A student investigates the rate of decay of fruit peels in three identical insulated bins: Bin X, Bin Y, and Bin Z.
She designs an experiment to see if the frequency of watering affects how quickly the organic waste decays.
She waters:
- Bin X: daily
- Bin Y: once a week
- Bin Z: never (not watered)
The student wants to obtain valid results. Explain one factor (other than the frequency of watering) that she should keep constant and suggest why.
The student measures the temperature in each bin for five weeks. She knows that heat is released by microbes during decay.
The graph shows her results:
Write down two differences between the change in temperature in Bin X and the change in temperature in Bin Z.
The student decides that to decay the organic waste as quickly as possible, she should water the bins daily. Explain why she decides this.
The bins have mesh lids that allow air (containing oxygen) to enter. Explain why this helps the material to decay.