16 WJEC Biology AS Level - Marianne Izen - 2nd Edition

Question 1

What is the structural formula of a triose?

You will not be asked to draw the structural formulae of carbohydrates in an examination, but you may be asked to identify them and be asked questions about them, so it is important to understand them.

Answer 1

Question 2

What is the structural formula of ribose, a pentose?

You will not be asked to draw the structural formulae of carbohydrates in an examination, but you may be asked to identify them and be asked questions about them, so it is important to understand them.

Answer 2

Question 3

What is the structural formula of straight chain and ring forms of glucose, a hexose?

You will not be asked to draw the structural formulae of carbohydrates in an examination, but you may be asked to identify them and be asked questions about them, so it is important to understand them.

Answer 3

Question 4

How do you show the arrangement of atoms?

Answer 4

It is usual to show the arrangement of the atoms using a diagram known as a structural formula.

Question 5

Describe the functions of monosaccharides

Answer 5

Monosaccharides have several functions and can act as:

A source of energy in respiration. Carbon-hydrogen and carbon-carbon bonds are broken to release energy, which is transferred to make adenosine triphosphate (ATP).

Building blocks for larger molecules. Glucose, for example, is used to make the polysaccharides starch, glycogen, cellulose and chitin.

Intermediates in reactions. e.g. trioses are intermediates in the reactions of respiration and photosynthesis.

Constituents of nucleotides. e.g. deoxyribose in DNA, ribose in RNA, ATP and ADP.

Question 6

What is the difference between a molecule and a structural formula?

Answer 6

A molecule is a three-dimensional structure but a structural formula is in two dimensions on the page.

Question 7

What is the significance of the direction in which a bond is drawn?

Answer 7

When a bond is drawn pointing upwards, it means that the group it is attached to is above the plane of the drawing, and if it is drawn pointing downwards the group is below the plane.

Question 8

Look at the atoms attached to carbon atom 1 (C1) on alpha-glucose and on beta-glucose and describe the difference.

Answer 8

In beta glucose, the bond between C1 and OH is drawn pointing upwards, it means that the OH group is above the plane of the drawing

In alpha glucose, the bond between C1 and OH is drawn pointing downwards, it means that the OH group is below the plane of the drawing