Cellulose is another long polymer of glucose. Plant cells make their cell walls out of cellulose. In fact, 100 billion tons of cellulose is made every year on earth. Cellulose is indigestible in most animals, including us. Ever eat a cardboard box? You get the picture. We simply lack cellulase, the enzyme that can break it down. Some bacteria, some single-celled protists, and fungi have the enzyme. Animals that feed on cellulose harbor these microbes that help them digest it. Even though, we cannot break down this molecule, we do need cellulose in our diet. We call it “fiber”. Cellulose stimulates the colon to produce regular bowel movements and helps make the stools large and soft. A diet rich in fiber can prevent a painful intestinal disorder called diverticulosis. Hard impacted stools can sometimes cause the walls of the colon to form blind outpockets called diverticula which can periodically inflame. So what makes cellulose different from starch? Isn’t it made of glucose? Well it is but the glucose monomers are organized in an interesting fashion. The orientation of the glucose molecules alternates. So if the first one is right side up, the next one is upside down and then the next is right side up and the next one is upside down. Apparently this is a tricky arrangement for an enzyme to break.
<span>The mammalian sperm cell consists of a head, a midpiece and a tail. The head contains the nucleus with densely coiled chromatin fibres, surrounded anteriorly by an acrosome, which contains enzymes used for penetrating the female egg.</span>
Scientists often perform experiments to check and recheck their work. They also redo these experiments to ensure correct results.
Crossing over at prophase I results in the linked genes (those on the same chromosome) becoming unlinked and separated. Prophase I is this first stage of meiosis, the chromosomes condense, form tetrads, and exchange DNA. The nucleolus and nuclear envelope disappear.
True. The crust of the Earth has some permanent magnetization, and the Earth's core generates its own magnetic field, sustaining the main part of the field we measure at the surface. So we could say that the Earth is, therefore, a "magnet."
