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Cell Membrane Images
Instructions: For each image, determine an appropriate title and a description for what is happening in each.
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Label: hydrophilic region, hydrophobic region, carbohydrates, glycolipids, glycoproteins, integral proteins, peripheral proteins, cytoplasmic side of membrane, extracellular side of membrane, cholesterol
OSMOSIS AND CELLS
Example Problem: a plant cell with 2% solutes in the cytoplasm is placed in a beaker containing 1% salt (NaCl). What will happen to this cell, and is the solution hypotonic, isotonic, or hypertonic?
To predict how cells will be affected by different environments or solutions that they are in, and to correctly identify the osmolarity of a solution, follow these steps:
1. Determine the amount of water in the cell and the solution. In the example, the amount of water in the cell is 98% (100% - 2%); the amount of water in the solution is 99% (100%-1%).
2. Determine the direction that water will move (greater to lesser concentration). In the example, water will move from the solution (99% water) into the cell (98% water). Remember that in most cells the solutes cannot diffuse across a membrane - water does.
3. Determine how the cell reacts. First, what kind of cell is it? Does it have a cell wall or not? If a cell wall is present, like in plants, algae, bacteria, and fungi, the cell wall prevents the cell from lysing (bursting), and instead, turgor pressure results when water enters the cell (in hypotonic solutions). If water is leaving a cell that has a cell wall (such as in hypertonic solutions), the membrane shrinks away from the rigid cell wall, and this is called plasmolysis. Animal cells (no cell wall present) swell and lyse when water enters the cell ( in hypotonic solutions) and shrivel when water leaves the cell (in hypertonic solutions). In the example, water is entering a plant cell (cell wall present). The cell will swell, but turgor pressure will prevent it from lysing.
4. Identify the cell's environment, or solution it is in. If the solution has more solutes than the cell, the solution in hypertonic. If the solution has less solutes than the cell, the solution is hypotonic. If the solute concentration is the same in the cell and the solution, the solution is isotonic. In the example, the solution has 1% solutes, which is less than the 2% in the cell; therefore the solution is hypotonic.
Sample problems:
1. A human red blood cell (.9% solutes) is placed in a solution with 5% solutes. What happens to the cell, and is the solution isotonic, hypertonic, or hypotonic? What would happen if the red blood cell were placed in pure, distilled water?
2. Bacteria and fungi are decomposers, and are responsible for making food rot. Our ancestors preserved food by heavily salting meat and fish, and making jelly "preserves" by adding lots of sugar to fruit. Why does this work? What will happen to bacteria and fungi in these environments? Are the foods hypertonic, hypotonic, or isotonic to the microbes?