1991 Woodrow Wilson Biology Institute
These two simple experiments/demonstrations show some properties of enzymes and can be used at any level. I use them with my low-level Biology students (reading stanines 1-3) because they are very straightforward, require hypothesizing, and use fairly common materials.
These experiments can be done as a demonstration although I recommend that students set them up themselves.
- For each experiment, give the student an appropriate amount of background information and then have them hypothesize as to what they think will happen and why.
- Carry out the experiment or demonstrations.
- Go over the observations made with the students and then have them draw conclusions.
Experiment 1: Apple Juice from Apple Sauce
(adapted from Kemtec kit)
(per group or demonstration) 3 funnels, 3-50mL graduated cylinders, 3-100mL beakers, 3 pieces of cheesecloth, a dropper bottle of pectinase, a beaker to boil pectinase, heat source, ring stand with 3 rings, applesauce (120 mL)
- Set up a ring stand with 3 rings with a funnel and a double layer of cheesecloth in each. Put a 50mL graduated cylinder under each funnel.
- Put 40 mL of applesauce into each of 3 beakers.
- Mix one of the following into each beaker: 20 drops of pectinase, 20 drops of water (control), 20 drops of boiled pectinase
- Filter each mixture and after 3 minutes measure the volume of filtrate.
Pectinase breaks down pectin, a polymer found primarily in fruits. The result is a rapid release of liquid of the cell contents. The control will yield a small amount of juice but it is very obvious from this experiment that an enzymes speeds up a reaction. The boiled pectinase shows that heat will denature the enzyme, yielding results similar to the control. Pectinase is inexpensive and keeps in a refrigerator for at least two years.
Experiment 2: The Papaya Puzzle
(Thanks to Dr. Art Mori, Chaminade University, for introducing me to this activity.)
paper cups (2/student, one for seeds and one for rinsing their mouths), papaya, knife and spoon to get seeds out of papaya, Pyrex cooking container to boil seeds.
There is no danger in eating papaya seeds. There are commercial salad dressings made with crushed papaya seeds as a flavoring ingredient.
- Distribute a few raw seeds and a few boiled seeds (both with gelatinous coating intact) in a small paper cup to each student.
- Have students eat a raw papaya seed, making sure they crush it with their teeth.
- After rinsing, do the same with a papaya seed with its gelatinous coating removed.
- After rinsing, do the same with a papaya seed (with gelatinous coating) that has been boiled.
I'm not sure of the exact biochemistry here but students will get a very peppery taste with the whole seed. The seed with the coating removed and the one that is boiled have less of a taste indicating that an enzyme is present in the gelatinous coating that works to activate a chemical reaction that results in the peppery taste. Some people may not get any noticeable difference in taste (maybe genetic!).
Numerous open-ended student projects can be generated from these labs. Does pectinase act similarly on other fruits or fruit products? Are the enzymes in papaya seeds or in the gelatinous coating? Etc.
Goggles should be worn. In experiment 2 students will be eating seeds, therefore, all materials touching the seeds should be cleaned and not have been used for other lab work.