Passive and Active Transport

p. 41

•          the cell membrane acts as a selectively-permeable barrier

•          the cell must be able to take in food and eliminate wastes

•          the movement of materials across a cell membrane without cell energy expenditure is called Passive Transport

•          transport proteins in the cell membrane can allow certain materials to diffuse across the membrane.

•          There are 3 types of passive transport:

                                                            i) diffusion

                                                            ii) osmosis

                                                            iii) facilitated diffusion

Diffusion

•          molecules move about randomly and collide (called Brownian motion)

•          diffusion is the movement of molecules from an area of high concentration to an area of low concentration (e.g. Perfume)

•          molecular collisions cause diffusion

Osmosis

•          Osmosis is the diffusion of water through a selectively-permeable membrane. (Such as cheese cloth of a coffee filter)

•          solute - molecules that dissolve in water

•          solvent - water or the dissolver

•          Isotonic solutions - are solutions in which the concentration of solute molecules outside the cell are equal to the concentration inside the cell. (Water in the cell does not move)

•          Hypotonic solutions - are solutions in which the concentration of the solute molecules outside the cell is lower than inside the cell. (Water moves into the cell)

•          Hypertonic solutions - are solutions in which the concentration of the solute molecules outside the cell is higher than inside the cell. (Water leaves the cell)

Facilitated Diffusion

•          transport proteins in the cell membrane are similar in function to enzymes. When they come in contact with specific molecules or ions they activate and bind with the molecule. To unbind with the molecule that protein must expel the molecule into the cell.

Active Transport

•          This involves the use of cell energy to move materials across the cell membrane against the concentration gradient.

•          The movement of materials from an area of low concentration to an area of higher concentration is called active transport.

•          Endocytosis - is the process by which particles too large to pass through the cell membrane are transported into the cell. There are two types: Pinocytosis and Phagosytosis.

•          certain ions and amino acids are moved into the cell by active transport. This means that the cell is using transport proteins and at the same time using up metabolic energy to obtain these particles of matter.