Carbohydrates

Question 1

What is the function of carbohydrates?

Answer 1

To provide energy. This can be immediately (e.g. glucose) or as stored energy (e.g. glycogen in animals and starch in plants).

Question 2

What are the 3 broad groups carbohydrates can be split into?

Answer 2

Monosaccharides, disaccharides, and polysaccharides

Question 3

What is the general formula for monosaccharides?

Answer 3

C_n(H₂O)_n

Question 4

What properties must a substance have to be classed as a sugar?

Answer 4

• Must dissolve in water
• Must be crystalline
• Must be sweet to taste

Question 5

Are all monosaccharides classed as sugars?

Answer 5

Yes

Question 6

What is the general name for monosaccharides containing:

a) 3 carbons
b) 5 carbons
c) 6 carbons

Answer 6

a) triose
b) pentose
c) hexose

Question 7

Give an example of a 3 carbon sugar

Answer 7

G3P

Question 8

How is sucrose formed?

Answer 8

A condensation reaction between alpha glucose and fructose

Question 9

What hydrolyses sucrose?

Answer 9

Sucrase

Question 10

Give 3 examples of disaccharides

Answer 10

Maltose, sucrose, and lactose

Question 11

What kind of bond forms between sugars in a condensation reaction?

Answer 11

A glycosidic bond

Question 12

How is maltose formed?

Answer 12

From a condensation reaction between two alpha glucose molecules

Question 13

What hydrolyses maltose?

Answer 13

Maltase

Question 14

How do two alpha glucose molecules bond to form maltose?

Answer 14

There is a reaction between the hydroxyl group of Carbon 1 of one molecule and Carbon 4 of the other molecule (be careful to specify C1 of one molecule and C4 of another)

Question 15

Is the bond formed in the condensation reaction of alpha glucose above or below the plane of the ring?

Answer 15

Below

Question 16

Give the two functions of polysaccharides

Answer 16

1) Energy storage
2) Structure in the form of cellulose in plant cell walls or chitin in insect wings and fungi walls

Question 17

In what form is energy stored in:

i) plant cells
ii) animal cells

Answer 17

i) Starch
ii) Glycogen

Question 18

Why are polysaccharides not classed as sugars? (3 reasons)

Answer 18

• They do not taste sweet
• They are not crystalline
• They do not dissolve in water

Question 19

What are the three physical properties of both starch and glycogen that make them excellent storage molecules?

Answer 19

• They are insoluble in water
• They form very compact molecules
• They can be easily hydrolysed to release a glucose

Question 20

(i) How does Starch and glycogen’s insolubility in water make them good storage molecules?
(ii) What would happen if they were soluble in water?

Answer 20

(i) They do not dissolve and therefore do not affect the water potential of cells
(ii) They would dissolve and change the water potential of the cell, causing water to move into the cell by osmosis and cause cell damage

Question 21

Why is the ability to form compact molecules favourable for a storage molecule?

Answer 21

A lot of the molecules can fit into a small space, meaning more efficient storage

Question 22

Why is it beneficial that starch and glucose can be easily hydrolysed?

Answer 22

Easy hydrolysis means that both starch and glycogen can provide a readily available source of glucose for respiration and so provide quick release energy.

Question 23

What reacts to form glycogen?

Answer 23

Alpha glucose

Question 24

What type of bonding occurs in glycogen? Why?

Answer 24

1,4 and 1,6 glycosidic bonding

• This allows for branching so each molecule has many ends where glucose can be added
• This means glycogen is a more compact molecule
• This means more terminal glucose molecules that can be simultaneously hydrolysed

Question 25

What are the two components of starch?

Answer 25

Amylose and Amylopectin

Question 26

i) What happens to the shape of amylose once it has been formed? ii) What shape does this give it? iii) What causes this change in shape to occur?

Answer 26

i) It coils ii) Giving a helical shape iii) Hydrogen bonds form within the coil

Question 27

i) Which molecules make up amylose? ii) What kind of bonding links these together? iii) Therefore what kind of molecules is produced?

Answer 27

i) Alpha-glucose ii) 1,4 glycosidic bonds iii) Linear

Question 28

i) What molecules make up amylopectin? ii) What kind of bonding is present in amylopectin? iii) Therefore which molecule is amylopectin similar to?

Answer 28

i) Alpha-glucose ii) 1,4 and 1,6 glycosidic bonds iii) Glycogen

Question 29

i) How can the presence of starch be tested for? ii) What is observed if starch is present? iii) Why does this occur?

Answer 29

i) Potassium iodide solution is added ii) The solution will go from being orange/brown to black/blue iii) The iodine sits in the coils of the amylose component of starch, this complex appears blue/black

Question 30

Where is cellulose found?

Answer 30

In plant cell walls

Question 31

What is the monomeric unit of cellulose?

Answer 31

Beta glucose

Question 32

What is the difference between alpha and beta glucose?

Answer 32

The OH group on Carbon 1 is above the plane of the ring in beta glucose but below the plane of the ring in alpha glucose

Question 33

i) What bonding is present in cellulose? ii) What issue arises with this bonding? iii) Therefore what must happen to allow the bonding to occur?

Answer 33

i) 1, 4 glycosidic bonds between beta glucose molecule ii) The hydroxyl groups lie on different planes of the ring iii) Every other beta glucose must be rotated 180 degrees relative to the previous beta glucose

Question 34

What are the monomeric units of sucrose?

Answer 34

Alpha glucose and fructose

Question 35

Are all monosaccarides reducing sugars?

Answer 35

Yes

Question 36

Are all disaccharides reducing sugars?

Answer 36

No, only some are

Question 37

Give an example of a non-reducing sugar

Answer 37

Sucrose

Question 38

Give an example of a reducing sugar

Answer 38

Maltose or lactose

Question 39

Give an example of a 5 carbon sugar

Answer 39

Ribose or deoxyribose

Question 40

Give an example of a 6 carbon sugar

Answer 40

Glucose or fructose or galactose

Question 41

What type of reaction is the breakdown of maltose by maltase?

Answer 41

Hydrolysis

Question 42

What is produced by the hydrolysis of maltose?

Answer 42

Two alpha glucose molecules

Question 43

What is a reducing sugar?

Answer 43

Sugars that donate electrons resulting in the reduction of another molecule