chap. 5: homeostasis and the cell membrane
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Chap. 5: Homeostasis and the Cell Membrane. --- Homeostasis – steady state of balance between a cell and its environment. I. Types of Membranes. 1. Selectively (Semi) Permeable – decides what will enter or exit the cell. (What cell membrane is most of the time) - PowerPoint PPT PresentationTRANSCRIPT
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Chap. 5: Homeostasis and the Cell
Membrane
--- Homeostasis – steady state of balance between a cell and its environment.
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I. Types of Membranes
1. Selectively (Semi) Permeable – decides what will enter or exit the cell. (What cell membrane is most of the time)
2. Permeable – allows everything in or out of cell.
3. Impermeable – does not allow anything in or out of cell.
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II. How a Selectively (Semi) Permeable Membrane Selects What Enters or Exits
1. Size of Particle – small do (water, glucose, ions, etc) and large do not.
2. Chemical makeup – if water then automatically does and anything dissolved in it (sugar, salt, ions)
3.What conditions are inside and outside the cell
--- Diffusion and Osmosis
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III. Diffusion and Osmosis
-- diffusion – moving of particles from high concentration to low concentration. Requires no energy
-- osmosis – diffusion of only water -- solute – substance being dissolved
(smaller quantity) -- solvent – substance being dissolved into
(larger quantity)
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IV. Types of Solutions1. Hypertonic Solution – solute concentration is greater outside than inside so WATER rushes out.
Result : Causes Plasmolysis – cell shrinking. Common in salt water that is why skin shrivels up
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2.Hypotonic Solution – solute concentration is greater inside than outside so WATER rushes in.
Result : cell swelling which may result in Cytolysis (cell rupture).One-celled organisms(i.e ameoba, paramecium) that live in a water environment have Contractile Vacuoles to pump water out.
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3. Isotonic Solution – solute concentration is the same inside and outside.
Result : little or no movement of WATER into or out of the cell.
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*** In Plant Cells : Because they have a cell wall there are slight differences.
Hypertonic solution – causes cells to be limp (decreases turgor pressure)
Hypotonic solution – causes cells to be stiff (decreases turgor pressure )
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V. Types of Transport1. Passive Transport – Does not require energy. Follows concentration gradient (high to low) a. osmosis
b. diffusion c. facilitated diffusion – carrier molecules
(proteins) speed up the diffusion process
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d. Gated channels – channels in cell membrane that specifically allow some molecules to pass through that are not usually permeable to the membrane
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2. Active Transport – requires energy by cell to take place
A. contractile vacuoles B. sodium – potassium pumps (Na+--K+) – causes electrical charges to travel across cells which lead to muscular contractions and neurons firing. Must go against a concentration gradient. Pumps 3Na+ out and 2 K+ pumped in.
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c. Endocytosis – the entering of large molecules into the cell. (lipids, fats, polysaccharides, etc.)-- pinocytosis – (cell drinking)- movement of large molecules of fluid and/or ions into cell.-- phagocytosis – (cell eating) – movement of food molecules into cell.
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d. Exocytosis - exiting of large molecules out of the cell.