Carbohydrates

Question 1

What are the monomers that carbohydrates are made from?

Answer 1

Monosaccharides (eg. Glucose)

Question 2

How many carbon atoms are in each molecule of glucose?

Answer 2

6 (hexose sugar)

Question 3

What are isomers?

Answer 3

Molecules with the same molecular formula as each other, but with the atoms connected in a different way

Question 4

a-glucose

Answer 4

H
OH

Question 5

B-glucose

Answer 5

OH
H

Question 6

How are disaccharides formed?

Answer 6

Condensation reactions - a glycosidic bond forms between monosaccharides, joining them together

Question 7

Sucrose is a disaccharide formed from…

Answer 7

A condensation reaction between a glucose molecule and a fructose molecule

Question 8

Lactose is a disaccharide formed from…

Answer 8

A condensation reaction between a glucose molecule and a galactose molecule

Question 9

Benedict’s test for reducing sugars

Answer 9

Heat with Benedict’s reagent in a thermostatically controlled hot water Bath at ≈90°c. If reducing sugars are present, a brick red precipitate forms

Question 10

Benedict’s test for non-reducing sugars (eg. Sucrose)

Answer 10

Heat with dilute hydrochloride acid in a thermostatically controlled hot water Bath at ≈90°c. Neutralise with sodium hydrogen carbonate. Reheat sample with Benedict’s reagent. If reducing sugars are present, a brick red precipitate forms

Question 11

Maltose is a disaccharide formed from…

Answer 11

A condensation reaction between two glucose molecules

Question 12

When is a polysaccharide formed?

Answer 12

When more than two monosaccharides join together via condensation reactions

Question 13

Starch is a mixture of…

Answer 13

Two polysaccharides of a-glucose (amylose and amylopectin)

Question 14

How do plants use starch?

Answer 14

Store excess glucose as starch. When plant needs energy, starch is broken down to release glucose

Question 15

What do animals store excess glucose as?

Answer 15

Glycogen

Question 16

Why is starch good for storage?

Answer 16

Compact and insoluble in water (doesn’t effect water potential, so doesn’t cause water to enter cell via osmosis, making cell swell)

Question 17

Iodine test for starch

Answer 17

Add iodine dissolved in potassium iodide solution to sample. If starch is present, colour change to blue-black

Question 18

What is amylopectin and how is it structured?

Answer 18

• Long, branched chain of a-glucose
• Side branches allow the enzymes that break down the molecule to get at the glycosidic bonds easily (glucose can be released quickly)
• 1-4 and 1-6 glycosidic bonds

Question 19

What is amylose and how is it structured?

Answer 19

• Long, unbranched chain of a-glucose
• Angles of the glycosidic bonds give it a coiled structure, almost like a cylinder (compact)
• 1-4 glycosidic bonds

Question 20

What is cellulose and how is it structured?

Answer 20

• Long, unbranched chains of B-glucose
• When B-glucose molecules bond, they form straight cellulose chains
• Cellulose chains linked together by hydrogen bonds (forming microfibrils)
• 1-4 glycosidic bonds

Question 21

What is glycogen and how is it structured?

Answer 21

• Polysaccharide of a-glucose
• Lots of side branches coming off it (stored glucose can be broken down and released quickly)
• Compact molecule (good for storage)
• 1-4 and 1-6 glycosidic bonds