How to teach energy flow in ecosystems

Why this matters

A student can draw every arrow in a food web and still believe dead things in the soil give plants their energy. Her web then has an arrow from the soil back to the tree, and energy goes around in a circle. A finished worksheet doesn't show which students think that, and the teacher has to wait for quiz day to find out.

Energy flow in ecosystems

Energy enters most ecosystems as sunlight. Plants use it to make food by photosynthesis, and each animal that eats a plant or another animal takes in part of that energy. Between 80% and 90% of the energy at each step is lost as heat or waste, so less is left for the next eater, and the energy has to keep coming from the sun (National Geographic Education). Matter moves differently: decomposers break down dead plants and animals into nutrients in the soil, and plants take those nutrients up again. The NGSS asks middle schoolers to model both, the cycling of matter and the flow of energy (NGSS MS-LS2-3).

In the Flint activity, each student draws an arrow for each step energy takes on a whiteboard with five photos from Isle Royale: the sun, balsam fir, moose, wolf, and soil and decomposers. Sparky reads the arrows the student sends. When an arrow sends energy from the soil back to the fir, Sparky points the student to their own sun arrow, then has them relabel the soil arrow "nutrients". A student who finishes the web gets a harder question about the moose and the fir when the island's wolves nearly died out.

Nina's chat: where does the energy on Isle Royale go?

Nina is a middle schooler who goes camping with her family. She knows wolves eat moose. She thinks that when living things die, the soil passes their energy back to the trees.

The whole class gets the same activity: the same greeting, the same whiteboard with five photos from Isle Royale, an island in Lake Superior, and the same task of drawing an arrow for each step energy takes. Each student draws their own arrows, and Sparky's next message depends on what that student drew and wrote.

Sparky reads the student's whiteboardSparky sends the student back to an arrow she already drewA right answer gets a harder question

N

Nina

Interest: Camping with her familyStarting point: Thinks the soil gives the fir its energy

Sparky

Hi! This is Isle Royale, an island in Lake Superior where wolves hunt moose. Open the food web below and draw an arrow for each step energy takes, from the sun all the way to the wolf. Add arrows for what happens when living things die. Then send it to me, and tell me one thing you like to do outside.

Nina

i like camping with my family. here is my web. when stuff dies it goes in the soil and that gives the fir its energy so it keeps going around

Sparky

I can see your arrows going Sun → Balsam fir → Moose → Wolf, and Moose → Soil and decomposers. You mentioned the soil gives the fir its energy. Think back to the arrow you already drew from the sun to the fir. Where does the fir get the energy it uses to grow?

Nina

oh. the sun. the fir uses sunlight to grow. so what does the soil give it?

Sparky

Exactly, the fir gets its energy from the sun. The soil gives the fir matter, like nutrients, not energy. When decomposers break down dead things, they return nutrients to the soil, and the fir takes those up through its roots. Energy leaves as heat at every step, so it has to keep coming from the sun. Can you write "nutrients" on the arrow from Soil and decomposers to Balsam fir?

Nina

ok i wrote nutrients on it

Sparky

Good, "nutrients" is on that arrow. What happens to a wolf after it dies?

Nina

it rots and decomposers break it down. i added an arrow from the wolf to the soil

Understanding check

Exactly right, wolves decompose just like everything else. Here's a harder question: between 2009 and 2016, the wolves on Isle Royale went from 24 to just 2. Draw or explain what you think happened to the moose and the balsam fir during that time.

Nina

the moose would go up because nothing is eating them. so there are way more moose eating the fir in winter and the fir goes down

Sparky

That's exactly right. Fewer wolves meant more moose, and more moose meant less balsam fir. New wolves were brought to the island in 2018 and 2019. What do you predict happened to the moose and fir after that?

Relabeled her soil arrow as nutrients, then explained what happened when the wolves nearly died out

Nina drew her idea as an arrow from the soil to the fir. Sparky didn't cross the arrow out or tell her she was wrong. It pointed her to the sun arrow she had drawn herself, and she named the sun on her own. Only then did Sparky explain that the soil passes on nutrients while energy leaves as heat, and it had her relabel her own arrow. Her finished web is her own drawing, and the wolf question asks her to use it.

Sparky reads the arrows and words on each whiteboard a student sends. Sparky sometimes misses an arrow a student has drawn, so the activity tells Sparky never to say an arrow is missing. Sparky asks about the living thing instead, as it did with the wolf.

Nina is an example student, and Sparky's replies are shortened.

What Flint did for Nina

• The greeting opened a whiteboard with five photos in Nina's chat, so she drew the food web herself instead of filling in blanks.
• Sparky read Nina's arrows before it replied, and asked where the fir gets its energy instead of telling her the soil arrow was wrong.
• Once Nina named the sun, Sparky explained matter and energy in three sentences and asked her to label her own arrow "nutrients".
• When her web was complete, Sparky asked a harder question with the real wolf counts from Isle Royale.

A teacher can't do this by hand for 30 students, and Sparky does it in every student's chat.

Who still thinks the soil gives plants energy

When a student gives three wrong answers, Sparky flags them for the teacher under Needs attention while the class is still working. When students finish, Sparky grades each chat against the activity's rubric and sums up the class on the activity page: what most students understood, which mistake came up most, and what to practice next.

Set up the activity for free

The Isle Royale food web activity is in Flint's public library, with the starter whiteboard, Sparky's guidelines, the greeting and a rubric already set up. Open it, select Use activity to copy it into a free Flint account, and move it to a class. The whiteboard opens next to each student's chat, and the student sends it with a message when their arrows are done. In the activity's Preview tab, select Try session myself to test it as a student before you assign it.

For more science activities, see Flint for science.