Cell membrane outline I Controls homeostasis II Selectively

Cell membrane outline I. Controls homeostasis II. Selectively permeable III. Structure of membrane 1. lipid bilayer 2. transport proteins 3. cholesterol drawing IV. Diffusion V. Osmosis 1. isotonic 2. hypotonic plant cells animal cells 3. hypertonic

• A cell’s survival depends on the cell’s ability to maintain necessary conditions inside itself • Maintaining these constant internal conditions is called--homeostasis

What controls homeostasis in a cell? • Plasma (Cell) membrane: the flexible boundary between the cell and its environment. – It allows-- water and nutrients to enter the cell and wastes to leave the cell

• The cell membrane is selectively permeable. – Selective permeability--when a membrane allows some materials to pass through, while keeping others out. Examples: Spaghetti strainer— allows water, but not spaghetti to pass through

Summary Section 2 – pages 175 -178 mosquito netting— allows air molecules to pass through but not mosquitoes

Plasma Selective Permeability Membrane Water

Structure of the Plasma Membrane 1. Lipid Bilayer--The cell membrane is 2 layers thick; made of phosopholipids

Lipid Bilayer • Polar heads face out and are attracted to water • Nonpolar tails face in and repel water This arrangement makes the membrane selectively permeable.

2. Transport proteins: embedded in the membrane, they monitor which molecules enter and exit the cell

3. Cholesterol- stabilizes the cell membrane by preventing lipids from sticking together Cholesterol

Draw and label the parts of the cell membrane below:

Diffusion and Osmosis • What needs to cross a cell membrane? water, nutrients, oxygen • How do materials cross the cell membrane? Diffusion or osmosis

Diffusion Random movement of particles to establish dynamic equilibrium (balanced movement and concentration) • Occurs from high to low concentration gradient (moves from area where there is a lot to an area where there is little) • ex. Oxygen diffuses into bloodstream because higher conc. in lungs

Osmosis--Diffusion of water across a selectively permeable membrane Review--Diffusion occurs from an area of HIGH concentration to an area of LOW concentration

Osmosis Diagram

Example of osmosis? After Osmosis Before Osmosis Selectively permeable membrane Water molecule Sugar molecule

3 Types of Osmotic Solutions H 2 O Water Molecule Dissolved Molecule • Isotonic Solution-Equal concentrations of water, inside and outside of the cell. Water moves in and out of cell equally

Cells in an isotonic solution Shape of isotonic cell-Normal http: //www. visualsunlimited. com/images/watermarked/195901. jpg

Cells in a hypotonic solution • Hypotonic solution— More water outside the cell than inside the cell; water diffuses into the cell H 2 O Water Molecule Dissolved Molecule

Cells in a hypotonic solution • Shape of hypotonic cell— swells http: //www. visualsunlimited. com/images/watermarked/195902. jpg

• Plant cells have cell walls that allow a lot of water to enter without bursting; they stay plump and crisp (this is why grocers mist produce) • Animal cells do NOT have cell walls and could burst

Cells in a hypertonic solution • Hypertonic cell-More water on inside of cell than outside of cell. water moves out of cell H 2 O Water Molecule Dissolved Molecule

Cells in a hypertonic solution • Shape of hypertonic cell —Shriveled; this is why plants wilt http: //www. visualsunlimited. com/images/watermarked/899126. jpg