Can I make the carbon cycle shorter - by metamorphosis from plant to animal and vice-versa

EDITED to address the above suggestion. See below.

Most animals breathe in oxygen and breathe out carbon-dioxide.

Most plants take in carbon-dioxide and release oxygen.

Waste products from animals fertilise the soil and enable plants to grow.

Plants are eaten by herbivores.

I'm looking to create a world where this cycle is abbreviated.

When an animal eats enough vegetation it puts down roots and becomes a plant.

When a plant absorbs sufficient nutrients it metamorphoses into an animal and starts walking around.

This previous question is similar in some respects -

A plant/fungus and an animal that form a single species?. However the question there is, "How feasible would this be to evolve? What selection pressures would promote this adaptation? The ancestral organism doesn't need to be an animal."

I am not interested in evolution or selection. I want to know about the mechanism of metamorphosis.

Question

Specifically what biological mechanisms would be needed for a photosynthetic plant to metamorphose into an oxygen breathing animal and vice-versa?

posted about 6 years ago

chasly from UK‭

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