Domain: Natural Science — Cell & Developmental Biology
Target concept: Eukaryotic Cell Organelles (Mitochondrial Staining and Observation)

Video generation prompt: Stain the onion epidermal cells with Janus green B solution, cover with a coverslip, and observe the morphology and distribution of mitochondria under a light microscope.

Evaluation guide:
(i) Target concept: Vital staining of functional mitochondria in living plant cells using redox-sensitive Janus green B.
Minimum mechanism: Janus green B must remain oxidized (blue-green) only where mitochondrial membrane potential is maintained; thus, staining requires viable tissue, aqueous environment, and absence of fixation or permeabilization; mitochondria must appear as discrete, cytoplasm-localized granules, not diffuse or nuclear.
(ii)Storyline: [Frame 0–2] Onion epidermis laid flat on slide (visible cell wall grid, translucent). → [Frame 3–4] Janus green B solution applied: blue-green droplet contacts tissue and spreads radially with wetting front. → [Frame 5–6] Coverslip lowered vertically, making full contact; solution confined beneath glass, no overflow. → [Frame 7–10] Microscope field emerges: circular view centered on coverslip region, revealing epidermal cells with distinct cell walls, large vacuoles (empty), nuclei (pale), and scattered blue-green granules strictly within narrow cytoplasmic bands: no granules in vacuoles or nuclei; all granules are discrete and non-uniform in size/intensity. Perspective remains fixed overhead (slide-level) until microscope view, then shifts to optical axis (no lateral movement during observation). Visibility: mitochondria must be resolvable as subcellular features (not just colored noise), and cytoplasmic localization must be visually verifiable via spatial relationship to vacuole boundary.

Manual:
Experimental Procedure
1. Place a thin strip of fresh onion epidermis on a clean slide.
2. Add one drop of Janus green B solution onto the tissue.
3. Gently lower a coverslip onto the stained tissue.
4. Observe under light microscope at 400× magnification.
Observation of Experimental Phenomena
Blue-green granular mitochondria appear scattered exclusively in the cytoplasm of epidermal cells, avoiding the nucleus and large central vacuole.
Summary of Experimental Principles
Janus green B is a vital stain that selectively accumulates in active mitochondria due to their membrane potential; it remains oxidized (blue-green) in respiring organelles and is reduced to colorless leuco-form elsewhere.

Prompt Grounding rubric:
level_1: No onion epidermal tissue, no Janus green B solution, no coverslip, and no light-microscope field of view appear anywhere in the video; the scene shows an unrelated subject (e.g., a different plant organ, an animal cell, a fluorescence microscope, or only text/graphics).
level_2: Only one of the four required elements is present (onion tissue, or the Janus green B bottle/droplet, or the coverslip, or a microscope field of view), with no staining action, no coverslip placement, and no resulting circular microscope view; the sequence of setup steps is missing or shown in reverse order.
level_3: Onion epidermal tissue, Janus green B solution, a coverslip, and a circular light-microscope field containing cellular structures are all present at some point; the solution is shown touching the tissue and the coverslip is shown resting over it, and a static microscope view eventually appears, but the ordering is inconsistent (e.g., the coverslip appears before the solution is applied) or the coverslip is not aligned over the stained tissue in the final view.
level_4: The four elements appear in the correct procedural order: tissue laid flat, Janus green B solution applied onto the tissue, coverslip lowered directly over the stained area, and the final frame shows a circular microscope field over that same region; the solution stays confined to the tissue footprint and the microscope view is centered on the coverslip region throughout; no other stain or optical accessory (e.g., iodine solution, methylene blue, a fluorescence filter cube) is substituted for any required object.
level_5: All conditions of score 4 hold, and each transition is shown as a causal, continuous action: the droplet visibly wets the tissue before the coverslip makes contact, the coverslip descends with continuous motion until it lies flat against the tissue, and the microscope field only appears after that contact; no extraneous items (fingers, pipette tips, labels, unrelated tools) ever enter the frame, and the tissue, solution, and coverslip keep the same shape and identity in every frame without morphing, duplicating, or vanishing.

Scientific and Causal Correctness rubric:
level_1: No scientifically valid staining outcome is shown: the tissue is colorless, uniformly dark from overstaining, or tinted a color other than blue-green (e.g., red, purple, or yellow); mitochondria-like granules are absent, appear as large blobs/rods/rings instead of small granules, or sit inside the nucleus or vacuole rather than the cytoplasm; or no cellular structure is visible at all.
level_2: Granular structures are visible but fail a core staining attribute: either the color is not blue-green, or the granules sit mainly in the cell wall or vacuole rather than the cytoplasm, or their shape is an unrecognizable smudge or uniform haze rather than discrete granules; there is little to no color contrast between the granules and the surrounding pale cytoplasm.
level_3: Discrete blue-green granules appear inside the cytoplasm of onion epidermal cells, vary slightly in size, and are absent from the nucleus and the large central vacuole; however, a few granules still appear outside the cytoplasm, or excess unabsorbed dye pools in the space beyond the cell wall, or every granule sits in an identical evenly-spaced row rather than a natural scatter.
level_4: Every mitochondrial granule is blue-green, discrete, and confined to the cytoplasm (none in the nucleus or vacuole); the granules are scattered unevenly through the thin cytoplasmic layer (some closer to the cell wall, some closer to the vacuole membrane) rather than compressed into one tight clump or strung out in a single file; the granules contrast clearly against the paler cytoplasm, and no blue-green residue appears on the coverslip or outside the cell boundary.
level_5: All conditions of score 4 hold, and the granules show the heterogeneity real Janus-green-B-stained mitochondria show: sizes and staining intensity vary noticeably between granules within the same cell; every granule stays confined to the thin cytoplasmic band running between the vacuole membrane and the cell wall, consistent with a mature onion epidermal cell where the cytoplasm is pressed into a narrow parietal layer; no blue-green artifact appears on the coverslip, as a dye streak, or as an air bubble mistaken for a granule; granule shapes remain small ovoids or short rods, never elongated filaments or a connected reticular network.

Spatiotemporal Consistency rubric:
level_1: Severe continuity breaks: the coverslip appears already resting flat on the tissue with no descent shown, the onion tissue jumps to a different position on the slide between shots, the microscope field abruptly changes scale or rotates without cause, or the frame goes from bright to dark with no lighting event to explain it.
level_2: At least two of the following occur: the coverslip's descent is missing (it snaps from hovering to full contact), the Janus green B droplet appears on the tissue with no visible spreading, the microscope field appears with no preceding setup shot, or the tissue surface ripples or buckles without any liquid contact to cause it.
level_3: Only one small flaw remains: the coverslip motion is jerky but still ends flat on the tissue, or the droplet spreads in a couple of visible jumps rather than a smooth front but stays on the tissue, or the microscope field shifts slightly off-center for a moment before settling, or the overall brightness dips and recovers slightly across a few frames.
level_4: The droplet spreads outward from first contact in a continuous wetting front, the coverslip descends steadily and settles flat without tilting or bouncing, the microscope view comes into focus gradually rather than snapping sharp instantly, the tissue stays flat and stationary throughout, and overall brightness stays even with no object flickering, warping, or resizing unnaturally.
level_5: All conditions of score 4 hold, and frame-to-frame coherence is complete: the moving coverslip shows a plausible trailing blur while the stationary tissue shows none, the tissue, coverslip, and microscope field never drift relative to one another as if seen from a shifting camera, no shadow cast by the coverslip edge jumps to a different direction between frames, and the droplet is never shown appearing after the coverslip has already made contact.