Last Updated: April 2026
NEET 2027 | BIOLOGY — PLANT PHYSIOLOGY
Master all 5 plant physiology chapters (Ch 11–15 NCERT Class 11) with complete notes, comparison tables, key formulas and 10 NEET-level MCQs.
Plant Physiology covers 5 NCERT Class 11 chapters: Ch 11 — Transport in Plants, Ch 12 — Mineral Nutrition, Ch 13 — Photosynthesis in Higher Plants, Ch 14 — Respiration in Plants, and Ch 15 — Plant Growth and Development. Together, these chapters form one of the most scoring sections in NEET Biology.
| Chapter | Approx. NEET Questions/Year | Priority |
|---|---|---|
| Transport in Plants | 1–2 | High |
| Mineral Nutrition | 1–2 | Medium |
| Photosynthesis | 3–4 | Very High |
| Respiration in Plants | 2–3 | Very High |
| Plant Growth & Dev. | 1–2 | High |
Total: ~8–12 questions per year from Plant Physiology.
Chapter 11: Transport in Plants
Water Relations and Osmosis
Plants constantly move water, minerals, and organic solutes across short and long distances. Water movement is governed by water potential (Ψ):
Ψ = Ψs + Ψp
Where: Ψs = Solute potential (always negative in solution), Ψp = Pressure potential (positive in turgid cells, zero in flaccid cells, negative during transpiration pull).
Water moves from higher Ψ → lower Ψ (i.e., from less negative to more negative).
Osmosis is the movement of water across a semipermeable membrane from a region of high water potential to low water potential. Key terms:
- Plasmolysis: Shrinkage of protoplast due to loss of water in hypertonic solution. When the cell membrane just starts to pull away from the cell wall = incipient plasmolysis.
- Turgor pressure: Pressure exerted by the cell contents against the cell wall; responsible for rigidity of herbaceous plants.
- DPD (Diffusion Pressure Deficit): Old term; equals −Ψ (negative water potential). High DPD = sucks in water.
Apoplast vs Symplast Pathways
| Feature | Apoplast | Symplast |
|---|---|---|
| Route | Cell walls and intercellular spaces | Living cytoplasm via plasmodesmata |
| Living/Non-living | Non-living | Living |
| Casparian strip | Blocked here | Not blocked |
| Speed | Faster | Slower |
Ascent of Sap
Water moves upward through xylem vessels and tracheids. The cohesion–tension–transpiration pull theory (Dixon and Joly) is the most accepted explanation:
- Transpiration pull: Evaporation from mesophyll cells creates tension in xylem sap.
- Cohesion: Water molecules stick together via H-bonds — provides tensile strength to the water column.
- Adhesion: Water adheres to xylem walls, preventing column breakage.
Root pressure contributes to ascent of sap at night (when transpiration is minimal) and is responsible for guttation.
Chapter 12: Mineral Nutrition
Essential Elements
A mineral element is essential if: (1) its absence makes normal growth/reproduction impossible; (2) it cannot be replaced by another element; (3) it is directly involved in plant metabolism.
Macronutrients (needed in large amounts): C, H, O, N, P, K, Ca, Mg, S
Micronutrients (needed in trace amounts): Fe, Mn, Zn, Cu, Mo, B, Cl, Ni
Key Deficiency Symptoms:
- Nitrogen (N): Chlorosis (yellowing) of older leaves first (mobile nutrient)
- Iron (Fe): Interveinal chlorosis of young leaves (immobile)
- Magnesium (Mg): Interveinal chlorosis — Mg is part of chlorophyll
- Calcium (Ca): Death of growing tips (meristematic tissue)
- Boron (B): Death of apical meristem, poor fruit development
- Phosphorus (P): Purpling/reddening of leaves due to anthocyanin accumulation
Nitrogen Fixation — Free Living and Symbiotic
| Type | Organisms | Key Notes |
|---|---|---|
| Free-living aerobic | Azotobacter, Beijerinckia | Fix N2 in soil, do not form associations |
| Free-living anaerobic | Clostridium | Anaerobic, found in waterlogged soils |
| Symbiotic | Rhizobium (legumes), Frankia (Alnus) | Form root nodules; Rhizobium is gram-negative |
| Cyanobacteria | Nostoc, Anabaena (in Azolla) | In paddy fields; heterocysts fix N2 |
Enzyme involved: Nitrogenase — requires Mo and Fe, works only in anaerobic conditions (Leghemoglobin provides the oxygen-free environment in root nodules).
Nitrification: NH₄⁺ → NO₂⁻ (by Nitrosomonas) → NO₃⁻ (by Nitrobacter)
Denitrification: NO₃⁻ → N₂ (by Pseudomonas, Thiobacillus) — occurs in anaerobic conditions.
Chapter 13: Photosynthesis in Higher Plants
Light Reactions — Z-Scheme
Light reactions occur on the thylakoid membranes. Key events:
- PS II (P680): Absorbs light (680 nm); oxidizes water (photolysis): 2H₂O → 4H⁺ + 4e⁻ + O₂; releases O₂.
- Electron transport chain: Electrons pass through plastoquinone (PQ) → cytochrome b6f complex → plastocyanin (PC).
- PS I (P700): Absorbs light (700 nm); re-energizes electrons; passes to ferredoxin → NADP reductase → NADPH.
- ATP Synthesis: Chemiosmosis across thylakoid membrane using proton gradient.
Cyclic Photophosphorylation: Only PS I involved; electrons cycle back; produces only ATP (no NADPH, no O₂ release).
Non-cyclic Photophosphorylation: Both PS I and PS II; produces ATP + NADPH + O₂.
Products of Light Reactions per 2 water molecules: 1 O₂, 2 NADPH, 3 ATP (for 3-carbon pathway)
Dark Reactions — Calvin Cycle (C3 Pathway)
Occurs in the stroma. Three phases:
- Carbon fixation: CO₂ + RuBP (5C) → 2 × 3-PGA (3C) — catalyzed by RuBisCO
- Reduction: 3-PGA → G3P using ATP + NADPH
- Regeneration: G3P → RuBP using ATP
Net output per 3 CO₂ fixed: 1 G3P (half a glucose equivalent); requires 9 ATP + 6 NADPH
C3 vs C4 vs CAM Plants — Comparison Table
| Parameter | C3 Plants | C4 Plants | CAM Plants |
|---|---|---|---|
| First stable product | 3-PGA (3C) | Oxaloacetate/OAA (4C) | OAA (4C) |
| Primary CO₂ acceptor | RuBP (5C) | PEP (3C) | PEP (3C) |
| Carboxylating enzyme | RuBisCO | PEP Carboxylase (mesophyll) | PEP Carboxylase |
| Kranz anatomy | Absent | Present | Absent |
| Photorespiration | Present (significant) | Negligible (CO₂ concentrating) | Negligible |
| Examples | Wheat, rice, pea, sunflower | Maize, sugarcane, sorghum | Opuntia, Agave, pineapple |
| Stomata open | Day | Day | Night (CO₂ stored as malate) |
C4 Pathway (Hatch-Slack): CO₂ fixed in mesophyll cells as OAA → malate → transported to bundle sheath cells → decarboxylated to release CO₂ for Calvin cycle. Efficient in hot, dry, high-light conditions.
Photorespiration: At high O₂/CO₂ ratio, RuBisCO acts as oxygenase instead of carboxylase. Occurs in C3 plants. Site: chloroplasts + peroxisomes + mitochondria. No net ATP production — actually wasteful.
Chapter 14: Respiration in Plants
Glycolysis (in Cytoplasm)
Glucose (6C) → 2 Pyruvate (3C) + 2 ATP (net) + 2 NADH
- 8 total steps, occurs in cytoplasm
- Substrate level phosphorylation at 2 steps (PGA kinase and pyruvate kinase)
- Does not require O₂ (anaerobic)
Krebs Cycle / TCA Cycle (in Mitochondrial Matrix)
Per pyruvate (via acetyl CoA): 3 NADH + 1 FADH₂ + 1 GTP + 2 CO₂
Per glucose (2 pyruvates): 6 NADH + 2 FADH₂ + 2 GTP + 4 CO₂
Key enzymes: Isocitrate dehydrogenase, Alpha-ketoglutarate dehydrogenase, Succinyl CoA synthetase, Malate dehydrogenase
Electron Transport Chain (ETC) and Oxidative Phosphorylation
On inner mitochondrial membrane. Complexes I–IV pump H⁺ ions. ATP synthase (Complex V) generates ATP via chemiosmosis.
Glycolysis: 2 ATP + 2 NADH (cytoplasmic)
Pyruvate oxidation: 2 NADH
Krebs cycle: 2 GTP + 6 NADH + 2 FADH₂
ETC: ~26 ATP (from 10 NADH × ~2.5 + 2 FADH₂ × ~1.5)
Total: ~30–32 ATP per glucose
Fermentation
Alcoholic fermentation: Pyruvate → Acetaldehyde (by pyruvate decarboxylase) → Ethanol + CO₂ (by alcohol dehydrogenase). Occurs in yeast.
Lactic acid fermentation: Pyruvate → Lactate (by lactate dehydrogenase). Occurs in animal muscle cells under anaerobic conditions.
Respiratory Quotient (RQ)
| Substrate | RQ Value |
|---|---|
| Carbohydrates | 1.0 |
| Fats | ~0.7 |
| Proteins | ~0.8–0.9 |
| Organic acids | >1.0 |
RQ = CO₂ produced / O₂ consumed
Chapter 15: Plant Growth and Development
Plant Hormones (Phytohormones)
| Hormone | Site of Production | Key Functions |
|---|---|---|
| Auxin (IAA) | Shoot apical meristem | Cell elongation, apical dominance, phototropism, root initiation |
| Gibberellin (GA) | Young leaves, embryo | Stem elongation, seed germination, breaks dormancy, bolting |
| Cytokinin | Root apical meristem | Cell division (cytokinesis), delays senescence, nutrient mobilization |
| Abscisic Acid (ABA) | Mature leaves, roots | Stomatal closure, seed dormancy, inhibits growth (stress hormone) |
| Ethylene | Ripening fruits, nodes | Fruit ripening, abscission, promotes senescence, feminization |
Seed Dormancy and Vernalisation
Seed Dormancy is induced by ABA, hard seed coat, or immature embryo. Broken by: scarification, stratification (cold treatment), or gibberellins.
Vernalisation is the promotion of flowering by exposure to prolonged cold (0–5°C). Receptors are meristematic cells. Effect is remembered (epigenetic). Important for wheat, rye, and carrot.
Photoperiodism and Phytochrome
Flowering depends on critical night length, not day length:
- Short-Day Plants (SDP): Flower when night > critical length. E.g., Chrysanthemum, tobacco, soybean.
- Long-Day Plants (LDP): Flower when night < critical length. E.g., wheat, spinach, henbane.
- Day-Neutral Plants: Unaffected by photoperiod. E.g., sunflower, cucumber, tomato.
Phytochrome (Pr/Pfr system):
Pr (inactive, absorbs red 660 nm) ⇌ Pfr (active, absorbs far-red 730 nm)
Pfr promotes flowering in LDP and inhibits flowering in SDP.
Critical pigment: The ratio of Pr:Pfr at end of night determines flowering response.
- Photosynthesis is the highest-weightage topic — memorize the Z-scheme, Calvin cycle enzyme names, and C4 differences cold.
- For Respiration, practice ATP counting carefully. NEET often tests exact ATP from ETC.
- Learn plant hormones as mnemonics with their unique functions — many students confuse Cytokinin and Gibberellin.
- Mineral Nutrition deficiency symptoms are frequently tested — link element to function (Mg = chlorophyll central atom).
- Phytochrome and photoperiodism: focus on Pr/Pfr conversion and examples of SDP/LDP.
- Macronutrients: “C HOPKNS CaFe Mg” — C, H, O, P, K, N, S, Ca, Fe, Mg
- Micronutrients: “MnZn Cu Mo B Cl Ni Fe” — Manage Zinc, Copper Makes Beautiful Chlorine, Nickel’s Fine
- Calvin Cycle: “CO₂ + RuBP = 2 PGA” — remember R for RuBisCO, R for RuBP
- Krebs Cycle order: Acetyl CoA → Citrate → Isocitrate → α-Ketoglutarate → Succinyl CoA → Succinate → Fumarate → Malate → Oxaloacetate — “A Clever Idea — Keen Students Should Follow Malate Order”
- Plant hormones: “AG CAE” — Auxin (elongation), Gibberellin (germination), Cytokinin (division), ABA (abscission/dormancy), Ethylene (ripening)
- C4 plants: “Sugar Cane Makes Sorghum Shine” — Sugarcane, Maize, Sorghum are classic C4 examples
Frequently Asked Questions
What is the difference between C3, C4 and CAM plants in NEET Biology?
C3 plants fix CO₂ directly into 3-carbon compound (3-PGA) using RuBisCO. C4 plants first fix CO₂ into 4-carbon compound (OAA) in mesophyll cells using PEP carboxylase, then transfer it to bundle sheath cells for Calvin cycle — this minimizes photorespiration. CAM plants fix CO₂ at night (when stomata are open) as malate and release it during the day for the Calvin cycle — an adaptation to arid environments. Examples: C3 — wheat, rice; C4 — maize, sugarcane; CAM — cactus, pineapple.
How many ATP are produced in aerobic respiration of one glucose?
Modern estimates give approximately 30–32 ATP per glucose in aerobic respiration. This includes: 2 ATP from glycolysis, 2 GTP (= ATP) from Krebs cycle, and ~26–28 ATP from oxidative phosphorylation in the ETC (from 10 NADH × 2.5 ATP each + 2 FADH₂ × 1.5 ATP each). Older NCERT textbooks cite 36–38 ATP, but current biochemistry accepts 30–32.
What is the role of Rhizobium in nitrogen fixation?
Rhizobium is a symbiotic, gram-negative soil bacterium that forms root nodules in leguminous plants (pea, soybean, groundnut). Inside the nodules, Rhizobium fixes atmospheric N₂ into NH₄⁺ using the enzyme nitrogenase. The plant provides carbohydrates to Rhizobium, while Rhizobium provides fixed nitrogen to the plant. Leghemoglobin (pink-coloured) in nodules maintains the anaerobic environment needed for nitrogenase activity.
What is the function of Phytochrome in plants?
Phytochrome is a photoreceptor protein that exists in two interconvertible forms: Pr (absorbs red light, 660 nm, inactive) and Pfr (absorbs far-red light, 730 nm, active). Pfr is the active form that promotes flowering in long-day plants and inhibits flowering in short-day plants. The Pr/Pfr ratio at the end of the night period determines whether a plant will flower. Sunlight (which has more red than far-red) converts Pr → Pfr; darkness slowly converts Pfr → Pr.
Which plant hormone promotes stomatal closure?
Abscisic Acid (ABA) promotes stomatal closure by causing efflux of K⁺ ions from guard cells, leading to loss of turgor pressure and closure of stomata. ABA is produced in response to water stress (drought conditions) and is therefore called the “stress hormone.” It also promotes seed dormancy and inhibits germination. Interestingly, cytokinins and auxins can promote stomatal opening.
[cg_quiz id=”neet-plant-physiology-2027″ data=”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”]