Page 75 - Demo 1

Figure 35. Water can cross through the membrane, but the solute (sugar molecules)
cannot. Therefore, there will be a net movement of water from the le side
of the membrane to the right unl there is an equal concentraon of water on
both sides of the membrane.
Source: https://biology-esl.wikispaces.com/file/view/Osmosis2.jpg/247254647/Osmosis2.jpg

In the laboratory, cells are normally placed in isotonic (iso, same as)
soluons where the concentraon of water is equal on both sides of the
membrane. In this type of soluon, the cell neither gains nor loses water. In
medical sengs, a 0.9% salt soluon (NaCL) is known to be isotonic to red blood
cells; therefore, intravenous soluons normally have this concentraon.

Another type of soluon is referred to as hypotonic (hypo, less than)
where the concentraon of solute outside the cell is less than inside the cell;
thus, the tendency of water molecules is to move into the cell. Animal cells
placed in a hypotonic soluon gain water, swell and somemes burst. Cell bursng
is called lysis; hemolysis, then is the bursng of red blood cells. On the other
hand, plant cells placed in a hypotonic soluon do not burst. Instead, the plant
cell becomes turgid as the large central vacuole gains water and the cell
membrane pushes against the rigid cell wall. Turgor pressure is especially
important for plants to maintain their erect posion.

Cells placed in a hypertonic (hyper, greater than) soluon lose water
because the concentraon of solute outside the cell is greater than the inside,
thus, the tendency of water molecules is to move out of the cell. Animal cells
placed in a hypertonic soluon lose water and shrink. A plant cell placed in the
same soluon also loses water from its large central vacuole as the cell
membrane pulls away from the cell wall. This process that causes the
cytoplasm to shrink due to osmosis is referred to as plasmolysis.

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