In the Gizmos: Ecosystems STEM Case Study (Food Web Mystery), what organisms complete the energy-flow chain “Willow Tree ➔ _____ ➔ _____” in the food web?

What the arrows mean in a food web

In a food web, arrows show the direction of energy transfer. The arrow points from the organism being eaten to the organism that eats it.

Identifying each role in the chain

• Willow tree is a producer, it makes its own food by photosynthesis.
• The next organism should be a primary consumer (herbivore) that eats willow.
• The last organism should be a secondary consumer (predator) that eats the herbivore.

Filling in the two blanks

• Elk eat willows, so energy flows from willow trees to elk.
• Wolves prey on elk, so energy then flows from elk to wolves.

So the completed chain is:

$$\text{Willow Tree} \rightarrow \text{Elk} \rightarrow \text{Wolf}$$