Osmosis: Concentration and Potato Tissue

Topics: Concentration, Osmosis, Water Pages: 7 (1638 words) Published: June 23, 2013
Unit 4 Lab – Effects of Osmosis on Living Tissue
Assignment Total: 35 Points Course Weight: 6 Pre-Lab Preparation - Review the following resources to complete this assignment: Textbook: Chapter 5, pg. 83-86 Mastering Biology / Study Area / Chapter 05 – The Working Cell / Student Home Key Concepts Video: Plasmolysis Video: Turgid Elodea Activity: Membrane Structure Activity: Diffusion Activity: Osmosis and Water Balance in Cells Bioflix: Membrane Transport Additional Resources Blast Animation: Diffusion Blast Animation: Passive Diffusion Across a Membrane TLM / Handouts: View the PowerPoint presentation titled ‘Identifying Variables’. Print out the Osmosis Lab Student Worksheet on pages 4-7 of this document and complete it as instructed throughout the lab.

Introduction:
Water, the major component of cytoplasm and extra-cellular fluids, can diffuse back and forth through membranes with little difficulty. This process is known as osmosis. The direction of motion is regulated by the relative concentrations of water and dissolved substances inside and outside the cell. Water will move from an area of high concentration of water molecules (low concentration of dissolved particles) to an area of low concentration of water molecules (high concentration of dissolved particles). It is difficult to observe osmosis at the cellular level since cells are very tiny and can only be seen with a microscope, so you are going to use sticks of potato tissue in solutions that have different concentrations of dissolved substances to observe the effects of osmosis on living tissue. There are three basic relative concentrations of solutions. An isotonic solution has a concentration of dissolved particles equal to that of cells or body tissues; no net water flow occurs. A hypertonic solution has a lower concentration of water (higher concentration of dissolved particles) than that of cells or body tissues; water flows out of the cell. A hypotonic solution has a higher concentration of water (lower concentration of dissolved particles) than that of cells or body tissues; water flows into the cell. Complete Part One of the Osmosis Lab Student Worksheet, pg. 4-7 of this document.

Purpose of Lab:
To measure the effect of osmosis on potato tissue and use the data to estimate the concentration of dissolved substances in the cytoplasm of potato cells.

Experimental Variables:
In this experiment freshly cut strips of potato tissue will be measured with a ruler before being placed in separate solutions with increasing concentrations of salt. After 6 hours the potato strips will be removed from the solutions and measured again. Complete Part Two of the Student Worksheet.

Materials:
• • • • • • • 6 bowls or jars of equal size (at least 200 ml) 1 large potato sharp kitchen knife ruler with cm/mm markings glass or plastic measuring cup (1 or 2 cup size) measuring spoons (1/ 4 , ½, and 1 tsp. size) distilled H 2 0 if possible (dehumidifier water is distilled, or ask at the nearest campus if you can take some from a lab, or you can purchase distilled water in drugstores, or filtered water is close to distilled water) • salt • paper towel • paper and tape to label jars

Procedure:
1) Prepare solutions for containers 1-6 as follows. Allow all solutions to come to room temperature before placing potato tissue in containers. • Container 1 (0% salt): Measure 100 ml distilled water in a measuring cup and pour into container. • Container 2 (tap water): Measure 100 ml of tap water in a measuring cup and pour into container. • Container 3 (0.5% salt): Fill a measuring cup to the 200 ml mark with tap water. Add ¼ teaspoon of salt to the water and stir until all salt is dissolved. Pour 100 ml of salt solution into container. • Container 4 (1.0% salt): Fill a measuring cup to the 100 ml mark with tap water. Add ¼ teaspoon of salt to the water and stir until all salt is dissolved. Pour whole solution into container. • Container 5 (2.5% salt): Fill a...
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