---
title: "Ectotherms — AP Biology Definition & Exam Guide"
description: "Ectotherms rely on external heat instead of metabolism to control body temperature, a key energy-allocation strategy tested in AP Bio Unit 8 ecology."
canonical: "https://fiveable.me/ap-bio/key-terms/ectotherms"
type: "key-term"
subject: "AP Biology"
---

# Ectotherms — AP Biology Definition & Exam Guide

## Definition

Ectotherms are organisms that rely on external sources of body heat.

## Related Study Guides

- [8.2 Energy Flow Through Ecosystems](/ap-bio/unit-8/energy-flow-through-ecosystems/study-guide/A1PeQD1Zy3BIMu1zSMzd)

## Review

### Related Terms

- Endotherm: An organism that generates its own body heat internally, much like a battery-powered device.
- Poikilotherm: An organism whose internal temperature varies considerably. It's like a chameleon changing colors based on its surroundings.
- [Thermoregulation](/ap-bio/key-terms/thermoregulation): The process by which animals maintain an optimal body temperature, similar to how you would adjust your home's thermostat to keep it comfortable.