Passive Transport

Passive Transport

1. Brownian Motion

• Molecules are constantly in motion, even those in a solid vibrate slightly. This random movement is referred to as Brownian motion.

2. Net Movement

• Imbalances in pressure, temperature, or concentration lead to a specific direction of molecular movement.
• These imbalances are referred to as gradients.

3. Concentrations and Solutions

• Percent Concentration:

  • Percent concentration indicates that % solute and solvent always add up to 100%.
  • For example, a solution with 70% solute contains 30% solvent.

• Molarity:

  • Molarity is a measurement of solute concentration; higher molarity indicates a higher solute concentration.
  • Example: Solution B with more salt compared to Solution A has a higher molarity.

4. Moving Along the Concentration Gradient

• Moving down or with the gradient involves moving from an area of high concentration to low concentration.
• Conversely, moving up or against the gradient means moving from low to high concentration.

5. Types of Transport

Passive Transport

• Molecules are allowed to move across the membrane due to natural chemical and electrical forces, following the concentration gradient from high to low concentration.
• This process does not require additional ATP energy.

Active Processes

• Active transport refers to processes where molecules are moved against their concentration gradient, requiring energy (ATP).
• This involves transporting molecules from a low concentration area to a high concentration area, opposing natural forces.

6. Passive Processes

Simple Diffusion

• Simple diffusion involves the tendency of molecules to evenly distribute themselves, moving from an area of high concentration to low concentration until equilibrium is reached.

7. Factors Affecting the Rate of Diffusion/Osmosis

Tonicity

• Tonicity refers to the difference in solute concentration between two solutions across a membrane. The greater the difference, the faster diffusion occurs.

Temperature

• Higher temperatures result in faster diffusion rates.
  • Example: Red water (hot) vs. blue water (cold).

Size of Molecules

• The size of the molecules also affects diffusion rates; larger molecules typically diffuse more slowly.

8. Other Types of Diffusion

Dialysis

• Dialysis is the diffusion of solutes across a semipermeable membrane from an area of high concentration to low concentration.

Osmosis

• Osmosis is the diffusion of solvent (usually water) across a membrane from a region of higher solute concentration to lower solute concentration.

9. Osmosis and Solutions

• Tonicity of solutions can be categorized into three environments:
  1. Hypertonic: Higher concentration of solutes (lower concentration of water).
  2. Hypotonic: Lower concentration of solutes (higher concentration of water).
  3. Isotonic: Same concentration of solutes (equal concentration of water).

10. Comparison of Solutions

• When comparing solutions:
  • One will always be hypertonic and the other hypotonic or both solutions can be isotonic.

11. Water Movement in Solutions

• Water moves from areas of high concentration to low concentration and also from low solute concentration to high solute concentration (i.e., it moves towards salt).

12. Cellular Reactions to Solutions

• Isotonic Environment: Water enters and leaves the cell at the same rate.
  • Result: Stable, normal red blood cells.
• Hypertonic Environment: Water leaves the cell, causing it to shrink (crenate).
• Hypotonic Environment: Water enters the cell, which may cause it to swell and burst (lyse).

13. Water Properties

• Water is a polar molecule but can pass through membranes by osmosis due to its small size.
• Cells also utilize specialized channels called aquaporins for water transport.

14. Facilitated Diffusion

• Large molecules can move through a membrane with the assistance of proteins.
• Facilitated diffusion is a passive transport method that requires no additional energy.
• Two Types of Transport Proteins:
  1. Channel Proteins: Form tubes for ions or polar molecules, can change shape to open or close.
  2. Carrier Proteins: Bind to the substance for transport and release it on the other side of the membrane.