IB DP Biology Topic 6: Human physiology : 6.2 The blood system Question Bank SL Paper 2


The diagram shows the structure of the human heart.

(a) Annotate the diagram by adding arrows to show how deoxygenated blood enters the heart.

(b) Identify the blood vessel labelled X.

(c) Explain the function of the left ventricle.



(a) arrows added to the diagram to show how deoxygenated blood enters the heart;

(b) aorta;

a. contracts to generate high pressure / pumps blood at high pressure;
b. pump blood (through the aorta) to all parts of the body (apart from the
c. receives blood from the left atrium;
d. contraction is stimulated by the AV node;


Consumption of dark chocolate has been shown to have health benefits. A study was undertaken to see the effects of epicatechin (Epi), a substance in dark chocolate, on the aerobic capacity of leg muscles of mice.

A group of adult mice was used to measure the effects of a low dose of Epi given over 15 days. The mice were divided into four groups and given either water or Epi and were either kept idle (no exercise) or made to exercise on a treadmill.

After 15 days, the results were analysed. The blood capillary density in leg muscle was measured under the light microscope.

Leg muscle tension was measured over time during a treadmill exercise in all four groups. The muscle is considered to reach a point of fatigue when there is a decrease in tension to 50 % of the initial tension.

The scientists tested the expression of four different mitochondrial proteins. The protein samples were taken from leg muscles. The technique that was used to quantify the amount of protein expressed was Western blotting. In this procedure the thickness of the band is an indicator of the amount of protein.


State the significance of the statement: p<0.05.


Outline the trends in capillary density in the results of this experiment.


Describe how increased capillary density could affect the aerobic capacity of muscle.


State the time when the point of fatigue occurred in the Epi–exercise group.


Compare and contrast the results for the water–no exercise group and the Epi–no exercise group.


Discuss the effect of exercise on the results of the experiment.


Analyse the effect of exercise on the presence of the mitochondrial proteins in the leg muscle.


Mitochondria are essential for aerobic respiration. Suggest one possible role of the proteins that were studied.


The scientists concluded that Epi significantly increased aerobic capacity in leg muscle.

Evaluate the strength of the evidence provided by all of the data for dark chocolate improving the aerobic capacity of athletes.



there is a significant «statistical» difference between two experimental values
there is a less than 5 % chance that the difference is random
95 % or more probability that results are due to the experiment «IV» and not random/can reject the null hypothesis
there is a relationship/correlation between doing exercise and capillary density



a. exercise «significantly» increased the density with both water and Epi 

“both” or OWTTE must be mentioned

b. Epi «significantly» increased the density with and without exercise 

c. Epi–exercise had the greatest increase in the density
Epi increases the density more than exercise alone


a. increases amount of blood taken to the muscle 

b. increases the delivery of oxygen/glucose/nutrients for aerobic respiration 

c. increases the removal of carbon dioxide/wastes
increased gas exchange


175 «seconds»

Accept 170 to 180 «seconds».


a. in both cases the tension decreased over time  

b. Epi–no exercise lasts longer/more time until «onset of» fatigue «than water–no exercise» 

c. the rate of decrease in tension is the same/similar in both 

d. Epi–no exercise has more contractions per second before fatigue point «than water–no exercise»

Do not accept numerical comparisons without justification.


a. «exercise with» water has no impact 

b. «exercise with» Epi promotes higher levels of tension for more time 

c. «exercise with» Epi increases the time to fatigue


a. exercise has no/very little effect with water 

b. exercise with Epi increased III/IV 

c. «it appears that» exercise with Epi has no/very little effect on II
Epi relative to water increases all 4
exercise has little/no effect on protein I/II 

d. exercise with Epi «appears to» decrease I


a. protein channels
pumps in membranes of mitochondria
hormone binding sites 

b. structural/integral/peripheral/glyco/surface proteins 

c. enzymes/catalysts  

Accept verifiable names of specific membrane enzymes.

d. electron transport chain proteins



a. study done on mice and may not apply to humans 

b. levels of Epi administered in experiment may exceed levels in a sample of dark chocolate
levels of Epi administered in experiment may have different levels in a sample of dark chocolate
chocolate may have other components with unknown effects on aerobic capacity 

c. mitochondrial proteins may not improve aerobic capacity 


d. data supports as dark chocolate contains EPI 

e Epi improves capillary density and would therefore increase aerobic capacity 

f. Epi improves fatigue resistance 

g. Epi in combination with exercise improves it further 

h. Epi increases mitochondrial proteins therefore/presumably increasing aerobic capacity




The human circulatory system is structured to serve the organs and tissues of the body efficiently. 

Outline the exchange of materials between capillaries and tissues.


Explain the structures and functions of arteries and veins.


Describe what happens in alveoli.



a. molecules move by diffusion / move down a concentration gradient

b. nutrients move into tissues

c. gas exchange / Oxygen and carbon dioxide exchange between tissues and blood/capillaries

d. (nitrogenous) wastes/excess water move from cells/tissues into blood/capillaries

e. hormones leave capillaries in target tissues/to attach to receptors on cells / (endocrine) organs/gland tissues release hormones into the bloodstream


a. arteries and veins have three layers in their walls
walls of arteries and veins have tunica externa, media and intima

b. pressure is high in arteries/pressure is low in veins

c. arteries receive blood from ventricles/heart / carry blood away from heart

d. lumen of artery is small to keep pressure high

e. arteries have thick (muscular) walls (with elastic fibres) to withstand pressure

f. elastic fibres recoil in response to ventricle/heart contraction

g. muscle / elastic fibres help maintain pressure between heartbeats
muscle / elastic fibres help propel blood toward capillary beds

h. veins receive blood from capillaries/capillary beds / carry blood to heart

i. large lumen of veins so there is less resistance to blood flow

j. valves in veins keep blood flowing toward heart/prevent backflow


a. gas exchange

b. oxygen diffuses from air to blood and carbon dioxide diffuses from blood to air

c. oxygen binds to hemoglobin in red blood cells

d. pressure inside/volume of alveoli increases/decreases / air enters/exits alveoli during inspiration/expiration/ventilation

e. blood flow through capillaries / concentration gradients of gases/oxygen/CO2 maintained

f. type II pneumocytes secrete fluid/surfactant / secretion of surfactant to prevent sides of alveolus adhering

Accept answer in a clearly annotated diagram.



Draw a labelled diagram of the human heart showing the attached blood vessels.


Describe the action of the heart in pumping blood.


Nerves connecting the brain and heart contain neurons that control heart rate.  Explain how a nerve message passes from one neuron to another neuron.



Remember, up to TWO “quality of construction” marks per essay.

NBDrawings must be correctly proportioned and clearly drawn showing connections between structures. The drawing may show the heart without contraction or in any stage of contraction. Award [1] for any correctly labelled part that has been drawn to the stated standards.
a. atria/right atrium/left atrium – shown above the ventricles and must not be bigger than ventricles;
b. ventricle/left ventricle/right ventricle – shown below the atria, must have thicker walls than atria;
c. vena cava/superior vena cave/inferior vena cava – connected to right atrium;
d. pulmonary artery – shown from right ventricle (to lungs);
e. pulmonary vein(s) – shown (from lungs) to left atrium;
f. aorta – shown as large artery from left ventricle out of heart;
g. AV valves/atrioventricular valves / mitral/bicuspid and tricuspid – named correctly and shown between both atria and ventricles and labelled at least on one side;
h. semilunar valves – shown in aorta/pulmonary artery;
Valves need to open in correct direction.


Remember, up to TWO “quality of construction” marks per essay.

a. (both) atria collect blood (from veins);
b. sinoatrial/SA node sends impulses to muscle/fibres initiating contraction;
c. blood is pushed to ventricles by contraction of atria/atrial systole;
d. AV (atrioventricular) valves are open (as atria contract);
e. semilunar valves are closed so that ventricles fill with blood;
f. ventricles contract / ventricular systole;
g. AV (atrioventricular) valves close (and preventing backflow);
h. blood is pushed out through the semilunar valves/into pulmonary artery and aorta;
i. when ventricles relax/diastole, semilunar valves close preventing backflow of blood;
Do not accept the description of blood flow without a clear action.
Do not accept general statements such as systole = heart contraction and diastole = heart relaxation.

[4 max] if suggests that left and right sides are contracting at different times or simultaneous contraction not indicated.


Remember, up to TWO “quality of construction” marks per essay.

a. nerve impulse reaches the end of the presynaptic neuron;
b. (depolarization causes) calcium channels in membrane (to) open;
c. calcium diffuses into the presynaptic neuron;
d. vesicles of/containing neurotransmitter move to and fuse with presynaptic membrane;
e. (neurotransmitter) released (by exocytosis) into synaptic space/cleft;
f. (neurotransmitter) diffuses across the space/synapse;
g. (neurotransmitter) attaches to receptors on postsynaptic neuron;
h. receptors cause ion channels to open and sodium diffuses into the postsynaptic neuron;
i. the postsynaptic neuron membrane is depolarized;
j. (depolarization) causes a new action potential;
k. (neurotransmitter) on postsynaptic membrane is broken down;
l. (neurotransmitter) is reabsorbed into the presynaptic neuron;



Humans ingest food which provides energy and nutrients to carry out life processes.

(a) Outline how starch in the diet is modified for absorption in humans.[3]

(b) Describe how the small intestine is adapted for efficient absorption of nutrients.[5]

(c) Blood transports nutrients to all tissues of the body. Explain the initiation of the heartbeat and how blood flow is controlled in the heart.[7]


a a. starch is broken down by the enzyme amylase;
b. (amylase) secreted by the pancreas/salivary glands;
c. acts in the duodenum/small intestine/mouth;
d. starch is broken down into monomers/maltose/glucose;
e. products of digestion are smaller/more soluble molecules for absorption

b a. small intestine is very long;
b. small intestine contains villi/microvilli;
c. the epithelial cells of villi have microvilli
d. these increase the surface area for absorption;
e. the cells of the small intestine contain (a large number of) mitochondria;
f. these provide energy for active transport;
g. the walls contain proteins for active transport/ facilitated diffusion
h. the villi have a rich blood supply/ lacteals;
i. the walls of the villi are thin so less distance for diffusion;

c a. the contraction of the heart is myogenic / heart beat initiates within the heart tissue itself;
b. heart beat initiates in the sinoatrial node
SA acts as a pacemaker;
c. the SA node is located in the right atrium;
d. electrical impulses pass over the atria then the ventricles;
e. nerves from the medulla can control the rate of heart beat/ blood flow;
f. epinephrine/adrenaline can increase the rate of the heart/blood flow;
g. contraction of heart/cardiac muscle causes blood to flow;
h. ventricles send blood to the organs/cells of the body
i. the direction of flow is controlled by valves/valves prevent backflow
when the heart/named chamber contracts the valves/named valve open.
j. AV valves prevent backflow from ventricles/into atria
k. semilunar valves prevent blood returning/backflow to the heart/ventricles

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