IB Biology II: Osmosis Design Lab
Objective: To determine the solute concentration of a potato.
Background: Diffusion refers to the desire of all matter to be equally concentrated in its environment. If a large concentration of something is put into a particular region of the environment, it will disperse until its concentration is uniform throughout the environment, provided it does not encounter any barriers through which it cannot pass.
Salts, ions, and large starch molecules can be found in potatoes. Charged ions like sodium ions and chloride ions as well as large molecules like starch are unable to pass through most biological membranes. However, water molecules are able to pass through most biological membranes so concentration imbalances within organisms are naturally corrected via the diffusion of water across semi-permeable membranes to equalize solute concentrations on both sides of the membrane. This process is known as osmosis .
When the concentration of dissolved solutes are equal on both sides of an organism’s cell membrane, the solution is said to be isotonic and there is no net flow of water to either side of the membrane. This means that both environments have equal concentrations.
When the concentration of dissolved solids is greater inside an organism’s cell membrane than outside the cell membrane, the solution outside the membrane is said to be hypotonic and water will diffuse across the membrane from outside to inside in an effort to decrease the concentration of the organism’s cells. When the concentration of dissolved solutes is greater outside of an organism’s cell membrane than inside the membrane, the solution outside the cell membrane is said to be hypertonic and water will diffuse across the cell membrane, from inside to outside, in an effort to decrease the concentration of solutes outside the cell membrane.
Materials Available:
Potato, distilled water, digital scale, sugar, salt, beakers, hot plate
Your Lab Must: have a minimum of 5 treatments, have a way to measure/determine results, have a way of making equally potato segments
Today’s Goal: Design your lab with your group. Figure out necessary materials
(anything you need to bring from home) and write your hypothesis and lab procedure. Be sure to specify variables, controls, and how you will measure/determine if your hypothesis is supported or unsupported.
Next Class: Complete the lab experiment.
Class After Next: Go to computer lab and make sure we all can make Excel graphs of our results.