3.1.2 Carbohydrates

Question 1

Name the 3 Hexose monosaccharides

Answer 1

• Galactose
• Glucose
• Fructose
  all have the molecular formula C6H12O6

Question 2

What are Monosaccharides?

Answer 2

The monomers from which larger carbohydrates are made

Question 3

Name the type of bond formed when monosaccharides react

Answer 3

Glycosidic bond

Question 4

What does Disaccharide mean?

Answer 4

2 monomers so 1 chemical bond

Question 5

What does Polysaccharide mean?

Answer 5

Multiple monomers so many chemical bonds

Question 6

How are Disaccharides formed?

Answer 6

Condensation reaction of 2 monosaccharides

Question 7

Name 3 Disaccharides

Answer 7

Maltose = glucose + glucose
Sucrose = glucose + fructose
Lactose = glucose + galactose
all have the molecular formula C12H22O11

Question 8

Glucose has..

Answer 8

2 Isomers
- Alpha glucose
- Beta glucose

Question 9

How are Polysaccharides formed?

Answer 9

Condensation of many glucose units

Question 10

How are Glycogen and Starch formed ?

Answer 10

By the condensation of alpha glucose

Question 11

How is Cellulose formed?

Answer 11

By the condensation of beta glucose

Question 12

Describe the structure of Cellulose

Answer 12

• Straight unbranched chain
• Alternate glucose molecules are rotated 180°
• Hydrogen bonds form cross links between parallel strands, forming microfibrils, which give high tensile strength

Question 13

Function of Cellulose

Answer 13

Polymer of beta glucose and gives rigidity to plant cell walls, preventing bursting under turgor pressure holding the stem up

Question 14

Describe the structure of Starch

Answer 14

• Insoluble so no osmotic effect on cells
• Large so doesn’t diffuse out of cells
• Compact
• Branched so many terminal ends for hydrolysis into glucose

Question 15

Function of Starch

Answer 15

Major energy source in diets and storage of polymer alpha glucose in plant cells

Question 16

Describe the structure of Glycogen

Answer 16

• Compact
• Insoluble so no osmotic effect and doesn’t diffuse out of cells
• Branched so many terminal ends for hydrolysis

Question 17

Function of Glycogen

Answer 17

Main storage polymer of alpha glucose in animal cells (liver and muscle cells) and is also found in plant cells

Question 18

Describe the test for Starch

Answer 18

• Add iodine solution
• Positive result: colour change from orange to blue-black

Question 19

Describe the Benedict’s test for reducing suguars

Answer 19

• Add an equal volume of Benedict’s reagent to a sample
• Heat the mixture in an electric water bath at 100 degrees for 5 mins
• Positive result: colour change from blue to orange and brick red precipitate forms

Question 20

Describe the Benedict’s test for non-reducing suguars

Answer 20

Negative result: Benedict’s reagent remains blue
- Hydrolyse non reducing suguars into their monomers by adding by adding 1cm cubed of HCL
- Heat in a boiling water bath for 5 mins
- Neutralise mixture using sodium carbonate solution
- Proceed with the benedict’s test as usual