Although nitrogen gas makes up 78% of the atmosphere, we can't use it because nitrogen gas is explosive we must absorb it through the soil nitrogen atoms must be broken apart first we must absorb it through the sun

Nitrogen, even though makes for about 78% of our atmosphere, and is by far the most abundant gas in it, we can not use it because it can not be taken out of the atmosphere as it is. If we take nitrogen in the form as it is in the atmosphere it is useless for both humans and plants. It has to go through a process of ''fixation'' first before we can actually use it in our food.

- nitrogen atoms must be broken apart first

Explanation:

You might think we have plenty of nitrogen because the atmosphere consists of about 78% nitrogen. However, plants and animals cannot use nitrogen gas as they use carbon dioxide and oxygen gases. The nitrogen atoms in the gas must be separated before the nitrogen can combine with other elements.

after receiving a stimus, the sensory receptors send(s) signals to the appropriate area of the body.  

the must be sensory neurons.  

hope its .