Using Models to Understand Cellular Respiration1

1. Why do cells need to carry out cellular respiration?

A scientific model is a simplified representation of reality that highlights certain key features of a process like cellular respiration.

These chemical equations are one model of cellular respiration. The curved arrows represent coupled chemical reactions; the top reaction provides the energy needed for the bottom reaction.

2a. Describe in words what these chemical equations tell us about cellular respiration.

2b. Add a reverse arrow to show the hydrolysis of ATP. Why do cells carry out the hydrolysis of ATP?

This figure presents another model of cellular respiration. It shows the three main stages of cellular respiration.

3. To describe each stage of cellular respiration, choose the best matches (one per blank). (Use one of the matches twice.)

Glycolysis ___Krebs cycle ___Electron transport chain + ATP synthase ___ ___

a. Makes most of the ATP produced by cellular respirationb. Occurs in mitochondria (plural of mitochondrion)c. Uses glucose as an input

4. The figure does not show most of the inputs and outputs of cellular respiration. Add the missing inputs and outputs to the figure. (The electron transport chain needs O2 as an input and produces H2O. The Krebs cycle produces CO2.)

5. Explain why mitochondria are often called the powerhouse of the cell.

1 By Dr. Ingrid Waldron, Dept Biology, Univ Pennsylvania, © 2020. This Student Handout (including a Google Docs version) and Teacher Notes (with background information and instructional suggestions) are available at https://serendipstudio.org/exchange/bioactivities/modelCR. This activity is intended to follow "How do organisms use energy?" (https://serendipstudio.org/exchange/bioactivities/energy).

6. List each type of input molecule that is required for cellular respiration. For each type of input molecule, explain how the body gets this molecule or how this molecule is made inside each cell.

Input Molecule How the Body Gets this Molecule orHow this Molecule is Made Inside Each Cell

7. Use what you have learned to construct a model of cellular respiration in this drawing of a cell with a mitochondrion. (In an actual cell there are many mitochondria.)

Write the three stages of cellular respiration in the appropriate blanks. Label each arrow with an appropriate input or output. (Use the information from question 6

to identify inputs that come from outside vs. inside the cell. For simplicity, this diagram omits electron transport by NADH, which is discussed on the next page.)

8a. Different types of models have different advantages for understanding cellular respiration. Complete the table below to describe an advantage of each type of model.

What This Model Contributes to Your Understanding of Cellular Respiration

Chemical equations (on page 1)

The figures shown above and on page 1

8b. What are some features of cellular respiration that are shown in both types of models?

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Understanding the Structure and Function of Mitochondria

Since most of the ATP is produced in the mitochondria, we will analyze the structure and function of mitochondria.

Mitochondria have an outer membrane and an extensive inner membrane, with many folds. Structure is related to function, so we wonder, “How does the extensive, folded inner membrane of mitochondria contribute to the production of ATP?” To answer this question, you will analyze the figure below.

9. Both figures show the Intermembrane space. Explain why this space is called “Intermembrane”.

10. The paragraph below explains how the electron transport chain (ETC) works with ATP synthase to make ATP. Use the information in the second figure to fill in each blank with “intermembrane space” or “matrix”.

The electron transport chain pumps H+ from the matrix to the __________________________ . Therefore, the concentration of H+ is higher in the intermembrane space and lower in the matrix. Because of this concentration gradient, H+ tends to diffuse from the _______________________

to the _______________________. The only place that H+ can cross the inner membrane is through the channels in the ATP synthase molecules. The movement of H + through ATP synthase

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provides the energy to make ATP. This is similar to how the flow of water through a turbine provides the energy to generate electricity.

11. Imagine a mitochondrion that has electron transport chain proteins and ATP synthase, but no inner membrane. Explain why the ATP synthase would not be able to make ATP.

The top drawing shows a magnified cross-section through a real mitochondrion. The bottom drawing shows a magnified cross-section through a hypothetical mitochondrion with an inner membrane that does not have any folds.

12a. Which mitochondrion would be expected to produce more ATP?a. the mitochondrion with an inner

membrane that has foldsb. the mitochondrion with an inner

membrane that does not have folds

12b. Explain your reasoning.

13. Explain how the folded inner membrane of mitochondria contributes to the production of ATP. (Hint: Use your answers to questions 11 and 12 as the basis for your answer to this question.)

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