Carbohydrates

Question 1

Polymer

Answer 1

Chains of repeating monomer units

Question 2

Monosaccharides (monomers)

Answer 2

Sweet tasting, soluble substances
E.g. Glucose
Monosaccharides join by together by condensation reactions and forms a glycosidic bond.

Question 3

Disaccharides (polymers)

Answer 3

Two monosaccharides joined
E.g. a glucose + a glucose = maltose
Can break into monosaccharides by adding water (hydrolysis reaction) and breaks glycosidic bonds

Question 4

Polysaccharide

Answer 4

Many monomers joined in condensation reactions
Insoluble - good for storage
E.g. Starch
Can break into monosaccharides by adding water (hydrolysis reaction) and breaks glycosidic bonds

Question 5

Common disaccharides

Answer 5

Maltose (a glucose + a glucose)
Sucrose (a glucose + fructose)
Lactose (a glucose + galactose)

Question 6

Monomers

Answer 6

Individual molecules

Question 7

Reducing sugars

Answer 7

All monosaccharides and some disaccharides.
Can donate electrons (reduce) other chemicals
E.g. Maltose, glucose

Question 8

Non-reducing sugars

Answer 8

The other disaccharides and all polysaccharides.
Can’t donate electrons.
E.g. Sucrose

Question 9

Test for reducing sugar

Answer 9

Add Benedict’s reagent and heat

Turns red/orange/yellow/green

Question 10

Test for non-reducing sugar

Answer 10

Add Benedict’s and heat, it will remain blue
Add hydrochloric acid, which hydrolyses it
Add sodium hydrogen carbonate sodium to neutralise the HCl
Then do the test for a reducing sugar

Question 11

Test for starch (polysaccharide)

Answer 11

Add iodine solution

Turns blue/black

Question 12

Viking tubing experiment

Points to consider:

Answer 12

Protein molecules are too large to pass through the tubing
Starch molecules pass through tubing
Once starch is hydrolysed to maltose it can pass through the tubing

Question 13

Starch (made of a glucose chains)

Answer 13

Branched / coiled / alpha helix, so makes the molecule compact and can fit into a small space.
It is insoluble so it stops osmosis and doesn’t affect water potential.
A long chain so it can’t cross the cell membrane.
It’s a polymer of alpha glucose so provides glucose for respiration.
Branched so glucose is easily released in respiration (means more ends for enzyme action)
Monomers linked by glycosidic bonds through condensation reactions.

Question 14

Cellulose (B glucose chains)

Answer 14

Gives the cell strength because:
Long, unbranched (straight) chains of B glucose
Several chains lie side by side and form micro fibrils
Hydrogen bonds hold these chains together
Hydrogen bonds are strong in large numbers
Cellulose only has 1,4-glycosidic bonds

Question 15

Glycogen (alpha glucose chains)

Answer 15

Shorter, more branched chains than starch
Can be hydrolysed to monomers more easily (quicker energy)
Spiral shape means it’s more compact and can fit into a small space
Coiled as opposed to straight
Glycogen has 1,4 and 1,6-glycosidic bonds

Question 16

Using a calibration curve to find a sugar, concentration

Answer 16

Make different known sugar concentrations
Use a colorimeter to measure the absorbance of each concentration and plot calibration curve on a graph
Find concentration of sample from calibration curve
You may be given data points plotted on a graph, you would have to draw a line of best fit to then read off to determine the value.