There are three basic types of light switches used in the home: single-pole, 3-way, and 4-way switches. The single-pole switch is used when one or more lights are to be controlled from a single location. The 3-way switch is used in pairs when one or more lights are to be controlled from two locations. The 4-way switch is used in combinations with two 3-way switches when one or more lights are to be controlled from three or more locations. The terminology used with these switches may sound daunting but the actual wiring is straight-forward and simple. Turn off the circuit breaker supplying power to the switch circuit that you will be working on.

Lichens are so enormously successful and widespread because of their unusual partnership. The algal cells, through the process of photosynthesis, provide the fungus with some of the organic nutrients which it needs. In lichens where the partner is a species of Nostocorganic nitrogen is also supplied to the fungus, because Nostoc is able to fix atmospheric nitrogen. In return, the water, nutrients and gases absorbed from the environment by the fungus are shared with the algae. The fungus also plays a vital role in providing a physical structure to shelter the algae from excess sunlight and in particular, water loss. There is uncertainty over the exact nature of the relationship between the fungus and the alga.

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