Lichens are not a single plant themselves, they are actually a fungus and algae growing together. The result, lichen, is completely different to both of its parts. Lichens can grow almost anywhere, but prefer to grow on tree branches or on bare rock. Lichen is often seen growing on gravestones, statues and roof tiles.
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A lifeguard is someone who watches over people on a public beach, river or swimming pool. If any of them get into trouble, the lifeguard will be there to rescue them.
Light is a type of energy that makes you able to see things. Things like light bulbs, candles and the sun emit light.
Things that don't emit light reflect light, which makes you able to see them.
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A light bulb is a device that converts electricity into light, so you can see when it is dark. The picture is of an incandescent light bulb, which works by running electricity through a filament, which glows white hot. Other kinds of light bulb work in different ways, but they all convert electricity to light.
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A lighthouse is a tower that is built on a dangerous, rocky coastline. A lighthouse has a bright light in the top of it so ships can see it from a long way away. Lighthouses were built so that ships would know not to go too close to a rocky shore, so they didn't crash. Lighthouses were also used to mark the entrance to a harbour so ships could find where they were going at night.
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Lightning is a discharge of static electricity during a thunderstorm. Thunder is actually the sound of the lightning, but if you are a long way away from the lightning it may take a while for the thunderclap to reach you.
Lightning is caused by a similar process to being 'zapped' when you touch a car after a drive, or if you scuff your feet along carpet and then touch someone. Lightning is on a much larger scale though, and being hit by lightning can kill you.