State the main function of veins in human circulatory system. Why do they not need thick walls?
State the main function of veins in human circulatory system. Why do they not need thick walls?
Main function of veins: Veins are the blood vessels that collect deoxygenated blood (carrying carbon dioxide and other wastes) from various organs and tissues of the body and bring it back to the heart (specifically, to the right atrium).
Why veins do not need thick walls: As given in the chapter, 'Veins collect the blood from different organs and bring it back to the heart. They do not need thick walls because the blood is no longer under pressure, instead they have valves that ensure that the blood flows only in one direction.' By the time blood reaches the veins (after passing through the fine capillaries), it has lost most of the pumping pressure imparted by the heart, so veins do not need to withstand high pressure the way arteries do. Instead of thick, elastic, muscular walls, veins have thin walls and contain valves along their length, which prevent the backflow of the low-pressure blood and ensure it moves in only one direction, towards the heart.
Marking Scheme
- 11 mark for stating the function: veins carry deoxygenated blood from body organs back to the heart.
- 21 mark for the reason: blood in veins is not under high pressure (pressure has dropped after passing through capillaries), so thick walls are not required; valves ensure one-way flow instead.
Hint
Compare the pressure of blood in arteries versus veins, and think about what structural feature (other than wall thickness) veins use to keep blood flowing one way.
Analysis & Explanation
This is a direct recall-cum-reasoning question grounded in the 'The tubes – blood vessels' section of the chapter. It contrasts veins with arteries: arteries carry blood away from the heart under high pressure, so they need thick, elastic walls; veins carry blood back to the heart under low pressure, so they can have thin walls, compensating for the lack of pressure-driven one-way flow with internal valves.
Common Mistakes
- 1Confusing the function of veins (carrying blood to the heart) with that of arteries (carrying blood away from the heart).
- 2Omitting the reason (low blood pressure in veins) and only stating the fact that veins have thin walls without explanation.
- 3Forgetting to mention the valves that veins possess to prevent backflow.
Interesting Facts
Unlike arteries, most veins (especially in the limbs) rely partly on the squeezing action of surrounding skeletal muscles to help push blood towards the heart against gravity — this is called the 'muscle pump'.
Not all veins carry deoxygenated blood — the pulmonary veins are an exception, carrying oxygenated blood from the lungs to the left atrium of the heart.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2025?
This question carries 2 marks in the CBSE Class 10 Science 2025 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Life Processes" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Transportation in Human Beings — Blood Vessels (Veins)" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2025 paper?
This is a Very Short Answer question from Section B in the CBSE Class 10 Science 2025 paper.