Read and make notes on membrane transport mechanisms

There are two main categories:

1. Passive Transport: This does not require the cell to expend energy. Substances move down their concentration gradient (from high to low concentration).

   • Simple Diffusion: Small, nonpolar molecules (like O₂ and CO₂) can pass directly through the lipid bilayer.
   • Facilitated Diffusion: Polar molecules or ions move across the membrane with the help of transport proteins (channels or carriers). This still moves down the concentration gradient.
   • Osmosis: The diffusion of water across a selectively permeable membrane.

2. Active Transport: This requires the cell to expend energy, usually in the form of ATP, to move substances against their concentration gradient (from low to high concentration).

   • Primary Active Transport: Uses ATP directly to pump substances across the membrane (e.g., the sodium-potassium pump).
   • Secondary Active Transport: Uses an electrochemical gradient established by primary active transport to move another substance against its gradient.

Bulk Transport is also a mechanism for moving large molecules or particles across the membrane, requiring energy:

• Endocytosis: The cell takes in substances by engulfing them with its membrane. This includes phagocytosis (cell eating) and pinocytosis (cell drinking).
• Exocytosis: The cell expels substances by fusing vesicles containing the material with the cell membrane.