the archetypal carnivore, the venus flytrap, grows in soils with almost immeasurable nitrate and calcium levels. plants need nitrogen for protein synthesis, calcium for cell wall stiffening, phosphate for nucleic acid synthesis, and iron and magnesium for chlorophyll synthesis. the soil is often waterlogged, which favours the production of toxic ions such as ammonium, and its ph is an acidic 4 to 5. ammonium can be used as a source of nitrogen by plants, but its high toxicity means that concentrations high enough to fertilise are also high enough to cause damage.