BIO 101 Lab 05: Osmosis and Diffusion in
, Red Blood Cells, and Potatoes
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before soaking, and 3) photo of potato strips after soaking to Canvas.
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Review osmosis, diffusion, and cell membrane structure.
Observe plant and animal cells placed in solutions, hypotonic, isotonic, and hypertonic to the cells and
observe the effect of each of the solutions on the cells.
Interpret images of plant cells or red blood cells in different solutions.
Reinforce understanding of the experimental approach and data analysis.
Measure changes in potato cells to observe the effects of hypotonic and hypertonic and isotonic
solutions on plant cells.
Draw conclusions about osmosis across plant and animal cell membranes.
Cells and Cell Membrane structure.
Living cells are filled with an aqueous solution, the cytosol. Many small solutes or particles, are dissolved in this
watery cytosol, including ions, nutrients, waste, and enzymes. Larger organelles (such as mitochondria and
chloroplasts) and large complexes of molecules (e.g. ribosomes) are also located in this cytosol; organelles and
complexes combine with the cytosol to form the cytoplasm of cells.
The exterior barrier of all cells is a cell membrane (plasma membrane). Because the cell membrane is made of
both phospholipids and proteins it is semi-permeable:
some molecules can easily pass through the phospholipid
bilayer, while other molecules cannot. Phospholipids have hydrophobic fatty acid tails and hydrophilic phospho-
heads. In the bilayer, the hydrophobic fatty acids are sandwiched between the hydrophilic heads; one layer of
polar heads lines the inside (cytosolic face) of the cell membrane and a second layer of polar heads lines the
outside (extracellular face) of the cell membrane or surface.
Transport through membranes.
Molecules that can easily pass through a cell membrane are small and nonpolar, such as gases: oxygen, carbon
dioxide, and nitrogen. Hydrophobic lipids (fats and steroids) can dissolve in the hydrophobic fatty layer of the cell
membrane and will diffuse into or out of a cell.
Some small molecules (e.g. sugars) and ions (sodium or chloride) can diffuse across a membrane if there is a
protein (transport protein or ion channel) These small solutes will move from areas of high concentration to low
concentration through a select protein that is part of the membrane.