1 Osmosis

Water and other small molecules that do not dissolve in lipids diffuse through openings formed by proteins that go through the entire membrane. Diffusion of water through a membrane is called osmosis.

Osmosis Since water makes up 70 - 95% of a living cell, its movement in and out is of vital importance. The cell has no control over osmosis. Osmosis will end when equilibrium is reached. The water concentration is determined by the concentration of solutes in the water.

Isotonic Solution concentration of solutes equal in and out of cell Iso = same

Hypotonic Solution concentration of solutes outside is lower more water, less solutes ex: distilled water hypo = under

Hypertonic Solution concentration of solutes outside is higher less water, more solutes ex: saltwater hyper = above

What is the effect of hypotonic solutions on cells?

Cells in hypotonic solutions take in water. In plant cells, the cell wall can take the increased pressure and turgor results. The plant cells are stiff.

Animal cells can use excretion or contractile vacuoles (found in unicellular organisms) to keep from bursting - cytolysis. cyte = cell - lysis = to burst

When cells are put in distilled water and burst due to cytolysis the membranes and contents can be separated by a centrifuge for detailed study.

What is the effect of hypertonic solutions on cells?

Cells in hypertonic solutions lose water Cells in hypertonic solutions lose water. This causes cells to shrink - plasmolysis.

Onion cells in saltwater Normal onion cells

Elodea leaf in saltwater

Elodea cell in a hypotonic solution Elodea cell in a hypertonic solution Water Water

If humans drink seawater, their cells lose more water than they take in.

Animal Cells

Plant Cells

Since osmosis and diffusion take place without any use of energy by the cell, they are forms of passive transport.

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