3.1.1 monomers/polymers and 3.1.2 carbohydrates

Question 1

define monomer

Answer 1

smaller units that join together to form larger molecules

Question 2

examples of monomers

Answer 2

• monosaccharides e.g. glucose, fructose, galactose
• nucleotides
• amino acids

Question 3

define polymer

Answer 3

molecules formed when many monomers are joined together

Question 4

polymer examples

Answer 4

• polysaccharides
• proteins
• DNA/RNA

Question 5

What happens in a condensation reaction?

Answer 5

joins two molecules together with the formation of a chemical bond, and involves the elimination of a water molecule

Question 6

what happens in a hydrolysis reaction?

Answer 6

a water molecule is used to break a chemical bond between two molecules

Question 7

name the 3 hexose monosaccharides

Answer 7

• glucose
• fructose
• galactose
  all of the above are energy sources and have the molecular formula C6,H12,O6

Question 8

name the type of bond formed when monosaccharides react

Answer 8

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

Question 9

name 3 disaccharides an describe how they form

Answer 9

-condensation reaction forms glycosidic bond between 2 monosaccharides
- maltose = glucose +glucose
- sucrose = glucose + fructose
- lactose = glucose + galactose
-all have molecular formula C12,H22,O11

Question 10

alpha glucose and beta glucose

Answer 10

• isomers of each other
• alpha glucose =OH group is below carbon 1
• beta glucose = OH group is above carbon 1

Question 11

describe structure/functions of starch (1)

Answer 11

• storage polymer of alpha glucose in plant cells
• insoluble = no osmotic effect on cell
• large = doesn’t diffuse out of cells

Question 12

describe structure/functions of starch (2)

Answer 12

• made from amylose
• 1,4 glycosidic bonds
• helix with intermolecular H bonds = compact

Question 13

describe structure/functions of starch (3)

Answer 13

• made from amylopectin
  
  • 1,4 and 1,6 glycosidic bonds
  • branched = many terminal
    ends for hydrolysis into glucose

Question 14

describe the structure and functions of glycogen

Answer 14

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

Question 15

describe the structure and functions of cellulose

Answer 15

polymer of beta 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 degrees
- H bond crosslinks between parallel strands from microfibrils = high tensile strength

Question 16

describe the benedict’s test for reducing sugars

Answer 16

• add an equal volume of benedict’s reagent to a sample
• heat the mixture in an electric water bath at 100 degrees C for 5 mins
• positive result = colour change from blue to brick red

Question 17

describe the benedict’s test for non reducing sugars

Answer 17

• negative result = benedict’s reagent remains blue
• hydrolyse non reducing sugars e.g. sucrose into their monomers by adding 1cm^3 of HCl. Heat in boiling water bath for 5 minutes
• neutralise the mixture using sodium carbonate solution
• proceed with the benedict’s test as usual

Question 18

describe the test for starch

Answer 18

• add iodine solution
• positive result = colour change from orange to blue/black

Question 19

outline how colorimetry can be used to give qualitative results for the presence of sugars and starch

Answer 19

• make standard solutions with known concentrations. record absorbance or % transmission values
• plot calibration curve : absorbance or % transmission (y axis), concentration (x axis)
• record absorbance or % transmission values of unknown samples. Use calibration curve to read off concentration