1.1 - Monomers & Polymers, 1.2 - Carbohydrates

Question 1

Define ‘monomer’

Answer 1

Monomers are smaller units that join together via condensation reactions to form larger molecules.

Question 2

Give some examples of monomers

Answer 2

-monosaccharides (glucose, fructose, galactose)
-amino acids
-nucleotides

Question 3

Define ‘polymer’

Answer 3

Polymers are molecules which are formed when many monomers join together through condensation reactions.

Question 4

Give some examples of ‘polymers’

Answer 4

-polysaccharides
-proteins
-DNA
-RNA

Question 5

What happens in a condensation reaction?

Answer 5

A chemical bond forms between 2 molecules
A water molecule is released

Question 6

What happens in a hydrolysis reaction?

Answer 6

The breaking of a chemical bond between molecules using a water molecule.

Question 7

Name the 3 hexose monosaccharides.

Answer 7

Glucose, fructose and galactose

Question 8

What is the formula of all 3 hexose monosaccharides

Answer 8

C6 H12 06

Question 9

Name the type of bond formed when monosaccharides react.

Answer 9

Glycosidic bond
Usually between 1,4 or 1,6

Question 10

What is a disaccharide?

Answer 10

2 monosaccharides joined together by the formation of a glycosidic bond in a condensation reaction.

Question 11

What is a polysaccharide?

Answer 11

Multiple monosaccharides joined together by many glycosidic bonds through many condensation reactions.

Question 12

Name 3 disaccharides

Answer 12

Maltose, sucrose and lactose

Question 13

How is maltose formed?

Answer 13

Maltose is composed of 2 alpha glucose molecules joined together by a glycosidic bond through a condensation reaction.

Question 14

How is sucrose formed?

Answer 14

Sucrose is composed of a glucose and a fructose molecule joined by a glycosidic bond through a condensation reaction.

Question 15

How is lactose formed?

Answer 15

Lactose is composed of a glucose and a galactose molecule joined by a glycosidic bond through a condensation reaction.

Question 16

What is the chemical formula of all 3 disaccharides (maltose, sucrose + lactose)?

Answer 16

C12 H 22 011

Question 17

Describe the structure and functions of starch

Answer 17

Polymer of alpha glucose in plant cells
It is insoluble, so has no osmotic effect on cells
It is large so doesn’t diffuse out of cells
It is made of amylose - a long unbranched chain of alpha glucose, attached by 1,4 glycosidic bonds giving it a helical structure = compact, so good for storage
It is also made of amylopectin - a long branched chain of alpha glucose, attached by both 1,4 and 1,6 glycosidic bonds. Branched = many ends for hydrolysis into glucose (quick release of energy)

Question 18

Describe the structure and functions of glycogen

Answer 18

Main storage polymer of alpha glucose in animal cells (also found in plant cells)
1,4 & 1,6 glycosidic bonds
Highly branched = many ends for hydrolysis
Insoluble = no osmotic effect & doesn’t diffuse out of cells
Compact

Question 19

Describe the structure and functions of cellulose

Answer 19

Major component of cell walls in plant cells
Polymer of beta glucose
Gives plant cell walls rigidity, preventing them from bursting under turgor pressure & holds stem up
1,4 glycosidic bonds
Straight-chain (unbranched)
Chains linked together parallel by hydrogen bonds to form strong fibres called microfibrils

Question 20

Describe the Benedict’s test for reducing sugars

Answer 20

Add an equal volume of Benedict’s reagent (which is blue) to sample
Heat in a water bath that has been brought to the boil for approximately 5 mins
If positive: green, yellow, orange or brick-red precipitate forms

Question 21

What can a Benedict’s test tell us about the concentration of reducing sugars?

Answer 21

The higher the concentration, the further the colour change (green > yellow > orange > brick-red)
To compare volume of reducing sugars in different samples, filter, then weigh the precipitate.

Question 22

Describe the Benedict’s test for non-reducing sugars.

Answer 22

If you obtain a negative result from the initial Benedict’s test for reducing sugars then…
Get a new sample of the test solution
Add dilute hydrochloric acid
Heat in a water bath that has been brought to the boil for approximately 5 mins, in order to break down sugars into monosaccharides
Neutralise sample with sodium hydrogencarbonate
Then carry out the Benedict’s test as usual

Question 23

Give examples of reducing sugars

Answer 23

All monosaccharides (e.g. glucose)
And some disaccharides (e.g. maltose and lactose)

Question 24

Describe the test for starch

Answer 24

Add iodine dissolved in potassium iodine solution to test sample
If present, sample changes from browny-orange to a dark blue-black

Question 25

Outline how colorimetry could be used to give qualitative results for the presence of sugars and starch.

Answer 25

1) Make standard solutions with known concentrations
Record absorbance or % transmission values
2) Plot calibration curve: concentration (x-axis) & absorbance or % transmission (y-axis)
3) Record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration.