BIO 101 Lab 2

Identifying lipids

Cut or tear open a small paper bag so that it will lay flat. Rub a small amount of some of the following foods in a small patch and write below it the name of the food.

If the food doesn't completely rub into the paper, wipe the excess off with a paper towel. Immediately hold the paper up to the light and observe how much light is let through each spot. After about 10 minutes (or when some of the spots have dried, hold the paper up to the light again. If the food has oil in it, the spot will remain translucent (more light will come through).

Old time windows

Open up a second paper bag and cover a large part of the middle of it with oil. Wipe off the excess with a paper towel. Hold it up to the light. Years ago, pioneers used oiled paper as window material when glass was not available. It increased the amount of light that came in the house. Can you see objects through the oiled paper? Hold it close to some writing. Careful, you might get it oily. Can you read through it?

Starch and Sugar

Plants store up extra energy in the form of long chains of sugar molecules called starch. Some plants like the potato and carrot, put their starch into roots or stems in the ground so that in the spring they can use it to grow a new top. Other plants like corn, wheat, and barley will store their starch in seeds that can use it to germinate after the parent plant has died.

When seeds start to germinate, they first break down the starch into sugars. One of those sugars in maltose. From this we get the name malt. Malted barley has started to germinate, and has broken down some of its starch into sugar. Brewers use malted barley because the yeast can ferment the sugar into alcohol and carbon dioxide more quickly than it can ferment starch.

We also can use that starch as a source of energy after breaking down the starch into sugar. Then the sugar is broken down inside our cells to release the stored energy. A soda cracker is primarily made up of flour, baking soda, and water. The flour contains a lot of starch but no sugar so a plain cracker does not taste sweet.

Chew a soda cracker well and hold it in your mouth for several minutes. Does the taste change? There are enzymes in your saliva that begin the process of breaking down the starch into sugars. This process should make the cracker taste sweeter over time.

You can also try chewing wheat seeds. They turn into a gum-like material that gets sweeter the longer you chew it.

Iodine test on common foods

Take a plastic plate and place some of the following foods on it.

Caution - We use iodine on our skin to protect a cut from infection. We also need a small of iodine in our diet to avoid an enlargement of the thyroid gland (goiter). However, iodine can be a poison and will also stain clothes so use it carefully.

Remove the applicator from a bottle of iodine. Use a small dropper to put a drop of iodine on each of the foods you selected. Note that iodine by itself is a dark reddish-brown so if the iodine on the food is that same dark reddish-brown, no chemical reaction has taken place. If the color of the iodine changes to a blue-black, that indicates that starch is present.

Make a list of the foods you checked and indicate by a +, +/-, or a - whether or not a color change occurred. Were there any surprises? Baking powder and baking soda are both primarily sodium bicarbonate which causes things to rise because of the bubbles it forms. One of them gives a positive test and the other doesn't. Look at the ingredients to see why.

Breaking down cellulose

Plants also make long strings (poly) of sugar molecules (saccharides) to form another polysaccharide called cellulose. We are unable to digest cellulose because we don't have the enzyme that is able to break apart the kind of link that holds cellulose together. So, cellulose (fiber) goes right through our digestive system, undigested. (We do have an enzyme that will break the starch style links between sugars.) We often like to cook cellulose containing material to soften it so it will pass through our digestive systems more easily. Cows have bacteria in their stomachs that have the required enzyme so they can get nutrition from hay and grass that is unavailable to us.

Peel several potatoes with a vegetable parer. Cut them into cubes about an inch in each direction. Make up 30 of these cubes. Place 10 in each of 3 small saucepans and just cover them with water. Add two tablespoons of vinegar to one pan, one tablespoon of baking soda to the second and leave the third with plain water.

Bring the water to a boil in each pan. Continue boiling the water while you gather your data.

Every 2 minutes, take a piece of potato from each of the pans and try to mash it with a fork. Note how soft it is by seeing how easy it is to mash it. Continue this for at least 12 minutes.

Does the baking soda (which raises the pH of the water) speed up or slow down the softening process?

Does the vinegar (which lowers the pH of the water) speed up or slow down the softening process?

When cooking a vegetable stew, the instructions may suggest that tomatoes (which are acidic) be added after the stew is nearly finished. Why?

The cooking time for vegetables depends on the amount of cellulose in the plant. Spinach has little cellulose while artichokes have a lot. Can you guess the cellulose content of some other vegetables?

Resources used:

Monomer and Polymer Chemistry by Jerome Jensen,