Cell growth emphasis — Which phase of the eukaryotic cell cycle is considered the primary growth phase in which cells increase in size and synthesize RNAs and proteins for the next steps?

Introduction / Context:
Cell growth and biosynthesis do not occur uniformly across the cycle. Understanding when mass increase, organelle biogenesis, and preparation for DNA replication occur helps interpret experimental data and tissue physiology.

Given Data / Assumptions:

• G1 precedes DNA replication.
• S is DNA synthesis; G2 prepares for mitosis; M is mitosis; G0 is quiescence.
• Protein and RNA synthesis occur in multiple phases but are most prominent for growth in G1.

Concept / Approach:
During G1, cells expand, synthesize enzymes and structural proteins, and monitor environmental cues. Although G2 includes biosynthesis for mitosis, the ‘‘primary growth phase’’ label is reserved for G1. G0 represents exit from the cycle into a non-dividing state.

Step-by-Step Solution:

Verification / Alternative check:
Flow cytometry and pulse-chase labeling show mass accumulation in G1 before DNA content doubles in S.

Why Other Options Are Wrong:

• b: G2 growth is secondary and focused on mitotic readiness.
• c: M is segregation, not growth.
• d: G0 is non-cycling; many differentiated cells reside here.
• e: S is DNA synthesis, not bulk growth emphasis.

Common Pitfalls:
Confusing general biosynthesis across phases with the specific designation of ‘‘primary growth’’ for G1.

Final Answer:
G1