Homeostasis and Transport

I.         Homeostasis:

            A.        The tendency of biological systems to maintain a state of equilibrium

            B.        Reacts to changes in external environment

            C.        Uses negative feedback loop

            D.        May be within organisms or across biomes

            E.        Chapter will cover the processes involved.

            F.        Some classified differently than text

II.        Negative Feedback

            A.        Change to normal is resisted

            B.        Set Point: normal conditions

            C.        Require

                        1.         Receptor

                        2.         Control center

                        3.         Effector

            D.        Receptor

                        1.         Located in various organs

                        2.         Monitor internal conditions

                        3.         Report to control center

            E.        Control Center

                        1.         Normally brain or central nerve bundle

                        2.         Integrate information from receptors

                        3.         Send out signals to correct imbalance and return to set point

            F.        Effectors

                        1.         Muscles, organs, glands, or other structures

                        2.         Receive signal from control center

                        3.         Act to return organisms to set point

            G.        Blood pressure example. Done in class

III.       Transport: Passive

            A.        Movement is from high to low concentration

            B.        Use no extra energy

            C.        Diffusion

            D.        Facilitated Diffusion

            E.        Ion Channels

            F.        Osmosis

IV.      Diffusion

            A.        Movement from high level to low level

            B.        Energy not required

            C.        Diffusion gradient determines rate

            D.        Driven by KE of molecules

            E.        Stops at equilibrium

V.        Diffusion: Membrane Effects

            A.        Move directly through membrane

            B.        Permeability depends on type and size

            C.        Types of Molecules

                        1.         Lipid soluble

                        2.         Non-polar

            D.        Small molecules

VI.      Facilitated Diffusion

            A.        Molecule types

                        1.         Lipid insoluble

                        2.         Large

            B.        Movement from high to low concentration

            C.        Carrier proteins

                        1.         Each protein only passes one type of molecule

                        2.         Change shape to allow molecules to pass

                        3.         Molecule binds to protein

                        4.         Protein changes shape to open path

                        5.         Molecule passes through membrane

                        6.         Eg. Glucose page 85

VII.     Ion Channels

            A.        Insoluble ions use carrier proteins

            B.        Each ion has specific protein

            C.        Channels normally closed

            D.        Respond to

                        1.         Stretching of membrane

                        2.         Electrical signal

                        3.         Chemicals in cytosol or environment

VIII.    Osmosis

            A.        Diffusion of water across membrane

            B.        Water moves both ways

            C.        Concentration of water determines net direction

IX.      Hypotonic

            A.        Extracellular concentration lower than cytosol

            B.        More water flows into cell

X.        Hypertonic

            A.        Cytosol concentration is lower

            B.        More water flows out of cell

XI.      Isotonic

            A.        Cytosol concentration equal to extracellular

            B.        Equal water flow both ways

XII.     Impact on Cells

            A.        Normally isotonic to environment

            B.        Fresh water is hypotonic

                        1.         Constant inflow of water

                        2.         Single cells use contractile vacuole

                                    a.         Collect excess water

                                    b.         Contract to push out

                        3.         Multicellular organisms

                                    a.         Solute is pumped out

            C.        Plasmolysis (Plants)

                        1.         Hypotonic

                                    a.         Water flows in

                                    b.         Turgor pressure increases

                                    c.         Push on cell wall makes plant rigid

                        2.         Hypertonic

                                    a.         Water flows out

                                    b.         Turgor pressure drops

                                    c.         Plants wilt

XIII.    Transport: Active

            A.        Movement may be from low to high concentration

            B.        Use extra energy

            C.        Membrane pumps

            D.        Endocytosis

            E.        Exocytosis

XIV.   Membrane pumps

            A.        Primary (transfers ions)

                        1.         Energy changes shape of channel

                        2.         Change allows ions to pass

                        3.         Na⁺ - K⁺ Pump (page 85)

            B.        Secondary (symport)

                        1.         Energy creates ion gradient

                        2.         Molecules bind to ions and are carried down

                        3.         Na⁺ glucose filter in gut

                                    a.         Acts as filter between gut and blood

                                    b.         Na⁺ gradient created

                                    c.         Na⁺ binds to glucose

                                    d.         Glucose carried through cells to blood

XV.     Endocytosis

            A.        Cells ingest material too big to pass membrane

                        1.         Pinocytosis: fluids or solutes

                        2.         Phagocytosis: large particles of cells

            B.        Membrane forms pocket

            C.        Pocket forms vesicle and moves into cell

XVI.   Exocytosis

            A.        Cells expel material

                        1.         Neurotransmitters

                        2.         Proteins

                        3.         Hormones

            B.        Vesicles form (Golgi bodies) and move to membrane

            C.        Merge with membrane

            D.        Membrane opens to outside of cell to release contents