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

Small black molecules allowed through

Large red molecules NOT allowed through

Large red molecules NOT allowed through

WHY?WHY?

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

2 layers = 1 plasma membrane

2 layers = 1 plasma membrane

Phosphate head

Lipid tails

• phosphate group: phosphate (PO4)

>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 2O

solu

ble

H 2O

solu

ble

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

98.6ºF98.8ºF99.0ºF

Increase in heat makes temperature

rise

Increase in heat makes temperature

riseCell will seek to cool

itself downCell 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:Three methods:a.a. Simple diffusion Simple diffusion – particles – particles

(solutes)(solutes)b.b. OsmosisOsmosis – diffusion of water – diffusion of water

(solvent)(solvent)c.c. Carrier-facilitated diffusionCarrier-facilitated diffusion – –

particles (solutes) with protein particles (solutes) with protein assistanceassistance

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% H90% H22OO10% 10%

particlesparticles(inside (inside

cell)cell)90% H90% H22OO

10% 10% particlesparticles(outside (outside

cell)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% H30% H22OO70% 70%

particlesparticles(inside (inside

cell)cell) 70% H70% H22OO30% 30%

particlesparticles(outside (outside

cell)cell)

Osmosis of waterDiffusion of particles

♦ 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% H55% H22OO45% 45%

particlesparticles(inside (inside

cell)cell)45% H45% H22OO

55% 55% particlesparticles(outside (outside

cell)cell)

Osmosis of water

Diffusion of particles

Hypertonic Isotonic Hypotonic

Higher solute OUTSIDE

Equal solute Higher solute INSIDE

Higher water INSIDE

Equal water Higher water OUTSIDE

Water moves OUT

No net movement

Water moves IN

Cell SHRINKS Normal Cell SWELLS

Hypertonic vs. Isotonic vs. Hypotonic Solutions

Hypertonic vs. Isotonic vs. Hypotonic Solutions

Hypertonic vs. Isotonic vs. Hypotonic Solutions

Often times, diffusion of large particles can’t happen or happen fast enough

Water will diffuse via osmosis to regulate concentration (PERCENTAGES)•Outside cell is 50% solute, 50% water• Inside cell is 10% solute, 90% water•Solute is too big to move. Will we die? No.

Water will move to get concentration equal

90% H90% H22OO10% 10%

particlesparticles(inside (inside

cell)cell)

50% H50% H22OO50% 50%

particlesparticles(outside (outside

cell)cell)

Hint: look at water % only. Where will the water go?

20% H20% H22OO80% 80%

particlesparticles(inside (inside

cell)cell) 80% H80% H22OO20% 20%

particlesparticles(outside (outside

cell)cell)

Diffusion of particles

Osmosis of water

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 vesicles3. 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, foodPhagocytosis – large, solid particles

Pinocytosis – small, liquid particles

STARRINGSTARRING

train as the CELLtrain as the CELL

platform as the platform as the EXTRACELLULAR SPACEEXTRACELLULAR SPACE

people as the people as the PARTICLESPARTICLES

conductors as the ATPconductors as the ATP

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

Test Wednesday:40 points multiple choice10 points short answer