Osmotic Solutions

Open Ended

Define osmosis and explain why water movement is important for cells.

Vocab in a Minute:

• hyper: more (prefix)

• hypo: less (prefix)

1. Diffusion

• Definition: The movement of molecules from an area of high concentration to an area of low concentration until equilibrium is reached.

• Key Concept: Molecules move down the concentration gradient (from high to low).

• Does Not Require Energy: Diffusion is a type of passive transport, meaning no energy (ATP) is required.

• Examples:

  • Oxygen and carbon dioxide moving in and out of cells during respiration.

  • Perfume spreading throughout a room.

​2. Osmosis

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

• Key Concept: Water moves to balance solute concentrations on both sides of the membrane.

• Passive Process: Osmosis is also a form of passive transport and does not require energy.

• Tonicity Terms:

  • Hypertonic: Higher solute concentration outside the cell → water moves out of the cell, causing the cell to shrink.

  • Hypotonic: Lower solute concentration outside the cell → water moves into the cell, causing the cell to swell.

  • Isotonic: Equal solute concentration inside and outside the cell → water moves equally in and out, and the cell stays the same size.

3. Similarities Between Osmosis and Diffusion

• Both Are Passive Transport: Neither requires energy (ATP).

• Movement from High to Low: In both processes, molecules move down their concentration gradient (for osmosis, water moves towards a higher solute concentration).

• Achieve Equilibrium: Both processes continue until the concentrations are equal on both sides of the membrane.

4. Differences Between Osmosis and Diffusion

• Osmosis: Only involves the movement of water through a semipermeable membrane.

• Diffusion: Involves the movement of any type of molecule (solids, liquids, gases) across a concentration gradient.

5. Importance in Cells

• Diffusion: Helps cells take in oxygen and nutrients and remove waste products like carbon dioxide.

• Osmosis: Regulates the water balance in cells, maintaining proper cell function and preventing damage from dehydration or swelling.

​On the following slide you will be directed to a virtual lab. Use your lab hand-out to complete the lab.

You have until the end of class.

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