True or false your cells do not need nitrogen to make DNA

Tropical rain forests support more species per unit area than any other terrestrial ecosystem. what is one way rain forests are important to the health of the biosphere?

Which number represents a basic ph, 4 or 9? numerical answers expected! answer for blank 1: i'll give

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