3.1.2

Question 1

Describe the chemical formula of carbohydrates.

Answer 1

Organic compounds comprising of only carbon, hydrogen and oxygen
Hydrogen and oxygen present in a 2:1 ratio

Question 2

What are monosaccharides? Name three.

Answer 2

Single sugar units - the monomers from which larger carbohydrates are made
Eg glucose,galactose,fructose

Question 3

What is an isomer?

Answer 3

Chemicals with the same formula but different arrangements

Question 4

What are the isomers of glucose? Draw them.

Answer 4

Alpha glucose

H |_ O H
X X
HO — OH

Beta glucose

H |_ O OH
X X
HO — H

Question 5

What are disaccharides? How are they formed? Name 3 and what they are made from.

Answer 5

Double sugar units formed by the condensation of two monosaccharides
Sucrose=glucose+fructose
Maltose=glucose+glucose
Lactose=glucose+galactose

Question 6

Describe polysaccharides

Answer 6

Large polymers of monosaccharides
Insoluble, unlike monosaccharides and disaccharides

Question 7

How is a glycosidic bond formed?

Answer 7

A condensation reaction between two monosaccharides

Question 8

How are carbohydrates classified?

Answer 8

Carbohydrates
Sugars Polysaccharides
Monosaccharides Disaccharides Storage Structural

Question 9

What are carbohydrates used for?

Answer 9

Sources of energy in all organisms
Structural material within cells

Question 10

Why is glucose not stored as glucose in plants and animals?

Answer 10

Glucose is soluble so would change the water potential

Question 11

Describe what starch is and what it is made of.

Answer 11

Storage compound in plants
Made from amylose (long unbranched chain of glucose units) and amylopectin (highly branched polymer of glucose units)

Question 12

Describe the structure of amylose.

Answer 12

Alpha glucose molecules joined by alpha 1,4 glycosidic bonds
CH2OH side chains stick out on same side causing chain to coil into a helix

Question 13

How is amylose adapted for its function?

Answer 13

Compact - can store lots of energy in a small space
Can be hydrolysed to release many glucose molecules for respiration
Large - can’t diffuse out of cell
Insoluble - doesn’t affect water potential

Question 14

Describe the structure of amylopectin.

Answer 14

Branched chain of alpha glucose
Straight chain bonded by alpha 1,4 glycosidic bonds
Branching caused by alpha 1,6 glycosidic bonds

Question 15

How is amylopectin adapted for its function?

Answer 15

Compact - lots of energy stored in a small space
Can be quickly broken down to release many glucose molecules (branched ends means higher surface area)
Insoluble - doesn’t affect water potential
Large - won’t diffuse out of cell Insoluble

Question 16

Describe the structure of glycogen.

Answer 16

Storage compound in animals
Branched polymer of alpha glucose
Stored in liver and muscles
More highly branched by amylopectin - more alpha 1,6 glycosidic bonds
Each branch shorter - only 8-12 residues per chain
Whole molecule coils

Question 17

How is glycogen adapted for its function?

Answer 17

Compact - lots of energy stored in a small space
Can be very quickly hydrolysed to release many glucose molecules due to many branched ends
Insoluble - doesn’t affect water potential
Large - can’t diffuse out of cell

Question 18

Describe the structure of cellulose.

Answer 18

Structural polysaccharide- major component of plant cell walls
Straight chain polymer of beta glucose
Side chains of CH2OH stick out on alternate sides making the molecules very straight
Long straight chains parallel to each other linked by hydrogen bonds

Question 19

Describe the arrangement of beta glucose in cellulose.

Answer 19

Every alternate beta glucose is flipped to form a straight chain molecule.

Question 20

How is cellulose arranged?

Answer 20

Small bundles of cellulose chains make thin fibres called microfibrils - extremely strong
Cross linking prevents hydrolysis by water - isn’t a good dietary carbohydrate in animals

Question 21

Describe the biochemical test for reducing sugars.

Answer 21

Add Benedict’s solution and heat in a water bath at a minimum of 60’C
Positive result will go from blue to brick red

Question 22

Describe the test for non reducing sugars.

Answer 22

Boil sample in hydrochloric acid (to break glycosidic bonds by acid hydrolysis releasing reducing sugars)
Neutralise sample by adding an alkali eg sodium hydrogen carbonate
Add Benedict’s solution and heat in a water bath at a minimum of 60’C
Positive result goes from blue to brick red

Question 23

Describe the test for starch.

Answer 23

Add iodine solution to the sample
Positive result goes from brown to blue black