November Activities

It's been awhile since I last posted about what we are up to in biology class.  It has been a busy November- a lot has been going on, including my formal observation- but things haven't slowed down in class, so I want to give some updates about our activities this month.

We have been talking about chemistry and biochemistry lately.  Our study of chemistry began with matter, atoms, covalent and ionic bonding, and the Periodic Table.  We don't go into a lot of detail with these topics, but students do need a bit of background here before we move into biochemistry and discuss the macromolecules that organisms are made of.

We then spent some time talking about water.  While water is not an organism, it is a vital molecule to organisms.  We talked about how water's polar nature allows it to form hydrogen bonds, and this gives water several unique properties, including cohesion, adhesion, capillarity, high specific heat, and its ability to serve as a solvent for many other substances.  Students spent several days exploring the properties of water in a rotating lab station activity.  The first station showed students that a polar molecule like water will be attracted to static charges, while a nonpolar substance like oil will not be.  The second station had students comparing the dissolving ability of water and isopropyl alcohol for four different solutes.  In the third station, students used litmus and pH paper to discover the pH of several common solutions.  The fourth station had students explore the density of water in its solid form compared to its liquid form- the fact that liquid water is more dense than solid water is quite unique!  The fifth station had students playing with surface tension, the sixth station demonstrated capillarity, and the final station had students explore water's high specific heat.  Whew!!! It was a lot to get through, but I believe it was worth the time to give students a first-hand experience with the properties of water- rather than being abstract, they can see the properties at work and hopefully understand them better as a result.

Students measure room temperature for alcohol and water and then determine how long it takes each substance to change temperature when heated.

Students determine the pH of several common solutions.

Surface tension allows students to float a paper clip on top of the water- but you have to have a good technique to get it there!

Students attempted to dissolve four different solutes in water and alcohol- overall, water was a better solvent, although it could not dissolve sulfur!

After water, we moved on to the four major organic macromolecules in organisms- carbohydrates, lipids, proteins, and nucleic acids.  We discussed how each of these molecules is a large polymer made up of monomers joined together by covalent bonds.  We discussed how prefixes like mono (one), poly (many), and macro (large) can help us to more easily learn and use these words.  To introduce the macromolecules, students completed a group activity in which they worked together to try to identify elements, monomers, functions, examples, and pictures of each of the four different molecules.  After successfully making these identifications, students were given various short scenarios and had to relate each scenario to one of the macromolecules along with an explanation of why they chose that particular molecule.  Students then worked individually or in small groups to complete three different "Patient Case Studies," in which they assumed the role of a physician and were encountered with a patient with symptoms related to either carbohydrates, lipids, or proteins in their diets.  Students had to diagnose the patient, explain which type of molecule was involved and why, and develop a treatment plan- a revised diet- for the patient.  We followed up the case studies with a lab that allowed students to test for the various macromolecules found in foods.  More about that in the next post!

Student groups work to determine which type of macromolecule most closely relates to various scenarios.

Enzymes!!

Recently we have been talking about those wonderful biological catalysts that are vital for our metabolisms- you guessed it, enzymes!!  We discussed the roles enzymes play in speeding up our chemical reactions and ensuring that important chemical reactions occur in our bodies.  We learned that enzymes: lower the activation energy needed to start chemical reactions, are reusable and specific to the molecules they act upon, are usually proteins, and that enzymes can be deactivated (denatured) by environmental factors such as temperature and pH.  In order to drive these points home, we set up and performed several lab activities to view the action of enzymes.

Our first lab was a popular chemical reaction sometimes called "Elephant's Toothpaste."  This is a fairly simple reaction that even young children can do, but we did it in class to emphasize the role of enzymes in the chemical reaction.  Students set up flasks containing hydrogen peroxide, dish soap, and food coloring.  They then added a mixture of yeast and warm water to the flasks and quickly saw a reaction as hydrogen peroxide broke down into water and oxygen.  The oxygen gas was trapped by the dish soap, creating a cool foam!  I love hearing the students react when they observe this reaction!  Students also were able to observe that the foam was warm, because the reaction is exothermic and releases energy.  We discussed how the reaction happened instantaneously when the yeast was added because the yeast have the enzyme that catalyzes the break down of hydrogen peroxide into water and oxygen.  The breakdown would happen without the enzyme, but would take years!  We discussed how, like yeast, many living things contain an enzyme that catalyzes this breakdown- including humans!

Students prepare flasks for the reaction with hydrogen peroxide, dish soap, and food coloring to make it pretty!

The chemical reaction causes hydrogen peroxide to break down into water and oxygen gas.  The oxygen gas is trapped by the dish soap, creating the foam!

Our second lab of the week demonstrated how various factors can affect the action of enzymes in chemical reactions.  Students role-played as the enzyme "toothpickase," which catalyzed the breakdown of toothpicks.  Students acting as the enzyme were blindfolded and were given a sample of 30 toothpicks, which represented the substrate for the reaction.  They then had to break as many toothpicks as possible in 30 seconds to simulate the action of the enzyme.  We then added various factors to compare with the original reaction.  To simulate a temperature or pH imbalance, students had to break the toothpicks with their fingers taped together.  To simulate enzyme inhibitors, students were given 15 regular toothpicks and 15 colored toothpicks to break (blindfolded), but only the regular toothpicks were counted as  "metabolized."  To simulate enzyme cofactors, two students acted as enzymes, breaking toothpicks together for 30 seconds.

Students set up toothpicks in preparation to run the toothpickase simulation!

A student acts as the "toothpickase" enzyme, metabolizing toothpicks by breaking them in half!

We found that the pH/temperature imbalance had a negative effect on the number of toothpicks that were metabolized by the chemical reaction, and we talked about how that made sense because these factors can deform or "denature" enzymes, which prevents them from working.  We also found that in the inhibitor simulation, fewer toothpicks were metabolized.  We discussed how enzyme inhibitors typically bind to enzymes, preventing them from being able to catalyze reactions.  As expected, enzyme cofactors greatly increased the number of toothpicks that were metabolized, as these molecules assist enzymes during chemical reactions.  Students made bar graphs of their data to visualize how the different factors affected the ability of the enzymes to catalyze the toothpicks.

A student graph of toothpick metabolism data.

Our final lab of the week demonstrated how temperature specifically can affect the action of enzymes.  Similar to the Elephant's Toothpaste lab, students were exploring the breakdown of hydrogen peroxide into water and oxygen.  We didn't use soap this time, so no foam, but the breakdown of hydrogen peroxide can be noted by the bubbles formed as the oxygen gas is produced.  For this lab, students were given three small pieces of beef liver.  Liver was used because it contains lots and lots of enzymes!  One piece served as the control and was kept at room temperature.  Another piece was chilled on ice and the third piece was heated in a boiling water bath.  Students measured temperature of all three pieces using a thermometer and then placed a few drops of hydrogen peroxide on the liver to note how easily it was broken down by looking for the bubbles.  Typical results had an instantaneous reaction in the piece of liver that was kept at room temperature, and pretty much instantaneous for the iced liver as well.  When the hydrogen peroxide was placed on the heated liver, there was almost no reaction at all.  Students connected this observation to the idea that hot temperatures can cause enzymes to denature, which negatively affects their ability to catalyze reactions.

A student measures temperature in liver pieces.

Students add hydrogen peroxide to liver pieces.  Enzymes in the liver catalyze the breakdown of hydrogen peroxide into water and oxygen gas, causing the bubbles.