Movement of Fluids in Cells

1. Movement of Fluids in Cells

2. The Cell Membrane By the late 18th century, microscopes had shown that all cells have one structure in common. This was the cell membrane, which holds the cell together. It allows some substances to pass into the cell, but excludes others. For this reason, it is called a semi-permeable membrane.

3. Diffusion Diffusion is the process of particles moving, in order to balance their concentrations. For example, if a single sugar cube is placed in a cup of tea, and left to sit, the sugar will eventually dissolve, and will spread evenly (diffuse) throughout the solution. The solute will always move from an area of high concentration, to an area of low concentration, in order to make the concentration balanced.

4. Diffusion Across the Cell Membrane

5. Osmosis Sometimes, molecules may be too large to pass through a membrane. In this case, water molecules will pass across the membrane, in order to attempt to balance the concentrations on both sides. This process is called osmosis.