Gases are constantly consumed and produced by cellular and metabolic reactions in most living things, so an efficient system for gas exchange between, ultimately, the interior of the cell(s) and the external environment is required. Small, particularly unicellular organisms, such as bacteria and protozoa, have a high surface-area to volume ratio.
Polyploid. (genetics) an organism or cell having more than twice the haploid number of chromosomes.Of a cell or organism having more than twice the haploid number of chromosomes; a polyploid cell; a polyploid species .Organisms that possess two sets of each chromosome.
Polyplacophorans or chitons are flat long mollusks with a shell made of eight plates. Chitons live on rocky shorelines and graze on plants. Scaphopods also known as tusk shells, and have a long tube-shaped shell tapered at one end and open on both ends. These mollusks burrow into the sand. Mollusk shells are made from calcium that is extracted from the waters in which they live or from the food the mollusks eat. There are two common forms of calcium carbonate, aragonite and calcite.