Monosaccharides and Disaccharides

Question 1

What do glucose and glucose form when they join?

Answer 1

Maltose

Question 2

What do glucose and fructose join to form?

Answer 2

Sucrose

Question 3

What do glucose and galactose join to form?

Answer 3

Lactose

Question 4

What happens when monosaccharides join together?

Answer 4

A molecule of water is removed and the reaction is therefore called a condensation reaction.

Question 5

What is the bond that is formed when monosaccharides join together and lose a molecule of water?

Answer 5

A glycosidic bond.

Question 6

What happens when water is added to a disaccharide under suitable conditions?

Answer 6

It breaks the glycosidic bond releasing the constituent monosaccharides. This is called hydrolysis.

Question 7

How do we test for reducing/ non-reducing sugars?

Answer 7

We use Benedict’s test.

Question 8

How do we deter,one if something is a non-sugar?

Answer 8

They do not change the colour of Benedict’s Reagent when they are heated with it. In order to detect a non-reducing sugar it must first be hydrolysed into its monosaccharide components by hydrolysis.

Question 9

What do the colours that the Benedict’s reagent turn into mean?

Answer 9

Green- very low
Yellow- low
Brown- medium
Brick-red/ orange-red- high

Question 10

What is the method to test for reducing sugars?

Answer 10

1. Add 2cm^3 of the sample to be tested to a test tube. If the sample is not already in liquid form, first grind it up in water.
2. Add 2cm^3 of Benedict’s reagent.
3. Heat the mixture in a gently boiling water bath for 5 minutes.

Question 11

What are NOT reducing sugars?

Answer 11

Sucrose and polysaccharides

Question 12

What is the method that tests for non-reducing sugars?

Answer 12

1. Add 2cm^3 of the sample to be tested to a test tube. Then add 2cm^3 of dilute hydrochloric acid. Heat for 3 minutes to hydrolyse the glycosidic bond.
2. Add solution hydrogen carbonate powder to neutralise the solution (should fizz).
3. Add 2cm^3 of Benedict’s reagent and heat the mixture in gently boiling water bath for 5 minutes.

Question 13

What type of structure does starch have?

Answer 13

Starch has an alpha-helical structure.This makes it good for storage as it is compact

Question 14

What does starch’s structure mean?

Answer 14

Starch is insoluble due to its structure. Therefore, it doesn’t affect water concentration/ osmosis.

Question 15

What other properties does starch have?

Answer 15

It is the main way that plants store sugar. It is large so cannot diffuse out of cells. When it is hydrolysed it forms a-glucose. It rarely has branches so many enzymes can act on one molecule

Question 16

Where is starch found?

Answer 16

Starch is found in plants but never animals.

Question 17

How do we test for starch?

Answer 17

The iodine test is used. The product will turn blue/ black if starch is present

Question 18

What is cellulose?

Answer 18

Polymer of b-glucose

Each monomer is inverted

Question 19

What consequences does cellulose have because of its properties?

Answer 19

Forms chains which run parallel with hydrogen bonds between the chains to form microfibrils.
Microfibrils are strong- they group together to form fibres.
Being fibrous (able to make fibres), cellulose is structurally important in plant cell walls.

Question 20

What structure does glycogen have?

Answer 20

It has a similar structure to starch.

Question 21

Where is glycogen found?

Answer 21

Found in animals and bacteria- never plants.

Question 22

How is glycogen different to starch?

Answer 22

Shorter chains and more branches than starch. It is found in granules in the muscles and liver

Question 23

What properties does glycogen have?

Answer 23

Insoluble so does not affect osmosis.
Compact
More branched than starch so more attachment places for enzymes