Describe the Fluid-Mosaic Model of a Plasma Membrane. Discuss the Role of the Membrane in the Movement of Materials Through It by Each of the Following Processes: A. Active Transport B. Passive Transport

661 Words Oct 25th, 2012 3 Pages
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Describe the fluid-mosaic model of a plasma membrane. Discuss the role of the membrane in the movement of materials through it by each of the following processes:
a. Active transport
b. Passive transport

The plasma membrane is a semi permeable barrier that separates the inside of the cell from the outside environment. The plasma membrane is made up of carbohydrates, cholesterol, proteins, and a lipid bilayer, or double layer of lipids. The plasma membrane may be known as a fluid mosaic model where the membrane is a fluid structure with various proteins embedded in or attached to the bilayer of phospholipids. The plasma membrane possesses hydrophilic tails and hydrophobic tails, which may be referred to as
amphiphilic.
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Active transport is movement across the membrane that does require energy to occur. ATP will supply the energy for active transport. During active transport, molecules will move from places of low concentration to places of high concentration. Active transport requires energy because it must transport the molecules against their concentration gradient. There are four different subdivisions of active transport, primary, secondary, endocytosis, and exocytosis. Primary active will manifest in the form of certain transport proteins that require energy to function, such as the sodium-potassium pump. Secondary active transport is another subdivision of active transport. During secondary active transport molecules may move by symtransport, which is particles moving in the same direction, or antitransport, which is particles moving in the opposite direction. Primary and secondary active transport is utilized for small particles to be transported across the plasma membrane. Endocytosis is the cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle. Endocytosis is

for materials that may be entering the cell. Endocytosis may be completed by phagocytosis, pinocytosis, and receptor-mediated endocytosis. Phagocytosis is a cell engulfing a particle by wrapping pseudopodia

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