Biomolecules in Food

Read through the lab and fill in the following information
Purpose:
Hypothesis:
Pre-lab questions:
1. How do you know if a food contains protein?
2. How do you know if a food contains starch?
3. What is the difference between starch and sugar?
4. Why should you be careful of biuret solution? What should you do if you spill some on yourself?
Procedure:
1. Split the responsibility for testing the food products amongst your group. Write the initial of each group member by the food item
they will test on the lab sheet
Part 1 Testing for Carbohydrates (Polysaccharides- Starch)
2. Use a dropper or the tweezers to place a small amount of the food item into your test tube
3. Add 1-2 drops of Iodine to the test tube
4. Observe the test tube, if the food contains starch it will turn a blue- black color. If the color remains brown, no starch is present.
5. Empty the test tube into the waste container and rinse with water.
Part 2 Testing for Carbohydrates (monosaccarides- sugar)
6. Use a dropper or the tweezers to place a small amount of the food item into your test tube
7. Add 5 drops of benedicts solution to the test tube
8. Carefully place the test tube into the hot water bat. Heat the tube for 2-3 minutes. (use a test tube holder to remove the tube from
the hot water.)
9. Observe the test tube, look at the following table to determine the quantity of sugar in the food.
Amount of sugar in food
None        Trace amounts          Little Sugar            Some Sugar                              A lot of sugar        Blue           Blue/green              Green/Yellow            Orange                                         Red
10. Empty the test tube into the waste container and rinse with water.
Part 3 Testing for Protein
11. Use a dropper or the tweezers to place a small amount of the food item into your test tube
12. Add 5 drops of biuret reagent to your tube (Biuret can burn your skin, wash off spills with lots of water.)
13. Observe the test tube, if the food contains protein it will turn a pinkish purple.
14. Empty the test tube into the waste container and rinse with water.
Part 4 Testing for Lipids
15. Use a dropper or tweezers to place a small out of food onto the newspaper, If the food is a solid, rub onto the newspaper.
16. Wait for 2 mins, remove any large pieces of food and observe.
17. Look at the paper against a light source. There are lipids present if a lot of light can pass through the paper. If little or no light can pass through then there is little or no lipids present.
18. Throw the piece of paper away.
Data
Post lab questions
1. Which foods come from plants? What biomolecule is most common in these foods?
2. Which foods come from animals? What biomolecule is most common in these foods?
3. Does water contain any of the macromolecules that you tested for? Explain why water is used as a control.
4. Fill out the following table by listing the foods that you tested.
                                                                         High in Carbohydrates High in Protein High in Lipids
FOOD                      LIPIDS                    PROTEINS            STARCH                  SUGAR
POTATO
Initial_____
BUTTER
Initial_____
EGG WHITE
initial _____
FISH
initial _____
APPLE
initial _____
SPINACH
initial _____
OIL
initial _____
WATER
initial _____
5. What is a macromolecule? Give examples of macromolecules from this lab.
6. Most macromolecules are made from chains of much simpler molecules (subunits). Name the subunits that
link up to form the following macromolecules and draw a picture of each one
Carbohydrate
Proteins