I read that banana contains Potassium-40 isotope. But most common isotope is K-39. K-40 makes up 0.012% (120 ppm) of the total amount of potassium found in nature. I need to ask why banana contains majority of that rare isotope instead K-39. And also I need to ask how chemistry works inside banana to capture only that isotope.

Say I need to ask "Why banana capture more K-40 and what mechanisms they use to identify that specific isotope?" along with "How banana extract that much of K-40 while it composes only 0.012% and make hundreds of tons of banana?" I know these questions are related to biology, but I need chemistry behind it also need to be properly explained.

Where should I ask that question?

Both Biology Stack Exchange and Chemistry Stack Exchange have a [biochemistry] tag.

  • 2
    $\begingroup$ I'd add to AliceD's excellent answer that if you ever want to ask a SE question on a scientific stack about "why" something happens you need to be ready to point to a reliable source that says it does happen, as part of the prior research we require. So, in this case you need a source showing bananas have more Potassium-40 than other natural sources. Possibly this search will answer your question for you. $\endgroup$
    – Bryan Krause Mod
    Jan 8, 2021 at 17:03

1 Answer 1


Welcome and thanks for your question.

First of all, it is best practice to ask one question at a time.

Secondly, many questions touch upon different disciplines; the physics of biology is a discipline that spans both fields, and et voila biophysics was born. Where to ask multidisciplinary questions on the SE network? Well, you have to look at the relative contribution of the different disciplines. Suppose you are wondering how NMR manages to characterize different types of chemical bonds in complex proteins, it may be best asked over at Chemistry.SE; when your question is why bond A yields a different NMR response than bond B, it's probably best off at Physics.SE; if you ask whether protein complex A and B can be analytically separated by NMR, Biology may be the place to ask. Does that make sense?

In this case, the question why/how fruit A sequesters isotope B, it's probably Biology. However, there may be a reason involved where one isotope is bound to a certain soil component in the bottom and the question may be more of a geological question and better of at EarthSciences!

When you ask how radioactive compounds can be enriched, it's Physics. It doesn't matter if it's raw uranium or bananas. Likely some kind of centrifugal force will be applied to make use of the different masses of the isotopes. This shows well why you should ask a single question at a time.

To determine what the relative weights are of the disciplines you need to do prior research and include that research in the question. If your question has fleshed out, assess yourself where the question is veering at.

And, if all falls apart, the community can guide you through the process further and mods are able to migrate posts across the network. But key to questions like this is prior research effort to generate focused, fleshed out questions.


You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .