Diffusion and osmosis

What the syllabus asks of you

• Describe the role of water as a solvent in organisms with reference to digestion, excretion and transport
• Understand that the energy for diffusion and osmosis comes from the kinetic energy of random movement of molecules and ions
• Understand diffusion as the net movement of molecules or ions from a region of their higher concentration to a region of their lower concentration (i.e. down a concentration gradient), as a result of their random movement
• Investigate the factors that influence diffusion, limited to: surface area, temperature, concentration gradient and distance
• Understand osmosis as the net movement of water molecules from a region of higher water potential to a region of lower water potential, through a partially permeable membrane
• Understand that plants are supported by the pressure of water inside the cells pressing outwards on the cell wall
• Describe the effects of osmosis on plant and animal tissues and explain the importance of water potential gradient and osmosis in the uptake and loss of water
• Investigate and explain the effects on plant tissues of immersing them in solutions of different concentrations, using the terms turgid, turgor pressure, plasmolysis and flaccid
• Investigate osmosis using materials such as dialysis tubing