Why are some substances odorless and tasteless?
In: Chemistry
Taste and smell are sensed by nerves called chemoreceptors, which detect chemical properties of the compounds that enter the nose and mouth. For instance, the sour receptor reacts to low pH values of acids, bitter receptors react to chemicals called alkaloids, and sweet receptors react to chemical structures found in sugars (not sugars themselves, which is why artificial sweeteners work). If a chemical does not trigger any of these receptors it has no sourness, no bitterness, and no sweetness. Water does not trigger any of them because it has a neutral pH and doesn’t have the chemical structures to trigger the other two. So, water has no taste, but the things dissolved in it might.
From an evolutionary perspective, senses evolved to help us move toward things that are good for us and away from things that are bad. If a chemical is neither good nor bad, like the nitrogen that is 70% of the atmosphere, there’s no reason for us to notice it.
Our bodies evolve to detect chemical compounds which are either useful to us or common and dangerous. Taste and smell are basically caused by nerve endings sensitive to certain types of chemicals (sugar on your tong will excite certain types of receptors and tell your brain you are tasting sugar). So tasteless odorless substances are typically things that either don’t contain anything useful for the body, or something harmful that is no common enough that we evolved a sense of smell/taste for it.
Because we never evolved receptors for their taste/smell. A common case is Carbon Monoxide. THAT is completely odourless and very deadly to us. You’d think being able to smell it would be an advantage.
Well yes but lethal concentrations of carbon monoxide only happen in enclosed spaces from incomplete combustion. Our far away ancestors just never had those situations, being able to smell CO was never an advantage and so we don’t.
Smell and taste are ways of the body sensing different molecules. This happens by these molecules coming in contact with receptors designed to detect them, which then inform the body that the molecule in question is nearby. This manifests itself through the sensation of taste or smell. If there is no receptor for this molecule it will not be detected.
As stated by other people, we only sense things we have receptors for. That’s why we can’t see infrared light even when some animals can. Just because something is odorless and tasteless to humans does not make that the case for all animals.
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