Transport across membranes (Facilitated dffusion (Channel proteins…
Transport across membranes
The movement of molecules from a region of high concentration to a region of low concentration ie. down a concentration gradient.
Rate is affected by
Surface area of the membrane
Thickness of the exchange surface or distance to travel
Size of diffusing molecule
The nature of the diffusing moecules
ions and molecules such as glucose cannot pass through the cell membrane because they are insoluble in the phospholipid bilayer.
A special form of diffusion which allows movement of these molecules (glucose) across a membrane, down a concentration gradient.
Occurs at specific sites on the plasma membrane where there are transport protein molecules. Their number and availability limit the rate of facilitated diffusion.
molecules with pores linked with polar groups. As the channels are hydrophilic ions, being water soluble, can pass through. The channels open and close according t the needs of the cell.
Allow diffusion of larger polar molecules, such as sugars and amino acids, across the membrane. A molecule attaches to its binding site, on the carrier protein. he carrier protein changes shape and releases the molecule on the other side of the membrane.
The exchange of substances between cells and their surroundings occurs in ways that involve metabolic energy (active transport) and ways that do not (passive transport).
Experiments show an increase in active transport when more oxygen is available to the cells.
Features of active transport
The process requires energy from ATP
Process occurs through intrinsic carrier proteins spanning the membrane.
Ions and molecules are moved from a lower to a higher concentration against a concentration gradient.
The rate is limited by number and availability of carrier proteins
Active transport is an energy requiring process in which ions and molecules are moved across membranes against a concentration gradient.
Processes involving active transport
nerve impulse transmission
Reabsorption of glucose in the kidney
Mineral uptake into plant root hairs
A type of facilitated diffusion that brings molecules and ions into cells together on the same transport protein molecule.
How it works
A glucose molecule and 2 sodium ions outside the cell attach to a carrier protein in the cell membrane.
The carrier protein changes shape and deposits the glucose molecule and the sodium ions inside the cell.
The glucose molecule and sodium ions separately diffuse through the cell to the opposite membrane.
The glucose passes into the blood by facilitated diffusion and sodium ions are carried by active transport.