Cellular Respiration Lab

1. Cellular Respiration Lab Lab Design Tutorial

2. Instructions • Use this tutorial along with the lab papers and sample lab materials to help your group understand the details of this lab • Follow the directions on the instruction paper • When your group feels confident that you understand all aspects of the lab, come up to the teacher for your oral quiz! • Click on the buttons (like the one below) to advance… NEXT… 

3. Review Questions • What is the equation for cellular respiration? C6H12O6 + 6 O2  6 CO2 + 6 H2O + 686 kcal/mol • Discussion Questions: • What could you measure in an experiment that tests the amount of cellular respiration? NEXT… 

4. Focusing on one variable… • You could use any of the reactants or products, but for this experiment we are going to measure change in oxygen over time. • What will you observe in this experiment as it progresses? (click on one) O2 will DECREASE O2 will INCREASE

5. Correct! • Since oxygen is consumed during cellular respiration, the amount of O2 will decrease as more cellular respiration occurs. Click HERE to continue

6. Oops!  Try Again! • Sorry, that isn’t the right answer. Click on the box below to return to the last page Click HERE to return to previous page

7. Background - Gases and Pressure • Oxygen (O2) is a gas. • You will measure the amount of gas by measuring the pressure of the gas. • Pressure = amount of force exerted on the walls of container by the molecules of gas. NEXT… 

8. Gases (continued) • Click on the link below to review the relationship between pressure and the number of gas molecules. • http://legacyweb.chemistry.ohio-state.edu/betha/nealGasLaw/fr2.2.html NEXT… 

9. Check your understanding… • Discuss the following questions with your lab group: • What happens to the pressure when the number of gas molecules increases? • What happens to the pressure when the number of gas molecules decreases? • What is the relationship between pressure and volume? Click HERE for answers

10. Gases… Answers • The relationship between number of gas molecules and pressure is directly proportional • When # of gas molecules increases, so does pressure • When # of gas molecules decreases, so does pressure NEXT… 

11. Gases… (Answers) • The relationship between volume and pressure is inversely proportional. • When volume INCREASES, pressure DECREASES • Discuss WHY with your lab group. • The relationship between temperature and pressure is directly proportional. • When Temperature INCREASES, so does pressure • Wait… I think I remember something like this from Chemistry… NEXT… 

12. Ideal Gas Law • PV = nRT • P = pressure • V = volume • n = # of moles of gas • R = Gas constant • T = temperature NEXT… 

13. Using the Ideal Gas Law • In this experiment, we are going to be measuring pressure. So, the equation can be rewritten like this: P = nRT/V NEXT… 

14. Experimental Set-up • This lab will use the respirometer to measure the change in oxygen pressure • Any living organism that fits in the vial can be used. NEXT… 

15. Linking to the ideal Gas Law • Considering the Ideal Gas Law, how do we make sure we are only dealing with 1 variable? • Lab Design: In order to make the experiment valid, there can only be one unknown factor (dependent variable). This means all the other variables should be held constant. • Which of the variables in the Ideal Gas Law equation is the dependent variable (what is being measured)? (CLICK ON ONE) Pressure Temperature Volume

16. CORRECT! • Pressure (of oxygen) is what you will be measuring the change in, so this is your dependent variable. • The volume is held constant because the glass vial doesn’t change in volume throughout the experiment (and the volume taken up by organism is also held constant). • Temperature will be held constant with the water bath NEXT… 

17. Hold on… O2 isn’t the only gas! • CO2 is also produced during cellular respiration. • So how will we make sure the pressure measured is only O2? • Change the CO2 into a solid so it doesn’t contribute to the pressure measurement! • How? Use KOH to convert it • CO2(g) + 2 KOH(s)  K2CO3(s) + H2O O2 (g) KOH Soaked Cotton CO2 (g) NEXT… 

18. How will you SEE the change in O2 pressure? • Use the water bath • When you put the respirometer into the water bath, what happens? • Hint: Think about where the pressure is higher. Inside or outside the respirometer? • Given this consideration, where will water go? Why? NEXT… 

19. High to Low…  • Water will rush into the Pipette • Why? • Because the pressure outside (in the water) is higher than the pressure inside the vial • Discussion question: When will the water stop moving into the pipette? NEXT… 

20. How will you measure CR in this lab? • Discuss these questions with your group: • As the organism performs cellular respiration, what will happen to the pressure in the respirometer vial? • What will you see happen in the pipette? • Why? (Link this back to the Ideal Gas Law) NEXT… 

21. Animation • Click below for an animation of a respirometer • http://www.phschool.com/science/biology_place/labbench/lab5/respwork.html NEXT… 

22. Control • What is the control for this experiment? • Glass beads in the respirometer instead of live organism • Why? • Discuss: • Why this would be a control for the experiment with your lab group? • How will it be used quantitatively (how will you use it to adjust the readings you get for your live organism)? NEXT… 

23. THE END! Please follow the instructions on the orange paper and review with your group until you are ready to be tested