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Question 18N.3.hl.TZ0.10

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Date November 2018 Marks available [Maximum mark: 5] Reference code 18N.3.hl.TZ0.10
Level hl Paper 3 Time zone TZ0
Command term Name, Outline Question number 10 Adapted from N/A
10.
[Maximum mark: 5]
18N.3.hl.TZ0.10

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.

(a)

Name the type of link between the two monosaccharide residues.

[1]

Markscheme

«1,4-»glycosidic ✔

 

Do not accept “glucosidic”.

(b)

Outline how the two monomer structures, galactose and glucose, differ.

[1]

Markscheme

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 and cellulose are both formed from glucose and have similar structures.

(c.i)

Outline the difference between their structures.

[1]

Markscheme

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”.

(c.ii)

Outline why cellulose is an essential part of human diet.

[2]

Markscheme

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 ✔

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