Carbohydrates and fats
a. can be used as an energy source by organisms
b. can be bonded together to construct dna molecules
c. are made up of the glucose monomer
d. are monomers that can be made into large polymer chains

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