Getting In & Out of a Cell

Osmosis & Diffusion

Cell Membrane

• Remember: The Cell Membrane is SEMI-PERMEABLE– It doesn’t let

EVERYTHING inside the cell

• Cells do this to maintain homeostasis– Stable internal

environment

PASSIVE TRANSPORT

• Substances that cross the cell membrane without taking energy from the cell

DIFFUSION• The movement of

molecules from an area of high concentration to low concentration– Concentration

gradient = difference in concentration!

• Eventually this leads to equilibrium– Equal concentration

throughout space

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Sugar Molecules

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OSMOSIS

• Process of WATER diffusing across a cell membrane from an area of higher concentration to an area of lower concentration

Directions of Osmosis

• The net direction of osmosis depends on the concentration of solutes outside & inside the cell– Hypotonic– Hypertonic– Isotonic

HYPOTONIC

• Concentration of molecules are lower on OUTSIDE of cell

• Water diffuses INTO the cell

HYPERTONIC

• Concentration of molecules are lower on the INSIDE of the cell

• WATER diffuses OUT of the cell

ISOTONIC

• Concentration of molecules is equal inside & outside the cell– At equilibrium

• Water diffuses equally into and out of the cell– No NET movement

of water

Examples

ION CHANNELS – FACILITATED DIFFUSION

• Membrane proteins that allow ions to enter the cell

• Ions must go through channels because they can’t dissolve through lipid bilayer

ACTIVE TRANSPORT

• Movement of materials against the concentration gradient

• Requires energy

• Called “pumps”

ENDOCYTOSIS

• Process of cells ingesting external fluid, macromolecules, other cells, etc.

• Cells do this for substances that are too BIG to pass through the cell membrane

ENDOCYTOSIS CONT…

• External materials are enclosed in a membrane-bound organelle called a VESICLE

• These can fuse with lysosomes to be digested

PINOCYTOSIS & PHAGOCYTOSIS

• Pinocytosis– Solutes or fluid

• Phagocytosis– Large particles or

whole cells

EXOCYTOSIS

• Vesicles in the cell fuse with the cell membrane and release the contents

EXAMPLES