She noticed a pressing human need, this is why she formed the American Red Cross.
Scientists use a system called Classification of Living Things, which categorizes each living organism into the following groups: Kingdom, Phylum, Class, Order, Family, Genus, and Species.
Explanation:
Why (for what reasons) is it believed that oxygen was not present when life formed on Earth? The life forms were anaerobic, and did not make oxygen. There is a lack of oxidized iron in rocks that are a few billion years old. Eventually oxygen from the oceans moved into the atmosphere, and iron could be oxidized.
I think its a hypothesis (let me know if i'm wrong)
The two cells that result from a single cell need to have the same amount of genetic material as the initial cell, therefore the DNA needs to be duplicated before the cell divides.
The sister chromatids are attached together so that during anaphase the daugther cells will receive the same chromosomes
