Chapter 3 Part 2 Biology

• receptor molecules on the surface of a cell sit waiting until the one type of molecule they recognize bumps into them
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• The movement of water down its concentration gradient – through a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration
• or
• Osmosis is a type of passive transport by which water diffuses across a membrane, in order to equalize the concentration of water inside and outside the cell. The direction of osmosis is determined by the total amount of solutes on either side of the membrane.

the relationship between the concentrations of solute inside the cell and solutes outside the cell.

• if the concentration of solutes outside the cell is equal.
• Solute concentrations are balanced
• Water movement is balanced.
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• when the concentration solute outside the cell is lower than the concentration inside the cell.
• Water diffuses into cells

• the concentration of solute outside the cell is higher than the concentration inside the cell
• Water diffuses out of cells.
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• a molecule small enough that carry no charge can pass directly though the phospholipid bilayer of the membrane without the assistance of any other molecule.
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• when spontaneous diffusion across a plasma
• membrane requires a transport protein.
• 

the type of active transport that occurs when energy from ATP is used to fuel the transport of molecules.

the transport protein simultaneously moves one molecule against its concentrated gradient while letting another flow down its concentrated gradient

• form continuous, water-tight seals around cells and also anchor cells in place
• they prevent fluid flow between cells.
• Tight junctions are particularly important in the small intestine, where digestion occurs
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• Act like Velcro and fasten cells together
• are like spot welds or rivets that fasten cells together into strong sheets
• they hold cells together but are not water-tight, allowing fluid to pass around them
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• Act like secret passageways and allow materials to pass between cells.
• are pores surrounded by special proteins that form open channels between two cells
• Functioning like secret passageways, these junctions are large enough for salts, sugars, amino acids, and the chemicals that carry electrical signals to pass through but are too small for the passage of organelles or very large molecules such as proteins and nucleic acids.
• Gap junctions are an important mechanism for cell-to-cell communication
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• phagocytosis
• pinocytosis
• receptor-mediated endocytosis

All three involve the basic process of the plasma membrane oozing around an object that is outside the cell, surrounding it,forming a little pocket called a vesicle, and then pinching off the vesicle so that it is inside the cell but separated from the rest of the cell contents.