Biologically: Nitrogen gas (N2) diffuses into the soil from the atmosphere, and species of bacteria convert this nitrogen to ammonium ions (NH4+), which can be used by plants. Legumes (such as clover and lupins) are often grown by farmers because they have nodules on their roots that contain nitrogen-fixing bacteria. (Learn more about this process in the article The role of clover.)
Through lightning: Lightning converts atmospheric nitrogen into ammonia and nitrate (NO3) that enter soil with rainfall.
Industrially: People have learned how to convert nitrogen gas to ammonia (NH3-) and nitrogen-rich fertilisers to supplement the amount of nitrogen fixed naturally.
An impulse relayed along a myelinated axon jumps from node of Ranvier to node of Ranvier.
HDLs and LDLs are examples of cholesterol
1. Consumers are basically animals and producers are plants. Producers (ex. grass) make their own food and get energy from the Sun. Consumers (ex. rabbit) receive food and nutrients from producers and/or consumers.
2. Decomposers are important because they break down dead plants and animals. If they weren't there, plants, wouldn't get nutrients and waste would pile up.
3. Sorry-- I don't remember what chemosynthesis is.
4. I'd suggest looking up a food chain and going to images-- it's simple to find a diagram with all five of those. Sorry-- I can't think of any off the top of my head
5. The Sun.
Sorry-- I've only got some of it. I'm sure looking up #3 and #4 are easy to find answers to. Hope this helps. :)