4 The Chemicals of Life

Question 1

Chemical elements in carbohydrates (COH)

Answer 1

carbon, oxygen, hydrogen

Question 2

Chemical elements in fats (COH)

Answer 2

carbon, oxygen, hydrogen

Question 3

Chemical elements in proteins

Answer 3

carbon, oxygen, hydrogen, nitrogen and small amounts of sulfur

Question 4

Test for starch

Answer 4

• Iodine test
• add iodine solution to food
• positive test: orange-brown to blue-black

Question 5

Test for reducing sugars

Answer 5

• Benedict’s test
• add benedict’s solution to food followed by heating it
• positive test: blue to red

Question 6

Test for proteins

Answer 6

• Biuret test
• mix food with water, add dilute copper sulfate solution then dilute potassium hydroxide gently
• positive test: blue to purple

Question 7

Test for fats and oil

Answer 7

• Ethanol emulsion test
• add ethanol to food, shake thoroughly, add distilled water
• positive water: colorless mixture turns cloudy

Question 8

Test for Vitamin C

Answer 8

• DCPIP test
• positive test: blue to colorless

Question 9

Describe the structure of a DNA molecule

Answer 9

• two strands coiled together to form a double helix
• each strand contains bases
• bonds between the pairs of bases hold the strands together
• the bases always pair in the same way (A&T, C&G)