Carbohydrates

Question 1

Food Test- Reducing Sugars

Answer 1

Benedict’s Test:
-Heat sample with Benedict’s reagent
Positive Result: Orange-red precipitate forms

Question 2

Food Test- Non-Reducing Sugars

Answer 2

Benedict’s Test:
-Check for reducing sugars first
-Hydrolise sample by heating with dilute HCl
-Neutralise by adding sodium hydrogen carbonate
-Test again with Benedict’s reagen
Positive result: Orange-red precipitate formed

Question 3

What is a monosaccharide?

Answer 3

Single sugar, e.g. glucose

Question 4

What is a disaccharide?

Answer 4

Two monosaccharides joined together, e.g. sucrose

Question 5

What is a polysaccharide?

Answer 5

Many monosaccharides joined together to form a very large molecule, e.g. starch

Question 6

What bond forms between two monosaccharides in a condensation reaction?

Answer 6

Glycosidic bond, e.g. maltose from alpha glucose forms 1,4-glysodic bonds

Question 7

Describe the structure of amylose

Answer 7

• Joined together by alpha glucose monosaccharides
• Coils up in helix
• Bonded by 1,4-glycosidic bonds

Question 8

Describe the structure of amylopectin

Answer 8

• Branched chains of alpha glucose residues

- This is because joined by 1,6 and 1,4-glycosidic bonds`

Question 9

Difference between the structure of starch molecules and cellulose molecules

Answer 9

• Starch is formed from alpha-glucose whereas cellulose if formed from beta-glucose
• The position of H and OH groups on Carbon-1 is inverted
• Starch doesn’t contain fibrils
• Starch doesn’t have H bonds between molecules

Question 10

Name 3 adaptations of starch and explain why they are beneficial

Answer 10

1) Insoluble, so it won’t affect water potential
2) Helical, so it’s compact
3) It’s a large molecule, so it cant leave the cell

Question 11

Describe the structure of glycogen

Answer 11

• Alpha glucose polymer

- Many branches on molecules, so high SA, faster hydrolysis for glucose production

Question 12

What is the purpose of glycogen?

Answer 12

It is a polysaccharide made of excess glucose that is stored in muscles for respiration but mostly in the liver and is continuously broken down to maintain blood sugar levels.

Question 13

Explain how cellulose is adapted to its function

Answer 13

1. Long and straight chains;
2. Become linked together by many hydrogen bonds to form fibrils;
3. Provide strength (to cell wall).

Question 14

Describe the structure of cellulose

Answer 14

• Made of beta glucose
• Every other glucose is upside down
• 1,4-glycosidic bonds
• Chains linked by H bonds
• Formed into strong microfibrils
• Abundant polysaccharide, enzymes can’t hydrolyse

Question 15

What monosaccharides make up maltose?

Answer 15

Two glucose molecules

Question 16

What monosaccharides make up sucrose?

Answer 16

A glucose molecule and a fructose molecule

Question 17

What monosaccharides make up lactose?

Answer 17

A glucose molecule and a galactose molecule

Question 18

Structure of glucose

Answer 18

alpha glucose (l-r excl. carbons)
H, O, H HO, OH
beta glucose
H, O, OH OH, H

Question 19

What forms from a condensation of alpha-glucose?

Answer 19

Glycogen

Question 20

What forms from a condensation of beta-glucose?

Answer 20

Cellulose

Question 21

Alpha glucose

Answer 21

H |__O H
\ / \ /
/ \ ___ / \
HO OH

Question 22

Beta glucose

Answer 22

H |__O OH
\ / \ /
/ \ ___ / \
HO H

Question 23

Describe how the scientist would have produced the calibration curve and used it to obtain the results in a graph with concentrations of maltose

Answer 23

1. Make/use maltose solutions of known concentrations and carry out quantitative Benedict’s test on each
   2.Measure colour/colorimeter value of each
   solution and plot calibration curve/graph described;
   3.Find concentration of sample from calibration curve;