WELCOME! IN Question : How do unicellular organisms maintain homeostasis when responding to various stimuli in their environment. Give 1 example to support your answer.

CELL MEMBRANE: Draw and label a lipid bilayer.

CELL BOUNDARIES TEKS 4B Investigate and explain cellular processes, including homeostasis, energy conversions, transport of molecules, and synthesis of new molecules

Chapter 7.3-7.4 Cell membrane regulates what enters and leaves the cell and also provides protection and support Cells in a multicellular organism develop in different ways to perform particular functions within the organism.

Cell Walls vs. Cell Membranes Both provide support and protection. Only the cell membrane regulates what enters and leaves. The cell wall is too porous to do that.

Cell Membrane Regulation The cell membrane is made out of a lipid bilayer that is semipermeable. So….only some things go in and out.

Cell membrane Lipid Bilayer: Two layers of fat molecules. Forms the cell membrane

Draw and label a lipid bilayer.

Cell Membrane Transportation Diffusion – Molecules move from a concentrated (crowded) area to a less concentrated area to be in equilibrium. Equilibrium – equal concentration, no net movement of molecules Osmosis - Diffusion of water through a selectively permeable membrane

Diffusion

Is this really osmosis?

Hypertonic Concentration of solutes is more outside the cell than in Water flows out of cell The cell shrivels and may die.

Isotonic Concentration is the same inside and out No net movement The cell stays the same

Hypotonic Concentration of solutes is less outside the cell than in. Water flows in The cell swells with water, becomes “turgid”, and dies.

Facilitated Diffusion Helps large molecules move through protein channels found in the membrane No energy required

Active Transport Forces large molecules to move in and out through protein pumps found in the membrane Energy is required

Endocytosis Cell takes material into cell by infolding the cell membrane with vesicles Phagocytosis – eating – cell engulfs large particles Pinocytosis – drinking – cell takes in liquid

Phagocytosis engulfing solid particles by the cell membrane

Exocytosis Cell releases large amounts of material

Cell Specialization The cells in multicellular organisms can develop in different ways to perform different tasks.

H.W. Cell Membrane & Transport Activity (See Our Course Web Links Page)

EXIT TICKET OUT Question : Explain why a freshwater fish cannot survive in a saltwater environment?