Decay – lipase and milk practical, compost heap and biogas digester
BiologyEcology & EnvironmentAges 15–16Virtual lab
Loading…
Sign in to play
Three screens on decomposers. Lipase practical: milk, sodium carbonate solution and phenolphthalein are pink; add lipase at 5–60 °C, time the loss of the pink colour, work out rate = 1/t and plot it against temperature (with bile salts and boiled lipase as a control). Compost heap: set the temperature, water and oxygen and follow the mass left over 12 weeks with the CO₂ and CH₄ given off. Biogas digester fed with cattle dung: set the temperature, the dung fed per day and the retention time and read the gas made, its methane share and the pH.
Lesson: Decomposition: factors affecting the rate of decay, composting and biogas
What it shows
Decomposers such as bacteria and fungi digest dead material with enzymes, respire the products and return carbon and minerals to the environment. The lipase practical measures enzyme activity: lipase breaks milk fat into fatty acids, which lower the pH until phenolphthalein turns from pink to colourless, so rate = 1/t. The compost heap shows how temperature, water and oxygen control decay and when methane forms. The biogas digester uses anaerobic bacteria and methanogenic archaea to turn cattle dung into a fuel that is about 60 % methane.
How to use
On Lipase and milk, set the Water bath temperature, Lipase concentration, Bile salts and Lipase, then press Add lipase; the stopwatch stops at the end point and the trial is added to the table and graph. On Compost heap, set the three factors and press Start to run 12 weeks. On Biogas digester, set the Digester temperature, Cattle dung fed per day and Retention time, then press Start to run 60 days.
Parameters you can change
- Screen Lipase and milk, Compost heap, Biogas digester
- Water bath temperature 5–60 °C
- Lipase concentration 1–5 %
- Bile salts None, 1 cm³ added
- Lipase Fresh, Boiled (control)
- Heap temperature 0–70 °C
- Water content 0–100 %
- Oxygen in the heap air 0–21 %
- Digester temperature 10–45 °C
- Cattle dung fed per day 20–200 kg/day
- Retention time 5–60 days
Questions to explore
- Why does the pink colour disappear more slowly at 10 °C than at 35 °C, and why does it not disappear at 60 °C?
- Why do gardeners turn a compost heap, and what happens to the methane released when the heap is waterlogged?
- Why does a biogas digester in a cold climate need a longer retention time and so a larger tank?
