... plasma membrane is partially permeable so therefore some substances can cross more easily than others. A cell must also excrete waste products made in the cell through the cell's plasma membrane. There are many ways in which substances pass through the plasma membrane, these are by diffusion, facilitated diffusion, osmosis, active transport, endocytosis and exocytosis. In prokaryotes and plants, the membrane in the inner layer of protection surrounded by a rigid cell wall, these membranes also regulate the passage of nutrients in and the waste products out. The cell contains membranes inside as well as the outside of the cell. Below (Figure 1) is a simplified plant cell, the dotted lines show the membranes. Figure 1 Cell Wall Endoplasmic Reticulum All the dotted lines represent membranes, it doesn't matter if the membrane is on the outside of the cell or the inside of the cytoplasm, the structure of the membranes are ...

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