Homeostasis and Transport
• Cells need to get materials in and out of the cell in order to maintain cellular processes
• Some substances can move freely to and from the cell – Passive Transport
• Others need assistance from cell – Active Transport
Homeostasis
• Every cell seeks a state of equilibrium.
• This is a balanced state where concentrations of chemicals are within a tolerable range.
• This state of equilibrium is called Homeostasis
• Homeo = Same Stasis = State
Passive Transport
• Two types of Passive Transport
– Diffusion
– Osmosis
Diffusion• Solute molecules
moving from an area of high concentration to an area of low concentration
– Random motion drives diffusion
– Equilibrium is reached when there is an even distribution of solute molecules
2
3
14
(water)
Diffusion across the Membrane
• Some molecules that are soluble in lipids are able to cross the phospholipid membrane of the cell.
• Because they do this on their own – the cell doesn’t expend any energy
• Examples– Oxygen and Carbon Dioxide
Osmosis
• Osmosis is a passive process in which water moves from areas of high concentration to low areas.
• Water moves down its concentration gradient a crossed a semi-permeable membrane.
• Like diffusion….it does not require cells to expend energy
•Solutes are chemicals suspended in water.•Solvent is water.
Osmosis in Red Blood Cells
Osmosis in Living Cells
Cellulose in cell wall
Active Transportation of Molecules
• Passive Transport
-Movement of molecules across a semi-permeable membrane
- no energy required
• Active Transport
-Movement of molecules across a semi-permeable membrane against a concentration gradient with a protein
- ENERGY – ATP
• Facilitated Diffusion
-Movement of molecules across a semi-permeable membrane with a protein
- no energy required
Active Transport
• Carrier proteins also assist cell in active transport.
• In active transport these proteins act as “Membrane Pumps” to get ions out or into cell.
• Cell has to expend energy (ATP)
• Example– Sodium-Potassium Pump
Endocytosis and Exocytosis
• Some substances are too large to pass through membrane – Macromolecules and food particles.
• So cell develop another way to get these particles in and out using vesicles.
• Vesicles are pinched off sacs created by the membrane.
Endocytosis
• Endo = inside
• Two type of endocytosis– Pinocytosis – Transportation of liquids– Phagocytosis – Transportation of Solids or
whole cells
• Some unicellular organisms use these processes to ingest food
Dealing with Visitors
• Also used to capture bacteria and viruses from extra cellular fluid and destroy them with the help of the lysosomes.– Phagocytes
Exocytosis
• Exo = Outside
• Reverse of Endocytosis
• Particles that come from golgi bodies or are free floating fuse with cell membrane.
• Particles are enclosed in a membrane sac
• Cell wall then opens the external side of the sac and particles is allowed to exit.
Animations
Dialysis Bag Experiment• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStud
yPages/Diffusion_Osmosis/Baggif.swf
Elodea Cell• http://ccollege.hccs.cc.tx.us/instru/Biology/AllStud
yPages/Diffusion_Osmosis/Elodeagif.swf
Osmosis• http://ull.chemistry.uakron.edu/genobc/
animations/osmosis.mov
