Passive and Active Transport

Importance Every living cell exists in a liquid environment. One of the most important functions of the cell membrane is to keep the cell’s internal conditions relatively constant. It does this by regulating the movement of molecules from one side of the membrane to the other side.

Passive Transport Cell membranes help organisms maintain Homeostasis by controlling what substances may enter or leave cells Doing this WITHOUT energy is called passive transport  Diffusion  Facilitated Diffusion  Osmosis

Can you think of a time you move but do not require any energy?

Molecules moving down hill require no energy. It just happens!! High concentration Low concentration This is passive transport. It just happens!!!!

Diffusion The simplest form of passive transport Does not require energy Is the movement of molecules from an area of HIGH concentration to an area of LOW concentration High concentration of dye Low concentration of dye Ex: Perfume or Cologne

Facilitated Diffusion Most molecules cannot cross the cell membrane by simple diffusion Some Molecules are CARRIED across by CARRIER PROTEINS EMBEDDED IN the Cell Membrane Requires NO energy

Osmosis The diffusion of WATER over a semi- permeable membrane Does NOT require energy From HIGH concentration of WATER to LOW concentration of WATER

Osmotic Conditions Isotonic Hypertonic Hypotonic

Isotonic “same strength” In an Isotonic solution  Under these conditions, water diffuses into and out of the cell at EQUAL RATES, so there is NO net movement of water  Remains at equilibrium “Like a full restaurant – one family must leave for another to enter”

Cells in isotonic solutions… No net movement of water Cells are normal

Hypertonic “above strength” WATER DIFFUSES OUT OF THE CELL until Equilibrium is established Plasmolysis: the cell shrinks “Hyper kids run out of school”

Cells in hypertonic solutions… Water moves out of the cell Cells shrivel (plasmolysis)

Hypotonic “below strength” WATER DIFFUSES INTO THE CELL until Equilibrium is established Cytolysis: the cell explodes

Cells in hypotonic solutions… Water moves into the cell Animal cells burst (cytolysis) Plant cells become turgid

Active Transport In many cases, cells must move materials from an area of low concentration to high concentration This requires energy

Endocytosis During ENDOCYTOSIS the cell membrane folds into a POUCH that encloses the particles INSIDE the cell.

Pinocytosis and Phagocytosis Two forms of Endocytosis Pinocytosis is often referred to as “cell drinking”  Bring in fluids and solutes Phagocytosis is often referred to as “cell eating”  Brings in food or other cells

Exocytosis The opposite of endocytosis  Gets rid of wastes