Which nitrogenous bases are always paired with each other in the dna double helix?

Jason adds the antibiotic penicillin to a bacterial culture. the bacteria develop genetic modifications in their genome, which gives them resistance to the antibiotic penicillin. what caused this genetic modification?

How do all types of diffusion/passive transport actually ‘work’ without using even the smallest amount of cellular energy?

This is the interaction of two organisms where one is and the other is neither nor harmed.