Cell Membrane & Transport Unit 2: The Cell

Types of Outer Cell Boundaries: CELL WALL outer boundary found in plant cells, bacteria, fungi, some protists Thick and inflexible Function: Provides support for plant cell Never found in animal cells

Cell (Plasma) Membrane Thin, flexible barrier between cell & environment (All cells) Selectively permeable Functions: Controls movement in and out of cell Allows cell recognition; boundary for cell Maintains homeostasis: balance within the cells

Fluid Mosaic Model The fluid mosaic model states that the cell membrane is a lipid bilayer made up of molecules which are free to move. Phospholipids: fatty areas that attract and repel water causing the membrane to behave like a fluid Hydrophilic heads (Polar): close to water as possible Hydrophobic tails (Non-polar): far away from water as possible Animation: http://www.johnkyrk.com/cellmembrane.html

Embedded Proteins Determine which particles can pass through Serve as recognition markers Form channels from one side of the cell to the other Used in facilitated diffusion

Movement Across the Membrane PASSIVE Transport: requires no energy, movement from HIGH to LOW concentration * Examples: diffusion, osmosis *No Energy required ACTIVE Transport: requires energy, movement from LOW to HIGH concentration * Examples: endocytosis, exocytosis *Energy required! ATP

Types of PASSIVE Transport Movement WITH the concentration gradient DIFFUSION: movement of particles from high concentration to low concentration Causes substances to move across membrane Does not require the cell to use energy Substances move across membrane until both sides are equal (EQUILIBRIUM)

OSMOSIS: diffusion of water through a membrane water moves from where there is a lot to where there is a little until it reaches equilibrium exerts pressure (OSMOTIC PRESSURE) which can cause cell swelling Higher Concentration of Water Water molecules Lower Concentration of Water Sugar molecules

Diffusion may be: FACILITATED Process by which proteins in the membrane help substances enter the cell Protein channels are SPECIFIC only allowing some things in/out Movement from HIGH to LOW

Types of ACTIVE Transport Movement AGAINST the concentration gradient Energy required ENDOCYTOSIS: cells ingest external fluid, macromolecules, and large particles Phagocytosis: cell takes in food Pinocytosis: cell takes in water EXOCYTOSIS: cells remove fluids, macromolecules and large particles

HYPERTONIC: concentration is higher inside the cell than outside (water) HYPER means “above strength” Water moves OUT of cell causing it to shrivel Can result in PLASMOLYSIS in plants which causes wilting TYPES OF SOLUTIONS

ISOTONIC: solution where concentrations of dissolved substances outside the cell is the same as the inside of the cell ISO- means “equal to” Movement into cell= movement out of cell

HYPO means “below strength” HYPOTONIC: concentration of water is higher outside the cell than inside HYPO means “below strength” Water will move INTO cell causing it to swell Cells could rupture if the cell takes in too much water This increases pressure inside of cell (TURGOR PRESSURE) Animation: http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm

Hippo Hypo