Domain: Engineering — Biomedical Engineering
Target concept: Electrophoretic DNA Band

Video generation prompt: Agarose gel electrophoresis system, DNA samples (with 100 bp, 500 bp, 1000 bp fragments), ethidium bromide (EB) staining solution, UV gel imaging system, electrophoresis buffer (TAE); Procedure: Mix DNA samples with loading buffer and load into gel wells, run electrophoresis at 120 V for 30 minutes, then visualize the migration position, intensity, and distribution pattern of DNA bands under UV light and capture images.

Evaluation guide:
(i) Target concept: Size-dependent electrophoretic mobility of double-stranded DNA in agarose gel under constant electric field.
Minimum mechanism: DNA is negatively charged → migrates toward anode; pore size of agarose matrix impedes larger fragments more than smaller ones → differential migration rate; EB binding enables UV-excited orange-red fluorescence proportional to DNA mass.
(ii)Storyline: Frame 1–2: Static shot of intact agarose gel in horizontal electrophoresis chamber, filled with clear TAE buffer, wells visible at cathode end, three DNA+loading buffer samples deposited in separate wells (blue color visible). Frame 3–4: Electrodes connected, current applied (subtle indicator light or label “120 V” appears). Frame 5–6: Time-lapse effect (no real-time duration) showing bands beginning to emerge from wells and migrating downward as discrete orange-red entities. Frame 7–8: Final UV image: gel centered under UV imager, three sharp, aligned, non-overlapping bands in descending molecular weight order with correct intensity gradient. Perspective: Fixed overhead view throughout; no camera movement; gel fills ≥70% of frame; no occlusion of wells or band region.

Manual:
Experimental Procedure
1. Load DNA samples (100 bp, 500 bp, 1000 bp) pre-mixed with blue loading buffer into wells of agarose gel submerged in TAE buffer.
2. Apply electric current (120 V) across gel for electrophoresis.
3. After 30 min, image gel under UV light using ethidium bromide staining.
Observation of Experimental Phenomena
Three discrete orange-red fluorescent bands appear, migrating downward from wells: highest band (faintest) = 1000 bp, middle band (medium intensity) = 500 bp, lowest band (strongest) = 100 bp.
Summary of Experimental Principles
DNA fragments separate by size in electric field; smaller fragments migrate faster through agarose matrix; EB intercalates DNA and fluoresces orange-red under UV; band intensity correlates with DNA mass.

Prompt Grounding rubric:
level_1: None of the required objects appear together: no agarose gel slab, no sample wells, no DNA-loaded lanes, no TAE buffer chamber, and no UV imaging setup; the scene is unrecognizable as a gel electrophoresis run.
level_2: A gel-like slab or a UV light source appears, but essential objects are missing: no visible wells, no loaded lanes, no electrode terminals, no buffer-filled chamber, and no band pattern under UV, so the scene cannot be identified as this electrophoresis setup.
level_3: An agarose gel slab with distinct wells sits in a buffer-filled chamber with electrodes at both ends, three DNA samples are loaded into separate wells, and a UV imaging system is in view, but at least one of the following is missing or inconsistent: the loading buffer is not visibly mixed into the samples, no band pattern appears under UV, or the stated run conditions (voltage/time) are not reflected by any on-screen cue.
level_4: All the requirements for a 3 are met, and beyond that: the gel sits horizontally with wells aligned at one end, the three samples show visible blue loading-buffer color in the wells, the electrodes are connected with visually distinguishable polarity, and the UV imager sits directly above the gel, but the resulting band pattern shows only one diffuse smear rather than three separated bands, so the three lanes cannot be told apart under UV.
level_5: All the requirements for a 4 are met, and beyond that: the wells have sharp, well-defined edges; the chamber is filled with clear buffer up to the gel's base; and the final UV image shows exactly three discrete bands, one per lane, each at a distinct vertical position with sharp edges, no smearing, no trailing beneath any band, no overflow back into the wells, and no stray fluorescence in the buffer outside the bands themselves.

Scientific and Causal Correctness rubric:
level_1: The three bands migrate in a size-inverted order (e.g., the smallest fragment ends up closest to the wells), or show no size-dependent separation at all: all bands sit at the same position, fluorescence is absent, the color is wrong (e.g., green/blue instead of orange-red), or no fluorescence appears under UV at all.
level_2: Bands are visible under UV but violate migration logic, for instance the 100 bp band sits highest as if it moved slowest, or the 1000 bp band sits lowest as if it moved fastest; or the brightness pattern is reversed (largest fragment brightest, smallest faintest); or fluorescence appears only inside the wells with no migration; or the lanes look like continuous unbroken streaks rather than discrete bands.
level_3: All three bands migrate downward from the wells in the correct relative order (1000 bp nearest the wells, 500 bp in the middle, 100 bp farthest), and all fluoresce orange-red under UV, but the brightness does not clearly favor the 100 bp band over the 1000 bp band, or the 100 bp and 500 bp bands overlap enough that they cannot be told apart, or background fluorescence across the gel is high enough to wash out the contrast between bands.
level_4: All three bands migrate downward in the correct order (1000 bp highest/nearest the wells, 500 bp middle, 100 bp lowest/farthest) and fluoresce orange-red under UV, with brightness visibly increasing from the 1000 bp band down to the 100 bp band, but the band shapes are somewhat irregular (e.g., curved or tapered ends) without disturbing the correct position or brightness ranking.
level_5: All three bands fluoresce a uniform orange-red under UV, appear in strict order by fragment size (1000 bp nearest the wells, then 500 bp, then 100 bp farthest), and grow progressively brighter from the 1000 bp band to the 100 bp band; every band is straight, evenly thick, sharply bounded, and fully separated from its neighbors, with no fluorescence in the buffer outside the three bands and no smearing or leakage back toward the wells.

Spatiotemporal Consistency rubric:
level_1: The gel slab vanishes and reappears, the wells jump to different positions between frames, the electrodes detach and reattach with no visible cause, the UV light switches on/off with no transition, band positions jump discontinuously between frames, or the gel visibly wobbles, warps, or stretches as if it weren't a rigid slab.
level_2: The gel rotates or slides sideways by roughly a quarter of its width between key frames; the blue loading buffer vanishes from the wells after loading and then reappears; band positions shift upward (backward) partway through the run; the UV illumination's brightness or coverage changes abruptly; or the electrode wiring visibly disconnects and reconnects with different routing.
level_3: A slight jitter in the gel's position (well under an eighth of its width) is visible across frames, or the UV brightness flickers slightly without changing which bands are visible, or a hand or tool briefly blocks the wells for a moment, but the gel, wells, electrodes, and buffer chamber all stay continuously present and spatially coherent throughout.
level_4: All the requirements for a 3 are met, and beyond that: the gel stays stationary and flat, the wells stay aligned, the electrodes stay attached at the same points, the UV imager stays centered overhead, and the bands move smoothly and only downward across frames, with at most one small lighting glint that briefly appears and fades, or one moment of motion blur during the cut from loading to imaging.
level_5: All the requirements for a 4 are met, and beyond that: the gel stays perfectly still and flat with the wells keeping identical shape, size, and alignment throughout; the electrodes and chamber edges show no visible shifting or drift; the UV illumination stays uniform and steady across the whole sequence; and the bands migrate as one smooth, continuous downward motion with no jumps, pauses, reversals, or lighting flicker at any point.