Osmosis

Section 1: Understanding Osmosis

  • Osmosis is a special type of diffusion involving the movement of water molecules.
  • It occurs from a place of high water concentration (or low solute concentration), to a place of low water concentration (or high solute concentration), across a semi-permeable membrane.
  • Osmosis does not require an input of energy (hence it’s a type of passive transport) as it follows a concentration gradient.
  • Semi-permeable membranes are membranes that allow certain types of molecules to pass through but restrict others. They allow water molecules to pass but often hinder solutes like ions or larger particles.

Section 2: Hypertonic, Hypotonic, and Isotonic Solutions

  • In a hypertonic solution, the environment surrounding the cell has a higher solute concentration than the cell’s interior. Water will move out of the cell, causing it to shrink or shrivel.
  • A hypotonic solution has a lower solute concentration than the cell. Therefore, water moves into the cell and causes it to swell or burst.
  • An isotonic solution has the same solute concentration inside and outside the cell. Hence, the movement of water is balanced – there is no net movement of water in or out of the cell.

Section 3: Role and Relevance of Osmosis

  • Osmosis is crucial for the transportation of nutrients and wastes in and out of cells, contributing to cell nourishment and detoxification.
  • It also helps to maintain the correct pressure within cells, known as turgor pressure, particularly important in plant cells to keep them firm.
  • Osmosis plays a vital role in various biological processes, for example, water absorption in the gut, through intestinal cells’ membranes.

Section 4: Potential Exam Topic Questions

  • Define osmosis and explain how it differs from simple diffusion.
  • Describe the differences between a hypertonic, hypotonic and isotonic solution and the effects of these different solutions on cells.
  • Explain the role of osmosis in transportation of nutrients and wastes in and out of cells.
  • Discuss the importance of turgor pressure in plant cells and how osmosis helps to maintain it.