Biology – Movement into and out of cells | e-Consult

Variables:

• Independent Variable: Temperature (e.g., 10°C, 20°C, 30°C, 40°C). Maintain a constant temperature for each trial.
• Dependent Variable: Rate of oxygen diffusion (e.g., measured by the time taken for a specific concentration of oxygen to diffuse across the membrane).
• Controlled Variables:

• Size and type of semi-permeable membrane (e.g., dialysis tubing).
• Concentration of oxygen on both sides of the membrane.
• Volume of the diffusion medium (e.g., water).
• Pressure of the diffusion medium.
• Surface area of the membrane exposed to the diffusion medium.

Controls:

• A control experiment with the membrane in the diffusion medium at room temperature (e.g., 20°C) would be used to establish a baseline rate of diffusion.
• Ensure the oxygen concentration on both sides of the membrane is consistent and known.

Apparatus:

• Dialysis tubing (semi-permeable membrane).
• Beakers or containers of water.
• Thermometer.
• Water bath to maintain constant temperatures.
• Oxygen source (e.g., oxygen gas cylinder with regulator).
• Stopwatch.
• Measuring cylinders.

Procedure:

1. Cut a length of dialysis tubing and tie off one end to create a bag.
2. Place a known volume of water with a known concentration of oxygen into the bag.
3. Place the bag in a beaker of water maintained at a specific temperature (e.g., 10°C, 20°C, 30°C, 40°C) using a water bath.
4. Record the time taken for the oxygen concentration in the water surrounding the bag to reach a specific level (e.g., a certain partial pressure of oxygen).
5. Repeat the experiment multiple times (e.g., 3-5 trials) for each temperature.

Data Analysis:

1. Calculate the rate of oxygen diffusion for each temperature by dividing the amount of oxygen diffused (e.g., change in partial pressure) by the time taken.
2. Plot a graph of temperature (independent variable) against the rate of oxygen diffusion (dependent variable).
3. Analyze the graph to determine the relationship between temperature and the rate of oxygen diffusion. Expect the rate of diffusion to increase with increasing temperature up to a certain point, after which it may plateau or decrease due to denaturation of enzymes involved in oxygen transport.