What would happen it the palisade mesophyll were below the spongy mesophyll

Photosynthesis will be affected or may not occur.

Explanation:

This is because palisade mesophyll are packed cells and have cylindrical shape with chloroplasts. Chloroplast are present here which control chlorophyll and this area specialises in absorbing light energy from the sun efficiently. If it is below spongy mesophyll, it's ability to absorb light energy is affected as there is an hindrance layer, and when chlorophyll couldn't absorb light energy, photosynthesis cannot occur.

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