3.1.2 Carbohydrates

Question 1

State the 3 common monosaccharides

Answer 1

• Glucose
• Fructose
• Galactose

Question 2

State the 3 common disaccharides, and describe how they are formed

Answer 2

• glucose +glucose -> maltose +water
• glucose +fructose -> sucrose+water
• glucose +galactose-> lactose +water

Question 3

Describe what is meant by isomers and state examples

Answer 3

• Isomers are molecules with the same molecular formula, but different arrangement of atoms
• Examples include alpha and beta glucose

Question 4

Describe the difference between reducing and non-reducing sugars, and state examples

Answer 4

A reducing sugar can donate an electron to another molecule, whereas a non-reducing sugar cannot.

Question 5

Describe how to test for reducing sugars

Answer 5

• Heat with benedict’s solution (which is blue because it contains Cu2+ ions)
• A brick red precipitate indicates that a reducing sugar is present (because Cu2+ is reduced to Cu+)

Question 6

Describe how to test for non-reducing sugars

Answer 6

• Heat with HCL (hydrolyses the glycosidic bonds)
• neutralise by adding sodium hydrogen carbonate
• heat with benedict’s solution
• a brick red precipitate indicates that a non-reducing sugar is present

Question 7

Lactose is synthesised in the
Golgi apparatus and
transported in vesicles through
the cytoplasm. The vesicle
membranes fuse with the
plasma membrane and the
vesicles empty their contents
out of the cell. The lactosecontaining vesicles increase in
diameter as they move towards
the plasma membrane of the
milk-producing cell. Use your
knowledge of water potential
to explain why

Answer 7

The water potential inside the vesicle is lower and therefore water moves into the vesicle via osmosis