Chapter 2: Biological Molecules

Question 1

Test for reducing sugars

Answer 1

1. add HCL to the test tube and heat in a water bath
2. Neutralise with sodium hydrogencarbonate
3. Heat with benedict’s solution
   If the color changes from blue to brick red then glucose is present
   Measuring the time taken for the color to change can be used to esimate the concentration of glucose.

Question 2

Test for starch

Answer 2

turns blue/black in iodine

Question 3

Test for lipids

Answer 3

add ethanol to the substance and shake it. Mix with water.
A milkly color will show a positive result
(emulsion test)

Question 4

Test for proteins

Answer 4

add a few drops of sodium hydroxide then copper (II) sulphate solution. Proteins are present if color changes from Blue to purple
(the biuret test)

Question 5

Test for non-reducing sugars

Answer 5

1. add few drops of HCL
2. Heat gently to ensure hydrolysis
3. add few drops of NaHCO3 to neutralize the acidic solution
4. add benedict’s solution
5. heat for few minutes
   If sugars are present the solution will turn from green to yellow, orange or red.
   if it doesn’t change color then there are non-reducing sugars present

Question 6

Carbohydrates

Answer 6

energy source
Energy Storage

Question 7

Types of carbohydrates

Answer 7

monosaccarides
Disaccharides
Polysaccharides

Question 8

Monosaccarides

Answer 8

consisting of a single sugar unit
Soluble in water and have a general formula of (CH2O)n
Based off the number of carbon atoms:
1. Triose (3 carbons)
2. Pentose (5)
Hexose (6)

Question 9

Glucose (C6H12O6)

Answer 9

main source of energy in cells. exist in two forms:
Alpha and beta glucose

Involved in respiration, photosynthesis and energy storage.

Question 10

Disaccharides

Answer 10

formed when two monsaccharides undergo a condesation reaction where a molecule of water is released and a glycosidc bond is formed between the sugar units
Soluble in water and taste sweet.
Can be broken down into monosaccharides through hydrolysis (adding of water)

Question 11

Examples of Disaccharides

Answer 11

Maltose (Glucose + glucose)
Sucrose (glucose + fructose)