Test#2 study Q

Question 1

Why do phospholipids form bilayers when mixed with water?

A.The hydrophobic fatty acids H-bond with each other and exclude the hydrophilic headgroups.
B. Transmembrane proteins organize them into bilayers.
C. Water excludes the hydrophilic headgroups but H-bonds with the hydrophobic fatty acids.
D. Water H-bonds with the hydrophilic headgroups and excludes the hydrophobic fatty acids.
E. The hydrophobic headgroups H-bond with each other and exclude the hydrophilic fatty acids.

Answer 1

D

Water H-bonds with the hydrophilic headgroups and excludes the hydrophobic fatty acids.

Question 2

Membranes are fluid because:

A. the fatty acids forming the core are held together by exclusion from water rather than by affinity for each other, so they are free to move within the bilayer
B. the polar headgroups forming the core are held together by exclusion from water rather than by affinity for each other, so they are free to move within the bilayer
C. the proteins forming the core are held together by exclusion from water rather than by affinity for each other, so they are free to move within the bilayer
D. the fatty acids forming the core are held together by their affinity for water rather than by affinity for each other, so they are free to move within the bilayer
E. the polar head
groups forming the core are held together by their affinity for water rather than by affinity for
each other, so they are free to move within the bilayer

Answer 2

A
the fatty acids forming the core are held together by exclusion from water rather than by affinity for each other, so they are free to move within the bilayer

Question 3

Why do all cells have a plasma membrane?

A.To provide a scaffold for attaching the cell wall to.
B.To prevent gases and non-polar substances from freely entering and exiting the cell.
C.To prevent necessary molecules from exiting and unwanted molecules from entering the cell.
D.To strengthen the cell wall to prevent it from bursting because of turgor pressure.
E.To provide a scaffold for attaching the cytoskeleton to.

Answer 3

C

To prevent necessary molecules from exiting and unwanted molecules from entering the cell.

Question 4

What is the difference between receptor-mediated endocytosis and active transport?

A.In receptor-mediated endocytosis a receptor protein binds the solute and triggers the formation
of a transport vesicle, whereas in active transport a protein carrier binds the molecule and uses energy to transport it across the membrane.
B.In receptor-mediated endocytosis a protein carrier binds the molecule and uses energy to transport it across the membrane, whereas in active transport a receptor protein binds the solute and triggers the formation of a
transport vesicle.
C.In receptor-mediated endocytosis a receptor protein binds the solute and triggers the formation of a transport vesicle, whereas in active transport a protein channel permits the solute to diffuse through the membrane.
D.In receptor-mediated endocytosis a receptor protein binds the solute and triggers the formation of a transport
vesicle, whereas in active transport a protein carrier binds the solute and transports it across the membrane to whichever side has the lower concentration.
E.In receptor-mediated endocytosis a protein carrier binds the solute and transports it across the membrane to
whichever side has the lower concentration, whereas in active transport a protein carrier binds the molecule
and uses energy to transport it across the membrane.

Answer 4

A
In receptor-mediated endocytosis a receptor protein binds the solute and triggers the formation
of a transport vesicle, whereas in active transport a protein carrier binds the molecule and uses energy to transport it across the membrane.

Question 5

Which of the following is least likely to diffuse across a plasma membrane?

A. O2         
B. CO2
C. ethanol    
D. a sodium ion
E. a small, non-polar molecule

Answer 5

D

a sodium ion

Question 6

If a red blood cell explodes when it is placed in a solution, the cell is:

A. Isosmotic
B. Hyperosmotic
C. Hypoosmotic
D. Psychotic
E. Hyperbolic

Answer 6

B

Hyperosmotic

Question 7

Why are you killed by ouabain, the poison from poison arrow frogs?

A.It inactivates electron transport by binding to cytochrome oxidase and stops ATP generation.
B.It inactivates the sodium/potassium pump, so potassium accumulates inside cells to toxic levels.
C.It inactivates the sodium/potassium pump, so sodium accumulates inside cells to toxic levels.
D.It inactivates lysosomes, so garbage accumulates inside cells to toxic levels.
E.It forms pores in membranes which allow the sodium expelled by the sodium/potassium pump to diffuse
back into the cells

Answer 7

C

It inactivates the sodium/potassium pump, so sodium accumulates inside cells to toxic levels.

Question 8

Why do some RNA molecules act as catalysts?

A. They fold into just the right shape to bind inhibitors and thus allow certain react
ions to proceed.
B. They kinase critical proteins which then activate key intermediates in chemical reactions.
C. They fold into just the right shape to bind substrates and stress critical bonds so as to lower the energy of activation of certain reactions.
D. They fold into just the right shape to bind signaling molecules and activate a signal transduction pathway.
E. ATP is used both to make RNA molecules and to supply the energy for chemical reactions, therefore RNA molecules can use some of their ATP to supply the energy for chemical reactions.

Answer 8

C
They fold into just the right shape to bind substrates and stress critical bonds so as to lower the energy of activation of certain reactions.

Question 9

Why do all enzyme-catalyzed reactions have an optimum temperature?

A. The rate of all chemical reactions increases with temperature; however, enzymes are proteins and therefore denature when a critical temperature is exceeded.
B. The rate of all chemical reactions increases with temperature; however, the substrates decompose when a critical temperature is exceeded.
C. The rate of all chemical reactions increases with temperature; however, the energy of activation decreases with temperature to the point that catalysis no longer affects the rate.
D. The rate of all chemical reactions increases with temperature; however, entropy increases as well and because enzymes are proteins they lose activity when entropy exceeds a critical value.
E. The rate of all chemical reactions decreases with temperature because free energy decreases; however, enzymes are proteins and therefore stop working when they get too cold.

Answer 9

A
The rate of all chemical reactions increases with temperature; however, enzymes are proteins and therefore denature when a critical temperature is exceeded.

Question 10

Which of the following factors will NOT affect the activity of an enzyme?

A. gravity         
B. pH          
C. Salt concentration         
D. Organic solvents 
E. Temperature

Answer 10

A

gravity

Question 11

What is a coupled reaction?

A. A reaction in which two energetically unfavorable reactions are coupled together, resulting in a net decrease in free energy because two reactions are better than one.
B. A reaction in which energy consumed by an endergonic reaction is used to synthesize ATP.
C. A reaction in which energy released by an exergonic reaction is used to synthesize ATP.
D. A reaction in which ATP hydrolysis is coupled to an exergonic reaction, resulting in a net increase in free energy which allows the reaction to occur.
E. A reaction in which ATP hydrolysis is coupled to an endergonic reaction, resulting in a net decrease in free energy which allows the reaction to occur.

Answer 11

E
A reaction in which ATP hydrolysis is coupled to an endergonic reaction, resulting in a net decrease in free energy which allows the reaction to occur.

Question 12

What are the two distinct phases of oxidative respiration?

A. 
1) Removing electrons from reduced organic molecules, 
2) recovering the energy stored in these electrons and using it to make ATP. 
B. 
1) Glycolysis, 
2) Beta-oxidation
C. 
1) Glycolysis, 
2) substrate-level phosphorylation
D. 
1) Removing electrons from reduced organic molecules, 
2) making ATP by substrate-level
phosphorylation.
E. 
1) Fermentation, 
2) regeneration of ADP and NAD+.

Answer 12

A

1) Removing electrons from reduced organic molecules,
2) recovering the energy stored in these electrons and using it to make ATP.

Question 13

Regardless of the electron or hydrogen acceptor used, one of the products of fermentation is always

A. NAD+
B. glucose
C. acetyl-CoA
D. CO2
E. ethanol

Answer 13

A

NAD+

Question 14

Which of the following statements is TRUE?

A. Two molecules of pyruvate contain less energy than one
molecule of glucose.
B. One molecule of pyruvate contains more energy than one molecule of lactic acid.
C. Pyruvate is more oxidized than CO2.
D. Pyruvate is more reduced than glucose.
E. One molecule of acetyl-CoA contains more energy than one molecule of pyruvate.

Answer 14

A
Two molecules of pyruvate contain less energy than one
molecule of glucose.

Question 15

Cellular respiration converts oxygen to:

A. CO2
B. ATP 
C. NADH
D. H2O
E. part of a sugar

Answer 15

D

H2O

Question 16

What is done by the Krebs cycle?

A. Acetyl-CoA is completely oxidized to CO2 and its electrons are given to carriers which shuttle them
to the electron transport system.
B. Pyruvate is oxidized to form acetyl-CoA and the energy released is used to make ATP.
C. Fatty acids are oxidized sequentially to form acetyl-CoA and their electrons are given to carriers
which shuttle them to the electron transport system.
D. Glucose is oxidized to pyruvate and its electrons are given to carriers which shuttle them to the
electron transport system.
E. Electrons are transferred from one carrier to another and energy released is used to make ATP.

Answer 16

A
Acetyl-CoA is completely oxidized to CO2 and its electrons are given to carriers which shuttle them
to the electron transport system.

Question 17

Carbon monoxide competes with oxygen for the active site in hemoglobin, and therefore inhibits oxygen
transport within our bodies. Why is carbon monoxide such a lethal poison?

A. Oxygen is a substrate in several of the oxidation reactions in glycolysis. Cells deprived of oxygen
cannot oxidize glucose, so ATP synthesis stops and the cell dies.
B. Oxygen is the terminal electron acceptor in oxidative respiration. Cells deprived of oxygen can only make ATP by fermentation, which is too inefficient to satisfy our energy requirements.
C. Oxygen is a substrate in several of the oxidation reactions in the Krebs cycle. Cells deprived of
oxygen cannot complete the Krebs cycle, so ATP synthesis stops and the cell dies.
D. Oxygen is a substrate in many of the digestive reactions. Cells deprived of oxygen cannot make
glucose, so ATP synthesis stops and the cell dies.
E. Oxygen is an essential cofactor in the ATP synthetase enzyme. In cells deprived of oxygen the ATP
synthetase enzyme is inactive, so ATP synthesis stops and the cell dies.

Answer 17

B
Oxygen is the terminal electron acceptor in oxidative respiration. Cells deprived of oxygen can only make ATP by fermentation, which is too inefficient to satisfy our energy requirements.

Question 18

Your research team has identified a new drug which specifically inhibits the mitochondrial ATP synthase.
Which of the following would you expect to occur first in cells treated with this drug?

A. ATP synthesis will increase B. Glycolysis will stop
C. the Krebs cycle will stop D. electron transport will stop
E. the pH gradient across the inner mitochondrial membrane will increase

Answer 18

E

the pH gradient across the inner mitochondrial membrane will increase

Question 19

What is the general rule for how all food sources are oxidized?
A. Most foods are already oxidized.
B. Most foods are oxidized to release heat rather than to make ATP.
C. All foods are changed to an intermediate in glucose oxidative respiration in as few steps as possible.
D. Most foods are used to make ATP by substrate-level phosphorylation rather than by chemiosmotic
ATP synthesis.
E. Each food is completely oxidised to CO2 by its own unique biochemical pathway.

Answer 19

C

All foods are changed to an intermediate in glucose oxidative respiration in as few steps as possible.

Question 20

The rate of glycolysis is

A. stimulated by ATP
B. stimulated by citric acid C. inhibited by oxygen
D. inhibited by ADP
E. inhibited by ATP

Answer 20

E

inhibited by ATP

Question 21

2,4-dinitrophenol makes membranes permeable to H+ ions. What will happen to an animal given daily
sublethal doses of this chemical if it is kept on the same diet?

A. It will gain weight 
B. It will lose weight. 
C. Its metabolic rate will decrease
D. Its body temperature will decrease 
E. It will produce excessive amounts of ATP.

Answer 21

B

It will lose weight.

Question 22

Why do we say that photosynthesis reverses oxidative respiration?

A. Photosynthesis combines energy, water and CO2 to form glucose, whereas respiration converts
glucose to energy, water and CO2
B. Photosynthesis makes ADP and NAD+, whereas respiration produces ATP and NADH
C. Photosynthesis occurs only in the light whereas respiration occurs only in the dark
D. Photosynthesis absorbs photons whereas photons are created by photorespiration
E. Photosynthesis uses ATP to make pH gradients whereas respiration uses pH gradients to make ATP

Answer 22

A
Photosynthesis combines energy, water and CO2 to form glucose, whereas respiration converts
glucose to energy, water and CO2

Question 23

The light-independent reactions of photosynthesis:

A. only occur in the dark
B. convert CO2 into sugars C. convert light into dark
D.convert water into hydrogen and oxygen.
E. are also temperature-independent

Answer 23

B

convert CO2 into

Question 24

Chlorophyll b absorbs green wavelengths that chlorophyll a cannot absorb. Chlorophyll b thus acts as

A. an accessory pigment
B. a fluorescent molecule C. a more efficient pigment
D. a reaction center chlorophyll
E. an energizer for photosynthetic bacteria

Answer 24

A

an accessory pigment

Question 25

How many photons must be absorbed to create a molecule of O2?

A. 1 
B. 2 
C. 4 
D. 6 
E. 8

Answer 25

E

8

Question 26

How many revolutions of the Calvin cycle are required to produce a 6 carbon sugar?

A. 1 
B. 2 
C. 3 
D. 6 
E. 12

Answer 26

D

6

Question 27

What happens first inside a chloroplast when you turn off the lights?

A. Photorespiration stops
B. Carbon fixation stops
C. Sugar synthesis stops.
D. Electron transport stops E. ATP synthesis stops

Answer 27

D

Electron transport stops