The atmospheric oxygen initially came from the water molecule
Explanation:
Condition on the primitive Earth , about 4 billion year ago were such which favored chemical evolution. . When the temperature of the Earth was less than 100 degree Celsius. Its atmosphere had nitrogen in the form of ammonia, carbon in the form of carbon dioxide and oxygen in the form of water vapour. There was no free oxygen available and so the atmosphere was reducing.
Then spontaneously biomolecules originated which further gave rise to protobionts. These protobionts evolved into several unicellular organisms among which one was cyanobacteria.
Cyanobacteria are considered as the organisms which added the first molecule of free atmospheric oxygen into the atmosphere. They carried out photosynthesis and split the water molecules to release oxygen as the bye product of the process.
It shows which consumes which. A basic food chain.
Explanation:
Wherever the arrowhead is pointed at, shows that it consumes the specie next to the nock. For example, the arrow on the left has its arrowhead directed at the butterfly. This means that the butterfly consumes the flower. The next arrowhead points at the bird, which means that this bird consumes the butterfly.
