Choose which fungus you would like to experiment with first:
- Gibberella zeae is responsible for what is known as ‘head blight of wheat’. This causes the ears of corn on wheat, maize, barley and other cereals crops to rot. It affects cereals worldwide, but mainly favours countries that have a mild climate. In this experiment the fungus is grown on an agar of potato dextrose.
- Alternaria solani causes a disease called ‘early blight’, which affects tomatoes, potatoes, peppers and several other crops. It leaves dark lesions on the leaves, stems and fruit of the plants it attacks. This fungus is also seen worldwide, but prefers hotter climates and so is seen a lot in the tropics. In this experiment it is grown on an agar of V8 juice (the same one you can buy in the supermarket!).
Using the interactive ruler, take measurements of the diameter of the fungus for every 6 hours of the experiment ( - you can do it less frequently than that, but the more readings you take, the better results you will get!). As the diameter will not be the same all the way around, you will need to take several measurements for each time interval in order to work out the average.
Now use the averages you have calculated to plot a graph to show the rate of growth. Remember to think carefully about which variable you need to put on which axis!
When you’ve plotted your graph, don’t forget to identify any outliers, and suggest a reason for each.
Using your graph, try to work out the overall rate of growth for the fungus you have chosen.
The petri dish that the fungus is growing on is what’s known as a ‘closed system’. That means that the resources such as space and nutrients are limited.
If the petri dish were the size of a football field, use your result form the question above to work out an approximate size for the diameter of the fungus after… 108 hours? 180 hours?
Considering the petri dish as a closed system again, what might cause the fungal culture to die?
Teachers' notes for this experiment