Movement in and Out Cells

• Passive


  Doesn't need energy
• Diffusion


  Movement of molecules from area of high concentration to area of low concentration due to the random movement of molecules
• Factors affecting rate of diffusion

  • Temperature (increases kinetic energy of molecules)
  • Concentration gradient (difference between high and low concentration / slope)
  • Size of molecule (smaller molecules can pass through membrane, larger molecules like starch and proteins cannot)
  • Surface area (more molecules can diffuse at same time)
  • Thickness of membrane (thinner membrane has shorter diffusion distance)
• Osmosis


  Diffusion of water molecules from area of high water potential to area of low water potential (down water potential gradient) through a partially permeable membrane, through protein pores
• Water moves by osmosis from higher water potential outside the cell to lower water potential inside the cell


  Cell swells and then bursts
• Water moves by osmosis from higher water potential inside the cell to lower water potential outside the cell


  Cell shrinks
• Water potential inside the cell is equal to the water potential outside the cell


  No net movement of water molecules by osmosis, cell keeps its normal shape
• Water moves by osmosis from higher water potential inside the cell to lower water potential outside the cell


  Vacuole shrinks, cytoplasm shrinks, cell becomes flaccid
• Water moves by osmosis from higher water potential inside the cell to lower water potential outside the cell


  Cell becomes plasmolysed - cytoplasm and vacuole shrink, cell membrane detaches from cell wall
• Active transport


  Movement of molecules from area of low concentration to area of high concentration / against their concentration gradient using energy from respiration through carrier proteins
• Active transport needs energy to change the shape of carrier proteins to move molecules against their concentration gradient
• Examples of substances transported by active transport

  • Mineral ions in soil absorbed by root hair cells
  • Glucose absorbed in our body
• Diffusion


  Passive movement with no energy needed, down the concentration gradient
• Active transport


  Active process that needs energy, against the concentration gradient
• Diffusion doesn't need a membrane, active transport needs a membrane to have carrier proteins
• Examples of substances transported by diffusion: oxygen, CO2, iodine, glucose, urea
• Cell membrane made from proteins and fats, protein at high temperature denatures, boiling plant damages cell membrane and denatures proteins inside, preventing osmosis