During interphase in the eukaryotic cell cycle, which of the following key events occurs as the cell prepares for subsequent mitosis?

Introduction / Context:
The cell cycle is divided into interphase and the mitotic phase. Interphase is often misunderstood as a resting phase, but in reality the cell is very active, growing and preparing for division. This question asks you to identify which event occurs during interphase rather than during the visible stages of mitosis.

Given Data / Assumptions:

• We focus on events of interphase in a typical eukaryotic cell.
• Options include cell growth, spindle formation, centromere division, nuclear membrane breakdown, and chromosome alignment.
• We assume the standard sequence G1, S, G2, followed by M phase.

Concept / Approach:
Interphase is divided into three main subphases. In G1, the cell grows and synthesises proteins and organelles. In S phase, DNA is replicated. In G2, the cell continues to grow and prepares enzymes and structures needed for mitosis. Most of the cell s life is spent in interphase. Events such as spindle formation, nuclear membrane breakdown, centromere division, and chromosome alignment occur during prophase, prometaphase, metaphase, and anaphase of mitosis. Therefore, the event that clearly belongs to interphase is cell growth and synthesis of new molecules.

Step-by-Step Solution:
Step 1: Recall that interphase includes G1, S, and G2 phases before mitosis begins. Step 2: In G1, the cell increases in size and produces RNA, proteins, and organelles. Step 3: In S phase, DNA replication occurs, and in G2, the cell continues to grow and prepares for mitosis. Step 4: Recognise that spindle fibres form and attach to chromosomes during prophase and prometaphase, not in interphase. Step 5: Understand that centromere division and separation of chromatids occur in anaphase. Step 6: Note that nuclear membrane breakdown and chromosome alignment on the equator are also mitotic events. Step 7: Conclude that the key interphase event listed is cell growth and synthesis of organelles and molecules.

Verification / Alternative check:
Cell cycle diagrams show interphase as the long period where the cell grows, replicates DNA, and prepares for division. These diagrams and accompanying text emphasise that structures like the mitotic spindle and events such as chromosome alignment are hallmarks of the mitotic phase, not interphase. This confirms that cell growth is the correct interphase event among the options given.

Why Other Options Are Wrong:
Spindle fibres begin to form and attach to chromosomes: Characteristic of prophase and prometaphase of mitosis. Centromeres divide and sister chromatids separate: Defines anaphase, a stage within mitosis. The nuclear membrane completely breaks down: Occurs in prometaphase during mitosis, not in interphase. Chromosomes align on the equatorial plate: A key feature of metaphase, not interphase.

Common Pitfalls:
Because chromosomes are not individually visible in interphase, students sometimes think nothing important happens then. This is a misconception. Interphase is when the cell performs most of its normal functions, grows, and duplicates its DNA. Remembering that mitosis is relatively brief and that interphase is the preparation and normal working period helps separate these events correctly.

Final Answer:
During interphase, the cell grows and synthesises new organelles and molecules.