- Green plants provide food for themselves / animals / consumers by performing photosynthesis
- A source of something provides that something
- Therefore, green plants are a source of food for animals

- Green plants are a source of food for animals
- A tree is a kind of plant
- So, a tree is a source of food for animals

- A tree is a source of food for animals
- A tree is a source of shelter for animals in an ecosystem
- Hence, a tree is a source of food and shelter for animals

- A tree is a source of food and shelter for animals
- An oak is a kind of tree
- So, an oak tree is a source of food and shelter for animals

So, an oak tree is a source of food and shelter for animals
Q: Noah visited a park that had many oak trees. Which best describes the role of an oak tree in its ecosystem?
Context:
- An oak is a kind of tree 
- A tree is a source of shelter for animals in an ecosystem 
- Green plants provide food for themselves / animals / consumers by performing photosynthesis 
- A tree is a kind of plant 
- A source of something provides that something