Biological Membranes and Transport

Biological Membrane

  • Composed of a phospholipid bilayer.
  • Contains transmembrane (embedded) and surface proteins.
  • Selectively permeable, allowing certain substances to pass while restricting others.

Diffusion

  • The simplest method for substances to enter or leave a cell.
  • Movement of substances from an area of higher concentration to an area of lower concentration.
  • Passive transport, meaning it does not require cellular energy (ATP).

Factors Influencing Diffusion Rate

  • Temperature: Higher temperature usually increases the rate of diffusion.
  • Size of Substance: Smaller substances typically diffuse faster.
  • Concentration: A greater concentration gradient increases the rate of diffusion.

Types of Diffusion

  1. Osmosis: Movement of water across a membrane.
  2. Simple Diffusion: Substances pass directly through the biological membrane without any barrier.
  3. Facilitated Diffusion: Carrier proteins assist in the transport of substances across the membrane.

Percent Solutions

  • Based on 100%:
    % solute+% solvent=100%\% \text{ solute} + \% \text{ solvent} = 100\%

    Example: 20% Sucrose + 80% dH20 = 100%

Experiment on Osmosis

  1. Procedure:
    • Place a dialysis bag containing 20% sucrose into a beaker with an unknown solution.
    • Monitor the weight of the bag for 30 minutes.
  2. Data Analysis:
    • Graph the change in weight over time using Excel.
  3. Determination:
    • Determine if the unknown solution is isotonic, hypotonic, or hypertonic relative to the sucrose solution in the bag.

Isotonic Solution

  • No net water movement. The concentration of solutes is the same inside and outside the cell.

Hypotonic Solution

  • Net water movement into the cell. The concentration of solutes is lower outside the cell than inside.

Hypertonic Solution

  • Net water movement out of the cell. The concentration of solutes is higher outside the cell than inside.

Unknown Solutions in Beaker

  • Possible solutions:
    1. Water
    2. 5% sucrose
    3. 20% sucrose
    4. 30% sucrose
  • Formulate a hypothesis statement for each solution to predict the outcome of the osmosis experiment.