Final answer:
The plant cell primarily increases in size during the G1 phase of interphase, a period of active growth and preparation for DNA replication.
Step-by-step explanation:
A plant cell increases in size primarily during the G1 phase of interphase. The G1 phase is considered a period of significant growth where the cell grows rapidly, performs routine metabolic processes, and prepares for DNA replication by making proteins and copying some of its organelles. This stage is vital for accumulating the building blocks of chromosomal DNA and the associated proteins, as well as energy reserves needed for subsequent stages of the cell cycle. Following the G1 phase, the cell enters the S phase (Synthesis phase) where DNA replication occurs, and then it moves into the G2 phase (second growth phase), where the cell makes final preparations to divide, including the synthesis of proteins that assist with cell division.
During interphase, a plant cell primarily increases in size during the G1 phase (first growth phase). This is the stage when the cell doubles in size and doubles the number of organelles. It also accumulates the building blocks of DNA and proteins needed for replication.