Protoplast is the contents excluding the cell wall (pictured below).

Parenchyma Cells.

These are the least specialized plant cells.  They have a thin, flexible cell wall and perform most metabolic functions.  The ones in the stem and roots may contain colorless plastids that store starch while those in the leaves (mesophyll cells) have pigmented plastids.  Also the fruit you eat is mostly parenchyma cells.  Parenchyma cells are derivations of embryo cells and do not participate in cell division, but can divide and differentiate when necessary.  They can even regenerate an entire plant!

Collenchyma Cells.

In newer areas of a plant, you will find collenchyma cells.  Collenchyma cells group together in strands or cylinders just below the surface of the plant to support the surrounding, maturing tissue.  They lack secondary walls but have unevenly thick primary walls; however, the primary walls lack the structural support polymer lignin and therefore do not inhibit the growth the new tissue.  Collenchyma cells also elongate themselves as needed.

Sclerenchyma Cells.

Sclerenchyma cells also support tissue but these do have lignin and are dead at maturity.  For these reasons sclerenchyma cells are isolated only from non-growing areas of a plant.  There are two major forms of these cells: fiber cells and sclereids.  Fibers are long, slender, tapered groups of cells.  Sclereids are short and irregular in shape.  They harden nutshells and seed coats; and, when sclereids are scattered in fruit (clumps of parenchyma), the texture becomes gritty.

Tracheids and Vessel Elements.

Tracheids and vessel elements are water-allocating (xylem) cells.  Tracheids are dead and shaped much like fibers, but have pits between individual tracheids for water to pass.  Tracheids actually perform two functions in one due to the presence of lignin in their walls:  they support and conduct.  Vessel elements have perforated ends as well, but are wider and shorter cells aligned end-to-end forming a pipe-like structure.  Sometimes these cells will be caught in growing areas of a plant and to comply with that trend, the cells secondary walls are uneven in diameter forming a spiral-pattern like a screw or spring.  This allows the xylem cells to be more stretchy.

Sieve-Tube Members and Companion Cells.

These are food-moving, or phloem, cells.  Unlike traheids, vessel elements and sclereids and fibers, sieve-tube members are alive at maturity without a normal protoplast configuration of a nucleus, central vacuole and ribosomes.  End walls have a series of pores called sieve-tube plates.  Companion cells are alongside every sieve-tube member and connected via plasmodesmata.  Their organelles might help sustain sieve-tube members.

Next:  "Tissues."