1. Cellular Respiration: An Overview
Read the lesson title aloud to students.

2. Learning Objectives
Explain where organisms get the energy they need for life processes.
Define cellular respiration.
Compare photosynthesis and cellular respiration.
Click to reveal each of the learning objectives.
Write the term “cellular respiration” on the board. Then make a T-chart below it. Label one column “Facts” and the other “Questions.” Have each student come up to the board and write either a fact he or she knows or a question he or she has about cellular respiration. Discuss the T-chart as a class.
Answer any questions that students will need to know before reading the lesson.
Make sure students understand that at the end of the presentation they should be able to describe cellular respiration.

3. Cellular Respiration
Cellular respiration is a process of energy conversion that releases energy from food in the presence of oxygen.
Explain to students that cellular respiration involves a series of controlled reactions that slowly release energy.
Ask students: In this image, what form is the energy being released from the marshmallow?
Answer: Energy is being released in the form of light and heat.

4. Cellular Respiration The chemical summary of cellular respiration is:
What does the equation look like expressed in symbols?
Click to reveal the chemical summary of cellular respiration in words and discuss what this means.
Then click to reveal the lead-in sentence to how cellular respiration could be expressed in symbols. Ask for volunteers to write any portions of the equation they already know.
Click to reveal the complete equation.
Make sure students understand the overall chemical summary for cellular respiration. Explain that the reactions shown are simplifications, or summations, of many sub-reactions.
Have students verify that the reaction shown in symbols is balanced by counting the molecules of each element on the right and left sides of the reaction.

5. Stages of Cellular Respiration
Glycolysis
Krebs cycle
Electron transport
Click to reveal the stages of cellular respiration.
Help students make the connection between this visual and the chemical summary equations from the previous slide.
Ask: Where are glucose and oxygen used during cellular respiration?
Answer: Glucose is the molecule that undergoes glycolysis. Oxygen is involved in electron transport.
Click to highlight glucose and oxygen.
Ask: Where do you see water, carbon dioxide, and energy in this diagram?
Answer: Carbon dioxide is released during the Krebs cycle. Water is released during electron transport. Energy is released at each stage.
Click to highlight water, carbon dioxide, and energy.
Explain to students that cellular respiration can be divided into three basic stages. Tell them that they will learn more detailed information about each of these stages in later lessons.

6. Stage 1: Glycolysis
Glucose first enters a chemical pathway known as glycolysis. A small amount of energy is captured to produce ATP.
Tell students that glycolysis is the first part of cellular respiration.
Click to highlight the glycolysis portion of the diagram.
Ask: What happens to glucose during glycolysis?
Answer: It is broken into two smaller molecules.
Tell students that at the end of glycolysis, about 90 percent of the chemical energy that was available in glucose is still unused, locked in chemical bonds of a molecule called pyruvic acid.

7. Stage 2: Krebs Cycle
In the second stage of cellular respiration a little more energy is converted.
Tell students that the Krebs cycle is the second part of cellular respiration.
Click to highlight the Krebs cycle portion of the diagram.
Explain that a little more energy is converted during this stage.

8. Stage 3: Electron Transport
The final stage requires reactants from the other two stages of the process.
Tell students that electron transport is the final stage of cellular respiration.
Click to highlight the electron transport portion of the diagram.
Explain to students that the bulk of the energy comes from this stage.
Ask: What do you think the dashed arrows indicate in this diagram?
Answer: The dashed arrows indicate that reactants from both of the previous stages are required for this stage.
Misconception: Students may have difficulty distinguishing between the concepts of cellular respiration and respiration as breathing. Have students read the first paragraph of the Oxygen and Energy section and lead a discussion to highlight the connections between the processes and the differences.

9. Photosynthesis and Cellular Respiration
Photosynthesis and cellular respiration can be thought of as opposite processes.
Ask: Why doesn’t Earth run out of oxygen?
Possible answer: Cellular respiration is balanced by another process—photosynthesis.
Tell students that photosynthesis removes carbon dioxide from the atmosphere.
Click to highlight this in the image.
Tell students that photosynthesis releases oxygen into the atmosphere—which is then used in cellular respiration to release energy from food.