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Question #46368
The Question
When an ectothermic vertebrate (e.g., a lizard) is exposed to a sudden drop in environmental temperature outside its thermal tolerance range, its systemic blood pressure collapses. In contrast, a mammal maintains stable hemodynamics under similar acute environmental exposure. Which of the following best explains the primary physiological mechanism behind this divergence?
Options
- A.
Ectothermic vertebrates possess a neurogenic heart, making their cardiac conduction system highly susceptible to environmental thermal fluctuations.
- B.
The spontaneous depolarization rate of the SA node in ectotherms decreases due to the temperature-dependent kinetics of pacemaker ion channels, causing systemic bradycardia.
- C.
Mammalian SA node cells possess inherently cold-resistant voltage-gated channels that maintain constant chronotropy regardless of core body temperature.
- D.
The cold-induced denaturation of SA node proteins in ectotherms permanently halts the generation of action potentials, leading to an irreversible collapse in blood pressure.
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Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Evolutionary_Exception
Tackle problems where standard rules evolve or change based on specific environmental constraints.
Concepts Behind This Question
Conducting System Sequence|Thermal Tolerance Ranges|Evolutionary Ecology of Parasitism
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often misunderstand the evolutionary mechanism of homeothermy.
A common misconception is that mammalian cells themselves are structurally immune to cold (Option C).
In reality, mammalian cells are just as susceptible to the Arrhenius/Q10 effect; homeothermy is an evolutionary adaptation to expend metabolic energy to keep the internal environment warm, thereby protecting the temperature-dependent kinetics of the SA node.
The question also tests the fundamental NCERT distinction between myogenic (vertebrate) and neurogenic (invertebrate) hearts.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Body Fluids and Circulation - Class 11 |
| Concept | Conducting System Sequence |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |