Domain: Natural Science — Chemistry
Target concept: Comparison of the reaction of iodine with linear amylose solution and that with highly branched glycogen solution

Video generation prompt: Two transparent beakers are placed side by side: the left one contains a turbid starch solution, and the right one contains a clear glycogen solution. Iodine solution is added to both, and they are gently shaken.

Evaluation guide:
Target Concept: The differential iodine-color reaction arises from the strict dependence of polyiodide helix stabilization on glucan chain linearity and minimum length: amylose (linear, >50 units) forms stable blue-black complexes; glycogen (branched every 8–12 units, outer chains <15 units) forms transient, low-stoichiometry reddish-brown complexes. Minimum mechanistic assumption: iodine does not react chemically but forms reversible, geometry-dependent physical inclusion complexes. Phased Storyline: (1) Initial State: Two identical beakers, left turbid (amylose-rich starch suspension), right clear (molecularly dispersed glycogen). (2) Causal Trigger: Simultaneous iodine addition introduces I₃⁻ ions. (3) Structural Filtering: Amylose helices entrap I₃⁻ → strong charge-transfer absorption → blue-black; glycogen branches sterically limit helix formation → weak absorption → reddish-brown. (4) Visual Verification: Within 10s, high-contrast, stable, non-overlapping colors emerge, blue-black (opaque) vs. reddish-brown (translucent), requiring frontal, well-lit, static framing to resolve both hue and transparency differences. Visibility constraints: Must capture simultaneous color development *and* baseline turbidity/clarity; no zoom or cutaways. Single continuous shot essential.

Manual:
I. Basic Demonstration Information
Demonstration Title: Iodine Reaction Contrast: Linear Amylose (Starch) vs. Highly Branched Glycogen
Subject: Chemistry - Natural Science - Carbohydrate Chemistry
Demonstration Purpose: Visually compare the distinct color reactions of iodine with linear amylose (in turbid starch solution) and highly branched glycogen (in clear solution) to demonstrate how polysaccharide chain architecture determines iodine complex formation and resultant color; establish structure–property relationship central to carbohydrate identification.

II. Demonstration Carrier/Equipment
Core Carrier: Two identical transparent glass beakers (100 mL, cylindrical, clean, dry); starch solution (1% w/v potato starch, freshly prepared, turbid/milky-white, no sediment); glycogen solution (1% w/v, purified bovine liver glycogen, fully dissolved, crystal-clear, particle-free); iodine solution (0.01 M I₂ in KI aqueous, amber-brown).
Auxiliary Equipment: Dropper (calibrated, dual-tip or two identical droppers); neutral background board; white lab bench surface; timer (for synchronization).

III. Demonstration Content Description
Layout: Place two beakers side-by-side on neutral background, left = starch (turbid), right = glycogen (clear), 5 cm apart, centered in frame.
State Control: Ensure starch solution is freshly vortexed (uniform turbidity, no settling); glycogen solution must be filter-sterilized or centrifuged to guarantee optical clarity.
Procedure: Simultaneously add 3 drops of iodine solution to each beaker using identical droppers; immediately perform identical gentle horizontal swirling (3–4 sec, ~1 Hz oscillation) for both beakers.

IV. Observation of Core Phenomena
Left Beaker (Starch/Amylose): Turbid white suspension rapidly transforms into homogeneous, opaque deep blue-black color — intense, high-contrast, non-translucent.
Right Beaker (Glycogen): Clear solution transforms into translucent, warm reddish-brown — lighter, lower saturation, remains see-through; no blackening or purple hues.
Characteristic Stability: Colors stabilize within 2–3 seconds post-shake and remain stable for ≥5 s; no fading, phase separation, or precipitation.
Auxiliary Comparison: Identical beaker geometry, lighting, and timing ensure color difference arises solely from molecular structure — not container or procedural artifact.

V. Summary of Key Knowledge Points and Principles
Core Concept Definition: Iodine forms inclusion complexes with helical segments of glucose polymers; linear amylose adopts extended helices that trap polyiodide (I₃⁻/I₅⁻), yielding blue-black; highly branched glycogen has short outer chains (<10–15 glucose units), forming unstable, shorter helices that yield reddish-brown.
Chemical Significance: This colorimetric distinction is a foundational qualitative test for starch vs. glycogen in biochemistry labs — directly linking macromolecular architecture to observable optical property.
VI. Demonstration Precautions
— Starch solution must be freshly prepared and agitated: aged or overheated starch gels and yields false-negative (weak color) or false-positive (black precipitate).
— Glycogen must be high-purity and fully solubilized: trace amylose contamination causes blue tinge; undissolved particles mimic turbidity.
— Iodine concentration must be standardized: too dilute → weak colors; too concentrated → over-saturation masking distinction.
— Avoid direct sunlight: UV degrades iodine complex; use diffuse white LED lighting for true color rendering.
— Shaking must be gentle and identical: vigorous shaking introduces air bubbles (false turbidity) or shear-induced amylose denaturation.

Prompt Grounding rubric:
level_1: No two transparent beakers are arranged side by side; neither one shows the turbid-on-the-left, clear-on-the-right contrast; no iodine solution is added to either beaker; no shaking or swirling motion occurs; nothing in the shot resembles the two-beaker setup described in the prompt.
level_2: Two beakers are present but not arranged side by side (for instance stacked or set at an angle to each other), or the turbid and clear liquids are on the wrong sides (turbid on the right, clear on the left), or iodine is added to only one beaker, or a shaking motion is applied to only one beaker or to neither.
level_3: Two beakers sit side by side, the left one visibly turbid (milky or cloudy) and the right one visibly clear, matching the prompt's left/right assignment; an amber-brown iodine solution is visibly dispensed into both, but no shaking or swirling motion follows the addition.
level_4: The left-turbid, right-clear arrangement is correct, iodine solution is visibly added to both beakers, and a gentle swirling motion is applied to both shortly afterward, but the two shaking actions are noticeably out of step with each other, or one beaker's turbidity or clarity looks weaker than it should before anything is added.
level_5: Two beakers sit side by side on a plain background, the left one holding a uniformly turbid, milky liquid and the right one a fully clear, particle-free liquid; an amber-brown iodine solution is added to both at essentially the same moment; both beakers then receive a similar gentle swirling motion applied together rather than one after the other; the setup and action sequence match the prompt exactly, independent of whatever color the liquids turn afterward.

Scientific and Causal Correctness rubric:
level_1: Neither beaker shows a scientifically sensible color change: for instance both end up the same color, neither changes color at all despite the iodine, or the color that appears doesn't resemble the blue-black or reddish-brown outcome this reaction should produce.
level_2: The two beakers develop different colors, but the assignment is backwards: the left (starch-like, turbid) liquid ends up reddish-brown while the right (glycogen-like, clear) liquid ends up blue-black, or both settle into the same in-between purple shade rather than two distinguishable hues.
level_3: The left liquid darkens toward blue-black and the right liquid takes on a brownish tint, in the correct direction, but the contrast between them is weak: for example the right looks nearly as dark as the left, or the left looks pale rather than a deep blue-black.
level_4: The left liquid clearly turns a deep blue-black and the right liquid clearly turns a lighter reddish-brown, matching the expected iodine-with-amylose versus iodine-with-glycogen outcome, with a visible difference in both hue and depth of color between the two beakers.
level_5: The contrast is unmistakable and appears quickly: the left beaker becomes a deep, saturated blue-black, while the right beaker becomes a clearly lighter, warmer reddish-brown that never approaches blue-black or matches the left's intensity; a viewer can tell which beaker is which at a glance, with no ambiguity.

Spatiotemporal Consistency rubric:
level_1: A beaker is missing from a shot and then present again a moment later, the iodine solution appears already mixed into a beaker before any addition is shown, the shaking motion happens before the iodine is added, or a color change appears before the iodine has actually touched the liquid, or the lighting on the beakers shifts abruptly between frames with no visible cause, or a beaker visibly warps or changes shape.
level_2: The two beakers are shaken with clearly different vigor or for different lengths of time (one swirled hard, the other barely moved), the iodine is added to the two beakers more than a second or two apart, or a color develops in one beaker with no clear connection in time to when it was shaken.
level_3: Both beakers stay in place and receive a similar shaking motion, the iodine additions happen close together in time, and color starts developing in both shortly after, but one beaker's color settles noticeably earlier than the other, by around 2 seconds, or there's a brief flicker in the lighting.
level_4: The iodine is added to both beakers at essentially the same time, both then receive matching swirls of similar speed and duration (roughly 3 seconds each), and color begins developing in both at a similar pace shortly after, with steady lighting and no shift in beaker position throughout.
level_5: Both beakers hold fixed positions and receive iodine at the same moment via matching dropper motions, followed immediately by matching swirling in both; color develops in the two beakers together, at the same pace, under steady, unchanging lighting from start to finish, with nothing appearing, disappearing, or happening out of order.