Other Free Encyclopedias » Science Encyclopedia » Science & Philosophy: Categorical judgement to Chimaera » Cellulose - Structure Of Cellulose, How Cellulose Is Arranged In Plant Cell Walls, Cellulose Digestion

Cellulose - Cellulose Digestion

fiber animals anaerobic digestive

Humans lack the enzyme necessary to digest cellulose. Hay and grasses are particularly abundant in cellulose, and both are indigestible by humans (although humans can digest starch). Animals such as termites and herbivores such as cows, koalas, and horses all digest cellulose, but even these animals do not themselves have an enzyme that digests this material. Instead, these animals harbor microbes that can digest cellulose.

The termite, for instance, contains protists (singlecelled organisms) called mastigophorans in their guts that carry out cellulose digestion. The species of mastigophorans that performs this service for termites is called Trichonympha, which, interestingly, can cause a serious parasitic infection in humans.

Animals such as cows have anaerobic bacteria in their digestive tracts which digest cellulose. Cows are ruminants, or animals that chew their cud. Ruminants have several stomachs that break down plant materials with the help of enzymes and bacteria. The partially digested material is then regurgitated into the mouth, which is then chewed to break the material down even further. The bacterial digestion of cellulose by bacteria in the stomachs of ruminants is anaerobic, meaning that the process does not use oxygen. One of the by-products of anaerobic metabolism is methane, a notoriously foul-smelling gas. Ruminants give off large amounts of methane daily. In fact, many environmentalists are concerned about the production of methane by cows, because methane may contribute to the destruction of ozone in Earth's stratosphere.

Although cellulose is indigestible by humans, it does form a part of the human diet in the form of plant foods. Small amounts of cellulose found in vegetables and fruits pass through the human digestive system intact. Cellulose is part of the material called "fiber" that dieticians and nutritionists have identified as useful in moving food through the digestive tract quickly and efficiently. Diets high in fiber are thought to lower the risk of colon cancer because fiber reduces the time that waste products stay in contact with the walls of the colon (the terminal part of the digestive tract).

See also Rumination.

Resources

Books

Brett, C.T. Physiology and Biochemistry of Plant Cell Walls. London: Unwin Hyman, 1990.

Van Soest, Peter J. Nutritional Ecology of the Ruminant. 2nd ed. Ithaca: Comstock Press, 1994.


Periodicals

Benedict, C. R., et al. "Crystalline Cellulose and Cotton Fiber Strength." Crop Science 24 (January-February 1994): 147.

Dunkle, Richard L. "Food Science Research: An Investment in Health." Agricultural Research 41 (December 1993): 2.

Dwyer, Johanna. "Dietary Fiber and Colorectal Cancer Risk." Nutrition Reviews 51 (May 1993): 147.

Kleiner, Susan M. "Fiber Facts: How to Fight Disease with a High-fiber Diet." The Physician and Sportsmedicine 18 (October 1990): 19.

Slavin, Joanne L. "Dietary Fiber: Mechanisms or Magic on Disease Prevention?" Nutrition Today 25 (December 1990): 6.

Young, Stephen. "How Plants Fight Back." New Scientist 130 (June 1, 1991): 41.


Kathleen Scogna

KEY TERMS

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Anaerobic

—Describes biological processes that take place in the absence of oxygen.

Cell wall

—The tough, outer covering of plant cells composed of cellulose microfibrils held together in a matrix.

Cellulose synthetase

—The enzyme embedded in the plasma membrane that synthesizes cellulose.

Colon

—The terminal portion of the human digestive tract.

Golgi body

—The organelle that manufactures, sorts, and transports macromolecules within a cell.

Lignin

—A polysaccharide that forms the secondary cell wall in some plants.

Matrix

—The material, composed of polysaccharides and protein, in which microfibrils of cellulose are embedded in plant cell walls.

Methane

—A gas produced during the anaerobic digestion of cellulose by bacteria in certain animals.

Microfibril

—Small fibrils of cellulose; consists of parallel arrays of cellulose chains.

Polysaccharide

—A molecule composed of many glucose subunits arranged in a chain.

Ruminant

—A cud-chewing animal with a four-chambered stomach and even-toed hooves.

[back] Cellulose - How Cellulose Is Arranged In Plant Cell Walls

User Comments

Your email address will be altered so spam harvesting bots can't read it easily.
Hide my email completely instead?

Cancel or

Vote down Vote up

over 3 years ago

very good information resource!

Vote down Vote up

over 3 years ago

Correction: Methane is odorless. In order to make leaks easily detectable, mercaptans are added to methane.

Vote down Vote up

almost 7 years ago

METHANE DOES NOT SMELL! What we smell as "notoriously foul-smelling gas" is small amounts of H2S

Vote down Vote up

about 2 years ago

3r5f

Vote down Vote up

about 2 years ago

you folks are enlightened idiots.
it's fabulous that you know the origins of the odor that is associated with methane.
however, this person is talking about the digestion of cellulose and biology.
and he didn't misinform because any persons needing verification or to cross-reference merely need refer to the sources that he CITED if they truly want to know a little more on mercaptans and methane.

i think it's pretty smooth and simple enough for a general audience to grasp and delivers informatively.

the critics, "scholars," aren't so enlightened after all

chalk it up to methane...mercaptans....digestion of cellulose

Vote down Vote up

over 3 years ago

Zoey is correct: methane has essentially no smell.

"Natural gas", which is mainly methane, has the smell deliberately added to it to make it easier for people to notice leaks. The smell isn't actually H2S (which is fairly toxic), but instead a different sulfur compound such as t-butyl mercaptan or thiophane.

Vote down Vote up

almost 4 years ago

Dear Directorate
This side is very interested in order of enlighting and educating people, and it is really highly rational and motivated side of education.

Vote down Vote up

over 3 years ago

u stupid asian

Vote down Vote up

almost 2 years ago

Methane is odorless.

Vote down Vote up

about 1 year ago

Thank you sooo much!
This really helped me with my AP essay!!

Vote down Vote up

over 2 years ago

cellulose digestions examples enzymes, micro-organism

Vote down Vote up

about 3 years ago

very gud and nice information source.

Vote down Vote up

about 3 years ago

its truly right. grest information

Vote down Vote up

about 3 years ago

sorry great

Vote down Vote up

over 2 years ago

thank you for a great side it is very educating, and can we have more information and picturers to understand more please.

Vote down Vote up

about 3 years ago

Really helpful material. I had to complete a project and this site relly helped a lot.

Vote down Vote up

over 2 years ago

suck ya mom

Vote down Vote up

about 1 year ago

It always amazes me that insecure and angry people feel free to put down and call people vile names for slight errors that may be made. If they were to do that in public face to face with the author they would be considered rude assholes! If someone makes an error correct them with respect.

Vote down Vote up

12 months ago

what

Vote down Vote up

12 months ago

aks easily detectable, merc

Vote down Vote up

12 months ago

askjhgfd

Vote down Vote up

12 months ago

uhhhhhhhhhhhhhhhhhhh