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absorption acid animals atoms auxin Bibliography called carbon dioxide cause cells chemical chlorophyll choanocytes color common compounds containing crystal Demospongiae density diffusion disease effect electric electrons elements energy enzyme equation example factors fibers field film frequency function gametes groups growth heat hormone hydrogen ions known layer light lower magnetic material measured mechanism ment metabolism metal methods mineral mold molecules monomer motion occur optical organic oxidation oxygen particles pathogens permeability Permian petroleum phase phenol phloem phosphate photocathode photoconductivity photographic photosynthesis phototube physical piezoelectric pigments plant plasma plastic plate polar polymer polymerization polyploids population positronium potassium potential potentiometer pressure produced radiation reaction regions relatively reservoir resins resistance respiration result rocks root salts seeds sodium soil solution species sponges stem structure surface temperature tion tissue tive tube ture types United usually vary voltage wave plate xylem