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CELL STRUCTURE

 

Cell Wall
Each cell is surrounded on all sides by the cell wall.  The cells of herbaceous tissue (primary tissue) have only the primary cell wall and middle lamella, which are not very rigid.  Most of the plant tissue we eat only has primary cell walls.  When fruits ripen, the middle lamella breaks down due to pectin digestion, thus the cells slip past each other and the tissue seems softer.  The  cellulose microfibrils in the primary cell wall are parallel, which allows the cell wall to expand as the cell grows.  The cells of woody or wood-like (lignified) tissue possess a secondary cell wall. In the secondary cell wall, the cellulose microfibrils are criss-crossed and are impregnated with lignin, both of which make secondary cell walls very hard and rigid.  Generally, only xylem and sclerenchyma cells (fibers and sclereids)  have secondary cell walls; all of which are dead at maturity. 

Cytoplasm
The cytoplasm is basically a soup of organelles surrounded by the selectively permeable plasmalemma.  Plasmodesmata connect the cytoplasm of adjacent cells.  The fluid portion is called the cytosol and contains dissolved nutrients, gases (oxygen and carbon dioxide), sugars and other carbohydrates, oil/fat droplets, proteins, enzymes (catalytic proteins), hormones, and all the other components essential for cell metabolism.  The metabolic reactions of the cell occur in either the cytosol or the organelles .  Each organelle has specific metabolic functions.  In addition, many organelles are designed for storage (carbohydrates, proteins, fats, organic acids, pigments, wastes, etc.).