Cell TRANSPORT SB1d. Explain homeostasis and describe the movement of materials through the cell membrane. Explain the impact of water on life processes eq: how does the cell membrane help the cell maintain homeostasis?

Cell Transport  The cell must move different substances into and out of the cell  This happens in a variety of ways…  Sometimes the cell has to use energy, sometimes they do not

Passive Transport  Diffusion - passive transport of substances DOWN a concentration gradient (from high to low concentration)  Concentration gradient - one area has a higher concentration than another area  Equilibrium - when a space is filled evenly  Diffusion is simplest type of passive transport  Some substance diffuse through lipid bilayer  Others though transport proteins

Diffusion  Cell membrane is selectively permeable  Nonpolar interior of lipid bilayer repels ions and most polar molecules  These substances are prevented from diffusing across membrane  Very small or nonpolar molecules can diffuse across the membrane down their concentration gradient

Simple Diffusion  Moves small, nonpolar molecules directly through lipid bilayer  Ex-  O2  CO2

Facilitated Diffusion Moves ions and polar molecules that simple diffusion cannot Transport proteins help these substances diffuse through the cell membrane Two types: Channel protein Carrier protein

Channel Proteins  Ions, sugars, and amino acids can diffuse with help of channel proteins  Proteins, sometimes called pores, serve as tunnels through the lipid bilayer  Each channel allows the diffusion of a specific substance  Ex - only sodium ions can pass through sodium ion channels

Carrier Protein  Transport substances that fit within their binding site  (1)Carrier protein binds to specific substances on one side of cell membrane  (2)Binding causes protein to change shape  (3)As shape changes, the substance is moved across the cell membrane and released on other side

Facilitated Diffusion

Diffusion

Model of Diffusion

Osmosis  Definition - diffusion of water across selectively permeable membrane  Type of diffusion (passive transport)  From high to low concentration  Allows cells to maintain water balance as environment changes  Pass through water channels  Protein channels specific to water..

Osmosis  There are three possibilities for the direction of water movement:  Water moves out - (hypertonic solution)  Causes cell to shrink  Water moves in - (hypotonic solution)  Causes cell to swell  Cell could burst if it swells too much  Plant cells have rigid cell wall to prevent this  No net water movement - (isotonic solution)  No change in cell volume

Osmosis

Hypertonic, Hypotonic, and Isotonic Solutions

Active Transport  Transports substances against concentration gradient  Low to high concentration  Active Transport - requires energy  Most energy supplied directly or indirectly in the form of ATP (adenosine triphosphate)

Pumps  Substances bind to carrier proteins in low concentrations, released in higher concentration  Carrier proteins function as “pumps” - move substances against their concentration gradient called membrane pumps

Movement in Vesicles  Many substances, like proteins and polysaccharides, are too large to be transported by carrier proteins  So, they are moved across the cell membrane by vesicles  The movement of a substance into a cell by a vesicle is called endocytosis Pinocytosis- “cell drinking” Phagocytosis- “cell eating”  The movement of a substance by a vesicle to the outside of a cell is called exocytosis

ENDOCYTOSIS

EXOCYTOSIS