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3.3b

QuestionAnswer
Simple diffusion is the net movement of particles from a place of high concentration to a place of lower concentration as a result of their constant, spontaneous motion. In other words, substances diffuse down their concentration gradients.
Molecules move at astonishing speeds. At body temperature, the average water molecule moves about 2,500 km/h (1,500 mi./h)! However, molecules are so crowded they can travel only a short distance before colliding with each other and careening off in a new direction, like colliding billiard balls.
The rate of diffusion, therefore, is much slower than the speed of molecular motion
Diffusion occurs readily in air or water and doesn’t necessarily need a membrane—for example, when an odor spreads from its source to your nose. This is how oxygen passes from the air we inhale into the bloodstream. However, if there is a membrane in the path of the diffusing molecules, and if it is permeable to that substance, the molecules will pass from one side of the membrane to the other
Dialysis treatment for kidney patients is based on diffusion of solutes through artificial dialysis membranes.
Diffusion rates are important to cell survival because they determine how quickly a cell can acquire nutrients or rid itself of wastes.
Some factors that affect the rate of diffusion through a membrane are as follows: Temperature, Molecular weight, Steepness” of the concentration gradient, Membrane surface area, Membrane permeability
-------, Molecular weight, Steepness” of the concentration gradient, Membrane surface area, Membrane permeability Temperature
Temperature, ------, Steepness” of the concentration gradient, Membrane surface area, Membrane permeability Molecular weight
Temperature, Molecular weight, ----- , Membrane surface area, Membrane permeability Steepness” of the concentration gradient
Temperature, Molecular weight, Steepness” of the concentration gradient, Membrane surface area, ------ Membrane permeability
Temperature. Diffusion is driven by the kinetic energy of the particles, and temperature is a measure of that kinetic energy.
Temperature. The warmer a substance is, the more rapidly its particles diffuse. This is why sugar diffuses more quickly through hot tea than through iced tea.
Molecular weight. Heavy molecules such as proteins move more slowly than light particles such as electrolytes and gases. Small molecules also pass through membrane pores more easily than large ones.
“Steepness” of the concentration gradient. The steepness of a gradient refers to the concentration difference between two points. Particles diffuse more rapidly if there is a greater concentration difference, like a ball rolling faster down a steeper slope.
Membrane surface area. As noted earlier, the apical surface of cells specialized for absorption (for example, in the small intestine) is often extensively folded into microvilli. This makes more membrane available for particles to diffuse through.
Membrane permeability. Diffusion through a membrane depends on how permeable it is to the particles. For example, potassium ions diffuse more rapidly than sodium ions through a plasma membrane.
Membrane permeability. Nonpolar, hydrophobic, lipid-soluble substances such as oxygen, nitric oxide, alcohol, and steroids diffuse through the phospholipid regions of a plasma membrane.
Membrane permeability. Water and small charged, hydrophilic solutes such as electrolytes don’t mix with lipids but diffuse primarily through channel proteins in the membrane.
Membrane permeability. Cells can adjust their permeability to such a substance by adding channel proteins to the membrane, by taking them away, or by opening and closing membrane gates.
Created by: Russells3709
 

 



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