Chapter 5: Homeostasis and Cell Transport

 The steady – state physiological condition of the body of a cell.  Cell membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells.

 Lipid Bilayer with embedded proteins. Phospholipid bilayer with some proteins extending from one side of the membrane to another and some proteins are embedded only half-way  Proteins are utilized for both PASSIVE AND ACTIVE TRANSPORT  Carbohydrate chains are located on the outer surface of the membrane. If they are attached to phospholipids they are known as GLYCOLIPIDS. If they are attached to proteins they are called GLYCOPROTEINS.  Carbohydrate chains help with cell to cell recognition

 What determines the permeability of a substance across the cell membrane? o Size o Polarity o Hydrophobic vs. hydrophilic o Charge

 The cell membrane is described as selectively permeable because it allows some substances to pass in or out but not others.  The size, charge, and polarity of a substance determines its permeability.  The cell membrane is permeable to gases such as carbon dioxide and oxygen since gases are small.  The cell membrane is permeable to water and other small, polar molecules.

 CELL MEMBRANES help organisms maintain HOMEOSTASIS by controlling what substances may enter or leave the cell.

 Some substances can cross the cell membrane without any input of energy by the cell in a process called PASSIVE TRANSPORT.  The simplest type of PASSIVE TRANSPORT is DIFFUSION.

 Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration

 The difference in the concentration of molecules across a distance or across a membrane is known as a Concentration Gradient.

 In the absence of other influences, diffusion will eventually cause the molecules to be in equilibrium.  Equilibrium – the concentration of molecules will be the same throughout the space the molecules occupy.

 How does the cell membrane help the cell to maintain homeostasis?  Why is the cell described as selectively permeable? What characteristics of a substance can determine its permeability?  Draw and label a cross section of the cell membrane. Make sure to include the phospholipids, embedded carrier proteins, ion channel proteins, carbohydrate chains as recognition antennas.