we shall look at the type of transport involves in transporting substances in & out of the cell.
1) There are 2 types of transport: Passive transport (PT) and Active transport (AT)
- PT:
i) No energy (ATP) is used by cell during movement of substances.
ii) substances move according to their concentration gradient.
* concentration gradient is the difference in the concentration of a substance between 2 regions. - AT:
i) needs energy (ATP)
ii) substances (ions/molecules) move against concentration gradient across the PM.
2) There are 3 different types of PT: Simple diffusion, Osmosis, Facilitated diffusion.
- Simple diffusion:
i) a physical process
ii) definition: is the net movement of molecules/ions from a region of higher concentration to a region of lower concentration, according to a concentration gradient, until an equilibrium is achieved. (dynamic equilibrium)
iii) Eg: the exchange of gases between the alveoli & the blood cap. at the lungs. - Osmosis:
i) involves only water molecules.
ii) definition: is the net movement of water molecules from a region of low solute concentration to a region of high solute concentration through a semi-permeable membrane.
iii) you can study osmosis using a simple osmometer at the lab.
iv) Eg: the uptake of water by the plant roots. - Facilitate diffusion:
i) definition: movement of hydrophilic molecules/ions (eg: glucose, ions) across the PM with the help of transport protein.
ii) Carrier protein: are specific, has binding sites for molecules to bind on.
iii) Pore protein: are transporters which are always open, usually hv charges & specific shape, to transport small, dissolved particles (ions)
iv) Eg: Absorption of certain digested foods/nutrients in the villi of the small intestine. eg; glucose.
*transport proteins such as uniport, symport, antiport are not in spm syllabus.
3) The Active Transport:
- i) definition: is the movement of molecules or ions across the PM against their concentration gradients, that is from a region of lower concentration to a region of higher concentration, which requires carrier proteins & cellular energy (ATP).
- ii) Carrier proteins, often called pump, has active sites. One site binds with a particular molecule/ion. The other site binds with ATP (phosphate molecule).
- iii) Eg: sodium-potassium pumps in animal cells (nerve & muscle cells)
* 3 sodium ions are released to the outside of the cell while 2 potassium ions are brought into the cell. - iv) other eg: the uptake of mineral ions by the plant roots.
