2. Osmosis diffusion of WATER across a cell membrane The direction the water moves depends on the concentration of water on either side of the membrane Three types of osmosis: A. Hypertonic B. Hypotonic C. Isotonic

A. Hypertonic osmosis Water moves OUT of a cell when the concentration of water is higher INSIDE the cell But, If too much water moves out of a cell, the cell will die

B. Hypotonic osmosis Water moves INTO a cell when the concentration of water is higher OUTSIDE the cell But, If too much water moves into a cell, the cell will burst

C. Isotonic osmosis Equal amounts of water on each side of the membrane Equal amounts of water will move into and out of the cell This is where the body tries to be This is homeostasis!

3. Facilitated Diffusion This is the movement of large molecules across a membrane They need the help of the large proteins in the membrane to move across the membrane There are two kinds of Proteins that do this: Carrier proteins move neutral particles This is how glucose is moved Ion Channels move electrically charged particles (ions) VERY specific!

Active Transport 1. Pumps 2. Endocytosis 3. Exocytosis Sometimes a cell must move a substance against the concentration gradient This requires the cell to use energy to move something across the cell membrane There are three types of active transport 1. Pumps 2. Endocytosis 3. Exocytosis

1. Pumps One of the most important pumps is the sodium potassium pump (Na+-K+) Pumps are very specific - not only in WHAT they move but also HOW they move them 60085.mov

2. Endocytosis Some substances are so large that carrier proteins & ion channels cannot handle them The cell then uses a vesicle system to bring extra large molecules into the cell There are two steps: 1. The cell membrane surrounds the molecule to be moved into the cell & forms a pouch 2. The pouch then breaks free from the cell membrane and the molecule is now inside the cell

3. Exocytosis The opposite process of moving a very large molecule OUT of a cell is called exocytosis Quick Review

Energy Used by cells Cells do not know how to use carbohydrates, fats, proteins and sugars from your food So each of your cells transform food energy into Adenosine Triphosphate (ATP) ATP fuels EVERYTHING your cells do

Organelles Organelles are small organ-like structures that make the cell work properly. Each one has a specific job to do much like your organs do for your body. They are all surrounded by a membrane to separate them from the other contents of the cell

The Nucleus This organelle contains the DNA of a cell It acts as the mayors office of the cell, controlling everything that happens in the cell

Endoplasmic Reticulum (ER) Acts as a highway within the cell In places, there are ribosomes attached to the ER: this is called rough ER & membrane proteins are made here In other places, there are no ribosomes attached: this is called smooth ER Ribosomes are small organelles responsible for making protein