MadSci Network: Botany

Re: Mold

Area: Botany
Posted By: Tobias Baskin, Fac Bio Sci
Date: Fri Mar 29 17:29:57 1996


Dear Jessica,

You asked about why mold grows faster when it is warm compared to when it is cold. To understand the answer, I need to tell you a little bit about growth. As you know, something grows it gets bigger. When an organism gets bigger, there are many different chemical reactions that happen. The organism has to take in nutrients from its surroundings and it has to convert those nutrients into the proteins and other big molecules that the mold needs to build its body. Now it turns out that most chemical reactions are sensitive to temperature, so that the hotter it is, the faster the reaction goes. So when its warm, all of those chemical reactions causing the mold to grow happen faster than when its cold. Therefore, the mold grows faster.

Let me add that if it gets too hot, the growth of the mold will actually get slower because in this case the reactions go too fast for the mold to control them properly.

Your second question about whether mold grows faster in the light or dark is actually quite complicated. First of all, we have to be very careful about this question. To see why, lets pretend to do a simple experiment: say we got two pieces of bread, put the same number of mold spores on each one, and put one in the light and the other in the dark. Then we came back after some time, maybe one week, and found that there was a whole lot more mold on the bread that had been put in the light than there was on the piece in the dark. You might then want to say that the mold grew better in the light. BUT the problem is that the light would also have raised the temperature of the bread. And so the reason the mold grew better in the light than the dark could be because the light made the mold warmer.

Now, if you want to know if light all by itself affects mold growth, then the answer has to be it depends on what kind of mold you have. As you may know, the word "mold" refers to a huge group of organisms. It is equivalent to saying "green plant". There are many different kinds of mold, some grow on bread, some grow on dying or dead things, others grow on living things, some grow in the soil, others grow above ground. These all may look about alike to you, they look like mold, but biologically, these are all very different organisms, as different as a giant red wood to a tulip. So, depending on in what kind of environment a given type of mold is used to, it might or might not respond to light. For example, a mold that grows deep inside soil may never see light normally, and so if you exposed this mold to light, it may have no way to protect itself and it would get the mold equivalent to sunburn. It would not grow well. On the other hand, a mold that lives on leaves of wheat is very used to light, and if you grew this mold in the dark, it might not grow well because its waiting for light to tell it that its in the right environment. Other mold organisms might not care at all about whether they grow in light or dark.

Hope this helps,

Tobias Baskin

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