Question

Cows can digest cellulose, but humans can't. Why not?

Short answer

Cows can digest cellulose because they have a specialized four-compartment stomach and host cellulase-producing microorganisms, which help break down cellulose into simple sugars. However, humans have a single-chambered stomach and lack cellulase-producing microorganisms, making them unable to digest cellulose.

Step-by-step solution

Difference in digestive systems

The digestive systems of cows and humans are different which consequently leads to varied digestive capabilities. Cows belong to a group of animals called ruminants, which have a specialized stomach with four compartments, whereas humans have a simple single-chambered stomach.

Ruminant digestion

Ruminants, like cows, have a complex stomach with four compartments (the rumen, reticulum, omasum, and abomasum). This type of stomach allows them to break down tough plant materials, such as cellulose, that other animals cannot. The rumen contains beneficial microorganisms, including bacteria, protozoa, and fungi, which aid in breaking down fibrous materials like cellulose.

Human digestion

Humans, on the other hand, have a single-chambered stomach and lack the necessary microorganisms to break down cellulose effectively. As a result, humans cannot digest cellulose and it passes through their digestive system mostly unchanged, providing no nutritional benefits.

Cellulase enzyme

The key to digesting cellulose lies in the presence of an enzyme called cellulase, which can break down cellulose into simple sugars. Cows and other ruminant animals have microorganisms in their rumen that produce cellulase, allowing them to digest cellulose. Conversely, humans do not naturally produce cellulase and thus cannot break down cellulose into useable energy. In conclusion, cows can digest cellulose because they have a specialized digestive system with four compartments and a host of microorganisms that produce the necessary cellulase enzyme. In contrast, humans have a single-chambered stomach and lack the cellulase-producing microorganisms, making it impossible for them to digest cellulose.