GoalDescribe useful microbes and how they are used in farming, food and medicine.
New words
decomposer · a microbe that breaks down dead matter and returns nutrients to the soillactic acid bacteria · bacteria that turn milk sugar into lactic acidpenicillin · the first effective antibiotic, made from a mouldyeast · a single-celled fungus used for bread
Explanation
Many microbes help us. Root nodule bacteria live in nodules on the roots of clover, beans and peas and give the plant nitrogen in a form it can use. Decomposers return nutrients from dead matter to the soil, which is why farmers may leave legume roots in the soil. Lactic acid bacteria change lactose, the sugar in milk, into lactic acid, which gives yoghurt its taste and thickness. Yoghurt is kept cold to slow the bacteria. In pickled olives, sugar in the brine feeds helpful bacteria that make lactic acid. The green-blue veins of Roquefort cheese come from the fungus Penicillium roqueforti. In 1928 the Scottish scientist Alexander Fleming noticed that a mould, Penicillium notatum, stopped bacteria from growing near it. From this came penicillin, the first effective antibiotic, which kills some disease bacteria. Fleming shared the 1945 Nobel Prize in Medicine. Yeast, a single-celled fungus, is used to make bread and, in industry, ethyl alcohol for uses such as cleaning and medicine.
Yoghurt flow, as an idea only. Milk has lactose. Lactic acid bacteria turn the lactose into lactic acid. The milk gets thick and tangy. The yoghurt is kept cold to slow the bacteria. We do not make yoghurt at home from boiled milk because hot liquids are dangerous. An adult may show you a shop yoghurt.
Fleming noticed that bacteria did not grow near a mould. The mould made a substance that stopped them. This became penicillin, an antibiotic. Antibiotics work on bacteria, not on viruses or protozoa, and only a doctor decides when to use one.
A farmer plants beans in a field and, after the harvest, leaves the roots in the soil. The nodule bacteria on the roots made nitrogen that plants can use, and decomposers will slowly return nutrients to the soil.
Class activity
Rising dough, with an adult. An adult mixes flour, a spoon of dried yeast, a pinch of sugar and warm (not hot) water in a clean bag, closes it loosely, and keeps it in a warm place. Look at it every ten minutes and draw how it changes. Do not taste raw dough or mouldy food. Draw the yoghurt flow as boxes and arrows for the rest of your class.
Practice
1
What do root nodule bacteria do for plants?
They give the plant nitrogen in a form it can use.
2
What do lactic acid bacteria do in milk?
They change lactose into lactic acid, which makes yoghurt thick and tangy.
3
Who noticed in 1928 that a mould stopped bacteria growing, and what came from it?
Alexander Fleming; penicillin, the first effective antibiotic.
4
Do antibiotics work on viruses? Who decides when to use one?
