Chapter 13: Diffusion and Osmosis

==What does permeable mean?==

A membrane can be:

  1. Permeable: molecules can pass in or out of the membrane
  2. Semi-permeable: controls what molecules can pass in or out of the membrane
  3. Impermeable: no molecules can pass in or out of the membrane

==Define Homeostasis:== the ability for an organism to maintain a constant internal environment.

e.g. maintaining temperature, correct pH, keep proper concentration of nutrients and water and eliminate wastes.

==What is diffusion?==

  • Movement of molecules from an area of high concentration to an area of low concentration.
  • It’s a form of passive transport: no external energy is needed.

==What is osmosis?==

  • Specific type of diffusion: movement of water molecules from a region of high water concentration to a region of low water concentration across a semi-permeable membrane.
  • Passive Transport.

==Osmosis and animal cells:==

Animal cells in a solution that is the:

  1. Same concentration as the cell: cell will stay the same size.
  2. Higher concentration solution of solutes: loses water, shrivels and dies.
  3. Lower concentration solution of solutes: gains water, swells and may burst.

Define osmoregulation: process of maintaining salt and water balance across membranes.

  • Example: an amoeba in fresh water need a __contractive vacuole __to expel water to prevent bursting.
  • Example 2: an amoeba in salt water don’t need this vacuole as the concentration of the salt outside the cell is the same as inside the cell.

==Osmosis and plant cells:==

Plants in a:

  1. Less concentrated solution than their cytoplasm: gains water, becomes turgid and strong.
  2. More concentrated solution: loses water, becomes plasmolysed (shrunk) and weak.

==Define Turgid Pressure: ==the outward pressure of the cytoplasm and the vacuole against the cell wall of the plant.

  • Gives plants their strength.
  • If plants didn’t have this, they would wilt. The vacuole has shrunk due to it lacking water.

==Osmosis and Food Prevention:==

  • Bacteria and fungi are the most common causes of food spoilage.
  • If a food is placed in a high sugary or salty solution, then any bacteria or fungi present will lose the water in their cells by osmosis; causing them to shrivel and die. e.g. salting fish.