AQA Biology Topic 1 Carbohydrates

Question 1

What are the three main types of carbohydrates?

Answer 1

1. Monosaccharides
2. Disaccharides
3. Polysaccharides

Question 2

What is a monosaccharide? Give examples.

Answer 2

A monosaccharide is a single sugar molecule, the simplest form of carbohydrate.
Examples: Glucose, Fructose, Galactose

Question 3

What is the difference between α-glucose and β-glucose?

Answer 3

α-glucose: OH group on carbon 1 is below the ring.
β-glucose: OH group on carbon 1 is above the ring.

Question 4

What is a disaccharide? Give 3 examples.

Answer 4

A disaccharide is formed when two monosaccharides join by a condensation reaction, forming a glycosidic bond.
Examples:
1. Maltose = Glucose + Glucose
2. Sucrose = Glucose + Fructose
3. Lactose = Glucose + Galactose

Question 5

What is a polysaccharide? Name three polysaccharides.

Answer 5

A polysaccharide is a polymer made up of many monosaccharide units.
Examples: Starch, Glycogen, Cellulose

Question 6

What is the structure and function of starch?

Answer 6

Structure: Made of α-glucose, with amylose (unbranched) and amylopectin (branched).
Function: Main storage polysaccharide in plants, insoluble, compact, and easily hydrolysed.

Question 7

What is the structure and function of glycogen?

Answer 7

Structure: Made of α-glucose, highly branched for rapid hydrolysis.
Function: Main storage polysaccharide in animals, stored in liver and muscles.

Question 8

What is the structure and function of cellulose?

Answer 8

Structure: Made of β-glucose, straight chains with hydrogen bonds forming microfibrils.
Function: Provides structural support in plant cell walls.

Question 9

What reaction forms a glycosidic bond?

Answer 9

Condensation reaction – releases a molecule of water.

Question 10

What reaction breaks a glycosidic bond?

Answer 10

Hydrolysis – adds a molecule of water.

Question 11

How do you test for reducing sugars?

Answer 11

Benedict’s Test:
1. Add Benedict’s reagent.
2. Heat in a water bath.
3. Positive result: Brick-red precipitate.

Question 12

How do you test for non-reducing sugars?

Answer 12

Benedict’s Test after Hydrolysis:
1. Hydrolyse with dilute HCl.
2. Neutralise with sodium hydrogen carbonate.
3. Repeat Benedict’s test.

Question 13

How do you test for starch?

Answer 13

Iodine Test:
1. Add iodine solution.
2. Positive result: Blue-black color.