Life’s Molecules Lab
Purpose: Today we will be conducting tests to determine if certain substances contain
the molecules that are essential for life: proteins, carbohydrates and lipids (fats). We
will be using a variety of indicators to help in our determination. An indicator is a
substance that changes color in reaction to the presence of a specific chemical or
condition (e.g. acid or base).
WEAR GOGGLES (you’ll look cool)
Materials:
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test tubes
stoppers
goggles
droppers
test solutions
• Benedict’s solution
• Biuret’s solution
• Iodine
• paper bag squares
• glucose test strips
Methods:
Starch test:
• iodine
• yellow/brown liquid - reacts with starch to make blue/black color
• starches will not test positive for a glucose test
• the glucose molecules are all bound together - not individual
• 20 drops test solution
• 2 drops iodine
• cover
• shake
• observe results
• dump all liquids in large container labelled WASTE
+ for starch = black/blue color
- for starch = yellow/brown color
Glucose tests:
• Benedict’s solution
• clear blue solutions - reacts with glucose to make green, yellow or red
color depending on how much glucose is present
• 20 drops test solution
• 5 drops Benedict’s solution
• cover
• shake
• place test tube in rack in water bath (40-50 degrees celsius)
• the chemical reaction is helped along with heat
let
stand in water bath for 3 minutes
•
• observe results
• dump all liquids in large container labelled WASTE
+ for glucose = green, yellow or red
- for glucose = blue
• Glucose test strips
• carefully dip one test strip into your test solution
• compare the color on the dipped test strip to the color chart on the
container
• throw test strip into the garbage
check chart for color comparison results
Protein test:
• Biurets solution
• blue solutions - reacts with protein to make pink/purple color
• add 20 drops test solution
• add 15 drops Biurets solution - let the drops slide down the side of the
test tube
• cover
• shake
• observe results
• dump all liquids in large container labelled WASTE
• BE CAREFUL - Biurets solution is made of lye (a strong base) - it can burn
your skin - wash carefully and quickly under running water
+ for protein = pink/purple
- for protein = blue
Lipid Test:
• The simplest lipid test involves placing a drop of the test substance on a
piece of brown paper bag from a grocery store. If the test substance
contains lipids, the paper bag near the spot will become translucent and
allow light to shine through. The greater the lipid content, the larger the
translucent spot will be. If there are no lipids, the substance will evaporate
and the paper bag will remain opaque.
• put your names on paper bag square
• place 10 drops of solution onto paper bag square
• dry the paper square under the heat lamp
• hold up paper bag square to the light
• positive for lipids = translucent spot, spot will not dry
• negative for lipids = spot dries and is not translucent
• dump all liquids in large container labelled WASTE
+ for lipids = wet, translucent spot on paper
- for lipids - dry, not translucent
Solution List:
GLUCOSE TESTS
Starch
Test
milk
honey
egg white
chicken
broth
potatoes
hair
conditioner
Glucose
Test
Glucose
Strip
Protein
Test
Lipid
Test
Alive?
GLUCOSE TESTS
Starch
Test
Glucose
Test
Glucose
Strip
Protein
Test
Lipid
Test
Alive?
cool whip
Presence of all three molecules means that substance is or was alive
Notes for me:
Starch is a long chain of glucose molecules
honey needs to be diluted in water