Membranes and Diffusion

Cell Membranes Phospholipids have two regions: Polar head is hydrophilic, meaning it plays well with water Nonpolar tails (fatty acid chains) are hydrophobic, meaning they avoid water at all costs

Cell Membranes Phospholipids are arranged in a bilayer that surrounds the cell The heads are on the outside and inside of the cell The tails are buried between the heads

What makes up membranes? Phospholipids – create the main barrier Proteins – channels and receptors (to receive signals from other cells) Carbohydrates – ID tags (to say what kind of cell it is and who the cell belongs to)

Membranes aren’t stiff! The membrane components move around, so we say they’re fluid! http://www.stolaf.edu/people/giannini/flashanimat/lipids/membrane%20fluidity.swf

Food Oxygen What do membranes do? Nutrients Carbon Dioxide Keep bad things out Let needed things in Let wastes out Maintain homeostasis (what is that again??) Food Oxygen Carbon Dioxide Nutrients

How do things get through the membrane? Diffusion – the movement of molecules from an area of high to low concentration Concentration gradient – a difference in concentration from one place to another

Types of diffusion Simple diffusion – movement of a particle through the membrane (O2, CO2, nonpolar things) Facilitated diffusion – movement of a particle through a protein channel (polar things)

Types of Diffusion Osmosis – movement of water through the membrane When the particle (solute) can’t move through the membrane, water moves instead

Osmosis Terms to compare external and internal environment of the cell Isotonic solutions – same concentration of solute as inside the cell Water moves equally in both directions 5% NaCl 95% water 5% NaCl 95% water

Osmosis Hypertonic solutions – higher concentration of solute, lower concentration of water than cell More water moves out of the cell than into it (to dilute the high salt outside??) 20% NaCl 80% water 5% NaCl 95% water

Osmosis Hypotonic solutions – lower concentration of solute, higher concentration of water than cell More water moves into the cell than out of it (to dilute the high salt inside??) 0% NaCl 100% water 5% NaCl 95% water

Active Transport Requires energy Particles do not necessarily move from high to low concentration Can be through a protein pump

Active Transport Phagocytosis – membrane reaches out and grabs food (larger particles) Pinocytosis – membrane folds inward (smaller particles/water) Exocytosis – vesicle fuses with outer membrane, pushing particles out