Biology
The figures given below show diagrammatic cross-sections of three kinds of blood vessels.

(a) Identify the blood vessels A, B and C.
(b) Name the parts labeled 1-4.
(c) Mention two structural differences between A and B.
(d) Name the kinds of blood that flow through A and through B respectively.
(e) In which one of the vessels referred to in (a) above does the exchange of gases actually take place?
Circulatory System
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Answer
(a) The blood vessels A, B and C are:
- A → Artery
- B → Vein
- C → Capillary
(b) The parts labeled 1-4 are:
- 1 → External layer made of connective tissue
- 2 → Lumen
- 3 → Middle layer of smooth muscles and elastic fibres
- 4 → Endothelium
(c) Two structural differences between Artery and Vein are:
| Artery | Vein |
|---|---|
| Have thick and more muscular walls. | Have thin and less muscular walls. |
| Have narrower lumen. | Have wider lumen. |
(d) The kinds of blood that flow through A and through B are:
- A (Artery) → Oxygenated blood
- B (Vein) → Deoxygenated blood
(e) At the capillary level the actual exchange of gases takes place.
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The diagram given below represents the human heart in one phase of its activity. Study the same and then answer the questions that follow:

(a) Name the phase.
(b) Which part of the heart is contracting in this phase? Give a reason to support your answer.
(c) Name the parts numbered 1 to 6.
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Study the following diagram carefully and then answer the questions that follow:

(a) Name the cell labelled 1.
(b) Identify the phenomenon occurring in A.
(c) Mention two structural differences between 1 and 2.
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