Cellular Respiration Lab

Lab Design Tutorial

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…

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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?

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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

Correct!

• Since oxygen is consumed during cellular respiration, the amount of O2 will decrease as more cellular respiration occurs.

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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.

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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

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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

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

pressureNEXT…

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…

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Ideal Gas Law

• PV = nRT– P = pressure– V = volume– n = # of moles of gas– R = Gas constant – T = temperature

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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

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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.

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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

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

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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)

CO2 (g)KOH Soaked Cotton

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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?

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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?

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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)

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Animation

• Click below for an animation of a respirometer• http://www.phschool.com/science/

biology_place/labbench/lab5/respwork.html

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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)?

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THE END! Please follow the instructions

on the orange paper and review with your group until you are ready to be tested