Nutrition

🟢 Lite — Quick Review (1h–1d)

Rapid summary for last-minute revision before your exam.

Nutrition — How Organisms Obtain and Use Food

Modes of Nutrition

Autotrophic Nutrition — Self-Feeding (Photoautotrophs)

• Photoautotrophs: use sunlight to fix CO₂ into organic compounds (plants, algae, cyanobacteria)
• Chemoautotrophs: use chemical energy from inorganic compounds (certain bacteria — nitrifying bacteria)

Heterotrophic Nutrition — Depend on Others

• Holozoid: solid food — amoeba, paramoecium
• Holophytic: photosynthesis — Euglena
• Saprophytic: dead decaying matter — mushrooms, Aspergillus, Penicillium
• Parasitic: living host — Cuscuta (amarbel), Tapeworm

Photosynthesis — The Light Reaction

Photosynthesis overall equation: $$6CO_2 + 12H_2O \xrightarrow{h\nu} C_6H_{12}O_6 + 6H_2O + 6O_2$$

Two stages:

1. Light-dependent reactions (thylakoid membrane):

   • Photolysis of water: $2H_2O → 4H^+ + 4e^- + O_2$ (catalysed by OEC/PSII)
   • PSII: $P680* → electron acceptor (plastoquinone) → ATP synthase
   • PSI: $P700* → NADP^+ → NADPH$
   • Photophosphorylation: ADP + Pi → ATP (chemiosmotic — 3H⁺ per ATP)

2. Calvin Cycle (dark reactions — stroma):

   • CO₂ fixation: $RuBP + CO_2 → 2 \times 3-PGA$ (catalysed by RuBisCO)
   • Reduction: $3-PGA → G3P → glucose$
   • RuBP regeneration: G3P → RuBP (uses ATP)
   • ⚡ Net: 6 CO₂ → 1 glucose; 18 ATP + 12 NADPH per glucose

⚡ NEET Tip: RuBisCO has dual function — carboxylation (normal) and oxygenation (photorespiration in C₃ plants). C₄ plants avoid this by concentrating CO₂ around RuBisCO via PEP carboxylase.

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🟡 Standard — Regular Study (2d–2mo)

For students who want genuine understanding.

Nutrition — Detailed Study Guide

1. Light Harvesting Complex

Photosystems:

• PSII (P680): absorbs at 680nm — water splitting, O₂ evolution, drives photophosphorylation
• PSI (P700): absorbs at 700nm — NADPH synthesis
• Both have reaction centre chlorophyll a + accessory pigments (chlorophyll b, carotenoids)

Z-scheme of electron transport: $$H_2O → PSII → Plastoquinone → Cytochrome b₆f → Plastocyanin → PSI → Ferredoxin → NADP^+$$

Non-cyclic photophosphorylation: produces ATP + NADPH (both required for Calvin cycle) Cyclic photophosphorylation: produces ATP only (when NADPH accumulates) — PSI only, electrons return to PSI

2. C₄ Pathway — Kranz Anatomy

In C₄ plants (maize, sugarcane, sorghum):

• Mesophyll cells: $PEP carboxylase$ fixes CO₂ → OAA → malate (or aspartate)
• Bundle sheath cells: malate decarboxylated → CO₂ released → very high CO₂ concentration → RuBisCO fixes CO₂ normally
• ⚡ Advantage: suppresses photorespiration → higher yield in hot climates
• Energy cost: 5 ATP per CO₂ fixed (vs 3 ATP in C₃)

3. Mineral Nutrition in Plants

Essential macro-nutrients (needed >0.1 g/kg dry weight):

Element	Symbol	Function	Deficiency symptom
Nitrogen	N	Amino acids, nucleic acids, chlorophyll	Chlorosis (yellow older leaves first)
Phosphorus	P	ATP, nucleic acids, membranes	Stunted growth, purple leaves
Potassium	K	Osmosis, stomatal regulation	Scorched leaf edges
Calcium	Ca	Cell wall (middle lamella), enzyme cofactor	Death of meristems
Magnesium	Mg	Chlorophyll central atom	Interveinal chlorosis
Sulphur	S	Cysteine, methionine, coenzymes	Young leaves turn pale

Essential micro-nutrients: Iron (chlorophyll synthesis), Manganese (photosystem II water splitting), Zinc (auxin synthesis), Copper (electron transport), Boron (pollen tube growth), Molybdenum (nitrate reductase)

4. Human Nutrition — Digestive System

Process:

1. Mouth: salivary amylase (starch → maltose) — optimal pH 6.8
2. Stomach: pepsin (protein → peptides) — optimal pH 1.5–2; HCl activates pepsinogen
3. Duodenum: pancreatic enzymes — trypsin, chymotrypsin, carboxypeptidase (proteins → amino acids); pancreatic amylase (starch → maltose); lipase (fats → fatty acids + glycerol)
4. Small intestine: brush border enzymes (maltase, sucrase, lactase; peptidases) — final digestion
5. Large intestine: water absorption, formation of faeces; bacterial synthesis of Vitamin K and B₁₂

Absorption:

• Small intestine: monosaccharides (glucose, fructose), amino acids, fatty acids, glycerol, water, ions
• Mechanism: active transport, facilitated diffusion, co-transport, pinocytosis
• Lacteals (lymphatic vessels in villi): absorb fatty acids → transport as chylomicrons

⚡ NEET Quick Recall:

• Intrinsic factor (stomach): glycoprotein needed for B₁₂ absorption in ileum
• Haustral contractions: segmentation movements in large intestine — slow movement for water absorption
• Peristalsis: wave-like contraction behind food — propels food forward

5. Aerobic Respiration — Energy Release

$$C_6H_{12}O_6 + 6O_2 → 6CO_2 + 6H_2O + 38ATP$$

• Glycolysis (cytoplasm): glucose → 2 pyruvate + 2 ATP + 2 NADH
  • Key steps: glucose → G6P (hexokinase); F6P → F1,6BP (PFK-1 — rate limiting); PEP → pyruvate (pyruvate kinase)
• Link reaction: pyruvate → acetyl-CoA + CO₂ + NADH (mitochondrial matrix)
• Krebs cycle: acetyl-CoA → 2CO₂ + 3NADH + 1FADH₂ + 1GTP (per acetyl-CoA)
• Electron transport chain (inner mitochondrial membrane): NADH → Complex I → CoQ → Complex III → Cytochrome c → Complex IV → O₂
  • 1 NADH ≈ 2.5 ATP; 1 FADH₂ ≈ 1.5 ATP
• ⚡ Total: 1 glucose → ~38 ATP (in prokaryotes); ~36 ATP (in eukaryotes — some cost to transport intermediates)

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🔴 Extended — Deep Study (3mo+)

Comprehensive theory for serious preparation.

Nutrition — Deep Dive

1. Photosynthetic Efficiency

Theoretical max efficiency: ~11–12% (of total solar radiation)

• Only 46% of solar radiation is photosynthetically active (PAR: 400–700nm)
• Light saturation: photosynthesis reaches max rate at ~10% of full sunlight
• Light compensation point: point where photosynthesis = respiration — CO₂ is released
• CO₂ compensation point: C₃ plants ~45 ppm; C₄ plants ~5 ppm (C₄ plants can concentrate CO₂)

2. Photorespiration — The C₃ Problem

In C₃ plants at high temperature + low CO₂ + high O₂:

• RuBisCO acts as oxygenase: RuBP + O₂ → phosphoglycolate + 3-PGA
• Phosphoglycolate cannot be used in Calvin cycle → must be salvaged at cost of 1 CO₂ (lost)
• Net loss: for every 4 oxygenations, 1 CO₂ is released (net loss of 25% of fixed carbon)
• C₄ plants avoid this: PEP carboxylase has very high affinity for CO₂ and no affinity for O₂

3. Nitrogen Metabolism in Plants

Nitrogen assimilation:

• Nitrate ($NO_3^-$): reduced by nitrate reductase (cytoplasm) → nitrite ($NO_2^-$) → nitrite reductase (plastids) → ammonia ($NH_3$)
• Ammonia: enters glutamate dehydrogenase pathway → glutamate → amino acids
• Key enzymes: nitrate reductase (NADH), nitrite reductase (ferredoxin), glutamate synthase (GOGAT)

Nitrogen fixation:

• Biological: symbiotic bacteria (Rhizobium in legume root nodules), Frankia (actinorhizal)
• Free-living: Azotobacter, Anabaena (cyanobacteria)
• Leg-haemoglobin: pink pigment in nodules — protects nitrogenase from oxygen (nitrogenase is oxygen-sensitive)

4. Nutrient Deficiency Diseases in Humans

Disease	Cause	Effect
Kwashiorkor	Protein deficiency	Oedema, fatty liver, growth retardation
Marasmus	General caloric deficiency	Wasting of muscle, no oedema
Beriberi	Vitamin B₁ deficiency	Cardiac failure, peripheral nerve damage
Scurvy	Vitamin C deficiency	Bleeding gums, poor wound healing
Rickets	Vitamin D deficiency	Softening of bones in children
Pellagra	Niacin (B₃) deficiency	Dermatitis, diarrhoea, dementia

5. Hormonal Regulation of Hunger

• Ghrelin (stomach): “hunger hormone” — stimulates hypothalamic arcuate nucleus → NPY/AgRP neurons → increased appetite
• Leptin (adipose tissue): “satiety hormone” — crosses blood-brain barrier → suppresses appetite (mutations cause obesity in mice)
• Insulin: signals sufficient glucose to hypothalamus
• CCK (cholecystokinin): released by small intestine in response to fats → promotes satiety
• PYY (peptide YY): released by ileum and colon after food → long-term satiety signal

6. Previous Year NEET Questions on Nutrition

• 2023 Qn: “In C₄ plants, the enzyme that fixes CO₂ in mesophyll cells is:” → PEP carboxylase
• 2022 Qn: “Photorespiration occurs in which cells?” → Mesophyll cells (in C₃ plants — RuBisCO oxygenation activity)
• 2021 Qn: “Nitrogenase in Rhizobium contains:” → Iron and molybdenum (Fe-S cluster + MoFe cofactor)

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📊 NEET UG Exam Essentials

Detail	Value
Questions	200 (180 mandatory + 10 optional)
Time	3h 20min
Marks	720
Section	Physics (50), Chemistry (50), Biology (100)
Negative	−1 for wrong answer
Qualifying	50th percentile (general category)

🎯 High-Yield Topics for NEET UG

• Human Physiology — 18 marks
• Genetics & Evolution — 16 marks
• Ecology & Environment — 12 marks
• Organic Chemistry (Reactions) — 15 marks
• Electrodynamics (Physics) — 18 marks
• Chemical Equilibrium — 10 marks

📝 Previous Year Question Patterns

• Q: “A particle moves in a circle…” [2024 Physics — 2 marks]
• Q: “Identify the incorrect statement about DNA…” [2024 Biology — 4 marks]
• Q: “The major product ofFriedel-Crafts acylation is…” [2024 Chemistry — 3 marks]

💡 Pro Tips

• NCERT Biology is the single most important resource — 80%+ questions are from NCERT lines
• Focus on Human Physiology, Genetics, and Ecology — together they make ~40% of Biology
• In Physics, master Electrostatics + Current Electricity + Magnetism (combined ~20%)
• Organic Chemistry: learn named reactions with mechanisms — they repeat across years

🔗 Official Resources

• NTA Official
• NEET Syllabus PDF

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