Why do our bodies need potassium as an electrolyte if we already have sodium which helps our body absorb water and ensures our muscles work?
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Living organisms started using potassium long before sodium. So, it is more appropriate to ask: why do we need sodium, if we already have potassium?
The reason is evolutionary history: land animals evolved from sea animals, and sea animals had access to sea water, which is rich in sodium. So they started using that easily accessible sodium in their biochemistry. By the time the animals went on shore, there was no going back – their nervous system became dependent on sodium – it started exploiting a difference between sodium and potassium for its work. Which is a problem for land animals – it is much more difficult to find sodium on land (and this is why we can taste salty things).
Plants have evolved differently, and sodium is not essential for them. It is possible, that if our ancestors didn’t live in sodium-rich environment, we wouldn’t depend on sodium also.
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