<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif; }
    body {
      background: #f8fafc;
      color: #1e293b;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .formula-bar {
      background: #ffffff;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 6px 14px;
      font-size: 13px;
      font-weight: 600;
      color: #475569;
      display: flex;
      align-items: center;
      gap: 8px;
      margin-bottom: 12px;
    }

    .fraction {
      display: inline-flex;
      flex-direction: column;
      vertical-align: middle;
      text-align: center;
      font-size: 12px;
      line-height: 1.1;
      padding: 0 4px;
    }
    .numerator { border-bottom: 1.5px solid #64748b; padding-bottom: 2px; }
    .denominator { padding-top: 2px; }

    .cards-grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
      max-width: 600px;
    }

    @media (max-width: 480px) {
      .cards-grid { grid-template-columns: 1fr; }
    }

    .calc-card {
      background: #ffffff;
      border-radius: 10px;
      border: 1px solid #e2e8f0;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
      position: relative;
    }

    .card-gain { border-top: 4px solid #16a34a; }
    .card-loss { border-top: 4px solid #ea580c; }

    .card-header {
      display: flex;
      justify-content: space-between;
      align-items: center;
      font-size: 13px;
      font-weight: 700;
    }
    .card-gain .card-header { color: #16a34a; }
    .card-loss .card-header { color: #ea580c; }

    .data-row {
      display: flex;
      justify-content: space-between;
      background: #f1f5f9;
      padding: 6px 8px;
      border-radius: 6px;
      font-size: 13px;
      font-weight: 500;
    }
    .data-val { font-weight: 700; color: #0f172a; }

    .step-box {
      border-radius: 6px;
      padding: 8px;
      font-size: 13px;
      display: flex;
      flex-direction: column;
      gap: 4px;
      transition: opacity 0.3s ease;
    }

    .card-gain .step-box { background: #f0fdf4; border: 1px solid #bbf7d0; }
    .card-loss .step-box { background: #fff7ed; border: 1px solid #ffedd5; }

    .step-label {
      font-size: 11px;
      font-weight: 700;
      text-transform: uppercase;
      letter-spacing: 0.5px;
    }
    .card-gain .step-label { color: #15803d; }
    .card-loss .step-label { color: #c2410c; }

    .math-line {
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
      font-weight: 600;
      font-size: 13px;
    }

    .result-badge {
      text-align: center;
      padding: 6px 8px;
      border-radius: 6px;
      font-weight: 800;
      font-size: 15px;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 6px;
    }
    .badge-gain { background: #dcfce7; color: #15803d; }
    .badge-loss { background: #ffedd5; color: #c2410c; }

    .controls {
      display: flex;
      gap: 8px;
      margin-top: 12px;
    }
    .btn-step {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      padding: 5px 12px;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 600;
      color: #475569;
      cursor: pointer;
    }
    .btn-step.active {
      background: #0284c7;
      color: #ffffff;
      border-color: #0284c7;
    }
  </style>
</head>
<body>

  <div class="formula-bar">
    <span>% Change =</span>
    <span class="fraction">
      <span class="numerator">Final − Initial</span>
      <span class="denominator">Initial</span>
    </span>
    <span>× 100</span>
  </div>

  <div class="cards-grid">
    
    <div class="calc-card card-gain">
      <div class="card-header">
        <span>Box A · Pure Water</span>
        <span>💧 + Water</span>
      </div>

      <div class="data-row">
        <span>Initial: <span class="data-val">2.50g</span></span>
        <span>Final: <span class="data-val">2.85g</span></span>
      </div>

      <div class="step-box step-1">
        <span class="step-label">Step 1: Change in Mass</span>
        <div class="math-line">
          2.85 − 2.50 = <strong>+0.35g</strong>
        </div>
      </div>

      <div class="step-box step-2">
        <span class="step-label">Step 2: % Calculation</span>
        <div class="math-line">
          <span class="fraction">
            <span class="numerator">+0.35</span>
            <span class="denominator">2.50</span>
          </span>
          <span>× 100 =</span>
          <strong>+14.0%</strong>
        </div>
      </div>

      <div class="result-badge badge-gain step-2">
        <span>▲ +14.0%</span>
      </div>
    </div>

    
    <div class="calc-card card-loss">
      <div class="card-header">
        <span>Box B · Salt Water</span>
        <span>💧 − Water</span>
      </div>

      <div class="data-row">
        <span>Initial: <span class="data-val">2.40g</span></span>
        <span>Final: <span class="data-val">2.04g</span></span>
      </div>

      <div class="step-box step-1">
        <span class="step-label">Step 1: Change in Mass</span>
        <div class="math-line">
          2.04 − 2.40 = <strong>−0.36g</strong>
        </div>
      </div>

      <div class="step-box step-2">
        <span class="step-label">Step 2: % Calculation</span>
        <div class="math-line">
          <span class="fraction">
            <span class="numerator">−0.36</span>
            <span class="denominator">2.40</span>
          </span>
          <span>× 100 =</span>
          <strong>−15.0%</strong>
        </div>
      </div>

      <div class="result-badge badge-loss step-2">
        <span>▼ −15.0%</span>
      </div>
    </div>
  </div>

  <div class="controls">
    <button class="btn-step" id="btn1" onclick="setStep(1)">Step 1</button>
    <button class="btn-step active" id="btn2" onclick="setStep(2)">Step 2 (All)</button>
  </div>

  <script>
    function setStep(step) {
      document.getElementById('btn1').classList.toggle('active', step === 1);
      document.getElementById('btn2').classList.toggle('active', step === 2);
      
      const step2Elements = document.querySelectorAll('.step-2');
      step2Elements.forEach(el => {
        el.style.opacity = step === 1 ? '0.15' : '1';
      });
    }
  </script>

</body>
</html>

Required Practical: Investigating Osmosis in Potato Cylinders

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
      background: transparent;
      color: #1e2945;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      width: 100%;
      min-height: 100vh;
      padding: 12px 10px;
    }
    .graph-container {
      width: 100%;
      max-width: 520px;
      position: relative;
    }
    svg {
      width: 100%;
      height: auto;
      display: block;
      overflow: visible;
    }
    .axis-line { stroke: #94a3b8; stroke-width: 1.5; }
    .zero-line { stroke: #94a3b8; stroke-width: 1.5; stroke-dasharray: 4,4; }
    .grid-line { stroke: #e2e8f0; stroke-width: 1; }
    .curve {
      fill: none;
      stroke: #2563eb;
      stroke-width: 3;
      stroke-linecap: round;
    }
    .data-point {
      fill: #2563eb;
      stroke: #ffffff;
      stroke-width: 2.5;
      cursor: pointer;
      transition: r 0.15s ease, fill 0.15s ease, filter 0.15s ease;
    }
    .data-point:hover, .data-point.active {
      r: 7;
      fill: #1d4ed8;
      filter: drop-shadow(0 2px 4px rgba(37, 99, 235, 0.4));
    }
    .intercept-point {
      fill: #16a34a;
      stroke: #ffffff;
      stroke-width: 3;
      cursor: pointer;
      transition: r 0.15s ease, fill 0.15s ease, filter 0.15s ease;
    }
    .intercept-point:hover, .intercept-point.active {
      r: 8;
      fill: #15803d;
      filter: drop-shadow(0 2px 5px rgba(22, 163, 74, 0.45));
    }
    .axis-label {
      font-size: 11px;
      fill: #64748b;
      font-weight: 600;
      text-anchor: middle;
      user-select: none;
    }
    .axis-title {
      font-size: 12px;
      fill: #1e2945;
      font-weight: 700;
      text-anchor: middle;
      user-select: none;
    }
    .callout-box {
      fill: #f0fdf4;
      stroke: #16a34a;
      stroke-width: 1.5;
      rx: 6;
      filter: drop-shadow(0 2px 4px rgba(22, 163, 74, 0.12));
    }
    .callout-text-title {
      font-size: 11px;
      font-weight: 700;
      fill: #15803d;
      text-anchor: middle;
    }
    .callout-text-sub {
      font-size: 10.5px;
      font-weight: 600;
      fill: #166534;
      text-anchor: middle;
    }
    .zone-label {
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 0.3px;
      user-select: none;
    }
    .gain-zone { fill: #0284c7; }
    .loss-zone { fill: #e11d48; }

    /* Interactive Status pill */
    .status-bar {
      margin-top: 8px;
      width: 100%;
      max-width: 520px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 8px;
      padding: 7px 14px;
      font-size: 12px;
      font-weight: 600;
      color: #334155;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 8px;
      text-align: center;
      min-height: 36px;
    }
    .status-dot {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #16a34a;
      flex-shrink: 0;
      transition: background 0.2s ease;
    }
  </style>
</head>
<body>

  <div class="graph-container">
    <svg viewBox="0 0 520 360" id="osmosisGraph" aria-label="Potato Osmosis Practical Graph">
      <defs>
        <marker id="arrow" viewBox="0 0 10 10" refX="6" refY="5" markerWidth="6" markerHeight="6" orient="auto-start-reverse">
          <path d="M 0 1.5 L 8 5 L 0 8.5 z" fill="#16a34a" />
        </marker>
      </defs>

      
      <rect x="65" y="30" width="415" height="130" fill="#f0f9ff" opacity="0.6" rx="4" />
      <rect x="65" y="160" width="415" height="130" fill="#fff1f2" opacity="0.6" rx="4" />

      
      <text x="470" y="48" text-anchor="end" class="zone-label gain-zone">▲ Water Enters (Turgid)</text>
      <text x="470" y="182" text-anchor="end" class="zone-label loss-zone">▼ Water Leaves (Flaccid)</text>

      
      
      <line x1="65" y1="30" x2="480" y2="30" class="grid-line" />
      <text x="56" y="34" class="axis-label">+20%</text>

      <line x1="65" y1="95" x2="480" y2="95" class="grid-line" />
      <text x="56" y="99" class="axis-label">+10%</text>

      
      <line x1="65" y1="160" x2="480" y2="160" class="zero-line" />
      <text x="56" y="164" class="axis-label" style="font-weight:700; fill:#1e2945;">0%</text>

      <line x1="65" y1="225" x2="480" y2="225" class="grid-line" />
      <text x="56" y="229" class="axis-label">-10%</text>

      <line x1="65" y1="290" x2="480" y2="290" class="grid-line" />
      <text x="56" y="294" class="axis-label">-20%</text>

      
      <line x1="65" y1="25" x2="65" y2="295" class="axis-line" />

      
      <text x="65" y="308" class="axis-label">0.0</text>
      <text x="145" y="308" class="axis-label">0.2</text>
      <text x="225" y="308" class="axis-label">0.4</text>
      <text x="305" y="308" class="axis-label">0.6</text>
      <text x="385" y="308" class="axis-label">0.8</text>
      <text x="465" y="308" class="axis-label">1.0</text>

      
      <text x="272" y="332" class="axis-title">Sucrose Concentration (M)</text>
      <text x="18" y="160" class="axis-title" transform="rotate(-90 18 160)">Percentage Change in Mass (%)</text>

      
      
      <path d="M 65 56 C 95 76, 120 95, 145 108 C 168 120, 178 142, 193 160 C 205 174, 212 181, 225 186 C 255 198, 275 220, 305 231.5 C 340 245, 360 258, 385 264 C 415 271, 440 275, 465 277" class="curve" />

      
      
      <line x1="218" y1="92" x2="197" y2="153" stroke="#16a34a" stroke-width="1.5" stroke-dasharray="3,3" marker-end="url(#arrow)" />

      <g transform="translate(138, 48)">
        <rect x="0" y="0" width="168" height="44" class="callout-box" />
        <text x="84" y="18" class="callout-text-title">0% Change = Isotonic</text>
        <text x="84" y="33" class="callout-text-sub">Cell Concentration (0.32 M)</text>
      </g>

      
      <g id="pointsGroup">
        
        <circle cx="65" cy="56" r="5" class="data-point" data-m="0.0 M" data-change="+16%" data-state="Pure water / Hypotonic (Potato swells)" />
        
        
        <circle cx="145" cy="108" r="5" class="data-point" data-m="0.2 M" data-change="+8%" data-state="Hypotonic solution (Water enters cell)" />
        
        
        <circle cx="193" cy="160" r="6.5" class="intercept-point" data-m="0.32 M" data-change="0%" data-state="Isotonic (No net osmosis / Equilibrium)" />
        
        
        <circle cx="225" cy="186" r="5" class="data-point" data-m="0.4 M" data-change="-4%" data-state="Hypertonic solution (Water leaves cell)" />
        
        
        <circle cx="305" cy="231.5" r="5" class="data-point" data-m="0.6 M" data-change="-11%" data-state="Hypertonic (Potato shrinks / mass lost)" />
        
        
        <circle cx="385" cy="264" r="5" class="data-point" data-m="0.8 M" data-change="-16%" data-state="Concentrated solution (Cells becoming flaccid)" />
        
        
        <circle cx="465" cy="277" r="5" class="data-point" data-m="1.0 M" data-change="-18%" data-state="Highly hypertonic (Plasmolysed / Flaccid)" />
      </g>
    </svg>
  </div>

  <div class="status-bar" id="statusBar">
    <div class="status-dot" id="statusDot"></div>
    <span id="statusText">Hover or tap any point to inspect osmosis data</span>
  </div>

  <script>
    const points = document.querySelectorAll('.data-point, .intercept-point');
    const statusText = document.getElementById('statusText');
    const statusDot = document.getElementById('statusDot');

    points.forEach(pt => {
      const showData = () => {
        points.forEach(p => p.classList.remove('active'));
        pt.classList.add('active');
        const conc = pt.getAttribute('data-m');
        const change = pt.getAttribute('data-change');
        const state = pt.getAttribute('data-state');
        
        statusText.innerHTML = `<strong>${conc}</strong>: ${change} mass → <em>${state}</em>`;
        if (change.startsWith('+')) {
          statusDot.style.background = '#0284c7';
        } else if (change === '0%') {
          statusDot.style.background = '#16a34a';
        } else {
          statusDot.style.background = '#e11d48';
        }
      };

      pt.addEventListener('click', showData);
      pt.addEventListener('mouseenter', showData);
    });
  </script>
</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
      color: #1e2945;
      background: transparent;
      width: 100%;
      user-select: none;
      -webkit-user-select: none;
    }
    .diagram-wrap {
      display: flex;
      flex-direction: column;
      gap: 8px;
      width: 100%;
      max-width: 620px;
      margin: 0 auto;
      padding: 6px;
    }

    /* Dedicated Header Section to prevent particle overlap */
    .header-bar {
      display: grid;
      grid-template-columns: 1fr auto 1fr;
      gap: 6px;
      align-items: stretch;
      width: 100%;
    }
    .solution-card {
      padding: 6px 8px;
      border-radius: 8px;
      border: 1px solid #cbd5e1;
      display: flex;
      flex-direction: column;
      justify-content: center;
      min-width: 0;
    }
    .dilute-card {
      background: #e0f2fe;
      border-color: #bae6fd;
      text-align: left;
    }
    .conc-card {
      background: #ede9fe;
      border-color: #ddd6fe;
      text-align: right;
    }
    .sol-title {
      font-size: 13px;
      font-weight: 700;
      line-height: 1.25;
      word-break: normal;
      overflow-wrap: break-word;
    }
    .sol-sub {
      font-size: 11px;
      font-weight: 600;
      color: #475569;
      line-height: 1.2;
      margin-top: 2px;
      word-break: normal;
      overflow-wrap: break-word;
    }

    .membrane-badge {
      background: #ffffff;
      border: 1px solid #94a3b8;
      padding: 4px 6px;
      border-radius: 6px;
      font-size: 10px;
      font-weight: 700;
      text-align: center;
      line-height: 1.2;
      color: #334155;
      box-shadow: 0 1px 3px rgba(0,0,0,0.06);
      max-width: 90px;
      display: flex;
      align-items: center;
      justify-content: center;
    }

    /* Chambers Simulation Area */
    .chamber-frame {
      position: relative;
      width: 100%;
      height: 250px;
      border-radius: 10px;
      overflow: hidden;
      display: flex;
      border: 1px solid #94a3b8;
      background: #ffffff;
    }
    .chamber-half {
      flex: 1;
      height: 100%;
    }
    .dilute-bg {
      background: #f0f9ff;
    }
    .conc-bg {
      background: #f5f3ff;
    }

    /* Net Movement Banner at Bottom */
    .net-arrow-badge {
      position: absolute;
      bottom: 10px;
      left: 50%;
      transform: translateX(-50%);
      background: #0284c7;
      color: #ffffff;
      padding: 4px 12px;
      border-radius: 16px;
      font-size: 11px;
      font-weight: 700;
      letter-spacing: 0.2px;
      z-index: 4;
      display: flex;
      align-items: center;
      gap: 6px;
      box-shadow: 0 2px 6px rgba(2, 132, 199, 0.35);
      white-space: nowrap;
      pointer-events: none;
    }
    .net-arrow-badge .arrow-anim {
      display: inline-block;
      animation: nudge 1.6s infinite ease-in-out;
    }
    @keyframes nudge {
      0%, 100% { transform: translateX(0); }
      50% { transform: translateX(4px); }
    }

    canvas {
      position: absolute;
      inset: 0;
      width: 100%;
      height: 100%;
      z-index: 2;
      pointer-events: none;
    }

    /* Legend & Controls */
    .footer-bar {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      justify-content: space-between;
      gap: 8px;
      padding: 2px 0;
    }
    .legend {
      display: flex;
      flex-wrap: wrap;
      align-items: center;
      gap: 10px;
      font-size: 11px;
      font-weight: 600;
    }
    .legend-item {
      display: flex;
      align-items: center;
      gap: 5px;
    }
    .dot-water {
      width: 8px;
      height: 8px;
      border-radius: 50%;
      background: #0284c7;
      border: 1px solid #0369a1;
    }
    .dot-sugar {
      width: 14px;
      height: 14px;
      border-radius: 50%;
      background: #7c3aed;
      border: 1px solid #6d28d9;
    }
    .pore-icon {
      display: inline-block;
      width: 3px;
      height: 10px;
      border-left: 2px dashed #64748b;
    }
    .controls {
      display: flex;
      gap: 6px;
    }
    .btn {
      background: #f8fafc;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      padding: 4px 10px;
      border-radius: 6px;
      font-size: 11px;
      font-weight: 600;
      cursor: pointer;
      display: inline-flex;
      align-items: center;
      gap: 4px;
      transition: background-color 0.25s ease, border-color 0.25s ease, color 0.25s ease;
    }
    .btn:hover {
      background: #f1f5f9;
      border-color: #94a3b8;
    }
    .btn:active {
      background: #e2e8f0;
    }

    @media (max-width: 480px) {
      .header-bar {
        gap: 4px;
      }
      .solution-card {
        padding: 4px 6px;
      }
      .sol-title {
        font-size: 11px;
        line-height: 1.15;
      }
      .sol-sub {
        font-size: 9.5px;
        line-height: 1.15;
        margin-top: 1px;
      }
      .membrane-badge {
        font-size: 8.5px;
        padding: 3px 4px;
        max-width: 72px;
        line-height: 1.1;
      }
      .chamber-frame {
        height: 220px;
      }
      .net-arrow-badge {
        font-size: 10px;
        padding: 3px 10px;
      }
      .legend {
        font-size: 10px;
        gap: 8px;
      }
      .btn {
        font-size: 10px;
        padding: 3px 8px;
      }
    }
  </style>
</head>
<body>

<div class="diagram-wrap">
  
  <div class="header-bar">
    <div class="solution-card dilute-card">
      <div class="sol-title">Dilute solution</div>
      <div class="sol-sub">High water potential</div>
    </div>
    <div class="membrane-badge">
      Partially permeable membrane
    </div>
    <div class="solution-card conc-card">
      <div class="sol-title">Concentrated solution</div>
      <div class="sol-sub">Low water potential</div>
    </div>
  </div>

  
  <div class="chamber-frame" id="chamber">
    <div class="chamber-half dilute-bg"></div>
    <div class="chamber-half conc-bg"></div>

    
    <div class="net-arrow-badge">
      <span>Net water movement</span>
      <span class="arrow-anim">➔</span>
    </div>

    
    <canvas id="simCanvas"></canvas>
  </div>

  
  <div class="footer-bar">
    <div class="legend">
      <div class="legend-item">
        <span class="dot-water"></span>
        <span>Water (small)</span>
      </div>
      <div class="legend-item">
        <span class="dot-sugar"></span>
        <span>Sucrose (large)</span>
      </div>
      <div class="legend-item">
        <span class="pore-icon"></span>
        <span>Pore</span>
      </div>
    </div>
    <div class="controls">
      <button class="btn" id="toggleBtn" aria-label="Pause or play simulation">⏸ Pause</button>
      <button class="btn" id="resetBtn" aria-label="Reset simulation">↺ Reset</button>
    </div>
  </div>
</div>

<script>
(function() {
  const canvas = document.getElementById('simCanvas');
  const ctx = canvas.getContext('2d');
  const frame = document.getElementById('chamber');
  const toggleBtn = document.getElementById('toggleBtn');
  const resetBtn = document.getElementById('resetBtn');

  let width = 0;
  let height = 0;
  let running = true;
  let particles = [];

  const PORE_SPACING = 30;
  const PORE_GAP = 14; 
  const WATER_RADIUS = 4.2;
  const SUCROSE_RADIUS = 9.5;

  function resize() {
    const rect = frame.getBoundingClientRect();
    const dpr = window.devicePixelRatio || 1;
    width = rect.width;
    height = rect.height;
    canvas.width = width * dpr;
    canvas.height = height * dpr;
    ctx.resetTransform?.();
    ctx.scale(dpr, dpr);
  }

  function initParticles() {
    particles = [];
    const midX = width / 2;

    // Left side (Dilute): High water concentration, low sucrose
    const leftWaterCount = 38;
    const leftSucroseCount = 2;

    // Right side (Concentrated): Low water concentration, high sucrose
    const rightWaterCount = 12;
    const rightSucroseCount = 8;

    // Slower, smooth speeds to prevent jitter and flicker
    const createParticle = (type, minX, maxX) => {
      const isWater = type === 'water';
      const r = isWater ? WATER_RADIUS : SUCROSE_RADIUS;
      const speed = isWater ? (0.55 + Math.random() * 0.25) : (0.25 + Math.random() * 0.15);
      const angle = Math.random() * Math.PI * 2;
      return {
        type: type,
        radius: r,
        x: minX + r + Math.random() * Math.max(10, (maxX - minX - 2 * r)),
        y: 12 + r + Math.random() * Math.max(10, (height - 45 - 2 * r)),
        vx: Math.cos(angle) * speed,
        vy: Math.sin(angle) * speed,
        color: isWater ? '#0284c7' : '#7c3aed',
        stroke: isWater ? '#0369a1' : '#5b21b6'
      };
    };

    for (let i = 0; i < leftWaterCount; i++) {
      particles.push(createParticle('water', 6, midX - 8));
    }
    for (let i = 0; i < leftSucroseCount; i++) {
      particles.push(createParticle('sucrose', 12, midX - 16));
    }
    for (let i = 0; i < rightWaterCount; i++) {
      particles.push(createParticle('water', midX + 8, width - 6));
    }
    for (let i = 0; i < rightSucroseCount; i++) {
      particles.push(createParticle('sucrose', midX + 16, width - 12));
    }
  }

  function isInsidePore(y) {
    const relY = ((y % PORE_SPACING) + PORE_SPACING) % PORE_SPACING;
    return relY < PORE_GAP;
  }

  function update() {
    const midX = width / 2;
    const topLimit = 6;
    const bottomLimit = height - 34; // leave buffer above the bottom badge

    for (let p of particles) {
      const prevX = p.x;
      p.x += p.vx;
      p.y += p.vy;

      // Outer boundary bounces
      if (p.x - p.radius < 4) {
        p.x = 4 + p.radius;
        p.vx = Math.abs(p.vx);
      } else if (p.x + p.radius > width - 4) {
        p.x = width - 4 - p.radius;
        p.vx = -Math.abs(p.vx);
      }

      if (p.y - p.radius < topLimit) {
        p.y = topLimit + p.radius;
        p.vy = Math.abs(p.vy);
      } else if (p.y + p.radius > bottomLimit) {
        p.y = bottomLimit - p.radius;
        p.vy = -Math.abs(p.vy);
      }

      // Membrane interaction at midX
      const crossingFromLeft = prevX <= midX && p.x + p.radius >= midX;
      const crossingFromRight = prevX >= midX && p.x - p.radius <= midX;

      if (crossingFromLeft || crossingFromRight) {
        if (p.type === 'sucrose') {
          // Large sucrose molecule bounces back
          if (crossingFromLeft) {
            p.x = midX - p.radius;
            p.vx = -Math.abs(p.vx);
          } else {
            p.x = midX + p.radius;
            p.vx = Math.abs(p.vx);
          }
        } else {
          // Small water molecule can pass through pores
          if (!isInsidePore(p.y)) {
            // Hits membrane solid segment
            if (crossingFromLeft) {
              p.x = midX - p.radius;
              p.vx = -Math.abs(p.vx);
            } else {
              p.x = midX + p.radius;
              p.vx = Math.abs(p.vx);
            }
          }
        }
      }
    }
  }

  function draw() {
    ctx.clearRect(0, 0, width, height);

    const midX = width / 2;

    // Draw Partially Permeable Membrane Structure
    ctx.lineWidth = 3.5;
    ctx.strokeStyle = '#64748b';
    ctx.lineCap = 'round';

    for (let y = 0; y < height; y += PORE_SPACING) {
      ctx.beginPath();
      ctx.moveTo(midX, y + PORE_GAP);
      ctx.lineTo(midX, y + PORE_SPACING);
      ctx.stroke();
    }

    // Draw Particles
    for (const p of particles) {
      ctx.beginPath();
      ctx.arc(p.x, p.y, p.radius, 0, Math.PI * 2);
      ctx.fillStyle = p.color;
      ctx.fill();
      ctx.lineWidth = 1;
      ctx.strokeStyle = p.stroke;
      ctx.stroke();

      // Subtle gloss highlight
      ctx.beginPath();
      ctx.arc(p.x - p.radius * 0.32, p.y - p.radius * 0.32, p.radius * 0.28, 0, Math.PI * 2);
      ctx.fillStyle = 'rgba(255,255,255,0.45)';
      ctx.fill();
    }
  }

  function loop() {
    if (running) {
      update();
    }
    draw();
    requestAnimationFrame(loop);
  }

  // Event Listeners
  window.addEventListener('resize', () => {
    resize();
    initParticles();
  });

  toggleBtn.addEventListener('click', () => {
    running = !running;
    toggleBtn.textContent = running ? '⏸ Pause' : '▶ Play';
  });

  resetBtn.addEventListener('click', () => {
    initParticles();
  });

  // Init
  resize();
  initParticles();
  requestAnimationFrame(loop);
})();
</script>

</body>
</html>

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta name="aspect-ratio" content="4:3">
  <style>
    * { box-sizing: border-box; margin: 0; padding: 0; }
    body {
      font-family: system-ui, -apple-system, sans-serif;
      background: #ffffff;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      gap: 10px;
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    /* Variable Callouts */
    .vars-bar {
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      padding: 6px 8px;
      font-size: 11px;
      line-height: 1.25;
      text-align: center;
      border: 1px solid #e2e8f0;
      background: #f8fafc;
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    .var-pill strong {
      display: block;
      font-size: 10px;
      text-transform: uppercase;
      letter-spacing: 0.4px;
      margin-bottom: 2px;
    }
    .var-pill.iv strong { color: #0284c7; }
    .var-pill.dv strong { color: #16a34a; }
    .var-pill.cv strong { color: #7c3aed; }
    
    /* Navigation / Tabs */
    .stepper-nav {
      display: flex;
      gap: 6px;
    }
    .step-btn {
      flex: 1;
      padding: 6px 4px;
      border: 1px solid #e2e8f0;
      background: #f8fafc;
      border-radius: 6px;
      font-size: 12px;
      font-weight: 600;
      color: #64748b;
      cursor: pointer;
      display: flex;
      align-items: center;
      justify-content: center;
      gap: 4px;
      box-shadow: none;
      transition: background-color 0.2s, color 0.2s, border-color 0.2s;
    }
    .step-btn.active {
      background: #e0f2fe;
      color: #0369a1;
      border-color: #38bdf8;
    }

    /* Stage Container */
    .stage {
      position: relative;
      height: 230px;
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 10px;
      overflow: hidden;
    }
    .step-view {
      position: absolute;
      inset: 0;
      opacity: 0;
      pointer-events: none;
      transition: opacity 0.3s ease;
      display: flex;
      align-items: center;
      justify-content: center;
    }
    .step-view.active {
      opacity: 1;
      pointer-events: auto;
    }

    svg text {
      user-select: none;
      font-family: system-ui, -apple-system, sans-serif;
    }

    /* Bottom playback bar */
    .controls {
      display: flex;
      align-items: center;
      justify-content: space-between;
      padding: 0 4px;
    }
    .play-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #334155;
      border-radius: 6px;
      padding: 4px 10px;
      font-size: 12px;
      font-weight: 600;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
    }
    .step-label {
      font-size: 12px;
      font-weight: 600;
      color: #475569;
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    @media (max-width: 480px) {
      .vars-bar { grid-template-columns: 1fr; gap: 4px; }
      .var-pill { font-size: 10px; padding: 4px 6px; }
      .stage { height: 210px; }
      .step-btn { font-size: 11px; padding: 5px 2px; }
    }
  </style>
</head>
<body>

  
  <div class="vars-bar">
    <div class="var-pill iv">
      <strong>Independent</strong>
      Sucrose Conc. (0.0–1.0 M)
    </div>
    <div class="var-pill dv">
      <strong>Dependent</strong>
      Change in Mass (%)
    </div>
    <div class="var-pill cv">
      <strong>Controls</strong>
      Length (30mm), Diameter, 24h
    </div>
  </div>

  
  <div class="stepper-nav">
    <button class="step-btn active" data-step="0">1. Cut & Trim</button>
    <button class="step-btn" data-step="1">2. Initial Mass</button>
    <button class="step-btn" data-step="2">3. Osmosis (24h)</button>
    <button class="step-btn" data-step="3">4. Blot & Reweigh</button>
  </div>

  
  <div class="stage">

    
    <div class="step-view active" id="view0">
      <svg viewBox="0 0 420 220" width="100%" height="100%">
        
        <path d="M 40 80 Q 70 40 120 50 Q 170 60 175 110 Q 180 160 130 170 Q 70 180 45 140 Z" fill="#d4a373" stroke="#b07d50" stroke-width="2.5"/>
        <circle cx="110" cy="110" r="10" fill="#fefae0" stroke="#b07d50" stroke-width="1.5" stroke-dasharray="3 3"/>
        
        
        <rect x="95" y="15" width="30" height="70" rx="3" fill="#cbd5e1" stroke="#64748b" stroke-width="2"/>
        <rect x="80" y="8" width="60" height="10" rx="3" fill="#94a3b8" stroke="#475569" stroke-width="2"/>
        <text x="110" y="3" text-anchor="middle" font-size="11" font-weight="700" fill="#475569">Cork Borer</text>
        
        
        <rect x="220" y="85" width="140" height="24" rx="4" fill="#faedcd" stroke="#d4a373" stroke-width="2"/>
        
        
        <rect x="220" y="115" width="160" height="28" fill="#fef08a" stroke="#ca8a04" stroke-width="1.5" rx="2"/>
        
        <line x1="220" y1="115" x2="220" y2="128" stroke="#854d0e" stroke-width="1.5"/>
        <line x1="260" y1="115" x2="260" y2="123" stroke="#854d0e" stroke-width="1"/>
        <line x1="300" y1="115" x2="300" y2="123" stroke="#854d0e" stroke-width="1"/>
        <line x1="340" y1="115" x2="340" y2="128" stroke="#854d0e" stroke-width="1.5"/>
        <text x="220" y="138" font-size="9" fill="#854d0e" text-anchor="middle">0</text>
        <text x="260" y="138" font-size="9" fill="#854d0e" text-anchor="middle">10</text>
        <text x="300" y="138" font-size="9" fill="#854d0e" text-anchor="middle">20</text>
        <text x="340" y="138" font-size="9" fill="#854d0e" text-anchor="middle">30 mm</text>

        
        <line x1="340" y1="65" x2="340" y2="112" stroke="#ef4444" stroke-width="2" stroke-dasharray="4 3"/>
        <polygon points="340,65 355,50 348,45 335,62" fill="#94a3b8" stroke="#475569" stroke-width="1"/>
        
        
        <line x1="220" y1="75" x2="340" y2="75" stroke="#0284c7" stroke-width="1.5"/>
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        <polygon points="340,75 335,72 335,78" fill="#0284c7"/>
        <text x="280" y="70" text-anchor="middle" font-size="12" font-weight="700" fill="#0284c7">Trim to 30 mm</text>
      </svg>
    </div>

    
    <div class="step-view" id="view1">
      <svg viewBox="0 0 420 220" width="100%" height="100%">
        
        <rect x="110" y="70" width="200" height="110" rx="12" fill="#e2e8f0" stroke="#94a3b8" stroke-width="2.5"/>
        
        <ellipse cx="210" cy="65" rx="75" ry="12" fill="#cbd5e1" stroke="#64748b" stroke-width="2"/>
        
        
        <rect x="160" y="50" width="100" height="16" rx="4" fill="#faedcd" stroke="#d4a373" stroke-width="2"/>
        
        
        <rect x="140" y="110" width="140" height="46" rx="5" fill="#0f172a" stroke="#334155" stroke-width="2"/>
        <text x="235" y="142" font-size="24" font-weight="700" fill="#38bdf8" text-anchor="end" font-family="monospace">2.45</text>
        <text x="245" y="142" font-size="16" font-weight="600" fill="#38bdf8">g</text>
        <text x="148" y="124" font-size="9" fill="#22c55e">STABLE [0.00g TARE]</text>

        
        <text x="210" y="198" text-anchor="middle" font-size="13" font-weight="700" fill="#0f172a">Record Initial Mass (g)</text>
      </svg>
    </div>

    
    <div class="step-view" id="view2">
      <svg viewBox="0 0 420 220" width="100%" height="100%">
        
        <rect x="35" y="145" width="350" height="12" fill="#e2e8f0" stroke="#94a3b8" stroke-width="1.5" rx="2"/>
        <rect x="35" y="65" width="350" height="10" fill="#e2e8f0" stroke="#94a3b8" stroke-width="1.5" rx="2"/>
        <rect x="45" y="75" width="10" height="70" fill="#cbd5e1"/>
        <rect x="365" y="75" width="10" height="70" fill="#cbd5e1"/>

        
        <rect x="65" y="40" width="34" height="110" rx="14" fill="#f0f9ff" stroke="#64748b" stroke-width="2"/>
        <path d="M 66 85 Q 82 83 100 85 L 100 136 A 14 14 0 0 1 66 136 Z" fill="#bae6fd" opacity="0.85"/>
        <rect x="77" y="95" width="12" height="40" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1.5"/>
        <rect x="62" y="162" width="40" height="22" rx="4" fill="#e0f2fe" stroke="#38bdf8"/>
        <text x="82" y="177" font-size="11" font-weight="700" fill="#0369a1" text-anchor="middle">0.0 M</text>

        
        <rect x="130" y="40" width="34" height="110" rx="14" fill="#f0f9ff" stroke="#64748b" stroke-width="2"/>
        <path d="M 131 85 Q 147 83 165 85 L 165 136 A 14 14 0 0 1 131 136 Z" fill="#93c5fd" opacity="0.85"/>
        <rect x="142" y="95" width="12" height="40" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1.5"/>
        <rect x="127" y="162" width="40" height="22" rx="4" fill="#f1f5f9" stroke="#cbd5e1"/>
        <text x="147" y="177" font-size="11" font-weight="700" fill="#475569" text-anchor="middle">0.2 M</text>

        
        <rect x="195" y="40" width="34" height="110" rx="14" fill="#f0f9ff" stroke="#64748b" stroke-width="2"/>
        <path d="M 196 85 Q 212 83 230 85 L 230 136 A 14 14 0 0 1 196 136 Z" fill="#60a5fa" opacity="0.85"/>
        <rect x="207" y="95" width="12" height="40" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1.5"/>
        <rect x="192" y="162" width="40" height="22" rx="4" fill="#f1f5f9" stroke="#cbd5e1"/>
        <text x="212" y="177" font-size="11" font-weight="700" fill="#475569" text-anchor="middle">0.4 M</text>

        
        <rect x="260" y="40" width="34" height="110" rx="14" fill="#f0f9ff" stroke="#64748b" stroke-width="2"/>
        <path d="M 261 85 Q 277 83 295 85 L 295 136 A 14 14 0 0 1 261 136 Z" fill="#3b82f6" opacity="0.85"/>
        <rect x="271" y="95" width="12" height="40" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1.5"/>
        <rect x="257" y="162" width="40" height="22" rx="4" fill="#f1f5f9" stroke="#cbd5e1"/>
        <text x="277" y="177" font-size="11" font-weight="700" fill="#475569" text-anchor="middle">0.8 M</text>

        
        <rect x="325" y="40" width="34" height="110" rx="14" fill="#f0f9ff" stroke="#64748b" stroke-width="2"/>
        <path d="M 326 85 Q 342 83 360 85 L 360 136 A 14 14 0 0 1 326 136 Z" fill="#2563eb" opacity="0.85"/>
        <rect x="336" y="95" width="12" height="40" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1.5"/>
        <rect x="322" y="162" width="40" height="22" rx="4" fill="#fef2f2" stroke="#f87171"/>
        <text x="342" y="177" font-size="11" font-weight="700" fill="#dc2626" text-anchor="middle">1.0 M</text>

        <text x="210" y="25" text-anchor="middle" font-size="12" font-weight="700" fill="#0f172a">Submerge in Sucrose Solutions (24h)</text>
      </svg>
    </div>

    
    <div class="step-view" id="view3">
      <svg viewBox="0 0 420 220" width="100%" height="100%">
        
        <polygon points="50,140 180,120 230,165 100,185" fill="#f1f5f9" stroke="#cbd5e1" stroke-width="2"/>
        <path d="M 70 145 L 170 130 M 90 160 L 190 145" stroke="#e2e8f0" stroke-width="2" stroke-dasharray="6 4"/>
        
        
        <g transform="translate(110, 120)">
          <rect x="0" y="0" width="80" height="22" rx="6" fill="#faedcd" stroke="#d4a373" stroke-width="2"/>
          
          <path d="M 40 -12 C 55 -12, 65 -2, 55 8" fill="none" stroke="#0284c7" stroke-width="2"/>
          <polygon points="58,11 50,8 57,3" fill="#0284c7"/>
          
          <circle cx="15" cy="30" r="3" fill="#38bdf8"/>
          <circle cx="35" cy="34" r="2" fill="#38bdf8"/>
          <circle cx="65" cy="28" r="2.5" fill="#38bdf8"/>
        </g>
        
        <text x="130" y="75" text-anchor="middle" font-size="12" font-weight="700" fill="#0369a1">Gently Blot Excess Surface Water</text>
        <text x="130" y="92" text-anchor="middle" font-size="10" fill="#64748b">(Do not squeeze!)</text>

        
        <path d="M 235 110 L 275 110" stroke="#94a3b8" stroke-width="2" stroke-dasharray="4 3"/>
        <polygon points="280,110 272,106 272,114" fill="#94a3b8"/>

        
        <g transform="translate(290, 75)">
          <rect x="0" y="25" width="100" height="50" rx="6" fill="#e2e8f0" stroke="#94a3b8" stroke-width="1.5"/>
          <ellipse cx="50" cy="22" rx="40" ry="7" fill="#cbd5e1" stroke="#64748b" stroke-width="1.5"/>
          <rect x="25" y="14" width="50" height="10" rx="3" fill="#faedcd" stroke="#d4a373" stroke-width="1"/>
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          <text x="65" y="61" font-size="12" font-weight="700" fill="#4ade80" font-family="monospace" text-anchor="end">Final g</text>
          <text x="50" y="92" font-size="11" font-weight="700" fill="#16a34a" text-anchor="middle">Calculate %Δ</text>
        </g>
      </svg>
    </div>

  </div>

  
  <div class="controls">
    <button class="play-btn" id="toggleBtn">⏸ Pause</button>
    <span class="step-label" id="stepIndicator">Step 1 of 4</span>
  </div>

  <script>
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    const views = document.querySelectorAll('.step-view');
    const toggleBtn = document.getElementById('toggleBtn');
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      playing = true;
      toggleBtn.textContent = '⏸ Pause';
    }

    function stopTimer() {
      clearInterval(timer);
      playing = false;
      toggleBtn.textContent = '▶ Play';
    }

    buttons.forEach((btn) => {
      btn.addEventListener('click', () => {
        stopTimer();
        setStep(parseInt(btn.dataset.step, 10));
      });
    });

    toggleBtn.addEventListener('click', () => {
      if (playing) {
        stopTimer();
      } else {
        nextStep();
        startTimer();
      }
    });

    startTimer();
  </script>
</body>
</html>

UK-GCSE-SCIENCE-BIO-TS-01-01

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