Tonicity_Lab

Hypertonic, Hypotonic, and Isotonic Solutions Impact on Cells

Experimental Question

• How does the concentration of dissolved particles affect the movement of water across the membrane and internal environment of the cell?

Hypothesis

• The hypothesis is not explicitly stated but suggests an examination of how different solute concentrations influence cell behavior.

Background

• Osmosis: A form of passive transport, specifically of water across cell membranes, influenced by solute concentrations.

• Environmental Interaction: Organisms must adapt to their surrounding environmental solute conditions.

• Types of Solutions:

  • Hypertonic Solutions:

    • Cause water to move into the cell, resulting in cell expansion.

    • Cell has a higher solute concentration compared to the external solution.

    • In plants, creates turgor pressure for structural support.

    • In animal cells, can lead to bursting and cell death.

  • Hypotonic Solutions:

    • Water moves out of the cell, causing it to shrink.

    • Cell has a lower solute concentration than the external solution.

    • In plants, causes wilting.

    • In animal cells, leads to loss of shape and eventual death.

  • Isotonic Solutions:

    • Equal concentration of solutes inside and outside the cell membrane.

    • Results in dynamic equilibrium, maintaining cell status.

• Homeostasis: The regulation of internal environments to maintain balance and function.

• Water Potential:

  • Defined as the ability of water to move based on solute concentration gradients.

  • Greater differences in solute concentrations lead to increased water movement from high to low concentration.

Materials

• Onion skin

• Elodea leaf

• Water microorganisms from pond water

• Slide with cover slip

• Scalpel

• Dropper

• Distilled water

• 1.5M NaCl solution

• Tap water

• Compound microscope

Procedure

Part 1 – Onion Skin

1. Cut a thin section of onion (1cm x 1cm) using a scalpel.

2. Peel the outer layer to obtain a nearly single cell thick sample.

3. Create a wet mount slide with tap water.

4. Observe the size and shape of cells.

5. Add 1.5M NaCl solution:

   • Observe changes in cell size and shape.

6. Add distilled H2O:

   • Observe changes in cell size and shape.

Part 2 – Elodea Leaf

1. Cut a thin leaf of Elodea using a scalpel.

2. Create a wet mount slide with tap water.

3. Observe the size and shape of cells.

4. Add 1.5M NaCl solution:

   • Observe changes in cell size and shape.

5. Add distilled H2O:

   • Observe changes in cell size and shape.

Part 3 – Water Microorganisms

1. Create a wet mount slide using pond water sample.

2. Observe size and shape of microorganisms.

3. Add 1.5M NaCl solution:

   • Observe changes in size and shape.

4. Add distilled H2O:

   • Observe changes in size and shape.

Conclusions

• Predict impacts of exposure to hypertonic, hypotonic, and isotonic solutions on cells.

• Explain the relationship between osmosis and the types of solutions.

• Discuss why plant cells cease swelling in hypotonic solutions.

• Reflect on the significance of homeostasis in cells and articulate the consequences of drinking saltwater versus freshwater.