![Q.24 Determine the correctness or otherwise of the following Assertion [a] and the Reason [r]. Assertion [a]: The cardiovascular organization called double circulation provides vigorous flow of blood to the brain, muscles, and other organs. Reason [r]: The blood is pumped a second time after it loses pressure in the capillary beds of the lungs or skin. (A) Both [a] and [r] are true and [r] is the correct reason for [a] (B) Both [a] and [r] are true but [r] is not the correct reason for [a] (C) Both [a] and [r] are false (D) [a] is true but [r] is false](https://www.letstalkacademy.com/wp-content/uploads/2025/12/slide_24-4.jpg)
Q.24 Determine the correctness or otherwise of the following Assertion [a] and the
Reason [r].
Assertion [a]: The cardiovascular organization called double circulation provides
vigorous flow of blood to the brain, muscles, and other organs.
Reason [r]: The blood is pumped a second time after it loses pressure in the capillary
beds of the lungs or skin.
(A) Both [a] and [r] are true and [r] is the correct reason for [a]
(B) Both [a] and [r] are true but [r] is not the correct reason for [a]
(C) Both [a] and [r] are false
(D) [a] is true but [r] is false
Double circulation in humans ensures efficient oxygen delivery by passing blood through the heart twice per cycle, supporting high metabolic demands in organs like the brain and muscles. The assertion-reason question evaluates this concept precisely for CSIR NET Life Sciences preparation.
Assertion Analysis
The assertion states that double circulation provides vigorous blood flow to the brain, muscles, and other organs. This holds true because the systemic circuit pumps oxygenated blood at high pressure (~100 mmHg mean) from the left ventricle directly to body tissues, enabling rapid nutrient and oxygen delivery without mixing deoxygenated blood. In contrast, single circulation (as in fish) mixes blood, reducing efficiency for active mammals.
Reason Evaluation
The reason claims blood is pumped a second time after losing pressure in capillary beds of the lungs or skin. This is false for mammals: after low-pressure (~15 mmHg) pulmonary capillaries, oxygenated blood returns directly to the left heart for systemic pumping; no extra pump addresses capillary pressure loss. “Skin” references amphibian pulmocutaneous circulation, irrelevant to complete mammalian double circulation.
Option Breakdown
| Option | Correctness | Explanation |
|---|---|---|
| (A) Both true, [r] explains [a] | Incorrect | Assertion true, but reason false, so cannot explain. |
| (B) Both true, [r] does not explain [a] | Incorrect | Reason false due to inaccurate pressure/pump description. |
| (C) Both false | Incorrect | Assertion true. |
| (D) [a] true, [r] false | Correct | Matches analysis: vigorous flow from high-pressure systemic circuit; reason misstates mammalian process. |
Answer: (D)
Double circulation assertion reason questions test core CSIR NET Life Sciences concepts on cardiovascular organization. This Q.24 evaluates how double circulation delivers vigorous blood flow to brain, muscles, and organs via separate pulmonary (lungs) and systemic circuits.
Why Double Circulation Enables Vigorous Flow
In mammals, deoxygenated blood flows from body capillaries (pressure drop) to right heart, then low-pressure lungs for oxygenation, returning to left heart for high-pressure systemic pumping (~120/80 mmHg). This separation prevents mixing, ensuring pure oxygenated blood reaches demanding organs like brain and muscles at higher pressure than single circuits.
Flaw in the Reason Statement
Reason [r] incorrectly implies a “second pump” post-lung/skin capillary pressure loss. Pulmonary capillaries operate at low pressure (~10-15 mmHg drop total), but left ventricle repumps without special “second” mechanism for loss recovery—it’s inherent to the dual pump design. Skin capillary reference fits amphibians, not mammals.
CSIR NET Exam Tips
Focus on pressure gradients: systemic high vs. pulmonary low. Practice similar assertion-reason on capillary beds, blood flow efficiency. Correct answer (D) hinges on reason’s mammalian inaccuracy.
