Domain: Healthcare — Digestive Physiology
Target concept: Lactase Activity Assay (Lactose Fermentation Method)

Video generation prompt: Prepare two test tubes containing lactose solution. Add lactase to one test tube and leave the other as a control without enzyme. Incubate both test tubes at a warm temperature. After incubation, add Benedict's reagent and gently heat. Clearly demonstrate the step-by-step procedure using test tubes, pipettes, water bath, and heating apparatus.

Evaluation guide:
(i) Target concept: Enzyme-specific catalytic hydrolysis of lactose that increases the number of free reducing-sugar ends, verified by a difference in the degree of Benedict's colorimetric reaction rather than a simple present/absent color change.
Minimum mechanism: Lactase must be present and active to cleave lactose into glucose and galactose; the lactase-treated tube must end up with more free reducing ends than the untreated lactose in the control tube; Benedict's reagent must be added after incubation and heated to develop color; the reduction of Cu2+ to Cu2O requires the alkaline, heated conditions of Benedict's test.
(ii)Storyline: Frame opens on a fixed frontal view of two upright test tubes in a rack. A pipette approaches the first tube, dispenses liquid (lactase), and retracts; the second tube is not touched. A water bath appears beneath both tubes (steam visible) during incubation. After a brief pause, a Benedict's reagent bottle enters frame, dispenses into the first tube, retracts, then repeats the same action for the second tube. A heating apparatus activates under both tubes at the same time. Color develops selectively: the first tube moves from blue through green and yellow to brick-red with visible settled precipitate; the second tube shifts only slightly from blue toward a faint green or yellow-green tint and stops there, clearly less advanced than the first tube's end point, since untreated lactose still carries one reducing end of its own. The two tubes stay framed together for the whole sequence, with no viewpoint change.

Manual:
Experimental Procedure
1. Place two identical test tubes side-by-side.
2. Add lactose solution to both tubes.
3. Use a pipette to add lactase to the first tube only; leave the second tube untreated.
4. Incubate both tubes in a warm water bath.
5. Add Benedict's reagent to both tubes.
6. Heat both tubes gently and simultaneously.
Observation of Experimental Phenomena
The lactase-treated tube develops a brick-red/orange precipitate that settles at the bottom. The untreated control tube shows only a faint shift from blue toward green or yellow-green, with little or no settled precipitate, since intact lactose is itself a weak reducing sugar. The two tubes are distinguished by a clear difference in how far the reaction has progressed, not by a strict present/absent color change.
Summary of Experimental Principles
Lactase hydrolyzes lactose into glucose and galactose, roughly doubling the number of free reducing ends available and driving a strong reduction of blue Cu2+ in Benedict's reagent to red-orange Cu2O precipitate. Because intact lactose already carries one free reducing end (on its glucose unit), the untreated control tube still reduces some Cu2+ and shows a faint green or yellow-green tint rather than remaining perfectly blue; it is the enzyme tube's much stronger, more complete reaction (full brick-red color with settled precipitate) that demonstrates lactase activity.

Prompt Grounding rubric:
level_1: No test tubes are visible in the shot; there is no lactose solution, no lactase, and no Benedict's reagent shown; no water bath or heating apparatus appears; no pipette is used; the video shows no addition, incubation, reagent-addition, or heating step at all.
level_2: Only one test tube is shown, or the containers shown are not recognizable as test tubes; two tubes may appear but never together in the same shot; there is no visible difference in treatment between the tube meant to get lactase and the tube meant to stay as a control; a pipette, water bath, or heating apparatus is missing from the sequence.
level_3: Two clear cylindrical test tubes holding a pale liquid (lactose solution) sit side by side in the same shot; a pipette adds a second liquid (lactase) to only one of the two tubes while the other is left untouched; both tubes are then placed in or beside a water bath (steam visible or a labeled bath vessel); after this warming step, a Benedict's reagent bottle dispenses into both tubes, and a heating apparatus (flame or hot plate) is placed under both.
level_4: Everything required for score 3 is shown AND: a labeled lactase container or dropper is visible just before the pipette touches the first tube; the second (control) tube is not touched at all during the lactase-addition step; Benedict's reagent is dispensed into the two tubes as two separate, visible additions after the water-bath step, not as one shared pour; the heating apparatus is applied under both tubes at the same time rather than one after the other.
level_5: Everything required for score 4 is shown AND: the pipette tip visibly touches only the lactase tube and never approaches the control tube; which tube is the enzyme tube and which is the control is unambiguous from the order and position of actions even without any on-screen text label; the two Benedict's-reagent additions are shown as distinct actions with visually matching dispensed volumes; the heating apparatus sits at the same height and angle under each tube for the simultaneous heating step.

Scientific and Causal Correctness rubric:
level_1: After heating, neither tube shows a color change consistent with Benedict's chemistry (e.g., both stay Benedict's blue, or both change to the same hue); the tube that received lactase shows no more color change or precipitate than the untreated tube, even though lactase and heat were both applied.
level_2: The lactase tube changes to an unlikely hue for this reaction (e.g., black, purple, or grey) instead of moving toward orange/brick-red; or the untreated control tube ends up with the same brick-red precipitate as the lactase tube; or the control tube looks perfectly untouched (identical to fresh Benedict's reagent) with almost no visible difference from the lactase tube.
level_3: The lactase tube shows an orange-to-brick-red precipitate consistent with a strong Benedict's reaction; the control tube shows only a mild shift from blue toward green or yellow-green, a visibly weaker reaction consistent with untreated lactose still carrying one reducing end, and it stays clearly less advanced than the lactase tube; the gap in how far each tube's reaction has progressed is the visible evidence of lactase's activity.
level_4: Everything in score 3 holds AND: the lactase tube's precipitate is granular and has settled rather than staying suspended as a haze; the control tube's green or yellow-green tint stays faint, does not progress toward orange or red, and produces no settled precipitate; the two tubes are separable at a glance by both their hue and by whether solid precipitate has settled out.
level_5: Everything in score 4 holds AND: the lactase tube's color has moved fully past yellow-green into an unambiguous brick-red/orange with a clearly settled mass of precipitate; the control tube's tint stops at a pale green-yellow with no precipitate at all, visibly less reacted than the lactase tube at every point after Benedict's reagent is added; a viewer can tell at a glance that the difference between the tubes is one of degree (partial reaction vs. strong reaction), correctly reflecting that lactose is a weak reducing sugar even before lactase acts on it.

Spatiotemporal Consistency rubric:
level_1: A test tube visible in one shot is simply missing from the rack in the next shot with no pour, spill, or removal shown; the camera cuts from a close view of the tubes to a wide view (or the reverse) with no camera movement bridging the two; the room goes from lit to dark, or the reverse, within a single beat with no dimming action shown; a tube's glass appears to bend, stretch, or melt; the pipette is mid-stroke in one frame and simply gone from the next without being withdrawn; the flame or hot-plate glow switches on and off repeatedly with no hand or switch causing it; the liquid level inside a tube rises or falls with no pour, evaporation, or spill shown.
level_2: A tube's position on the rack shifts slightly between the lactase-addition shot and the Benedict's-addition shot with no pan or push-in to explain the change; the pipette tip is shown approaching a tube but is missing at the moment it should make contact; one tube tilts or rotates while the other stays perfectly upright with no cause shown; the flame or hot-plate glow appears fully lit with no visible ignition moment; the heating apparatus appears to have shifted position under the tubes between the water-bath step and the Benedict's-heating step.
level_3: Both tubes stay in the same spot on the rack for the entire sequence; no tube or piece of equipment goes missing or is suddenly relocated between shots; the pipette's lowering, dispensing, and withdrawal for each addition play out as one continuous motion rather than being cut together from separate shots; the flame or hot-plate glow builds up gradually as it is switched on and then stays steady under both tubes; each tube keeps its cylindrical shape and its liquid surface stays flat throughout.
level_4: Everything in score 3 holds AND: the pipette's approach, contact, and retraction for each addition (lactase, then Benedict's reagent) plays out without any jump cut partway through the motion; steam over the water bath is visible continuously while the tubes warm and has cleared by the time Benedict's reagent goes in; the flame or hot-plate glow stays the same brightness and stays centered under each tube through the whole heating step; the framing of the two tubes shows no sudden jitter or skew from one moment to the next.
level_5: Everything in score 4 holds AND: the liquid surface in each tube stays undisturbed, without rippling or wobbling, during the pauses when nothing is being added; the two tubes keep the same spacing and relative size on screen as the camera holds its position, with no drift between them; any shadow cast by the pipette or rack falls on the same side and at a length consistent with the rest of the shot's lighting; every motion (pipette lowering, flame catching) eases to a stop rather than halting abruptly, and the flame or hot-plate glow holds steady without dying down or flaring up.