The Photosynthesis Simulation (VB version)

On running the program the user is presented with a workspace screen containing the variables which MAY control the volume of oxygen liberated by photosynthesis from a sample of pondweed irradiated by an incandescent lamp. The variables are as follows:-

  1. Colour of light (red/ orange/ yellow/ green/ cyan/ blue/ white). These are available from an option choice box.

The values of the following variables are all available from horizontal scroll bars…

  1. The number of leaves (1-20)
  2. The power of the lamp (1-20 W)
  3. The distance between the lamp and the pondweed (10-50 cm)
  4. The temperature of the water containing the pondweed (5-600 C)
  5. The time of illumination (1-15 hours)
  6. The concentration of bicarbonate in the water (0-10 mg/ml)

Any option choice produces the Volume of Oxygen in ml value in a label at right. The amount is continually updated as quantities are altered. The user may quit the program by clicking the ‘Exit’ button.

Use of Program and Model.

  1. Alter the horizontal slider bars to produce a reasonable oxygen volume (above 10 ml). Determine the amount of oxygen produced under these conditions for each of the light colours. The amounts of oxygen are in the order white>blue>cyan>red> orange> yellow> green (very small).
  2. Using an efficient light, obtain a large oxygen volume (above 10 ml) for 20 leaves. Alter the number of leaves between 1 and 20 to provide at least 7 values of oxygen and plot a graph of Oxygen Volume as Y-axis vs. Leaf number as X-axis. The graph is linear, but not through the origin due to a small amount of photosynthesis in the model by the plant stem.
  3. Using an efficient light and a large number of leaves , obtain a large oxygen volume (above 15 ml) for 20 W of lamp power. Reduce the lamp power to 1 W and obtain at least 7 values of oxygen production with lamp power. Plot a graph of Oxygen Volume as Y-axis vs. Power as X-axis. The graph is linear, starting at 1 W (a threshold value to initiate photosynthesis) and rises to a plateau where power increase (light intensity) produces no oxygen increase.
  4. Using an efficient light and a large number of leaves, obtain conditions with lamp distance =10 cm to produce a large oxygen volume. Alter the lamp-pondweed distance up to 50 cm to obtain at least 7 values of oxygen production, concentrating the values towards the 10 cm end of the range. The oxygen production decreases rapidly with increasing distance (inverse square law) and there may (under the correct conditions) be an initial plateau where increasing the distance has no effect on the oxygen production (the light intensity is the limiting factor).
  5. Using an efficient light source and other factors, obtain a large oxygen volume at 400 C. Alter the temperature from 5 to 600 C, concentrating the temperatures about that temperature at which there is a biological cut-off of activity. Temperatures in excess of this value produce no oxygen. There is a very rapid increase of oxygen production as the cut-off temperature is reached.
  6. Using factors to give a large oxygen volume with an illumination time of 10 hours, alter the time to obtain at least 7 values between 1 and 12 hours. The relationship is one of direct proportion up to 12 hours when this plant ceases its activity and the oxygen level reaches a plateau.
  7. Using factors to give a large oxygen value with a bicarbonate concentration of 6 mg/ml, alter the concentration to obtain at least 7 values between 0 and 10 mg/ml. the relationship is almost linear from a non-zero starting value and reaches a plateau at a concentration of 7 mg/ml. Increasing the concentration above this amount produces no extra oxygen.

J.G.Evans. K.E. Birmingham. 20/11/98. Transposed from RMBasic.