Experiment with Enzymes

1
Experiment with Enzymes

• Teacher Workshop Notes
• VAST October 19, 2001
• Get graph paper here http//www.mathematicshelpcen
  tral.com

2
Q and Q Qualitative

• What did you observe?
• 1. Disks floated to the top
• 2. Floated faster w/ more peroxide
• 3. If H202 was high, never sank
• 4. Smaller volume of liquid made it hard to time
  very well
• 5. Disk never left the bottom in pure H2O
• 6. Bubbles in the liquid
• 7. Sometimes the disk goes up and down

3
Quantitative Observations (should have
associated numbers or values)

• More peroxide (qualitative phrase, not
  quantitative). There were more bubbles when we
  used 5 drops or peroxide per 3 drops water than
  less peroxide, or, the disk rose to the top
  faster.
• W/ 40 drops total and peroxide from 2-32 drops,
  all popped up at the same time (2,4,8,16,32).
  Facilitator Did you mix/stir the water and
  peroxide in the well before you added the disc???
  Was the water or peroxide added first? 9Could the
  concentrated peroxide be on top of the water in
  the well?)
• It took 12 seconds for the disc to rise in 1/1
  peroxide (50/50)

4
questions

• Did you mix?
• When did you add the disk?
• Did you time using a clock/timer or by just
  counting??
• Did you soak or did you dip?

5
Class ExperimentTeacher guides after students
discuss

• What things had we better keep constant?
• What variables does this introduce?
• How do you know everybody got the same amount of
  yeast? (Keep yeast stirring? Suspend at table?)
  Kids just stir it themselves or swirl, or stir
  or suck in and out w/ dropper.

6
Constants and Decisions

• Yeast prepare enough for the entire class.
• H202 have enough for entire class.
• Students need to agree on a method for how get
  yeast onto disk
• What about putting the disk in the wells?
  Before/after adding water and peroxide?
• When should we start counting?
• Make sure the kids discuss stirring (density and
  great variation depending on order of addition of
  peroxide and water) Some teachers color the water
  with a bit of food dye.
• How to make the different concentrations--specify
  total volume decide on. Suggest 2 ml since the
  well holds 3 ml to the very top and we already
  know that it is hard to see the discs rise when
  there is only 1 ml.

7
What cant we control? Possible sources of error

• Time, cost
• Limitations to the methods
• A limitation is NOT---if I follow the directions
  properly then I will get a result!

8
Timing for using Experiment with Enzymes

• Day 1 preliminary exploration
• Day 2 discuss in class
• Day 3 discuss class expt
• Homework come up w/ procedure
• Only tricky part is coming up w/ dilution series.
  For intro students can set units in terms of
  drops. For a challenge or for advanced students
  have them calculate in terms of peroxide (the
  bottle is 3 peroxide)

9
What would be the Independent variable? Conc of
peroxideDependent variable rising time

• Values
• Same volume
• 2 ml, 40 drops
• How do we set up reasonable range
• Water only---control
• Peroxide only
• Leave the yeast out

10
What would be the independent variable? Conc of
peroxidedependent variable rising time

• Values
• Same volume
• 2 ml, 40 drops
• How do we set up reasonable range
• Water only---control
• Peroxide only
• Leave the yeast off

11
Looking at the data

• Write down what the data looks like to you
• Eg, all eyes look _at_ dadleys data---why is his
  data so much higher all the way across???
• Data analysis terms these ARE 9th graders
• Terms (w/ IB can discusss mode and median)
• What does an average tell you?how can we find
  words or equations or expressions that will
  describe those differences (Variance and SD---do
  one column by hand)new column-difference betw
  average and individual value--steps square in 3rd
  column--mean of this IS the variance

12
Interpreting statistical data

• Why is there so much variation?
• Variance is much smaller when using all
  peroxide--because how well the solutions are
  mixed is no longer a factor
• Volume measurement
• Evenness, homogeneity, uniformity of the
  dilutions---evident even w/ just counting off,
  not timing by clock

13
Interpreting stat data

• Why is there so much variation?
• Variance is much smaller when using all
  peroxide--
• Volume measurement
• Evenness, homogeneity, uniformity of the
  dilutions---evident even w/ just counting/not
  timing by clock

14
Describe Variance

• eg 15 /- 5 or 6
• When the kids graph the means only-graph always
  looks good
• If plot error bars see another amazing
  feature---would you believe it???!!!!
• Can do other parts of data analysis later on
• Even 9th graders may ask to later use graphing
  calculator
• Is a good model for returning for data analysis

15
URL for graph paper

• http//www.mathematicshelpcentral.com
• Web site to download free graph paper
• New edition of biology with computers
  (http//www.vernier.com)
• oxygen gas probe detailed instructions

16
Have IB students explore using the probes

• 5 concs for peroxide
• And conc of yeast
• Students develop expt and using the probe (have
  to adapt method/volumes to use the probe)
• Can max out the probe (all methods work in a
  range (not at EVERY possible whatever)

17
Conclusions and follow-on questions-plan for
future expts

• W/ some students, use the pathway all year long
• W/ other can go other places---like
  potqato,liver,fruit,cafeteria food
• Aging and catalase--antioxidants
• Send kids to web, research and applications

18
Pedagogy

• Explore first w/ little instruction
• Ask --- and remind--- students to take careful
  notes
• Are yeast different at the beginning vs the end?
  Teacher WILL fix enough yeast for entire class
  (physiology lag, growing, etc)
• Why is peroxide in brown bottle---breaks down in
  light spontaneously. Buy double-size