Movement In and Out of cells

• Diffusion


  The net movement of particles from a region of their higher concentration to a region of their lower concentration, down a concentration gradient, as a result of their random movement
• Diffusion


  • How molecules move in and out of cells through the cell membrane
  • Molecules that cells need move into the cell for use in metabolic reactions and storage
  • Waste products that need to be disposed of move out of the cell into the blood to be excreted
• Diffusion occurs


  Until the number of nutrients inside and outside the cell are balanced
• Factors influencing diffusion


  • Surface area
  • Temperature
  • Concentration gradient
  • Distance
• Osmosis


  The net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane
• Role of water


  • Acts as a solvent in which substances are dissolved and transported
  • Needed for digestion and excretion
• Water potential


  A measure of the tendency of water to move from one area to another by osmosis
• Osmosis experiment using dialysis tubing

  1. Dialysis tubing filled with concentrated sucrose solution suspended in distilled water

  2. Water moves from higher water potential (distilled water) to lower water potential (sucrose solution) through the partially permeable membrane
• Effect of different solutions on plant cells

  • In dilute solution, water moves into the cell, making it turgid
  • In concentrated solution, water moves out of the cell, making it flaccid and potentially plasmolysed
• Turgor pressure


  The pressure on the cell wall from the cell membrane pushing upon it
• Importance of osmosis in plants

  • Plants obtain water by osmosis through their roots
  • Water transports minerals and nitrate ions
  • Water maintains cell turgidity, providing support and strength
• Active transport


  The movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration, against a concentration gradient, using energy from respiration
• When diffusion or osmosis cannot be relied upon


  Active transport is used to absorb extra nutrients from outside the cell despite having a higher concentration inside
• Active transport


  • Uses embedded protein molecules or carriers in the cell membrane
  • Protein captures molecules on one side and changes shape to transport them to the other side
  • Requires energy from respiration to alter the protein shape