Answer:
The proportion of oxygen went up because of photosynthesis by plants. The proportion of carbon dioxide went down because: it was locked up in sedimentary rocks (such as limestone) and in fossil fuels. it was absorbed by plants for photosynthesis.
Explanation:
Carbon Dioxide or CO2 is the waste product of the Krebs Cycle
Answer:
Since a species' chromosome count doesn't change from generation to generation, meiosis requires that the number of chromosomes in germ cells be cut in half. Meiosis, unlike mitosis, achieves this accomplishment by requiring a single round of DNA replication followed by two rounds of cell division.
You end up with a polyploid condition. Not uncommon in organisms, especially plants, like angiosperms.
Look up "polyploidy".