Well one reason would be that plant cells are permanent hence need additional protection in order to stay longer unlike animal cells which "die" as time goes by.
So animal cells can have various shapes, but plant cells only havethe shapes of their cell walls. That's nice for plants, because it gives them the ability to grow up and out, where they can get lots of sunlight for making their food.
In particular, organelles called chloroplasts allow plants to capture the energy of the Sun in energy-rich molecules; cell walls allow plants tohave rigid structures as varied as wood trunks and supple leaves; and vacuoles allow plant cells to change siz Exactly why plant cell have wall and animal cell don't :-Cell walls are supporting structures that help the plant to have a fixed shape and protect it from injury. Other than that, it helps to keep the plant turgid so that it can stay firm and upright. Because when it enters a high water potential solution, as water moves in, the water exerts turgor pressure on the cell wall and the cell wall thus exerts an opposing pressure to keep water out. Hence cell wall is needed for the plant.
On the other hand, animal cells do not need to keep the structures, as they have the skeletal system to protect the organs and cushion them against any external Injuries.
Biological diversity is the variety of species in a given area. If a new species is added there are more species and therefore greater biological diversity and if one goes extinct there are less species and therefore less biological diversity.
