diffusion and osmosis

• What does it mean if a substance is described as permeable?

  Substances can pass through it.
• What does it mean if a substance is described as impermeable?


  It does not allow any substances to pass through.
• What is meant by selectively permeable?

  It allows some substances through but not all.
• What is diffusion?

  Diffusion is the spreading out of molecules from a region of high concentration to a region of low concentration.
• Is diffusion an active or passive process?

  Diffusion is passive; it doesn’t require energy.
• What are some examples of diffusion in biological systems?

  • CO2 diffusing into a leaf, O2 diffusing out of a leaf.
  • Exchange of nutrients from the placenta to a developing baby.
  • Water entering the roots of a plant.
• What is osmosis?

  Osmosis is the movement of water molecules across a semi-permeable membrane from a region of high water concentration to a region of low water concentration.
• Is osmosis an active or passive process?

  Osmosis is passive.
• What happens to animal cells in a less concentrated solution?

  Water will move into the cell due to osmosis, causing the cell to enlarge and possibly burst and die.
• What happens to animal cells in a more concentrated solution?

  Water will move out of the cell due to osmosis, causing the cell to shrivel and possibly die.
• What occurs to animal cells in a solution of equal concentration as their cytoplasm?

  Water will move in and out through the cell membrane at the same rate, keeping cell volume the same.
• What is the role of cell walls in plant cells regarding osmosis?

  • Cell walls are fully permeable to water, gases, and many solutes.
  • Turgor pressure is the outward pressure of the cytoplasm and vacuole against the cell wall.
  • Turgor provides strength to the plant.
• What is turgor pressure in plant cells?

  Turgor pressure is the outward pressure of the cytoplasm and vacuole against the cell wall of a plant.
• Why do plants want to be turgid?

  To prevent wilting.
• How does osmosis relate to food preservation?

  • Salting fish or meats removes water from harmful microorganisms, causing them to die and preventing spoilage.
  • Sugaring fruit also removes water from harmful microorganisms, preventing spoilage.
  • Salting or sugaring does not remove water from the actual food itself.
• What is the purpose of visking tubing?

  To act as a selectively permeable membrane.
• How can you tell that osmosis has occurred in visking tubing?

  The mass of the visking tubing increased.
• What do you understand by the term turgor in plant cells?

  It is the pressure of cell contents against the cell wall.
• How do plants remain turgid for a considerable period of time?

  By taking in as much water as they lose by means of osmosis.
• What happens to a plant if many of its cells lose turgidity?

  They wilt or droop.
• What occurs to animal cells when they become too turgid?

  The cell bursts.
• Distinguish between diffusion and osmosis.

  • Diffusion: Movement of material from a region of high concentration to a region of low concentration.
  • Osmosis: Movement of water from a region of high water concentration to a region of low water concentration across a semi-permeable membrane.
• In relation to cell membranes, what does selectively permeable mean?

  Only certain substances are allowed through.
• What is an advantage of a cell having a selectively permeable membrane?


  Substances can be kept in or out.
• Name two substances that enter a human muscle cell by diffusion.

  Oxygen and glucose.
• Suggest a way in which turgor is of value to plants.

  Support.