Diagram Bank

---
name: diagram-bank
description: Every diagram that carries marks in CBSE Science. Students lose 1-2 marks per paper for missing or poorly drawn diagrams. This lists ALL mandatory diagrams.
---

# Diagram Bank — Every Mark-Carrying Diagram

## Why Diagrams = Free Marks
CBSE awards dedicated marks for diagrams in 3M and 5M questions. A correct text answer WITHOUT diagram loses 1 mark. A labeled diagram alone can earn 1-2 marks even if text is weak.

## MUST-KNOW Diagrams (Board Exam Mandatory)

### Biology (12 diagrams)
```
1.  Human digestive system (with labels: mouth, oesophagus, stomach,
    small intestine, large intestine, liver, pancreas)
2.  Human heart (4 chambers, valves, blood vessels, oxygenated/deoxygenated)
3.  Nephron / Excretory unit (Bowman's capsule, glomerulus, tubule, collecting duct)
4.  Human brain (cerebrum, cerebellum, medulla, pons)
5.  Neuron (cell body, dendrite, axon, nerve ending, myelin sheath)
6.  Reflex arc (receptor → sensory nerve → spinal cord → motor nerve → effector)
7.  Human eye (cornea, lens, retina, optic nerve, iris, pupil)
8.  Male reproductive system (testes, vas deferens, urethra, penis, prostate)
9.  Female reproductive system (ovary, fallopian tube, uterus, vagina)
10. Flower structure (sepal, petal, stamen, pistil, anther, stigma, ovary)
11. Stomata (guard cells, chloroplast, stomatal pore, epidermal cells)
12. DNA double helix (simple representation with base pairs)
```

### Physics (10 diagrams)
```
1.  Concave mirror ray diagram (rules: parallel→focus, centre→retrace, focus→parallel)
2.  Convex mirror ray diagram
3.  Concave lens ray diagram
4.  Convex lens ray diagram (all 6 positions of object)
5.  Refraction through glass slab (incident, refracted, emergent rays)
6.  Refraction through prism (dispersion, spectrum VIBGYOR)
7.  Electric circuit (series and parallel with ammeter, voltmeter, battery, resistors)
8.  Magnetic field lines (bar magnet, solenoid)
9.  AC generator (coil, magnet, slip rings, brushes)
10. DC motor (coil, magnet, split ring commutator, brushes)
```

### Chemistry (5 diagrams)
```
1.  Electrolysis of water setup
2.  Lab setup for CO₂ gas preparation
3.  Activity series / Reactivity series (K > Na > Ca > Mg > Al > Zn > Fe > H > Cu > Ag > Au)
4.  Electron dot structures (ionic: NaCl, MgCl₂ | covalent: H₂O, CH₄, NH₃)
5.  Carbon chain structures (methane, ethane, ethanol, ethanoic acid)
```

## Diagram Rules for Full Marks
```
✅ Use pencil for diagram, pen for labels
✅ Labels on RIGHT side with horizontal lines
✅ Title below the diagram
✅ Clean lines (use ruler for straight parts)
✅ Minimum 6-8 labels for full marks
✅ Arrows showing direction (blood flow, nerve impulse, light rays)
❌ Never free-hand what should be straight
❌ Never skip labels (unlabeled diagram = half marks)
❌ Never draw too small (use at least ¼ page)
```