Biology Test 3

Which stage of cellular respiration appears to have evolved first?

glycolysis Glycolysis can occur in the absence of oxygen and evolved prior to oxygenic photosynthesis.

Where does glycolysis occur in a eukaryotic cell?

in the cytoplasmic fluid Glycolysis occurs in the cytoplasmic fluid.

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).

A molecule is oxidized when it __________

loses an electron During oxidation, an electron is removed.

In cellular respiration, which of the following outcomes is the result of electrons moving through the electron transport chain (or its components)?

A proton gradient is formed. The energy released by the electron transport chain is used to create a proton gradient across the inner mitochondrial membrane. This allows the production of ATP by chemiosmosis. Provide Feedback

The energy production per acetyl CoA molecule through the citric acid cycle is __________.

1 ATP, 3 NADH, 1 FADH2 Then NADH and FADH2 go through the electron transport chain.

During glycolysis, a molecule of glucose is partially oxidized. What is the net gain of ATP and NADH for each glucose molecule during this chemical pathway?

2 ATP and 2 NADH The net gain at the end of glycolysis is 2 ATP and 2 NADH.

Through respiration, humans breathe in O2 and breathe out CO2. However, what would happen if we 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.

A small amount of ATP is made in glycolysis _____

by the transfer of a phosphate group from a fragment of glucose to ADP (substrate-level phosphorylation) Remember that, at the beginning of glycolysis, phosphate is added to glucose.

Substrate-level phosphorylation directly generates ATP during a chemical reaction. As a single molecule of glucose is completely oxidized in the presence of oxygen, what is the net yield of molecules of ATP made by substrate-level phosphorylation?

4 ATP Substrate-level phosphorylation produces 2 ATP (net) in glycolysis and 2 ATP in the citric acid cycle

In preparing pyruvate to enter the citric acid cycle, which of the following steps occurs?

A compound called coenzyme A binds to a two-carbon fragment. Coenzyme A binds to the two-carbon fragment derived from pyruvate to form acetyl coenzyme A.

In the first stage of cellular respiration (glycolysis), two molecules of pyruvate are produced. In the remaining stages of cellular respiration, a number of additional products are produced, such as __________. These other stages occur in the __________.

ATP ... mitochondria ATP, CO2, and H2O are the products of cellular respiration. As pyruvate is oxidized further, it is moved into a mitochondrion where the remaining stages of cellular respiration occur.

Which 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 of the following statements regarding aerobic cellular respiration is TRUE?

Glucose is completely oxidized to form carbon dioxide. Much of the energy released in this process is captured and stored in the form of ATP.

Which of the following statements regarding glycolysis is FALSE?

Glycolysis evolved in an oxygen-rich environment. Correct, this is the FALSE statement. Glycolysis does not require O2, and likely evolved nearly a billion years before oxygen began accumulating from photosynthesis.

In the absence of oxygen, cells need a way to regenerate which compound?

NAD+ The NAD+ needs to be regenerated, which is why ethanol or lactic acid is formed.

As shown below, an electron carrier, such as __________, acts as an energy-storage molecule when it is __________.

NADH ... reduced NADH is the reduced form of this molecule and it carries high energy electrons. This makes it an energy storage molecule.

In an experiment, mice were fed glucose (C6H12O6) containing a small amount of radioactive carbon. The mice were closely monitored, and in a few minutes, radioactive carbon atoms showed up in __________.

carbon dioxide Cellular respiration, or the oxidization of glucose, involves the release of CO2.

The O2 required for __________ is supplied by __________.

cellular respiration ... breathing Breathing supplies the O2 required for cellular respiration, and also disposes of the CO2 produced as a waste product during cellular respiration.

A single glucose molecule produces about 38 molecules of ATP through the process of cellular respiration. However, this only represents approximately 34% of the chemical energy present in this molecule. The rest of the energy from glucose is __________.

converted to heat The majority of the energy in a molecule of glucose is lost as heat.

Which of the following is the source of the energy that produces the chemiosmotic gradient in mitochondria?

electrons Energy from the flow of electrons along the electron transport chain is used to pump hydrogen ions (protons) across the inner mitochondrial membrane, creating the chemiosmotic gradient.

In cellular respiration, glucose _____ electrons, whereas _____ electrons.

loses ... oxygen gains During cellular respiration, glucose loses electrons and oxygen gains electrons. Oxidation and reduction always go together, as electron transfer requires both a donor and an acceptor.

A molecule that functions as the electron donor in a redox reaction __________.

loses electrons and becomes oxidized In cellular respiration, glucose is oxidized when it loses electrons in hydrogen atoms. Oxygen is reduced as it gains electrons attached to hydrogen atoms.

Primarily, cellular respiration serves to _____.

make ATP to power the cell's activities The energy made available during cellular respiration is coupled to a process that phosphorylates ADP, making ATP.

The electron transport chain is a series of electron carrier molecules. In eukaryotes, where can this structure be found?

mitochondria The electron transport chain molecules are embedded in the inner mitochondrial membrane.

Why is the citric acid cycle called a cycle?

Acetyl CoA binds to oxaloacetate and this compound is restored at the end of the cycle. The cycling referred to is that of the resynthesis of the four-carbon compound. One turn of the citric acid cycle is completed with the regeneration of oxaloacetate, which is then ready to start the next cycle by accepting an acetyl group from acetyl CoA.

In the reaction that creates acetyl CoA (coenzyme A) from pyruvate

In the reaction that creates acetyl CoA (coenzyme A) from pyruvate Carbon dioxide is produced in the transition between glycolysis and the citric acid cycle when the three-carbon pyruvate is cleaved to a two-carbon acetyl molecule with the remaining carbon of pyruvate released as carbon dioxide. Carbon dioxide is also produced in the citric acid cycle itself.

During fermentation, __________ that was produced during glycolysis is converted back to __________.

NADH; NAD+ NADH molecules produced during glycolysis are converted back to NAD+ during fermentation. This NAD+ is used again in a new round of glycolysis.

Consider the figure below. __________ is to a mitochondrion as __________ is to a chloroplast.

O2 ... CO2 Cellular respiration utilizes O2, and photosynthesis utilizes CO2.

What is the purpose of embedding the electron transport chain in the membrane of a cell?

The electron acceptors can transport H+ across the membrane, which is otherwise impermeable to H+. Chemiosmosis relies on the properties of the membrane that prevent hydrogen ions (H+) from flowing down their concentration gradient. Hydrogen ions are permitted to reenter the cell across the membrane through ATP synthase, which captures their potential energy and uses it to synthesize ATP.

What is the ultimate fate of the electrons that are stripped from glucose during cellular respiration?

They are used to form water. At the end of the electron transport chain, the electrons and hydrogen ions are used to reduce oxygen to form water.

What happens to the energy that is released by electrons as they move through the electron transport chain?

What happens to the energy that is released by electrons as they move through the electron transport chain? In eukaryotes, many of the electron transport molecules in the mitochondrion pump a hydrogen ion into the intermembrane space when they pass an electron along the chain.

The electron transport chain is, in essence, a series of redox reactions that conclude cellular respiration. During these redox reactions, __________

electrons are transferred through a series of electron acceptors embedded within the inner mitochondrial membrane NADH provides these electrons to the membrane-embedded electron acceptors.

Cellular respiration completely breaks down a glucose molecule through glycolysis and the citric acid cycle. However, these two processes yield only a few ATPs. The majority of the energy the cell derives from glucose is _____.

found in NADH and FADH2 The energy in these molecules is used to drive the synthesis of ATP in the electron transport chain and chemiosmosis.

Each turn of the citric acid cycle generates one ATP and ___ additional energy-rich molecules: __________.

four; 3 NADH and 1 FADH2 The citric acid cycle generates 3 molecules of NADH and 1 molecule of FADH2. These molecules carry high energy electrons that will be delivered to the electron transport chain.

In the equation shown below, during cellular respiration __________ is oxidized and __________ is reduced.

glucose ... oxygen In cellular respiration, electrons and hydrogen are removed from glucose and added to oxygen.

What is the name of the process in which glucose is converted to pyruvate?

glycolysis Glycolysis, or the splitting of sugar, splits a six-carbon glucose into two three-carbon pyruvate molecules.

A chemist has discovered a drug that blocks phosphoglucoisomerase, an enzyme that catalyzes the second reaction in glycolysis. He wants to use the drug to treat people with bacterial infections. However, he can't 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.

Sports physiologists at an Olympic training center want to monitor athletes to determine at what point their muscles begin to function 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.

A scientist wants to study the enzymes of the citric acid cycle in eukaryotic cells. What part of the cell would she use as a source of these enzymes?

mitochondrial matrix The water-soluble citric acid cycle intermediates and enzymes of a eukaryotic cell are found in the mitochondrial matrix, where the newly synthesized NADH and FADH2 diffuse to proteins of the electron transport chain held within the inner mitochondrial membrane. The matrix corresponds to the cytoplasm of the bacterium from which mitochondria are descended.

Some human cells, such as nerve cells, are restricted to aerobic respiration to recycle NADH and FADH2. If these cells are deprived of oxygen, then __________.

oxidative phosphorylation would come to a halt because there wouldn't be any oxygen to "pull" the electrons down the transport chain Without electronegative oxygen waiting at the end of the chain, electron flow would cease, along with the action of the protein complexes that create the proton gradients.

Bacteria have no membrane-enclosed organelles. However, some still generate ATP through cellular respiration. Where might the electron transport chain be found in these organisms?

plasma membrane The electron transport chain requires a membrane that will act as a barrier to hydrogen ions that are being pumped across this space. The only membrane in a bacterial cell is the plasma membrane. Note that the inner membrane of a mitochondrion is a bacterial membrane obtained by the eukaryote through endosymbiosis.

In oxidative phosphorylation, electrons are passed from one electron carrier to another. The energy released is used to __________.

pump protons (H+) across the mitochondrial membrane The energy harvested from many redox reactions is used to power proton pumps that span the inner mitochondrial membrane.

A muscle cell deprived of molecular oxygen will convert glucose to lactic acid to __________

recycle NADH through fermentation During lactic acid fermentation, pyruvate is reduced directly by NADH to form lactate. This recycles NAD+, so the cycle continues.

In eukaryotes, most of the high-energy electrons released from glucose by cellular respiration __________.

reduce NAD+ to NADH, which then delivers them to the electron transport chain.

Glycolysis is the only stage of cellular respiration that __________.

requires ATP to make ATP Glycolysis contains an "investment" phase and a "payoff" phase. Two ATP are required to make four ATP.

Most NADH molecules generated during cellular respiration are produced during __________.

the citric acid cycle There are 6 NADH molecules produced by the citric acid cycle per molecule of glucose. Two molecules of FADH2 are also produced by this cycle, which makes it a big source of high energy electron carriers.

Sunlight is essential for the varied life on Earth. Sunlight provides energy to photosynthetic organisms by providing

the energy necessary to power the rearrangement of chemical bonds in H2O and CO2 This is what photosynthesis accomplishes in the conversion of water and carbon dioxide to sugars.

Where do the reactions of the citric acid cycle occur in eukaryotic cells?

the mitochondrion The citric acid cycle, which takes place in mitochondria, completes the degradation of glucose.

The enzyme ATP synthase catalyzes the phosphorylation of ADP to form ATP. In eukaryotic cells, the energy needed for this endergonic reaction is directly derived from __________.

the movement of hydrogen ions across the mitochondrial membrane The electron transport chain is an energy converter that uses the exergonic flow of electrons to pump hydrogen ions across the inner mitochondrial membrane from the matrix to the intermembrane space. Hydrogen ions diffuse back into the matrix via a channel in ATP synthase.

Oxidation phosphorylation could not occur without glycolysis and the citric acid cycle, because

these two stages supply the electrons needed for the electron transport chain