Poikilotherms
குளிர் இரத்த விலங்குகள்
Do not confuse 'cold-blooded' with the actual temperature of the blood. Poikilotherms lack internal thermoregulation, making their metabolic rate a slave to the ambient temperature. If the environment shifts, their enzymes shift. This is a physiological constraint, not a choice.
The idea
Poikilotherms are organisms that cannot maintain a constant body temperature. Their internal body temperature fluctuates in accordance with the environmental temperature. Unlike homeotherms, they lack the complex physiological mechanisms required for thermoregulation. Consequently, their metabolic activities are directly dependent on external thermal conditions.
Why it matters
This exists because these organisms lack internal physiological mechanisms to maintain a constant body temperature, relying on external heat sources.
NEET lens
NEET asks you to distinguish between poikilotherms and homeotherms based on metabolic stability. Remember: all reptiles, amphibians, and fishes are poikilotherms. Do not mistake 'cold-blooded' for 'low-temperature blood'; it refers to the inability to regulate.
Clinical significance
In humans, who are homeotherms, the failure of thermoregulation leads to hyperthermia or hypothermia. Unlike poikilotherms, our enzymes are optimized for a narrow 37°C range. Deviating from this causes protein denaturation and multi-organ failure.
Introduction
Poikilotherms (ectotherms) are animals whose body temperature varies with the environmental temperature. They cannot internally regulate their body temperature.
Core concept
Examples: all fish, amphibians (frogs), reptiles, invertebrates. Contrast: Homeotherms (endotherms) = birds and mammals that maintain constant body temperature. Poikilotherm metabolism: slower in cold (enzymes less active), faster in warmth. Cannot survive extreme temperatures.
Go deeper
Poikilotherms save energy by not producing metabolic heat — don't need to 'burn' food to maintain temperature. In warm environments they can be very active. Trade-off: vulnerable in temperature extremes, hence need dormancy.
From Class 10
Warm-blooded animals maintain constant body temperature. Cold-blooded animals like frogs change temperature with the environment.