Biology lab

1. Biochemical
Tests
describe how to carry out chemical
tests to identify the presence of the
following molecules: protein (biuret
test), reducing and non-reducing
sugars (Benedict’s test), starch (iodine
solution) and lipids (emulsion test);

2. Protein (biuret test)
1. Add sample to a test tube.
2. Add sodium hydroxide and shake to mix.
3. Add a small amount of copper sulphate
drop by drop, shaking between each
addition.
4. Positive result shown by
mauve

3. Reducing sugars (Benedict’s test)
1. Add sample to a test tube
2. Add Benedict’s solution and put in a
water bath.
3. Positive test will show a brick red and a
range of colours between depending on
amount.

4. Non - reducing sugars (Benedict’s
test),
1. Add sample to a test tube
2. Add HCl to hydrolyse any non-reducing
sugars and put in a water bath.
3. Add sodium hydrogencarbonate to the
tube and wait for the fizzing to stop.
4. Add Benedicts Solution

5. Starch (iodine solution)
1. Add sample to a
well in a spotting
tile
2. Add iodine
solution to the
well
3. Positive result will
show a colour
change from
orange to black

6. Lipids (emulsion test)
1. Add sample to a test tube
2. Add ethanol and shake well to mix.
3. Fill a second test tube about two-thirds
full of water.
4. Pour the ethanol mixture onto the water
5. A positive result will
be shown by a cloudy
white precipitate