Obtaining Ions, Nutrients and Water

 semipermeable membranes regulate cell interaction with surroundings

→ small openings (pores) allow certain molecules to penetrate cell but denies others making it semi  Small black molecules allowed through  Large red molecules NOT allowed through WHY?

o Plasma membrane is composed of a phospholipid bilayer (two layers of phospholipids or lipids with phosphates) 2 layers = 1 plasma membrane

♦ Phospholipids composed of: lipids (fats): glycerol group and two fatty acid straight tails > Nonpolar / hydrophobic (water-fearing), can’t dissolve in water, found in interior of plasma membrane Phosphate head Lipid tails

phosphate group: phosphate (PO 4 ) > Polar / hydrophilic (water-loving) globular heads, form outside of membrane (can be exterior or interior side of cell) > Can dissolve in water, allows plasma membrane of cell to interact with watery environment of cell. Phosphate head Lipid tail

properties of phospholipids do NOT allow water-soluble molecules to move through membrane easily.

H 2 O soluble

o Proteins embedded within membrane move about in a fluid fashion ♦ Fluid mosaic model explains how structural properties of plasma membrane allow lipids & proteins to move freely in membrane Mosaic: something consisting of variety of components

o Plasma membrane also contains: ♦ Transport proteins: allow substances or waste materials to move through plasma membrane ♦ Proteins & carbohydrates: stick out from cell and help cells identify each other – Proteins: give cell flexibility – Carbohydrates: act as identifier of cell type

 Cell constantly interacts with environment & has to respond to external conditions to maintain homeostasis 98.6ºF 98.8ºF 99.0ºF Increase in heat makes temperature rise Cell will seek to cool itself down Homeostasis at work! Homeostasis at work!

Eating a bag of chips will cause cell to respond to new salty condition

 Cell membranes maintain homeostasis by regulating passage of materials into and out of the cell: Passive Transport – no energy required to move solute or solvent from high to low concentration (down concentration gradient) Active Transport – energy required to move solute from low to high concentration (against concentration gradient) Outside Cell (16)Inside Cell (4)

outside  concentration gradient = difference in amount of substance present inside the cell versus outside the cell inside

→ Molecules will freely flow from high concentration to low concentration

→ Pathway from high to low concentration is concentration gradient → Eventual point where concentration is equal = equilibrium (particles still randomly move but equal in/out) Concentration Gradient High Concentration Low Concentration

 Three methods: a. Simple diffusion – particles (solutes) b. Osmosis – diffusion of water (solvent) c. Carrier-facilitated diffusion – particles (solutes) with protein assistance

 Simple diffusion – free movement of ions & molecules through protein channels in membrane Outside cell Inside cell

 Simple Diffusion – the homemade animation

o Osmosis – free movement or diffusion of solvent (water) ONLY Note how the red sugar particles stay put. Only the blue water molecules move.

 Osmosis – the homemade animation

o three types of solutions that determine direction of water : ♦ isotonic solution ♦ hypotonic solution ♦ hypertonic solution

♦ Isotonic Solution > concentration of water on outside of cell is same as on inside of cell > Cells do not experience overall osmosis (or diffusion) > retain their normal shape, > Still random movement for an overall net gain of 0

90% H 2 O 10% particles (inside cell) 90% H 2 O 10% particles (outside cell)

♦ Hypotonic Solution > concentration of water is higher outside cell than concentration of water inside cell. > Cells experience osmosis (and diffusion) > water moves into cell > cell swells and will burst if animal cell but will not burst if plant cell due to cell wall

30% H 2 O 70% particles (inside cell) 70% H 2 O 30% particles (outside cell) O s m o s i s o f w a t e r D i f f u s i o n o f p a r t i c l e s

♦ Hypertonic Solution > concentration of water is higher inside cell than concentration outside cell. > Cells experience osmosis (and diffusion) > water moves out of cell > Cells shrink > Plant wilts because of a decrease in pressure on cell wall

55% H 2 O 45% particles (inside cell) 45% H 2 O 55% particles (outside cell) O s m o s i s o f w a t e r D i f f u s i o n o f p a r t i c l e s

HypertonicIsotonicHypotonic Higher solute OUTSIDE Equal soluteHigher solute INSIDE Higher water INSIDE Equal waterHigher water OUTSIDE Water moves OUTNo net movementWater moves IN Cell SHRINKSNormalCell SWELLS

Hypertonic vs. Isotonic vs. Hypotonic Solutions

20% H 2 O 80% particles (inside cell) 80% H 2 O 20% particles (outside cell) D i f f u s i o n o f p a r t i c l e s O s m o s i s o f w a t e r Question1: Which way will the particles move? Question 2: Which way will the water move? outside inside

OSMOSIS DIFFUSION

 free movement of larger molecules with aid (help) of a transport/carrier protein Large solutes (sugars, amino acids) are too big to go through plasma membrane unaided

 Facilitated Diffusion – the homemade animation

 Needs energy (ATP) to move particles across plasma membrane Three types: 1.Active transport – small molecules AGAINST concentration gradient (from low to high) 2.Endocytosis – large molecules being engulfed by plasma membrane into vesicles 3.Exocytosis – large molecules being expelled out by vesicles out of plasma membrane

 Requires energy (ATP) to move materials against gradient (low to high concentration) ♦ carrier protein allows specific molecule or ion to bind o Example: sodium/potassium (Na/K) pump ♦ ATP changes shape of protein to move molecule or ion across plasma membrane ATP

 cell surrounds material with a portion of its plasma membrane and forms a vesicle  Vesicle moves particle inside cell for digestion Bacteria, food  Phagocytosis – large, solid particles  Pinocytosis – small, liquid particles

 Vesicle brings material to cell membrane & expels (secretes) it Wastes, hormones

Test Wednesday: 40 points multiple choice 10 points short answer