diffusion and osmosis

• What is the definition of diffusion?

  Diffusion is the movement of molecules from areas of high concentration to areas of lower concentration.
• Give an example of diffusion.

  Oxygen and carbon dioxide diffuse freely in and out of cells.
• What does it mean for a cell membrane to be selectively permeable?

  A selectively permeable membrane allows some substances to pass through while blocking others.
• What substances can pass through biological membranes?


  Water, oxygen, and carbon dioxide can pass through biological membranes.
• What substances cannot pass through biological membranes?


  Sugars, proteins, and salts cannot pass through biological membranes.
• What is osmosis?


  Osmosis is the movement of water from an area of high concentration to an area of lower concentration across a semi-permeable membrane.
• How is osmosis related to diffusion?


  Osmosis can be considered a special case of diffusion, specifically the movement of water only.
• What happens to an animal cell in pure water?

  The cell would fill up with water and burst.
• What is an isotonic solution?


  An isotonic solution has the same concentration as the cytoplasm, so water moves in and out at the same rate.
• What occurs in a hypotonic solution for an animal cell?


  The cell will gain water due to osmosis, enlarge, and may burst.
• What happens to an animal cell in a hypertonic solution?


  The cell will lose water due to osmosis and shrivel (crenation).
• What is osmoregulation?

  Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids to maintain water content homeostasis.
• Why is osmoregulation important for animal cells?

  It prevents cells from shrinking or swelling excessively, ensuring proper conditions for cellular reactions.
• What happens to plant cells in pure water?

  The water enters the cell, pushing the cytoplasm against the cell wall, making the cell turgid.
• What is turgidity in plant cells?

  Turgidity is the state of being swollen or firm due to water pressure against the cell wall.
• What is plasmolysis in plant cells?

  Plasmolysis is when the cell membrane shrinks and pulls away from the cell wall due to loss of water.
• What is turgor pressure?

  Turgor pressure is the force of the cell contents against the cell wall in a plant cell.
• Why is turgor pressure important for herbaceous plants?

  Turgor pressure is important for the structural rigidity of herbaceous plants.
• What happens when a plant loses too much water?

  The plant loses turgor and will wilt.
• How do plants prevent wilting?

  Plants need to take in as much water as they lose through transpiration.
• What is active transport?

  Active transport is the process where chemicals are taken into a cell against the diffusion gradient, requiring energy.
• How do proteins in the cell membrane assist in active transport?

  Proteins in the cell membrane drag the chemicals into the cell against the diffusion gradient.
• What are the learning outcomes related to diffusion and osmosis?

  • Define diffusion and give examples.
  • Explain how cell membranes are selectively permeable.
  • Define osmosis and give examples.
  • Explain the term turgid.
  • Describe how turgidity is used in plants for support.
  • Explain how high salt or sugar concentration can preserve food.
  • Describe an experiment to demonstrate osmosis.
• What are the key concepts related to the movement of molecules?

  • Molecules are in constant random motion.
  • Movement is due to kinetic energy.
  • Adding heat increases kinetic energy.
  • Temperature measures kinetic energy.
• What are the characteristics of selectively permeable membranes?

  • Allow some substances to pass through.
  • Biological membranes are selectively permeable.
  • Water, oxygen, and carbon dioxide can pass through.
  • Sugars, proteins, and salts cannot pass through.
• What are the effects of osmosis on animal cells?

  • In pure water: cell fills with water and bursts.
  • Isotonic solution: water moves in and out at the same rate.
  • Hypotonic solution: cell gains water, enlarges, may burst.
  • Hypertonic solution: cell loses water, shrivels (crenation).
• What are the effects of osmosis on plant cells?

  • In pure water: cell becomes turgid.
  • In less concentrated solution: maximum turgor pressure.
  • In highly concentrated solution: cell loses water (plasmolysis).
  • Turgor pressure is important for structural rigidity.
• What is the significance of osmoregulation in animals?

  • Active regulation of osmotic pressure.
  • Maintains homeostasis of water content.
  • Prevents cells from shrinking or swelling excessively.
  • Ensures proper conditions for cellular reactions.
• What is the role of active transport in cells?


  • Takes in chemicals against the diffusion gradient.
  • Requires energy.
  • Undertaken by proteins in the cell membrane.