Types of transport
Partially permeable cell membranes
All cells have a cell membrane. This membrane controls what goes into and out of the cells. Some substances, such as gases and water, can pass across the membrane easily by diffusion. However, other substances, such as glucose, need to be transported across the cell membrane. This is why the membrane is Also called semi-permeable. A partially permeable membrane allows water and other small molecules to pass through, but not larger molecules such as starch. - it controls which substances can travel across it easily.
Diffusion
Oxygen will diffuse from a high concentration at the alveoli in the lungs, to a lower concentration in the red blood cells. This is a passive process, which means it does not need energy. The oxygen diffuses across the partially permeable membrane of the alveoli cells and the capillary wall, into the red blood cells to be carried around the body.
Osmosis
The movement of water molecules across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration. is the net movement of water molecules from a high concentration to a lower concentration across a partially permeable membrane. Osmosis is a passive process so does not require energy.
Active transport
Some substances that need to get into cells get there by The transport of molecules against their concentration gradient from a region of low concentration to a region of high concentration.. This transport process moves substances against the concentration gradient - the substances move from a low concentration to a higher concentration. It requires an energy input. Glucose can be taken into cells by active transport if the concentration of glucose inside the cell is already quite high. This requires A carrier protein is a protein which is responsible for transporting specific substances through the cell membrane and into the cell..
