1.2

Question 1

Give 3 examples of disaccharides. (3)

What are each of them made from? (3)

Answer 1

(1) maltose —> (4) 2 a-glucose
(2) lactose —> (5) glucose & galactose
(3) sucrose —> (6) glucose & fructose

Question 2

What is the formula of the 3 disaccharide examples? (1)

What are they an example of? (1)

Answer 2

(1) C12 H22 O11
(1) isomers

Question 3

What happens during a condensation reaction between 2 monosaccharides? (2)

Answer 3

(1) a molecule of water = REMOVED…
(2) forming a GLYCOSIDIC bond

Question 4

What happens during a hydrolysis reaction in a disaccharide/polysaccharide? (2)

Answer 4

(1) a molecule of water = ADDED…
(2) breaking the GLYCOSIDIC bond

Question 5

Where is the glycosidic bond located in a disaccharide? (2)

Answer 5

(2m) between Carbon-1 & Carbon-4

Question 6

Give 3 examples of polysaccharides. (3)
What are they made from? (3)
What is their function? (3)

Answer 6

(1) cellulose —> (2) B-glucose —> (3) structural support in plants
(1) starch —> (2) a-glucose —> (3) plant storage molecule
(1) glycogen —> (2) a-glucose —> (3) animals storage molecule

Question 7

Describe how you would test for non-reducing sugars? (10 steps)

Answer 7

(1) Add 2cm. of food sample
(2) Add 2cm of Benedict’s reagent
(3) Place tube in gently boiling water for 5 mins
(4) if solution doesn’t change colour, it’s a non-reducing sugar
(5) Add 2cm of food to 2cm of dilute HCl
(6) Place test tube in gently boiling water for 5 mins
(7) SLOWLY add NaHCO3 to it
(8) test with pH paper to check if the solution is alkaline
(9) retest the solution by heating it with Benedict’s reagent
(10) result should be a red precipitate

Question 8

Why is dilute HCl added to the food sample? (1)
After the NaHCO3 is added, why do we need to check it’s pH? (1)

Answer 8

(1) because it will hydrolyse the disaccharide
(1) because Benedict’s reagent doesn’t work in acidic conditions. (NaHCO3 neutralises HCL)

Question 9

What is the main property of polysaccharides? (1)
What does it help them with? (1)

Answer 9

(1) they’re usually INSOLUBLE
(1) which makes them suitable for STORAGE

Question 10

How do you test for starch? (3)

Answer 10

(1) Place 2cm of the sample in a test tube
(2) add 2 drops of iodine solution & stir
(3) presence of starch = blue-black coloration

Question 11

“To hydrolyse a disaccharide, it can be boiled with HCl acid. But if hydrolysis is carried out by an enzyme, a much lower temp. is needed. Why?” (2)

Answer 11

(1) enzymes are DENATURED at higher temps
(2).. which prevents them from FUNCTIONING