<span>The chromosome number in animals is kept the same from one generation to the next because of binary fission </span>
That would be the Endoplasmic Reticulum my good friend hope this helped... :D
Oxygen is a small molecule and it's nonpolar, so it easily passes through a cell membrane. Carbon dioxide, the byproduct of cell respiration, is small enough to readily diffuse out of a cell. Small uncharged lipid molecules can pass through the lipid innards of the membrane.
Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution.
This would be the somatic nervous system :)
