Transport, ATP + Water

• Co-transport: Na-K pump:

  • sodium moves out
  • potassium moves in via active transport
  • this maintains concentration gradient for sodium between the lumen and the cell
  • protein channel allows co-transport of glucose and sodium into the cell
  • this allows glucose to diffuse through the cell, into the blood to be used in respiration
• Osmosis (PLANT CELLS)- hypotonic solution:

  • water potential in solution > water potential in cell
  • water moves into the cell
  • cell expands
  • puts turgor pressure on cell wall
• Osmosis (PLANT CELLS) - isotonic solution:

  • water potential in solution = water potential in cell
  • water moves in both directions (no net movement)
  • less turgor pressure on cell wall
  • cell membrane begins to pull away from cell wall
• Osmosis (PLANT CELLS) - hypertonic solution:

  • water potential in solution < water potential in cell
  • water moves out the cell
  • low turgor pressure
  • cell surface membrane becomes broken away from cell wall
• Osmosis (ANIMAL CELLS) - hypotonic solution:

  • water moves into cell
  • cell swells + bursts
• Osmosis (ANIMAL CELLS) - isotonic solution:

  • water moves in both directions
  • no overall effect on cell
• Osmosis (ANIMAL CELLS) - hypertonic solution:

  • water moves out the cell
  • cell shrivels
• Active transport:

  • ATP binds to carrier protein and is hydrolysed, producing ADP and a phosphate
  • phosphate binds to protein, causing a change in shape so the molecule can cross
  • process resets when phosphate unbinds
• Bulk transport:

  • vesicles engulf substances, then bind with cell membrane to transport them across
  • into cell = endocytosis
  • out of cell = exocytosis
• Water is a polar molecule so has an uneven charge distribution.
• Water is a metabolite in metabolic reactions, including condensation and hydrolysis, and is an important solvent in which metabolic reactions occur.
• Water has a relatively high heat capacity, buffering changes in temperature.
• Water has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation.
• There is strong cohesion between water molecules; this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air.
• Hydrolysis of ATP

  ATP + H2O -> ADP + P (+energy)
• Hydrolysis of ATP

  • Exothermic hydrolysis - more energy in reactants than products
• The enzyme that catalyses the hydrolysis of ATP is ATPase.
• Synthesis of ATP

  ADP + P (+energy) -> ATP + H2O
• Synthesis of ATP

  • Endothermic condensation - more energy in products than in reactants, uses water.
• The enzyme that catalyses the synthesis of ATP is ATP synthase.
• ATP is a good energy source as it is an immediate source - it does not need to be broken down.
• Compared to glucose, ATP releases less energy.
• ATP is used in metabolic processes - it provides energy needed to build up macromolecules, e.g. starch from glucose.
• ATP is used in movement - it provides energy needed for muscle contractions.
• ATP is used in secretion -needed to form the vesicles necessary for cellular transport and release from cells.
• ATP is used in activation of molecules - inorganic phosphate released can be used to phosphorylate other compounds to make them more reactive.
• A mitochondrion is adapted for its function as it has a folded inner membrane that forms cristae, so has a larger surface area to maximise movement across the membrane.