Agenda Turn in drawings – make sure your name is on them Quickly review 4.1 and 4.2 Current Event Present videos Cell Transport Prepare Osmosis Lab Work on HW OR review unit test Quiz Thursday HW: Cell Transport WS

4.2 Level 2 - Structure (Membrane)

Other Examples of Structure

4.2 Level 3 Part 1 How 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?

Activity 1 Start in one corner Try to move randomly- when you (Carefully) bump into somebody “bounce” the other direction What happens?

Diffusion We 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 process However, they must be able to somehow cross the membrane Cytosol

Membranes Keeps Cells Separate Most 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 Diffusion Very 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 Diffusion Other small molecules need to move through a protein channel (small polar or ionic compounds)

Concentration Gradient Molecules 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 Gradient No 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

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

Review Small, 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

Osmosis Special name for diffusion of water When molecules can’t diffuse, water does Water 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 solute Less free water, so it’s like a low concentration of water

Big Things E.g. macromolecules Too large to fit through membrane or proteins Membrane folds in

Endo/Exocytosis Big 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-Lab Work in groups of 4 on setting up the lab Check in periodically and definitely after question 5 Be ready to run the lab tomorrow When finished work on HW or reviewing test or studying for quiz