Cellulose, chitin, and peptidoglycan are all considered as
carbohydrates. Now in the molecular level of these carbohydrates, structural polysaccharides exist as sets of long, parallel
strands that are linked to one another. Due to this arrangement, pulling
and pushing forces are being withstand.
Fossils only form if certain qualifications are met, and some organisms cannot meet them, so they just cease to exist, not a single sign of them. This could happen if they were organisms that decayed completely. Fossilization can include freezing, drying, and encasement, usually in tar or resin.
<span>This barrier is known as reproductive isolation and and generally occurs when two species have incompatible genitalia which are unable to function together. It can also occur when the sperm of the male species is unable to be fertilized by the female, regardless of genital compatibility.</span>
I googled it and it said it is estimated that 5 percent of human DNA encodes protein. Not sure if it is correct or not.
