Unit 2: Cell structure and function

• centrosomes = parts necessary for creating spindle fibers; contain centrioles

• centromere = the middle part of a chromosome through which sister chromatids attach.

• cell diffusion:

  • simple diffusion = small, nonpolar molecules + lipids (fats and steroids)

  • facilitated diffusion = polar molecules (glucose, amino acids) + ions

    • requires channeled proteins

  • Diffusion is always down a concentration gradient (does not involve active transport)

• types of transport:

  • passive

    • down the concentration gradient

    • simple + facilitated diffusion

  • active

    • up the concentration gradient

    • requires energy (ATP → ADP, or electron flow)

• bulk flow:

  • endocytosis (intake of molecules through the formation of vesicles from the cell membrane)

  • exocytosis (molecules exiting the cell through vesicles that become part of the cell membrane at the end of the process)

  • requires energy

• membrane potential = electrical charge across a membrane created by pumping ions across their membranes.

  osmosis terms:

• hypotonic

  • relatively more water

  • relatively less solute

  • cell shrinks if it’s hypotonic to the environment (it has less solute so water moves into the environment)

• hypertonic

  • relatively less water

  • relatively more solute

  • cell expands if it’s hypertonic to the environment (it has more solute so water moves into the cell)

    • dangerous for animal cells - they mostly explode

    • perfect for plant cells - creation of Turgor pressure (pressure of the cell against the cell wall)

    • protists save themselves from exploding by having contractile vacuoles - they pump excessive water out of the cell so the protist does not explode

      THESE TERMS ARE ALWAYS RELEVANT TO SOMETHING.

      WATER DIFFUSES FROM HYPOTONIC TO HYPERTONIC.

water potential

• A measurement of water’s tendency to move from a place where it is, to a place where it is not.

• formula: ψ = ψs + ψp

  • ψ = water potential

  • ψs = solute potential

  • ψp = pressure potential

    • adding ψs decreases ψ

    • adding ψp increases ψ

      WATER MOVES FROM HIGHER WATER POTENTIAL TO LOWER WATER POTENTIAL