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Date May 2017 Marks available 3 Reference code 17M.2.SL.TZ1.6
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Outline Question number 6 Adapted from N/A

Question

James Beard, a famous chef, once said “Food is our common ground, a universal experience.”

Explain how the small intestine moves, digests and absorbs food.

[8]
a.

Distinguish between the structures of the different types of fatty acids in food.

[4]
b.

Outline how leptin controls appetite.

[3]
c.

Markscheme

a. contraction of muscle «layers»/peristalsis helps move food
OR
circular muscle contraction prevents backward movement of food
OR
longitudinal muscle contraction moves food along gut 

b. peristalsis/muscle contractions mix food with intestinal enzymes 

c. enzymes digest macromolecules into monomers 

Accept an example for mp c

d. pancreatic enzymes/amylase/lipase/endopeptidase «chemically» digest food in«lumen of» small intestine 

e. «pancreatic» amylase digests starch
OR
lipases digest lipids/fats/triglycerides
OR
endopeptidases/dipeptidases digest proteins/polypeptides 

f. bile/bicarbonate secreted into the small intestine creates favorable pH for enzymes
OR
bile emulsifies fat 

g. some final digestion into monomers is associated with epithelial cells/epithelium «of small intestine» 

h. mucosa layer/inside surface/lining of small intestine contains villi/finger-like projections 

i. villi/microvilli increase surface area for better absorption 

j. villi absorb products of digestion/monomers/mineral «ions»/vitamins

k. glucose/amino acids enter blood «capillaries»
OR
lipids enter lymph vessels/lacteals 

l. absorption involves active transport/diffusion/facilitated diffusion 

m. different nutrients are absorbed by different transport mechanisms

a.

a. fatty acids can be saturated or unsaturated 

b. unsaturated can be monounsaturated or polyunsaturated 

c. saturated fats have no double bonds/have maximum number of hydrogen atoms
OR
unsaturated fatty acids have «at least one» double C=C bond
OR
polyunsaturated fatty acids have more than one double bond / OWTTE 

d. cis-form has hydrogen atoms on same side of carbon double bond
OR
cis-form has bend at carbon double bond 

e. trans-form has hydrogens on opposite sides of carbon double bond
OR
trans-form makes a straight carbon chain 

f. length of hydrocarbon chain can vary
OR
position/number of carbon double bonds can vary

Accept labeled diagrams that illustrate these marking points

b.

a. leptin suppresses/inhibits appetite 

b. is secreted by adipose tissue/fat «storage» tissue 

c. level is controlled by amount of adipose tissue/«ongoing» food intake 

d. leptin targets cells in hypothalamus/appetite control centre in brain 

e. causes hypothalamus/control centre in brain to inhibit appetite 

f. if amount of adipose tissue increases, blood leptin concentration rises

c.

Examiners report

[N/A]
a.
[N/A]
b.
[N/A]
c.

Syllabus sections

Core » Topic 6: Human physiology » 6.6 Hormones, homeostasis and reproduction
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