Why is circulation in humans called closed double circulation?

How would you describe the the organisms in the second row of model 1 that are connected to the parents by a line

Omg substrates with the same size and shape as the active site will bind to the enzyme. why is the key labeled the “bad” substrate?

Which of the following matches the organisms described with the correct domain? a. archaea--multicellular, eukaryotic organisms that do not have cell walls b. eukarya--single-celled and multicellular organisms, with a defined nucleus and a variety of nutritional sources c. bacteria--unicellular, eukaryotic organisms with cell walls that do not contain peptidoglycan d. bacteria--unicellular, eukaryotic organisms that always lack cell walls