Energy Bar Lab
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Your body needs certain building materials that it cannot make itself since you are a
heterotroph, which means you have to rely on eating plants and animals to get your nutrients.
The main nutrients any living thing needs are:
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Carbohydrates – which are sugars and starches and can be used for energy or for
storing or for building structural units, such as the cell wall in plants which is mostly
made from cellulose. Some of the “carbs” you ingest are actually not even
digestible in your system, but are still important to provide fiber to your colon’s
bacteria. They are the bristle brushes of life. 
Lipids – fats and waxes, which can be used for energy, maintaining body temperature
(blubber), protecting structures such as leaves and even as steroid hormones.
Proteins – amino acid polymers that are the most important part of your diet, because
they act as immune system components, structural building materials, enzymes,
energy storage and hemoglobin in your blood.
On top of these main macromolecules, your body needs water as the solvent to get the
reactions going, vitamins which act as co-enzymes in many reactions and some
minerals like Calcium, Iron, Potassium, which are used as building blocks for DNA,
ATP, bone, etc.
Nutritionists are concerned with measuring the amount and presence of nutrients in the foods
that you eat. You have undoubtedly noticed that each food sold at the grocery store has a
nutrition label:
According to this nutrition label, a potato has about 100 calories,
lots of potassium, a good amount of fiber, some protein, lots of
vitamin C and many vitamins and minerals – yeah, good to eat.
Question is, how do they actually know this? In this lab you will
meet the following objectives:
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Learn which chemical reactants are used to determine if a
food contains sugar or starch or protein or fat or vitamins
Chemical reagents that indicate what nutrient is in a food
Make a data table that shows what happens with each food sample that you tested.
Benedict's solution is used to test for simple sugars, such as glucose. It is a clear blue
solution. In the presence of simple sugars, the blue solution changes color to green, yellow, and
brick-red, depending on the amount of sugar.
To a test tube, add 40 drops of liquid to be tested. If it is a solid, you need to liquefy it in water.
1. Add 10 drops of Benedict's solution. Carefully heat the test tube by suspending in a hot water
bath at about 40-50 degrees Celsius for five minutes. (Microwave also works)
2. Note any color change. If sugar is present solution will turn green, yellow, or brick-red,
depending on sugar concentration. NO sugar present means the solution stays blue.
Lugol's iodine is used to identify the presence of starch. The solution is yellow-brown, but
when it reacts chemically with starch, a blue-black substance called ìodide starch is produced.
1. Add five (5) drops of Lugols Iodine to 5 ml of the liquefied sample. Agitate sample and mix
thoroughly.
2. Observe any color change. If starch is present, a blue-black precipitate will form. Compare
color of each sample. Darker blue-black represents more starch present.
Biuret solution is used to identify the presence of protein. Biuret reagent is a blue solution that,
when it reacts with protein, will change color to pink-purple.
1. To a test tube, add 40 drops of liquid to be tested.
2. Add 10 drops of Biuret reagent solution to the test tube. Shake gently to mix.
3. Note any color change. Proteins will turn solution pink or purple.
Vitamin C Reagent (indolphenol) indicator solution is blue. The solution turns colorless when
it contains vitamin C.
1. To a test tube, add 20 drops of indolphenol.
2. Add the liquefied sample to the test tube by the drop. Shake gently to mix.
3. Note any color change. Continue until the color changes to clear, the more drops it
takes, the less Vitamin C in the juice.
Lipids – the most generic of all tests, uses Ranum paper towel. You have experineced this in a
non scientific setting. When brown bags get fat on them they stain, if it’s just water, the stain
dries clear. If it is really fat, the stain stays after drying.
1. Rub the food on the bag and dry it. Notice stain or no stain?