This document discusses the movement of substances across the plasma membrane through three main processes: simple diffusion, facilitated diffusion, and active transport. It defines osmosis as the passive movement of water molecules across a semi-permeable membrane from an area of higher water concentration to lower concentration. Osmosis is demonstrated using a Visking tube experiment where water diffuses into or out of the tube depending on if it is placed in a hypertonic or hypotonic solution. The movement of water in plant and animal cells is also explained.

1. Chap 3: Movement of Substances
Across Plasma Membrane
Structure of Concept of osmosis
plasma membrane
Movement Visking tube Cells
• In hypertonic
solution – H2O
• Animal
diffuse out
 Lysis
• In hypotonic
 Crenation
solution – H2O
diffuse in
• Plant
 Turgid
 Plasmolysis
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coloured box
for more info.
Application
• Wilting
• Food preservation

2. Structure of Fluid mosaic model
plasma membrane
Eg
Movement • Simple diffusion
 Does not need energy
 Small uncharged
molecules (O2 & CO2)
 Fat-soluble
substances
 Lipid
• Facilitated diffusion
 Does not need energy
 H2O-soluble
substances
(glucose, amino acid)
[carrier protein] Protein
 Small polar molecules channel
(ions, H2O) [channel]
 Channel for H2O is
aquaporin
• Active
 Needs energy
 Na+-K+ pump
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Passive transport

3. Definition
Concept of osmosis Movement of H2O molecules
(Passive transport) from higher [H2O] region to
lower [H2O] region through
semi-permeable membrane
Eg
Visking tube Cells
• In hypertonic
solution – H2O
Plants
diffuse out
• In hypotonic
solution – H2O
diffuse in
Animals
Lysis Crenation