Movement into and out of cells

• Diffusion


  Net movement of molecules and ions from a region of higher concentration to region of the lower concentration down a concentration gradient as a result of their random movement
• Higher temperature


  Atoms molecules and ions move faster
• Solid substance


  Particles cannot move very far
• Liquid solution


  Particles move more freely knocking into one another and rebounding
• Gas solution


  Particles move freely with no attractive forces between the molecules atoms
• When molecules can move freely

  They tend to spread out as evenly as they can
• How does living organisms obtain many of their requirements?

  Diffusion
• How does living organisms get rid of their waste?

  Diffusion
• Atom


  Particle from which all substances are made

  Simplest form in which an element exists
• Element


  Substance which is pure

  Composed of atoms of the same type
• Simplest element


  Hydrogen
• Molecules


  Atoms joint together
• Oxygen molecule


  2 oxygen atoms joint together
• Water molecule


  2 hydrogen atoms joined with one oxygen atom
• Gas


  State of matter where molecules are spread far apart and move quickly
• Liquid


  State of matter when molecules are loosely packed and move around slower
• Solid


  Molecules are closely packed and are strongly held together
• Concentration gradient


  Difference in concentration of molecules when separated in space
• Solution


  Liquid in which a substance called the solid mixed with a liquid called solvent
• Solvent


  Liquid in which a solid can dissolve
• Sugar water solution


  Sugar is solid water is solvent
• Oxygen and diffusion


  Concentration of about 20% in the air

  Lower concentration of oxygen in our bodies

  Enters body by diffusion

  Air move into lungs air sacks

  Air separated from red blood cells which transport oxygen by thin wall of the air sack

  Oxygen diffuses into the blood
• Carbon dioxide and diffusion

  Gas passes into palisade cells of the leaf through stomata by diffusion during photosynthesis
• Diffusion in living organisms

  Gases move into and out of and around animals and plants by diffusion
• Osmosis


  Diffusion of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane
• Diluted solution


  Higher water potential
• Concentrated solution


  Lower water potential
• Visking tubing


  Partially permeable membrane that allows water to pass through and not solid molecules

  Human made
• Partially permeable membrane


  Cytoplasm inside the cell

  Solution outside the cell
• Animal cell membrane


  Surrounded by tissue fluid
• Root cell membrane


  Surrounded by film of water
• Water potential and osmosis

  Molecules push against the membrane and exert pressure

  More Molecules equals more pressure
• Water potential


  The pressure that water molecules exert
• Osmosis in animal cells

  Animal cells burst if placed in pure water

  Water molecules are small enough to get out but proteins and others are too large to go through

  As more water moves into animal cell the cell swells and eventually burst the membrane

  In concentrated solutions an animal cell shrinks

  Water will diffuse out of the cell and if it continues the cytoplasm will shrink and the cell wall shrivel up
• Osmosis in plant cells

  Plant cells do not burst in pure water

  The pressure that water molecules exert

  As water enters the vacuole swells and pushes the cytoplasm up against the cell wall

  Cell wall prevents the cell from bursting

  The plant cell is said to be turgid and firm

  If placed in a concentrated solution water passes out

  The cell vacuole and cytoplasm shrink away from the cell wall

  Cell is now flaccid

  Plant loses its firmness and begins to wilt and eventually die
• Plasmolysed


  When cytoplasm shrink further into the centre of the cell

  The cell wall gets left behind

  The cell membrane tears away from the cell wall

  This normally kills a plant
• Active transport


  Movement of molecules and ions in and out of the cell through the cell membrane against a concentration gradient using energy from respiration

  Make use of active transport proteins - ATP

  Opposite of osmosis and difficult

  Atoms moved From low concentration to high concentration against the concentration gradient

  The process requires energy which it obtains from the process in the cell that is respiration