Have your review of cell structure and function out.

1.So, we know cells are processing energy… 2.We know the PM (plasma membrane) is letting some things in/out and not others… 3.How DO substances get into/out of the cell???

I.Transport of molecules in/out of cells takes place across the Plasma Membrane A. General Information 1.The structure of the p.m. makes it semi (or selectively) permeable. Meaning it only allows certain materials in & out. 2.Ex dialysis tubing 3.This is important for maintaining homeostasis inside our cells and keeping the proper amounts of solutes (sugars, salts, oxygen, carbon dioxide) and solvents (water) inside our cells.

Side Bar HOMEOSTASIS: keeping the cell balanced. Too much/too little of most anything can kill a cell/organ/person. Ex: too little oxygen in a cell- dies Too much carbon dioxide in a cell- dies Thus your body is constantly bringing oxygen in & releasing carbon dioxide.

Reminder! Molecules are constantly moving. Thus, they collide with each other randomly and spread out. Ex: beaker collision This random motion is responsible for the movement of most molecules in/out of our cells through the plasma membrane.

NOTE: The movement of particles is random & constant (except for absolute zero). However, overall movement of molecules is from HIGH to LOW concentration. 1.) Why? Molecules tend to spread from where they are more concentrated to where they are less concentrated. (They “bump” each other farther & farther away from the “crowd” of molecules). 2.) The movement of molecules from high to low concentration is called DIFFUSION

Dye in water: diffusion example 1.draw 3 rectangles 2.The 1 st one is labeled “Dye is dropped in” 3.The 2 nd one is labeled “diffusion begins” 4.The last is labeled “dye is evenly distributed. 5.Represent water and dye molecules with circles (water) and x’s (dye). 6.After I drop the dye into the beaker draw the above stages. You will have about 3 minutes.

Share your diagram with your table. Notice similarities/differences.

NOTE: For diffusion to work there must be a difference in solute concentration OR a concentration gradient.

To simplify this concept we can say that molecules move down their concentration gradients from high concentration to low concentration. Just as rolling down a ramp NO added energy is needed. It is run on random molecular movement.

Diffusion is how solute molecules move in/out of our cell. Ex: oxygen (O2) into the blood from lungs and then into the cell from blood. Both blood and cells in this case have a LOW amount of O2. Ex: digestion: macromolecules diffuse through the small intestine membrane into the blood & then into cells that have a LOW concentration of macromolecules.

Diffusion also applies to water molecules but has a different name to distinguish the diffusion of water from the diffusion of solutes…..

III. Osmosis – the diffusion of water across a semi- permeable membrane from an area of high water concentration to an area of low water concentration. High water/ low salt Low water/ High salt Water moves towards the low concentration of water

1. A cell loses water by osmosis when the area outside of the cell has less water. a. Ex: Cells shrink in highly salty water “Normal” Interstitial Fluid, Homeostasis between water and salt Low water / High salt in Interstitial Fluid Water moves out of cell and cell shrinks!

2. Cells will gain water when the area outside of the cell has more water. a. Ex: Cells bloat / explode “Normal” Interstitial FluidInterstitial Fluid too watery Water moves into cell & cell bloats

NOTE: A cell is usually at equilibrium with the surrounding fluid. This means there is an even amount of diffusion of water & solutes back and forth across the membrane. NOTE: Osmosis and diffusion NEVER STOP because molecular movement never stops.

VI. Passive vs. Active Transport 1. Passive transport = does not use energy. This type of movement relies on molecular motion. a.Diffusion & osmosis are passive. b.Many solutes & water molecules enter our cells because they are moving naturally from areas of high concentration to areas of low concentration

b. Facilitated Diffusion – cell does not use energy, but molecules use protein channels in the plasma membrane to enter the cell. Ex: glucose Passive Transport: no energy required! Osmosis/Diffusion Facilitated Diffusion High to low

2. Active transport= needs energy (ATP) a.Cells must use energy to move molecules from areas of low concentration to areas of high concentration. b.) THIS IS AGAINST THE NATURAL FLOW! Low to High!

Diffusion, osmosis & facilitated diffusion: With the concentration gradient = No Energy Active Transport: Against the concentration gradient = Uses Energy!

Active transport is used in many cell processes: Ex: contracting muscles, nerve impulses, cellular respiration….

Also… Cells are really small s/scale/ s/scale/ For efficiency & getting stuff in & out. Has large surface area to volume ratio. –As a cell increases in size the volume increases much faster then the surface area so as a cell increases in size it decreases in efficiency. –Exception to rule: Having multiple nucli or multinucleated. Skeletal muscle & giant amoeba are 2 examples

FYI: the nucleus is the purple dot. “nutrients” must be able to get to & from the nucleus. Q: From these pictures determine WHY the cell getting bigger and bigger is an issue.

Answer

Review: How things get in/out… PASSIVE TRANSPORT 1. Diffusion: high to low of solutes. Goes with concentration gradient. (inc. facilitated diffusion with proteins) 2. Osmosis: diffusion of water high to low. Goes with concentration gradient. ACTIVE TRANSPORT 3. Active Transport: low to high of all substances. Needs ATP to go against the natural flow of concentration gradient AND SIZE MATTERS!

HOMEWORK Organelle chart/table Diffusion & osmosis HW Quiz on ATP, Cell & organelles You have 5 days to complete this HW. Visit the HW web for ways to study and Crash Course links!