Domain: Natural Science — Cell & Developmental Biology
Target concept: During the anaphase of mitosis in a dividing cell, sister chromatids are pulled toward opposite poles.

Video generation prompt: Live-cell fluorescence microscopy images of a single animal cell captured as it transitions from metaphase into anaphase of mitosis, with the chromatids and spindle fibers fluorescently labeled for visibility.

Evaluation guide:
(i) Target concept: Anaphase chromosome segregation driven by spindle microtubule depolymerization and motor protein activity.
Minimum mechanism: Sister chromatids must be physically linked prior to anaphase onset; spindle fibers must be mechanically coupled to kinetochores; pole separation must pre-exist and remain stable; force generation must produce unidirectional, synchronous movement of intact sister pairs.
(ii)Storyline: Frame 1–2: Cell in late metaphase (chromatid pairs aligned at center, spindle fibers taut and pole-anchored). Frame 3–5: Chromatid pairs disengage and initiate movement; each pair remains intact and begins sliding along its attached spindle fiber. Frame 6–8: Continuous poleward migration (chromatid pairs maintain equal spacing from equator, spindle fibers shorten visibly, poles remain stationary). Frame 9–10: Near-complete separation (chromatid pairs approach opposite poles, no overlap or crossing, spindle fibers remain continuous and anchored). Perspective: Fixed wide-field fluorescence view capturing entire cell; no zoom, pan, or rotation; background is dark with minimal cytoplasmic fluorescence to ensure chromatid and spindle visibility.

Manual:
Experimental Procedure
1. Image a single living animal cell expressing fluorescently tagged histones (marking chromatids) and tubulin (marking spindle fibers).
2. Capture time-lapse fluorescence microscopy video focused on a cell entering anaphase.
3. Record 10 seconds showing continuous sister chromatid separation.
Observation of Experimental Phenomena
Two identical pairs of bright, rod-shaped chromatids detach from the metaphase plate and move synchronously along visible spindle fibers toward two fixed, opposite poles of the cell.
Summary of Experimental Principles
During anaphase of mitosis, sister chromatids—held together at the centromere—are pulled apart by microtubule-based spindle fibers attached to kinetochores; each sister pair moves toward opposite spindle poles.

Prompt Grounding rubric:
level_1: No cell is shown, no spindle fibers appear, no chromatids appear, there is no separation of chromatid groups toward opposite sides of the cell, and the cell is not shown in an anaphase-like configuration.
level_2: A single animal cell is shown, but no distinct sister chromatids or spindle fibers are identifiable, and there is no spatial separation of duplicated genetic material toward two sides of the cell.
level_3: A single animal cell shows two distinct groups of brightly labeled, rod-like structures (chromatids) inside it; spindle fibers, if present, are faint or not clearly resolved; the two groups are beginning to separate but are not both clearly linked to a distinct pole on each side.
level_4: A single animal cell shows clearly labeled sister chromatid groups and thin, linear spindle-fiber structures extending from two opposite sides of the cell; each chromatid group appears connected to fibers reaching one of the poles, and the two groups are visibly moving apart from the center toward the two poles; all of these elements are visible together in the same fixed-viewpoint shot.
level_5: A single animal cell shows two chromatid groups, four chromatids total, each group attached to fibers running to one of two clearly separated poles on opposite sides of the cell, with both groups visibly underway toward their respective pole; no extraneous cells, artifacts, or inconsistent labeling appear; the full cell cross-section stays visible in the same fixed viewpoint for the whole sequence.

Scientific and Causal Correctness rubric:
level_1: No causal link is shown between the spindle fibers and chromatid movement; the chromatid groups do not separate; or the movement contradicts anaphase, for example drifting randomly, collapsing back together, or fusing.
level_2: The chromatid groups separate, but with no visible spindle attachment; the movement is not directed toward two opposite poles, for example both groups drifting toward the same side; or the chromatids appear as unpaired single strands or shapeless blobs rather than matched sister pairs.
level_3: Two chromatid groups, matching each other in shape, size, and color, are visible and move apart toward opposite sides of the cell; however the spindle fibers are missing or clearly mis-attached, not anchored at the poles or not touching the chromatids, so the link between the fibers and the movement is not visually supported.
level_4: The two chromatid groups match each other in shape, size, and fluorescence color; each is connected to a spindle fiber running to one of two poles on opposite sides of the cell; both groups move continuously toward their own pole; no chromatid group fragments, merges with the other group, or is lost during the motion.
level_5: The two chromatid groups stay matched in shape and brightness throughout, each moving as one intact group rather than splitting apart, toward its pole while its spindle fiber stays taut and connected from pole to chromatid the whole time; neither group reverses direction, stalls, or veers off its path toward the pole; the two poles stay in the same place relative to the cell's outline; the two chromatid groups never cross paths or mix together.

Spatiotemporal Consistency rubric:
level_1: Severe break in continuity: chromatids jump across the frame with no in-between motion, spindle fibers blink in and out of view, the poles shift position abruptly between frames, the cell's outline deforms suddenly, or the lighting changes partway through the sequence.
level_2: Noticeable break: chromatids disappear for a frame or more and reappear elsewhere, spindle fibers flicker or break apart partway along their length, the poles drift sideways by more than about a quarter of the cell's width between frames, or the cell outline warps unevenly.
level_3: Minor but visible hiccups: the chromatids briefly stop moving for a couple of frames before continuing, the spindle fibers show slight waviness or thinning but stay unbroken and anchored, the poles stay on the same side of the cell but shift by less than about an eighth of the cell's width between frames, and the cell outline holds its shape with only gentle pulsing.
level_4: Everything at the 3-point level is satisfied, and moreover, the chromatids move smoothly with no stutter, teleporting, or blinking; the spindle fibers stay fully visible, unbroken, and anchored at both ends the whole time; the poles stay fixed relative to the cell's edge; the cell outline stays stable and convex; and the lighting stays even and consistent throughout.
level_5: Everything at the 4-point level is satisfied, and moreover, the chromatids' motion shows no visible jerk, freezing, or overshoot as they approach the poles; the spindle fibers keep a steady thickness and brightness along their whole length; the poles do not visibly shift position once anaphase begins; there is no flickering brightness between frames, and no motion blur that looks inconsistent with how fast the chromatids are moving.