Diagram Bank

---
target: 495+/500
author: Senior Sibling
name: diagram-bank
description: >-
  12th Grade Mandatory Diagram List (PCMB). 
  Covers Physics Ray/Circuit diagrams, Biology Reproductive/Genetics structures, and Chemistry Mechanism visualizations.
---

# Diagram Bank — 12th Grade "Mark-Magnet" Diagrams

In 12th Grade Science, a diagram is not an "option"—it is a **Value Point**. An answer without a diagram in Section E (5 Marks) is automatically capped at 4/5.

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## 🧬 Biology (The Most Diagram-Heavy)

1.  **Reproduction:**
    - TS of Anther (showing 4 layers + Pollen sacs).
    - Mature Embryo Sac (7-celled, 8-nucleate).
    - Human Sperm (Head, Middle piece, Tail).
    - TS of Ovary/Testis.
2.  **Genetics & Molecular:**
    - DNA Replication Fork (showing Leading/Lagging strands).
    - Lac Operon (Switch ON/OFF states).
    - tRNA Adapter Molecule (Clover leaf model).
3.  **Biotech & Human Health:**
    - Antibody Molecule (Y-shaped with H and L chains).
    - Cloning Vector pBR322 (Mandatory: Mark all restriction sites).
    - Bioreactor (Simple Stirred-tank vs Sparged).

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## 🔭 Physics (Ray & Circuit Precision)

1.  **Optics:**
    - Ray Diagram: Compound Microscope (Final image at $D$ and $\infty$).
    - Ray Diagram: Astronomical Telescope (Normal adjustment).
    - Wavefronts: Reflection and Refraction using Huygens' Principle.
2.  **Electricity & Magnetism:**
    - Cyclotron (Dee structures and path).
    - Moving Coil Galvanometer (Internal parts).
    - AC Generator (Armature, Rings, Brushes).
3.  **Modern Physics:**
    - Experimental setup of Photoelectric Effect.
    - Energy Level Diagram for Hydrogen atom (Lyman, Balmer, etc.).
    - P-N Junction: Forward and Reverse bias circuits.
    - Zener Diode as a Voltage Regulator.

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## 🧪 Chemistry (Visualizing Mechanisms)

1.  **Organic Mechanisms:**
    - Transition state of $S_N 2$ reaction.
    - Carbocation formation in $S_N 1$.
2.  **Physical Chemistry:**
    - Galvanic Cell ($Zn-Cu$ with Salt Bridge).
    - Standard Hydrogen Electrode (SHE).
    - Fuel Cell ($H_2-O_2$).
3.  **Biomolecules:**
    - Structure of Glucose (Open vs Pyranose).
    - Peptide bond formation.

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## ✍️ Presentation Rules (Senior Sibling)
- **The Box:** Enclose your diagram in a neat pencil-drawn box.
- **Single-Side Labeling:** Draw all labels on the **Right** side with straight horizontal lines.
- **Arrows:** For Physics, arrows on light rays and current paths are **Non-negotiable**.
- **Scale:** A diagram should be roughly **1/3 of a page**. Never draw "micro-diagrams".

**Command Integration:** Use `/diagram-drill` to get a list of diagrams to practice for a specific chapter.