Homeostasis Maintenance of a stable internal environment Maintaining the proper balance Cell membrane helps maintain the cell’s homeostasis by regulating the movement of substances across the membrane

Homeostasis Cell membrane is SEMIPERMEABLE The cell controls what comes in or goes out

Cell Membrane Phospholipid Bilayer Phospholipid Bilayer Phosphate “head” Two fatty acid “tails” Bilayer Two layers

Cell Membrane Phosphate “head” Two fatty acid “tails” Hydrophilic Hydro = Water Philic = Attraction “Water-loving” Two fatty acid “tails” Hydrophobic Phobic = opposite of attraction = aversion “Water Hating”

Cell Membrane Barrier to outside Only very small substances can pass through it

Cell Transport Cells need to move substances in and out of the cell for many reasons Get food, to remove waste, to maintain homeostasis Variety of ways that substances can move across cell membrane Passive transport Active transport

Passive Transport Substances move across the membrane without an energy input – Passive Equilibrium State of balance, stability Chemical equilibrium = equal concentration If concentrations are not equal… Cell membrane will move substances to create equilibruim

Passive Transport If the concentration on one side of the cell membrane is higher than the other, a CONCENTRATION GRADIENT exists Substances will move from high concentrations to low concentrations DIFFUSION Moving down the concentration gradient No energy input

Two Types of Diffusion Simple Diffusion Facilitated Diffusion Small nonpolar substances can move directly through the phospholipid bilayer Facilitated Diffusion Other substances cannot pass through the lipid bilayer They require assistance in movement across the membrane

Facilitated Diffusion Required assistance Cannot just move the membrane wherever it wants Proteins are present in cell membrane Two types of proteins can give assistance: Channel Proteins Carrier Proteins

Facilitated Diffusion Channel Proteins Proteins located in the lipid bilayer that act as tunnels Each protein is made for the transport of a certain substance Sodium ions pass through sodium ion channels

Facilitated Diffusion Carrier Proteins Proteins located in the lipid bilayer that bind to certain substances After the substance binds to its binding site, the protein changes shape This change in shape moves the substance across the membrane

Channel Proteins vs Carrier Proteins

Osmosis Water can move in and out of the cell too Water can diffuse across the cell membrane through osmosis

Osmosis Water is polar Water uses channel proteins (only nonpolar substances can move directly across the membrane) Water uses channel proteins Water moves down the concentration gradient for water

Osmosis If the sugar were to move down its concentration gradient it would move which direction? If the water were to move down its concentration gradient which way would it move

Osmosis in a Cell HYPERTONIC Hyper = excessive Tonic = solution with concentration High solute concentration outside the cell INSIDE OUTSIDE High water Low water Low solute high solute Water moves OUT

Osmosis in a Cell HYPOTONIC Hypo = low Tonic = solution with concentration Low solute concentration outside the cell INSIDE OUTSIDE Low water High water High solute Low solute Water moves IN

Osmosis in a Cell ISOTONIC Iso = equal Tonic = solution with concentration Equal solute concentration outside the cell INSIDE OUTSIDE Same water Same water Same solute Same solute Water does NOT move Equilibrium

Active Transport Sometimes substances have to move against the concentration gradient Working against the concentration gradient requires energy input from the cell ACTIVE

Active Transport Facilitated diffusion uses carrier proteins to move substances WITH the concentration gradient No energy needed Active Transport can use carrier proteins to move substances AGAINST the concentration gradient Energy required

Pumps Carrier proteins that move substances against the concentration gradient are called PUMPS The substance to be moved attaches to the carrier protein ATP is added for energy The carrier protein then changes shape and moves the substance

ACTIVE TRANSPORT - Pumps

ACTIVE TRANSPORT - Vesicles Vesicles can trap substances from outside the cell and bring them into the cell Movement into a cell via vesicles ENDOCYTOSIS Movement out of a cell via vesicles EXOCYTOSIS

ACTIVE TRANSPORT - Vesicles

ACTIVE TRANSPORT - Vesicles

CONCENTRATION GRADIENT CARRIER PROTEIN

Homework DR Cell Transport : 7-17