Consider the following statements about thermoregulation in animals.

A. It uses external environment to regulate internal body temperature
B. It does not use external environment to regulate internal body temperature
C. It can vary internal temperature considerably
D. It can maintain thermal homeostasis in a narrow range of temperatures

Which one of the following options correctly describes a poikilothermic ectotherm?

Correct option is C

Explanation-

Poikilothermic = internal body temperature varies widely with the environment.
Ectotherm = relies on external environmental heat to regulate body temperature (not internal mechanisms like mammals do).

Evaluate Statements:
A."It uses external environment to regulate internal body temperature"
→ This is true for ectotherms.
B. "It does not use external environment to regulate internal body temperature"
→ This is the definition of an endotherm, not an ectotherm.
C.  "It can vary internal temperature considerably"
→ This is true for poikilotherms (unlike homeotherms).
D.  "It can maintain thermal homeostasis in a narrow range of temperatures"
→ This describes homeotherms, not poikilotherms.

Correct statements: A and C (Option c)