Why is it necessary to have a membrane around the cytoplasm

In plants, the cell wall is full of small holes called plasmodesmata. If there were no cellular membrane all of the fluid in the cell (cytoplasm) would just leak out. The membrane also acts as a barrier to the outside world, controlling the influx of nutrients, hormones, chemicals and other substances the cell uses.

In animals, if there is no cell wall so the absence of a cellular membrane would make all animals a pile of goop on the ground.

Explanation: in other words its important because it protects it from harmful things