1. 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!).
2. 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.
1. Use the averages calculated from your measurements to plot a graph to show the rate of growth of each fungus. Think carefully about which variable you need to put on which axis. Remember to state what is being measured on each axis, and to include units of measurement.
2. Using your data and your graph, describe the trend that the growth rate shows. Why do you think this tren occurs?
3. Assuming a linear growth rate, calculate the rate of growth for your chosen fungus for the duration of the experiment.
4. Using the growth rate from question 3 and imagining that the size of the petri dish is unlimited, work out an approximate size for the diameter of the fungus after:
i) 200 hours?
ii) 3 Weeks?
5. The petri dish that the fungus is growing on is what’s known as a ‘closed system’. What does this mean?
6. In this experiment, what is affecting the rate of growth of the fungus? What would you expect to see if the experiment continued to run in the closed petri dish? What would be the limiting factor(s)?
7. The temperature inside the growth room was recorded throughout the experiment.
i) Plot the temperature on your graph as a second y-axis.
ii) Does the temperature have an effect on the growth of the fungus?
8. How could you improve this experiment to achieve more precise, accurate and reliable results?