1.1 - Monomers and polymers 1.2 - Carbohydrates

Question 1

Define monomer. Give some examples.

Answer 1

smaller units that join together to form larger
molecules
● monosaccharides (glucose, fructose,
galactose)
● amino acids
● nucleotides

Question 2

Define polymer. Give some examples.

Answer 2

molecules formed when many
monomers join together
● polysaccharides
● proteins
● DNA / RNA

Question 3

What happens in a condensation

reaction?

Answer 3

A chemical bond forms between 2
molecules & a molecule of water is
produced.

Question 4

What happens in a hydrolysis reaction?

Answer 4

A water molecule is used to break a

chemical bond between 2 molecules.

Question 5

Name the 3 hexose monosaccharides.

Answer 5

● glucose
● fructose
● galactose
all have the molecular formula C6H12O6

Question 6

Name the type of bond formed when

monosaccharides react.

Answer 6

(1,4 or 1,6) glycosidic bond
2 monomers = 1 chemical bond = disaccharide
multiple monomers = many chemical bonds =
polysaccharide

Question 7

Name 3 disaccharides. Describe how

they form.

Answer 7

condensation reaction forms glycosidic bond
between 2 monosaccharides
● maltose: glucose + glucose
● sucrose: glucose + fructose
● lactose: glucose + galactose
all have molecular formula C12H22O11

Question 8

Draw the structure of ⍺-glucose.

Answer 8

Draw the structure of
𝛼-glucose.
(OH is below)

Question 9

Draw the structure of 𝛽-glucose.

Answer 9

(OH is above)

Question 10

Describe the structure and functions of

starch

Answer 10

storage polymer of 𝛼-glucose in plant cells
● insoluble = no osmotic effect on cells
● large = does not diffuse out of cells

made from amylose:
● 1,4 glycosidic bonds
● helix with intermolecular
H-bonds = compact

and amylopectin:
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal
ends for hydrolysis into
glucose

Question 11

Describe the structure and functions of

glycogen.

Answer 11

main storage polymer of 𝛼-glucose in animal cells
( but also found in plant cells)
● 1,4 & 1,6 glycosidic bonds
● branched = many terminal ends for hydrolysis
● insoluble = no osmotic effect & does not diffuse
out of cells
● compact
w

Question 12

Describe the structure and functions of

cellulose.

Answer 12

polymer of 𝛽-glucose gives rigidity to plant cell walls
(prevents bursting under turgor pressure, holds stem up)
● 1,4 glycosidic bonds
● straight-chain, unbranched molecule
● alternate glucose molecules are rotated 180°
● H-bond crosslinks between parallel strands form
microfibrils = high tensile strength

Question 13

Describe the Benedict’s test for reducing

sugars.

Answer 13

1. Add an equal volume of Benedict’s reagent
   to a sample.
2. Heat the mixture in an electric water bath at
   100℃ for 5 mins.
3. Positive result: colour change from blue to
   orange & brick-red precipitate forms.

Question 14

Describe the Benedict’s test for

non-reducing sugars.

Answer 14

1. Negative result: Benedict’s reagent remains blue
2. Hydrolyse non-reducing sugars e.g. sucrose into their
   monomers by adding 1cm3
   of HCl. Heat in a boiling
   water bath for 5 mins.
3. Neutralise the mixture using sodium carbonate solution.
4. Proceed with the Benedict’s test as usual.

Question 15

Describe the test for starch

Answer 15

1. Add iodine solution.
2. Positive result: colour change from
   orange to blue-black.

Question 16

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

Answer 16

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