Chapter 9 Study Guide – Cellular Respiration and Metabolism (Bio 101)

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Q1. What is the difference between an autotroph and a heterotroph?

Background

Topic: Nutrition and Metabolism

This question tests your understanding of how organisms obtain carbon and energy for metabolism, and the distinction between organisms that make their own food versus those that consume others.

Key Terms

Autotroph: An organism that produces its own organic molecules from inorganic sources (like CO2).
Heterotroph: An organism that obtains organic molecules by consuming other organisms.
Metabolism: All chemical reactions involved in maintaining the living state of cells and organisms.

Step-by-Step Guidance

Consider how autotrophs obtain their carbon source. Think about the process of photosynthesis and the use of CO2.
Think about how heterotrophs obtain their carbon and energy. What do they eat or absorb?
Compare and contrast the two strategies in terms of their source of organic molecules and energy.
Summarize the main difference in one or two sentences, focusing on the origin of their carbon-containing molecules.

Try solving on your own before revealing the answer!

Final Answer:

Autotrophs make their own energy-containing molecules (like glucose) using carbon from CO2 gas, typically through photosynthesis. Heterotrophs must consume organic molecules made by other living things and metabolize them for energy. The key difference is that autotrophs are self-feeders (using inorganic carbon), while heterotrophs rely on organic carbon from other organisms.

Q2. Explain how energy flows through an ecosystem, while carbon-containing molecules cycle within it. (Refer to the equations for cellular respiration and photosynthesis.)

Background

Topic: Energy Flow and Biogeochemical Cycles

This question tests your understanding of the movement of energy and matter (carbon) in ecosystems, and the relationship between photosynthesis and cellular respiration.

Key Terms and Equations

Photosynthesis:
Cellular Respiration:
Energy Flow: Energy enters as sunlight and leaves as heat.
Carbon Cycle: Carbon atoms are recycled between CO2 and organic molecules.

Step-by-Step Guidance

Identify the main processes that move energy and carbon through an ecosystem: photosynthesis and cellular respiration.
Describe how energy enters the ecosystem (sunlight) and how it is transferred and eventually lost as heat.
Explain how carbon atoms cycle between inorganic (CO2) and organic forms (glucose and other molecules).
Relate the products of one process (e.g., O2 and glucose from photosynthesis) to the reactants of the other (cellular respiration), and vice versa.
Set up a diagram or summary statement showing the cyclical nature of carbon and the one-way flow of energy.

Try solving on your own before revealing the answer!

Final Answer:

Energy flows through an ecosystem in a one-way stream: it enters as sunlight, is captured by autotrophs via photosynthesis, and is eventually lost as heat through metabolic processes like cellular respiration. Carbon-containing molecules, however, cycle within the ecosystem: CO2 is fixed into glucose by photosynthesis, and glucose is broken down back into CO2 by cellular respiration. The products of one process are the reactants of the other, creating a cycle for carbon but a flow for energy.

Q3. Is cellular respiration a catabolic or anabolic process? Explain.

Background

Topic: Metabolic Pathways

This question tests your understanding of the difference between catabolic and anabolic reactions, and how cellular respiration fits into these categories.

Key Terms

Catabolic Pathway: Breaks down molecules, releasing energy.
Anabolic Pathway: Builds complex molecules, requiring energy input.
Cellular Respiration: The process of breaking down glucose to produce ATP.
ΔG (Gibbs Free Energy): Indicates whether a reaction releases or requires energy.

Step-by-Step Guidance

Recall the definitions of catabolic and anabolic processes.
Think about what happens to glucose during cellular respiration—does it get broken down or built up?
Consider the energy changes: is energy released or required overall?
Relate the process to ΔG (is it negative or positive for cellular respiration?).

Try solving on your own before revealing the answer!

Final Answer:

Cellular respiration is a catabolic process because it breaks down glucose into smaller molecules (CO2 and H2O), releasing energy that is used to make ATP. The overall ΔG is negative, indicating energy release. Although ATP is produced, the process itself is about breaking down a larger molecule, not building one.

Q4. What does it mean to say that a molecule has been “reduced”, and what is the significance of it? Use NAD+ as an example.

Background

Topic: Redox Reactions in Metabolism

This question tests your understanding of oxidation-reduction (redox) reactions, especially as they relate to electron carriers like NAD+ and NADH.

Key Terms

Reduction: Gain of electrons (and usually hydrogen) by a molecule.
Oxidation: Loss of electrons.
NAD+ / NADH: Electron carriers involved in cellular respiration.

Step-by-Step Guidance

Recall the definitions of reduction and oxidation (OIL RIG: Oxidation Is Loss, Reduction Is Gain of electrons).
Consider what happens to NAD+ when it is reduced—what does it gain?
Think about the change in charge and energy content when NAD+ becomes NADH.
Explain why reduction is important in cellular respiration and photosynthesis.

Try solving on your own before revealing the answer!

Final Answer:

When a molecule is reduced, it gains electrons (and often hydrogen ions). For example, NAD+ is reduced to NADH by gaining two electrons and one H+. This increases its free energy, making NADH a high-energy electron carrier. Reduction reactions are crucial for transferring energy during cellular respiration and photosynthesis.

Q5. Draw and label the structures of the mitochondria, including the two membranes and the two spaces within/in-between these membranes.

Background

Topic: Cell Structure – Mitochondria

This question tests your ability to identify and label the main structural features of mitochondria, which are essential for cellular respiration.

Key Terms

Outer Membrane
Inner Membrane
Intermembrane Space
Matrix

Step-by-Step Guidance

Start by drawing an oval to represent the mitochondrion.
Draw two membranes: an outer smooth membrane and an inner folded membrane (cristae).
Label the space between the two membranes as the intermembrane space.
Label the innermost area as the matrix.
Double-check that all four structures are clearly labeled.

Try solving on your own before revealing the answer!

Final Answer:

Your drawing should include:

Outer membrane (outermost boundary)
Inner membrane (folded into cristae)
Intermembrane space (between the two membranes)
Matrix (innermost compartment)

These structures are essential for the function of mitochondria in cellular respiration.

Q6. Complete the following table to show what happens at each step of cellular respiration/fermentation.

Background

Topic: Cellular Respiration Pathways

This question tests your ability to compare the main steps of cellular respiration and fermentation, including oxygen requirements, ATP yield, and location in the cell.

Key Terms

Glycolysis
Krebs Cycle (Citric Acid Cycle)
Electron Transport Chain/Oxidative Phosphorylation
Fermentation
Aerobic vs. Anaerobic

Step-by-Step Guidance

For each process, determine if oxygen is required (aerobic), not required (anaerobic), or can occur either way.
Recall the number of ATP molecules produced at each stage.
Identify where in the cell each process occurs (cytoplasm or mitochondria).
Fill in the table with this information for glycolysis, Krebs cycle, electron transport chain, and fermentation.

Try solving on your own before revealing the answer!

Final Answer:

Process	Oxygen Needed?	# of ATP Made	Location
Glycolysis	No O2 needed (can occur with or without O2)	2	Cytoplasm
Krebs Cycle	Aerobic	2	Mitochondria
Electron Transport Chain/Oxidative Phosphorylation	Aerobic	28	Mitochondria
Fermentation	Anaerobic	4 (including 2 from glycolysis and 2 from fermentation, net)	Cytoplasm

Q7. How does the location of cellular respiration differ between prokaryotes and eukaryotes?

Background

Topic: Cell Structure and Function

This question tests your understanding of the differences between prokaryotic and eukaryotic cells, especially regarding where cellular respiration occurs.

Key Terms

Prokaryote: Cell without a nucleus or membrane-bound organelles.
Eukaryote: Cell with a nucleus and membrane-bound organelles (like mitochondria).
Cellular Respiration Location

Step-by-Step Guidance

Recall the main structural differences between prokaryotic and eukaryotic cells.
Identify where cellular respiration occurs in eukaryotes (think mitochondria).
Consider what structures prokaryotes lack, and where similar processes must occur instead.
Summarize the main difference in location for cellular respiration between these two cell types.

Try solving on your own before revealing the answer!

Final Answer:

In eukaryotes, cellular respiration takes place in the mitochondria. In prokaryotes, which lack mitochondria, cellular respiration occurs in the cytoplasm and across the cell membrane.

Q8. What is chemiosmosis, and what is the main enzyme that makes it happen?

Background

Topic: Cellular Respiration – Electron Transport Chain

This question tests your understanding of how ATP is produced during the final stage of cellular respiration, focusing on the role of proton gradients and ATP synthase.

Key Terms

Chemiosmosis: The movement of H+ ions down their electrochemical gradient to drive ATP synthesis.
ATP Synthase: The enzyme that synthesizes ATP from ADP and inorganic phosphate.
Proton Gradient: Difference in H+ concentration across the mitochondrial membrane.

Step-by-Step Guidance

Define chemiosmosis in the context of cellular respiration.
Describe where the H+ ions are moving (from intermembrane space to matrix).
Identify the enzyme that allows H+ ions to flow back into the matrix and what this enzyme does.
Explain how this process leads to the production of ATP.

Try solving on your own before revealing the answer!

Final Answer:

Chemiosmosis is the movement of H+ ions from the intermembrane space into the mitochondrial matrix through ATP synthase. This flow of protons powers ATP synthase to convert ADP and inorganic phosphate into ATP. ATP synthase is the main enzyme responsible for this process.

Q9. What is the difference between lactic fermentation and alcoholic fermentation? What organisms perform them?

Background

Topic: Fermentation Pathways

This question tests your understanding of the two main types of fermentation, their byproducts, and which organisms use each pathway.

Key Terms

Lactic Acid Fermentation: Produces lactic acid as a byproduct.
Alcoholic Fermentation: Produces ethanol and CO2 as byproducts.
Organisms: Bacteria, yeast, muscle cells, etc.

Step-by-Step Guidance

Identify the main byproduct of lactic acid fermentation and which organisms perform it.
Identify the main byproducts of alcoholic fermentation and which organisms perform it.
Compare the two processes in terms of products and typical organisms.
Summarize the key differences in one or two sentences.

Try solving on your own before revealing the answer!

Final Answer:

Lactic fermentation produces lactic acid and is performed by many animal cells (including human muscle cells) and some bacteria. Alcoholic fermentation produces ethanol and CO2 and is performed mainly by yeast and some types of bacteria. The main difference is the byproducts and the organisms that use each pathway.

Q10. What other molecules can be metabolized as an energy source, and how do they differ from the process in glucose?

Background

Topic: Alternative Energy Sources in Metabolism

This question tests your understanding of how cells can use molecules other than glucose for energy, and how these molecules enter cellular respiration.

Key Terms

Fats
Proteins
Carbohydrates (other than glucose)
Krebs Cycle

Step-by-Step Guidance

List other types of organic molecules that can be used for energy (besides glucose).
Consider how these molecules are broken down (digested) into smaller units.
Think about where these smaller units enter the cellular respiration pathway (e.g., glycolysis, Krebs cycle).
Summarize how the entry points and processing differ from glucose metabolism.

Try solving on your own before revealing the answer!

Final Answer:

Other molecules that can be metabolized for energy include fats, other carbohydrates (like starch or sucrose), and proteins. These molecules are broken down into smaller components that enter cellular respiration at different points (e.g., fatty acids enter the Krebs cycle, amino acids can enter at various steps). The main difference is the entry point and the specific enzymes required, but ultimately, all are used to produce ATP.