| Date | November 2018 | Marks available | 1 | Reference code | 18N.3.hl.TZ0.10 |
| Level | HL | Paper | 3 | Time zone | TZ0 |
| Command term | Outline | Question number | 10 | Adapted from | N/A |
Question
Lactose, found in milk and dairy products, is a disaccharide formed from two different monosaccharides. The structure of lactose is shown with numbered carbon atoms.
Starch and cellulose are both formed from glucose and have similar structures.
Name the type of link between the two monosaccharide residues.
Outline how the two monomer structures, galactose and glucose, differ.
Outline the difference between their structures.
Outline why cellulose is an essential part of human diet.
Markscheme
«1,4-»glycosidic ✔
Do not accept “glucosidic”.
H and OH are reversed/in different positions on C-4 ✔
C-4 must be specified.
Do not penalize if reference is made to H and OH above and below ring/in alpha and beta positions on C-4 incorrectly.
Starch: α«-glucose/links»
AND
Cellulose: β«-glucose/links» ✔
Accept “Starch: coiled/spiral structure OR cross-links AND Cellulose: uncoiled OR straight chains/linear polymer OR no/few cross-links”.
Any two of:
helps food pass through intestine
OR
adds bulk/dietary fibre ✔
reduces appetite
OR
helps prevent obesity ✔
prevents constipation
OR
reduces risk of hemorrhoids/diverticulosis/Crohn’s disease/irritable bowel syndrome/bowel cancer ✔
