cell, procaryotic, eucaryotic, organelles, diffusion, osmosis, active transport, endocytosis, exocytosis, photosynthesis, cell respiration, enzymes, unicellular, colonial, multicellular, autotrophs, heterotrophs, macroscopic, microscopic, concentration gradient, xylem, phloem, stomates, digestion, surface area, substrates, active site, denature, gas exchange, blood