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Scholar Name:
Class: College Prep Biology
Period:
Teacher: Mr. Free
Date: 09/17/2014
W
Waarrm
mU
Upp:: ““TTeessttiinngg ffooooddss ffoorr P
Prrootteeiinn””
Lesson Objectives
Objective 1: Scholars understand that proteins are macromolecules with
amino acid monomers.
Objective 2:Scholars will then use Biuret’s reagent to test for the presence of
protein ( Biuret Test).
DIRECTIONS: Read the following information and complete the Warm
Up Task.
Background Information: Just like glucose and starch, protein is also a
chemical that our food may be made from. Protein is similar to starch in that it
is made from chains of smaller molecules. However, protein is not a
carbohydrate, so the smaller molecules are not glucose, but other chemicals
called amino acids.
Warm Up Task: Now that scholars have mastered the scientific method,
below are 4 steps in random order on how one could test for the presence of
proteins using Biuret’s test. Using your knowledge of experimental
procedures, what do you think should be correct order for this experimental
procedure?
(A) If testing more than one liquid, label each test tube with a marker.
(B) To a test tube, add up to a third of the test tube, the liquid to be tested.
(C) Note any color change. Proteins will turn solution pink or purple.
(D) Add Biuret reagent (3 drops of copper sulfate and 10 drops of sodium
hydroxide solutions) to each test tube. Shake gently to mix.
WARM UP RESPONSE: The correct order of the steps should be ___,
then,___, next___ and finally ___.
Class Notes as Mr. Free teaches the scholars:
Move the following labels to the correct test tubes in the picture
Blue
Colour
Protein
present
NO
Protein
present
Conclusion:
Biuret Reagent changes from …………. to ………………
color when protein is present.
Discussion:
Biuret reagent is a mixture of sodium …………….. and
copper ………….. . It is the copper sulfate that gives the
Biuret reagent its blue color.
Purple
Colour
Scholar Name:
Class: College Prep Biology
Period:
Teacher: Mr. Free
Date: 09/17/2014
Proteins are essential to us because we use them for gr……… of new bones
skin etc. and the re…….. of damaged tissue. Your body also uses proteins to
control the chemical reactions in our body and can also be used as an energy
source. Some common examples of protein foods include mi…, f……, m…..
eggs and seeds.
Discuss any problems or ways to improve the experiment.
Scholar Name:
Class: College Prep Biology
Period:
Teacher: Mr. Free
Date: 09/17/2014
MACROMOLECULE LAB REPORT: Testing food
samples for protein
(a) In your lab write up, record your observations in the table below and analyse your
findings using the new knowledge you learned in Mr. Free’s class today.
(b) Label six test-tubes 1-6.
(c) If the food is a solid, crush a small piece (about 5 mm cube) in a mortar with about
10 cm3 water. (If the food is a liquid, simply pour about 20 ml of it into a test-tube.)
(d) Pour about 20 ml of the crushed mixture or liquid into a test-tube.
(e) Add about 10 ml of Biuret’s reagent or indicator (Indicator contains sodium
hydroxide and copper sulphate (HANDLE WITH CARE *)
(f) Shake the tube gently sideways to mix the contents. Return the tube to the rack
and wait for a few seconds.
(g) Record the results in the table in your lab report.
Food
Result on adding sodium hydroxide and
copper sulphate
Interpretation
Milk
Egg white
Egg Yolk
Agar Gel
Water
Glucose
Solution
* CARE. Sodium hydroxide is caustic and dissolves clothing, skin and bench tops. It
is destructive, so if any is spilt on the bench, neutralize it at once with an equal
volume of dilute hydrochloric acid and wipe dry. If spilt on clothing, do the same but
follow with a wash in as much water as possible. If spilt on the skin, do not add acid
but wash under the tap until the 'soapy' feeling is removed.
Data Analysis and Discussion
1 In which of your samples do you think protein is fairly abundant?
2 In which samples do you think protein is absent or in very low concentration?
3 If one of your samples gives no purple colour with the biuret test, does this result
mean
the sample contains no protein?
Scholar Name:
Class: College Prep Biology
Period:
Teacher: Mr. Free
Date: 09/17/2014
4 If a food sample gives a purple colour with the biuret test does this mean that it
contains
only protein?