Hi and welcome back to freesciencelessons.co.uk. By the end of this video you should be able to describe the conditions required for decomposition, in other words decay. You should then be able to describe what's meant by anaerobic decay and all of this is for triple biology students only.
In a previous video we looked at the carbon cycle. We saw that decomposing microorganisms, such as bacteria and fungi, carry out the decomposition of waste materials and dead remains. As well as returning carbon to the atmosphere, decomposers also return mineral ions back to the soil. So in this video we're looking at the conditions required for decomposition to take place.
I'm showing you here a compost heap, and we often find these in gardens or on farms. Gardeners put dead plant material such as grass onto the compost heap and over time bacteria and fungi decompose the plant material and produce compost. Gardeners and farmers then use the compost as a natural fertilizer and that's because compost is very rich in the minerals that plants need to grow. So in this video we're looking at the optimal conditions for decomposition. In other words the conditions that make decomposition take place most rapidly.
The first condition is temperature. Decomposition takes place faster at warmer temperatures. That's because the decomposers use enzymes to break down the plant materials, and these enzymes work faster in warm conditions.
Now compost heaps tend to be quite warm anyway. That's because decomposers release energy when they carry out aerobic respiration. However, it's important that the compost does not get too hot. If that happens then the enzymes and decomposers can denature. and the decomposers can die.
The second important condition is the amount of water. Decomposing microorganisms work faster if the compost is moist, and that's because many of the chemical reactions in decay require water. So it's important that gardeners do not allow a compost heap to dry out.
Okay, now the final important condition for decay is the amount of oxygen. Remember that decomposers carry out aerobic respiration, and this requires a good supply of oxygen. This compost bin has holes in the walls to allow oxygen to enter, and many gardeners use a gardening fork to mix their compost regularly, allowing more oxygen to pass into the centre. Mixing the compost also breaks up large clumps, and it increases the surface area for decomposers to act on.
So as we've seen, in a compost heap, decomposing microorganisms carry out aerobic respiration. But what happens if there's no oxygen? In the absence of oxygen the decomposing microorganisms carry out anaerobic decay.
Anaerobic decay produces a mixture of gases including methane and scientists call this biogas. In many parts of the world small-scale biogas generators are used to provide fuel for homes and these often use plant materials such as food waste or animal manure. And don't forget that decomposers produce biogas under anaerobic conditions.
Remember you'll find plenty of questions on decomposition in my vision workbook and you can get that by clicking on the link above