Movement of Substances ✏ Biology In a Nutshell

Rucete ✏ Biology In a Nutshell

1. Key Principles of Substance Movement

• Movement occurs across a selectively permeable membrane.
• Substances transported include:
  • Solvent (e.g., water).
  • Solute (dissolved particles like ions or sugars).
• Movement usually follows a concentration gradient (high → low).
• Over time, the solute concentration equalizes on both sides.

Tonicity (Relative Solute Concentration in Solutions)

1. Hypertonic: Higher solute concentration outside the cell → water leaves the cell.
2. Hypotonic: Lower solute concentration outside the cell → water enters the cell.
3. Isotonic: Equal solute concentration inside and outside the cell → no net water movement.

 

 

2. Bulk Flow

• Definition: The collective movement of substances in the same direction due to pressure or force.
• Example: Blood flow in blood vessels.

 

 

 

3. Passive Transport (No Energy Required)

• Moves substances with the concentration gradient (high → low).

Types of Passive Transport:

1. Simple Diffusion:

   • Random molecular movement from high to low concentration.

2. Osmosis:

   • Diffusion of water across a selectively permeable membrane.

3. Dialysis:

   • Diffusion of solutes across a selectively permeable membrane.

4. Plasmolysis:

   • Water leaves the cell, causing it to shrink.

5. Facilitated Diffusion:

   • Movement of solutes or water via channel proteins in the membrane.
     

4. Active Transport (Requires Energy - ATP)

• Moves solutes against the concentration gradient (low → high).
• Used to transport small ions, amino acids, and other molecules.

 

 

5. Vesicular Transport (Transport of Large Particles)

• Uses vesicles to transport large molecules or particles across the membrane.

Types of Vesicular Transport:

1. Exocytosis (Cell Secretion):

   • Vesicles fuse with the plasma membrane to release substances outside the cell.

2. Endocytosis (Cell Uptake):

   • The cell engulfs external substances into the cytoplasm.
   • Types:
     • Phagocytosis ("Cell Eating") – Engulfs solid particles (e.g., bacteria).
     • Pinocytosis ("Cell Drinking") – Engulfs dissolved materials (e.g., liquids).
       

 

 

In a nutshell

• Passive Transport = No Energy (Simple Diffusion, Osmosis, Facilitated Diffusion).
• Active Transport = Needs ATP (Moves against concentration gradient).
• Vesicular Transport = Bulk Movement (Endocytosis & Exocytosis).