7-3 CELL BOUNDARIES

CELL MEMBRANE

• Define: The cell membrane regulates what enters and leaves the cell and also provides protection and support.

• Composition: Made up of a double-layered sheet called a lipid bilayer

• The lipid bilayer gives the cell membrane a flexible structure that forms a strong barrier between the cell and its surroundings.

• The lipid bilayer also includes proteins used to channel molecules across and carbohydrates for communication.

CELL WALL• The main function of the cell wall is to provide support and protection for the cell

• Plant cell walls are made up of cellulose

QUICK REVIEW• Solution – A mixture of two or more substance

• Solvent – The liquid in which a solute is dissolved to form a solution

• Solute – The substance dissolved in the solution

• Concentration – The mass of a solute found in a volume of solution. Mass / Volume (g/L)

• Transport across a membrane that requires the cell to use NO energy

• Transport across a membrane that requires the cell to use energy

TRANSPORT

Active Passive

DIFFUSION

• Diffusion is the process of particles moving from an area of high concentration to an area with low concentration

• When the concentration of the solute is the same throughout a system, the system has reached equilibrium

• Because diffusion depends upon random particle movement, substances diffuse across membranes without requiring the cell to use energy

• Diffusion does not require energy!

DIFFUSION

FACILITATED DIFFUSION

• Few molecules are too big to get through the membrane by themselves.

• Facilitated: Make an action or process easier.

• Facilitated diffusion: Molecules that cannot normally pass through the cell membrane get help using their own personnel protein channel.

• NO ENERGY REQUIRED!!!

ACTIVE TRANSPORT

• Uses energy

• Generally carried out by transport proteins or “pumps”

• “Pumps” work pumping concentration from low to high. (Backwards from normal)

• Most biological membranes are selectively permeable. Only allowing some substances through and denying others.

• Osmosis is the diffusion of water across a selectively permeable membrane.

OSMOSIS

HOW OSMOSIS WORKS

• Movement of WATER from an area of high concentration to an area with low concentration.

• Water will continue to move across a membrane until equilibrium is complete.

• Isotonic – Same strength of solute

• Hypertonic – Above strength of solute

• Hypotonic – Below Strength of solute

OSMOTIC PRESSURE

• For cells to survive, they must find a way to balance the intake and outtake of water.

• If balance is not met, a force called osmotic pressure occurs. Creating a situation where cells will struggle to survive.

ENDOCYTOSIS • Process of taking material into the cell by means of infolding or pockets.

• Pocket breaks loose and forms a vacuole.

• Two main types of endocytosis

• Phagocytosis

• Pinocytosis

PHAGOCYTOSIS

• “Cell Eating”

• Cell slowly surrounds and engulfs the food.

PINOCYTOSIS

• “Cell Drinking”

• Cells form tiny pockets around the cell wall and fill them with liquid and pinch off

EXOCYTOSIS

• Removal from the cell

• Vacuole fuses with the cell membrane, forcing the contents out of the cell

• Contractile vacuole in some fresh water protists.