Levels of organization are structures which describes relationships with things at higher levels are made of things at the next lower level. This helps in knowing the structure and function of the organisms.
The sequence of the level of organization is cells – tissues - organs - organ systems –Organism.
Therefore, the cell is the lowest level of an organization and an organism is the highests level of organization.
Cellular respiration that proceeds in the absence of oxygen is anaerobic respiration. Cellular respiration that proceeds in the presence of oxygen is aerobic respiration. Anaerobic respiration evolved prior to aerobic respiration.
The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed. More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago.
