What Defines a Poikilothermic Ectotherm?

Animals use various mechanisms to regulate their internal body temperature—key among these are their reliance on external versus internal heat sources and how much their internal temperature varies. A poikilothermic ectotherm is an organism whose internal temperature is largely determined by the environment and can vary considerably.

Key Thermoregulatory Characteristics of Poikilothermic Ectotherms

• Use of External Environment:
  Poikilothermic ectotherms depend heavily on the external environment to regulate their body temperature. They do not produce sufficient metabolic heat internally to maintain constant temperatures. Examples include most fish, amphibians, and reptiles that bask in the sun or seek shade to adjust their temperature.

• Variable Internal Temperature:
  Unlike homeotherms that keep a stable internal temperature, poikilotherms’ body temperatures fluctuate with external conditions, which influences their metabolic rate and activity levels.

• Thermal Homeostasis:
  Poikilotherms generally do not maintain thermal homeostasis within a narrow range of temperatures. Their internal temperature varies markedly with the ambient temperature.

Analyzing Statements to Identify Correct Descriptors

• A. It uses external environment to regulate internal body temperature: True for poikilothermic ectotherms.

• B. It does not use external environment to regulate internal body temperature: False for poikilothermic ectotherms (more true for endotherms).

• C. It can vary internal temperature considerably: True for poikilothermic ectotherms.

• D. It can maintain thermal homeostasis in a narrow range: False for poikilothermic ectotherms.

Correct Option

The combination correctly describing a poikilothermic ectotherm is:
(3) A and C