Once equilibrium is reached, .a. molecules move, but there is no net movement in a particular direction. b. passive transport starts over to create a concentration gradient. c. the membrane permits all molecules to freely move across the membrane. d. molecules no longer move.

The body is protected against harmful flu viruses by

The earth consists of a variety of different organisms. despite their diversity, however, some similarities on the structural and metabolic levels may be seen. these similarities can be attributed to a. similarities among organisms in their proteins and nucleic acids. b. the ability of organisms to readily adapt to sudden environmental changes. c. similarities in organisms' habitats and niches. d. the ability of all organisms to interbreed and produce new species.

What were the main components of earth’s earliest atmosphere? oxygen and ammonia hydrogen and helium oxygen and nitrogen hydrogen and nitrogen