Biology

 Cell Membranes and Homeostasis  Passive Transport Diffusion Facilitated Diffusion Osmosis  Active Transport Molecular Transport Bulk Transport (Endocytosis and Exocytosis)

 Function- regulates what enters and leaves the cell, and also protects and supports the cell

 Components- Phospholipids Proteins Carbohydrates

 Phospholipids Consist of phosphate “head”  water loving 2 fatty acid “tails”  water fearing Forms a bilayer with heads facing out and tails facing in

 Proteins “float” and move along the lipids Form channels and pumps that help to move materials across the membrane

 Carbohydrates Usually attach to proteins Act like chemical “ID cards”; allow cells to recognize one another.

 Fluid Proteins literally float among the lipids  Mosaic So many different molecules make up the cell membrane; it looks like a mosaic (a kind of art that involves bits and pieces of different colors or materials)

 Semipermeable membrane: Only some things can enter the cell membrane, other things cannot. Things that are too large or too strongly charged will have difficulty entering, or will not be able to enter at all

 All living things want to maintain homeostasis, relatively constant internal physical and chemical conditions.  To stay in balance, molecules in the cell will move across the cell membrane until equilibrium is reached.

 What is passive transport? The movement of molecules from high concentration to low concentration Requires no energy (ATP) Molecules move with the concentration gradient Eventually equilibrium is reached (but molecules keep moving!)

 Types of Passive Transport: Diffusion Facilitated diffusion Osmosis

 Diffusion The process by which particles move from an area of high concentration to low concentration. How small, nonpolar molecules move across the cell membrane. For example, O 2 and CO 2

 Facilitated diffusion Molecules that cannot directly diffuse across the membrane because of size, charge, or polarity pass through special protein channels. For example, molecules like starch are too large, and require proteins to diffuse into the cell.

 Osmosis The facilitated diffusion of water across a selectively permeable membrane through proteins called aquaporins. Water will move based on its concentration in solution (solute + solvent):  Isotonic  Hypertonic  Hypotonic

 Osmosis: Hypertonic  Solute concentration is lower inside cell (solvent concentration is higher inside cell) ;Water goes out  Cell shrivels  Causes plasmolysis in plant cells

 Osmosis: Isotonic Solution  Equal concentration of solvent inside and outside of cell; water goes in and out  Cell’s volume remains the same; equilibrium

 Osmosis Hypotonic  Solute concentration is greater inside the cell (solvent concentration is lower inside the cell); water goes in  Cell swells and may lyse  Causes cytolysis in animal cells

 What is active transport? The movement of molecules from low to high concentration. Requires energy (ATP) Molecules move against the concentration gradient

 Types of active transport: Molecular transport Bulk transport

 Molecular transport For example, sodium/potassium pump Small molecules and ions like sodium (Na+) and potassium (K+) are carried across membrane proteins

 Bulk transport Moves larger molecules and even solid clumps of material Involves the formation of a vesicle Types:  Endocytosis  Phagocytosis  Pinocytosis  Exocytosis

 Bulk Transport: Endocytosis Movement of large molecules or particles into the cell. The cell membrane folds in, taking in materials, and forms a vesicle to bring the contents into the cell. Phagocytosis  “cell eating”  solid, can be food particles Pinocytosis  “cell drinking”  liquid particles

Endocytosis

 Exocytosis The vesicle carrying molecules or particles fuses with the cell membrane, forcing the contents out of the cell.