Hypothesis: If physical activity increases, then CO₂ produced also increases, and more drops of NaOH is needed to bring the solution pH to slightly basic.

Table 1 - Average number of Drops of NaOH added to restore initial pink color

Trial #	Rest	Moderate Activity	Strenuous Activity
1	15	25	35
2	20	30	40
3	25	35	45
Average	20	30	40

Graph of Average Respiration Rates at Various Activity Levels:
What are the independent and dependent axes?
X (independent) axis = activity level
Y (dependent) axis = # drops NaOH
Conclusion: CO₂ production increases with activity level.

QUESTIONS (p. 80)

1. Do your experimental results agree or disagree with your hypothesis?
   Hypothesis: If physical activity increases, then CO₂ exhaled should increase.
   Hopefully your experimental results support your hypothesis.

2.  
   1. Explain why CO₂ quantities are a good measure of respiration.
      CO₂ is released as an output of cellular respiration.

   2. Explain why NaOH is used to measure the amount of CO₂.
      NaOH is a base and neutralizes the carbonic acid formed by CO₂, and brings the Phenolphthalein solution back from acidic (clear) to the starting pH (pink).

3. After exercise, do you produce less, the same, or more CO₂? Explain why.
   More, because respiration rate increases to meet the energy needs of exercise.

4. What do your results tell you about how the rate of cellular respiration changes when you increase your energy demand?
   As energy demand increases, cellular respiration increases.

5. Explain why individuals vary as to their level of respiration.
   Different individuals have different lung/heart capacities, red blood cells, body weight, etc.

6. Explain why you get hot when you exercise. (p. 81)
   Some heat is generated when potential energy is converted to kinetic energy.

7. Explain the relationships for the following terms: activity level, respiration rate, drops of NaOH, and CO₂ production.
   They are all directly related: as activity level increases, respiration rate goes up, and more NaOH is needed to neutralize the CO₂ produced.

8. What is the difference between breathing and cellular respiration?
   Breathing takes in O₂ necessary for cellular respiration and releases waste products CO₂ and H₂O via the heart, lungs, and blood vessels.
   Individual cells do not "breathe", and process the inputs and outputs by diffusion to carry on cellular respiration.

9. Explain why organisms must carry out cellular respiration to survive.
   All organisms need energy (ATP), and most obtain it from aerobic respiration. BUT:
   some organisms are capable of anaerobic fermentation.