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Date May 2019 Marks available 2 Reference code 19M.2.SL.TZ1.3
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Explain Question number 3 Adapted from N/A

Question

The diagram shows the human heart.

On the diagram, label the aorta.

[1]
a.i.

On the diagram, label the right atrium. 

[1]
a.ii.

Explain how valves control the flow of blood through the heart.

[2]
b.

Outline the causes and consequences of blood clot formation in coronary arteries.

[2]
c.

Outline the role of lymphocytes in defence against disease.

[2]
d.

Markscheme

both labelled clearly as in diagram ✔

[Source: BlueRingMedia/Shutterstock]

a.i.

both labelled clearly as in diagram ✔

[Source: BlueRingMedia/Shutterstock]

a.ii.

a. valves open and close in response to changes in blood pressure/heart contraction/pumping ✔

b. valve prevents backflow/maintains direction of blood flow ✔

c. valves allow heart chambers to fill/to empty ✔

b.

a. coronary heart disease/CHD/coronary artery disease/CAD occurs when there is reduction of oxygen to the heart muscle ✔

b. high ratio of LDL to HDL/fatty diet leads to plaque formation in arteries ✔

c. plaque breaks off causing damage that activates blood clot formation ✔

d. clots «in the bloodstream» may block a coronary artery/coronary thrombosis reducing blood flow/oxygen
OR
clots can cause heart attack/muscle death ✔

e. sickle cell anemia «crisis» produces blood clots «that can cause coronary/arterial blockage» ✔

c.

a. produce antibodies ✔

b. memory cells confer immunity ✔

c. specific immunity results from production of antibodies specific to a particular antigen ✔

d. recognize pathogens ✔

e. destroy foreign cells/cancer cells ✔

d.

Examiners report

Labelling the heart was generally ok, though the rest of this question was weakly answered.

a.i.

Labelling the heart was generally ok, though the rest of this question was weakly answered.

a.ii.

Most candidates knew that heart valves prevent backflow of blood but that was all. There were a variety of misconceptions such as that valves pump blood or that the SA node sends signals to the valves to make them open/close.

b.

Clots were related to a fatty diet or cholesterol but rarely to plaque build-up. The idea that plaque breaking could activate clot formation was seldom mentioned. Without really giving any accurate information, candidates got a mark just by linking blood clots to heart attack. There were many misconceptions and confusion. The first confusion was that blood clots lead to strokes. Quite a few responses focused on seizures and strokes as a possible consequence. In fairness to candidates, there is ambiguity in the way we use terminology in the common parlance. Cardiac arrest, cardiac failure, CHD and heart attack are technically not synonyms, though they are often used interchangeably. A student of biology is expected to understand the differences.

c.

Many candidates correctly stated that lymphocytes produce antibodies. Lymphocytes were often mistaken for phagocytes and lengthy descriptions of engulfing of diseases were given. 

d.

Syllabus sections

Core » Topic 6: Human physiology » 6.2 The blood system
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