30. Respiration requires O2 .How did the first cells on the earth manage to survive in an atmosphere that lacked O2 ?
Respiration always does not require O2. There are organisms which respire even in absence of O2 through anaerobic respiration.
The first cells of earth i.e., chemosynthetic bacteria are the primitive organisms of early life on earth. Obtained energy by breaking down inorganic molecules like H2S, NO2- , etc.
e.g., chemosynthesis occured in sulphur bacteria in the following way :
