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Introduction
Living cells are made up of organic and inorganic molecules. It is possible to identify
the chemicals that occur in cells using laboratory tests. In Part A of this activity you
will carry out these tests on known samples, and in Part B, you will carry out identical
tests on unknown samples in order to identify the chemicals that occur within the
sample.
Glossary
Carbohydrates- essential structural component of biological organisms and one source
of energy for animals; includes simple sugars and macromolecules
Monosaccharide- simple carbohydrate; 1 sugar molecule like glucose or fructose
Disaccharides- sugar or carbohydrate composed of two or more monosaccharides
Proteins- large inorganic compounds of amino acids arranged in a linear chain joined
by peptide bonds
Lipids- oily organic compound that is insoluble in organic solvents; essential structure
component of living cells
Purpose
To use laboratory tests to find the chemicals in known and unknown samples of noncellular and cellular material.
Materials
Benedict’s solution (in a dropper bottle)
Iodine solution (in a dropper bottle)
20% sodium hydroxide solution (NaOH) (in a dropper bottle)
1% copper sulphate solution (CuSO4) (in a dropper bottle)
5% glucose solution (in a dropper bottle)
5% starch solution (in a dropper bottle)
Gelatin or egg albumin
24 micro test tubes
Micro test-tube stand
Micro test-tube holder
Permanent marker
Clean spatulas
100 mL beaker
Hot plate
Thermometer
Sample of unkown material such as rice, potato, milk, cheese, sweet biscuit, cereal
Procedure
Part A
Half-fill the 100 mL beaker with water and place it on the hot plate. Heat the water to
80˚ C and maintain it at this temperature.
Place 12 micro test tubes into the micro test-tube stand (in three rows of four tubes).
Label your rows A, B and C.
Label your test tubes 1, 2, 3 and 4.
Place 5 drops of glucose solution into the first test tube in each row (A1, B1 and C1).
Place 5 drops of starch solution into the second test tube in each row (A2, B2 and C2).
Place 5 drops of gelatine or egg albumin into the third test tube in each row (A3, B3
and C3).
Place 5 drops of water into the fourth test tube in each row (A4, B4 and C4).
Monosaccharide test
Add one drop of Benedict’s solution to all of the test tubes in row A.
Use the test-tube holder to place all three of row A test tubes into the beaker of warm
water. Be careful not to get water inside the test tubes. Leave them there for 5 minuets
and record any colour change in Table 2.2 under “Observations” below.
Starch test
Add 1 drop of iodine solution to all of the test tubes in row B.
Do not heat these tubes. Simply record any colour changes to the test material in
Table 2.2 under “Observations” below.
Protein test
Add 10 drops of sodium hydroxide solution and 15 drops of copper sulphate solution
to the row C test tubes.
Record any colour changes to the test material in Table 2.2 under “Observations”
below.
Part B
Place the remaining test tubes in rows of three into the micro test-tube holder.
Place a small sample of one of the unknown materials into three of the test tubes.
Perform the three tests from Part A on each of the test tubes.
Record any colour changes in the unknown material in Table 2.3 in “Observations”
below. Make sure you indicate whether it was a strong (+++) or weak (+) colour
change.
Repeat the above steps using a different unknown material.
Discussion Questions
We did three tests during this prac. The first test used Benedict’s solution and tested
for glucose. The expected colour change for a positive reaction to this test was orange.
The second test used iodine solution and tested for starch. The expected colour change
for a positive reaction was dark blue or black. The third and final test used s mixture
of the sodium hydroxide and copper sulphate solutions and tested for protein. The
expected colour change for a positive reaction to this test was a cloudy blue colour
over a cloudy clear liquid. When we did these tests with known substances we used
water as our control substance. We needed a control substance to know what colour
would be expected for a negative reaction to one of the tests. For Part B of this prac
we chose three different substances. We chose to test milk, potato and a sugar biscuit.
From our tests we were able to conclude that potatoes contain mostly starch and a
little bit of protein. For milk we were able to conclude that it contained protein and a
trace amount of glucose. We were also able to conclude that the sugar biscuit
contained glucose and starch.
Conclusion
The purpose of the prac “To use laboratory tests to identify the chemicals in known
and unknown samples of non-cellular and cellular material” was met. In doing this
activity we learned that certain cellular and non-cellular substances react with certain
chemicals to show a positive presence. Those substances that do not react with a
certain chemical must be tested using a different chemical.
Alexis Dosh