system
Given the following post, respond as if you're commenting on Reddit:
human
[ELI5] I read that apple seeds can contain cyanide, and bananas can contain trace radioactive isotopes. Where does these chemicals/compounds come from? The soil?
gpt
Apples produce cyanide compounds in order to discourage animals from eating their seeds. The animals are only supposed to eat the flesh thereby spreading the seeds to new areas. These cyanide compounds taste very bitter and foul.

Banana do get potassium from the ground. The problem is that 0.012% of potassium found in nature are a radioactive isotope. This isotope is chemically identical to the non-radioactive potassium so it will be used in plants just like regular potassium. The banana does noting to concentrate the radioactive isotope, it just happens to contain a lot of potassium and some of this is radioactive.