Question

What is the longest phase in the life of a cell?

Answer 1

The life of a cell or the cell cycle is made up of four phases namely the ${G_0}$ phase, ${G_1}$ phase, S phase and ${G_2}$ phase. The ${G_2}$ phase is followed by a brief mitotic phase where chromosome separation occurs. These phases help the cell to divide into two daughter cells. During cell division, duplication of DNA and organelles followed by the partitioning of cytoplasm and other components into two daughter cells takes place.

Complete explanation:
${G_0}$ phase is also known as the resting phase. The cell in the ${G_0}$ phase has left the cell cycle and stopped dividing. Some of the fully differentiated cells remain in this phase for a long period of time. For other cells, the cell cycle starts with this phase.
The ${G_1}$, ${G_2}$ and S phases are collectively known as the interphase. In this phase the cell prepares itself for cell division. The cell grows, produces metabolites and replicates its DNA. The interphase is the longest phase of a cell cycle taking about $91\%$ of the total time of the cycle.
After the interphase comes the mitotic phase or M phase. Here nuclear division or karyokinesis takes place. M phase is the shortest phase of the cell cycle. Duplication of organelles and partitioning of cell components into two daughter cells occurs through different stages of M phase namely prophase, prometaphase, metaphase, anaphase and telophase.

Note:
The cell cycle contains several checkpoints to check progression of a cell to the next stage and can be halted if the condition of the cell is unfavourable. There are three checkpoints namely the ${G_1}$ checkpoint, ${G_2}$ checkpoint and metaphase checkpoint. The ${G_1}$ checkpoint checks for optimal nutrients, growth factors and damage in the DNA. ${G_2}$ checkpoint checks for proper DNA replication and cell size. The metaphase checkpoint checks for chromosome spindle attachment.