Biological Processes and Membrane Functions

Exam Structure

The exam consists of multiple-choice questions, true/false statements, and short-answer questions.
Total points: 100.

Multiple-Choice Questions

Enzymes

Question: Which of the following correctly describes enzymes?
- A. They alter the change in free energy for a reaction.
- B. They become permanently modified as a consequence of a reaction.
- C. They lower the activation energy for a reaction.
- D. Enzymes promote exergonic reactions but not endergonic.
- E. Enzymes promote endergonic reactions but not exergonic.
- Correct Answer: C. Enzymes lower the activation energy for a reaction.
  - Explanation: Enzymes act as catalysts, which increase the rate of a reaction by lowering the activation energy without being consumed in the reaction.

Cell Energy Currency

Question: What is the primary energy currency for a cell?
- A. adenosine triphosphate
- B. enzymes
- C. glucose
- D. glycogen
- E. photons
- Correct Answer: A. adenosine triphosphate (ATP).
  - Explanation: ATP is critical for storing and transferring energy within cells.

Organelle Functionality

Question: In which organelle does the citric acid cycle occur?
- A. cell membrane
- B. chloroplast
- C. mitochondrion
- D. nucleus
- E. prokaryote
- Correct Answer: C. mitochondrion.
  - Explanation: The citric acid cycle, also known as the Krebs cycle, takes place in the mitochondrial matrix.

Biomembrane Composition

Question: A biomembrane is primarily comprised of which molecule?
- A. cholesterol
- B. phospholipid
- C. protein
- D. carbohydrate
- E. triglyceride
- Correct Answer: B. phospholipid.
  - Explanation: Phospholipids form the bilayer structure of cell membranes, providing a barrier and fluidity to the membrane.

Photosynthesis Process

Question: The process by which light energy is captured to generate molecules is known as…
- A. catabolism
- B. concentration gradient
- C. oxidative phosphorylation
- D. photosynthesis
- E. producer
- Correct Answer: D. photosynthesis.
  - Explanation: Photosynthesis converts light energy into chemical energy (glucose) in plants using chlorophyll and other pigments.

Membrane Permeability and Diffusion

Membrane Passage

Question: Which atom/molecule will most readily pass through a membrane?
- A. O2
- B. H2O
- C. glucose
- D. H+
- E. Na+
- Correct Answer: A. O2.
  - Explanation: Oxygen is nonpolar and small, allowing it to diffuse easily across lipid membranes.

Reduced Electron Carriers

Question: Which of the following is an example of a reduced electron carrier?
- A. ATP
- B. FAD
- C. NAD+
- D. coenzyme A
- E. NADH
- Correct Answer: E. NADH.
  - Explanation: NADH represents the reduced form of NAD+ and carries electrons for use in metabolic reactions.

False Statements about Diffusion

Question: Which statement about diffusion is false?
- A. Diffusion is a random process.
- B. Simple diffusion depends upon specific carrier proteins.
- C. Diffusion continues until the molecular concentrations are in equilibrium.
- D. Facilitated diffusion does not require ATP.
- E. In diffusion, molecules move from areas of greater concentration to areas of lesser concentration.
- Correct Answer: B. Simple diffusion depends upon specific carrier proteins.
  - Explanation: Simple diffusion does not require specific carriers, whereas facilitated diffusion does.

True/False Questions

Statement: Concentration gradients can be established across the cell membrane for molecules that are unable to permeate the cell membrane.
- Answer: True
  - Explanation: Concentration gradients can be maintained by mechanisms such as active transport.
Statement: Many plant tissues are green due to the fact that their pigments absorb green light less efficiently than other wavelengths.
- Answer: True
  - Explanation: Green pigments like chlorophyll reflect green light rather than absorb it, appearing green.
Statement: The purpose of the cyclic electron flow in plants is to generate ATP.
- Answer: True
  - Explanation: Cyclic electron flow helps generate ATP while maintaining electron flow through the photosystems.
Statement: Since plants lack mitochondria, they cannot undergo cellular respiration.
- Answer: False
  - Explanation: Plants have mitochondria and can perform cellular respiration alongside photosynthesis.
Statement: Blue light contains more energy than red light.
- Answer: True
  - Explanation: Blue light has shorter wavelengths and thus higher energy compared to red light.

Role of Electrons in Energy Currency

Question: Which statement best describes the role(s) played by electrons as energy currency?
- A. An electron can only be transferred to reactants as a proton.
- B. Electrons will momentarily contain energy when they are displaced to higher energy orbitals of atoms.
- C. Carbon dioxide represents a single carbon molecule in its most reduced state.
- D. Reactants are reduced when they lose electrons.
- E. Within a reaction, an electron will be transferred to a reactant that has the lower reduction potential.
- Correct Answer: B. Electrons will momentarily contain energy when they are displaced to higher energy orbitals of atoms.
  - Explanation: Electrons in higher orbitals have more energy and can be transferred during redox reactions.

Ion Channels and Membrane Proteins

Question: A protein that forms an ion channel through a membrane is most likely…
- A. a peripheral membrane protein.
- B. an enzyme.
- C. entirely outside the phospholipid bilayer.
- D. a phospholipid.
- E. a transmembrane protein.
- Correct Answer: E. a transmembrane protein.
  - Explanation: Transmembrane proteins span the membrane and facilitate the transport of ions and molecules.

Plant Cell Conditions

Question: Which condition is considered to be the best for plant cells?
- A. crenated
- B. isotonic
- C. hypertonic
- D. hypotonic
- E. plasmolysis
- Correct Answer: D. hypotonic.
  - Explanation: Hypotonic conditions allow plant cells to become turgid, supporting structure without bursting.

Enzyme Interaction Phases

Question: The phenomenon in which a molecule other than the substrate binds the active site of an enzyme is called…
- A. allosteric regulation
- B. competitive inhibition
- C. noncompetitive inhibition
- D. feedback
- E. none of the above
- Correct Answer: B. competitive inhibition.
  - Explanation: Competitive inhibition occurs when an inhibitor competes with the substrate for the active site of the enzyme.

Short Answer Questions

Cofactors in Metabolic Pathways

Question: Cofactors that shuttle substrates between the enzymes of a metabolic pathway are generally known as
- Answer: Coenzymes.

Glycolysis Outputs

Question: The molecule that is produced from the investment phase of glycolysis is a 3C molecule known as
- Answer: Glyceraldehyde-3-phosphate (G3P).
- The molecule that is produced from the energy harvesting phase of glycolysis is a 3C molecule known as
- Answer: Pyruvate.

Photosynthesis Waste Product

Question: The “waste product” of photosynthesis is
- Answer: Oxygen (O2).

ATP Generation Methods

Question: The generation of ATP via the transfer of phosphates from molecular intermediates is known as…
- A. autophosphorylation
- B. chemical phosphorylation
- C. oxidative phosphorylation
- D. photophosphorylation
- E. substrate-level phosphorylation
- Correct Answer: E. substrate-level phosphorylation.
  - Explanation: Substrate-level phosphorylation directly generates ATP during reactions in metabolic pathways.

Linear Electron Flow in Light Reactions

Question: What is the purpose of linear electron flow associated with the light reactions?
- A. It generates the ATP and NADPH to be used for the generation of sugars.
- B. It generates the ADP and NADP+ to be used for the generation of sugars.
- C. It regenerates 5C molecules from 3C precursors.
- D. It provides electrons to photosystem II (P680).
- E. It is used to oxidize the products of glycolysis.
- Correct Answer: A. It generates the ATP and NADPH to be used for the generation of sugars.
  - Explanation: The linear electron flow transfers electrons through the electron transport chain, yielding ATP and NADPH for sugar synthesis in the Calvin cycle.

Light Reactions Misconception

Question: Which statement about the light reactions is incorrect?
- A. The reactions convert light energy into chemical energy in the form of ATP and NADPH.
- B. The reactions utilize electron transport chains.
- C. The reactions take place within the thylakoids of chloroplasts.
- D. The reactions fix carbon dioxide within the reaction centers.
- E. The reactions can only occur in the presence of visible light.
- Correct Answer: D. The reactions fix carbon dioxide within the reaction centers.
  - Explanation: Carbon fixation occurs in the Calvin cycle, not during the light-dependent reactions.

Redox Reactions

Question: What is a redox reaction? What is the biological significance/purpose of the redox reactions that occur within metabolic pathways?
- Answer: Redox reactions involve the transfer of electrons between substances. They play a critical role in energy metabolism as they help to convert stored energy into usable forms. For example, during cellular respiration, the oxidation of glucose via a series of redox reactions releases energy that is ultimately used to produce ATP.

Membrane Potential Explanation

Question: What is membrane potential? Explain how animal cells can establish a membrane potential.
- Answer: Membrane potential, or membrane voltage, is the electrical potential difference across a cell membrane due to the distribution of ions. Animal cells establish membrane potential primarily through ion channels and pumps, particularly the sodium-potassium pump (Na+/K+). This pump actively transports Na+ out of the cell and K+ into the cell, leading to a negative charge inside the cell relative to the outside environment, thus creating a membrane potential.

Chemiosmosis and ATP Production

Question: The generation of ATP via ATP synthase – driven by chemiosmosis – is known as…
- A. autophosphorylation
- B. chemical phosphorylation
- C. oxidative phosphorylation
- D. osmotic phosphorylation
- E. substrate-level phosphorylation
- Correct Answer: C. oxidative phosphorylation.
  - Explanation: Oxidative phosphorylation occurs when ATP is formed using energy from electron transport chains and the resulting proton gradient.

Calvin Cycle Location

Question: Where do the dark reactions (Calvin cycle) occur?
- A. stroma of the chloroplast
- B. thylakoid membranes
- C. the lysosome
- D. cytosol around the chloroplast
- E. intermembrane space
- Correct Answer: A. stroma of the chloroplast.
  - Explanation: The Calvin cycle occurs in the stroma where carbon fixation takes place.

Protons in Cellular Respiration

Question: During cellular respiration and oxidative phosphorylation, in which compartment are protons concentrated?
- A. mitochondrial matrix
- B. thylakoid lumen
- C. smooth endoplasmic reticulum
- D. intermembrane space of the mitochondrion
- E. stroma of the chloroplast
- Correct Answer: D. intermembrane space of the mitochondrion.
  - Explanation: Protons are pumped into the intermembrane space during electron transport, creating a proton gradient used to synthesize ATP.

Pyruvate Oxidation Products

Question: The end products of pyruvate oxidation are
- A. glucose, ATP, and FADH2.
- B. pyruvate, ATP, and NADH.
- C. pyruvate, ATP, and NAD+.
- D. acetyl CoA, ATP, and NAD+.
- E. acetyl CoA, CO2, and NADH.
- Correct Answer: E. acetyl CoA, CO2, and NADH.
  - Explanation: Pyruvate is converted to acetyl CoA, releasing CO2 and generating NADH in the process.

Biomembrane Fluidity Factors

Question: Which of the following parameters is least likely to alter biomembrane fluidity?
- A. The length of fatty acids associated with the phospholipids.
- B. The presence or absence of cholesterol.
- C. The environmental temperature.
- D. The tonicity of the aqueous environment.
- E. The saturation of the fatty acids associated with the phospholipids.
- Correct Answer: D. The tonicity of the aqueous environment.
  - Explanation: While tonicity affects cell volume and shape, it is less directly involved in influencing membrane fluidity compared to the other factors listed.

Fermentation Significance

Question: Which statement describes the significance of fermentation?
- A. It generates the oxygen to create aerobic environments.
- B. It enables the oxidation of electron carriers under anaerobic conditions.
- C. It promotes the production of sugars in the absence of light.
- D. It is used to generate NADH.
- E. It promotes pyruvate oxidation under anaerobic conditions.
- Correct Answer: B. It enables the oxidation of electron carriers under anaerobic conditions.
  - Explanation: Fermentation is a metabolic process that restores the oxidized form of electron carriers, allowing glycolysis to continue in the absence of oxygen.

Additional True/False Questions

Statement: Glucose for glycolysis can enter the cell via simple diffusion.
- Answer: False
  - Explanation: Glucose requires facilitated diffusion or active transport to enter cells due to its larger size and polarity.
Statement: Within a photosystem, electrons are transported between chlorophylls of the light harvesting complexes until they reach the reaction center.
- Answer: True
  - Explanation: Electrons are indeed transferred between chlorophyll molecules and reach the reaction center to initiate the light-dependent reactions.
Statement: Facilitated diffusion relies upon concentration gradients to operate.
- Answer: True
  - Explanation: Facilitated diffusion occurs down a concentration gradient and requires specific transport proteins but does not require ATP.
Statement: Shorter wavelengths of light contain less energy than longer wavelengths.
- Answer: False
  - Explanation: Shorter wavelengths, such as ultraviolet light, contain more energy than longer wavelengths, such as infrared.
Statement: Exergonic reactions create free energy.
- Answer: False
  - Explanation: Exergonic reactions release free energy; they are characterized by a negative change in Gibbs free energy (ΔG < 0).
Statement: In an endergonic reaction, the products will be at a greater energy level than the reactants.
- Answer: True
  - Explanation: Endergonic reactions store energy in the products, leading to a positive change in Gibbs free energy (ΔG > 0).
Statement: In order to maintain the proper health of blood cells, hospital patients should be administered intravenous (IV) solutions that are isotonic.
- Answer: True
  - Explanation: Isotonic solutions prevent the movement of water into or out of cells, maintaining cell integrity.

Reactions Overview

Glucose and Oxygen Reactions

Questions: Consider the following reactions:
- (1) glucose + O2 → CO2 + H2O + energy
- (2) CO2 + H2O + energy → glucose + O2 a. In reaction (1), how is the H2O generated?
  - Answer: Water is generated as a product during the process of respiration when glucose is oxidized.
    b. In reaction (2), how is the O2 generated?
  - Answer: Oxygen is generated during photosynthesis when water is split in the light-dependent reactions.
    c. In reaction (2), from where does the energy come to drive these reactions?
  - Answer: The energy comes from sunlight, which is captured in the light-dependent reactions of photosynthesis.

Reaction Coupling and Its Significance

Question: Explain reaction coupling – what is reaction coupling, and what is its significance?
- Answer: Reaction coupling refers to the process of linking an energetically unfavorable reaction with a favorable one, allowing the overall reaction to proceed. This is significant in metabolism as it enables cellular processes to perform work despite some reactions being energetically unfavorable independently.

Protein Conformation and Function

Question: An aspect of a protein’s function is tied to its ability to alter its conformation. What is meant by “protein conformation”? Explain the significance of protein conformation as it relates to noncompetitive inhibition.
- Answer: Protein conformation refers to the three-dimensional structure of a protein, which is critical for its function. The structure can change in response to environmental conditions or binding of molecules. In noncompetitive inhibition, an inhibitor binds to an enzyme at a site other than the active site, causing a conformational change that decreases the enzyme's activity, illustrating that conformation is crucial for enzyme function.

Citric Acid Cycle Intermediate

Question: In the citric acid cycle, a 4C molecule is covalently linked to an acetyl to create a 6C molecule known as
- Answer: Citrate (or citric acid).

Aquaporin Role

Question: A channel known as an
- Answer: Aquaporin enables the rapid movement of water across a membrane.

Enzyme Functions

Question: The general name given to an enzyme that covalently links a phosphate to a substrate is
- Answer: Kinase.

NAD+ and NADH Conversions

Question: The conversions between NAD+ and NADH are mediated by enzymes known as
- Answer: Dehydrogenases.

Rubisco Function

Question: Rubisco fixes CO2 to what substrate?
- Answer: Ribulose bisphosphate (RuBP).