why is it important to know the 3 simple ground tissues in plant cells:?

Parenchyma is the fundmental or the ground tissue occupying most part of the plant body. This tissue serves the plant body in so many ways. This tissue helps the storage of food in plant (ex: starch stored in parenchyma tissue of potato tuber), helps in photosynthesis (parenchyma containing chlorenchyma is present green leaves), provide buoyancy to plant parts (Leaves of duck weed plants in ponds float on water due to storage of air containing parenchyma called aerenchyma in its leaves).
Collenchyma gives mechanical support, flexibility and elasticity to the plant parts. Sclerenchyma even though it is a dead tissue it provides mechanical support to the plant parts.
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 http://en.wikipedia.org/wiki/Ground_tissue