1.2

Question 1

What are monosaccharides?

Answer 1

The monomers, from which larger carbohydrates are made

Question 2

Give three examples of common monosaccharides

Answer 2

Glucose galactose fructose

Question 3

What does a condensation reaction between two monosaccharides form?

Answer 3

A Glycosidic bond

Question 4

How are disaccharides formed

Answer 4

By the condensation of two monosaccharides

Question 5

Give three examples of disaccharides

Answer 5

Sucrose maltose lactose

Question 6

How is maltose formed?

Answer 6

By the condensation of two glucose molecules

Question 7

How is sucrose formed?

Answer 7

By the condensation of a glucose molecule and a fructose molecule

Question 8

How is lactose formed?

Answer 8

By condensation of a glucose molecule and a galactose molecule

Question 9

Draw the structure of a-glucose

Question 10

Draw the structure of b-glucose

Question 11

How are polysaccharides formed?

Answer 11

By the condensation of many glucose units

Question 12

Give 3 examples of polysaccharides

Answer 12

Glycogen, starch and cellulose

Question 13

How are glycogen and starch formed

Answer 13

By the condensation of a-glucose

Question 14

How is cellulose formed?

Answer 14

By the condensation of B – glucose

Question 15

Describe the structure and functions of starch

Answer 15

– Never found in animal cells
– Polysaccharide found in many parts of a plant in the form of small grains
– Made up of chains of a glucose monosaccharides linked by GlycoSid if bonds that are formed by condensation reactions
– The chains, maybe branched or unbranched
– the unbranched chain is wound in a tight coil that makes molecule very compact

Question 16

How does the structure of starch relate to its function?

Answer 16

The main role of starch is energy storage.
– it is insoluble therefore doesn’t affect water potential. So water is not drawn into the cells by osmosis.
– doesn’t diffuse out of cells because it is large and insoluble.
– compact, so lots of it can be stored in a small space.
– One hydrolysed, it forms a glucose, which is both easily transported and readily used in respiration
– The branched form has many ends each of which can be acted on by enzymes simultaneously, meaning glucose monomers are released very rapidly

Question 17

Describe the structure and functions of glycogen

Answer 17

– Found in animals and bacteria, but never in plant cells.
– similar structure to starch, but has smaller chains and is more highly branched.
– the major carbohydrate storage project of animals.
– in animals, it is stored as small granules, mainly in muscles and the liver.

Question 18

How does the structure of glycogen relate to its function?

Answer 18

It’s structure suits it for storage because:
– It is insoluble, and therefore does not time to draw water into the cells by osmosis
– It does not diffuse out of cells because it is insoluble.
– it is compact so a lot of it can be stored in a small space.
– It is more highly branched than starch and so has more ends that can be acted on simultaneously by enzymes. It is therefore more rapidly broken down to full glucose monomers which are used in respiration. This is important to animals which have a higher metabolic rate and therefore respiratory rate the plants because they’re more active .

Question 19

Describe the structure and functions of Celulose

Answer 19

– Made of monomers of B-glucose.
– Cellulose has straight unbranched chains. These run parallel to one another, allowing hydrogen bonds to form cross linkages between adjacent chains.

Question 20

How is the structure of Celulose suited to its function?

Answer 20

Its function is to provide support and rigidity
– Cellulose molecules are made up of B-glucose and so form long, straight unbranched chains
– The cellulose molecular chains run parallel to each other, and are cross linked by hydrogen bonds, which provides yet more strength

Question 21

Describe Benedicts test for reducing sugars

Answer 21

1. Add an equal volume of Benedicks reagent to a sample.
2. Heat the mixture in an electric water bath at 100°C for five minutes.
3. Positive result: colour change from blue to orange and brick red precipitate forms.

Question 22

Describe benedicts test for non-reducing sugars?

Answer 22

1. Negative result: Benedicks reagent remains blue
2. Hydrolyse non-reducing sugars, E.G.sucrose into their monomers by adding 1 cm³ of HCl. Heat in a boiling water bath for five mins.
3. Neutralise the mixture using sodium carbonate solution.
4. Proceed with the Benedicks test as usual.

Question 23

Describe the test for starch

Answer 23

1. Add iodine solution.
2. Positive result: colour change from orange to blue black.