Homeostasis and Cellular Transport Biology Homeostasis and Cellular Transport

Homeostasis Literally means, “ inner balance” Keeping internal conditions within healthy limits It applies to things like body temperature and blood pressure

Feedback Loops or Homeostatic Mechanisms

Cellular Transport Cellular transport describes how substances cross the cell membrane. As you remember, the cell membrane controls what goes in and out of the cell.

Phospholipids The cell membrane is made mostly of phospholipids They have a hydrophilic head and hydrophobic tail Hydrophilic means water loving Hydrophobic means water fearing

Phospholipid Bilayer The cell membrane is made of two layers of phospholipids It also contains some proteins The hydrophilic heads face the cytoplasm and extracellular fluid, while the tails face inward

Types of Transport Passive Transport – Substances cross the membrane without the use of energy (ATP is the most used energy molecule in the human body) Active Transport – Substances cross the membrane through the use of energy, or ATP

Passive Transport Diffusion - The movement of substances from an area of high concentration to an area of low concentration

Passive Transport Cont’d Facilitated Diffusion – Diffusion that takes place using a membrane protein. They can open and close when needed.

Osmosis The diffusion of water.

Equilibrium After diffusion or osmosis has taken place and there is an equal concentration of substances.

Passive Transport Summary Passive transport usually moves things: 1. That are small 2. From high to low concentration 3. That are lipid soluble 4. Without using ATP

Active Transport Movement of substances across the cell membrane that requires the use of ATP (energy).

Types of Active Transport Protein Pumps – A membrane protein and ATP are used to pump substances against their concentration gradient across into or out of the cell. Example - Na/K ATP pump ://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

Exocytosis and Endocytosis Special vacuoles called vesicles, and ATP are used to add and remove substances from the cell. http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120068/bio02.swf::Endocytosis and Exocytosis

Exocytosis Substances in a vesicle are forced through the membrane using ATP and released in the fluid surrounding the cell.

Endocytosis Phagocytosis – “Cell eating,” cells use ATP and a vesicle to ingest solid molecules Pinocytosis – “Cell drinking,” cells use ATP and a vesicle to ingest liquids

Receptor Mediated Endocytosis Cells ingest molecules using ATP after they bond to special receptor proteins on the cell’s surface.

Active Transport Summary Active transport can move things in a wide variety of ways, but certain situations must use active transport: 1. Moving large molecules 2. Moving from low to high concentration 3. Moving things that are not lipid soluble 4. All situations must use ATP

Tonicity Cells will react differently when placed into solutions with varying concentrations of substances, an idea known as tonicity.

Isotonic Solutions Equal concentration of substances inside the cell and outside. The size of the cell does not change.

Hypertonic Solutions Concentration of substances is greater outside the cell than inside. The cell shrinks as a result.

Hypotonic Solution Concentration of substances is greater inside the cell than outside. The cell swells as a result. If the concentration is great enough, the cell will burst (aka lysis).

Comparison of Human Blood Cells