Cellular Biology

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• Cilia

  Appendages that propel the protist Paramecium
• Flagellum

  Longer than cilia but present in fewer numbers or as a sole structure per cell
• Cell Junctions


  Structures that allow cells to interact and communicate
• Extracellular matrix (ECM)


  Material secreted by animal cells that helps hold cells together and protects and supports the plasma membrane
• ECM

  • Main components are glycoproteins (proteins bonded with carbohydrates)
  • May attach to the cell through glycoproteins that bind to membrane proteins called integrins
  • Transmits signals between the ECM and cytoskeleton
• Types of Cell Junctions

  • Tight junctions
  • Anchoring junctions
  • Gap junctions
• Tight junctions


  Plasma membrane of neighboring cells is knit tightly together by proteins, preventing leakage of fluid across a layer of cells
• Anchoring junctions


  Fasten cells into strong sheets, connected to the cytoplasm by intermediate filaments, common in tissues subjected to stretching
• Gap junctions


  Allow small molecules to flow through protein-lined pores between cells, common in babies in the womb for communication between mother and developing baby
• Primary cell wall

  Relatively thin and flexible, allows the cell to continue to enlarge
• Pectin


  Sticky substance between adjacent plant cells, gluing them together
• Secondary cell wall

  Strengthened by the rigid molecule lignin, added next to the plasma membrane in some plant cells
• Plasmodesmata


  Structures in plant cell walls that allow water and other small molecules to freely move from cell to cell
• Materials need to be transferred within, between, and among cells, so different transport mechanisms are employed
• Passive transport


  Transport of substances that does not require energy
• Active transport


  Transport of substances that requires energy
• Simple diffusion


  Passive transport mechanism where molecules spread out into available spaces due to their constant movement and thermal energy
• Concentration gradient


  Difference in concentration between spaces
• Osmosis


  Special type of diffusion where water or other solvents diffuse through a semi-permeable membrane
• Tonicity


  Ability of the surrounding solution to cause cells to lose or gain water
• Isotonic solution


  Concentration of solutes is relatively equal to those of the outside environment
• Hypotonic solution


  Solute concentration of the environment is lower than that of the cell, resulting in water entering the cell and potentially causing lysis
• Hypertonic solution


  Water concentration in the cell is higher than in the outside environment, causing water to leave the cell and the cell to shrivel (crenation)
• Osmoregulation


  Control of water balance in the body
• Turgor pressure


  Pressure of the cell contents against the cell wall in plant cells, determined by the water content of the vacuole
• Plasmolysis


  Process where the plasma membrane pulls away from the cell wall in plant cells due to water loss in a hypertonic environment
• Facilitated diffusion


  Passive transport mechanism where transport proteins embedded in the plasma membrane assist the movement of molecules and ions across the membrane
• Aquaporins


  Protein channels that allow for rapid diffusion of water into and out of the cell
• Protein pumps


  Used in active transport to move solutes against a concentration gradient, using energy in the form of ATP
• Exocytosis


  Process where bulky materials such as proteins or polysaccharides are exported out of the cell
• Endocytosis


  Process where large molecules or droplets of fluid are taken into the cell
• Types of endocytosis

  • Phagocytosis
  • Receptor-mediated endocytosis
  • Pinocytosis
• The ability to reproduce is one of the key characteristics of life
• Binary fission


  Cell division in single-celled organisms resulting in offspring that are genetic replicas of the parent cells