What is transport?
Transport can be subcategorised as passive or active
There are 5 types of transport:
Passive transport is movement of molecules through the membrane in which no energy is required, molecules move in response to a concentration gradient.
Diffusion is movement of molecules from high concentration to low concentration. For example: movement of oxygen across the wall of an alveolus.
Selective permeability: integral membrane proteins allow the cell to be selective about what passes through the membrane
Channel proteins have a polar (hydrophillic) interior allowing polar molecules to pass through
Facilitated diffusion is movement of a molecule from high to low concentration with the help of a carrier protien. It is specific, passive, and saturates when all carriers are occupied. The carrier protein changes shape, facilitating diffusion. For example: release of glucose from liver cells into the bloodstream
Ion channels allow the movement of ions (charged or molecules) which are associated with water.
Gated channels are opened or closed in response to a stimulous
The stimulous may be chemical or electrical
In an aqeuas solution: water is the solvent
dissolved substances are the solvents
Osmosis is the movement of water from an area of high concentration to low concentration of water.
Movement of water toward an area of high solute solution for emample reabsorption of water molecules from the kidney tubule.
Involves a semi-permeable membrane.
When 2 solutions have different osmotic concentrations:
the hypertonic solution has a higher solute concentration
the hypotonic solution has a lower solute concentration
Water will move towards hypertonic solutions through aquaporins
Isotonic solution has a normal level
Requires energy- ATP is used directly or indirectly to fuel active transport. It moves substances from low to high concentration and it requires the use of carrier proteins.For example: pumping of calcium ions into storage vesicles inside muscle cells.
Carrier Protiens used in active transport include:
Uniporter- move one molecule at a time
Symporter- move two molecules in the same direction
Antiporter- move two molecules in opposite directions
Bulk transport of substances is accomplished by:
- Endocytosis- movement of substances into the cell
- Exocytosis- movement of materials out of the cell
phygocytosis- the cell takes in particular cell
pinocytosis- the cell takes in only fluid
receptor- mediated endocytosis: specific molecules are taken in after they bind to a receptor
Endocytosis is active
Example: Cholesterol is taken up into cells
Exocytosis occurs when material is discharged from the cell. Vesicles in the cytoplasm fuse with the cell membrane and release their contents to the exterior of the cell
- Used plants to export cell wall material
- Used in animals to secrete hormones, neurotransmitters, digestive enzymes
For example: Insulin is released into the bloodstream