Why do plants need mesophyll cell? What is its purpose and pathology?
There are two main types of mesophyll cell in plants - spongy and palisade. Mesophyll just refers to the fact that it is the inner material of the leaf - between the two epidermis layers. The mesophyll is tasked with providing food for the plant via photosynthesis.
Palisade cells are responsible for photosynthesis and therefore contain many chloroplasts. They are tall and thin so that lots can be packed into a small space, and the chloroplasts are located at the top of the leaf to optimise light absorption.
Spongy mesophyll is made up of cells that also photosynthesise, but this area of the leaf is primarily also vital for gas exchange and therefore has many spaces (hence the "spongey") so that gases can diffuse across.
I hope this helped; feel free to contact me if you have any other questions:)