1. Award [1] for every two correct.
Enzyme
Source
Optimum pH
Amylase
Salivary
gland
7
Lipase
Pancreas;
Allow any pH in
range 7–9
Substrate
Products
starch/amylose/ maltose/short
glycogen;
polysaccharides
/disaccharides
/dextrin;
Lipids
Fatty acids and
glycerol
2 max
2.
a. The rate of digestion at body temperature would be too slow / enzymes
increase the rate of digestion;
b. Enzymes help break large molecules down into small/soluble molecules for
absorption/diffusion into blood and assimilation in the body;
2 max
3. labelled sac-shaped gall bladder with a duct;
tubule/(bile) duct shown connecting gall bladder directly to small
intestine/duodenum / tubule/(bile) duct merging with the pancreatic
duct before entering small intestine; Alternative answers are
accepted because of variations in human anatomy.
pancreas drawn with pancreatic duct connected to small intestine
and pancreas labelled;
A duct is preferred to a line, but since this is a diagram, both are acceptable.
3
[7]
4. To achieve [1] answer must name the structure and relate it to its function.
a) the villus has a large surface area to volume ratio;
b) The epithelial cells of the villus have microvilli which increase surface area for
absorption;
c) The villus is lined with a thin surface (epithelial) layer so products of digestion can pass
easily through;
d) The cells membranes of the epithelial cells have channel proteins used for facilitated
diffusion;
e) Each villus has a network of capillaries inside each villus (so only short distance) for
movement of absorbed products;
f) The villus capillaries transport absorbed nutrients/sugars and amino acids away from
small intestine;
g) The blood flow in capillaries in the villus maintains concentration gradient between the
epithelial cells and the lumen of the small intestines and the blood plasma and the
epithelial cells;
h) The villus contain central lymph vessel/lacteal to transport absorbed fats/fatty acids
away from small intestine;
i) The epithelial cells of the villus have a large number of mitochondria provide ATP
needed for active transport;
j) The epithelial cells of the villus have protein pumps in membrane (of microvilli) carry out
active transport;
k) pinocytosis occurs at surface (epithelial) layer;
Accept any of the points above shown in a drawing.
IB Questionbank Biology
1
5.
Gastric juice
Pancreatic juice
produced by glands in stomach wall
produced by pancreas;
low pH / acidic
high pH / alkaline;
contains hydrochloric acid
contains HCO3–;
pepsinogen
trypsinogen;
no enzymes for lipid/starch digestion
lipase/amylase;
contains mucus
no mucus;
both contain protease;
Award [1] for each pair.
6. cellulose / lignin;
cellulase not present / no enzymes for digesting lignin;
Accept any other reasonable substance.
3 max
2
[7]
7. (a)
I.
II.
III.
hepatic cells / hepatocytes / liver cells / liver tissue;
hepatic vein / blood cells;
sinusoids;
3
(b) Award [1] for two of the following.
cellulose / lignin / bile pigments / bacteria / intestinal cells
Do not accept fibre.
1
IB Questionbank Biology
2
8.
a. erythrocytes rupture when they reach the end of their life span / after 120 days;
b. erythrocytes are absorbed by phagocytosis
of
the Kupffer cells in liver from blood;
c. hemoglobin from the erythrocytes is split into globin and heme groups;
d. iron is removed from heme leaving bile pigment / bilirubin;
e. bilirubin/ bile pigment released into alimentary canal for lipid digestion;
f.
The digestion of globin produces amino acids;
9.
a. Amino acids are actively transported from the lumen of the small intestine to the
epithelial cells of the ileum:
b. This active transport is against the concentration gradient and requires ATP and
protein pumps/transport proteins;
c. Amino acid will pass from the epithelial cells to the capillaries via simple diffusion:
passive diffusion requires no ATP and moves along the concentration gradient and
through protein channels; This concentration gradient is maintained by the transfer of
blood away from the small intestines via the blood vessels.
(b)
1. Prolonged and excessive drinking can cause damage to the liver cells
2. Damage to the liver from alcohol abuse includes inflammation (Hepatitis), fatty liver and
cirrhosis;
3. Damage to the liver is caused by the metabolism of alcohol, because the products of
alcohol metabolism are toxic to the liver cells.
4. Healthy Liver Cells that are damaged by the products of alcohol metabolism are replaced
of with fibrous/scar tissue and fatty liver cells;
5. This fibrous/ scar tissue of the liver blocks blood flow through liver.
6. Fatty liver cells and fibrous/ scar tissue of the liver blocks normal liver metabolism of
carbohydrates/fats/proteins;
7. Livers with a build up of fatty liver cells and fibrous/ scar tissue have a decreased ability
to remove toxins (through bile)/produce bile/ produce blood proteins/ store nutrients
(e.g. vitamin D, Iron, Glycogen, Vitamin A);
8. A damaged liver can cause malnutrition and make people more susceptible to infection
and hepatic viruses;
IB Questionbank Biology
3
10.
a. H. pylori is a bacterium which causes gastritis.
ulcers, stomach tumours and stomach cancer
H. pylori has been linked to stomach
b. Stomach ulcers are open sores in the stomach wall;
c. Prolonged presence of
stomach ulcers may lead to the formation of tumours;
d. Cancer of the stomach is a malignant tumour in the stomach wall;
e. About 80% of gastric ulcers are caused by H. pylori;
f.
H. pylori survives in the stomach mucosa;
g. H. pylori produces urease;
h. Urease neutralizes gastric acid;
i.
The neutralization of gastric acid allows for the colonization by H. pylori, and this
colonization opens up/weakens the (protective) (mucosal/mucus) lining;
j.
The weakened mucous lining o the stomach allows for digestive attack by gastric
acid/HCl causing ulcers;
k. The linking of H. pylori to stomach ulcers was a paradigm shift in medicine;
l.
The cause of ulcers was previously thought to be stress/lifestyle/diet;
m. H. pylori is now thought to be primary cause
infectious disease with antibiotics;
and can now be treated as
11.
a.
b.
c.
d.
9.
Pepsin cannot be released in its active form because it could digest the cells that secrete it;
So pepsinogen is released and it is the inactive form of pepsin;
pepsinogen is activated by hydrochloric acid / HCl / pepsinogen is converted into pepsin
(active form) by HCl;
In order to avoid activating pepsinogen inside the secretory cells, different cells in the stomach
wall secrete pepsinogen and HCl;
(a)
0.13 (pH min–1) (Allow values between 0.125 and 0.135)
(b)
(DIDS) reduces the rate of decrease of (extracellular) pH;
rate of decrease reduced less than control cells / some SCL26A9
are not inhibited;
1
1 max
(c)
The hypothesis supported because SCL26A9 in excess means more
transport of ions and more neutralization of extracellular membrane;
The hypothesis supported because when SCL26A9 is inhibited there is less transport
of ions needed to maintain neutral pH;
2
(d)
The host cell is trying to maintain its ability to decrease pH. The host cell does this by
increasing the gene expression of the SCL26A9 gene, and thus increasing transcription
(DNA to mRNA) and protein synthesis (translation/ mRNA to amino acids) of protein
SLC26A9. The host cell increases the amount of this membrane proteins to transport
ions and neutralize extracellular environment.
1
IB Questionbank Biology
4