Biology: Passive Transport and Osmosis

Study Notes

Also known as facilitated transport or passive-mediated transport
Movement of molecules down their concentration gradient with the assistance of transport proteins
No energy is required, as it is a spontaneous process
Types of transport proteins:
- Channel proteins: form a hydrophilic channel across the membrane
- Carrier proteins: bind to molecules and change shape to facilitate transport

Movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane
Helps maintain proper balance of fluids within cells
Types of osmotic situations:
- Isotonic: equal concentrations of solutes on both sides of the membrane
- Hypotonic: lower concentration of solutes outside the cell
- Hypertonic: higher concentration of solutes outside the cell

Movement of molecules from an area of high concentration to an area of low concentration
No transport proteins are involved
Occurs through the phospholipid bilayer of the cell membrane
Types of molecules that can diffuse:
- Small, non-polar molecules (e.g. oxygen, carbon dioxide)
- Hydrophobic molecules (e.g. steroids)

Facilitated diffusion is a spontaneous process that moves molecules down their concentration gradient with the help of transport proteins.
No energy is required for this process.
There are two types of transport proteins: channel proteins and carrier proteins.
Channel proteins form a hydrophilic channel across the membrane, allowing molecules to pass through.
Carrier proteins bind to molecules and change shape to facilitate transport.

Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration through a selectively permeable membrane.
Osmosis helps maintain the proper balance of fluids within cells.
There are three types of osmotic situations: isotonic, hypotonic, and hypertonic.
In an isotonic solution, the concentration of solutes is equal on both sides of the membrane.
In a hypotonic solution, the concentration of solutes is lower outside the cell.
In a hypertonic solution, the concentration of solutes is higher outside the cell.

Simple diffusion is the movement of molecules from an area of high concentration to an area of low concentration.
This process occurs through the phospholipid bilayer of the cell membrane.
No transport proteins are involved in simple diffusion.
Small, non-polar molecules such as oxygen and carbon dioxide can diffuse through the cell membrane.
Hydrophobic molecules like steroids can also diffuse through the cell membrane.