Exam 3 Biology

Which of the following correctly states the relationship between anabolic and catabolic pathways?

Anabolic pathways synthesize more complex organic molecules using the energy derived from catabolic pathways.

In which process is glucose oxidized to form two molecules of pyruvate?

Glycolysis

During the energy payoff phase of glycolysis, __________.

NADH and ATP are produced

Which of the following is true when comparing an uncatalyzed reaction to the same reaction with a catalyst?

The catalyzed reaction will have the same ΔG.

How does carbon dioxide enter the leaf?

Through the stomata

The most important role of pigments in photosynthesis is to __________.

capture light energy

A molecule becomes more oxidized when it __________.

loses an electron

When chloroplast pigments absorb light, __________.

their electrons become excited

The light reactions of photosynthesis occur in the __________.

thylakoids

The source of the oxygen produced by photosynthesis has been identified through experiments using radioactive tracers. The oxygen comes from __________.

water

Where do the electrons entering photosystem II come from?

water

The mathematical expression for the change in free energy of a system is ΔG =ΔH - TΔS. Which of the following is (are) correct?

ΔG is the change in free energy.

During aerobic respiration, molecular oxygen (O2) is used for which of the following purposes?

At the end of the electron transport chain to accept electrons and form H2O

Which of the following statements is a correct distinction between autotrophs and heterotrophs?

Autotrophs, but not heterotrophs, can nourish themselves beginning with CO2 and other nutrients that are inorganic.

Which of the following statements describes a key component of the induced fit hypothesis of enzyme catalysis?

Binding of substrate to the active site changes the shape of the active site of an enzyme

Which of the following statements correctly describes cofactors and coenzymes?

Both are nonprotein enzyme helpers; but most cofactors are metal ions, and coenzymes are organic molecules that are a specific type of cofactor.

What property of the pigment chlorophyll makes it appear green?

Chlorophyll absorbs all of the visible spectrum of light except green, which it reflects.

Which of the following states the relevance of the first law of thermodynamics to biology?

Energy can be freely transformed among different forms as long as the total energy is conserved.

If the entropy of a living organism is decreasing, which of the following is most likely to be occurring simultaneously?

Energy input into the organism must be occurring to drive the decrease in entropy.

Which of the following statements about enzyme function is correct?

Enzymes can lower the activation energy of reactions, but they cannot change the equilibrium point because they cannot change the net energy output.

Which metabolic pathway is common to both fermentation and cellular respiration of a glucose molecule?

Glycolysis

Most of the ATP in cellular respiration is produced by the process of chemiosmosis. How does this process produce ATP?

H+ flows across the inner mitochondrial membrane through the enzyme ATP synthase.

Which of the following statements is correct regarding kinetic and potential energy?

Kinetic energy is associated with the relative motion of objects, and potential energy is the energy that matter possesses because of its location or structure.

Which statement correctly describes the difference between alcohol fermentation and lactic acid fermentation?

Lactic acid fermentation produces lactate, and alcohol fermentation produces ethanol.

Which of the following is true regarding metabolic pathways?

Metabolic pathways consist of a series of reactions, each catalyzed by a different enzyme.

Which of the following statements is true of metabolism in its entirety in all organism?

Metabolism consists of all the energy transformation reactions in an organism.

During the Calvin cycle, what happens during the carbon fixation phase?

The Calvin cycle incorporates each CO2 molecule, one at a time, by attaching it to a five-carbon sugar named ribulose bisphosphate.

Which of the following is an example of the second law of thermodynamics as it applies to biological reactions?

The aerobic respiration of one molecule of glucose produces six molecules each of carbon dioxide and water.

Most of the NADH that delivers electrons to the electron transport chain comes from which of the following processes?

The citric acid cycle

Which part of the catabolism of glucose by cellular respiration requires molecular oxygen (O2) and produces CO2?

The combination of the citric acid cycle and electron transport

Which of the following metabolic pathways produce(s) the most ATP, per glucose molecule metabolized, during cellular respiration?

The electron transport chain and oxidative phosphorylation

Which of the following statements is correct regarding ATP?

The energy in an ATP molecule is released through hydrolysis of one of the phosphate groups.

At low pH, a particular enzyme catalyzes a reaction at a high rate. At neutral pH, the enzyme is completely inactive. What statement best explains the difference in how pH affects the function of this enzyme?

The enzyme is adapted for low pH but is denatured at neutral pH, leaving it nonfunctional.

Which of the following is an example of potential rather than kinetic energy?

a molecule of glucose

What is the name of the thermodynamic barrier that must be overcome before products are formed in a spontaneous reaction?

activation energy

The process of stabilizing the structure of an enzyme in its active form by the binding of a molecule is an example of __________.

allosteric regulation

In photosynthesis, plants use carbon from __________ to make sugar and other organic molecules.

carbon dioxide

Which of the following terms most precisely describes the cellular process of breaking down large molecules into smaller ones?

catabolism (catabolic pathways)

A chemical reaction that has a positive ΔG is best described as __________.

endergonic

substrate-level phosphorylation accounts for approximately what percentage of the ATP formed by the reactions of glycolysis?

100%

Starting with one molecule of glucose, glycolysis results in the net production of which of the following sets of energy-containing products?

2 NADH, 2 pyruvate, and 2 ATP

Starting with citrate, how many of the following would be produced with three turns of the citric acid cycle?

3 ATP, 6 CO2, 9 NADH, and 3 FADH2

As ATP begins to build up in a cell, metabolism slows down. How does this happen?

ATP acts as an allosteric inhibitor to many of the enzymes involved in metabolism, thus slowing their function.

The light reactions of photosynthesis supply the Calvin cycle with __________.

ATP and NADPH.

Cells use ATP constantly, but ATP is considered a renewable resource. What process makes this possible?

ATP can be regenerated by the addition of a phosphate group to ADP.

A photosystem consists of which of the following structures?Reaction-center complex Light-harvesting complexes Primary electron acceptor Chlorophyll molecules

All of the listed structures are parts of a photosystem.

Glucose is the primary fuel for cellular respiration. Which of the following molecules can also be used by cellular respiration to generate ATP?

Amino acids, glycerol, and fatty acids can all be used in cellular respiration.

At low temperatures, a particular enzyme catalyzes a reaction, but at a slow rate. At high temperatures, the enzyme is completely inactive. What statement best explains the difference in how temperature affects the function of this enzyme?

At low temperatures, there is not enough free energy for the enzyme to function at a high rate, and at high temperatures, the enzyme is denatured, leaving it nonfunctional.

How does ATP drive mechanical work inside a cell?

By binding to motor proteins

How does ATP drive transport work inside a cell?

By phosphorylating a transport protein

Which of the summary statements below describes the results of the following reaction? C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + Energy

C6H12O6 is reducing agents and O2 is oxidizing agent.

Which of the following pairs of pathways and their location in the cell is incorrectly matched? Citric acid cycle: cytosol Glycolysis: cytosol Electron transport chain: mitochondrion Oxidative phosphorylation: mitochondrion

Citric acid cycle: cytosol

Which of the following statements is correct regarding competitive and noncompetitive enzyme inhibitors?

Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to an enzyme away from the active site.

Which of the following statements about enzymes is true?

Enzymes speed up the rate of the reaction without changing the ΔG for the reaction.

The primary manner in which cells manage their energy resources in order to do work is called energy coupling. Which of the following statements accurately defines energy coupling?

Exergonic reactions drive endergonic reactions.

Cells must regulate their metabolic pathways so that they do not waste resources. What is the most common mechanism that regulates cellular respiration in most cells?

Feedback inhibition of glycolysis

Fermentation by itself produces no ATP but keeps glycolysis going, which produces a small amount of ATP. How does fermentation do this?

Fermentation oxidizes NADH to NAD+, which facilitates the production of ATP in glycolysis.

Which of the following reactions would be endergonic?

Glucose + fructose → sucrose

Why do hydrolysis reactions occur more readily in solution than dehydration reactions?

Hydrolysis reactions are exergonic and increase entropy of the system.

What is the role of oxygen in the electron transport chain?

It is reduced to form water.

Which of the following statements describes what happens to a molecule that functions as the reducing agent (electron donor) in a redox or oxidation-reduction reaction?

It loses electrons and loses potential energy.

After completion of the citric acid cycle, most of the usable energy from the original glucose molecule is in the form of __________.

NADH

In what molecule(s) is the majority of the chemical energy from pyruvate transferred during the citric acid cycle?

NADH and FADH2

The light reactions of photosynthesis generate high-energy electrons, which end up in __________. The light reactions also produce __________ and __________.

NADPH; ATP; oxygen

Which of the following is a correct description of the events of cellular respiration and the sequence of events in cellular respiration?

Oxidation of glucose to pyruvate; oxidation of pyruvate; oxidation of acetyl-coA; oxidative phosphorylation

All of the processes involved in cellular respiration produce ATP. Which of the following processes produces the most ATP?

Oxidative phosphorylation

In the light reactions of photosynthesis, ATP is produced by photophosphorylation. Which of the listed processes is most similar to photophosphorylation?

Oxidative phosphorylation in cellular respiration

What would the value of ΔS be for a chemical reaction in which a molecule is broken down into smaller components?

Positive

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

Pyruvate is oxidized and decarboxylated, and the removed electrons are used to reduce an NAD+ to an NADH.

Why is the ΔG of ATP hydrolysis in the cell about twice as great as the ΔG of ATP hydrolysis in a test tube under standard conditions?

Reactant and product concentrations in the test tube are different from those in the cell.

Most of the electrons removed from glucose by cellular respiration are used for which of the following processes?

Reducing NAD+ to NADH in glycolysis and the citric acid cycle AND producing a proton gradient for ATP synthesis in the mitochondria.

Which of these statements about enzyme inhibitors is true?

The action of inhibitors may be reversible or irreversible.

Which of the following is changed by the presence of an enzyme in a reaction?

The activation energy

Which of the following statements about the active site of an enzyme is correct?

The active site may resemble a groove or pocket in the surface of a protein into which the substrate fits.

Which of the following statements correctly describes the difference in carbon fixation between C3 and C4 plants?

The first product of carbon fixation in C4 plants is a four-carbon compound instead of a three-carbon compound.

The ATP synthase in a human cell obtains energy for synthesizing ATP directly from which of the following processes?

The flow of H+ across the inner mitochondrial membrane through the ATP synthase enzyme

What best characterizes the role of ATP in cellular metabolism?

The free energy released by ATP hydrolysis that may be coupled to an endergonic process via the formation of a phosphorylated intermediate.

During which process is molecular oxygen produced in photosynthesis?

The light reactions by linear electron flow

The energy from the electrons in NADH and FADH2 fuel what process in the electron transport chain?

The pumping of H+ across the cristae of the mitochondrion

If you were to add one of the eight citric acid cycle intermediates to the culture medium of yeast growing in the laboratory, what do you think would happen to the rates of ATP and carbon dioxide production?

The rates of ATP production and carbon dioxide production would both increase.

Why are most autotrophs referred to as the producers of the biosphere?

They are the ultimate sources of organic compounds for all nonautotrophic organisms.

Why are carbohydrates and fats considered high energy foods?

They contain many electrons associated with hydrogen atoms.

The light reactions of photosynthesis use chemiosmosis to produce ATP that will be used in the Calvin cycle. The electrochemical gradient that drives this chemiosmosis is formed across which structure(s)?

Thylakoid membrane

A small amount of ATP is made in glycolysis by which of the following processes?

Transfer of a phosphate group from a fragment of glucose to ADP by substrate-level phosphorylation

What is the total production of ATP, NADH, and FADH2 in the citric acid cycle from one molecule of glucose?

Two ATP, six NADH, and two FADH2

Metabolic pathways are typically redox processes. In photosynthesis, what molecule is oxidized and what molecule is reduced?

Water is oxidized and carbon dioxide is reduced.

You have a large, healthy philodendron that you carelessly leave in total darkness while you are away on vacation. You are surprised to find that it is still alive when you return. What has the plant been using for an energy source while in the dark?

While it did have access to light, the plant stored energy in the form of sugars or starch, and it was able to derive energy from the stored molecules during your vacation.

Fermentation is essentially glycolysis plus an extra step in which pyruvate is reduced to form lactate or alcohol and carbon dioxide. This last step __________.

enables the cell to recycle the reduced NADH to oxidized NAD+

The function of cellular respiration is to __________.

extract usable energy from glucose

ATP allosterically inhibits enzymes in ATP-producing pathways. The result of this is called __________.

feedback inhibition

During the energy investment phase of glycolysis, __________.

glucose is phosphorylated before it is split into two three-carbon molecules

In the overall process of glycolysis and cellular respiration, __________ is oxidized and __________ is reduced.

glucose; oxygen

An exergonic reaction __________ free energy, and an endergonic reaction __________ free energy.

releases; absorbs

In general, the hydrolysis of ATP drives cellular work by __________.

releasing free energy that can be coupled to other reactions

Enzyme activity is affected by pH because __________.

high or low pH may disrupt hydrogen bonding or ionic interactions and thus change the shape of the active site

Which of the following processes is driven by chemiosmosis

oxidative phosphorylation

Which of the following processes generates a proton-motive force in mitochondria?

pumping of hydrogen ions from the mitochondrial matrix across the inner membrane and into the intermembrane space

When a molecule of NAD+ (nicotinamide adenine dinucleotide) gains a hydrogen atom (not a proton), the molecule becomes

reduced

Muscle tissues make lactate from pyruvate to do which of the following?

regenerate NAD+

An exergonic (spontaneous) reaction is a chemical reaction that __________.

releases energy when proceeding in the forward direction