1 Some DMMs can simultaneously measure and display the ac and dc components of a signal. 2  The DMM display can show results three ways (see illustration below): 3  The ac portion of the signal appears in the primary display and the dc portion in the smaller secondary display.
Each lichen specie is one alga species plus one fungus. The alga, a microscopic green plant, makes the food for the duo, while the fungus, a non-green plant, gives the pair support and soaks up moisture.
In many cases the fungus and the alga which together make the lichen may each be found living in nature without its partner, but many other lichens include a fungus which cannot survive on its own -- it has become dependent on its algal partner for survival.