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Transcript
FACTORS AFFECTING THE RATE OF DIFFUSION I) Surface Area vs. Volume - Cells are limited in their size because they must maintain a high “Surface Area : Volume” ratio. - Nutrients (oxygen and glucose) must enter a cell while wastes (carbon dioxide and urea) must exit a cell through the cell membrane. - The amount of cell membrane = Surface Area of the cell. - Inside the cell, organelles use up nutrients and produce wastes. The larger the cell, the more nutrients needed and the more wastes produced. - The size of the cell (based on the number of organelles) = Volume of the cell. Cell S.A LxWx6 Volume LxWxH S.A. : Volume Ratio A 6 units2 1 unit3 6:1 B 24 units2 8 units3 3:1 C 96 units2 64 units3 1.5 : 1 D 384 units2 512 units3 0.75 : 1 - Small cells have a high “SA:Volume” ratio, they can supply the organelles with plenty of nutrients and rapidly remove wastes. - Large cells have a low “SA:Volume” ratio because volume rises faster than surface area. If a cell gets too big, wastes will build up and nutrients will run out; cell cannot survive. - Therefore, cells are limited in their size. The more active a cell is, the smaller it must be. Active cells need more nutrients and they produce more wastes. - How do cells occupy the large volumes associated with large organisms? The cells reproduce frequently through mitosis to maintain their small size (high “SA:Volume” ratios) while creating millions of cells to fill these larger volumes. (As opposed to using fewer larger cells) - Some cells can achieve a large size while still maintaining a high SA:Volume ratio. This is achieved by producing folds of the cell membrane (microvilli) to increase SA. - These folds allow the cell to gain more surface area without a large increase in volume. Checkout : http://www.hillstrath.on.ca/moffatt/bio3a/cellbio/sa-vsoln.htm II) FACTORS THAT WILL AFFECT THE RATE OF DIFFUSION 1. Concentration gradient: – the difference in concentration between two areas. -- the greater the [ ] gradient, the faster the diffusion. Higher Concentration Lower Concentration 2. The size and shape of the molecules: - Smaller molecules that fit through pores will pass at a faster rate. 3. Temperature: – Warmer = faster (more kinetic energy in the particles) http://mutuslab.cs.uwindsor.ca/schurko/animation s/waterphases/status_water.htm Click on the first button 4. Type of medium: – Diffusion is faster in gases than in liquids (more empty space between the molecules of a gas as well as greater Kinetic E) 5. Movement of the medium –Water or air currents speed up diffusion. Example: Stirring or heating can create currents (promotes mixing).