How come we can't break down cellulose and how can cows get energy from grass "which has cellulose in it".

Answer 1

As MissA excellently stated, cows (and other ruminants) require significant processing and digestion of cellulose rich material in order to garner nutrition from grass.

Even with all that processing, they still only get some of the energy from the cellulose. The rest gets passed through the system in the form of the rather high amount of poop that cows produce.

Horses deal with it in another way, passing through vast quantities of low quality forage, getting the minimal amount of nutrition they can, and then passing it through quickly. That's why horse poop is full of pretty much undigested grasses. Elephants are the extreme end of this strategy, using massive quantities of forage, with very little nutrition per pound, but by eating so much of it, they're able to get enough energy to survive.

Smaller herbivores, like rabbits, use other methods. Rabbits practice what is known as refection, in which they actually eat their own feces. Rather than horking it up as cud, they poop out little green pellets, eat them and send them for processing again. The little brown pellets we see as rabbit raisins are actually the end result of several passes through the digestive system.

Termites are the masters of cellulose breakdown, however. They accomplish it with the help of endosymbiotic bacteria that are able to break apart the cellulose on a molecular level, turning it into its component sugars. Termite guts are literally filled with these bacteria, and without them, the termites would starve.

Our own digestive systems have evolved for an omnivorous diet. We do pretty well with meat, grains, fruits, and veggies, but simply don't have the length and size of digestion chambers that would be required to break down cellulose. If we did, we'd be built more like, well, like gorillas - with big, farty guts processing plant material all day. Of course, some of us are closer to that ability than others already.

Answer 2

Because cows have a special kind of bacteria, that have the enzymes like termites do, in one of their stomachs that only breaks down cellulose into smaller chains of proteins and amino acids. From this, then, the cow gets its nutrition and converts those proteins and amino caids into energy, or ATP. Humans don't have the bacteria or the enzymes, so we can't break down the cellulose, which is found in fruit and vegetables. This cellulose benefits us because it srcapes off the dead epithelium (skin) cells from our intestines.

Answer 3

Cellulose has glucose molecules covalently bonded together in what are called "beta" links. Animals don't have a cellulase enzyme that can break these links apart. Bacteria do have such enzymes. Cows and other animals that chew their cud, and termites, have colonies of bacteria in their stomachs that break down the cellulose for them. So termites can live on wood cellulose.

Starch has the glucose molecules linked by "alpha" links. Plants and animals have enzymes that can both build up glucose into starch and break it down again.x

Answer 4

We can't digest cellulose because it is an extremely tough molecule. Even cows have trouble with it... that is why they, like all animals that eat grass, have specialized digestive systems.

In the case of the cow, they have four compartments in their guts which ferment the grass to allow it to be digested. For more mechanical breakdown, they also eject some of the partially digested material (cud) from their stomachs and chew it up again. The process of digestion in a cow takes several days because of this.

Answer 5

we do not have cellulase which the enzyme that breaks down the long chained cellulose cows have bacteria in their three stomachs which produce cellulase that is how they can utilize this carbohydrate

Answer 6

We don't have cellulase enzymes in our system ot digest it.