Osmosis

• What is the aim of the osmosis investigation using potatoes?

  To investigate osmosis using potatoes
• What apparatus is needed for the osmosis investigation?

  • Pieces of potato (about 3-1 cm)
  • Boiling tubes
  • Accurate balance
  • Paper towels
  • Forceps
  • Solutions of different solute concentrations (0.2, 0.4, 0.6, 0.8, 1.0 moldm^-3)
  • Marker pen
• What is the first step in the method for investigating osmosis in potatoes?

  Mark the value of one solute concentration on each boiling tube and fill each tube half full of the appropriate solution
• How should you prepare the potato pieces before placing them in the boiling tubes?

  Blot a piece of potato dry on a paper towel, then measure and record its mass
• What should you do after 20 minutes of soaking the potato pieces?

  Remove each piece of potato, blot it dry, and measure its mass again
• How is the percentage change in mass of each potato slice calculated?

  • % change in mass = $\frac{final\ mass - initial\ mass}{initial\ mass} \times 100\%$
• If the initial mass of a potato slice is 13.54g and the final mass is 14.06g, what is the percentage change in mass?

  The percentage change in mass is +0.27%
• Why is it important to repeat the test in the osmosis investigation?

  To reduce the effect of random variation
• What type of solute is often used in osmosis experiments?

  Sucrose
• How does boiling affect the accuracy of measurements in the osmosis experiment?

  Boiling removes surface water, increasing accuracy and repeatability
• What conclusions can be drawn from the results of the osmosis experiment?

  • Water enters potato cells in very dilute solutions
  • Water is lost from potato cells in concentrated solutions
  • The solute concentration inside potato cells is higher than in dilute solutions
• What is the initial mass of the potato at a solution concentration of 0.0 moldm^-3?

  16.52g
• What is the final mass of the potato at a solution concentration of 0.2 moldm^-3?

  16.70g
• What is the final mass of the potato at a solution concentration of 0.6 moldm^-3?

  14.36g
• What is the final mass of the potato at a solution concentration of 0.8 moldm^-3?

  12.32g
• What should you include when explaining the results of an experiment in your exam?

  • Describe what the graph shows
  • Use values from the graph
  • Include relevant scientific terminology
  • Link enzyme activity to the interaction of the active site and substrate
• What happens to enzyme activity as temperature increases up to the optimum temperature?

  Enzyme activity increases due to more kinetic energy in the active site
• What occurs to the active site of an enzyme beyond the optimum temperature?

  The shape of the active site starts to change, making it difficult for the substrate to bind
• What is the optimum temperature for the enzyme amylase?

  About 50°C
• What are the key points to remember when answering a 6-mark question in biology?

  • Think scientifically and structure your answer logically
  • Show how points are related to each other
  • Use relevant scientific terminology
  • Provide detailed explanations with examples
• What is the range of temperatures tested for the enzyme amylase in the experiment?

  Between 20°C and 70°C
• Why is it important to describe what the graph shows before explaining the results?

  To provide context and clarity for the explanation
• What is the command word used in the explain question example?

  Explain
• What should you do when you see the command word "explain" in a question?

  • Provide reasons for what is happening
  • Use linking words like "because"
  • Ensure clarity in your reasoning