced

In the citric acid cycle, ATP molecules are produced by _____.

substrate-level phosphorylation A phosphate group is transferred from GTP to ADP.

Which of the following is the most important result of the process of cellular respiration in biological systems?

transforming the energy in glucose and related molecules into a chemical form that cells can use for work The energy made available during cellular respiration is coupled to the production of ATP, the basic energy currency that cells use for work.

In the absence of oxygen, what is the net gain of ATP for each glucose molecule that enters glycolysis?

two ATP Four ATP are made, but two ATP are consumed to start the process of glycolysis.

The rate of cellular respiration is regulated by its major product, ATP, via feedback inhibition. As the diagram shows, high levels of ATP inhibit phosphofructokinase (PFK), an early enzyme in glycolysis. As a result, the rate of cellular respiration, and thus ATP production, decreases. Feedback inhibition enables cells to adjust their rate of cellular respiration to match their demand for ATP. Suppose that a cell's demand for ATP suddenly exceeds its supply of ATP from cellular respiration. Which statement correctly describes how this increased demand would lead to an increased rate of ATP production?

ATP levels would fall at first, decreasing the inhibition of PFK and increasing the rate of ATP production. An increased demand for ATP by a cell will cause an initial decrease in the level of cellular ATP. Lower ATP decreases the inhibition of the PFK enzyme, thus increasing the rate of glycolysis, cellular respiration, and ATP production. It is the initial decrease in ATP levels that leads to an increase in ATP production.

Which terms describe two atoms when they form a bond in which electrons are completely transferred from one atom to the other?

Anion and cation. Each atom will carry a charge from the transfer of electrons.

Select the correct statement about cellular respiration.

Cellular respiration and breathing differ in that cellular respiration is at the cellular level, whereas breathing is at the organismal level. Read about the distinction between cellular and organismal respiration.

Under anaerobic conditions (a lack of oxygen), glycolysis continues in most cells despite the fact that oxidative phosphorylation stops, and its production of NAD+ (which is needed as an input to glycolysis) also stops. The diagram illustrates the process of fermentation, which is used by many cells in the absence of oxygen. In fermentation, the NADH produced by glycolysis is used to reduce the pyruvate produced by glycolysis to either lactate or ethanol. Fermentation results in a net production of 2 ATP per glucose molecule. During strenuous exercise, anaerobic conditions can result if the cardiovascular system cannot supply oxygen fast enough to meet the demands of muscle cells. Assume that a muscle cell's demand for ATP under anaerobic conditions remains the same as it was under aerobic conditions. What would happen to the cell's rate of glucose utilization?

Glucose utilization would increase a lot. ATP made during fermentation comes from glycolysis, which produces a net of only 2 ATP per glucose molecule. In contrast, aerobic cellular respiration produces about 30 ATP per glucose molecule. To meet the same ATP demand under anaerobic conditions as under aerobic conditions, a cell's rate of glycolysis and glucose utilization must increase about 15-fold.

What are the inputs and outputs of oxidative phosphorylation?

Inputs: O2, NADH, and ADP+P(i) Outputs: water, NAD+, and ATP

What are the inputs and outputs of glycolysis?

Inputs: glucose, NAD+, and ADP+P(i) Outputs: pyruvate, NADH, and ATP

What are the inputs and outputs of pyruvate oxidation and the citric acid cycle?

Inputs: pyruvate, NAD+, and ADP+P(i) Outputs: CO2, NADH, and ATP

Identify all correct statements about the basic function of fermentation.

The basic function of fermentation is the regeneration of NAD+, which allows continued ATP production by glycolysis. Fermentation occurs in the absence of oxygen and does not yeild as much ATP. Read about fermentation.

Which of the following statements accurately describes the function of a metabolic pathway involved in cellular respiration?

The function of glycolysis is to begin catabolism by breaking glucose into two molecules of pyruvate, with a net yield of two ATP. Glycolysis is the first stage in cellular respiration and does not depend on the presence of oxygen.

Which of the following statements about the citric acid cycle is correct?

The last reaction in the citric acid cycle produces a product that is a substrate for the first reaction of the citric acid cycle.

The electrons stripped from glucose in cellular respiration ultimately end up in which compound?

water At the end of the electron transport chain, the electrons and hydrogen atoms are added to oxygen, forming water.