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M ethods of C ell T ransport, S uch A s D iffusion, O smosis, and A ctive T ransport

M ethods of C ell T ransport, S uch A s D iffusion, O smosis, and A ctive T ransport. P lasma M embrane I s a F luid M osaic. The plasma membrane is a selectively semipermeable barrier that defines the cell and controls the passage of substances into and out of the cell.

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M ethods of C ell T ransport, S uch A s D iffusion, O smosis, and A ctive T ransport

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  1. Methods of Cell Transport, Such As Diffusion, Osmosis, and Active Transport

  2. Plasma Membrane Is a Fluid Mosaic • The plasma membrane is a selectively semipermeable barrier that defines the cell and controls the passage of substances into and out of the cell. • Fluid Mosaic composed of Phospholipids, Proteins, Cholesterol, Glycolipids, and Glycoproteins.

  3. Phospholipid Bilayer Phopholipids are the main components of membranes. They arrange themselves in a bilayer, with their water-hating tails facing each other, and their water-loving heads facing the outside of the cell on one side, and the inside of the cell on the other side.

  4. Membrane Proteins • Roles ofmembrane proteins include: • Structural • Enzyme • Transport • Cell- recognition

  5. Transport Across the Membrane Diffusion is the passing of a substance from a region of high concentration of the substance to a region of low concentration of the substance until equilibrium of the substance is achieved. This is a passive process that does not require an energy input.

  6. Facilitated Diffusion • Transport Proteins on the cell membrane serve as channels for substances to enter or exit the cell through passive diffusion.

  7. Active Transport • Active transport occurs when the cell uses ATP energy for diffusion. • During active transport substances may move against their concentration gradients, that is from a region of low concentration on one side of the membrane to a region of high concentration on the other side.

  8. Osmosis: Diffusion of Water • Osmosis is the diffusion of water, across a semipermeable membrane, from a region of high concentration of water to a region of low concentration of water, until equilibrium of water on both sides of the membrane is reached.

  9. Osmoregulation: Control of H2OBalance in Cells • Tonicity: the movement of water into and out of cells in response to the water concentration on the outside of the cell. Water moves from where it is in high concentration to where it is in low concentration until an equilibrium of the water concentration is reached.

  10. Transport of Large Molecules Across the Membrane • Endocytosis – Large substances enter the cell through phagocytosis, cell “eating” or pinocytosis, cell “drinking”. • Exocytosis – vesicles fuse with the plasma membrane and its contents are ejected from the cell

  11. The Cell Is a Unit of Structure and Function Defined by Its Membrane • The cell’s internal environment can be very different than that of its surroundings. • The plasma membrane defines the area of the cell and controls the exit and entrance of substances into and out of the cell.

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