Parenchyma - most abundant cell type in plants (e.g. cells making up the fundamental ground tissues; usually unspecialized; characteristics include:
living at maturity with a very thin cell wall
large vacuole for storage and sequestering of materials
large amount of intracellular space
spherical
relatively regular shape
very elastic (can change shape and then return to original shape with little deformation)
Functions of parenchyma cells include:
photosynthesis
storage
secretion
Collenchyma - found just below the epidermis in petiole (e.g. celery stalks), leaves, and young stems; usually specialized; characteristics include:
living at maturity
irregularly thickened cell walls (+cellulose)
prism shaped
plastic (can change shape but do not usually return to the original shape; remain deformed)
Functions of collenchyma cells include:
support
some involvement in transport of nutrients
Sclerenchyma - in mature parts of the plant, especially in woody plants and herbaceous perennials; specialized; characteristics include:
dead at maturity - protoplast is absent
very thick, sclerified cell wall (+lignin)
impermeable to water and other nutrients
in cells specialized for transport of water and nutrients, the cell wall contains holes called pits.
Functions include:
support
protection
transport of water and nutrients
Specific examples of sclerenchyma cells:
fibers - long and slender
sclerids (stone cells) - relatively spherical; the gritty texture of pears is due to the presence of stone cells.
