what functions does a parenchyma have?

Parenchyma is the most common plant tissue. It is relatively unspecialized and makes up a substantial part of the volume of a herbaceous plant and of the leaves, flowers and the fruits of woody plants. The thin-walled parenchyma cells have large vacuoles and distinct intercellular spaces.

Functions:
the most important function of the parenchyma cells of roots and stem is the storage of food (e.g. starch) and water,
the intercellular air spaces permit gaseous exchange.

Parenchyma is the versatile ground tissue. It forms, for example, the cortex and pith of stems, the cortex of roots, the mesophyll of leaves, the pulp of fruits, and the endosperm of seeds. Parenchyma cells are living cells and may remain meristematic at maturity, meaning that they are capable of differentiated cell division if given the correct hormone stimulus. They have thin but flexible cellulose cell walls, and are generally polyhedral when close-packed, but approximately spherical when isolated from their neighbors. They have large central vacuoles, which allows the cells to store and regulate ions, waste products and water.

Parenchyma cells have a variety of functions:

    In leaves, they form the mesophyll and are responsible for photosynthesis and the exchange of gases, parenchyma cells in the mesophyll of leaves are a specialized parenchymatous tissue known as chlorenchyma (parenchyma with chloroplasts).
    Storage of starch, protein, fats and oils and water in roots, tubers (e.g. potato), seed endosperm (e.g. cereals) and cotyledons (e.g. pulses and groundnut)
    Secretion (e.g. hydathodes, nectaries and cells lining the inside of resin ducts)
    Wound repair and the potential for renewed meristematic activity
    Other specialized functions such as aeration (aerenchyma) and support

The form of parenchyma cells varies with their function. The epidermal parenchyma cells of a leaf are barrel shaped in cross section, but have a variety of outline shapes ranging from simple polygons to strongly branched and interlocked shapes resembling the pieces of a jigsaw puzzle, as in the leaves of Arabidopsis thaliana. In the epidermis of higher plants, only the guard cells have chloroplasts. This tissue serves as a barrier wall and protects the internal tissues from injury. In the spongy mesophyll of a leaf, parenchyma cells range from near-spherical and loosely arranged with large intercellular spaces to branched or stellate, mutually interconnected with their neighbours at the ends of the arms to form a three-dimensional network, as in the red kidney bean Phaseolus vulgaris and other mesophytes.These cells, with the epidermal guard cells of the stoma, form a system of air spaces and chambers that regulate the exchange of gases. They usually contain plastids.