During which stage of mitosis are sister chromatids clearly aligned along the equatorial plane of the cell?

Introduction / Context:
This question checks your understanding of the stages of mitosis, specifically when sister chromatids are clearly visible and aligned across the equatorial plane of a dividing cell. Knowing the visual and functional events in each stage of mitosis is essential for interpreting microscope images and understanding how genetic material is accurately distributed to daughter cells.

Given Data / Assumptions:

• We are dealing with mitosis in a typical eukaryotic somatic cell.
• Sister chromatids are identical copies of a chromosome joined at a centromere.
• The equatorial plane is the imaginary line at the center of the cell where chromosomes can align.
• The options list different stages of mitosis.

Concept / Approach:
Mitosis is divided into four main stages: prophase, metaphase, anaphase, and telophase. Each stage has characteristic events. The alignment of chromosomes, in the form of sister chromatids, at the equatorial plane of the cell is the hallmark of metaphase. By comparing what happens in each stage, we can identify the correct answer.

Step-by-Step Solution:
Step 1: Recall that in prophase, chromatin condenses into visible chromosomes and the spindle apparatus begins to form.Step 2: In metaphase, spindle fibers attach to the centromeres and pull sister chromatids so that they line up along the equatorial plane of the cell.Step 3: In anaphase, sister chromatids separate and move toward opposite poles of the cell.Step 4: In telophase, chromosomes reach the poles, decondense, and nuclear envelopes reform around each set.Step 5: From these descriptions, the stage where chromatids are aligned at the center is clearly metaphase.

Verification / Alternative check:
A quick way to verify is to remember a common teaching phrase: metaphase equals middle. In diagrams of mitosis, chromosomes lined up in the middle of the cell indicate metaphase. Whenever you see this characteristic alignment, you can confidently identify the stage as metaphase.

Why Other Options Are Wrong:
Prophase: Chromosomes are condensing and becoming visible, but they are not yet aligned at the equatorial plane, so this stage is not correct for this specific feature.
Anaphase: This stage is characterized by the separation and movement of sister chromatids toward opposite poles, not their alignment in the middle of the cell.
Telophase: Here, chromosomes reach the poles and decondense, and nuclear membranes reform, so alignment at the equatorial plane is no longer visible.

Common Pitfalls:
Students sometimes confuse metaphase and anaphase. They may think that any clear visibility of chromatids indicates alignment, but the key is to notice whether chromatids are still paired at the center or already moving apart. Another common mistake is to assume that prophase, where chromosomes become visible, must also be the stage of alignment, but visibility and alignment are distinct events.

Final Answer:
The stage of mitosis in which sister chromatids are clearly aligned along the equatorial plane of the cell is Metaphase.