Testing for starch

We continue with our unit about macromolecules and turn our focus on carbohydrates. All carbohydrates are formed from simple sugar monomers also called monosaccharides, examples include glucose, fructose, and galactose. Through the process of dehydration synthesis two monosaccharides become a disaccharide like sucrose made of one glucose and one fructose molecule. Start stinging more together and you get polysaccharides such as glycogen made by animals for glucose storage, cellulose by plants as a building material for sturdy cell walls (think the crunchiness of celery), and lastly starch also produced by plants for glucose storage and eaten by animals (including us) for energy (got to love those mashed potatoes).

Starch will react with an iodine solution to turn black. The iodine will react with the coil structure of starch but not with simple sugars or even carbohydrate food sources high in fiber. In the photo below you can see a sample of carbohydrates that we tested for the presence of starch. As a control I have the students start with a known sample of corn starch. Test items included: white potato, wheat bread, saltine cracker, apple, banana, table sugar, white flour, celery, lettuce, Chinese yam, macaroni, flaxseed meal, and a piece of notebook paper. Note that we give the students a wax coated paper plate to work on. Can you guess why? That's one of the post lab questions.

Macromolecules the "Legos" of life

The most challenging of all chapters in biology I think for sophomore level high school students is the one on the biochemistry of life. I try all types of techniques to help them with this subject matter. One thing is to use the molecule building kits to make the material presented on the 2-dimensional textbook page become a 3-dimensional reality. I remind them that they are made up of millions if not billions of these molecules and they are not flat structures themselves. Yesterday we built functional groups: hydroxyl, carbonyl, carboxyl, and amine. Then I had them put some of them together to build the simplest of all amino acids - alanine as pictured below. One of the biggest challenges is to convince them it is time to stop playing and clean up. Don't leave any atoms or bonds on the floor.

Water, water everywhere

In Biology class we are currently in our unit on the chemistry of life. This week our focus was on water chemistry, its properties, solutions, and The pH scale. We explored the properties of adhesion, cohesion, density and capillary action by carrying out several demonstrations based on the Project WET curriculum. It was amazing to hear the students' responses to some of the activities. One young man who was playing with a large drop of water on wax paper exclaimed, "why have I never done this before!" Many were fascinated with what happened when I slipped a sheet of print under the wax paper and it was magnified. Amazing what the property of cohesion can do. Hopefully seeing water in action will help them to remember the key terms and relate them to the role water plays in life on our planet.

Lions, tigers, and bears oh my - food webs

Producers, consumers, and decomposers too. Today in Ecology class I gave groups of students an envelope containing the names of various organisms and their feeding patterns. Their task was to organize a food web based on these organisms. Here is an example of one of the webs that was generated. Tomorrow we will discuss keystone organisms, energy pyramids, and biological magnification.