Chap 3

• Osmosis


  Net movement of water molecules from high water potential to low water potential
• Osmosis


  Net movement of water molecules from a region of higher water potential to lower water potential through a partially permeable membrane
• Ways substances move into and out of cells

  • Diffusion
  • Osmosis
  • Active transport
• Partially permeable membrane

  Allows only certain molecules or ions to pass through
• Water potential


  Shows the potential of water to move from high to low concentration
• Water moves into and out of cells through the partially permeable cell membrane
• Factors influencing diffusion

  • Surface area
  • Temperature
  • Concentration gradient
  • Distance
• Water potential

  High for very dilute solutions, low for concentrated solutions
• Diffusion

  Net movement of particles from a region of higher concentration to a region of lower concentration down a concentration gradient due to random movement
• Water is important for transport, digestion, and excretion in organisms
• Diffusion


  Molecules move in and out of cells through the cell membrane, from higher to lower concentration until balanced
• Dialysis tubing is used to investigate osmosis
• Turgidity


  State of being swollen or distended due to high water content
• Plants obtain water by osmosis through their roots
• Plasmolysis


  Shrinking of the cytoplasm due to excessive water loss in a plant cell
• Water is important for plants because

  It transports minerals and nitrate ions, maintains cell turgidity providing support and strength
• If plants lose more water than they gain, their cells will become flaccid and the plant will wilt
• Proteins in cell membranes carry out active transport by capturing molecules from one side of the cell, changing shape, and transporting the molecules to the other side using energy from respiration
• Flaccid


  State of being limp or drooping due to water loss
• Comparison between diffusion, osmosis, and active transport

  Diffusion: particles move down a concentration gradient, energy from kinetic energy, Osmosis: water molecules move from high to low water potential, Active transport: particles move against a concentration gradient, energy from respiration
• Active transport

  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
• Effects on plant tissues in different concentrations

  1. Adding a cell into pure water or dilute solution causes water to move into the cell, making it turgid or swollen

  2. Adding a cell into concentrated solution causes water to move out of the cell, making it flaccid or shrinks
• Dialysis tubing


  • Also known as whisking tubing, a non-living partially permeable membrane with small pores allowing water to pass through but blocking large molecules like sucrose
• Osmosis

  Water moves from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane
• Active transport is used when diffusion or osmosis cannot be relied upon, for example, when a cell needs to absorb extra nutrients despite having a higher concentration of those nutrients inside