Three properties that support the endosymbiotic theory are that chloroplasts and mitochondria contain a double membrane, each also contains genetic material that are duplicated with a separated cell cycle and both chloroplasts and mitochondria have their own ribosomes.
Endosymbiotic theory is a theory of evolution that eukaryotes came from prokaryotes. Mitochondria and chloroplasts both have the double membranes. Each of them also contain genetic material that are replicated with a separate cell cycle. Both organelles have their own ribosomes.
After oxygen was distributed to somatic cells, there are higher concentraion of carbon dioxyde. Therefore, it will move out from our cell to be exhaled by lungs. Vice versa for oxygen