What is the untimate source of energy for the biosphere and what has to happen in order for living things to use it?

How many copies of each chromosomes should be present in each of the 4 final haploid versions of gamete?

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins

Which of the following is an eon in the time scale? phanerozoic proterozoic archean all of the above