![9. Determine the correctness or otherwise of the following Assertion [a] and 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/2026/06/1-9-1.jpg)
9. Determine the correctness or otherwise of the following Assertion [a] and 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
Introduction
The circulatory system is responsible for transporting oxygen, nutrients, hormones, and metabolic waste products throughout the body. In mammals and birds, the cardiovascular system is highly efficient because it follows a double circulation pattern. In this arrangement, blood passes through the heart twice during one complete circulation—once through the pulmonary circuit and once through the systemic circuit. This mechanism ensures complete separation of oxygenated and deoxygenated blood, allowing tissues to receive oxygen-rich blood at high pressure.
Double circulation is considered one of the most significant evolutionary adaptations in vertebrates because it supports high metabolic activity, efficient oxygen delivery, and maintenance of constant body temperature in mammals and birds. By pumping blood twice, the heart restores blood pressure after pulmonary circulation, enabling rapid transport of oxygen and nutrients to highly active organs such as the brain, skeletal muscles, kidneys, and liver.
Correct Answer
Correct Option: (A) Both [a] and [r] are true and [r] is the correct reason for [a]
Detailed Explanation
The assertion is true because double circulation enables the heart to deliver oxygen-rich blood to body tissues at high pressure. In mammals, blood returning from the lungs enters the left atrium and is pumped by the powerful left ventricle into the systemic circulation. This high-pressure circulation ensures rapid and efficient delivery of oxygen and nutrients to metabolically active organs such as the brain, skeletal muscles, kidneys, and liver.
The reason is also true. During pulmonary circulation, blood flows through the capillary network of the lungs, where gas exchange occurs. As blood passes through these capillaries, its pressure decreases significantly. Instead of sending this low-pressure blood directly to the body, it returns to the heart, where the left ventricle pumps it again with high force into the systemic circulation. This second pumping restores blood pressure and is precisely why double circulation can maintain vigorous blood flow to all organs.
Therefore, the reason correctly explains the assertion, making Option (A) the correct answer.
Explanation of Assertion and Reason
Assertion [a]
The assertion is true. Double circulation ensures efficient oxygen transport by completely separating oxygenated and deoxygenated blood. The systemic circulation receives freshly oxygenated blood at high pressure, enabling rapid delivery of oxygen to tissues with high metabolic demands.
Reason [r]
The reason is true. Blood loses considerable pressure while flowing through the pulmonary capillaries. The left side of the heart restores this pressure by pumping the oxygenated blood into the systemic circulation, thereby maintaining efficient circulation throughout the body.
Relationship Between Assertion and Reason
The reason directly explains the physiological advantage mentioned in the assertion. The second pumping action after pulmonary circulation is the fundamental reason why double circulation provides high-pressure blood flow to body organs.
Explanation of Each Option
Option (A): Both Assertion and Reason are True, and Reason is the Correct Explanation
This statement is correct. Double circulation restores blood pressure after pulmonary circulation and ensures efficient systemic blood flow.
Option (B): Both Assertion and Reason are True, but Reason is not the Correct Explanation
This statement is incorrect. The second pumping of blood after pulmonary circulation is exactly the reason why double circulation maintains vigorous blood flow.
Option (C): Both Assertion and Reason are False
This statement is incorrect. Both the assertion and the reason are physiologically accurate.
Option (D): Assertion is True but Reason is False
This statement is incorrect. The reason correctly describes the physiological basis of double circulation.
Why Option (A) is Correct
Double circulation consists of pulmonary circulation followed by systemic circulation. Since blood pressure falls during pulmonary capillary exchange, the left ventricle pumps the oxygenated blood a second time, generating high arterial pressure that supports efficient blood supply to the entire body.
Comparison of All Options
| Option | Assertion | Reason | Correct or Incorrect |
|---|---|---|---|
| A | True | True and correctly explains Assertion | Correct |
| B | True | True but does not explain Assertion | Incorrect |
| C | False | False | Incorrect |
| D | True | False | Incorrect |
Pathway of Double Circulation
| Step | Blood Flow |
|---|---|
| 1 | Right atrium receives deoxygenated blood from the body |
| 2 | Right ventricle pumps blood to the lungs through pulmonary arteries |
| 3 | Gas exchange occurs in pulmonary capillaries |
| 4 | Oxygenated blood returns to the left atrium through pulmonary veins |
| 5 | Left ventricle pumps oxygenated blood into the aorta |
| 6 | Systemic arteries distribute oxygenated blood to all body organs |
Advantages of Double Circulation
| Advantage | Physiological Importance |
|---|---|
| Complete separation of blood | Prevents mixing of oxygenated and deoxygenated blood |
| High systemic pressure | Efficient oxygen delivery to tissues |
| Low pulmonary pressure | Protects delicate lung capillaries |
| Supports high metabolism | Essential for mammals and birds |
| Improved oxygen transport | Maintains continuous aerobic respiration |
Single Circulation vs Double Circulation
| Feature | Single Circulation | Double Circulation |
|---|---|---|
| Heart Pumping | Once per complete circulation | Twice per complete circulation |
| Blood Pressure | Lower | Higher in systemic circulation |
| Mixing of Blood | Generally absent but lower efficiency | Complete separation in mammals |
| Occurs In | Fishes | Mammals and birds |
Biological Significance of Double Circulation
Double circulation enables mammals and birds to maintain a high metabolic rate by delivering oxygen-rich blood rapidly to active tissues while simultaneously protecting the lungs from excessive blood pressure. This efficient circulatory organization supports continuous muscular activity, rapid nerve conduction, thermoregulation, and sustained aerobic respiration. It represents one of the most important evolutionary adaptations in vertebrate physiology.
Final Answer
Correct Option: (A) Both [a] and [r] are true and [r] is the correct reason for [a]
Double circulation provides vigorous blood flow because blood is pumped twice during one complete circulation. After losing pressure in the pulmonary capillary beds, oxygenated blood returns to the heart, where it is pumped again by the left ventricle into the systemic circulation at high pressure. This second pumping ensures efficient oxygen and nutrient delivery to the brain, muscles, and all other organs.
