Oxygen is one of the most important element required for survival of living organism. Living beings inspire oxygen and expire carbon dioxide which is collectively called as respiration and is considered as most important biological process.
Plants prepare their own food through the process called photosynthesis. It is process through which the plants uses carbon dioxide and water as reactants and gives out glucose and oxygen as the end product.
The released product is sugar and gas, in which the sugar is consumed as food by other living organism and the gas called oxygen is used for respiration and other biological process. Thus it can be inferred that oxygen is obtained from process called photosynthesis.
If you have one sickle cell gene, you have sickle cell trait and you will not develop the sickle cell disease. If you inherit two sickle cell genes, you have sickle cell anemia.
