Transport through Membranes

Diffusion is the net movement of molecules or ions from a region of high concentration to a region of low concentration. Diffusion continues until the particles are evenly distributed throughout the area. When the particles are evenly distributed it has established equilibrium. Diffusion is a passive process meaning it doesnt need energy for it to take place. The molecules that move through diffusion move down the concentration gradient. Molecules can move both in and out of the cell via diffusion. Oxygen and Carbon Dioxide move via diffusion.

Osmosisis the movement of water from a high water potential to a low water potential across a partially permeable membrane. Water potential is a measure of pressure exerted by water molecules, e.g pressure on the membrane. Pure water has the highest water potential. Isotonic is the concentration of water is the same inside the cell as outside the cell so no osmosis takes place. Hypertonic is when there is a higher concentration of water outside the cell to inside the cell. Hypotonic is when there is a higher concentration of water inside the cell to outside the cell. A partially permeable membrane is a membrane that only lets some molecules through.

Facilitated diffusion is the net movement of ions and large molecules from a high concentration across a cell membrane by carrier and channel proteins. Some larger molecules can't diffuse directly through the plasma membrane so have to diffuse through carrier or channel proteins by facilitated diffusion. Facilitated diffusion moves ions and large molecules down a concentration gradient. It is also a passive process meaning it doesnt require energy.

Active transport is the movement of ions or larger molecules across a cell membrane against a concentration gradient. Active transport uses energy for it occur. Carrier proteins and co-transporter proteins are used in active transport

Glucose moves by facilitated diffusion through a co-transporter protein by a passive process. Glucose moves from a high concentration of glucose to a low concentration down a concentration gradient.

1) No more glucose can move via facilitated diffusion becauseit has reached an equalibrium.

2) In the epithelial cells there is a low concentration of sodium ions compared to the blood which has a high concentration of sodium ions. Using a cotransporter protein called a sodium potassium pump sodium ions move via active transport against the concentration gradient.

3) This causes there to be less sodium inside the epithelial cell and a higher concentration inside the lumen of the small intestine.

4) A co-transporter protein that needs both sodium ions and glucose to change shape causes glucose and sodium to move into the epithelial cells and the the glucose to keep moving into the mitrochondria. This system enables glucose to move into the epithelial cell against the concentration gradient without the use of active transport.