VIEWS: 4 PAGES: 21 POSTED ON: 6/29/2012
Cells and Cell Transport Pre-AP Biology Cell Structure Despite differences in size and shape, certain structures are common to almost all cells. –Cell membrane- surrounds the cell –Nucleus or a concentrated area where the DNA is contained –Cytoplasm- jelly in the cell Two Types of Cells Prokaryotic- Cells that do not have a membrane bound nucleus or organelles. Only Bacteria Two Types of Cells Eukaryotic- Cells that have a membrane bound nucleus. Everything but bacteria. Transport Across the Cell Membrane All cells exist in a liquid environment This liquid environment makes it easier for materials such as food, water, and oxygen to move in and out of a cell. Cell membrane is selectively permeable – some materials can pass and others cannot. Cell Membrane Cell membrane is made of phospholipids. Cell Membrane Phospholipids align to form a phospholipid bilayer with hydrophilic heads on the outside and hydrophobic tails on the inside. Cell Membrane Molecules that can pass through cell membrane are small, hydrophobic, or uncharged. Molecules that cannot go through easily are large, hydrophilic, or charged and have to be let in another way Cell Membrane 4 ways that molecules get across the cell membrane: - diffusion - osmosis - facilitated diffusion - active transport Diffusion Definition: molecules moving from an area of high concentration to an area of low concentration until reaching an equilibrium. Molecules have kinetic energy which causes them to bounce around. Some molecules can pass through the cell membrane by diffusion. Osmosis Definition: the diffusion of water across a selectively permeable membrane Water moves until the concentration of molecules on either side of a selectively permeable membrane has reached an equilibrium. Osmosis The force exerted by osmosis, or osmotic pressure, tends to move water across membranes from a more dilute solution into a more concentrated solution. Osmotic pressure can cause serious problems for a cell. Isotonic solution In a solution that is just as salty as inside of the blood cells (0.9% NaCl). Hypotonic solution In a solution that is less salty than the inside of the blood cells (0.65% NaCl). Hypertonic solution In a solution that is saltier than the inside of the blood cells (1.01% NaCl). Other Types of Transport We are going to look at ways to transport those large, charged, and hydrophilic molecules that have to be carried across the cell membrane. 1. Facilitated Diffusion No ATP energy required. Molecules move down a concentration gradient (from high to low). Uses a transport protein. 2. Active Transport Requires ATP energy. Pumps particles against concentration gradient (low to high). Keeps important ions and nutrients in cells (ion pumps). 2. Active Transport Cotransport – 2 materials passing through the membrane. Na+ - K+ pump – conducts nerve impulses in animal cells. 3. Endocytosis Cell takes in molecules by forming vesicles around molecules with the cell membrane. 4. Exocytosis Vesicles from the ER or Golgi fuse with cell membrane and dump the contents outside of the cell. Secrete products into blood, like insulin from pancreatic cells.