Carbohydrates

Question 1

What are monosaccharides? (1)

Answer 1

Individual sugar molecules

Question 2

What is the general formula for monosaccharides? (1)

Answer 2

(CH 2 O)n

Question 3

What are disaccharides? (3)

Answer 3

• 2 monosaccharides bonded together by a
• glycosidic bond
• through a condensation reaction

Question 4

Give the 3 examples of disaccharides? (3) State whether they are reducing or non-reducing sugars. (3)

Answer 4

• glucose + glucose = maltose (reducing)
• glucose + galactose = lactose (reducing)
• glucose + fructose = sucrose (non-reducing)

Question 5

What are reducing sugars and can all saccharides be reducing sugars? (2)

Answer 5

• Reducing sugars can lose or donate electrons to other compounds
• All monosaccharides are reducing sugars as well as some disaccharides

Question 6

What two types of sugar molecules are there? (2)

Answer 6

• Pentose sugars - contain 5 carbon atoms
• Hexose sugars - contain 6 carbon atoms

Question 7

What type of sugar is glucose and why? (2)

Answer 7

Hexose sugar because it has 6 carbon atoms

Question 8

What is an isomer? (2)

Answer 8

• Two or more compounds with the same formula but different arrangement of atoms.
• Therefore it different isomers of a compound lead to different properties

Question 9

What are the two isomers of glucose? (2)

Answer 9

• Alpha-glucose
• Beta-glucose

Question 10

Draw an alpha and beta glucose

Answer 10

• Labelled carbons
• Correct arrangement of H and OH
• Oxygen in hexagon shape

Question 11

Explain the difference between an alpha and beta-glucose structure (2)

Answer 11

• The hydroxyl group in alpha-glucose is below the ring at carbon 1 whereas
• The hydroxyl group in beta-glucose is above the ring at carbon 1

Question 12

Draw a maltose made from alpha-glucoses bonding together

Answer 12

• 2 hexagons with oxygen and 6 labelled carbons
• OH and H in correct arrangement
• Glycosidic bond shown
• H20 removed due to condensation reaction

Question 13

What type of glycosidic bond forms between two alpha-glucoses? (1)

Answer 13

1-4 glycosidic bond

Question 14

Name the 3 polysaccharides (3)

Answer 14

• Starch
• Glycogen
• Cellulose

Question 15

What isomer of glucose is starch made from? (1)

Answer 15

Alpha-glucose

Question 16

What two polysaccharides make up starch? (2)
What are their glycosidic bonds? (2)
What are their shapes? (2)

Answer 16

• Amylose
  (1-4 glycosidic bond)
  Long, unbranched and coiled shape
• Amylopectin
  (1-6 glycosidic bond)
  Long and branched shape

Question 17

How is the shape of amylose and amylopectin useful? (2)

Answer 17

• The coiled shape of amylose makes starch compact so more excess glucose can be stored in a small amount of space
• The branches from amylopectin gives starch a large surface area for enzymes to hydrolyse glycosidic bonds to allow glucose to be released quickly when needed e.g. for respiration

Question 18

Why is starch a good place to store excess glucose? (2) Do not refer to amylose and amylopectin in answer

Answer 18

• Starch is insoluble and it is too large to diffuse out of cells so
• this does not affect the water potential of cells

Question 19

What isomer of glucose is glycogen made up of? (1)

Answer 19

Alpha-glucose

Question 20

What shape and glycosidic bond does glycogen have? (2)

Answer 20

• Long, branched shape (more branched than amylopectin)
• 1-6 glycosidic bond

Question 21

Why is the shape of glycogen useful? (2)
What else is useful about glycogen? (2)

Answer 21

• The branches give glycogen a larger surface area for enzymes to hydrolyse glycosidic bonds for quick release of glucose when needed for respiration e.g. when exercising
• It is also compact to allow more glucose to be stored in a small amount of space
• It is also insoluble so it doesn’t affect water potential or diffuse out of cells

Question 22

Where do animals store excess glucose as glycogen in? (2)

Answer 22

• Muscles
• Liver

Question 23

What isomer of glucose is cellulose made from? (1)

Answer 23

Beta-glucose

Question 24

What is the shape of cellulose and what glycosidic bond is it made from? (2)

Answer 24

• Long, unbranched straight chains
• (1-4 glycosidic bonds)

Question 25

What bonds link cellulose chains together and what does this form? (2) Describe the 2 properties of what it forms (2) and how this is useful to plants (2)

Answer 25

- Hydrogen bonds between the glucose molecules in each chain join the cellulose chains together - This forms thicker fibres called microfibrils - Microfibrils are strong due to the hydrogen bonds but they are still flexible - This provides support and allows cells to become turgid

Question 26

What two types of glycosidic bonds can polysaccharides have (2) and what do the numbers refer to? (1)

Answer 26

- (1-4 glycosidic bonds) - (1-6 glycosidic bonds) - The numbers refer to the carbon number where the molecules bind to each other

Question 27

Why does the glucose in cellulose rotate 180 degrees each time? (1)

Answer 27

To allow it to form hydrogen bonds with other parallel cellulose chains