notes

• single celled organisms

  • gain o2 and glucose directly from surroundings via diffusion
  • as diffusion distance is small
• larger organisms

  • diffusion distance too large
  • have high energy requirements so delivery of reactants must be quick
  • mass transport system needed
• mass transport system

  • bulk movement of gases or liquids in one direction via a system of vessels eg circulatory system

  features

  1. network to move through eg vessels
  2. medium for movement- blood
  3. controlled 1 way direction- valves
  4. maintanence of speed eg elastic recoil
• how mass transport systems help

  • move substances quickly
  • maintain diffusion gradients
  • ensure effective cell acitivty
• water

  • 1 atom of oxygen binds with 2 atoms of hydrogen in a covalent bond
  • polar molecule= molecule has one end positively charged and the other negatively

  oxygen- attracts electrons more strongly than h+= weak negatively charged region on oxygen atom

  hydrogens=weak positively shared region on hydrogen atoms

  • a dipole= seperation of charge due to electrons unevenly shared
• hydrogen bonds

  • form between + and - charged regions of H20 as part of polar nature
  • H+ bonds weak- constantly breaking and reforming= water is a liquid state
• properties of water

  1. dipole nature
  2. cohesion= attraction of water molecules to eachother- water flows easily and pulls other water moluecules along
  3. adhesion= water able to hydrogen bond to other molecules-water adheres to sides of vessels
  4. solvent- water is a polar molecule, ions and polar substances will dissolve in it- water molecules surround charged molecules forming hydrogen bonds, ions dissolved.