Review:
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diffusion
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osmosis
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facilitated diffusion
Oct 19­12:48 PM
Active Transport (Pg 59)
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this is the process of moving substances against a concentration gradient (this requires energy)
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it is necessary because sometimes a cell needs a high concentration of materials for growth or must remove all toxins completely
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passive transport cannot do this
NOTE: Most cells use 40% of their energy on active transport (Kidney cells use 90%)
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Passive vs Active Transport
Similarities
Differences
­particles enter and exit
the cell
­ active moves against
concentration gradient
passive with it
­proteins in membrane
act as doorways
­active requires energy
passive does not
Oct 19­12:54 PM
Types of Active Transport: Bulk Material Transport
(1) Exocytosis
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a vesicle containing material from inside the cell moves to the cell membrane
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it joins with the cell membrane and releases its contents into the extracellular fluid
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this material may be waste or manufactured material
(Ex. pancreatic cells release digestive enzymes such as hormones which help in the digestive process)
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exocytosis is the opposite of endocytosis
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see figure 2.36 on page 64
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Oct 19­1:14 PM
2. Endocytosis
­ the cell membrane folds inward trapping and enclosing small amounts of matter from the cellular fluid
­ it creates a vesicle which surrounds the material breaks off and carries it to the internal organelles of the cell
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there are three types of endocytosis
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(a)
Phagocytosis (Cellular Eating)
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the engulfing of extracellular fluid containing debris from bacteria and other particles
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the vesicles formed then move into the cell and fuse with lysosomes where the material being transported are broken down
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this is common among white blood cells such as macrophages which are a part of the immune system
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amoeba use this method to get food
­ see figure 2.33 on page 62, part A
Oct 19­1:17 PM
Oct 19­2:40 PM
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(b) Pinocytosis (Cellular Drinking)
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takes in fluid from the surrounding extracellular fluid
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this fluid contains particles which the cell can use in its functions
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similar to phagocytosis in how it functions
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for example the cells lining a blood capillary will take fluid from the blood, move it across the cytoplasm and then release it into the extracellular fluid surrounding the cells outside the capillary
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these cells can then take in particles from the fluid
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see figure 2.33, page 62, part B
Oct 19­2:40 PM
Oct 19­2:45 PM
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Oct 19­2:45 PM
(c)
Receptor­Assisted Endocytosis
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involves the intake of special molecules such as cholesterol that can only enter a cell by attaching to special proteins in the cell membrane
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these proteins act as receptors
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these receptors have a unique shape that will only fit the shape of a specific molecule
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see figure 2.34 on page 63
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Readings:
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pages 58 ­ 64
Questions:
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page 64, #'s 1,2,3,4,5
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