H1 Biology and H2 Biology
How are compounds taken up by cells via Diffusion, Osmosis and Active Transport?
Notes from the video ‘H2 Biology Tuition | H1 Biology Tuition | Diffusion, Osmosis and Active Transport in cells’:
In this Biology tutorial, we would learn how compounds are taken up by cells via diffusion, osmosis and active transport.
Small, non-polar molecules move from a region of high concentration outside the cell to one of lower concentration inside the cell, down a concentration gradient. No ATP is expended in the process. These molecules can pass through the gaps in the hydrophobic core of the bilayer easily.
Molecules are transported across the membrane down a concentration gradient via transport proteins such as channel and carrier proteins. This process does not require the use of ATP.
These molecules may be larger, polar or charged so they are unable to diffuse through the hydrophobic core of the membrane.
Channel proteins provide a hydrophilic pore that allows for free movement of the transported substance across the membrane.
On the other hand, carrier proteins undergo changes in conformation to bring a solute from one side of the membrane to the other when a molecule binds to the binding side.
There is a net movement of water molecules from a region of higher water potential outside the cell to a region of lower water potential in the cell through the selectively permeable membrane, down a concentration gradient. This process does not require the use of ATP.
Water is small enough to move across the membrane through transient pores and through the aquaporin proteins that facilitate their movement across the membrane.
Polar or charged molecules move from a region of low concentration outside the cell to one of high concentration inside the cell against a concentration gradient across the membrane. This requires ATP and involves carrier proteins and pumps that are solute-specific.