7-3: Cell Boundaries

Biology 1

• All cells are surrounded by a thin, flexible barrier– CELL MEMBRANE: thin, flexible

barrier around a cell; regulates what enters and leaves the cell

• Plant cells are also supported by a strong layer– CELL WALL: strong supporting layer

around the cell membrane in plants, algae, and some bacteria

Introduction

• Cell membrane regulates what enters and leaves the cell, also provides protection and support

• Cell membranes are made from double-layered sheets– LIPID BILAYER: double-layered

sheet that forms the core of nearly all cell membranes

Cell Membrane

• Cell walls are present in plants, algae, fungi and prokaryotes

• Main function is to provide support and protection

• Made of mostly carbs and proteins

Cell Wall

• Most important function of cell membrane is to move molecules from one side to other

• DIFFUSION: process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated

Diffusion

• Particles move back and forth across cell membrane

• Particles continue moving until they are equal everywhere– EQUILIBRIUM: when the concentration

of a solute is the same throughout a solution

• When perfume is sprayed in one corner, then the whole room smells

Diffusion

• The movement of water through the membrane of a cell

• OSMOSIS: diffusion of water through a selectively permeable membrane

Osmosis

• Water wants to move to where there is LESS

• ISOTONIC: when the concentration of two solutions is the same

• HYPERTONIC: when comparing two solutions, the solution with the greater concentration of solutes

• HYPOTONIC: when comparing two solutions, the solution with the lesser concentration of solutes

Osmosis

• Some molecules (like sugar) pass through cells very quickly

• Cell membranes have “helper” proteins that allow certain molecules to cross– ONLY allow specific molecule (like sugar)

to pass through)

• FACILITATED DIFFUSION: movement of specific molecules across cell membranes through protein channels

Facilitated Diffusion

Great Pacific Media

Cell Membrane Passive Transport

http://www.youtube.com/watch?v=JShwXBWGMyY