The leaves of plants have layers that perform different functions. The palisade layer contains the chlorophyll, which carries out most of the photosynthesis in the leaf.
In the palisade layer, the cells are arranged in an upright fashion. This means the light has no choice but to pass through the cell length ways which increases the chances of light hitting a chloroplast and subsequently being absorbed.
The spongy layer which is below the palisade layer has fewer chloroplasts and serves to catch the light that was not captured by the palisade layer.
