The technology must be wireless-http: Provide adequate bandwidth and Internet access to all schools, calculated on a per — student basis.
Water and Solute Movement Back to Top Cell membranes act as barriers to most, but not all, molecules. Development of a cell membrane that could allow some materials to pass while constraining the movement of other molecules was a major step in the evolution of the cell.
Cell membranes are differentially or semi- permeable barriers separating the inner cellular environment from the outer cellular or external environment. Water potential is the tendency of water to move from an area of higher concentration to one of lower concentration.
Energy exists in two forms: Water molecules move according to differences in potential energy between where they are and where they are going. Gravity and pressure are two enabling forces for this movement. These forces also operate in the hydrologic water cycle. Remember in the hydrologic cycle that water runs downhill likewise it falls from the sky, to get into the sky it must be acted on by the sun and evaporated, thus needing energy input to power the cycle.
Image from Purves et al. Diffusion is the net movement of a substance liquid or gas from an area of higher concentration to one of lower concentration. You are on a large 10 ft x 10 ft x10 ft elevator.
An obnoxious individual with a lit cigar gets on at the third floor with the cigar still burning. Eventually you are unable to escape the smoke! An example of diffusion in action.
Nearer the source the concentration of a given substance increases. You probably experience this in class when someone arrives freshly doused in perfume or cologne, especially the cheap stuff.
Since the molecules of any substance solid, liquid, or gas are in motion when that substance is above absolute zero 0 degrees Kelvin or degrees Cenergy is available for movement of the molecules from a higher potential state to a lower potential state, just as in the case of the water discussed above.
The majority of the molecules move from higher to lower concentration, although there will be some that move from low to high.
The overall or net movement is thus from high to low concentration. Eventually, if no energy is input into the system the molecules will reach a state of equilibrium where they will be distributed equally throughout the system.
The Cell Membrane Back to Top The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model also referred to as the fluid-mosaic model.
The most common molecule in the model is the phospholipidwhich has a polar hydrophilic head and two nonpolar hydrophobic tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane.
This layering is termed a bilayer since an electron microscopic technique known as freeze-fracturing is able to split the bilayer. Diagram of a phospholipid bilayer. Phospholipids and glycolipids are important structural components of cell membranes.
Phospholipids are modified so that a phosphate group PO4- replaces one of the three fatty acids normally found on a lipid. The addition of this group makes a polar "head" and two nonpolar "tails". Structure of a phospholipid, space-filling model left and chain model right.
Diagram of a cell membrane. This image is copyright Dennis Kunkel at www. Cholesterol is another important component of cell membranes embedded in the hydrophobic areas of the inner tail-tail region. Most bacterial cell membranes do not contain cholesterol.
Proteins are suspended in the inner layer, although the more hydrophilic areas of these proteins "stick out" into the cells interior as well as the outside of the cell. These integral proteins are sometimes known as gateway proteins.Hyperlinked definitions and discussions of many terms in cryptography, mathematics, statistics, electronics, patents, logic, and argumentation used in cipher construction, analysis and production.
A Ciphers By Ritter page. Study Exercise 5: The Cell: Transport Mechanisms and Permeability flashcards. Play games, take quizzes, print and more with Easy Notecards. Marieb Exercise 5B Cell Transport Mechanisms and Permeability: The answer key to the Ex 5B review sheet is available on the shared directory \\facstaff\biology (along with the answer key for Ex5A and the part of 37A for this week's lab).
Ex. 5A, Activity 1: Diffusion. Cell Transport Mechanisms and Permeability 1 EXERCISE 1 OBJECTIVES 1. To define the following terms: differential permeability, passive and active processes of transport, diffusion (simple diffusion, facilitated dif- fusion, and osmosis), solute pump, pinocytosis, and phagocytosis.
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