ECTOTHERM OR ENDOTHERM?

Objective

To explore the concept of thermoregulation and the different ways animals (including turtles!) maintain their body temperature.

Grades 5-12 Ectotherm or Endotherm?

ECTOTHERM OR ENDOTHERM?

Included in this Lesson Plan

Next Generation Science Standards (NGSS)

Lesson Background

Activities

1) Exploring with Graphs

2) Thermoregulation Scavenger Hunt

Discussion Questions

Related Materials Available

Ectotherm or Endotherm? Exploring with Graphs Worksheet

Ectotherm or Endotherm? Thermoregulation Scavenger Hunt Worksheet

Ectotherm or Endotherm? Discussion Question Worksheet

Ectotherm or Endotherm? PowerPoint Presentation

2 Grades 5-12 Ectotherm or Endotherm?

Next Generation Science Standards

HS-LS1-3. Plan and conduct an investigation to provide evidence that feedback mechanisms maintain homeostasis

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Lesson Background

Thermoregulation is the process by which animals maintain their body temperature. There are a few different ways this has evolved in different groups of animals, but they mostly fall into two categories: endotherms and ectotherms.

Endotherm bodies have internal metabolic processes that maintain a constant temperature—like humans! Endotherms must eat constantly and regularly to make enough heat to keep their bodies warm. Most mammals are endotherms. They don’t have to do anything special to maintain their body temperatures, but the food they eat is converted to energy and warmth. Even if endotherms are in very cold or very hot weather, their internal body systems are constantly operating to maintain an even temperature.

Ectotherms, on the other hand, rely on the environment to alter their temperatures. For the most part, they do not have internal processes that regulate temperature, so they have to move into the sun to warm up, or to the shade to cool down. They need to eat of course, but most do not need to eat as often or regularly as endotherms. Amphibians, reptiles and most fish are ectotherms, while most insects and invertebrates are largely ectothermic as well (although they’re a bit more complicated).

The figure below plots how environmental temperature affects body temperature in mammals (a mouse) and reptiles (a lizard).

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Figure from Wikimedia Commons

Endotherms and ectotherms used to be referred to as “warm-blooded” and “cold- blooded,” but those terms have fallen out of favor because they are misleading. Cold- blooded creatures do not always have cold blood.

Turtles and tortoises are ectotherms. That’s why you’ll often see them basking on a tree limb in a lake or pond; they’re trying to warm up after being in the cold water. Desert tortoises get hot in the desert sun and will lay in the shade of plants or deep in soil burrows with all of their limbs extended to cool down. The more surface area of their body that’s exposed to the sun or shade, the better they can offload or absorb heat.

Case Study: Leatherback Sea Turtles

Leatherbacks are anomalous among turtles in many ways. They don’t have a typical carapace; instead they have loosely interlocked bone covered by three centimeters of rubbery/oily skin and fibrous cartilage that is then covered by membrane bone called, “osteoderm.” This structure allows the large turtles to dive deep for food and withstand the pressure of the ocean. They can go as deep as 400 meters! Leatherbacks are

5 Grades 5-12 Ectotherm or Endotherm? ectotherms, yet that have adaptations that allow them to exploit food sources in very cold waters. They have a very high oil content and fat layers that insulate and keep the body temperature higher than the surrounding water. They also have something called a counter-current heat exchange system in the limbs. As the warm blood from the arteries flows past the cooler blood in the veins, the arteries transfer heat to the veins before the veins lose their heat to the surface of the skin. With a counter current heat exchange system, the veins don’t carry cold blood back to the heart and lower the core body temperature. When the blood gets back to the lungs and heart it is warm. If the animal is too hot the heat transfer can be reversed by transferring heat to the arteries so that the veins are cool when they flow back to the heart, thereby lowering the core body temperature.

Diagram credit: http://www.georgiaseaturtlecenter.org/kids-spot/words-to-know/

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Activity

Activity 1: Exploring with Graphs

Good for: Classroom activity or homework

Materials: Exploring with Graphs Worksheet

Give the students the “Ectotherm or Endotherm? Exploring with Graphs Worksheet.” Have them draw in the lines for endotherms (humans) and ectotherms. You could do one together as a class, and then have the students infer the other one based on their knowledge of how each operates.

Activity 2: Thermoregulation Scavenger Hunt

Good for: Outside activity or homework (class discussion can happen the following class).

Materials: Scavenger Hunt Worksheet

Each student should bring a “Ectotherm or Endotherm? Scavenger Hunt Worksheet” outside with a pen and clipboard, or something to write on. Instruct the students to wander around in some defined area (a school yard, a park, etc.) and search for animals. Any animals works, including birds, reptiles, insects, mammals, or even house pets! When they find an animal, they will observe it for 1-2 minutes and fill out the worksheet which has spaces for the animal’s name, a description of the animal’s activity, and whether they think it’s an endotherm or ectotherm and why. Ectotherm examples they

7 Grades 5-12 Ectotherm or Endotherm? might find: a butterfly spreading its wings in the sun, ants warming up around their nest, a bird spreading its wings in the sun, a lizard on a warm rock.

When you return to class, have the students make one long list of every animal they found, categorized by endotherms and ectotherms, and answer the following discussion questions.

Discussion Questions

These questions are the same as those listed on the “Ectotherm or Endotherm? Discussion Question Worksheet”.

1. Name three examples of endothermic animals.

2. Name three examples of ectothermic animals.

3. Name three ways that ectotherms can alter their body temperature.

4. What are the benefits and detriments of being an ectotherm?

5. What are the benefits and detriments of being an endotherm?

6. How does being an ectotherm affect a turtle’s ability to survive?

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