II active processes cellular energy is used to drive the substance uphill

Ii active processes cellular energy is used to drive

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II. active processes – cellular energy is used to drive the substance “uphill” against its concentration and electrical gradient. Cellular energy used is usually ATP. i.e. active transport. a. Vesicles – tiny, spherical membrane sacs that can be used by other substance to enter and leave cells. III. Diffusion – is a passive process in which the random mixing of particles in a solution occurs because of the particles’ kinetic energy. a. Solutes – dissolved substance. b. Solvents – the liquid that does the dissolving. IV. factors that influence diffusion rate
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a. steepness of the concentration gradient – the greater the difference in concentration between two side of the membrane, the higher is the rate of diffusion. b. Temperature – the higher the temperature, the faster the rate of diffusion. i.e. fever c. mass of the diffusing substance – the larger the mass of the diffusing particle, the slower its diffusion rate. d. surface area – the larger the membrane surface area available for diffusing, the faster is the diffusion rate. i.e. air sacs of lungs have large surface area for oxygen diffusion into the blood, but if affected by lung diseases, it reduce the surface area, slowing the oxygen diffusion rate which results to difficulty breathing. e. diffusion distance – the greater the distance over which diffusion must occur, the longer it takes. i.e. diffusion across plasma membrane only takes a fraction of a second because the membrane is so thin. V. simple diffusion – passive process in which the substances move freely though the lipid bilayer of the plasma membranes of cells without the help of membrane transport proteins; important in the movement of oxygen and carbon dioxide between blood and body cells and between blood and air within the lungs during breathing. VI. facilitated diffusion – passive process wherein an integral membrane assists a specific substance across the membrane. The integral membrane can either be a membrane channel or a carrier. a. channel-mediated facilitated diffusion – solute moves down its concentration gradient across the lipid bilayer through membrane channel. i. ion channels – integral transmembrane proteins that allow passage of small inorganic ions that are too hydrophilic to penetrate the non-polar interior of the lipid bilayer; most membranes are these. ii. gated channels – when part of the channel protein acts as a plug or gate changing the shape in one way to open the pore and in another way to close it; can be randomly alternate between open or closed positions; could be regulated by chemical or electrical changes inside and outside the cell. b. carrier-mediated facilitated diffusion – a carrier moves a solute down its concentration gradient across the plasma membrane; no cellular energy is required in this passive process.
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i. transport maximum – the upper limit on the plasma membrane placed by the carriers at which the facilitated diffusion can occur.
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