Quiz 4 Study Guide: Diffusion/Osmosis

General Terms to Understand

• Homeostasis

  • Definition: The body’s ability to maintain a stable internal environment despite external changes.

  • Mechanisms: Regulating temperature, hydration, blood sugar, etc.

• Active Transport

  • Definition: Energy-requiring process by which cells move molecules or ions across their membranes against their concentration gradient.

• Diffusion

  • Definition: The movement of molecules from an area of high concentration to an area of low concentration.

• Osmosis

  • Definition: Passive movement of water molecules across a semipermeable membrane from an area of high water concentration to an area of low water concentration.

• Selectively Permeable Membrane

  • Definition: A barrier that allows certain substances to pass through while preventing others.

• Concentration Gradient

  • Definition: The difference in concentration of a substance across a space.

  • Importance: The greater the concentration gradient, the faster the diffusion occurs.

Animal Cell (Human Red Blood Cell) Experiment

• Conditions Tested

  1. Isotonic Solution (0.9% NaCl)

     • Observation: Cells appear normal, tube is opaque.

  2. Hypertonic Solution (10% NaCl)

     • Observation: Cells shrivel and shrink, tube is opaque.

  3. Hypotonic Solution (Water)

     • Observation: Cells swell and burst, tube becomes transparent.

Plant Cell (Elodea Cell) Experiment

• Conditions Tested

  1. Isotonic Solution (Water)

  Observation: Cells appear normal (shown in image A).

  1. Hypertonic Solution (10% Salt Solution)

     • Observation: Cell membrane and vacuole shrink (shown in image B).

  • Key Point: Plant cells do not burst in hypotonic solutions due to the presence of a cell wall.

Dialysis Bag Experiment

• Procedure

  • A test strip was used to determine the presence of glucose.

  • Glucose and iodine were able to diffuse through the bag, while starch did not.

• Results

  • Conclusion: Starch, being larger in size, does not diffuse through the dialysis bag, which is selectively permeable.

  • The glucose diffused out of the bag into the beaker, while iodine diffused from the beaker into the bag, following their concentration gradient (high to low).

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