Page 43 - MNU microbiology theoritical 2025
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General Microbiology & Immunology (PM 401) Second level Semester 4 2024/2025
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A- Passive Transport
high
1- Simple diffusion
low
• Random movement of gases or small uncharged polar molecules across a
phospholipid bilayer membrane from an area of high concentration to an area of
low concentration. (High to Low)
• Diffusion continues until equilibrium is
reached.
Examples: gases: O2, and CO2.
Small polar molecules: ethanol, H 2O, and urea.
2- Facilitated diffusion
• Diffusion of specific particles through transport proteins, carriers or channels
found in the membrane and is aided by concentration gradient
- Transport Proteins are specific – they “select” only
certain molecules (polar molecules or ions) to cross the
membrane.
- Transports larger or charged molecules
3- Osmosis:
Diffusion of water through a selectively permeable
membrane
• Water moves from high to low water
concentrations
General Microbiology & Immunology (PM 401) theoretical handbook Page 32
