Question 1

Which of the following processes is classified as a metabolic pathway?
A) the synthesis of a protein
B) water moving across a membrane via osmosis
C) the death and lysis of a cell
D) the movement of oxygen across a membrane

Accepted Answer

A metabolic pathway involves a series of chemical reactions in a cell that results in the breakdown or synthesis of molecules, such as proteins. Options B, C, and D do not involve metabolic pathways.

Question 2

Which of the following statements regarding enzymes is true?
A) Enzymes are inorganic.
B) An enzyme's function is unaffected by changes in pH.
C) Enzymes catalyze specific reactions.
D) All enzymes depend on protein cofactors to function.

Accepted Answer

Enzymes are known for their ability to catalyze specific reactions, meaning that they are very selective in the substrates they can bind to and convert.

The other statements are false. Enzymes are organic molecules made up of proteins (and sometimes non-protein components known as cofactors). Enzyme function is affected by changes in pH and other environmental factors. And not all enzymes require protein cofactors – some require non-protein cofactors like vitamins or metals.

Question 3

The transfer of a phosphate group to a molecule or compound is called
A) carboxylation.
B) ionization.
C) phosphorylation.
D) hydrogenation.

Accepted Answer

Phosphorylation is the transfer of a phosphate group to a molecule or compound. It is a common biochemical process that plays a critical role in many cellular signaling pathways and metabolic reactions. Carboxylation is the addition of a carboxylic acid group to a molecule, ionization is the process of forming ions by adding or removing electrons, and hydrogenation is the addition of hydrogen atoms to a molecule. None of these processes involve the transfer of a phosphate group, so they are not the correct choice.

Question 4

When an enzyme catalyzes a reaction
A) it lowers the activation energy of the reaction.
B) it raises the activation energy of the reaction.
C) it acts as a reactant.
D) it is used once and discarded.

Accepted Answer

Enzymes lower the activation energy needed for a chemical reaction to occur, making it easier for the reaction to take place. This is achieved by binding to the reactants and stabilizing the transition state, leading to a faster reaction rate. Enzymes themselves are not consumed in the reaction and can be used multiple times.

Question 5

ATP can be used as the cell's energy exchange mechanism because
A) endergonic reactions can be fueled by coupling them with the formation of ATP from ADP.
B) ATP is the most energy-rich small molecule in the cell.
C) endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP.
D) ATP is a disposable form of chemical energy, used once and then discarded by the cell.

Accepted Answer

ATP can be used as the cell's energy exchange mechanism because endergonic reactions can be fueled by coupling them with the hydrolysis of high-energy phosphate bonds in ATP. This process releases energy, making it available for other cellular processes to use. Additionally, ATP is a relatively stable molecule that can be easily synthesized and broken down by enzymes within the cell.

Question 6

Glucose molecules provide energy to power the swimming motion of sperm. In this example, the sperm are changing
A) chemical energy into kinetic energy.
B) chemical energy into potential energy.
C) kinetic energy into potential energy.
D) kinetic energy into thermal energy.

Accepted Answer

Glucose is a form of chemical energy, and the sperm use this energy to power their swimming motion. Therefore, the sperm are converting chemical energy into kinetic energy.

Question 7

Which of the following statements regarding thermodynamics is false?
A) Thermodynamics is the study of energy transformations that occur in a collection of matter.
B) A single cell or the planet Earth could be a thermodynamic system.
C) An open system exchanges both energy and matter with its surroundings.
D) An automobile engine is a closed system because it does not exchange energy and matter with its surroundings.

Accepted Answer

An automobile engine is not a closed system because it exchanges energy with its surroundings through the release of heat and work.

Question 8

Most of a cell's enzymes are
A) lipids.
B) proteins.
C) amino acids.
D) carbohydrates.

Accepted Answer

Enzymes are typically proteins, not lipids, amino acids, or carbohydrates.

Question 9

Which of the following statements regarding enzyme function is false?
A) An enzyme's function depends on its three-dimensional shape.
B) Enzymes are very specific for certain substrates.
C) Enzymes are used up when they catalyze a chemical reaction so must be synthesized for each new chemical reaction.
D) Enzymes emerge unchanged from the reactions they catalyze.

Accepted Answer

Enzymes are not used up during chemical reactions, but rather they emerge from the reaction unchanged and available to catalyze additional reactions.

Question 10

Anything that prevents ATP formation will most likely
A) result in cell death.
B) force the cell to rely on lipids for energy.
C) force the cell to rely on ADP for energy.
D) have no effect on the cell.

Accepted Answer

ATP is the primary source of energy for most cellular processes. If ATP cannot be formed, the cell will not have the energy it needs to carry out its functions and will ultimately die.

Question 11

In the reaction A → B + C + heat
A) there is a net input of energy.
B) the potential energy of the products is greater than that of the reactant.
C) the potential energy of the products is less than that of the reactant.
D) entropy has decreased.

Accepted Answer

The reaction releases heat, indicating a decrease in potential energy. Therefore, the potential energy of the products (B and C) is less than that of the reactant (A). This process is exothermic, and there is no net input of energy. The entropy may or may not have changed, but it is not related to the potential energy.

Question 12

A steer must eat at least 100 pounds of grain to gain less than 10 pounds of muscle tissue. This illustrates
A) the first law of thermodynamics.
B) the second law of thermodynamics.
C) that some energy is destroyed in every energy conversion.
D) that energy transformations are typically 100% efficient.

Accepted Answer

This statement illustrates the second law of thermodynamics, which states that each energy transfer or transformation increases the entropy of the universe. In this case, the energy from the grain is not efficiently converted to muscle tissue, and some of it is lost as heat and other forms of energy, increasing the overall entropy of the system.

Question 13

Which of the following statements about ATP is true?
A) It contains five phosphate groups.
B) Extremely stable bonds link the second and third phosphate groups.
C) It contains the sugar glucose.
D) It releases energy when one phosphate group leaves ATP.

Accepted Answer

ATP releases energy when one phosphate group leaves, leaving ADP (adenosine diphosphate). ATP contains three phosphate groups, not five, and does not contain glucose. The bond between the second and third phosphate groups is actually unstable and high energy, which allows for efficient energy transfer.

Question 14

What is the basic difference between exergonic and endergonic reactions?
A) Exergonic reactions involve ionic bonds; endergonic reactions involve covalent bonds.
B) Exergonic reactions involve the breaking of bonds; endergonic reactions involve the formation of bonds.
C) Exergonic reactions release energy; endergonic reactions absorb it.
D) In exergonic reactions, the reactants have less chemical energy than the products; in endergonic reactions, the opposite is true.

Accepted Answer

Exergonic reactions release energy, while endergonic reactions absorb it. This means that exergonic reactions proceed spontaneously and release energy, whereas endergonic reactions require an input of energy to proceed. The other options (A, B, D) are not correct, as they do not accurately describe the difference between exergonic and endergonic reactions.

Question 15

Which of the following processes is endergonic?
A) the burning of wood
B) the synthesis of glucose from carbon dioxide and water
C) the breakdown of glucose
D) cellular respiration

Accepted Answer

Endergonic processes require energy input and store energy in complex molecules or bonds. The synthesis of glucose from carbon dioxide and water is an endergonic process that requires energy input from the sun during photosynthesis. The burning of wood and the breakdown of glucose are exergonic processes that release energy, while cellular respiration is both exergonic and endergonic, as it releases energy from glucose but also requires energy input for various steps of the process.

Question 16

An energy barrier
A) is the amount of energy that must be produced by the reactants to end a chemical reaction.
B) is higher than the activation energy of a reaction.
C) prevents the spontaneous breakdown of molecules in the cell.
D) can only be overcome with the use of enzymes.

Accepted Answer

An energy barrier is crucial for the stability of molecules within cells, as it prevents their spontaneous breakdown. This ensures that molecules only react under specific, controlled conditions, rather than reacting randomly, which could be harmful to the cell.

Question 17

Living systems
A) violate the first law of thermodynamics.
B) violate the second law of thermodynamics.
C) decrease their entropy while increasing the entropy of the universe.
D) are examples of a closed system.

Accepted Answer

Living systems decrease their own entropy by organizing molecules into complex structures, but this process requires energy, which increases the entropy of the universe overall, in accordance with the second law of thermodynamics. They do not violate the first or second laws of thermodynamics, nor are they closed systems, as they exchange energy and matter with their surroundings.

Question 18

The active site of an enzyme is
A) the region of a substrate that is changed by an enzyme.
B) the highly changeable portion of an enzyme that adapts to fit the substrates of various reactions.
C) the region of an enzyme that attaches to a substrate.
D) the region of a product that detaches from the enzyme.

Accepted Answer

The active site of an enzyme is the specific region of the enzyme where a substrate binds and undergoes a chemical reaction. It is located on the surface of the enzyme and has a shape and chemical makeup that is complementary to the substrate. Therefore, choice C is the correct answer because it correctly identifies the active site as the region of the enzyme that attaches to a substrate.

Question 19

Which of the following direct energy transfers is impossible in living systems?
A) light energy to chemical energy
B) chemical energy to kinetic energy
C) light energy to potential energy
D) heat to light energy

Accepted Answer

In living systems, heat is considered a byproduct of energy transformations, and it cannot be directly converted into light. In fact, the second law of thermodynamics states that energy transformations are always associated with some degree of energy loss in the form of unusable heat energy, so it is not possible to completely reverse or convert heat energy into other forms of energy.

Question 20

When a cell uses chemical energy to perform work, it uses the energy released from a(n) ________ reaction to drive a(n) ________ reaction.
A) exergonic; endergonic
B) endergonic; exergonic
C) exergonic; spontaneous
D) spontaneous; exergonic

Accepted Answer

An exergonic reaction releases energy, which can then be used to drive an endergonic reaction, one that requires an input of energy to proceed. This coupling of reactions is fundamental to cellular processes and energy management.

Quiz 5: The Working Cell

Which of the following processes is classified as a metabolic pathway?

Which of the following statements regarding enzymes is true?

The transfer of a phosphate group to a molecule or compound is called

When an enzyme catalyzes a reaction

ATP can be used as the cell's energy exchange mechanism because

Glucose molecules provide energy to power the swimming motion of sperm. In this example, the sperm are changing

Which of the following statements regarding thermodynamics is false?

Most of a cell's enzymes are

Which of the following statements regarding enzyme function is false?

Anything that prevents ATP formation will most likely

In the reaction A → B + C + heat

A steer must eat at least 100 pounds of grain to gain less than 10 pounds of muscle tissue. This illustrates

Which of the following statements about ATP is true?

What is the basic difference between exergonic and endergonic reactions?

Which of the following processes is endergonic?

An energy barrier

Living systems

The active site of an enzyme is

Which of the following direct energy transfers is impossible in living systems?

When a cell uses chemical energy to perform work, it uses the energy released from a(n) reaction to drive a(n) reaction.