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Lesson: Chapter 6 — The Structure and Function of Plant and Animal Cells

6.4. Cell organelles and structures 2 of 8

Cell wall and plasma membrane

Start with the two outermost parts of a cell. One belongs to the plant cell alone; the other is present in every cell there is.

The cell wall

Figure to be added

Figure 6.8 — the cell wall of a plant cell.

The outer covering of a plant cell is the cell wall, and it is non-living. Its main constituent is cellulose, with hemicellulose and pectin present as well.

Functions of the cell wall

  • Maintaining the shape of the cell
  • Support
  • Protection

The plasma membrane

Figure to be added

Figure 6.9 — the structure of the plasma membrane, showing the phospholipid and protein layers.

In plant cells the plasma membrane lies inside the cell wall; in animal cells the plasma membrane forms the covering itself. It is made mainly of phospholipids and proteins, and it is a semi-permeable membrane. The plasma membrane is also called the cell membrane.

Functions of the plasma membrane

  • Acting as the covering of the cell
  • Allowing water, ions and some molecules to enter the cell
  • Controlling what substances enter the cell and what leave it

The two are not the same thing

The cell wall is non-living; the plasma membrane is living. The wall gives shape and protection; the membrane chooses what goes in and out. So an animal cell having no wall is no handicap — the part that does the controlling is still there.