why cellulose is not present in human body?

Answer 1

Its not as complicated as every one else made it.

So we can move.

Cellulose keeps the cells ridged, with ridged cells we would have a very small range of motion.

Our cells need to be able to flex and squish so we can move. If we couldn't move we would need to be able to produce our own food, like plants do, or we would need to be single celled/simple organisms like bacteria.

Like two of the others said: we use our bones for structural support, so cellulose is not needed for that purpose. Why have something when you don't need it, that is what evolution is all about.

Answer 2

The correct answer is just because ;)
Cellulose is a special stuff developed by plants (and sea squirts AFAIK) which gives them mechanical support (and as a cell wall material, prevents plant cells from bursting due to osmosis). Animals don't have cell walls - I don't know how and where exactly sea squirts use cellulose, but certainly not for cell walls - and humans, being animals themselves, don't have cell walls either.

Other than that, the only reason I can think of is just because. The question "why organism X is NOT like that" is pretty nonsense in an evolutionary context, since evolution can't plan. It's driven by random processes - mutations and the environment - so asking why we don't have cellulose is something like asking why DIDN'T I get a head when I tossed a coin.

On the other hand, if you ask why, for instance, do birds have feathers, that's quite unlike asking why DID I get a tail in the same coin toss. The development of new structures starts out as random - for example, you have a mutant dinosaur with strange fuzzy-edged scales - but whether the mutation SURVIVES and spreads does depend on the benefits/disadvantages it gives to its carriers. Those strangely modified scales and their successively more feather-like mutations were preserved because they were good for the animal - for insulation, or courtship display, or whatever reason.

Answer 3

It sort of is. Just not in the cellulose form. Cellulose is made from glucose polymers. On the surface of human cells most proteins and lipids on the external surface are glycosylated. They form what is called a Glycocalyx. Check it out if you can find a picture. Cellulose forms a very very tigth sheet type of structure, this isn't as tight as that, but on human cells it's a more developed type of outter shell of sugars that actually have a purpose above and beyond being a protective layer. It turns out human cell membranes are kind of fragile. I mean they're not permeable to items no, but all it takes is one break in the membrane and the cell dies. So this Glycocalyx layer protects the cells membranes. It's pretty dense too...denser than most people suppose. Just the Glycocalyx is formed from many different types of sugars attached to proteins instead of being a self-standing solid sheet of only glucose.



Check it out I found some pics
http://www.chem.wisc.edu/Smith/research_areas/cell_binding.php
it's all the hairy stuff sticking off the bottom cell layer

Answer 4

Cellulose is a special plant trait...it helps to support the plant and protect the cells. The only time cellulose enters our body is when we eat plants.

Animals have cell membranes, which are admittedly more fragile than cell walls, but allow for mobility. Skeletons handle the support functions...be they endoskeletions or exoskeletons.

Answer 5

Animals do not need it for structural support so never evolved it. We have an internal support system that keeps us upright where as things that do have cellulose (plants) do not have bones and need a support structure. Cellulose fills this role for them

Answer 6

Because humans, as do all verebrates, produce bones (calcium phosphate and collagen) for support whereas plants produce cellulose for support.

Answer 7

c. cellulose digesting enzymes are absent. The reason is cellulose is a complex carbohydrates that only herbivores can do to digest it and can manufacture it for milk and meat for us.

Answer 8

Because we have flexible and elastic cell membrane.