CP 4: Osmosis

• What is the aim of the experiment described in CORE PRACTICAL 1.16?

  To investigate the effect of osmosis on the mass of potato chips placed in different concentrations of sucrose solution.
• What is osmosis?

  Osmosis is the movement of water molecules by diffusion through a selectively permeable membrane.
• When does water move by osmosis?

  Water moves by osmosis when there is a selectively permeable membrane present.
• What apparatus is needed for the osmosis experiment?

  • Potato x 1
  • 100ml Beakers x 5
  • Chinagraph pencil x 1
  • Tile x 1
  • Scalpel x 1
  • Ruler x 1
  • Timer x 1
  • Access to Balance
  • 5 Sugar solutions (2M, 1.5M, 1.0M, 0.5M, 0M)
• What safety equipment must be worn during the experiment?

  Lab coats and safety goggles must be worn at all times.
• What are the steps in the method for the osmosis experiment?

  1. Place different sucrose solutions in beakers and label them.
  2. Prepare 5 equally-sized potato chips and measure their initial mass.
  3. Place one potato chip into each beaker.
  4. Leave the chips in the solutions for 30 minutes.
  5. Remove the chips, dry them, and measure their mass again.
• What should be done with the potato chips before measuring their mass?

  They should be blotted dry with a paper towel.
• What is the aim of the osmosis experiment described?

  To investigate the movement of water by osmosis into or out of plant tissue
• What is the purpose of measuring the mass of the potato chips before and after the experiment?

  To determine how much water is absorbed or lost by the potato tissue.
• What do you think will happen to the potato chips in different sucrose solutions?

  Chips in higher sucrose concentrations will lose mass, while those in lower concentrations will gain mass.
• What equipment is needed for the osmosis experiment?

  • Plant tissue (e.g., potato)
  • Cork borer
  • Ruler
  • Measuring cylinder
  • Labels
  • Boiling tubes
  • Test tube rack
  • Paper towels
  • Sharp knife
  • White tile
  • Range of salt or sugar solutions
  • Distilled water
  • Top-pan balance
• How should the potato cylinders be prepared for the osmosis experiment?

  Cut with a cork borer, trimmed to about 3 cm using a ruler and sharp knife
• What happens to cells that gain mass in the experiment?

  Water moves into the cells, causing them to swell.
• What happens to cells that lose mass in the experiment?

  Water moves out of the cells, causing them to shrink.
• What would happen if a cell containing distilled water is placed into distilled water?

  The cell would remain unchanged because the concentration is equal.
• What is the first step in the method for the osmosis experiment?

  Use a cork borer to cut 5 potato cylinders
• How can you determine the validity of conclusions drawn from the experiment?

  By analyzing the consistency of results across different trials and concentrations.
• Why is it important to accurately measure and record the mass of each potato cylinder?

  To determine the change in mass after osmosis
• What is the initial and final weight data needed for the experiment?

  • Concentration (M)
  • Initial Weight (g)
  • Final Weight (g)
  • Weight Change (g)
• What is the significance of using sucrose in the osmosis experiment?

  • Sucrose molecules are too large to diffuse through cell membranes.
  • It allows for the measurement of water movement in plant tissue.
• How do you calculate the percentage change in mass of potato tissue?

  Percentage change = \(\frac{\text{Final Mass} - \text{Initial Mass}}{\text{Initial Mass}} \times 100\)
• What volume of the 1.0M sugar solution should be measured for the first boiling tube?

  10 cm³
• What is the role of halophytes in osmosis?

  • Halophytes are adapted to live in salty areas.
  • They absorb salts to facilitate osmosis from soil into the plant.
  • They have mechanisms to excrete excess salt.
• How long should the potato cylinders be left in the boiling tubes?

  At least 15 minutes
• What happens to plants when they are flooded with seawater?

  Most land plants die because water moves out of the roots into the salty soil.
• What is the purpose of the extension task in the experiment?

  To draw a graph showing the results of the experiment.
• What should be done after removing the potato cylinders from the boiling tubes?

  Carefully blot them dry with paper towels
• What should be done after removing the potato pieces from the solution?

  • Blot the potato pieces dry.
  • Measure and record their mass again.
• What is the purpose of plotting a graph of change in mass against the concentration of sugar solution?

  To find the concentration that is isotonic to the potato cells
• What controlled variables should be maintained during the osmosis experiment?

  • Temperature
  • Amount of drying
  • Type of potato
  • Age of potato
• What is a potential source of error in the osmosis experiment?

  Discs from different parts of the potato may have different water potentials
• What safety precautions should be taken during the experiment?

  Take care when handling the cork borer and sharp knife
• What calculations should be performed after measuring the final mass of the potato cylinders?

  • Calculate the change in mass
  • Calculate the percentage change in mass
• What is the initial mass recorded for the potato cylinders used in the experiment?

  It varies for each cylinder and should be recorded
• What is the final mass recorded for the potato cylinders used in the experiment?

  It varies for each cylinder and should be recorded
• What is the change in mass recorded for the potato cylinders used in the experiment?

  It varies for each cylinder and should be calculated
• What is the percentage change in mass recorded for the potato cylinders used in the experiment?

  It varies for each cylinder and should be calculated
• What concentrations of sugar solutions are used in the experiment?

  1. 0 M, 0.75 M, 0.5 M, 0.25 M, and distilled water
• What is the purpose of labeling the boiling tubes?

  To identify the concentration of the solution in each tube
• What is the significance of the x-intercept in the graph plotted?

  It indicates the concentration of sugar solution that is isotonic to the potato cells