AgendaTurn in drawings – make sure your name is

on themQuickly review 4.1 and 4.2Current EventPresent videosCell TransportPrepare Osmosis LabWork on HW OR review unit test4.1-4.2 Quiz ThursdayHW: Cell Transport WS

4.2 Level 2 - Structure

(Membrane)

Other Examples of Structure

4.2 Level 3 Part 1How would a Beta cell be specialized for its function? How might it look different from stem cells or other cells not specialized for this function?

Crossing the Membrane

Activity 1Start in one cornerTry to move randomly- when you (Carefully) bump into somebody “bounce” the other direction

What happens?

DiffusionWe call this phenomenon diffusion

Things naturally bounce off each other and spread apart – if they can

We say things move from “high concentration” to “low concentration”

What does this have to do with cells?Lots of things enter and exit this cell

by this processHowever, they must be able to

somehow cross the membraneCytosol

Membranes Keeps Cells SeparateMost things are either too big to cross the membrane

OR they are polar and won’t mix with the membrane

Creates an internal environment different from the outside world(e.g. it has enzymes, proteins, sugars, ATP, NADH, FADH etc. floating around)

1. Simple DiffusionVery small hydrophobic (non-polar) molecules

can simply slip between the membranes and cross the hydrophobic layer

Some small polar molecules can slowly cross

2. Facilitated DiffusionOther small molecules need to move

through a protein channel (small polar or ionic compounds)

Concentration GradientMolecules on the top are likely to collide and

knock each other towards the bottom

High Concentration

Zero Concentration

More collisions

No collisions

Diffusion

High Concentration

Low Concentration

More collisions

Fewer collisions

Some will still get knocked back, but more will come to this side

Equilibrium / No Concentration GradientNo net change in concentration. Molecules

still move but on average the concentrations stay the same

Molecules on either side are equally likely to collide and be knocked to the other side

Medium Concentration

Medium Concentration

What if We Want to Move Things Against the Gradient?Active Transport!We must invest energy to “pump”

molecules

ReviewSmall, non-charged

molecules can simply diffuse

Small, polar or charged molecules can pass through a protein

Energy must be invested to move things against the gradient

OsmosisSpecial name for

diffusion of waterWhen molecules can’t

diffuse, water doesWater diffuses

towards the more concentrated side until the concentrations are balanced*

*or another force is applied

Why?More solute, means more water bound to the

soluteLess free water, so it’s like a low

concentration of water

Big ThingsE.g. macromoleculesToo large to fit through membrane or

proteinsMembrane folds in

Endo/ExocytosisBig things must

enter through endocytosis and form a vesicle

Big things must exit by exocytosis, where the vesicle becomes part of the plasma membrane

Pre-LabWork in groups of 4 on setting up

the labCheck in periodically and definitely

after question 5Be ready to run the lab tomorrow

When finished work on HW or reviewing test or studying for quiz