Which one of these animals is not a homeotherm?

Animals that are capable of regulating and maintaining their internal body temperature without getting affected by the external environmental temperature are called homeotherms. A homeotherm maintains the body temperature so that the metabolic activities of the body can be performed without any influence of the external temperature. A. Camelus (camel) is a mammal and regulates its body temperature. It is a homeotherm. B. Macropus is a marsupial, so it is also a homeotherm. C. Psittacula (parrot) is an ave, it is a homeotherm as well. D. Chelone is a plant. It cannot regulate the internal body temperature. Hence, the correct answer is 'Chelone'.