Why do materials move across a membrane?

The united states produces an average of 429 billion pounds of food annually. about 133 billion pounds of that food ends up as waste. the percentage of food that the united states wastes each year is %.

How can antibodies "remember" a particular bacterial invader or "antigen" on that invader?

How can a geological time scale best be reconstructed? a) comparing vestigial structures in living species b) comparing homologous structures in living species c) examining homologous structures in fossil remains d) examining the written records of scientists from past cultures