<!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: #ffffff;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      gap: 10px;
      user-select: none;
    }

    .header-panel {
      width: 100%;
      max-width: 580px;
      display: flex;
      flex-wrap: wrap;
      justify-content: space-between;
      align-items: center;
      gap: 8px;
    }

    .generator-card {
      background: #f8fafc;
      border: 1px solid #e2e8f0;
      border-radius: 12px;
      padding: 8px 14px;
      display: flex;
      align-items: center;
      gap: 12px;
      font-size: 14px;
      font-weight: 600;
    }

    .coord-display {
      font-family: ui-monospace, SFMono-Regular, Menlo, monospace;
      background: #ffffff;
      border: 1.5px solid #22b7ff;
      color: #0284c7;
      padding: 3px 8px;
      border-radius: 6px;
      font-size: 15px;
      letter-spacing: 0.5px;
      min-width: 72px;
      text-align: center;
    }

    .count-badge {
      background: #ecfdf5;
      border: 1px solid #a7f3d0;
      color: #065f46;
      padding: 3px 8px;
      border-radius: 6px;
      font-size: 13px;
    }

    .controls {
      display: flex;
      gap: 6px;
      align-items: center;
    }

    .step-btn {
      background: #f1f5f9;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 12px;
      border-radius: 8px;
      cursor: pointer;
      transition: background 0.2s, border-color 0.2s;
    }

    .step-btn.active {
      background: #22b7ff;
      border-color: #0284c7;
      color: #ffffff;
    }

    .play-btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      font-size: 13px;
      font-weight: 600;
      padding: 6px 10px;
      border-radius: 8px;
      cursor: pointer;
    }

    .diagram-stage {
      width: 100%;
      max-width: 480px;
      aspect-ratio: 1 / 1;
      position: relative;
    }

    svg {
      width: 100%;
      height: 100%;
      display: block;
      overflow: visible;
    }

    .axis-tape {
      fill: #fef3c7;
      stroke: #d97706;
      stroke-width: 1;
    }

    .axis-tick {
      stroke: #78350f;
      stroke-width: 1.5;
    }

    .axis-num {
      font-size: 11px;
      font-weight: 700;
      fill: #1e2945;
      font-family: system-ui, sans-serif;
    }

    .proj-line {
      stroke: #22b7ff;
      stroke-width: 2;
      stroke-dasharray: 4 3;
      transition: opacity 0.4s ease;
    }

    .quadrat-box {
      fill: rgba(34, 183, 255, 0.18);
      stroke: #0284c7;
      stroke-width: 2.5;
      rx: 3px;
      transition: all 0.7s cubic-bezier(0.34, 1.2, 0.64, 1);
    }

    .dandelion {
      font-size: 15px;
      transform-origin: center;
      transition: transform 0.3s ease;
      cursor: default;
    }

    .dandelion-highlight {
      filter: drop-shadow(0 0 4px #fbbf24);
    }

    .target-dot {
      fill: #22b7ff;
      stroke: #ffffff;
      stroke-width: 2;
      transition: all 0.5s ease;
    }

    .corner-label {
      font-size: 12px;
      font-weight: 700;
      fill: #0284c7;
      background: white;
    }
  </style>
</head>
<body>

  <div class="header-panel">
    <div class="generator-card">
      <span>Random (X, Y):</span>
      <span id="coordText" class="coord-display">(3, 6)</span>
      <span id="countBadge" class="count-badge">🌼 5 counted</span>
    </div>

    <div class="controls">
      <button class="step-btn active" id="btn1" onclick="setStep(0)">Sample 1 (3,6)</button>
      <button class="step-btn" id="btn2" onclick="setStep(1)">Sample 2 (7,2)</button>
      <button class="play-btn" id="playBtn" onclick="togglePlay()">⏸</button>
    </div>
  </div>

  <div class="diagram-stage">
    <svg viewBox="0 0 470 470">
      <defs>
        
        <pattern id="quadratSubgrid" width="12.5" height="12.5" patternUnits="userSpaceOnUse">
          <path d="M 12.5 0 L 0 0 0 12.5" fill="none" stroke="#22b7ff" stroke-width="0.75" stroke-opacity="0.6"/>
        </pattern>
      </defs>

      
      <rect x="50" y="20" width="400" height="400" fill="#f0fdf4" stroke="#86efac" stroke-width="1.5" rx="4"/>

      
      <g stroke="#bbf7d0" stroke-width="1">
        
        <line x1="100" y1="20" x2="100" y2="420" />
        <line x1="150" y1="20" x2="150" y2="420" />
        <line x1="200" y1="20" x2="200" y2="420" />
        <line x1="250" y1="20" x2="250" y2="420" />
        <line x1="300" y1="20" x2="300" y2="420" />
        <line x1="350" y1="20" x2="350" y2="420" />
        <line x1="400" y1="20" x2="400" y2="420" />
        
        
        <line x1="50" y1="370" x2="450" y2="370" />
        <line x1="50" y1="320" x2="450" y2="320" />
        <line x1="50" y1="270" x2="450" y2="270" />
        <line x1="50" y1="220" x2="450" y2="220" />
        <line x1="50" y1="170" x2="450" y2="170" />
        <line x1="50" y1="120" x2="450" y2="120" />
        <line x1="50" y1="70"  x2="450" y2="70"  />
      </g>

      
      
      <text x="72" y="95" class="dandelion">🌼</text>
      <text x="120" y="240" class="dandelion">🌼</text>
      <text x="175" y="380" class="dandelion">🌼</text>
      <text x="220" y="160" class="dandelion">🌼</text>
      <text x="270" y="340" class="dandelion">🌼</text>
      <text x="320" y="80" class="dandelion">🌼</text>
      <text x="365" y="220" class="dandelion">🌼</text>
      <text x="420" y="130" class="dandelion">🌼</text>
      <text x="110" y="310" class="dandelion">🌼</text>
      <text x="280" y="210" class="dandelion">🌼</text>

      
      <g id="dandelionsS1">
        <text x="206" y="92" class="dandelion dandelion-highlight">🌼</text>
        <text x="232" y="88" class="dandelion dandelion-highlight">🌼</text>
        <text x="212" y="112" class="dandelion dandelion-highlight">🌼</text>
        <text x="236" y="114" class="dandelion dandelion-highlight">🌼</text>
        <text x="222" y="100" class="dandelion dandelion-highlight">🌼</text>
      </g>

      
      <g id="dandelionsS2" opacity="0.4">
        <text x="408" y="295" class="dandelion">🌼</text>
        <text x="432" y="290" class="dandelion">🌼</text>
        <text x="418" y="312" class="dandelion">🌼</text>
      </g>

      
      
      <line id="projX" class="proj-line" x1="200" y1="120" x2="200" y2="428" />
      
      <line id="projY" class="proj-line" x1="200" y1="120" x2="42" y2="120" />

      
      <rect id="ghostQuadrat" x="200" y="70" width="50" height="50" fill="none" stroke="#94a3b8" stroke-width="1.5" stroke-dasharray="3 3" opacity="0" rx="3"/>

      
      <g id="activeQuadratGroup">
        <rect id="quadratBox" class="quadrat-box" x="200" y="70" width="50" height="50" />
        <rect id="quadratWire" x="200" y="70" width="50" height="50" fill="url(#quadratSubgrid)" pointer-events="none" />
        <circle id="targetDot" class="target-dot" cx="200" cy="120" r="4.5" />
        <text id="coordLabel" class="corner-label" x="206" y="136">(3, 6)</text>
      </g>

      
      <g id="yAxis">
        <rect x="24" y="20" width="18" height="400" class="axis-tape" rx="2"/>
        <text x="14" y="225" font-size="11" font-weight="700" fill="#78350f" text-anchor="middle" transform="rotate(-90 14 225)">Y Tape (m)</text>
        
        
        
        <line x1="34" y1="420" x2="42" y2="420" class="axis-tick" />
        <text x="30" y="423" class="axis-num" text-anchor="end">0</text>
        
        
        <line x1="36" y1="370" x2="42" y2="370" class="axis-tick" />
        <text x="32" y="373" class="axis-num" text-anchor="end">1</text>
        
        
        <line x1="34" y1="320" x2="42" y2="320" class="axis-tick" />
        <text x="32" y="323" class="axis-num" text-anchor="end">2</text>
        
        
        <line x1="36" y1="270" x2="42" y2="270" class="axis-tick" />
        <text x="32" y="273" class="axis-num" text-anchor="end">3</text>
        
        
        <line x1="34" y1="220" x2="42" y2="220" class="axis-tick" />
        <text x="32" y="223" class="axis-num" text-anchor="end">4</text>
        
        
        <line x1="36" y1="170" x2="42" y2="170" class="axis-tick" />
        <text x="32" y="173" class="axis-num" text-anchor="end">5</text>
        
        
        <line x1="34" y1="120" x2="42" y2="120" class="axis-tick" stroke="#0284c7" stroke-width="2.5" />
        <text x="32" y="123" class="axis-num" text-anchor="end" fill="#0284c7">6</text>
        
        
        <line x1="36" y1="70" x2="42" y2="70" class="axis-tick" />
        <text x="32" y="73" class="axis-num" text-anchor="end">7</text>
        
        
        <line x1="34" y1="20" x2="42" y2="20" class="axis-tick" />
        <text x="32" y="24" class="axis-num" text-anchor="end">8</text>
      </g>

      
      <g id="xAxis">
        <rect x="50" y="428" width="400" height="18" class="axis-tape" rx="2"/>
        <text x="250" y="460" font-size="11" font-weight="700" fill="#78350f" text-anchor="middle">X Tape (m)</text>
        
        
        
        <line x1="50" y1="428" x2="50" y2="436" class="axis-tick" />
        <text x="50" y="443" class="axis-num" text-anchor="middle">0</text>
        
        
        <line x1="100" y1="428" x2="100" y2="434" class="axis-tick" />
        <text x="100" y="443" class="axis-num" text-anchor="middle">1</text>
        
        
        <line x1="150" y1="428" x2="150" y2="434" class="axis-tick" />
        <text x="150" y="443" class="axis-num" text-anchor="middle">2</text>
        
        
        <line x1="200" y1="428" x2="200" y2="436" class="axis-tick" stroke="#0284c7" stroke-width="2.5" />
        <text x="200" y="443" class="axis-num" text-anchor="middle" fill="#0284c7">3</text>
        
        
        <line x1="250" y1="428" x2="250" y2="434" class="axis-tick" />
        <text x="250" y="443" class="axis-num" text-anchor="middle">4</text>
        
        
        <line x1="300" y1="428" x2="300" y2="434" class="axis-tick" />
        <text x="300" y="443" class="axis-num" text-anchor="middle">5</text>
        
        
        <line x1="350" y1="428" x2="350" y2="434" class="axis-tick" />
        <text x="350" y="443" class="axis-num" text-anchor="middle">6</text>
        
        
        <line x1="400" y1="428" x2="400" y2="436" class="axis-tick" />
        <text x="400" y="443" class="axis-num" text-anchor="middle">7</text>
        
        
        <line x1="450" y1="428" x2="450" y2="436" class="axis-tick" />
        <text x="450" y="443" class="axis-num" text-anchor="middle">8</text>
      </g>
    </svg>
  </div>

  <script>
    const steps = [
      {
        coord: '(3, 6)',
        count: '🌼 5 counted',
        xVal: 3,
        yVal: 6,
        // SVG corner (x=3 -> 200, y=6 -> 120 from bottom = 420-300 = 120)
        // Quadrat spans x:[200, 250], y:[70, 120]
        quadratX: 200,
        quadratY: 70,
        originX: 200,
        originY: 120,
        labelX: 206,
        labelY: 136,
        ghost: false
      },
      {
        coord: '(7, 2)',
        count: '🌼 3 counted',
        xVal: 7,
        yVal: 2,
        // Quadrat spans x:[400, 450], y:[270, 320]
        quadratX: 400,
        quadratY: 270,
        originX: 400,
        originY: 320,
        labelX: 406,
        labelY: 336,
        ghost: true
      }
    ];

    let currentStep = 0;
    let autoPlay = true;
    let timer = null;

    function renderStep(idx) {
      currentStep = idx;
      const s = steps[idx];

      // Update UI Text
      document.getElementById('coordText').textContent = s.coord;
      document.getElementById('countBadge').textContent = s.count;

      // Update Buttons
      document.getElementById('btn1').classList.toggle('active', idx === 0);
      document.getElementById('btn2').classList.toggle('active', idx === 1);

      // Animate Quadrat Box & Wires
      const box = document.getElementById('quadratBox');
      const wire = document.getElementById('quadratWire');
      const dot = document.getElementById('targetDot');
      const label = document.getElementById('coordLabel');

      box.setAttribute('x', s.quadratX);
      box.setAttribute('y', s.quadratY);
      wire.setAttribute('x', s.quadratX);
      wire.setAttribute('y', s.quadratY);
      dot.setAttribute('cx', s.originX);
      dot.setAttribute('cy', s.originY);
      label.setAttribute('x', s.labelX);
      label.setAttribute('y', s.labelY);
      label.textContent = s.coord;

      // Update Projection Lines
      const projX = document.getElementById('projX');
      const projY = document.getElementById('projY');

      projX.setAttribute('x1', s.originX);
      projX.setAttribute('y1', s.originY);
      projX.setAttribute('x2', s.originX);
      projX.setAttribute('y2', 428);

      projY.setAttribute('x1', s.originX);
      projY.setAttribute('y1', s.originY);
      projY.setAttribute('x2', 42);
      projY.setAttribute('y2', s.originY);

      // Ghost quadrat visibility
      const ghost = document.getElementById('ghostQuadrat');
      ghost.setAttribute('opacity', s.ghost ? '0.7' : '0');

      // Highlight dandelion groups
      const d1 = document.getElementById('dandelionsS1');
      const d2 = document.getElementById('dandelionsS2');

      if (idx === 0) {
        d1.setAttribute('opacity', '1');
        d2.setAttribute('opacity', '0.35');
        d1.querySelectorAll('.dandelion').forEach(el => el.classList.add('dandelion-highlight'));
        d2.querySelectorAll('.dandelion').forEach(el => el.classList.remove('dandelion-highlight'));
      } else {
        d1.setAttribute('opacity', '0.5');
        d2.setAttribute('opacity', '1');
        d1.querySelectorAll('.dandelion').forEach(el => el.classList.remove('dandelion-highlight'));
        d2.querySelectorAll('.dandelion').forEach(el => el.classList.add('dandelion-highlight'));
      }
    }

    function setStep(idx) {
      renderStep(idx);
    }

    function togglePlay() {
      autoPlay = !autoPlay;
      document.getElementById('playBtn').textContent = autoPlay ? '⏸' : '▶';
      if (autoPlay) {
        startTimer();
      } else {
        clearInterval(timer);
      }
    }

    function startTimer() {
      clearInterval(timer);
      timer = setInterval(() => {
        if (autoPlay) {
          const next = (currentStep + 1) % steps.length;
          renderStep(next);
        }
      }, 3500);
    }

    // Initialize
    renderStep(0);
    startTimer();
  </script>
</body>
</html>

Understanding Sampling Bias and the Need for Randomisation

<!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: #f8f9fa;
      color: #1e2945;
      padding: 12px;
      display: flex;
      flex-direction: column;
      align-items: center;
      justify-content: center;
      min-height: 100%;
    }

    .grid {
      display: grid;
      grid-template-columns: 1fr 1fr;
      gap: 12px;
      width: 100%;
      max-width: 640px;
    }

    @media (max-width: 480px) {
      .grid {
        grid-template-columns: 1fr;
        gap: 10px;
      }
    }

    .card-panel {
      background: #ffffff;
      border-radius: 12px;
      padding: 10px;
      display: flex;
      flex-direction: column;
      align-items: center;
      box-shadow: 0 2px 6px rgba(0,0,0,0.05);
      border: 1px solid #e5e7eb;
    }

    .header-badge {
      font-size: 13px;
      font-weight: 700;
      padding: 4px 10px;
      border-radius: 20px;
      margin-bottom: 8px;
      display: flex;
      align-items: center;
      gap: 5px;
    }

    .badge-biased {
      background: #fee2e2;
      color: #b91c1c;
    }

    .badge-random {
      background: #dbeafe;
      color: #1d4ed8;
    }

    .svg-container {
      width: 100%;
      aspect-ratio: 16 / 11;
      border-radius: 8px;
      overflow: hidden;
      border: 1px solid #cbd5e1;
    }

    svg {
      width: 100%;
      height: 100%;
      display: block;
    }

    .result-badge {
      margin-top: 8px;
      font-size: 12px;
      font-weight: 700;
      text-align: center;
      padding: 4px 8px;
      border-radius: 6px;
      width: 100%;
    }

    .res-biased {
      background: #fef2f2;
      color: #dc2626;
      border: 1px solid #fca5a5;
    }

    .res-random {
      background: #eff6ff;
      color: #2563eb;
      border: 1px solid #bfdbfe;
    }

    .controls {
      margin-top: 10px;
      display: flex;
      gap: 8px;
    }

    .btn {
      background: #ffffff;
      border: 1px solid #cbd5e1;
      color: #1e2945;
      padding: 6px 14px;
      font-size: 12px;
      font-weight: 600;
      border-radius: 6px;
      cursor: pointer;
      display: flex;
      align-items: center;
      gap: 4px;
      box-shadow: 0 1px 2px rgba(0,0,0,0.05);
    }

    .btn:active {
      background: #f1f5f9;
    }
  </style>
</head>
<body>

  <div class="grid">
    
    <div class="card-panel">
      <div class="header-badge badge-biased">✕ Biased (Path Only)</div>
      <div class="svg-container">
        <svg viewBox="0 0 240 165" id="svgBiased">
          
          <rect width="240" height="165" fill="#dcfce7"/>
          
          
          <path d="M 0,0 L 90,0 L 0,80 Z" fill="#bbf7d0" opacity="0.7"/>
          <text x="8" y="18" font-size="9" fill="#15803d" font-weight="600">Shade</text>

          
          <rect x="0" y="115" width="240" height="50" fill="#fde68a" opacity="0.6"/>
          <text x="195" y="132" font-size="9" fill="#b45309" font-weight="600">Path</text>

          
          <g id="plantsBiased"></g>

          
          <rect x="18" y="122" width="34" height="34" fill="rgba(239, 68, 68, 0.25)" stroke="#dc2626" stroke-width="2" rx="2" stroke-dasharray="2,2"/>
          <rect x="74" y="122" width="34" height="34" fill="rgba(239, 68, 68, 0.25)" stroke="#dc2626" stroke-width="2" rx="2" stroke-dasharray="2,2"/>
          <rect x="130" y="122" width="34" height="34" fill="rgba(239, 68, 68, 0.25)" stroke="#dc2626" stroke-width="2" rx="2" stroke-dasharray="2,2"/>
          <rect x="186" y="122" width="34" height="34" fill="rgba(239, 68, 68, 0.25)" stroke="#dc2626" stroke-width="2" rx="2" stroke-dasharray="2,2"/>
        </svg>
      </div>
      <div class="result-badge res-biased">
        80 / m² (Overestimate)
      </div>
    </div>

    
    <div class="card-panel">
      <div class="header-badge badge-random">✓ Random (All Areas)</div>
      <div class="svg-container">
        <svg viewBox="0 0 240 165" id="svgRandom">
          
          <rect width="240" height="165" fill="#dcfce7"/>
          
          
          <path d="M 0,0 L 90,0 L 0,80 Z" fill="#bbf7d0" opacity="0.7"/>
          <text x="8" y="18" font-size="9" fill="#15803d" font-weight="600">Shade</text>

          
          <rect x="0" y="115" width="240" height="50" fill="#fde68a" opacity="0.6"/>
          <text x="195" y="132" font-size="9" fill="#b45309" font-weight="600">Path</text>

          
          <g id="plantsRandom"></g>

          
          <g id="randomQuadrats"></g>
        </svg>
      </div>
      <div class="result-badge res-random" id="randomResultText">
        22 / m² (Accurate)
      </div>
    </div>
  </div>

  <div class="controls">
    <button class="btn" id="btnResample">🎲 Resample Random</button>
  </div>

  <script>
    // Fixed plant layout for identical ground truth
    const pathPlants = [
      [22,128],[28,135],[35,126],[40,145],[46,132],[50,140],[58,148],[65,127],[78,133],[82,142],
      [88,127],[96,146],[102,130],[110,138],[118,144],[125,128],[135,134],[142,148],[148,126],[155,139],
      [162,145],[170,130],[178,140],[184,149],[190,127],[196,136],[204,144],[212,131],[220,142],[226,135]
    ];
    const fieldPlants = [
      [110,35],[135,50],[160,25],[180,45],[205,30],[220,60],[115,75],[140,85],[170,68],[195,80],[215,95],
      [80,65],[95,95],[60,85],[45,100],[130,105],[160,102],[185,108]
    ];
    const shadePlants = [
      [18,25],[35,40],[12,55]
    ];

    const allPlants = [...pathPlants, ...fieldPlants, ...shadePlants];

    function createPlantSvg() {
      let s = '';
      for (const [x, y] of allPlants) {
        s += `<circle cx="${x}" cy="${y}" r="2.5" fill="#eab308" stroke="#ca8a04" stroke-width="0.8"/>`;
      }
      return s;
    }

    document.getElementById('plantsBiased').innerHTML = createPlantSvg();
    document.getElementById('plantsRandom').innerHTML = createPlantSvg();

    // Random quadrat configurations: [x, y] coordinates
    const samplePresets = [
      { coords: [[20, 25], [120, 45], [175, 75], [95, 122]], est: '22 / m² (Accurate)' },
      { coords: [[45, 65], [150, 20], [190, 85], [160, 122]], est: '21 / m² (Accurate)' },
      { coords: [[15, 38], [80, 50], [130, 80], [30, 122]], est: '23 / m² (Accurate)' }
    ];

    let currentPreset = 0;

    function renderRandomQuadrats(index) {
      const p = samplePresets[index];
      const g = document.getElementById('randomQuadrats');
      let html = '';
      for (const [x, y] of p.coords) {
        html += `<rect x="${x}" y="${y}" width="34" height="34" fill="rgba(37, 99, 235, 0.2)" stroke="#2563eb" stroke-width="2" rx="2" stroke-dasharray="2,2"/>`;
      }
      g.innerHTML = html;
      document.getElementById('randomResultText').textContent = p.est;
    }

    renderRandomQuadrats(0);

    document.getElementById('btnResample').addEventListener('click', () => {
      currentPreset = (currentPreset + 1) % samplePresets.length;
      renderRandomQuadrats(currentPreset);
    });
  </script>
</body>
</html>

UK-GCSE-SCIENCE-BIO-HDM-05-03

Aligned learning resources

Related diagrams