Science · World of living · chapter 5 of 13

Class 10 Science Chapter 5: Life Processes case study question with answers

One case-based question of the kind the board asks in Section E: a passage and a figure, then 3 parts worth 4 marks in all, with the answer and the marking scheme for each. Written from the NCERT chapter.

Case study · 4 marks
The figure is a simplified block diagram of blood flow in a human being. The four chambers of the heart are drawn as boxes, with the right side of the heart on the left of the diagram, as when facing a person. The short arrows inside the heart show blood passing from each atrium to the ventricle below it. The arrows P, Q, R and S are the four great vessels that join the heart to the lungs and to the rest of the body. Lines show only the direction of flow, not the shape or length of the vessels.
LungsBody organsRight atriumLeft atriumRight ventricleLeft ventriclePQRS
Part 1 · 1 mark
Vessel S is the
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Answer: (c) aorta

S leaves the left ventricle for the body organs: the aorta leaves the left ventricle.

Part 2 · 1 mark
The two vessels that carry oxygen-rich blood are
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Answer: (b) R and S

R (pulmonary vein) brings oxygenated blood from the lungs to the left atrium; S (aorta) carries it from the left ventricle to the body. P and Q carry de-oxygenated blood.

Part 3 · 2 marks
Using the diagram, explain why this circulation is called double circulation. Why do the two lower boxes have thicker muscular walls than the two upper ones?
Answer and marking scheme

In one complete cycle blood passes through the heart twice: once through the right side (in by P, out by Q to the lungs) and once through the left side (in by R from the lungs, out by S to the body). The lower boxes are the ventricles, which have thicker walls than the atria because they pump blood out into the various organs.

  • blood passes through the heart twice per cycle, once to the lungs and once to the body (1)
  • ventricles pump blood to the organs, so their walls are thicker (1)
Or
In a fish, blood passes through the heart only once in each cycle. Compare this with the circuit in the diagram, and explain why a fish's heart only ever receives de-oxygenated blood.
Answer and marking scheme

In the diagram blood returns to the heart (by R) after the lungs and is pumped again (by S), so it passes through the heart twice per cycle. In a fish the heart pumps blood to the gills, where it is oxygenated, and it then passes directly to the rest of the body without returning to the heart; so the heart handles only blood coming back from the body.

  • human blood returns to the heart after the lungs and is pumped again: twice per cycle (1)
  • fish: gills to body directly, so the heart only receives blood from the body (1)
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