Hi - I wrote an answer to a question a few days ago, and although the question itself wasn't explicitly asking about G0, I gave an explanation of G0 in my answer. It might be of interest to you to read -
The question is below, and my answer to it is copied in below the link.
I will add a few thoughts beforehand however.
Also, the following analogy is something I just made up off the top of my head and it's 4am in the UK so I hope it makes sense!
G0 (I usually call this 'G naught' or 'G null') is a real phase in the cell cycle - that said, however, it is really better defined as the phase a cell is in whenever that cell has effectively left the cell cycle. So, you could examine a cell and deduct from its form and internal environment etc etc what phase of cell cycle it is in: G1, S, G2, M, and round and round, but some cells would be in another phase altogether, called G0, and whereas any of the other 4 phases can be thought of as leading into the next in the cycle (G1 into S, S into G2,etc) a cell in G0 shows no signs of it progressing into any other phase of the cycle. Remember, the cell cycle is only categorizing a cell that is capable, or in the process of, dividing. But very few cells are usually going through this process, because once you are going round the cycle, you are pretty much committed to completing it and that's bad news in a tightly regulated environment like a cell-dense tissue. For most types of cell, most of the time, they aren't dividing, so they slide out of the cell cycle shortly after M-phase. It's a bit like a car going around a Round-about, and the cell gets off at G1 and takes a road to a place called G0, instead of staying on the roundabout and going through S, and G2 and M again...
Importantly, the road to G0 is a two-way road, so traffic (cells) can go there and also come back to join the roundabout again. Later on when I mention hepatocytes, this is a good analogy of their behaviour.
Imagine, if you will, when the car (cell) reaches G0, it encounters another roundabout, with lots of exits on it. The road it took to get here was two-way, so it has the option of going around the roundabout and back the way it came, to the cell cycle, or it can go around this roundabout indefinitely until some time in the future it decides to go back to the cell cycle, in which case, it is said to be 'resting' or quiescent as it goes round and round, idling on the roundabout.
However, the car (Cell) might decide to take one of the other exits available on this G0 roundabout, but unlike the road that brought it here, these exits are one-way only. If the car goes off down one of them, it can't come back to G0, and it thus can't go back to the cell cycle either. this cell is no longer capable of replicating. Prime example is a nerve cell.
Way would a cell pick one of these one-way exits? The exits represent to road to differentiation of the cell so that it can perform a specialized function, and this is the price it must pay if it wants to be capable of doing such unique jobs well, it must relinquish its right to return.
With this in mind, read my answer to the following question and see if the details make sense in light of the silly analogy I just used.
Hope this helps.
https://answersrip.com/question/index?qid=20080609185128AAPRcaz&show=7#profile-info-ADesCLooaa
C) Some cells, like leaf cells, cease to divide after mature size is reached.
The answer is C). This is true of the majority of cells in the body - the only cells that continue to divide, despite having reached 'maturity,' are the adult stem cells. These are found in tissues in the body which are rapidly turned over (renewed).
A good example would be the hematopoietic stem cells in the bone marrow. Even though the bone marrow produces a wide lineage of immune cells which enter our circulatory system, the actual 'bone marrow cells' are the stem cells.
It is important to understand what is meant by maturity in this question. As you know, all cells in the body are ultimately derived from the embryonic stem cells. These cells can self-renew over and over and eventually the conditions inside the cell, and outside it also, are such that stem cells are no longer able to self-renew, and instead they begin to 'differentiate'. This is governed by a very complicated process of transcriptional control within the cell, but the details aren't important for now.
It is this act of differentiation that leads to the maturation of a cell. All cells in the body have the same genome, but different cell types are using different parts of this genome, and to varying degrees. Again, I will have to skimp on the details as there are many, but the key point to understand is that mitotic cell division is labor intensive on a cell - if a cell is cycling through rounds and rounds of DNA replication and division, it is committed to directing its energies and resources into producing the transcripts and the proteins that are needed for these processes (and these resources are in short supply especially in the crowded environment of a multicellular tissue). For a cell to be specialized (e.g. a neuron) it must direct its energies towards making the transcripts and proteins to become a nerve cell (i.e. forming the dendrites and making the synaptic vesicles and providing the cytoskeletal morphology for that sort of cell), and to do this it must no longer be a cycling cell that is capable of going through mitosis. If it were to attempt to divide under such conditions, then there would be a lot of mistakes made in the process and the results would at best be two malfunctioning cells, and at worst the cells undergo a malignant transformation.
As you know, there are 4 stages to Mitosis - G1-S-G2-M- and back to G1 again, and round and round, but in a cell that 'differentiates' it 'leaves' this cycle at the start of G1 and enters a resting ('quiescent') state called Go (G-null).
A cell can rest in Go for a very long time, and although it doesn't divide mitotically, it retains the option to one day, if stimulated to do so, it can re-enter the cycle and enter G1. From here it can enter S - G2 - M - etc etc.
This is the existence of many of those renewable tissue cells in the body. For instance, liver cells (hepatocytes) will rest in Go indefinitely until you happen to damage your liver, at which point they'll slide back into G1 and replenish themselves, and whenever they are mature, and other restraints kick in (such as 'contact inhibition' - whereby one cell touches another via surface adhesion molecules/receptors) and then the cells will slip into Go again and rest.
It is fair to say of such cells, that they are mature and no longer divide. They only will do so if the tissue is altered/damaged.
However, other cells that don't replenish themselves actually go one step further - they enter Go like the liver cell does, but once there they turn on a load of specific genetic pathways (that is, they start producing a very specific set of transcripts and proteins, and likewise they turn off some genes too) and these pathways cause that cells to differentiate into a specialized cell (e.g. a neuron). Once a cell has done this, gone into Go and kept on going, it is no longer able to slide back into G1 whenever it is stimulated to do so by tissue damage or whatever.
This is a mature cell that cannot self-renew. It has too much of its activities and resources and energies invested in performing its new role as a neuron, to be able to promote/support cell division also.
So, actually, answer C) probably describes liver cells and other cells that sit in Go most accurately.
As for why it can't be any of the rest-
A) This is clearly incorrect - we'd be riddled with tumors if this were the case. Even if the growth was controlled, we'd be wasting so much resources replicating cells, only to have to go and kill one of the daughter cells each time to maintain the integrity of a tissue. Also, the fact that nerve cells can't renew, and is the bane of many neurological pathologies, also serves to make us well aware of this.
B). This is same as A. Somatic cells are our body's cells (excluding the germ cells, which in males do divide continuously, thank heavens)
D). As said above, bone marrow = hematopoietic stem cells, which also divide continuously, thank heavens again.
E). Clearly incorrect, like said, brain cells/neurons have traveled past Go phase and cannot return to a replicative state.
Ok, there are a few exceptions to some of these statements, and I'm not a botanist, so can't comment on leaf cells, but these principles are true for all eukaryotic multicellular organisms in principle, so they will follow suite.
Hope this helps