Chapter 5 Homeostasis and Transport

Chapter 5 Homeostasis and transport

1. Distinguish between diffusion and osmosis. A. Diffusion - the movement of molecules from an area of higher concentration to an area of lower concentration 1) Concentration gradient - difference in the concentration of molecules across a space 2) driven by the kinetic energy - the constant and random movement of molecules 3) Equilibrium - when the concentration of the molecules of a substance is the same throughout a space 4) the ability of a molecule to diffuse across a cell membrane depends on the size and type of the molecule and on the chemical nature of the membrane A. Facilitated Diffusion 1) the movement of molecules that are too large or not soluble in lipids across the cell membrane is assisted by specific proteins in the membrane 2) uses carrier proteins – molecules still moving down their concentration gradient so no energy is needed to move them 3) carrier proteins are specific to the molecules they transport

B. Osmosis - the process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration 1) direction of osmosis – in relation to the solution outside the cell a) Hypotonic - when the concentration of solute molecules outside the cell is lower than the concentration in the cytosol - water diffuses into the cell until equilibrium is established b) Hypertonic - when the concentration of solute molecules outside the cell is higher than the concentration in the cytosol - water diffuses out of the cell until equilibrium is established c) Isotonic - when the concentrations of solutes outside and inside the cell are equal d) water tends to diffuse from hypotonic solutions to hypertonic solutions 2. Distinguish between passive transport and active transport A. Passive Transport - The movement of such substances across the membrane down their concentration gradient - requires no energy 1) Diffusion 2) Osmosis B. Active Transport – movement of materials up their concentration gradient, from an area of lower concentration to an area of higher concentration, which requires a cell to expend energy 1) Endocytosis 2) Exocytosis

3. Compare and contrast endocytosis and exocytosis A. Endocytosis and Exocytosis - used to transport large quantities of small molecules that are too large for channels and pumps into or out of cells at a single time – uses energy – active transport 1. Endocytosis - process by which cells ingest external fluid, macromolecules, and large particles, including other cells a) two types 1) Pinocytosis - transport of solutes or fluids – cell drinking 2) Phagocytosis - the transport of large particles or whole cells – cell eating

b) Phagocytes – cells that can engulf bacteria and viruses – vesicles containing the bacteria or virus is then merged with a lysosome containing digestive enzymes that kills the bacteria or virus 2. Exocytosis – reverse of endocytosis - vesicles in the cytoplasm fuse with the cell membrane and release their contents outside the cell - used to release large molecules such as proteins and other molecules used to control the activities of other cells Chapter 5 Homeostasis and Transport

 Passive transport involves the movement of molecules across the cell membrane without an input of energy by the cell.  Diffusion is the movement of molecules from an area of higher concentration to an area of lower concentration, driven by the molecules’ kinetic energy. It eventually leads to equilibrium, a condition in which the concentration of the molecules is the same throughout a space or on both sides of a membrane.  Molecules can diffuse across a cell membrane by dissolving in the lipid bilayer or by passing through pores in the membrane.  Osmosis is the diffusion of water across a membrane. The net direction of osmosis is determined by the relative solute concentrations on the two sides of the membrane.  When the solute concentration outside the cell is lower than that in the cytosol, the solution outside is hypotonic to the cytosol, and water will diffuse into the cell.  When the solute concentration outside the cell is higher than that in the cytosol, the solution outside is hypertonic to the cytosol, and water will diffuse out of the cell.  When the solute concentrations outside and inside the cell are equal, the solution outside is isotonic, and there will be no net movement of water.  To remain alive, cells must compensate for the water that enters the cell in hypotonic environments and leaves the cell in hypertonic environments.  In facilitated diffusion, a carrier protein binds to a molecule on one side of the cell membrane. The protein then changes its shape and transports the molecule down its concentration gradient to the other side of the membrane.  Ion channels are proteins that provide small passageways across the cell membrane through which specific ions can diffuse.  Active transport moves molecules across the cell membrane from an area of lower concentration to an area of higher concentration. It requires cells to expend energy.  Some types of active transport are performed by carrier proteins called cell membrane pumps.  One example of a cell membrane pump is the sodium-potassium pump. It moves three Na+ ions into the cell’s external environment for every two K+ ions it moves into the cytosol. ATP supplies the energy that drives the pump.  Endocytosis and exocytosis are active transport mechanisms in which large substances cross the membrane inside vesicles.  In endocytosis, the cell membrane folds around something in the external environment and forms a pouch. The pouch then pinches off and becomes a vesicle in the cytoplasm. Endocytosis includes pinocytosis, in which the vesicle contains solutes or fluids, and phagocytosis, in which the vesicle contains large particles or cells.  In exocytosis, vesicles made by the cell fuse with the cell membrane, releasing their contents into the external environment. Vocabulary List

Active transport Carrier protein Concentration gradient Contractile vacuole Cytolysis Diffusion Endocytosis Equilibrium Exocytosis Facilitated diffusion Hypertonic Hypotonic Ion channel Isotonic Osmosis Passive transport Phagocyte Phagocytosis Pinocytosis Plasmolysis Sodium-potassium pump Turgor pressure Vesicle