Bio I Exam 3 Review Problems

Question 1:

Niacin, a B vitamin, is crucial for cellular respiration because it is a precursor to NAD+. NAD+ functions as a...

A) Substrate in the Krebs cycle.

B) Coenzyme that carries electrons.

C) Structural component of the mitochondria.

D) Inhibitor of ATP synthase.

Correct Answer: B) Coenzyme that carries electrons.

Explanation: NAD+ is a coenzyme that accepts electrons and protons during redox reactions in cellular respiration, becoming NADH. It's essential for electron transport.

Question 2:

Why is it important to control the temperature when studying enzyme-catalyzed reactions in a laboratory setting?

A) To ensure the enzyme remains at its optimal pH.

B) To prevent the enzyme from denaturing.

C) To maintain a constant substrate concentration.

D) All of the above.

Correct Answer: B) To prevent the enzyme from denaturing.

Explanation: Temperature greatly affects enzyme activity. High temperatures can denature enzymes, causing them to lose their shape and function.

Question 1:

Niacin, a B vitamin, is crucial for cellular respiration because it is a precursor to NAD+. NAD+ functions as a...

A) Substrate in the Krebs cycle.

B) Coenzyme that carries electrons.

C) Structural component of the mitochondria.

D) Inhibitor of ATP synthase.

Correct Answer: B) Coenzyme that carries electrons.

Explanation: NAD+ is a coenzyme that accepts electrons and protons during redox reactions in cellular respiration, becoming NADH. It's essential for electron transport.

Question 2:

Why is it important to control the temperature when studying enzyme-catalyzed reactions in a laboratory setting?

A) To ensure the enzyme remains at its optimal pH.

B) To prevent the enzyme from denaturing.

C) To maintain a constant substrate concentration.

D) All of the above.

Correct Answer: B) To prevent the enzyme from denaturing.

Explanation: Temperature greatly affects enzyme activity. High temperatures can denature enzymes, causing them to lose their shape and function.

Question 3:

A scientist observes that an enzyme-catalyzed reaction proceeds at a slower rate when the temperature is lowered from 37°C to 25°C. Which of the following best explains this observation?

A) Lowering the temperature increases the activation energy required for the reaction.

B) Lowering the temperature causes the enzyme to permanently lose its active site.

C) Lowering the temperature decreases the kinetic energy of the molecules, reducing the frequency of effective collisions.

D) Lowering the temperature increases the concentration of the substrate, inhibiting the enzyme.

Correct Answer: C) Lowering the temperature decreases the kinetic energy of the molecules, reducing the frequency of effective collisions.

Explanation: Lower temperatures reduce molecular motion, decreasing the number of successful enzyme-substrate collisions and slowing down the reaction.

Question 4:

Consider a metabolic pathway where glucose is broken down to produce ATP. How would you classify this pathway in terms of energy release or consumption?

A) Anabolic and endergonic.

B) Anabolic and exergonic.

C) Catabolic and endergonic.

D) Catabolic and exergonic.

Correct Answer: D) Catabolic and exergonic.

Explanation: Catabolic pathways break down molecules, releasing energy (exergonic).

Question 5:

A bacterial infection is treated with an antibiotic that acts as a competitive inhibitor. After some time, the bacteria develop resistance to the antibiotic. Which of the following is the most likely mechanism of this resistance?

A) The bacteria increase the production of the enzyme targeted by the antibiotic.

B) The bacteria develop a mutation that alters the structure of the enzyme's active site.

C) The bacteria begin producing a new enzyme that degrades the antibiotic.

D) The bacteria modify the antibiotic, preventing it from binding to the enzyme.

Correct Answer: B) The bacteria develop a mutation that alters the structure of the enzyme's active site.

Explanation: Competitive inhibitors bind to the active site. Mutations that change the active site's shape can prevent the inhibitor from binding, conferring resistance.

Question 6:

Which of the following describes the key difference in energy storage between ADP and ATP?

A) ATP stores energy in the ribose sugar, while ADP stores it in the phosphate groups.

B) ATP has three phosphate groups, and the bond between the second and third phosphate groups holds usable energy, while ADP only has two.

C) ADP is a stable molecule, while ATP is highly unstable and readily releases energy.

D) ADP is used for short-term energy storage, while ATP is used for long-term energy storage.

Correct Answer: B) ATP has three phosphate groups, and the bond between the second and third phosphate groups holds usable energy, while ADP only has two.

Explanation: The energy in ATP is stored in the phosphate bonds, particularly the terminal one.

Question 7:

Which of the following statements correctly describes the relationship between electron transfer and redox reactions?

A) 'OIL RIG' stands for 'Oxidation Is Loss, Reduction Is Gain' of protons.

B) 'OIL RIG' stands for 'Oxidation Is Loss, Reduction Is Gain' of electrons.

C) 'OIL RIG' stands for 'Oxidation Is Reduction, Loss Is Gain' of electrons.

D) 'OIL RIG' stands for 'Oxidation Is Gain, Reduction Is Loss' of electrons.

Correct Answer: B) 'OIL RIG' stands for 'Oxidation Is Loss, Reduction Is Gain' of electrons.

Explanation: "OIL RIG" is a mnemonic device for remembering that oxidation is loss of electrons, and reduction is gain of electrons.

Question 8:

In the reaction NAD+ + 2e- + H+ → NADH, what happens to NAD+?

A) It is oxidized.

B) It is reduced.

C) It is polarized.

D) It is denatured.

Correct Answer: B) It is reduced.

Explanation: NAD+ gains electrons (and a proton), therefore it is reduced.

Question 9:

What is the consequence of a molecule being reduced?

A) It loses potential energy.

B) It gains potential energy.

C) It becomes more positively charged.

D) It becomes more unstable.

Correct Answer: B) It gains potential energy.

Explanation: Reduction involves gaining electrons, which increases the molecule's potential energy.

Question 10:

The second law of thermodynamics states that every energy transfer or transformation increases the entropy 1 of the universe. In the context of cellular respiration, how does this law explain the loss of energy from glucose?

A) The energy is converted to ATP with 100% efficiency.

B) Some energy is lost as heat, increasing disorder.

C) The energy is stored in the chemical bonds of glucose.

D) The energy is used to create more glucose.

Correct Answer: B) Some energy is lost as heat, increasing disorder.

Explanation: Energy transformations are never perfectly efficient; some energy is always lost as heat, which increases entropy (disorder).

Question 11:

Which of the following molecules has both genetic information storage and catalytic activity?

A) Proteins

B) DNA

C) Lipids

D) RNA

Correct Answer: D) RNA

Explanation: While DNA stores genetic information, RNA can also act as a catalyst (ribozymes).

Question 12:

How do catalysts, such as enzymes, affect the delta G of a reaction?

A) They increase the delta G.

B) They decrease the delta G.

C) They do not affect the delta G.

D) They reverse the delta G.

Correct Answer: C) They do not affect the delta G.

Explanation: Catalysts speed up reactions but do not change the overall free energy change (delta G).

Question 13:

A metabolic pathway is inhibited by a noncompetitive inhibitor. What aspect of the reaction will remain unchanged?

A) The reaction rate.

B) The enzyme's Vmax.

C) The reaction's delta G.

D) The enzyme's Km.

Correct Answer: C) The reaction's delta G.

Explanation: Noncompetitive inhibitors affect Vmax, but they do not alter the delta G of the reaction.

Question 14:

During a metabolic reaction, a molecule of NAD+ accepts two electrons and a proton to form NADH. This process is best described as:

A) Oxidation of NAD+.

B) Reduction of NAD+.

C) Hydrolysis of NAD+.

D) Phosphorylation of NAD+.

Correct Answer: B) Reduction of NAD+.

Explanation: NAD+ gains electrons, thus it is reduced.

Question 15:

Which metabolic pathway is the initial step in the breakdown of glucose and occurs in the cytoplasm of all cells?

A) Calvin cycle

B) Glycolysis

C) Beta-oxidation

D) Krebs cycle

Correct Answer: B) Glycolysis

Explanation: Glycolysis is the first stage of glucose breakdown and occurs in the cytoplasm.

Question 16:

An organism that obtains its carbon from organic molecules produced by other organisms is classified as a(n):

A) Phototroph.

B) Chemotroph.

C) Autotroph.

D) Heterotroph.

Correct Answer: D) Heterotroph.

Explanation: Heterotrophs obtain carbon from organic compounds made by other organisms.

Question 17:

What is the primary fate of the molecule that retains most of glucose's energy after glycolysis (pyruvate)?

A) It is converted directly into ATP.

B) It enters the citric acid cycle.

C) It is released as carbon dioxide.

D) It is used to synthesize glucose.

Correct Answer: B) It enters the citric acid cycle.

Explanation: Pyruvate is transported into the mitochondria and oxidized to acetyl-CoA, which enters the citric acid cycle.

Question 18:

What is the primary purpose of fermentation in anaerobic conditions?

A) To produce large amounts of ATP.

B) To regenerate NAD+ for glycolysis.

C) To synthesize glucose from pyruvate.

D) To completely oxidize pyruvate.

Correct Answer: B) To regenerate NAD+ for glycolysis.

Explanation: Fermentation regenerates NAD+ so glycolysis can continue in the absence of oxygen.

Question 19:

If glycolysis produces 4 ATP molecules but uses 2, what is the net gain of ATP?

A) 0

B) 2

C) 4

D) 6

Correct Answer: B) 2

Explanation: Net ATP gain is the total ATP produced minus the ATP used. 4 - 2 = 2

Question 20:

How does lactate fermentation differ from aerobic respiration in terms of oxygen requirement?

A) Lactate fermentation requires oxygen, while aerobic respiration does not.

B) Both lactate fermentation and aerobic respiration require oxygen.

C) Lactate fermentation does not require oxygen, while aerobic respiration does.

D) Oxygen is optional for both processes.

Correct Answer: C) Lactate fermentation does not require oxygen, while aerobic respiration does.

Explanation: Lactate fermentation is an anaerobic process; aerobic respiration requires oxygen.

Question 21:

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

A) It acts as the initial electron donor.

B) It acts as the final electron acceptor.

C) It facilitates the production of carbon dioxide.

D) It directly produces ATP.

Correct Answer: B) It acts as the final electron acceptor.

Explanation: Oxygen is the terminal electron acceptor in the electron transport chain, forming water.

Question 22:

Besides ATP, what is another major product of the electron transport chain?

A) Glucose

B) Carbon dioxide

C) Water

D) Pyruvate

Correct Answer: C) Water

Explanation: Water is formed when oxygen accepts electrons and protons at the end of the electron transport chain.

Question 23:

What is one of the products of the decarboxylation of pyruvate?

A) Glucose

B) Carbon dioxide

C) Lactate

D) Ethanol

Correct Answer: B) Carbon dioxide

Explanation: Decarboxylation of pyruvate removes a carbon atom, releasing it as carbon dioxide.

Question 24:

Which of the following processes involves the direct enzymatic transfer of a phosphate group to ADP, forming ATP?

A) Chemiosmosis

B) Oxidative phosphorylation

C) Substrate-level phosphorylation

D) Photophosphorylation

Correct Answer: C) Substrate-level phosphorylation

Explanation: Substrate-level phosphorylation involves the direct transfer of a phosphate group from a substrate to ADP.

Question 25:

What is produced during the stage of cellular respiration that can occur with or without oxygen?

A) Carbon dioxide and water

B) ATP, NADH, and pyruvate

C) Glucose and oxygen

D) Ethanol and carbon dioxide

Correct Answer: B) ATP, NADH, and pyruvate

Explanation: Glycolysis can occur with or without oxygen and produces ATP, NADH, and pyruvate.

Question 26:

Describe how the carbon skeletons of amino acids are integrated into cellular respiration. Explain why they can enter the process at different stages.

Correct Answer: Amino acids have different side chains, and depending on the side chain, they can be converted into pyruvate, acetyl-CoA, or citric acid cycle intermediates. This allows for the carbon skeletons to be utilized for ATP production.

Explanation: Amino acids can be deaminated and their carbon skeletons converted into different molecules that enter cellular respiration at various points.

Question 27:

Which electron carrier is essential for transferring electrons during both glycolysis and the citric acid cycle?

A) FAD

B) ATP

C) NAD+

D) Pyruvate

Correct Answer: C) NAD+

Explanation: NAD+ is used as an electron carrier in both glycolysis and the citric acid cycle.

Question 28:

In which cellular compartment does the citric acid cycle take place?

A) Cytoplasm

B) Mitochondrial matrix

C) Endoplasmic reticulum

D) Nucleus

Correct Answer: B) Mitochondrial matrix

Explanation: The citric acid cycle occurs in the mitochondrial matrix in eukaryotes.

Question 29:

Where does FADH2 deposit its electrons in the electron transport chain, compared to NADH?

A) At the same complex as NADH.

B) At a complex further down the chain than NADH.

C) At a complex earlier in the chain than NADH.

D) Directly to oxygen, bypassing the complexes.

Correct Answer: B) At a complex further down the chain than NADH.

Explanation: FADH2 delivers its electrons to a complex further down the electron transport chain than NADH.

Question 30:

Before pyruvate oxidation can occur, pyruvate must be transported from the cytoplasm into the:

A) Endoplasmic reticulum.

B) Lysosome.

C) Mitochondrial matrix.

D) Golgi apparatus.

Correct Answer: C) Mitochondrial matrix.

Explanation: Pyruvate is transported into the mitochondrial matrix for conversion to acetyl-CoA.

Question 31:

Explain the process of dehydrogenation. How does it relate to redox reactions and the formation of electron carriers like NADH?

Correct Answer: Dehydrogenation is the removal of hydrogen atoms (electrons and protons) from a molecule, which is a type of oxidation. This is often coupled with the reduction of electron carriers like NAD+ to NADH.

Explanation: Dehydrogenation is an oxidation reaction where hydrogen atoms are removed. These electrons and protons are often transferred to electron carriers like NAD+, reducing them to NADH.

Question 32:

Explain how sulfur-reducing bacteria use sulfate as an electron acceptor in anaerobic respiration. What are the products of this process, and how does it contribute to the environment?

Correct Answer: Sulfur-reducing bacteria use sulfate as a terminal electron acceptor in anaerobic respiration. This reduces the sulfate to sulfide, which reacts with hydrogen to form hydrogen sulfide. This occurs in anaerobic environments.

Explanation: In anaerobic respiration, sulfur-reducing bacteria use sulfate (SO4^2-) as a final electron acceptor, reducing it to sulfide (S^2-). Sulfide can then react with hydrogen ions to form hydrogen sulfide (H2S), a gas with a characteristic odor.

Question 33:

Which process uses glucose and oxygen as reactants to produce carbon dioxide, water, and ATP?

A) Fermentation

B) Anaerobic respiration

C) Aerobic respiration

D) Photosynthesis

Correct Answer: C) Aerobic respiration

Explanation: Aerobic respiration uses glucose and oxygen to generate carbon dioxide, water, and ATP.

Question 34:

What is the primary purpose of the two ATP molecules used in the initial steps of glycolysis?

A) To directly produce NADH.

B) To activate glucose and make it more reactive.

C) To create a proton gradient.

D) To synthesize pyruvate.

Correct Answer: B) To activate glucose and make it more reactive.

Explanation: The initial ATP input in glycolysis phosphorylates glucose, making it more reactive.

Question 35:

What is the primary function of cytochrome oxidase (complex IV) in the electron transport chain?

A) To pump protons into the intermembrane space.

B) To transfer electrons from NADH to FADH2.

C) To reduce oxygen to water.

D) To synthesize ATP.

Correct Answer: C) To reduce oxygen to water.

Explanation: Cytochrome oxidase (complex IV) catalyzes the final step in the electron transport chain, reducing oxygen to water.

Question 36:

Carotenoids are classified as accessory pigments in photosynthesis because they:

A) Are not involved in light absorption.

B) Capture light energy and transfer it to chlorophylls.

C) Primarily function in water transport.

D) Are only found in certain types of plants.

Correct Answer: B) Capture light energy and transfer it to chlorophylls.

Explanation: Carotenoids absorb light energy and pass it to chlorophylls, extending the range of light wavelengths that can be used for photosynthesis.

Question 37:

Chlorophyll, a molecule that absorbs light energy and uses it in photosynthesis, is a type of:

A) Enzyme

B) Pigment

C) Carbohydrate

D) Lipid

Correct Answer: B) Pigment

Explanation: Chlorophyll is a pigment that absorbs light energy.

Question 38:

Describe the process of chemiosmosis in photosynthesis. How does it contribute to the production of ATP, and what is the role of the thylakoid membrane?

Correct Answer: Chemiosmosis involves the movement of protons across the thylakoid membrane, driven by light energy. This creates a proton gradient that powers ATP synthase, producing ATP.

Explanation: Chemiosmosis in photosynthesis uses a proton gradient across the thylakoid membrane to power ATP synthesis by ATP synthase.

Question 39:

What is the primary role of carbon dioxide in the Calvin cycle?

A) To provide electrons for the electron transport chain.

B) To act as the final electron acceptor.

C) To serve as the carbon source for sugar synthesis.

D) To produce oxygen.

Correct Answer: C) To serve as the carbon source for sugar synthesis.

Explanation: Carbon dioxide is the source of carbon that is fixed into sugars in the Calvin cycle.

Question 40:

"A mutation drastically reduces the activity of PEP carboxylase in a C4 plant. What is the immediate effect on the production of oxaloacetate?"A) The production of oxaloacetate would increase.

B) The production of oxaloacetate would decrease.

C) The concentration of oxaloacetate would remain unchanged.

D) Oxaloacetate would be converted directly into RuBP.

*Correct Answer:* B) The production of oxaloacetate would decrease.

*Explanation:* PEP carboxylase is the enzyme that catalyzes the formation of oxaloacetate from PEP and CO2. If its activity is reduced, the rate of oxaloacetate production would directly decrease.

Question 41:

What is the source of energy that drives the Calvin cycle?

A) Light energy directly.

B) Chemical energy from ATP and NADPH.

C) Energy from the breakdown of glucose.

D) Energy from the oxidation of water.

Correct Answer: B) Chemical energy from ATP and NADPH.

Explanation: The Calvin cycle is powered by ATP and NADPH, which are chemical energy carriers produced during the light-dependent reactions of photosynthesis.

Question 42:

Describe the requirements of the Calvin cycle. What are the roles of ATP, NADPH, and carbon dioxide in this process?

Correct Answer: The Calvin cycle requires ATP as an energy source, NADPH as a reducing agent, and carbon dioxide as a carbon source, to produce sugars.

Explanation: ATP provides the energy, NADPH provides the reducing power (electrons), and carbon dioxide is the source of carbon atoms that are incorporated into carbohydrates.

Question 43:

What is the source of electrons that replenish Photosystem II after it loses electrons to the electron transport chain?

A) Glucose

B) Carbon dioxide

C) Water

D) NADPH

Correct Answer: C) Water

Explanation: Photosystem II regains electrons through the splitting of water molecules.

Question 44:

What are the products of the splitting of water in Photosystem II?

A) Glucose and oxygen

B) Carbon dioxide and ATP

C) Electrons, protons, and oxygen

D) NADPH and ATP

Correct Answer: C) Electrons, protons, and oxygen

Explanation: The splitting of water produces electrons, protons (H+), and oxygen (O2).

Question 45:

What is the role of light energy in the splitting of water in Photosystem II?

A) To directly synthesize glucose.

B) To excite electrons in chlorophyll.

C) To produce carbon dioxide.

D) To create a proton gradient.

Correct Answer: B) To excite electrons in chlorophyll.

Explanation: Light energy excites electrons in chlorophyll within Photosystem II, which initiates the electron transfer that leads to water splitting.

Question 46:

What is the primary function of the electron transport chain between Photosystem II and Photosystem I?

A) To directly synthesize glucose.

B) To generate a proton gradient.

C) To produce oxygen.

D) To reduce NADP+.

Correct Answer: B) To generate a proton gradient.

Explanation: The electron transport chain pumps protons into the thylakoid lumen, creating a proton gradient used for ATP synthesis.

Question 47:

If electron flow between Photosystem II and Photosystem I is inhibited, what is the immediate consequence?

A) Increased production of NADPH.

B) Decreased production of ATP.

C) Increased production of glucose.

D) Decreased production of oxygen.

Correct Answer: B) Decreased production of ATP.

Explanation: The electron transport chain is essential for generating the proton gradient that drives ATP synthesis.

Question 48:

How does the disruption of proton transport across the thylakoid membrane affect ATP synthesis?

A) It increases ATP synthesis.

B) It decreases ATP synthesis.

C) It has no effect on ATP synthesis.

D) It causes ATP to be converted into glucose.

Correct Answer: B) It decreases ATP synthesis.

Explanation: The proton gradient across the thylakoid membrane is essential for chemiosmosis and ATP production.

Question 49:

At the core of both Photosystem I and Photosystem II, you will find specialized proteins that contain:

A) Carotenoid pigments.

B) Chlorophyll b molecules.

C) A unique form of chlorophyll a.

D) Enzymes that directly fix carbon dioxide.

Correct Answer: C) A unique form of chlorophyll a.

Explanation: Both photosystems have a reaction center containing a specialized chlorophyll a molecule.

Question 50:

How many carbon dioxide molecules must be fixed by the Calvin cycle to produce one molecule of glyceraldehyde-3-phosphate (G3P)?

A) 1

B) 2

C) 3

D) 6

Correct Answer: C) 3

Explanation: Three molecules of CO2 are required to produce one molecule of G3P.

Question 51:

If the Calvin cycle completes 15 turns, how many molecules of glyceraldehyde-3-phosphate (G3P) will be produced?

A) 3

B) 5

C) 10

D) 15

Correct Answer: B) 5

Explanation: Since 3 turns are needed for one G3P, 15 turns will make 5 G3P.

Question 52:

What is the direct product of the Calvin cycle that can be used to synthesize glucose and other organic molecules?

A) Pyruvate

B) Acetyl-CoA

C) Glyceraldehyde-3-phosphate (G3P)

D) Citrate

Correct Answer: C) Glyceraldehyde-3-phosphate (G3P)

Explanation: G3P is the three-carbon sugar that is the direct product of the Calvin cycle and the precursor to glucose.

Question 53:

Why do plants appear green to our eyes?

A) Because chlorophyll absorbs green light.

B) Because chlorophyll reflects green light.

C) Because chlorophyll emits green light.

D) Because chlorophyll converts green light into red light.

Correct Answer: B) Because chlorophyll reflects green light.

Explanation: Chlorophyll absorbs red and blue light most effectively, reflecting green light, which is why plants appear green.

Question 54:

Explain how carbon dioxide is used to synthesize glucose in photosynthesis. What is the role of the Calvin cycle in this process?

Correct Answer: Carbon dioxide is fixed during the Calvin cycle. RuBisCO catalyzes the reaction that fixes the carbon dioxide, and the carbon is then used to synthesize glucose.

Explanation: Carbon dioxide is incorporated into organic molecules through carbon fixation in the Calvin cycle. RuBisCO catalyzes the initial step of this process, and the fixed carbon is used to build glucose.

Question 55:

Where in the chloroplast does the photosynthetic electron transport chain create a high concentration of protons (H⁺), contributing to the proton gradient used for ATP synthesis?

A) Chloroplast matrix

B) Outer chloroplast membrane

C) Stroma

D) Thylakoid lumen

Correct Answer: D) Thylakoid lumen

Explanation: Protons are pumped into the thylakoid lumen, creating a high concentration that drives ATP synthesis.

Question 56:

Where do the light-dependent reactions of photosynthesis take place within the chloroplast?

A) Stroma

B) Thylakoid membranes

C) Outer membrane

D) Intermembrane space

Correct Answer: B) Thylakoid membranes

Explanation: The light-dependent reactions occur in the thylakoid membranes.

Question 57:

What are the stacked, disc-shaped structures within chloroplasts that contain chlorophyll?

A) Grana

B) Stroma

C) Cristae

D) Matrix

Correct Answer: A) Grana

Explanation: Grana are stacks of thylakoids, which contain chlorophyll.

Question 58:

What is the primary function of the thylakoid membranes in photosynthesis?

A) To synthesize glucose.

B) To capture light energy and generate ATP and NADPH.

C) To fix carbon dioxide.

D) To store starch.

Correct Answer: B) To capture light energy and generate ATP and NADPH.

Explanation: Thylakoid membranes house the light-dependent reactions, where light energy is converted into ATP and NADPH.

Question 59:

How are the light-dependent reactions and the Calvin cycle connected?

A) By the direct transfer of glucose.

B) By the exchange of carbon dioxide and oxygen.

C) By the use of ATP and NADPH from the light reactions.

D) By the synthesis of water in the Calvin cycle.

Correct Answer: C) By the use of ATP and NADPH from the light reactions.

Explanation: The light-dependent reactions produce ATP and NADPH, which are used to power the Calvin cycle.

Question 60:

What process provides the electrons needed to replace those lost by Photosystem II?

A) Carbon fixation

B) Water splitting

C) Glucose synthesis

D) Oxygen release

Correct Answer: B) Water splitting

Explanation: Water splitting provides the electrons to replenish Photosystem II.

Question 61:

Describe the role of RuBisCO in photosynthesis. What would be the consequence for a plant if RuBisCO were non-functional?

Correct Answer: RuBisCO catalyzes carbon fixation, and without it, plants would be unable to fix carbon dioxide and produce sugars.

Explanation: RuBisCO is the enzyme that catalyzes the first step of carbon fixation in the Calvin cycle. Without it, the plant cannot convert CO2 into sugars.

Question 62:

The Calvin cycle takes place in the fluid-filled space of the chloroplast called the:

A) Grana

B) Thylakoid

C) Stroma

D) Matrix

Correct Answer: C) Stroma

Explanation: The Calvin cycle occurs in the stroma of the chloroplast.

Question 63:

How many molecules of carbon dioxide are required to synthesize 5 molecules of glucose in the Calvin cycle?

A) 5

B) 10

C) 30

D) 60

Correct Answer: C) 30

Explanation: Six CO2 molecules are needed to make one glucose, so 30 CO2 molecules are needed to make five glucose molecules (5 x 6 = 30).

Question 64:

How many molecules of glyceraldehyde-3-phosphate (G3P) are needed to synthesize 10 molecules of glucose?

A) 5

B) 10

C) 20

D) 30

Correct Answer: C) 20

Explanation: Two G3P molecules are needed to make one glucose, so 20 G3P molecules are needed to make ten glucose molecules (10 x 2 = 20).

Question 65:

If a plant needs to synthesize 3 glucose molecules, how many molecules of carbon dioxide and glyceraldehyde-3-phosphate are required?

A) 3 CO2 and 6 G3P

B) 6 CO2 and 3 G3P

C) 18 CO2 and 6 G3P

D) 6 CO2 and 18 G3P

Correct Answer: C) 18 CO2 and 6 G3P

Explanation: For 3 glucose, you need 3 x 6 = 18 CO2 and 3 x 2 = 6 G3P.

Question 66:

What is the critical function of ATP synthase's proper orientation in the thylakoid membrane?

A) To directly synthesize glucose.

B) To correctly utilize the proton gradient for ATP production.

C) To facilitate the splitting of water.

D) To regulate carbon dioxide uptake.

Correct Answer: B) To correctly utilize the proton gradient for ATP production.

Explanation: ATP synthase's orientation is crucial for it to use the proton gradient to produce ATP.

Question 67:

What is the main purpose of the Calvin cycle (cyclic carbon fixation reactions)?

A) To produce ATP using light energy.

B) To generate NADPH for cellular respiration.

C) To synthesize glucose from carbon dioxide.

D) To split water and release oxygen.

Correct Answer: C) To synthesize glucose from carbon dioxide.

Explanation: The Calvin cycle's main purpose is to fix carbon dioxide and produce glucose.

Question 68:

How does increasing substrate concentration affect the activity of an enzyme in the presence of a competitive inhibitor?

A) It decreases enzyme activity.

B) It reverses the effect of the inhibitor.

C) It has no effect on enzyme activity.

D) It increases the inhibitor's binding affinity.

Correct Answer: B) It reverses the effect of the inhibitor.

Explanation: Increasing substrate concentration can outcompete a competitive inhibitor, reversing its effect.

Question 69:

If a system loses energy, where does that energy go according to the First Law of Thermodynamics?

A) It is destroyed.

B) It is converted into matter.

C) It is transferred to the surroundings.

D) It becomes potential energy.

Correct Answer: C) It is transferred to the surroundings.

Explanation: The First Law of Thermodynamics states that energy is conserved; it can be transferred or transformed, but it cannot be created or destroyed.

Question 70:

Coenzymes are primarily composed of:

A) Proteins

B) Lipids

C) Organic molecules

D) Inorganic ions

Correct Answer: C) Organic molecules

Explanation: Coenzymes are organic molecules that assist enzymes in catalyzing reactions.

Question 71:

What is the primary role of the inner mitochondrial membrane in oxidative phosphorylation?

A) To provide a surface for glycolysis.

B) To house the enzymes of the citric acid cycle.

C) To establish a proton gradient for ATP synthesis.

D) To facilitate the diffusion of glucose.

Correct Answer: C) To establish a proton gradient for ATP synthesis.

Explanation: The inner mitochondrial membrane is the site of the electron transport chain and chemiosmosis, which are essential for establishing the proton gradient used in ATP synthesis.

Question 72:

How does substrate-level phosphorylation differ from oxidative phosphorylation?

A) Substrate-level phosphorylation requires oxygen, while oxidative phosphorylation does not.

B) Substrate-level phosphorylation uses a proton gradient, while oxidative phosphorylation does not.

C) Substrate-level phosphorylation involves direct phosphate transfer, while oxidative phosphorylation uses ATP synthase.

D) Substrate-level phosphorylation occurs in the mitochondria, while oxidative phosphorylation occurs in the cytoplasm.

Correct Answer: C) Substrate-level phosphorylation involves direct phosphate transfer, while oxidative phosphorylation uses ATP synthase.

Explanation: Substrate-level phosphorylation directly transfers a phosphate group from a substrate to ADP, while oxidative phosphorylation uses the proton gradient and ATP synthase.

Question 73:

How many molecules of carbon dioxide are released per turn of the citric acid cycle?

A) 1

B) 2

C) 3

D) 4

Correct Answer: B) 2

Explanation: Two molecules of carbon dioxide are released per turn of the citric acid cycle.

Question 74:

How many molecules of NADH are generated per turn of the citric acid cycle?

A) 1

B) 2

C) 3

D) 4

Correct Answer: C) 3

Explanation: Three molecules of NADH are produced per turn of the citric acid cycle.

Question 75:

How many molecules of FADH2 are produced per turn of the citric acid cycle?

A) 0

B) 1

C) 2

D) 3

Correct Answer: B) 1

Explanation: One molecule of FADH2 is produced per turn of the citric acid cycle.

Question 76:

How many ATP molecules are produced directly per turn of the citric acid cycle?

A) 0

B) 1

C) 2

D) 3

Correct Answer: B) 1

Explanation: One ATP (or GTP) molecule is produced directly per turn of the citric acid cycle through substrate-level phosphorylation.

Question 77:

Explain why Acetyl-CoA does not cross the inner membrane of the mitochondria. What is its role within the mitochondrial matrix, and how does it contribute to cellular respiration?

Correct Answer: Acetyl-CoA is produced in the mitochondrial matrix and does not leave. It is used in the citric acid cycle to generate NADH, FADH2, and ATP.

Explanation: Acetyl-CoA is the initial substrate for the citric acid cycle, which occurs exclusively in the mitochondrial matrix.

Question 78:

Which of the following molecules acts as an electron acceptor in the electron transport chain, oxidizing NADH?

A) Pyruvate

B) Oxaloacetate

C) Ubiquinone

D) Fumarate

Correct Answer: C) Ubiquinone

Explanation: Ubiquinone (coenzyme Q) is an electron carrier in the electron transport chain that accepts electrons from NADH and FADH2, thus oxidizing them.

Question 79:

What is the term for cellular respiration that uses electron acceptors other than oxygen?

A) Fermentation

B) Aerobic respiration

C) Anaerobic respiration

D) Glycolysis

Correct Answer: C) Anaerobic respiration

Explanation: Anaerobic respiration uses electron acceptors other than oxygen, such as sulfate or nitrate.

Question 80:

In the Citric Acid Cycle, oxidation reactions are typically coupled with:

A) Hydrolysis of ATP.

B) Reduction of electron carriers.

C) Addition of phosphate groups.

D) Isomerization of substrates.

Correct Answer: B) Reduction of electron carriers.

Explanation: Oxidation reactions in the citric acid cycle transfer electrons to electron carriers like NAD+ and FAD, reducing them to NADH and FADH2, respectively.

Question 81:

What happens to excess carbohydrates when ATP levels are high in cells?

A) They are excreted unchanged.

B) They are converted into glycogen for storage.

C) They are used to synthesize fatty acids.

D) They are used to produce oxygen.

Correct Answer: B) They are converted into glycogen for storage.

Explanation: Excess glucose is stored as glycogen in animals when ATP levels are high.

Question 82:

Explain how a diet high in carbohydrates but low in fat can still lead to fat storage. What are the metabolic pathways involved?

Correct Answer: Excess carbohydrates are converted into acetyl-CoA, which is then used to synthesize fatty acids through lipogenesis.

Explanation: When carbohydrate intake exceeds energy needs, excess glucose is converted to acetyl-CoA. Acetyl-CoA is then used in a process called lipogenesis to synthesize fatty acids, which are stored as fat.

Question 83:

Describe the roles of Photosystem I and Photosystem II in the light-dependent reactions of photosynthesis. How do they work together to generate ATP and NADPH?

Correct Answer: Both photosystems capture light energy in the form of photons to excite electrons in the reaction center. Photosystem II splits water to provide electrons, while Photosystem I ultimately transfers electrons to NADP+ to form NADPH. They work together to create a proton gradient that drives ATP synthesis.

Explanation: Photosystem II captures light energy and splits water, providing electrons to the electron transport chain. Photosystem I receives electrons from the electron transport chain and uses light energy to transfer electrons to NADP+, forming NADPH. The electron transport chain between the two photosystems also creates a proton gradient used to generate ATP.

Question 84:

What is the direct source of energy for ATP synthesis during photosynthesis?

A) Sunlight

B) A proton gradient across the thylakoid membrane

C) The breakdown of glucose

D) The oxidation of water

Correct Answer: B) A proton gradient across the thylakoid membrane

Explanation: ATP synthesis in photosynthesis is driven by the proton gradient across the thylakoid membrane, which is established by the electron transport chain.

Question 85:

During the light-dependent reactions, where are protons (H+) pumped?

A) From the stroma to the thylakoid space

B) From the thylakoid space to the stroma

C) From the cytoplasm to the intermembrane space

D) From the intermembrane space to the cytoplasm

Correct Answer: A) From the stroma to the thylakoid space

Explanation: Protons are pumped from the stroma into the thylakoid space, creating a proton gradient.

Question 86:

Which process directly uses the energy stored in a proton gradient to produce ATP during photosynthesis?

A) Photolysis

B) Carbon fixation

C) Chemiosmosis

D) Electron transport

Correct Answer: C) Chemiosmosis

Explanation: Chemiosmosis uses the proton gradient to power ATP synthase, which produces ATP.

Question 87:

What is the immediate product of the reaction catalyzed by RuBisCO?

A) Glucose

B) 3-phosphoglycerate (3-PGA)

C) ATP

D) NADPH

Correct Answer: B) 3-phosphoglycerate (3-PGA)

Explanation: RuBisCO catalyzes the reaction between CO2 and RuBP, which immediately results in the formation of 3-PGA.

Question 88:

The Calvin cycle is directly powered by:

A) Light energy

B) ATP and NADPH

C) Glucose

D) Carbon dioxide

Correct Answer: B) ATP and NADPH

Explanation: The Calvin cycle uses chemical energy from ATP and NADPH to fix carbon dioxide and produce sugars.

Question 89:

Explain how environmental conditions can influence RuBisCO's activity and affect the efficiency of photosynthesis.

Correct Answer: High temperatures and high oxygen concentrations can reduce the efficiency of photosynthesis by increasing RuBisCO's oxygenase activity, leading to photorespiration. Moderate temperatures and high carbon dioxide concentrations favor RuBisCO's carboxylase activity, promoting carbon fixation and glucose production.

Explanation: RuBisCO can catalyze two reactions: carbon fixation (adding CO2 to RuBP) and oxygenation (adding O2 to RuBP). High temperatures and high O2 levels favor oxygenation, leading to photorespiration, which reduces photosynthetic efficiency.

Question 90:

Where does the ATP used in the Calvin cycle come from?

A) Glycolysis

B) Cellular respiration

C) Light-dependent reactions of photosynthesis

D) Fermentation

Correct Answer: C) Light-dependent reactions of photosynthesis

Explanation: The ATP used in the Calvin cycle is produced during the light-dependent reactions of photosynthesis.

Question 91:

Why do plants need light energy to power the Calvin cycle?

A) Light energy is directly used to fix carbon dioxide.

B) Light energy is needed to produce ATP and NADPH for the Calvin cycle.

C) Light energy is required for the plant to take in carbon dioxide.

D) Light energy is used to break down glucose.

Correct Answer: B) Light energy is needed to produce ATP and NADPH for the Calvin cycle.

Explanation: Light energy is used in the light-dependent reactions to produce ATP and NADPH, which are then used to power the Calvin cycle.

Question 92:

Why wouldn't it be efficient for plants to rely solely on cellular respiration to power the Calvin cycle?

A) Cellular respiration does not produce enough NADPH.

B) Cellular respiration only occurs at night in plants.

C) Breaking down sugars to make sugars would be a wasteful energy conversion.

D) Cellular respiration occurs in the stroma, while the Calvin cycle occurs in the mitochondria.

Correct Answer: C) Breaking down sugars to make sugars would be a wasteful energy conversion.

Explanation: It would be energetically inefficient for plants to break down sugars through cellular respiration to power the synthesis of sugars in the Calvin cycle.

Question 93:

How does the antenna complex contribute to the function of the reaction center?

A) It provides electrons to the reaction center.

B) It captures and funnels light energy to the reaction center.

C) It converts light energy into chemical energy.

D) It protects the reaction center from damage.

Correct Answer: B) It captures and funnels light energy to the reaction center.

Explanation: The antenna complex contains pigment molecules that absorb light energy and transfer it to the reaction center.

Question 94:

In anaerobic conditions, which molecule acts as the final electron acceptor in alcohol fermentation, allowing NADH to be oxidized back to NAD⁺?

A. Oxygen

B. Pyruvate

C. Acetaldehyde

D. Ethanol

E. Ubiquinone

Correct Answer: C. Acetaldehyde

Explanation: In alcohol fermentation, pyruvate is converted to acetaldehyde, which then accepts electrons from NADH, becoming ethanol and regenerating NAD+.

Question 95:

An enzyme, Enzyme X, catalyzes a reaction essential for the synthesis of a particular amino acid. Enzyme X functions optimally only when a specific zinc ion (Zn2+) is bound to it. In this scenario, what is the role of the zinc ion?

A) Substrate

B) Product

C) Cofactor

D) Competitive inhibitor

Correct Answer: C) Cofactor

Explanation: The zinc ion is required for Enzyme X to function, which aligns with the definition of a cofactor.

Question 96:

Which of the following best describes the role of inorganic ions, such as magnesium or zinc, in enzyme activity?

A) They serve as substrates for the enzyme.

B) They act as cofactors, assisting in catalysis.

C) They function as competitive inhibitors of the enzyme.

D) They provide the energy needed for the reaction to occur.

Correct Answer: B) They act as cofactors, assisting in catalysis.

Explanation: Inorganic ions often act as cofactors, which are nonprotein helpers that assist enzymes in their catalytic activity.

Question 97:

The enzyme phosphofructokinase (PFK) is an important regulatory enzyme in glycolysis. High levels of ATP in the cell inhibit PFK activity by binding at a site distinct from the substrate-binding site. This is an example of:

A) Competitive inhibition

B) Allosteric activation

C) Feedback inhibition

D) Substrate-level regulation

Correct Answer: C) Feedback inhibition

Explanation: ATP, an end product of energy metabolism, inhibits PFK, an enzyme earlier in the pathway, demonstrating feedback inhibition.

Question 98:

In cellular respiration, at which stage are all six carbon atoms of the original glucose molecule completely oxidized and released as carbon dioxide?

A) Glycolysis

B) Pyruvate oxidation

C) Citric acid cycle

D) Electron transport chain

Correct Answer: C) Citric acid cycle

Explanation: The citric acid cycle is where the remaining carbons from the original glucose molecule are released as CO2.

Question 99:The process of beta-oxidation involves the breakdown of fatty acids into:

A) Glucose molecules

B) Amino acids

C) Acetyl-CoA molecules

D) Glycerol molecules

Correct Answer: C) Acetyl-CoA molecules

Explanation: Beta-oxidation is the catabolic process that breaks down fatty acids into two-carbon units that form acetyl-CoA.

Question 100:

The Calvin cycle, where carbon dioxide is converted into sugars, occurs in which part of the chloroplast?

A) Thylakoid membrane

B) Thylakoid lumen

C) Stroma

D) Outer membrane

*Correct Answer:* C) Stroma

*Explanation:* The Calvin cycle enzymes are located in the stroma.