Question

do plants depend on animals for carbon-dioxide?

Answer 1

Yes plants depend on animals for carbondioxide, but this is not the only source of Carbondioxide for them because.
1. Plants even can get CO₂ from other plants, as they decay when they die producing carbon which combines with oxygen present in atmosphere producing carbon dioxide.

2. There are lots of plants that existed before the first animals appeared on Earth. So they got CO₂ from some other sources.