The document discusses different nutrients including carbohydrates, proteins, and fats. It describes the chemical composition and tests used to identify these nutrients. Carbohydrates include monosaccharides like glucose, disaccharides like sucrose, and polysaccharides like starch. Proteins are made of amino acids linked together, while fats contain fatty acids and glycerol. Tests described include Benedict's test for reducing sugars, iodine test for starch, and Biuret test for proteins. The document provides information on the nutrients present in different foods.
2. • List the chemical elements which make up
carbohydrates, fats and proteins (Pure)
• Describe and carry out tests for starch,
reducing sugars, proteins and fats
• State that large molecules are synthesised
from smaller basic units
• State the roles of water in living organisms
Learning Outcome
7. Monosaccharides (Single sugar)
Single sugar Occurrence
Glucose
Fructose
Galactose
Found in all animals
Common in plants, but
rare in animals
Present in milk sugar
from mammals
8. Disaccharides (Double Sugars)
Double sugars Occurrence
Maltose
Sucrose
Lactose
Found in cereal
Found in cane sugar
(common table sugar)
Present in milk sugar
from mammals
10. Polysaccharides (Complex Sugars)
Complex sugars Occurrence
Starch
Storage form of
carbohydrate in plants
Glycogen •Storage form of
carbohydrate in animals
•Stored mainly in liver and
muscles
Cellulose
Structural form of
carbohydrate in plants
12. • Can starch diffuse
through the partially
permeable membrane?
• Can glucose diffuse
through the partially
permeable membrane?
13. Permeability
• Monosaccharides are small sugar molecules that
can pass through the visking tubing.
• Disaccharides and polysaccharides are large,
complex molecules that CANNOT pass through
the visking tubing.
14. Testing for Reducing Sugars
(Benedict’s Test)
About 2cm3 of
test solution
(In this case:
reducing
sugars e.g.
glucose)
Heat in water bath
Brick- Red
precipitate
Add an equal
amount of
Benedict’s
solution
15. Benedict’s Test for
Reducing Sugar
Step 1: Add 2cm³ of Benedict’s solution to
2cm³ of sample. Shake well to mix.
Step 2: Place test tube in a water bath
containing boiling water for 5 mins.
Step 3: Observe the change in colour and
record your observations.
16. Benedict’s Test for
Reducing Sugar
Colour Change Conclusion
Remains blue Reducing sugar absent
Blue to brick-red precipitate Reducing sugar
PRESENT
17. Benedict’s Test :
can be used to find out the amount of reducing sugar
Brick-
red ppt
Orange
red ppt
Green / yellow
ppt
Blue
solution
None Traces of
reducing sugar
Moderate Large
amount of
reducing
sugar
19. Iodine test for Starch
Step 1: Add a few drops of iodine solution to
sample on a white tile
(note: iodine solution = iodine + potassium iodide
solution)
Step 2: Observe and record your observations.
Colour Change Conclusion
Remains brown Starch absent
Brown to blue-black colour Starch
PRESENT
21. Fats / Lipids (Pure)
• Organic compounds made up of carbon,
hydrogen and oxygen.
• No general formula for fats.
• Found in butter, cheese,
fatty meat, nuts, oil etc.
23. Oil droplet
Add 2cm3 of
ethanol
Add 2cm3 of
water
Shake mixture
thoroughly
White
emulsion
2 layers of
immiscible
liquid
Test for oil/ fats
Ethanol/ Alcohol Emulsion test
24. Ethanol Emulsion Test
For liquid food:
Step 1: Add 2cm3 of ethanol to a few drops of the
sample. Shake the mixture well for about 5 mins.
Step 2: Add 2cm3 of water to the mixture and shake
it.
Step 3: Observe and record observations.
Observation Conclusion
Solution remains clear Fats absent
Cloudy white emulsion Fats PRESENT
25. For solid food:
Step 1: Cut the sample into small pieces and place the
pieces in a test tube.
Step 2: 2cm3 of ethanol is added. Shake
well for 5 mins.
Step 3: Allow the solid particles to settle.
Step 4: Decant ethanol portion to another test
tube containing 2cm3 of water.
Solid particles
Ethanol
Only pour off
the top layer
of ethanol
28. Proteins are built from….
Proteins are built up from smaller basic units
of amino acids
Many amino acids
linked together to form
Polypeptide / peptone.
29. Polypeptide
Folding of this long chain of amino acids to
give a unique three-dimensional shape
Protein is formed
From Polypeptides Proteins
30. Sample to
be tested:
in this case,
Egg white
(2cm3)
Add 1cm3 of
NaOH
Add 1%
CuSO4 drop
by drop
Shake mixture
thoroughly
Shake after
each drop
Allow
mixture to
stand for
5min
Violet colour
click
Testing for Proteins
(Biuret test) – 1st method
31. Step 1: Add 1 cm3 of sodium hydroxide solution to 2 cm3
of sample. Shake well.
Step 2: Add 1% copper(II) sulfate solution, drop
by drop, gently shaking after each drop
Step 3: Observe and record observations
Colour Change Conclusion
Remains blue Proteins absent
blue to violet Proteins PRESENT
Testing for Proteins
(Biuret test) – 1st method
32. Test for Proteins
(Biuret test) – 2nd method
Sample to
be tested:
in this case,
Egg white
(2cm3)
Add 2cm3 of
Biuret solution
Shake mixture well
Allow
mixture to
stand for
5min
Violet colour
33. Biuret Test for Proteins
(2nd Method)
Biuret solution = sodium hydroxide + copper(II)
sulphate solution
Step 1: Add 2 cm3 of Biuret solution to 2 cm3 of
the sample. Shake well.
Step 2:Observe and record observations after 5
minutes.
Colour Change Conclusion
Remains blue Proteins absent
blue to violet Proteins PRESENT
35. Based on these results, which one of the following
conclusions about the food is correct?
Micro Ques 1
( D )
Proteins
Reducing
Sugars
Starch
A
Absent Absent Absent
B
Absent Absent Present
C
Absent Present Absent
D
Present Absent Present
36. The table below shows the chemical elements present in
each of the four substances. Which substance, A, B, C or D
could be a protein?
Micro Ques 2
( C )
Substance Carbon Hydrogen Nitrogen Oxygen
A
B
C
D
37. Milk produces a red precipitate when heated with Benedict's
solution.
A purple colour develops when the biuret test is used on milk.
Using these results only, which nutrients does milk contain?
Micro Ques 3
( C )
A Fat and protein
B Fat and starch
C Reducing sugar and protein
D Reducing sugar and starch
Editor's Notes
Benedict's reagent and Fehling's solution are used to test for the presence of a reducing sugar. The reducing sugar reduces copper(II) ions in these test solutions to copper(I), which then forms a brick red copper(I) oxide precipitate. 3,5-Dinitrosalicylic acid is another test reagent that allows quantitative spectrophotometric measurement of the amount of reducing sugar present.
https://www.youtube.com/watch?v=TDFbtEwbmz0
The chemical reaction that makes Benedict’s solution turn from blue to red is a reduction of the Cu2+ ion by the various sugars to Cu2O which then precipitates. Cuprous Oxide is a reddish brown powder which is mostly insoluble in water. As larger amounts of the oxide are formed, the blue of the aqueous ion Cu2+(H2O)4 is decreased forming nice color sequence. When you have finally used up all of the Cu2+ ions, the solution will look a dirty red brown from the copper oxide suspended in the sugar, base, and leftover reagents.
emulsion test is a method to determine the presence of lipids using wet chemistry.
The procedure is for the sample to be suspended in ethanol, allowing lipids present to dissolve (lipids are soluble in alcohols). The liquid (alcohol with dissolved fat) is then decanted into water. Since lipids do not dissolve in water, when the ethanol is diluted, it falls out of solution to give a cloudy white emulsion
characterized by edema, irritability, anorexia, ulcerating dermatoses, and an enlarged liver with fatty infiltrates
oteins, mainly albumin, are responsible for creating the colloid osmotic pressure (COP) observed in the blood and tissue fluids. The difference in the COP of the blood and tissue is called the oncotic pressure.
draw water back into the capillary by osmosis
. This results in the pooling of fluids, causing the swelling and distention of the abdomen.[
Qn: what is the difference between polypeptide and protein?