Distinguish between the two types of layers that make up the parenchyma tissues?

Answer 1

Parenchyma is the most common ground tissue, it forms e.g. the cortex and pith of stems, the cortex of roots, the mesophyll (photosynthetic cells), the pulp of fruits, the endosperm of seeds, and the photosynthetic areas of a leaf. Parenchyma cells are capable of cell division even after maturation (i.e. they are still meristematic). They have thin, but flexible, cell walls, and are generally cube-shaped and are loosely packed. They have large central vacuoles, which allows the cells to store nutrients and water.

Parenchyma cells have a variety of functions;

* photosynthesis (may then be called Chlorenchyma /Mesophyll cells),
* gas exchange (Aerenchyma),
* storage,
* secretion (e.g. Epithelial cells lining the inside of resin ducts)
* healing
* other specialised functions.

Parenchyma differs depending on the varied functions they perform. The epidermal parenchyma cells of a leaf are barrel shaped and have no chloroplast. The parenchymatous layer just beneath the epidermis in the stem have chloroplasts. They take part in photosynthesis and are known as chlorenchyma in the leaf, just beneath the epidermis large parenchymatous cells with chloroplast are closely arranged,and are known as palisade tissues.palisade tissue along with the loosely arranged spongy tissue have major role in photosynthesis. There are many air cavities between the aerenchyma cells of water plants like lotus. These cells are known as parenchyma which help the plants to float in water. Parenchymma cells are arranged at the center of some types of stem, which perform the function of storing food. In certain types of roots, parenchyma cells also store food.

http://www.bio.txstate.edu/~dlemke/botany/1410lab/lab_exercises/lab3/tissues/parenchyma.html
http://www.biologie.uni-hamburg.de/b-online/e05/05d.htm

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