PASSIVE TRANSPORT One way cells maintain homeostasis is by controlling the movement of substances across their cell membrane. Cells want to reach “equilibrium”. Equilibrium – is a condition in which the concentration of a substance is equal throughout a space

Equilibrium: Molecules eventually spread out so that they are evenly distributed.

Passive Transport – the movement of substances across a cell membrane that does not require energy from the cell ***it does not require energy because substance are moving along or down the concentration gradient concentration gradient – the difference in the concentration of a substance across a space

1. Diffusion – the movement of a substance from an area of high concentration to an area of lower concentration High Concentration Low Concentration (substance)

Which diagram(s) shows a concentration gradient? B. C. D.

2. Osmosis – the diffusion of water through a selectively permeable membrane ONLY water is allowed to move across the membrane.

3. Facilitated Diffusion: Transport Proteins allow molecules that can’t pass the membrane by simple diffusion to pass. ex: ion channels – are a transport proteins which allow ions to pass

Some transport proteins are referred to as carrier proteins because they bind to specific substances on one side of the cell membrane then carry the substance across releasing it on the other side. Also known as facilitated diffusion.

Passive Transport Examples Osmosis Carrier Protein Transport Protein

The box is divided by a permeable membrane The box is divided by a permeable membrane. In the blank drawing on the right, draw what the solution would look like once equilibrium has been reached. A concentration gradient is present so particles will move from left to right. To reach equilibrium the particles will move until they are equal on both sides. Equilibrium 9 1 5 5

The square box indicates a cell membrane The square box indicates a cell membrane. Use arrows to indicate the direction of diffusion. is a solute that can pass through the cell membrane. Cell membrane inside outside 11 inside; 6 outside

The square box indicates a cell membrane The square box indicates a cell membrane. Use arrows to indicate the direction of diffusion. is a solute that can pass through the cell membrane. Cell membrane inside outside 6 inside; 12 outside

Passive Transport Summary: The movement of a substance down a concentration gradient, from high to low concentration, therefore NO energy is required from the cell! Three Examples: Diffusion (diffusion of any substance) Osmosis (diffusion of water) Facilitated Diffusion (transport proteins or carrier proteins )