To download a copy of the lab packet with the instructions, lab report, and results tables, click the link below:
For more information on osmosis, diffusion, and cell transport, click HERE
This lab demonstrated osmosis, which is the movement of water through the cell membrane. We used slices of potato as a source of cells. The lab had two parts, one where water moved into the cells, and the other part where water moved out of the cells.
It is important to understand that a slice of potato is really a collection of thousands of cells all stacked on one another. Think of the slice as a structure made up many many tiny water balloons stuck to each other. Here is a picture of a very thin sliver of potato from the microscope in class:
Situation #1 Water Moves Into The Cells (Distilled water beaker)
- The potato slice is placed into a cup of pure distilled water. (Remember that pure = concentrated.)
- There also is some water already inside the cells .
- The distilled water in the cup is more concentrated than the water inside the cells.
- Water molecules will move from an area of higher concentration to an area of lower concentration.
- The area of lower concentration is inside the cells, so the water will move there.
- The cell membrane is semi-permeable so the water molecules can get through.
- The cell will expand as the water flows in.
- As all the cells expand, the potato slice will expand and become more rigid.
Situation #2 Water Moves Out Of The Cells (Salt water beaker)
- The slice is placed in a cup of very salty water.
- The water in the cup is a lower concentration because the salt forces the water molecules apart from each other. (Less pure = less concentrated)
- The salt makes the water in the cup a lower concentration than the water inside the cells.
- The water molecules will move out of the cells to spread into the salty water in the cup.
- As water leaves the cells, they will shrink.
- As the cells shrink, the slice will shrink and become more flexible.
For your discussion: Write 3 full and complete paragraphs. Below is a list of suggested topics for each paragraph. Use vocabulary from the list above as much as you can in your paragraphs.
1. Explain what happened to the potato slice that soaked in the distilled water. You may make diagrams to go along with your writing. Be sure to explain the entire process. Use the proper vocabulary from the list above.
2. Explain what happened to the potato slice that soaked in the salt water. You may make diagrams to go along with your writing. Be sure to explain the entire process. Use the proper vocabulary from the list above.
3. Explain cell transport and why is is needed for some of the life processes. List which of the life processes need cell transport to work. You will need to refer back to your notes to find good information to put into this paragraph
If you do not want to write paragraphs, you may do a comic book style discussion instead. This type of discussion must cover all of the same science concepts listed above for the paragraphs. You would use a series of labed diagrams with good captions to explain the key concepts. We used a lot of diagrams for our notes in class, so you should be familiar with how diagams can be used to explain diffusion and osmosis. This alternative discussion is not easier than writing paragraphs, it is just a different way to communicate the information.
Conclusion: You may just copy the sentences below and fill in the blanks for your conclusion.
Osmosis was shown in the potato slice in the distilled water when the water moved ___________________ (into or out of) the cells in the slice.
Osmosis was shown in the potato slice in the salt water when the water moved ___________________ (into or out of) the cells in the slice.