🏥 Chapter 2 - Movement of Substances

• diffusion

  The net movement of particles from an region of higher concentration to an region of lower concentration. It is a passive transport as it does NOT require energy to take place

  
• how diffusion occurs


  It is caused by the random, constant movement of particles because they possess kinetic energy. It is due to this random movement, that they move down the concentration gradient until they are even spaced out (equilibrium) in all regions after some time.

  
  

  When the concentration of particles are EQUAL in all regions, the concentration gradient is no longer present and there will be NO net movement of particles between these regions anymore

  
• factors affecting rate of diffusion

  1) Surface area -to- volume ratio:

  2) Diffusion Distance

  3) Concentration gradient

  
• Surface area -to- volume ratio


  This the amount of surface area per unit volume. The greater the surface area -to- volume ratio, the higher the rate of diffusion of substances in and out of it. (i.e. for two cells with the same volume, the one with a larger SA enables substances to diffuse in and out of the cell faster.

  
• How do cells adapt to increase Surface area -to- volume ratio

  Some have elongated structures, biconcave shapes, and finger-like protrusions (microvilli), to increase surface area
• concentration gradient (diffusion)


  The difference in the concentration between 2 regions over a given distance

  
• Diffusion distance


  The distance that substances must diffuse. The shorter the diffusion distance, the faster the rate of diffusion.

  
• osmosis


  the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane

  
• when an animal cell is placed in a solution of higher water potential

  water molecules move from a region of higher water potential outside of the cell to a region of lower water potential in the cell, and due to the lack of a cell wall it bursts

  
• when a plant cell is placed in a solution of higher water potential

  water molecules move from a region of higher water potential outside of the cell to a region of lower water potential in the cell, and the vacuole increases in size and the cytoplasm is pushed against the wall, and since there is a cell wall the cell becomes turgid and doesn't burst

  
• when an animal cell is placed in a solution of lower water potential

  water molecules move from a region of higher water potential in the cell to a region of lower water potential outside of the cell, and hence the cell loses water, and shrinks to form spikes. This process is called crenation. the cell will die eventually

  
• when a plant cell is placed in a solution of lower water potential

  water molecules move from a region of higher water potential in the cell to a region of lower water potential outside of the cell, hence vacuole decreases in size and the cytoplasm moves away from the cell membrane. The shrinkage of the cell wall and membrane is called plasmolysis, and the plant becomes flaccid and limp

  
• why is turgor (turgidness) important

  it maintains the shape of soft tissues in plants, and allows non woody plants to be firm and erect. the movement of certain plant parts are due to changes in turgor, e.g opening and closing of stomata

  
• how do plasmolysed cells affect the plant

  cells will be killed if plasmolysed for too long the inability of the roots to absorb water continued with evaporation will cause the plant to wilt and die

  
• active transport


  Energy-requiring process that moves molecules across a partially-permeable membrane against a concentration gradient, from a region of lower to higher concentration. since it needs energy from respiration, it only occurs in living cells as they respire.