🖼️ Diagram Cheatsheet

NEET Biology Diagram Cheatsheet

Every diagram that appears in NEET Biology, described with labeled components. Master these for guaranteed marks.

🫀 Diagram 1: Structure of the Heart

         Superior Vena Cava
                 │
    ┌────────────┴────────────┐
    │  RIGHT ATRIUM  ←────── │ ← (deoxygenated blood from body)
    │  (thin-walled)          │
    └────────────┬────────────┘
                 ↓ [Tricuspid valve]
    ┌────────────┴────────────┐
    │  RIGHT VENTRICLE        │
    │  (muscular wall)        │
    └────────────┬────────────┘
                 ↓ [Pulmonary semilunar valve]
         Pulmonary Artery → LUNGS

    LUNGS oxygenate blood →

         Pulmonary Veins (4)
                 │
    ┌────────────┴────────────┐
    │  LEFT ATRIUM            │ ← oxygenated blood
    └────────────┬────────────┘
                 ↓ [Bicuspid/Mitral valve]
    ┌────────────┴────────────┐
    │  LEFT VENTRICLE         │
    │  (thickest wall!)       │
    └────────────┬────────────┘
                 ↓ [Aortic semilunar valve]
              AORTA → Body

Key NEET Points:
• Right side = deoxygenated blood
• Left side = oxygenated blood
• Left ventricle wall is thickest
• SA node in right atrium wall

Valves Summary:
• Tricuspid: Right AV valve (3 cusps)
• Bicuspid: Left AV valve (2 cusps)
• Semilunar: In aorta + pulmonary
• Prevent backflow

🌿 Diagram 2: Z-Scheme of Photosynthesis

  HIGH ENERGY
    ↑
    │   [Ferredoxin]
    │       ↑
    │   [Fe-S protein]
    │       ↑
    │   [Plastoquinone (PQ)]
    │       ↑
    P700 (PSI) ─→ excited P700* (absorbs 700nm)
    │
    │          [Cytochrome b6f complex]
    │                  ↑
    │          [Plastoquinone (PQ)]
    │                  ↑
    P680 (PSII) ─→ excited P680* (absorbs 680nm)
    │                  ↑
    │          [Water splitting: 2H₂O → 4H⁺ + 4e⁻ + O₂]
    │
  LOW ENERGY   ← OEC (Oxygen Evolving Complex)

Key Points: PSII (P680) absorbs first → water splits → electrons go UP the energy ladder → PSI (P700) absorbs again → final electron acceptor is NADP⁺ → NADPH formed. O₂ released from PSII water splitting (not from CO₂).

🧬 Diagram 3: Embryo Sac (Female Gametophyte)

         MICROPYLE END
        ┌──────────────┐
        │  Egg cell (n)│ ← fertilised by one male gamete → Zygote (2n)
        │  Synergids×2 │ ← guide pollen tube, have filiform apparatus
        ├──────────────┤
        │              │
        │ Polar nuclei │ ← 2 polar nuclei (n+n) in central cell
        │ (central cell│    fertilised by 2nd male gamete → Endosperm (3n)
        │              │    [This is DOUBLE FERTILISATION]
        ├──────────────┤
        │ Antipodals×3 │ ← no reproductive function
        └──────────────┘
         CHALAZAL END

    Total: 7 cells, 8 nuclei
    (Synergids×2 + Egg×1 + Central cell×1 + Antipodals×3 = 7 cells)
    (Synergids×2 + Egg×1 + Polar nuclei×2 + Antipodals×3 = 8 nuclei)

⚛️ Diagram 4: Nephron Structure

  Afferent arteriole → [GLOMERULUS] → Efferent arteriole
                            ↓ (filtration under pressure)
                    [Bowman's Capsule]
                            ↓
                    [PCT — Proximal Convoluted Tubule]
                    (maximum reabsorption: glucose, aa, Na⁺)
                            ↓
                    [Loop of Henle — descending limb]
                    (water permeable, solute impermeable)
                            ↓
                    [Loop of Henle — ascending limb]
                    (impermeable to water, solute leaves)
                            ↓
                    [DCT — Distal Convoluted Tubule]
                    (regulated by ADH and aldosterone)
                            ↓
                    [Collecting Duct] → Renal Pelvis
                    (ADH controls water here)
                            ↓
                         URINE (1.5 L/day)

Key Numbers: GFR = 125 mL/min = 180 L/day filtered. 178.5 L reabsorbed. 1.5 L excreted as urine. Glomerular filtrate = plasma minus proteins.

🧪 Diagram 5: DNA Double Helix Key Features

Structure:
• Right-handed double helix (B-DNA)
• Width = 2 nm diameter
• Pitch = 3.4 nm (per turn)
• Base pairs per turn = 10
• Rise per base = 0.34 nm

Base Pairing:
• A — T (2 hydrogen bonds)
• G — C (3 hydrogen bonds)
• Purines: A, G (double ring)
• Pyrimidines: T, C, U (single ring)
• Anti-parallel strands (3'→5' and 5'→3')

Replication:
• Semi-conservative (Meselson-Stahl)
• Origin: ARS (autonomously replicating seq.)
• Leading strand: continuous
• Lagging strand: Okazaki fragments
• DNA pol III does main synthesis

NEET Biology Diagram Cheatsheet

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