Unit 3 Test Review Guide: Metabolism, Cellular Respiration, and Photosynthesis

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Q1. How do enzymes speed up metabolic reactions, and what is the role of activation energy?

Background

Topic: Enzyme Function and Activation Energy

This question tests your understanding of how enzymes act as biological catalysts, specifically how they affect the activation energy of chemical reactions in cells.

Key Terms and Concepts:

Enzyme: A protein that speeds up chemical reactions in living organisms.
Activation Energy (Ea): The minimum amount of energy required to start a chemical reaction.
Substrate: The reactant molecule that an enzyme acts upon.
Active Site: The region on the enzyme where the substrate binds.

Key Concept:

Enzymes lower the activation energy required for a reaction, making it easier for the reaction to proceed.

Step-by-Step Guidance

Recall that every chemical reaction requires a certain amount of energy to get started, called the activation energy ().
Understand that enzymes work by binding to their specific substrate at the active site, forming an enzyme-substrate complex.
Recognize that this binding stabilizes the transition state and lowers the activation energy needed for the reaction to occur.
Visualize or sketch a graph showing the energy profile of a reaction with and without an enzyme, noting the difference in activation energy.

Try solving on your own before revealing the answer!

Final Answer:

Enzymes speed up metabolic reactions by lowering the activation energy barrier. They do this by binding to substrates and stabilizing the transition state, which reduces the amount of energy needed for the reaction to proceed. This allows reactions to occur more quickly and efficiently at the temperatures found in living organisms.

Q2. How does substrate concentration affect the rate of an enzyme-catalyzed reaction?

Background

Topic: Enzyme Kinetics

This question examines how changing the amount of substrate influences the speed of reactions catalyzed by enzymes.

Key Terms and Concepts:

Substrate Concentration: The amount of substrate available for the enzyme to act upon.
Reaction Rate: The speed at which the product is formed.
Saturation: The point at which all enzyme active sites are occupied by substrate.

Key Concept:

Increasing substrate concentration increases reaction rate up to a certain point, after which the rate levels off.

Step-by-Step Guidance

Recall that enzymes have a specific number of active sites where substrates can bind.
As substrate concentration increases, more active sites are occupied, and the reaction rate increases.
Consider what happens when all active sites are occupied (enzyme saturation).
Think about how the reaction rate changes before and after saturation is reached.

Try solving on your own before revealing the answer!

Final Answer:

As substrate concentration increases, the rate of an enzyme-catalyzed reaction increases until the enzyme becomes saturated. Once all active sites are occupied, adding more substrate does not increase the reaction rate further; the rate levels off at a maximum value (Vmax).

Q3. What is the difference between competitive and noncompetitive (allosteric) inhibitors of enzymes?

Background

Topic: Enzyme Regulation

This question tests your understanding of how enzyme activity can be regulated by different types of inhibitors.

Key Terms and Concepts:

Competitive Inhibitor: A molecule that binds to the active site of an enzyme, blocking the substrate.
Noncompetitive (Allosteric) Inhibitor: A molecule that binds to a site other than the active site, changing the enzyme's shape and reducing its activity.
Active Site: The region of the enzyme where the substrate binds.
Allosteric Site: A site on the enzyme other than the active site, where regulatory molecules can bind.

Step-by-Step Guidance

Recall that competitive inhibitors resemble the substrate and compete for binding at the enzyme's active site.
Understand that noncompetitive inhibitors bind to a different site (allosteric site), not the active site.
Consider how each type of inhibitor affects the enzyme's ability to catalyze reactions.
Think about whether increasing substrate concentration can overcome the effects of each inhibitor type.

Try solving on your own before revealing the answer!

Final Answer:

Competitive inhibitors block the active site, preventing substrate binding, but their effect can be overcome by increasing substrate concentration. Noncompetitive (allosteric) inhibitors bind elsewhere on the enzyme, changing its shape and reducing activity regardless of substrate concentration.

Q4. What are the three main stages of cellular respiration, and where does each occur in the cell?

Background

Topic: Cellular Respiration Pathway

This question tests your knowledge of the stages of cellular respiration and their cellular locations.

Key Terms and Concepts:

Glycolysis: The first stage, breaking down glucose in the cytoplasm.
Krebs Cycle (Citric Acid Cycle): The second stage, occurring in the mitochondrial matrix.
Oxidative Phosphorylation (Electron Transport Chain): The third stage, taking place in the inner mitochondrial membrane.

Step-by-Step Guidance

List the three main stages of cellular respiration in order.
Identify the specific location in the cell where each stage occurs.
Recall the main function of each stage (e.g., breaking down glucose, producing electron carriers, generating ATP).
Think about how the structure of the mitochondria supports these processes.

Try solving on your own before revealing the answer!

Final Answer:

The three main stages of cellular respiration are: (1) Glycolysis, which occurs in the cytoplasm; (2) Krebs Cycle (Citric Acid Cycle), which takes place in the mitochondrial matrix; and (3) Oxidative Phosphorylation (Electron Transport Chain), which happens in the inner mitochondrial membrane.

Q5. What is the role of NADH and FADH2 in cellular respiration?

Background

Topic: Electron Carriers in Cellular Respiration

This question focuses on the function of electron carriers in transferring energy during cellular respiration.

Key Terms and Concepts:

NADH and FADH2: High-energy electron carriers produced during glycolysis and the Krebs cycle.
Electron Transport Chain (ETC): A series of proteins in the inner mitochondrial membrane that use electrons to generate ATP.
NAD+ and FAD: The low-energy forms of these carriers.

Step-by-Step Guidance

Recall where NADH and FADH2 are produced during cellular respiration.
Understand that these molecules carry high-energy electrons to the electron transport chain.
Consider what happens to the electrons once they reach the ETC.
Think about what happens to NADH and FADH2 after they deliver their electrons.

Try solving on your own before revealing the answer!

Final Answer:

NADH and FADH2 carry high-energy electrons from glycolysis and the Krebs cycle to the electron transport chain, where their electrons are used to generate ATP. After delivering electrons, they return to their low-energy forms (NAD+ and FAD) to be reused in the cycle.

Q6. What are the reactants and products of photosynthesis, and where does it occur in the cell?

Background

Topic: Photosynthesis Overview

This question tests your understanding of the overall process of photosynthesis, including the inputs, outputs, and cellular location.

Key Terms and Concepts:

Photosynthesis: The process by which plants, algae, and some bacteria convert light energy into chemical energy.
Reactants: Carbon dioxide (CO2), water (H2O), and light energy.
Products: Glucose (C6H12O6) and oxygen (O2).
Chloroplast: The organelle where photosynthesis takes place.

Step-by-Step Guidance

Recall the overall chemical equation for photosynthesis.
Identify the reactants (inputs) and products (outputs) in the equation.
Remember that photosynthesis occurs in the chloroplasts of plant cells.
Think about the specific structures within the chloroplast involved in the process.

Try solving on your own before revealing the answer!

Final Answer:

The reactants of photosynthesis are carbon dioxide, water, and light energy. The products are glucose and oxygen. Photosynthesis occurs in the chloroplasts of plant cells, specifically within the thylakoid membranes and stroma.