IB DP Physics Option D: Human physiology (Core topics) :D.2 Digestion HL Paper 3

Date	May 2017	Marks available	3	Reference code	17M.3.HL.TZ2.20
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Outline	Question number	20	Adapted from	N/A

Question

Outline how infection by Vibrio cholerae can lead to dehydration.

Markscheme

a. V. cholerae produces toxin

b. «toxin» causes ions to be pumped into «small» intestine

c. drawing water into the intestine

d. through osmosis

e. leading to water loss through diarrhea/vomiting
OR
leading to dehydration

Date	May 2017	Marks available	2	Reference code	17M.3.HL.TZ1.21
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Explain	Question number	21	Adapted from	N/A

Question

The graph below shows the oxygen dissociation curve at a low CO2 concentration.

Outline the main changes in the lungs that occur in patients with emphysema.

[2]

a.i.

State a treatment for emphysema.

[1]

a.ii.

An increase in metabolic activity results in greater release of CO2 into the blood. On the graph, draw the oxygen dissociation curve during intense exercise when the CO2 concentration of the blood is high.

[1]

b.i.

Explain how the increase in CO2 concentration affects the release of oxygen to respiring cells.

[2]

b.ii.

Markscheme

a. air sacs/alveoli break down/rupture

b. creating one larger air space instead of many small ones / reduces the surface area of the lungs

c. loss of elasticity of lung tissue

a.i.

supplemental oxygen / breathing techniques / bronchodilators / inhaled steroids / lung surgery to remove damaged tissue / lung transplant

a.ii.

curve has to be towards the right and starting together

Must start together but can finish slightly below the original curve.

b.i.

a. increased levels of CO2 lower the pH of the blood

b. «which results in» decreased affinity of the hemoglobin for oxygen / greater release of oxygen

c. this shifts the oxygen dissociation curve to the right/Bohr shift

b.ii.

Date	May 2017	Marks available	1	Reference code	17M.3.HL.TZ1.18
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	State	Question number	18	Adapted from	N/A

Question

Cells on the surface of intestinal villi have microvilli, which provide a large surface area for absorption. State another structural characteristic of these villus cells that adapts them to the absorption of nutrients.

Markscheme

a. tight junctions

b. protein channels / membrane pumps

c. large number of mitochondria

Date	May 2016	Marks available	3	Reference code	16M.3.HL.TZ0.20
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Explain	Question number	20	Adapted from	N/A

Question

The graph shows the length of time that the content of a meal takes to pass through the gut as a function of digestible matter content. The more digestible matter present in the meal, the lower the dietary fibre content.

Estimate the mean residence time of a meal with 50 % digestible matter.

[1]

Explain the relationship between percentage of digestible matter and mean residence time.

[3]

Markscheme

38 hours

Accept 38 hours to 40 hours. Units required.

Higher digestible matter content, longer residence time

Slower movement/peristalsis due to lack of fiber

Fiber/indigestible material attracts water to feces/lumen/intestinal contents

More digestible material increases water absorption «into large intestine»

Hardens stool/constipation and further increases residence time

Date	May 2015	Marks available	1	Reference code	15M.3.HL.TZ1.14
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	State	Question number	14	Adapted from	N/A

Question

State one mechanism the ileum uses to absorb digested food into the bloodstream.

[1]

a (i).

State the role of the hepatic portal vein.

[1]

a (ii).

Label the line that represents the ventricle.

[1]

b (i).

Estimate the total time the atrioventricular valves are open.

[1]

b (ii).

Although some CO2 entering the blood simply dissolves in the plasma, most enters the erythrocytes (red blood cells).

Outline how CO2 interacts with hemoglobin once it enters erythrocytes.

[1]

c (i).

Describe the formation of HCO3– in erythrocytes.

[2]

c (ii).

Markscheme

active transport/facilitated diffusion/endocytosis

a (i).

transports blood from (capillaries of) small intestine to (capillaries/sinusoids of) liver

a (ii).

label should connect to solid line on graph.
Candidates should not use region with overlap of dotted and solid lines.

b (i).

0.4 (s) (allow 0.38 to 0.43)

b (ii).

CO2 attaches to protein portion (not Fe) in heme/carbaminohemoglobin formed;

c (i).

a. CO2 diffuses into erythrocytes;
b. joins water to form carbonic acid/H2CO3;
c. catalyzed by carbonic anhydrase (inside erythrocytes);
d. H2CO3 dissociates into H+ and HCO3–;

c (ii).

Date	May 2015	Marks available	2	Reference code	15M.3.HL.TZ2.14
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Identify	Question number	14	Adapted from	N/A

Question

The electron micrograph shows the epithelial cells of the villus.

Identify the parts labelled I and II.

I: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
II: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Markscheme

a. I: microvilli;
b. II: tight junction / plasma membrane;

Date	May 2013	Marks available	2	Reference code	13M.3.HL.TZ1.13
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Outline	Question number	13	Adapted from	N/A

Question

Distinguish between the mode of action of steroid and peptide hormones.

[2]

Outline the control of gastric juice secretion.

[2]

Markscheme

a. peptide hormones do not enter the cell whereas steroid hormones do;
b. peptide hormones bind to a cell surface receptor whereas steroid hormones bind to a receptor in the cytoplasm;
c. peptide hormones act through a secondary messenger/cAMP whereas steroid hormones have (direct) effect on DNA;
d. steroid hormones have effect on gene transcription whereas peptide hormones change activities of cell/influence enzyme activity;

a. involves both nerve impulses and the hormone gastrin;
b. sight/smell of food causes nerve impulses to be sent/reflex action;
c. food in stomach stimulates touch receptors/chemoreceptors/stretchreceptors releasing more gastric juice;
d. stretching of stomach wall stimulates secretion of the hormone gastrin;

Date	May 2011	Marks available	1	Reference code	11M.3.HL.TZ1.13
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Calculate	Question number	13	Adapted from	N/A

Question

Helicobacter pylori infection is a cause of stomach ulcers. It affects SLC26A9, which is a membrane protein present in the epithelial lining of the stomach. SLC26A9 takes part in the reversible transport of chloride and hydrogen carbonate ions into and out of the epithelial cells in order to raise the pH at the membrane to neutral levels. Entry of chloride ions into epithelial cells and removal of hydrogen carbonate ions both cause extracellular pH to increase.

To assess the function of SLC26A9, this process was reversed by artificially raising the external pH. The rate of change of extracellular pH was measured with normal epithelial cells and with modified cells with extra SLC26A9. The tests were also performed in the presence of DIDS, an inhibitor of SLC26A9.

Calculate the difference in the rate of decrease of pH between the control cells and the modified cells without DIDS.

……………… pH min–1

[1]

State the effect of DIDS on the rate of decrease of the extracellular pH.

[1]

Scientists hypothesized that Helicobacter pylori alters the ability to maintain neutral pH at the epithelial cell surface by inhibition of SLC26A9. Evaluate this hypothesis.

[2]

In further experiments, scientists observed that the levels of mRNA of SLC26A9 increased in epithelial cells when infected by Helicobacter pylori. Suggest a possible explanation for this increase.

[1]

Predict, with a reason, the effect of DIDS on stomach pH if given to an experimental subject.

[2]

Markscheme

0.13 (pH min−1) (Allow values between 0.125 and 0.135)

(DIDS) reduces the rate of decrease of (extracellular) pH;
rate of decrease reduced less than control cells / some SCL26A9 are not inhibited;

(hypothesis supported as) SCL26A9 in excess means more transport of ions;
(hypothesis supported as) when inhibited there is less transport of ions (needed to maintain neutral pH);

host cells increase transcription/ protein synthesis to make more carriers

pH will fall;
SLC26A9 transports less chloride/hydrogen carbonate ions;

Date	May 2012	Marks available	1	Reference code	12M.3.HL.TZ1.14
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	List	Question number	14	Adapted from	N/A

Question

In healthy adults, there are heart sounds during the cardiac cycle. Outline the causes of two of these sounds.

[2]

State two products resulting from the breakdown of erythrocytes (red blood cells) in the liver.

1. …………………………………………………………

2. …………………………………………………………

[2]

Compare gastric juice and pancreatic juice.

[3]

List one material that is egested after human digestion.

[1]

Markscheme

changing pressure of blood in heart automatically opens and closes the valves / the closing of valves generates the heart sounds;
first heart sound (S1) is produced by the closing of the AV valves/mitral and tricuspid valves;
second heart sound (S2) produced by the closing of semilunar valves/aortic and pulmonary valves;

iron;
bile pigments/bilirubin;
globin/amino acids;

Award [1] for each correct row.

cellulose / lignin / bile pigments / intestinal cells / bacteria

Date	May 2012	Marks available	6	Reference code	12M.3.HL.TZ2.15
Level	Higher level	Paper	Paper 3	Time zone	Time zone 2
Command term	Explain	Question number	15	Adapted from	N/A

Question

Explain the mechanisms used by the ileum to absorb and transport food.

Markscheme

absorption occurs through epithelial cells on villi/tiny projections;
microvilli/brush border on cell membrane increase surface area;
tight junctions prevent leakage of nutrients;
lipids/fat soluble/non-polar substances diffuse across membranes;
converted into tryglicerides / coated with proteins to form chylomicrons/lipoproteins;
which enter into lacteals/lymphatic system by exocytosis;
fructose/hydrophilic food enters by facilitated diffusion/through channel proteins;
active transport requires ATP (from many mitochondria in cells) / against concentration gradient through pump proteins;
e.g. glucose/amino acids/minerals enter through co-transported sodium carriers;
endocytosis of large molecules (e.g. vitamin B12) / pinocytosis of liquids;
capillaries (close to epithelial cells) transport substances (to body via bloodstream);

Date	May 2010	Marks available	2	Reference code	10M.3.HL.TZ1.14
Level	Higher level	Paper	Paper 3	Time zone	Time zone 1
Command term	Outline	Question number	14	Adapted from	N/A

Question

Define hormones.

[1]

a (i).

State one type of hormone, giving an example.

[1]

a (ii).

Compare gastric juice and pancreatic juice.

[3]

Outline the reason for one named substance found in food not being digested and absorbed by humans.

[2]

Markscheme

chemical messengers secreted by endocrine glands/specialized cells directly into the blood/body fluid (and transported to specific target cells);

a (i).

steroid hormone e.g. testosterone / peptide hormone e.g. insulin / tyrosine derivatives e.g. thyroxine;

a (ii).

Award [1] for each pair.

cellulose / lignin;
cellulase not present / no enzymes for digesting lignin;
Accept any other reasonable substance.

Date	November 2011	Marks available	2	Reference code	11N.3.HL.TZ0.14
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Outline	Question number	14	Adapted from	N/A

Question

The diagram below shows a section through the ileum.

Outline two important structural features of cell X.

[2]

a (ii).

Explain the role of bile in lipid digestion.

[2]

Explain why trypsin is initially synthesized as an inactive precursor and how it is activated.

[3]

Markscheme

microvilli/brush border to increase surface area;
enzymes (peptidases and disaccharase) bound to membranes (of microvilli) to complete hydrolysis/digestion;
tight junctions separate fluid of intestinal lumen from intercellular fluid/ impermeable barrier;
large number of mitochondria as high energy demand for active transport;
pinocytotic vesicles formed by endocytosis/uptake of fluid with products of digestion;

a (ii).

bile contains bile salts (and pigments);
bile salt molecules have both a hydrophilic and hydrophobic end;
reduces size of fat/lipid globules / emulsifies fats;
causes increase in total surface area so acted on more effectively by enzyme (lipase);

trypsin is protein-digesting enzyme/protease;
trypsinogen is inactive form produced by pancreas;
produced in inactive form to prevent it digesting cells of pancreas;
converted to active form trypsin in small intestine by enterokinase/ enteropeptidase;
enterokinase/enteropeptidase secreted by intestinal mucosa/wall of small intestine;

Date	November 2011	Marks available	1	Reference code	11N.3.HL.TZ0.5
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Label	Question number	5	Adapted from	N/A

Question

The diagram below shows a section through the ileum.

The diagram below shows the structure of the retina. Label I and II.

[1]

a (i).

Label I and II.

[1]

a (i).

Distinguish between rods and cones.

[2]

a (ii).

Outline the pupil reflex.

[2]

Discuss the use of the pupil reflex in testing for brain death.

[3]

Markscheme

I: ganglion cell
II: bipolar cell/neuron
(both needed)

a (i).

I: lacteal
II: longitudinal/smooth muscles / muscularis mucosa
(both needed)

a (i).

To award [2 max] responses need to be compared.
Responses do not need to be shown in a table format.

a (ii).

rapid unconscious response to change in light intensity / controls amount of light entering eye to prevent damage to retina/to see in darkness;
in bright light circular muscles in iris contract causing pupil to constrict / in dim light longitudinal/radial muscles in iris contract causing pupil dilation;
constriction by parasympathetic NS / dilation by action of sympathetic NS;

pupil reflex is a brain stem reflex / shows activity in the medulla oblongata;
pupil reflex must be absent in brain death;
pupil reflex is possible in coma victims where motor function is absent;
pupil reflex alone not enough to diagnose brain death;
other criteria include coma/absence of response to pain in all extremities/ absence of brain stem reflexes/lack of respiratory movements;
some cases of coma irreversible / some cases may recover;
doctors need to diagnose damage to decide treatment/long-term life support /organ donation;

Date	November 2009	Marks available	2	Reference code	09N.3.HL.TZ0.13
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	Calculate	Question number	13	Adapted from	N/A

Question

Helicobacter pylori is able to live inside the stomach wall of humans. This bacterium can cause inflammation of the stomach wall (gastritis). There may be a link between H. pylori and the development of stomach cancer.

The graph below shows the blood levels of antibodies resulting from H. pylori infection for a control group without stomach cancer and a group with stomach cancer. The solid lines show the median concentrations for the control group and the group with stomach cancer. Antibody concentrations above 10 μg ml–1 indicate that there has been infection with H. pylori.

47 % of the control group had been infected with H. pylori. Calculate the percentage of the group with stomach cancer that had been infected. Show your working.

[2]

Using all of the data, evaluate the hypothesis that H. pylori causes stomach cancer.

[3]

A study in gerbils indicated that infection with H. pylori leads to a decrease in the secretion of hydrochloric acid. Discuss the consequences of this finding for the digestion of proteins in the stomach in humans.

[2]

Markscheme

higher percentage of those with stomach cancer have H. pylori infection;

higher median of those with stomach cancer have H. pylori infection;

infection/high level antibodies does not mean that gastric cancer will always result / many infected did not develop gastric cancer;

not all of those with stomach cancer had H. pylori infection;

pepsinogen would not be broken down to pepsin;

pepsin would not work as well due to incorrect pH;

it is not known if humans would respond in the same way as gerbils;

Date	November 2009	Marks available	2	Reference code	09N.3.HL.TZ0.14
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	State	Question number	14	Adapted from	N/A

Question

The electron micrograph below shows cells from the intestine.

In the electron micrograph above, state the name of the

(i) structure labelled X.

(ii) type of cells labelled Y.

[2]

Define hormone.

[2]

Outline the circulation of blood through liver tissue.

[3]

Markscheme

(i) microvilli/microvillus

(ii) epithelial cell/enterocyte

chemical (messengers) secreted by (endocrine) glands;

into the blood / transported by the blood;

act on target organs/cells;

hepatic artery carries oxygenated blood;

hepatic portal vein carries blood from gut/deoxygenated blood;

blood from hepatic portal vein and hepatic artery mix;

flows through sinusoids;

hepatic vein carries blood away from liver;

Date	November 2010	Marks available	1	Reference code	10N.3.HL.TZ0.14
Level	Higher level	Paper	Paper 3	Time zone	TZ0
Command term	List	Question number	14	Adapted from	N/A

Question

Label the section of healthy liver tissue below.

II.

III.

[3]

Outline two roles of the liver.

[2]

List two materials that are not absorbed but are egested by the body.

[1]

State an example of a protein hormone.

[1]

Markscheme

I. hepatic cells / hepatocytes / liver cells / liver tissue;

II. hepatic vein / blood cells;

III. sinusoids;

a. storage of nutrients;

b. detoxification of poisons;

c. breakdown of hemoglobin;

d. production of bile pigments;

e. synthesis of plasma proteins;

f. synthesis of cholesterol;

Award [1] for two of the following.

cellulose / lignin / bile pigments / bacteria / intestinal cells

Do not accept fibre.

insulin / glucagon / prolactin / somatotrophin

Award other suitable examples.