Answer:
Sigma factors bind to the promoter region of a particular gene and facilitating the binding of RNA Polymerase to the promoter region (formation of the RNA polymerase holoenzyme complex) in order initiate transcription of the gene.
Put simply - Helps RNA Polymerase do it's job.
Okay. The destruction of tundra vegetation will not really freeze the soil or deepen the active zone much. Therefore, A and C are eliminated. The destruction of the vegetation can actually melt permafrost, which contributes to global warming. The answer is D.
Water! (abiotic)
If water runs out then everything dies! :)
Thanks for the opportunity to answer your question and I hope this help! :)
True
Because they break down what they are made of
Well, the food is in the environment. I would like to compare it with how bacteriae feed (however my biology is quite rusty), that is, they engulf their food and they "digest" -- not the proper term, since there are no organs to do real digestion -- it.