Answer:
Because meat is fairly simple to digest, carnivores have very short digestive systems, which results in high stomach acid levels. In contrast, herbivores have extensive digestive systems, which result in delayed digestion and high stomach acid levels.
How do the digestive systems of carnivores, herbivores, and omnivores different? What specific part of their anatomy makes carnivores unable to live off of plants and vice versa?
Carnivores have a very short digestive system, because meat is very easy to digest. They have very high acid levels in their stomachs.
Herbivores have very long digestive systems, because plants are very difficult to digest. They have low acid levels in their stomachs, or even a neutral PH. Various species use different methods of extracting nutrition from plants. Some re-ingest their feces, and pass everything through their digestive system twice. Some have fermentation chambers in their intestinal tracts, and use bacteria to break down the plants. (Hindgut and foregut fermentation). Some soften plants, the regurgitate and re-chew them once.
Omnivores tend to have digestive systems that are in between, and ideally suited to neither plants nor animals. They have acidic stomachs, but no always as acidic as carnivores. The length of their lower intestinal tract varies (animals that eat more plants have a longer lower gut).
Carnivores cannot live off of plants because they have such a short lower gut, they cannot ferment the plant matter, or extract many nutrients from it.
Herbivores can extract nutrients from meat, but their bodies are specialized to extract protein from plants, and meat represent an overload. Too much meat, and their organs cannot keep up with the protein overload. Plus, it basically rots inside of them, due to the low acid level. Still, many herbivores eat meat on occasion, often for the calcium in animal bones.
Thank you,
Eddie E.