There are three types of substances that life is dependent on. These are carbohydrates, proteins, and lipids (fats).
C
1. Carbohydrates: These are used to produce energy for cellular activities.
Types of carbohydrates: (a) simple sugars (monosaccharides): One sugar molecule– Examples: Glucose, fructose and galactose.
(b)
disaccharides: Two monosaccharide joined together.
Examples: Lactose = glucose + galactose; Sucrose = glucose + fructose; Maltose
= glucose + glucose
Exam hints: Memorize what the disaccharides are composed of. In order words, what are the end products if you break down or digest a disaccharide.
(c) Complex sugars: Starch, cellulose and glycogen are made up of so many
glucose joined together.
Exam hints: Glycogen is the storage form of carbohydrate in animals only . Cellulose
is only found in plant cells.
2. Proteins are made up of amino
acids. Proteins are the structural building blocks of the organism.
3. Lipids (Fats and
oil) are made up of fatty acids and
glycerol.
Test for some food
substances:
Type of food
substance
|
Test
|
Starch
|
Iodine test: Turns
blue-black
|
Simple sugar (Glucose)
|
(a) Benedicts test:
Brick-red coloration
(b) Fehlings test: brick red coloration
|
Protein
|
Biuret test:
light-blue color becomes purple
|
Lipid
|
Paper test: Oil
stains paper
|
Exam hints: Memorize the test for the food substances.
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