Farid Singh is second engineer, so he will have met Root before this, and certainly does not need a physical description. Mrrmr is merely being humourous.
There seems to be little in canon about what training Starfleet personel get, but for the purposes of this narrative, other ranks do a year-long training course in which they do get to choose to do extra training in some skills, earning a qualification called a proficiency. It is perhaps a sign of how complacent Starfleet have become over the infallibility of their technology that they consider zero-gravity training an optional extra.
Most enlisted people start basic training straight out of school at age 16 (or the equivalent for non-humans), but Root joined rather older. Having been more used to having things his own way, he found it hard at first to adapt to military-style discipline, and earned plenty of demerits in the process. When joining the Mumbai, he cut a deal with is Venkatrangan, his new c.o., partly to let him improve his record, and partly to show Venkatrangan how much he wanted to prove he can be depended on.
The bactry pit is a concept stolen from Vernor Vinge’s novel A Deepness in the Sky (1999). It is part of the hydroponic systems where CO2, organic waste and and raw materials are processed by genetically engineered plants and microoganisms in to the oxygen and ingredients used by the food synthesizers, amonst other things. Maintaining the filter system is dirty, smelly, physical labour. You won’t have heard about such things in TNG because the replicator las long made hydroponics unnecessary.
Why is the bactry pit in a zero-g environment? Because the special hydroponics and the organisms developed for them were designed long before artificial gravity was used on space ships, and it is not worth the effort of redesigning them.
With apologies to Gene Roddenberry and the many professionals and amateurs who have created the Star Trek universe over the years.
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