DNA replication occurs before mitosis. So, duplicated chromosomes are already present in mitosis. They are connected by centromeres. During different phases of mitosis, spindles are formed and pull chromosomes toward the opposite poles of the cell so centromeres must split.</span>
These are things that won't be going away. Natural gasses and fossil fuels will likely run out someday or become much harder to find. When you use these sources of energy, they won't be going away and therefore will be sustainable because we can always continue using them.
Plants make up most of our oxygen here on earth, because of the carbon cycle and photosynthesis. They take carbon dioxide, and turn it into oxygen. And not only that, but some animals live in trees to protect themselves from birds and other animals.
