Enzymes: Potato vs Liver with Hydrogen Peroxide (Gloria Hernandez Scipio)
Author
Gloria E. Hernandez Scipio
Principle(s) Illustrated
An enzyme speeds up a reaction
An enzyme is not part of the reaction
Chemical reactions can cause bubbling, a change in temperature, formation of a new substance
Standards
MS-PS1-2: Analyze and interpret data on the properties of substances before and after the substances interact to determine if a chemical reaction has occurred.
MS-PS1-6: Undertake a design project to construct, test, and modify a device that either releases or absorbs thermal energy by chemical processes
MS-LS3-2: Cause and effect relationships may be used to predict phenomena in natural systems
HS-LS-1-1: Construct an explanation based on evidence for how the structure of DNA determines the structure of proteins which carry out the essential functions of life through systems of specialized cells.
(Science and Engineering practices)
HS-LS1-3: Plan and conduct an investigation individually and collaboratively to produce data to serve as the basis for evidence, and in the design: decide on types, how much, and accuracy of data needed to produce reliable measurements and consider limitations on the precision of the data (e.g., number of trials, cost, risk, time), and refine the design accordingly.
HS-LS1-1: construct an explanation based on valid and reliable evidence obtained from a variety of sources (including students' own investigations, models, theories, simulations, peer review) and the assumption that theories and laws that describe the natural world operate today as they did in the past and will continue to do so in the future.
Questioning Script
Prior knowledge & experience:
Students should know that enzymes are catalyst- they can speed up chemical reactions.
Students should know that enzymes are not used up by the reaction.
Students should have a good understanding of how to tell if a chemical reaction is occurring: the change in temperature; bubbling; change from one thing to another (the hydrogen peroxide breaks down into water and oxygen).
Students should be given a brief lesson on catalase (or peroxidase)- the enzyme that naturally occurs in our bodies to break down the hydrogen peroxide (H2O2) in our bodies. Hydrogen peroxide is a naturally occurring byproduct of the chemical reactions that occur in our bodies. H2O2 is toxic to our bodies and catalase (or peroxidase) breaks down the H2O2 into H2O and O2, which our bodies are able to use.
Root question:
1.) Make a prediction: which will form a bigger reaction when mixed with H2O2, the potato or the liver?
2.) Why does the liver produce a bigger reaction?
3.) What are other variables we can test?
4.) In what ways does this show a chemical reaction is occurring?
5.) Is the liver and the potato part of the reaction? If we added enough H2O2, would the liver/potato eventually dissolve?
6.) If we added more H2O2, would the reaction continue?
7.) Which reaction takes longer to complete? (when do the bubbles stop?)
Target response:
1 and 2.) The liver will produce a bigger reaction because it has more of the enzyme peroxidase. Peroxidase is found in larger quantities in animals because of the chemical reactions that occur in our body that have a by product of H2O2. The potato does not need very much of the enzyme.
3.) The students can test if:
-Temperature affects the rate of reaction. They will see that a colder temperature and a warmer temperature slows down the reaction. This is because enzymes have an optimal temperature in which they work, hence why our body maintains a temperature of 98.6 degree fahrenheit. If the student cooks the liver or potato, the enzyme is actually denatured! and they will see no reaction.
-Surface Area: does more surface area affect the reaction rate? Students can cut the potato/liver the same size cubes. Then increase the surface area by cutting the cubes even smaller, keeping the volume the same in each but changing the surface area. See if there is a larger reaction. (youtube video of this experiment)
-If the amount of volume of H2O2 used affects how long it takes for the reaction to stop. (The more H2O2, the longer it takes for the reaction to stop because H2O2 is the limiting factor, and enzymes will continue to break down as long as there is a substance)
4.) Bubbling (these are oxygen bubbles. We know this because we know the chemical reaction and it is the break down of H2O2 into water and O2), temperature change (it is an exothermic reaction because it is releasing energy- the temperature of the liquid increases. This is because the bonds break, and it releases energy), and the formation of something new- the break down of H2O2.
5 and 6.) If students found the mass of potato before and after, they will notice that the mass stays the same. This emphasizes that the liver and potato are not part of the reaction. Enzymes are not part of the reaction, they are only the catalyst. If you add more H2O2, then the reaction will keep on going. Students can test how long it takes for the reaction to stop. Students can keep the size of the potato/liver the same and change the amount of liquid, and test to see how long it takes for the reaction to stop (when there are no more bubbles).
7.) The potato because there are few enzymes and it continues until the break down of the H2O2 is complete.
Common Misconceptions:
Students believe that the potato/liver are breaking down due to H2O2. This can be proven wrong by measuring the mass before and after the reaction.
The bubbles are CO2. This could be proven wrong by lighting a match, extinguishing it, and quickly putting the match in the graduated cylinder (not touching the liquid, and after or while the reaction is occurring). The match should be able to relight because of the oxygen it is exposed to.
We are all born with this enzyme. There is a disease called zellweger syndrome where babies are not born with peroxidase. Infants die within a few months because too many toxins build up inside their bodies.
Photographs and Movies
The reaction is as follows:
(2H2O2 à 2H2O + O2)
How enzymes work:
Potato (left) and Liver (right)