Domain: Natural Science — Cell & Developmental Biology
Target concept: Time-lapse images of yeast cells recorded under a microscope, showing shrinkage followed by recovery after osmotic adjustment

Video generation prompt: Time-lapse imaging under a light microscope: Live yeast cells observed within a droplet, first exposed to a hypertonic saline solution, then returned to an isotonic solution, with the cells remaining within the field of view throughout the process.

Evaluation guide:
(i) Target concept: Reversible osmotic volume regulation in live yeast cells via plasmolysis and deplasmolysis.
Minimum mechanism: Cells must be alive, intact, and surrounded by aqueous solutions differing only in solute concentration; water flux must drive passive volume change without membrane rupture or metabolic intervention.
(ii)Storyline: [Phase 1: Baseline] Live yeast cells in isotonic droplet: uniform size, smooth contour, moderate refractility. [Phase 2: Hypertonic trigger] Saline introduced at droplet edge: fluid advances, cells rapidly shrink synchronously, membrane pulls away from wall. [Phase 3: Stable plasmolysis] Shrunken cells persist with high refractility, no lysis. [Phase 4: Isotonic rescue] Isotonic buffer replaces saline at droplet edge: fluid re-advances, cells gradually swell. [Phase 5: Full recovery] Cells restore original size, contour, and optical density. All phases occur within a single, unbroken, fixed microscopic field-of-view; no cell exits frame; no external manipulation (e.g., pipetting into view) disrupts continuity.

Manual:
Experimental Procedure
1. Place live yeast cells suspended in isotonic buffer within a microscope slide droplet.
2. Apply hypertonic saline solution to the droplet margin to induce osmotic shock.
3. Observe immediate cell shrinkage (plasmolysis) within the same field of view.
4. Replace with isotonic buffer to restore osmotic balance.
5. Observe full cell recovery (deplasmolysis) while remaining in the field of view.
Observation of Experimental Phenomena
- Yeast cells visibly shrink (reduced area, increased refractility, membrane detachment) during hypertonic exposure.
- Cells fully regain original size, shape, and optical density after isotonic restoration.
- All cells remain continuously visible inside the droplet throughout both phases.
Summary of Experimental Principles
- Osmosis drives water out of yeast cells in hypertonic environments, causing plasmolysis.
- Return to isotonic conditions restores turgor pressure, enabling deplasmolysis and full morphological recovery.
- Time-lapse light microscopy captures dynamic, reversible volume regulation in living cells.

Prompt Grounding rubric:
level_1: No yeast cells are shown, no droplet is shown, no hypertonic saline application occurs, no return to isotonic solution occurs, there is no time-lapse progression, and there is no single fixed microscope field of view.
level_2: Yeast cells appear, but not inside a defined droplet; a solution is added at some point but it is unclear whether it is the hypertonic or the isotonic step; cells leave the field of view at some point; or no shrink-then-recover shape change is shown at all.
level_3: Yeast cells sit inside a clearly bounded droplet; two separate solution-exposure events are shown, a hypertonic saline addition and, later, an isotonic solution addition; the cells stay inside the same fixed field of view throughout; a shrinking phase and a size-recovery phase both appear somewhere in the sequence, though their order may be unclear or swapped.
level_4: All of the 3-point requirements are met, and further, the hypertonic addition clearly comes first and the isotonic addition clearly comes second; the cells stay in the same field of view the whole time; the shrinking phase is shown before the recovery phase; and the droplet, the two solution-addition events, and the cells are all clearly tied to their correct phase of the sequence.
level_5: All of the 4-point requirements are met, and further, each solution addition reads as a distinct, separate event, such as a visible change at the droplet's edge marking each transition, rather than one blurred change; the droplet stays as one continuous body of liquid with the cells never crossing its edge or leaving the field of view; and no extra objects, overlays, or scene cuts interrupt the sequence.

Scientific and Causal Correctness rubric:
level_1: No biologically plausible osmotic response occurs: the cells show no shape change, or they expand first and then shrink instead of the reverse, cells lyse or fall apart, or their color/transparency changes in a way inconsistent with live, unstained yeast under a light microscope (e.g., sudden fluorescence, pigment, or opacity).
level_2: The cells change shape, but the direction is biologically backwards, for example swelling rather than shrinking once the hypertonic solution arrives; the shrink-then-recover pattern is not tied to the two solution additions; recovery happens before shrinkage; or the cells take on an unnatural color shift or become uniformly opaque or transparent with no biological basis.
level_3: Cells shrink during the hypertonic phase and grow back during the isotonic phase, but incompletely: they still keep more than roughly 70% of their original area at maximum shrinkage, or recovery falls short of the pre-shrinkage size and shape; the cells stay intact and viable-looking throughout, with no non-biological artifacts such as crystallization or bubbling.
level_4: Shrinkage happens only during the hypertonic phase and recovery only during the isotonic phase; shrinkage shows up as a clear drop in each cell's cross-sectional area together with a visibly brighter, denser appearance; recovery shows a near-complete return to the pre-shrinkage size and a smooth outline with reduced refractility; no cell lyses, blebs, or is left permanently deformed.
level_5: Shrinkage is fast and affects essentially all visible cells together, consistent with plasmolysis, where the cell contents visibly pull inward and separate from the cell wall; recovery is gradual, happens together across the cells, and restores full size and a smooth, uniform outline with no lingering gap between contents and wall; no cell responds noticeably later, less, or not at all compared to the others.

Spatiotemporal Consistency rubric:
level_1: Cells teleport between frames, the droplet disappears and reappears, the lighting suddenly flashes from dark to bright with no cause, the view abruptly zooms or pans, the field of view rotates or crops mid-sequence, cells flicker in and out of view, or a cell appears split or misaligned across a cut.
level_2: The droplet's edge wobbles heavily or loses its outline for several consecutive frames, cells jump position or tremor unnaturally between frames, a solution change appears instantly with no visible flow or meniscus movement, or the background or focus shifts abruptly for no physical reason.
level_3: The droplet stays spatially stable with a continuous, unbroken edge; cells move only through gentle drift, not directed swimming or sliding; each solution change shows physically plausible fluid behavior such as an advancing meniscus or mixing front; lighting and focus stay steady; there are no dropped frames, stutters, or ghost images.
level_4: All of the 3-point requirements are met, and further, the droplet keeps a fixed position, shape, and edge curvature; every cell stays fully inside the field of view without crossing the edge; all motion is smooth, slow, and physically plausible with no sudden speed-ups or rigid spinning; each solution change spreads in continuously rather than swapping instantly; the background stays static and evenly lit.
level_5: All of the 4-point requirements are met, and further, the droplet's edge position does not visibly shift between frames; no cell jumps by more than roughly one cell-width between adjacent frames; the fluid transitions advance in one steady direction with no visible mixing reversal; focus and contrast stay steady with no visible hunting or exposure pulsing; and there is no motion blur inconsistent with the sequence unfolding over many seconds.