Download Exocytosis and Endocytosis

Active Transport
SBI 4U
Ms.Zafar
October 24th, 2012
Review
• Diffusion
• Osmosis
Facilitated Diffusion
• Protein carrier molecules, located in the cell
membrane, can aid in passive transport
Facilitated Diffusion, continued …
• Protein carriers speed up the movement of
molecules already moving across the cell
membrane
• Example: glucose diffuses into red blood cells
hundreds of times faster than other sugar
molecules that have similar properties, why? 
specialized carrier proteins
Active Transport
• When a cell uses its own energy to move materials from an
area of low concentration to an area of higher
concentration  active transport
Without active transport …
• Your kidneys would fail to reabsorb needed
materials
• Your muscles would not contract
• Your nerves would not carry impulses
Endocytosis & Exocytosis
• How do cells absorb larger molecules? Expenditure
of energy is required
• Endocytosis  process of ingesting materials
• Exocytosis  process of transporting materials to
outside environment
Process of Endocytosis
1.
2.
3.
Membrane folds around materials outside the cell
Ingested particle is trapped within a vacuole inside the
cytoplasm
Often lysosomes are used to digest the molecules absorbed
by endocytosis
Endocytosis, continued …
• Pinocytosis & Phagocytosis
• Pinocytosis: cells take up dissolved molecules
by engulfing small volumes of the external
solution. Ex: small intestine and fat droplets
• Phagocytosis: process by which cells engulf
solid particles. Ex: white blood cells and
microbes
• Cellular drinking vs. cellular eating
Exocytosis
• Process by which large molecules held within the
cell are transported to the external environment
• Waste materials are often released this way
• Useful materials, like transmitter chemicals
emitted from nerve cells are also released by
exocytosis
Process of Exocytosis
1. Golgi apparatus holds the secretions inside
fluid-filled membranes
2. Small vesicles break off and move toward the
cell membrane
3. The vesicles fuse with the cell membrane and
the materials is released into the external
environment