What cellular structure must oxygen cross to get from the outside to the inside of an animal cell?

Greenthe fossil record is the history of life recorded byhuman observationgod.climatologists.remains of the past.

Name the organs of humanelemintary canal.

Which of the following is a reason why early living organisms on earth could not have survived on the surface? 1. the lack of an ozone layer 2. the lack of oxygen in the atmosphere 3. the fact that these organisms were single-celled