Carbohydrates

Question 1

What are monosaccharides & 3 examples?

Answer 1

monomers from which larger carbohydrates are made
- glucose
- fructose
- galactose

Question 2

What are isomers?

Answer 2

• molecules with the same molecular formula but different arrangement of atoms
• alpha & beta are isomers of glucose

Question 3

What is the difference between alpha & beta glucose?

Answer 3

OH group is below carbon 1 in alpha glucose whilst it’s above in beta glucose

Question 4

What are disaccharides and how are they formed?

Answer 4

2 monosaccharides joined together with a glycosidic bond by a condensation reaction which releases a molecule of water

Question 5

Give 3 examples of disaccharides and what monosaccharides they are made from

Answer 5

maltose = glucose + glucose
sucrose = fructose + glucose
lactose = galactose + glucose

Question 6

What are polysaccharides and how are they formed?

Answer 6

many monosaccharides joined with a glycosidic bond formed by a condensation reaction which produces molecule s of water

Question 7

What is the structure and function of starch?

Answer 7

function: energy store in plant cells
structure:
- polysaccharide made of alpha-glucose
- amylose - 1,4 glycosidic bonds & unbranched
- amylopectin - 1,4 & 1,6 glycosidic bonds & branched

Question 8

How does structure of starch relate to its function?

Answer 8

• helical - compact for storage in cells
• large - can’t diffuse out of cells
• insoluble - doesn’t affect cell’s water potential

Question 9

What is the structure & function of glycogen?

Answer 9

function: energy store in animal cells
structure:
- polysaccharide made of alpha-glucose
- 1,4 & 1,6 glycosidic bonds - branched

Question 10

How does the structure of glycogen relate to its function?

Answer 10

• branched - more can fit in a small area & more ends for faster hydrolysis which releases glucose for respiration to produce ATP faster
• large - can’t diffuse out of cell
• insoluble - doesn’t affect cell’s water potential

Question 11

What is the structure & function of cellulose?

Answer 11

function: provides strength & structural support to plant cells
structure:
- polysaccharide made of beta-glucose
- 1,4 glycosidic bonds - straight unbranched
- chains linked in parallel by hydrogen bonds forming microfibrils

Question 12

How does the structure of cellulose relate to its function?

Answer 12

• straight unbranched chain - every other beta-glucose is inverted
• many hydrogen bonds link parallel strands forming microfibrils
• many H bonds together are very strong which provides strength to plant cell walls

Question 13

What are examples of reducing sugars & the test for them?

Answer 13

e.g. monosaccharides, maltose & lactose
1. add Benedict’s solution to sample
2. heat in boiling water bath
3. positive result produces red precipitate

Question 14

What is an example of a non-reducing sugar and the test for them?

Answer 14

e.g. sucrose
1. do Benedict’s test and stays blue
2. heat in boiling water bath with HCl
3. Neutralise with sodium hydrogen carbonate (alkali)
4. positive result produces red precipitate

Question 15

What is a method to measure the quantity of sugar in a solution?

Answer 15

• carry out Benedict’s test then filter & dry precipitate
• find the mass

Question 16

What is the biomedical test for starch?

Answer 16

1. add iodine dissolved in potassium iodide and shake
2. positive result produces blue/black colour of sample