Question

Given below are two statements : one is labelled as
Assertion (A) and the other is labelled as Reason (R).
Assertion (A): When an individual is exposed to hot climate, the body responds through vasodilation. Reason (R): Increased blood flow allows dissipation of heat from the core of the body to the environment through sweating. In the light of the above statements, choose the most appropriate answer from the options given below :

• A. Both (A) and (R) are correct and (R) is the correct explanation of (A)
• B. Both (A) and (R) are correct but (R) is not the correct explanation of (A)
• C. (A) is correct but (R) is not correct
• D. (A) is not correct but (R) is correct

Hint:

In hot weather, the body performs vasodilation to increase blood flow near the skin surface, helping heat escape through sweating and evaporation.

Answer 1

The Correct Option is A

Concept: Human beings maintain a constant internal body temperature through a process called thermoregulation. The body uses several physiological mechanisms to balance heat gain and heat loss. One important mechanism used in hot conditions is: \[ Vasodilation \] Vasodilation means widening of blood vessels near the skin surface. This process increases blood flow to the skin, allowing excess body heat to escape into the environment. Heat is then lost through:
• Sweating,
• Evaporation,
• Radiation,
• Conduction,
• Convection.

Step 1: Analyzing Assertion (A). Assertion (A) states: \[ \text{When an individual is exposed to hot climate, the body responds through vasodilation.} \] This statement is correct. When environmental temperature increases:
• Blood vessels near the skin widen,
• More blood flows close to the skin surface,
• Heat from the body core is transported outward,
• Excess heat is released into the surroundings. This physiological response is known as vasodilation. Therefore, Assertion (A) is true.

Step 2: Analyzing Reason (R). Reason (R) states: \[ \text{Increased blood flow allows dissipation of heat from the core of the body to the environment through sweating.} \] This statement is also scientifically correct. Due to increased blood flow:
• Warm blood reaches the skin surface,
• Sweat glands become more active,
• Sweat evaporates,
• Evaporation removes body heat efficiently. Thus, increased blood flow indeed helps the body lose heat.

Step 3: Checking whether Reason explains Assertion. The assertion tells us: \[ \text{The body responds through vasodilation in hot climate.} \] The reason explains: \[ \text{Why vasodilation occurs — to increase heat loss from the body.} \] Hence, the reason directly explains the physiological purpose of vasodilation. Therefore:
• Assertion (A) is correct,
• Reason (R) is correct,
• Reason correctly explains Assertion.

Step 4: Final conclusion. Thus, the correct answer is: \[ \boxed{\text{(A) Both (A) and (R) are correct and (R) is the correct explanation of (A)}} \]