Directions for teachers:

Ask students to read the online Science News “Sea otters stay warm thanks to leaky mitochondria in their muscles,” which explores scientists’ efforts to figure out how the ocean’s smallest mammal maintains an extreme metabolism. A version of the story, “How muscles keep otters warm,” appears in the August 14, 2021 issue of Science News.

1. What are sea otters? Describe the animals.

Sea otters are the ocean’s smallest marine mammal. They are lean, meaning they have little body fat, and muscular.

2. What is metabolism? What surprised scientists about sea otters’ metabolism while at rest?

Metabolism describes how food gets converted into cellular energy. While at rest, sea otters’ metabolism is three times as fast as predicted for a mammal their size.

3. How do sea otters keep their metabolism at such high levels?

Sea otters eat a quarter of their body mass in food every day.

4. What is sea otters’ average body temperature? How does metabolism relate to body temperature?

The rate at which food gets converted into energy in cells generates enough heat for sea otters to maintain an average body temperature of 37° Celsius.

5. What are mitochondria? How do mitochondria help sea otters’ muscle cells generate heat?

Mitochondria are organelles in cells that generate energy. These structures pump protons across their inner membrane to store energy that can be used to power cells. Some of that energy can be lost as heat if protons leak back over the membrane before they can be used for work.

6. How do leaky mitochondria contribute to sea otters’ extreme metabolism?

Sea otters need to eat more food to make up for the energy that was lost as heat, which revs up the animals’ metabolism. 

7. Is this heating method the main way that sea otters stay warm? When is the method probably used?

No, sea otters’ cells probably use this method when the animals need more heat than usual to maintain their body temperature.

8.  Why does ecophysiologist Terrie Williams say the finding could be a “game changer” for scientists’ understanding of marine mammal evolution?

The finding is one of the clearest pieces of evidence yet for how some marine mammals regulate their body temperature.

9.  What implications does the finding have for scientists’ understanding of sea otter evolution?  

In the future, the finding could help improve scientists’ understanding of how sea otter ancestors evolved to live and thrive in the seas.