Domain: Natural Science — Cell & Developmental Biology
Target concept: Chloroplast cytoplasmic streaming in Elodea leaf cells observed under a microscope

Video generation prompt: Place a fresh Elodea leaf on a microscope slide with a drop of water, cover it with a coverslip, and observe the leaf cells under an optical microscope for several minutes.

Evaluation guide:
(i) Target concept: Intracellular transport via actin-based cytoplasmic streaming in living plant cells.
Minimum mechanism: Leaf tissue must be alive and hydrated; cytoskeleton intact; no fixation or chemical treatment; motion must arise endogenously, not induced by external flow, vibration, or thermal convection.
(ii)Storyline: Frame 1–2: Fresh Elodea leaf placed flat on slide. Frame 3–4: Water droplet applied onto leaf surface, spreading to form continuous layer. Frame 5–6: Coverslip lowered vertically and settled onto water, sealing wet mount. Frame 7–10: Stable microscopic view reveals elongated cells; green oval chloroplasts appear within cells and move smoothly along cell periphery in consistent direction: no motion outside cells, no cessation, no reversal. Perspective: Fixed high-magnification view mimicking 40x objective; only cellular region visible: no slide edges, hand, or microscope body; lighting uniform and transmitted (no glare or shadows obscuring streaming).

Manual:
Experimental Procedure
1. Place a fresh Elodea leaf flat on a clean glass microscope slide.
2. Add one drop of water over the leaf.
3. Gently lower a glass coverslip onto the water to form a wet mount.
Observation of Experimental Phenomena
Under microscope magnification: green oval chloroplasts move continuously along the inner perimeter of elongated plant cells in a unidirectional circular path.
Summary of Experimental Principles
Cytoplasmic streaming in Elodea is driven by actin-myosin motility; chloroplasts are carried passively within flowing cytosol, enabling efficient photosynthetic positioning under light.

Prompt Grounding rubric:
level_1: No Elodea leaf, microscope slide, coverslip, or water droplet is visible; there is no depiction of a wet-mount preparation being assembled.
level_2: At least one correct object appears (a green leaf fragment, a glass slide, or a coverslip), but the leaf, water, slide, and coverslip never appear together; either the placement action is missing or misapplied (e.g., the leaf sits on a dry slide, or is covered by an opaque material instead of a coverslip), and the leaf never visibly touches a water layer.
level_3: The Elodea leaf, microscope slide, a drop of water, and a coverslip are all present; the leaf is placed on the slide, water is applied over the leaf, and the coverslip is lowered onto the water in that order (shown or clearly implied); all four objects appear together in the same fixed-viewpoint scene.
level_4: All conditions for score 3 are met, AND the leaf stays fully covered by the water layer and fully overlaid by the coverslip for the whole sequence; no object appears detached, floating, or occluded mid-action; the leaf lies flat on the slide, the water forms a continuous layer beneath the coverslip, and the coverslip rests directly on the water with no visible gap or trapped air bubble at its edges.
level_5: All conditions for score 4 are met, AND every object keeps its correct visual identity throughout: the leaf looks fresh with crisp, green, unbrowned edges; the slide is clear glass rather than plastic or frosted; the water layer is transparent and refractive rather than cloudy or opaque; the coverslip is a thin glass square or circle rather than a thick plate or plastic film; no object is duplicated, oddly sized, or wrongly colored relative to ordinary lab glassware.

Scientific and Causal Correctness rubric:
level_1: No chloroplasts are visible inside the leaf cells; no motion of any kind occurs in the tissue; the cell structure is missing or wrong for a plant leaf (e.g., a uniform green blob, animal-cell-like shapes, or a crystalline lattice pattern).
level_2: Green granules are visible inside the leaf tissue but stay still, or they move only in a single jerky direction along one edge rather than circulating around the cell; the granules are not oval and uniformly green like chloroplasts, and any motion looks like it comes from water current or vibration rather than from inside the cell.
level_3: Green, oval chloroplasts are visible inside at least one clearly resolved, elongated plant cell and move continuously around the cell's periphery in one consistent direction (clockwise or counterclockwise); the motion is smooth and uninterrupted across the sequence and stays confined within the cell wall, never crossing into the surrounding water layer.
level_4: All conditions for score 3 are met, AND the same directional streaming occurs at the same time in several neighboring cells, with matching flow direction from one cell to the next; the chloroplasts keep a uniform size, oval shape, and green color as they move; none of them detach, break apart, change color, or reverse direction, and no unrelated motion (whole-leaf drift, an air bubble moving, or the coverslip shifting) interferes with the view.
level_5: All conditions for score 4 are met, AND the streaming path follows the natural curve of each cell's boundary rather than moving in a rigid straight line, and keeps a smooth, continuous pace without robotic-looking constant-speed motion; chloroplasts never overlap, merge, or stack on one another; the water layer and coverslip outside the cells stay completely still while streaming occurs, and no flicker or artificial-looking texture appears on the granules or in the background.

Spatiotemporal Consistency rubric:
level_1: Severe spatiotemporal rupture: the leaf, coverslip, or slide jumps to a different position between frames instead of moving continuously; the leaf or water droplet vanishes and reappears without a visible application or removal action; the illumination suddenly switches from bright to dark within a single frame with no visible cause; the cell boundaries inside the leaf warp or dissolve; the coverslip appears fully seated in one frame after being off-screen in the previous frame, with no visible lowering motion in between.
level_2: Moderate discontinuity: the leaf's position or orientation changes between frames without a visible movement connecting the two states; the water layer appears or disappears without a visible application step; the coverslip's orientation changes (e.g., from edge-on to flat) without a visible rotation; playback stutters (freezing then jumping ahead), or the chloroplast streaming starts or stops abruptly with no gradual transition.
level_3: The leaf, water layer, and coverslip each keep the same position and orientation relative to one another across the sequence: the leaf stays fixed on the slide, the water layer stays continuous and unbroken, and the coverslip stays fully seated; none of the three warps, stretches, or shears; the brightness and color of the transmitted light illuminating the cells stay constant from frame to frame; the chloroplast streaming itself is continuous, with no dropped frames or unexplained pauses, and moves at a steady pace across the sequence.
level_4: All conditions for score 3 are met, AND the camera viewpoint stays completely fixed with no panning, tilting, or zooming; the leaf, the water meniscus at the coverslip edge, and the coverslip's own edge all stay in the same relative position with no parallax shift between them; there is no frame-to-frame flicker, brightness pulse, or color-tint shift; any motion blur on the moving chloroplasts points in the same direction as their streaming path rather than at an unrelated angle.
level_5: All conditions for score 4 are met, AND the depth relationships stay physically coherent throughout: the water layer subtly bends the visible edges of leaf structures beneath it (refraction), the coverslip shows a faint, consistent surface reflection matching the lighting direction, and the in-focus cell layer stays sharp while structures above or below it stay softly out of focus; the coverslip is never shown appearing behind or through the water layer, and no layer becomes see-through or opaque inconsistently between frames.