How can stomach acid be strong enough to dissolve thin razor blades, but stuff like corn and tomato skin can pass through seemingly completely untouched?
In: Biology
Because acids react very strongly with most metals but not so much with other elements such as carbon and silicon and their related compounds.
Hence you can store really strong acids in a glass jar but even the weakest acid can dissolve through a chalk stone it’s the chemistry of the components involved.
Humans can’t digest cellulose, which is the vegetable starch that passes through you. Our bodies lack the enzyme that can break the links in those carbs. The enzyme is lacking because we don’t need anything from those linkages but the cellulose moves through us as a “sweeper” to help clean out the intestines.
Some things have coatings that are resistant to acid. They don’t have any ions for the acid to bite away at
Time.
If you were to leave a razorblade in stomach acid (or similar acidic substance) for only the amount of time that something sits in your stomach, it would have damage but would be substantially there.
Likewise, if you left corn or tomato skin in an acidic bath for the same amount of time it takes to dissolve a razor blade, they would be long gone.
Your stomach acid is composed of HCl which is good at dissolving metals and peptide bonds (thus dissolving proteins). It’s not so great at dissolving sugars and fats. Your intestine releases two enzymes – amylase and lipase – which dissolve starches (long-chain sugars in alpha-glucose form, a 3D structure that is compact but has bonds that are easily attacked by these enzymes) and fats, respectively.
Notably, amylase can *only* effectively break down alpha-structured sugars. Cellulose, on the other hand, is composed of sugars in a beta orientation leading to long, tightly bound structural chains (or “fibres”). Your body cannot digest these sugars and so they are simply excreted as waste.
Aside from serving a structural/protective role for the plants they originate in, the body *does* still use cellulose. Whenever you hear that you need more “fibre” in your diet, that is what is being referred to. While not having any nutritional significance, these fibres stimulate mucous secretion in the intestine. This mucous later allows the diffusion of nutrients from the excrement into the body, as well as lubricates the intestine so that waste can move more easily.
Sorry, what is this about dissolving razor thin blades?
Because stomach acid isn’t inherently what breaks the food down. The stomach acid is what activates the enzyme that then breaks down the food. If you lack the enzyme to break the food down then your body won’t digest it and you poop it out.
All the stuff about enzymes etc here is correct. Yout stomach, like most bio systems, is complicated. Here’s a more general chem answer:
“Dissolving strength” is not universal. Different chemicals are good at dissolving different things, and can’t dissolve others.
Acid is good at dissolving metals, not good at dissolving cellulose (like corn in your example). Water is great at dissolving a lot of things (non eli5 water dissolves polar materials), but cannot dissolve many organic materials or fats. Water dissolves sugar but can’t dissolve wood or styrofoam (or corn). Organic solvents like acetone are [great at dissolving styrofoam](https://imgur.com/gallery/Yi7DT4w/comment/108207161), but can’t dissolve sugar much at all.
So your question “how can x be *strong enough* to dissolve this but not that” isn’t applicable because “dissolving power” isn’t just a linear scale that all solvents rank on.
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