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Osmosis and Diffusion (lecture 3)

by: Ruth carmona

Osmosis and Diffusion (lecture 3) BIOL 191B

Ruth carmona

GPA 3.8

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About this Document

Basic concepts on osmosis and diffusion along with tonicity.
Anatomy and Physiology B
Christopher Kehrier
Class Notes
Osmosis, Diffusion, tonicity
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This 3 page Class Notes was uploaded by Ruth carmona on Sunday September 11, 2016. The Class Notes belongs to BIOL 191B at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months taught by Christopher Kehrier in Fall 2016. Since its upload, it has received 4 views. For similar materials see Anatomy and Physiology B in Biology at 1 MDSS-SGSLM-Langley AFB Advanced Education in General Dentistry 12 Months.


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Date Created: 09/11/16
I. What are the main functions of your plasma membrane? Is the plasma membrane permeable, impermeable or semi-permeable? 1. Physical isolation- barrier. 2. Regulates exchange with environment- ions and nutrients enter; wastes eliminated and cellular products released. 3. Monitors the environment: extracellular fluid composition; chemical signals. Ex)neurotransmitters and hormones. Epinephrine increases heart rate and acetylcholine decrease heart rate. 4. Structural support: anchors cells and tissues. II. What types of molecules can cross the plasma membrane without the aid of transmembrane proteins? -Restricts materials based on lipid solubility (lipophilic/hydrophilic), size/shape (small/large), and electrical charge (nonpolar/polar & charged). Ex) Gases= O2, CO2, N2, hydrophobic molecules= benzene, small polar molecule=H20, ethanol. III. Transport mechanisms: o Passive transport: doesn’t require ATP. Diffusion/osmosis across the plasma membrane in living organisms. Does have a driving force= concentration gradient. Energy from the cell isn’t required.  Diffusion – movement of particles from an area of high concentration to the low concentration. Ex) small hydrophobic, small polar molecules, or gases.  Osmosis- method of diffusion. Only the movement of water. Passive movement across a semipermeable membrane. Water wants to dilute with excess particles. -The higher the concentration difference = the greater the movement of the molecules. Large molecules and ions behave in this way like Glucose. - Osmotic pressure: driving force from osmosis derived from solute concentration. These particles influence the movement of water. (The greater the particle concentrationthe greater the pressure) pulls water away from an area of high water concentration to an area with low water concentration. Important for homeostasis= water concentration. - The lesser solution concentration of solution is hyposmotic to the other solution. The solution with greater concentration of solute is hyperosmotic. Equal concentrations= isosmotic (no net movement).  TONICITY Refers to ONLY the solution outside of the cell. Hypertonic- net movement of water outside the cell causing it to crenate. Outside the cell has a higher solute concentration. Hypotonic- net movement into the cell causing it to swell or burst/lyse. Inside the cell has a higher solute concentration. Isotonic- no net movement.  Facilitated Diffusion: involves moving ions and large polar molecules down their concentration gradient with the help of transport proteins. (passive-no ATP).  Non-gated channel proteins: channel protein. Always open in normal cells. Responsible for the permeability of the plasma membrane to ions when the plasma membrane is at rest. (look like macaroni tubes)  Gated channel proteins: channel protein. Open or close by stimuli -Ligand gated: open in response to a certain substrate (small molecules that bind to integral proteins or glycoproteins). -Voltage gated: channels open when there is a change in charge across an area of the plasma membrane. Ex) important around nerves or cardiac cells for potassium and sodium across the plasma membrane.  Carrier proteins: carry large nonpolar, polar, or ionic molecules across the plasma membrane down the molc. Conc. Gradient. Transport amino acids, glucose, and proteins. Have specific binding site. Protein changes shape to transport ions/molecules. Resumes original shape after transport. Like a lock and key mechanism. -Exhibit specificity for a single type of molecule, competition among molecules of similar shape, and saturation rate of the transport limited to number of available carrier proteins.


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