Materials can move across the cell’s membrane Chapter Two – Section Three

Quickie Review All cells have a cell membrane surrounding them Cells need STARTER materials to do different processes (photosynthesis and cellular respiration) Cells need to get rid of Waste products and items that they make for the body

Colored Water Demonstration Describe what you saw…. Animation: How Diffusion Works

Some materials move by DIFFUSION Diffusion is when molecules spread out from where there is a lot – to where there is not a lot. It happens because molecules are in Constant motion in all directions (everywhere) Examples:  Any scent that “travels” through air  Food dye through water  Water, CO 2, O traveling in and out of cells

“Concentration” – page 57 Diffusion is movement from areas of High “concentration” to areas of Low “concentration” until there is EQUILIBRIUM (balance) The greater the difference in concentration, the faster the movement (diffusion) Adding Salt to Ocean Water…slow diffusion Adding Salt to Fresh Water…fast diffusion

Diffusion in cells happens the same way Small molecules (like O, H 2 O, CO 2 ) can move through the cell membrane without problem Diffusion across a Cell Membrane This is called PASSIVE TRANSPORT – Movement with out Energy required

Passive Transport in cells – No Energy needed Most Passive Transport happens with smaller molecules (O, H 2 O, CO 2 ) Some Molecules are Large (C 6 H 12 O 6 ) and require special “doors” to move through called “Passive Transport Proteins”

H 2 O H 2 O H 2 0 H 2 O H 2 0 H 2 O H 2 OH 2 OH 2 O H 2 OH 2 O H 2 0  BALANCE THIS PICTURE

Second Type of Passive Transport Osmosis  It is the “Diffusion” of Water ONLY across the cell membrane  It move on its “own” until there are the same amount of H2O’s on each side (Equilibrium)  Example: Page 59 – Wilting plants

Active Transport in cells Opposite from Passive in that this molecule movement needs ENERGY Movement from areas of Low Concentration to areas of High Concentration This usually happens when the molecules are very LARGE in size, or when more molecules have to get out of the cell, or come in the cell Example: Page 60 – Iguanas Active Transport Animation

Two types of Active Transport 1.Endocytosis When molecules that are too big to go through the cell membrane, need to get IN the cell 2.Exocytosis When molecules that are too big to go through the cell membrane, need to get OUT of the cell Example: Plastic Bag demo Amoeba eating

end

Cell Size will affect how molecules move Almost all cells are small Average human cell is.005mm in diameter Lots of things need to go in and out of cell for jobs to be done. Surface Area is needed More surface – more exchange can take place