Chapter 5 BCS 1005 Mr. Tidwell- There are 2 types of Transport Proteinso These proteins regulate the movement of hydrophilic molecules through the plasma membrane.o Channel Proteins form channels whose central pores allow specific ions or water molecules to pass through the membrane.o Carrier Proteins have binding sites that can temporarily attach to specific molecules on one side of the membrane and then move them through the membrane to the other side.- Fluid – A substance whose molecules can flow past one another and, therefore, have no defined shape.- Solute – A substance that can be dissolved in a solvent.- Solvent – A fluid capable of dissolving a solute.- Concentration – The amount of solute in a given amount of solvent.- Gradient – A physical difference in temperature, pressure, charge, or concentration of a particular substance in a fluid between two adjoining regions of space.- Movement through membranes occurs by passive transport and energy-driven transport.o Concentration gradients of ions and molecules exist across the plasma membranes of all cells.o Plasma membranes are selectively permeable because they only allow certain ions or molecules to permeate.- Passive transport is the diffusion of substances across cell membranes down concentration gradients and doesn’t require energy.o Passive transport includes simple diffusion, facilitated diffusion, and osmosis.o Simple Diffusion – Net movement of substances down their concentration gradients across a membrane. Molecules that move across membranes by simple diffusion include water, oxygen, carbon dioxide, and lipid-soluble molecules like alcohol and vitamins A, D, and E. For diffusion to occur there must be a gradient.o Facilitated Diffusion – Uses the aid of a channel and transport protein. Water soluble molecules like ions, amino acids, and sugars diffuse through facilitated diffusion.o Osmosis – The diffusion of water across selectively permeable membranes. Dissolved substances reduce the concentration of free molecules in a solution.Page 1 of 3Chapter 5 BCS 1005 Mr. Tidwell A hypertonic solution is one with a greater solute concentration.- Water moves across a membrane toward the hypertonic solution.- When cells are placed into a hypertonic solution, they shrivel, owing to water loss. A hypotonic solution has a lower solute concentration.- Water moves across a membrane away from the hypotonic solution.- When cells are placed into a hypotonic solution, they swell, owing to water entry. Isotonic solutions have equal concentrations of dissolved substances.- No net water movement occurs across the membrane.- Cells in isotonic solutions remain unaffected.- Energy-requiring transport – is transport that requires the use of cellular energy to occur.o Active transport – Membrane proteins use cellular energy to move molecules or ions across plasma membranes against their concentration gradient. Active transport proteins span the entire membrane. They often have a molecule binding site and an ATP binding site.o Endocytosis – Cells engulf particles or fluids by endocytosis. Pinocytosis – (“cell drinking”) moves liquids into the cell Receptor-mediated endocytosis – moves specific molecules into the cell through the use of receptors on the membrane. Phagocytosis – (“cell eating”) moves large particles into the cello Exocytosis – Moves materials out of the cell. Cells use energy to dispose of undigested particles of waste or to secrete substances into the extracellular fluid by exocytosis. Example: secretion of hormones- Exchange of material across membranes influence cell size and shape.o As a sphere enlarges, its innermost parts get farther away from the plasma membrane. As the cell gets larger, diffusion, which is relatively slow, can take too longto supply important processes deep within the cell. Because its volume increases more rapidly that its surface area, a larger cell has a relatively smaller area of membrane for acquiring nutrients and eliminating waste products than a smaller cell.o Nerve and muscle cells and microvilli overcome size restraints by elongating, thus keeping the ratio of surface area to volume relatively high.- Specialized Junctions allow cells to connect and communicate.o Desmosomes attach cells together.Page 2 of 3Chapter 5 BCS 1005 Mr. Tidwell Desmosomes are found where cells need to adhere tightly together under the stresses of movement.- Examples: skin, intestines, and urinary bladdero Tight junctions make cell attachments leak-proof. Tight junctions are found where tubes and sacs must hold contents without leaking. Examples: skin and urinary bladdero Gap junctions and Plasmodesmata-(plants only) allow direct communication between cells. Cell-to-cell protein channels allowing for passage of hormones, nutrients, and ions in animal cells are gap junctions. Plant cells have holes in the walls of adjacent cells forming cytoplasmic connections called Plasmodesmata.Page 3 of