4. What would happen if the plants on Earth were destroyed?

Everyone would die.

Explanation: plants clear out carbon dioxide. Without them we would eventually die.

as for symbolic actions, the narrator's tearing down the wallpaper in an attempt to find the "woman" in the wallpaper represents her struggle to retain or regain her sanity.   the wallpaper has been part of her confinement and by her tearing it down, she is freeing herself from that confinement.