10.1.2 Movement in cells + across cell membranes

• Methods of transport


  Materials need to move INTO and OUT of plant cells, across the cell wall and cell membrane. They can do this in 3 different ways:
• 3 methods of transport

  • Diffusion
  • Osmosis (water only)
  • Active transport
• Cell wall


  • Freely permeable, substances can move through it easily
• Cell surface membrane


  • Partially permeable, controls the substances that enter and leave, allows different environments to be created inside and outside the cell
• Cell membrane


  Made of proteins and lipids

  
• Diffusion


  The random movement of particles from an area of HIGHER concentration to an area of LOWER concentration, down the concentration gradient
• Diffusion happens until an equilibrium is reached
• Protein molecules are too large to cross the membrane directly
• Factors affecting rate of diffusion


  • Diffusion distances
  • Concentration gradient
  • Diffusion surfaces are large
  • Temperature
• Osmosis


  The movement of water from an area of higher water potential to an area of lower water potential through a partially permeable membrane, does not require energy
• Pure water has a high water potential, contracted solutions have lower water potentials
• Turgid


  When plant cells have a constant supply of water and are able to function correctly

  
• Flaccid


  When plant cells lose water and are not able to function correctly
• Investigating osmosis in plant cells

  1. Measure length/mass of potato before

  2. Immerse potato in solution and leave for 20 mins

  3. Re-weigh/measure potato and calculate change

  4. Plot a graph

  
• Plants need to have a constant supply of water to ensure water enters the cells and they stay turgid
• Active transport is the movement of substances from an area of lower concentration to an area of higher concentration (against the gradient), requires carrier proteins in the membrane and energy from respiration

  
• Root hair cells take up water by osmosis and take up mineral ions by diffusion and active transport

  
• Root hair cell


  • Elongated cell, increased surface area for absorption, thin cell wall to decrease distance substances have to move, no chloroplasts