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• Zoology


  The study of animals
• Zoology is one of the broadest fields in all of science because of the immense variety of animals and the complexity of the processes occurring within animals
• There are more than 28,000 described species of bony fishes and more than 400,000 described (and many more undescribed) species of beetles
• Specializations in Zoology by Taxonomic Categories

  • Hierarchy of Relatedness
• Ecology


  The study of the relationships between organisms and their environment
• Throughout our history, humans have depended on animals, and that dependence too often has led to exploitation
• Cells


  The functional units of life, in which all of the chemical reactions necessary for the maintenance and reproduction of life take place
• Prokaryotic cells


  Simpler cells that lack nuclei and other membrane-bound organelles
• Eukaryotic cells


  Larger and more complex cells that have a membrane-bound nucleus containing DNA and other organelles
• Three basic parts of eukaryotic cells

  • Plasma membrane
  • Cytoplasm
  • Nucleus
• Fluid-mosaic model of membrane structure

  A membrane is a double layer (bilayer) of proteins and phospholipids and is fluid rather than solid
• Important points of the fluid-mosaic model

  • Phospholipids have one polar end and one nonpolar end
  • Cholesterol is present in the plasma membrane and organelle membranes
  • Membrane proteins are individual molecules attached to the inner or outer membrane surface or embedded in it
  • Carbohydrates unite with proteins to form glycoproteins, and with lipids to form glycolipids on the surface of the plasma membrane
• Functions of cell membranes

  • Regulate material moving into and out of the cell
  • Separate the inside of the cell from the outside
  • Separate various organelles within the cell
  • Provide a large surface area on which specific chemical reactions can occur
  • Separate cells from one another
  • Site for receptors containing specific cell identification markers
• Selective permeability


  The ability of the plasma membrane to let some substances in and keep others out, which is essential for maintaining a "steady state" within the cell
• Mechanisms of movement across membranes

  • Simple diffusion
  • Facilitated diffusion
  • Osmosis
  • Filtration
  • Active transport
  • Bulk transport
• Simple diffusion


  Molecules move randomly from areas where they are highly concentrated to areas where they are less concentrated, until they are evenly distributed
• Facilitated diffusion


  Polar molecules diffuse through protein channels (pores) in the lipid bilayer
• Osmosis


  The diffusion of water across a selectively permeable membrane from an area of higher concentration to an area of lower concentration
• Tonicity


  The relative concentration of solutes in the water inside and outside the cell
• Filtration


  A process that forces small molecules across selectively permeable membranes with the aid of hydrostatic (water) pressure or some other externally applied force
• Active transport


  Processes that move molecules across a selectively permeable membrane against a concentration gradient, requiring ATP energy
• Bulk transport


  Endocytosis and exocytosis together provide bulk transport of large molecules into and out of the cell, respectively
• Pinocytosis


  The nonspecific uptake of small droplets of extracellular fluid
• Phagocytosis


  The uptake of solid material from the extracellular environment
• Receptor-mediated endocytosis


  Involves a specific receptor protein on the plasma membrane that "recognizes" an extracellular molecule and binds with it, stimulating the membrane to indent and create a vesicle
• Concentration


  Hundreds of times lower inside the cell than outside
• Bulk Transport


  1. Large molecules cannot be transported through the plasma membrane by diffusion or carrier proteins

  2. Endocytosis and exocytosis provide bulk transport into and out of the cell
• Endocytosis


  The plasma membrane envelops large particles and molecules and moves them in bulk across the membrane
• Forms of endocytosis


  • Pinocytosis
  • Phagocytosis
  • Receptor-mediated endocytosis
• Pinocytosis


  Nonspecific uptake of small droplets of extracellular fluid
• Phagocytosis


  Cell takes in solid material rather than liquid
• Receptor-mediated endocytosis


  Specific receptor protein on the plasma membrane binds to an extracellular molecule, stimulating the membrane to indent and create a vesicle containing the selected molecule
• Exocytosis


  1. Secretory vesicles fuse with the plasma membrane and release their contents into the extracellular environment

  2. Adds new membrane material to replace that lost during exocytosis
• Cytoplasm


  Has two distinct parts: cytomembrane (endomembrane) system and fluid cytosol
• Ribosomes


  Non-membrane-bound structures that are the sites for protein synthesis<|>Contain protein and ribosomal RNA<|>Some attach to the endoplasmic reticulum, some float freely
• Polyribosomes/Polysomes


  Clusters of ribosomes connected by messenger RNA
• Endoplasmic reticulum (ER)


  Complex, membrane-bound labyrinth of flattened sheets, sacs, and tubules that branches and spreads throughout the cytoplasm<|>Continuous from the nuclear envelope to the plasma membrane<|>Stores enzymes and other proteins<|>Attachment point for ribosomes
• Rough ER


  ER with attached ribosomes
• Smooth ER


  ER without attached ribosomes<|>Site for lipid production, detoxification, and calcium ion storage in muscle cells
• Golgi apparatus/complex


  Collection of membranes associated with the ER<|>Sorts, packages, and secretes proteins and lipids