Final answer:
The G1 phase is a period where cells grow, increases in size, perform normal functions, and prepare for division. Cells not dividing may enter the Go phase. After G1, cells that will divide proceed to the DNA synthesis (S) phase and then to the G2 phase for final preparations before mitosis.
Step-by-step explanation:
The G1 phase is a period of activity in which cells grow in size, carry out normal metabolic functions, and prepare for eventual division. During the G1 phase, cells engage in routine functions and biosynthetic activities, including the production of amino acids and proteins necessary for DNA replication. If a cell is set to divide, this phase is followed by the DNA replication which occurs during the S phase.
Alternatively, if the cell is not dividing, it may enter the Go phase, a quiescent state wherein the cell is inactive and has exited the cell cycle. Some cells can remain in this Go phase indefinitely, such as nerve and mature cardiac muscle cells.
It's also important to note the differences between the phases. After the DNA synthesis phase, the cell cycle proceeds through a second gap phase known as G2, in which the cell continues to grow and prepares for mitosis. The duration of the G1 phase can vary greatly between cells, and it's during this phase that a cell might spend from a couple of hours to many days, while the S phase typically lasts between 8-10 hours, and the G2 phase approximately 5 hours.