What is the best definition of an atom? a. an atom is the smallest part of an element that is still that element. b. an atom is matter that has been bonded. c. an atom is combination of several substances.

it is a limiting nutrient limited by a single nutrient in the ecosystem, & the single goes very slow.

the cell is the smallest structural and functional unit of living organisms, which can exist on its own. therefore, it is sometimes called the building block of life. some organisms, such as bacteria or yeast, are unicellular—consisting only of a single cell—while others, for instance, mammalians, are multicellular.