Biology Plants
Key Concepts & Formulas
| # | Concept | Quick Explanation |
|---|---|---|
| 1 | Photosynthesis | 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂; occurs in chloroplasts—grana (light) & stroma (dark). |
| 2 | C3 vs C4 Plants | C3: 1st product 3-PGA (rice, wheat); C4: 1st product 4-C oxaloacetate (maize, sugarcane) → better CO₂ fixation. |
| 3 | Plant Hormones | Auxin—apical dominance; Gibberellin—stem elongation & bolting; Cytokinin—cell division; ABA—dormancy; Ethylene—fruit ripening. |
| 4 | Transpiration Pull | Loss of water from leaves → tension → pulls water up xylem; cohesion-tension theory. |
| 5 | Legume Root Nodule | Rhizobium fixes N₂ → NH₃ via nitrogenase; pink leghaemoglobin keeps O₂ low. |
| 6 | Photoperiodism | Short-day (rice), Long-day (wheat), Day-neutral (tomato); flowering controlled by Phytochrome (Pᵣ ↔ Pᶠᵣ). |
10 Practice MCQs
Which pigment converts light energy into chemical energy during photosynthesis? A. Chlorophyll-a
B. Chlorophyll-b
C. Xanthophyll
D. Carotene
Answer: A
Solution: Only chlorophyll-a has the reaction centre (P680/P700) that directly converts photons → electrons.
Shortcut tip: “a” is the 1st letter → 1st & main pigment.
Concept tag: Photosynthesis pigmentsThe first stable product of Calvin cycle is: A. RuBP
B. 3-phosphoglyceric acid (3-PGA)
C. Oxaloacetic acid
D. Glucose
Answer: B
Solution: CO₂ combines with RuBP → 2 molecules of 3-PGA (C3).
Shortcut tip: Calvin = “3” letters in “Cal” → 3-PGA.
Concept tag: Calvin cycleWhich hormone causes bolting in rosette plants? A. Auxin
B. Cytokinin
C. Gibberellin
D. ABA
Answer: C
Solution: Gibberellin induces sudden internode elongation (bolting) before flowering.
Shortcut tip: “GIB” → “Grow Internode Big”.
Concept tag: Plant hormonesWater moves upward in plants chiefly because of: A. Root pressure
B. Transpiration pull
C. Capillarity alone
D. Imbibition
Answer: B
Solution: Transpiration pull (cohesion-tension) can lift water >100 m in tall trees.
Shortcut tip: “T” for Tall & Transpiration.
Concept tag: Transport in plantsWhich of the following is a C4 plant? A. Pea
B. Wheat
C. Maize
D. Barley
Answer: C
Solution: Maize uses PEP-carboxylase for initial CO₂ fixation → Kranz anatomy.
Shortcut tip: “C4—Corn” (both start with ‘C’).
Concept tag: C4 pathwayPink colour inside leguminous root nodules is due to: A. Rhizobium pigment
B. Leghaemoglobin
C. Anthocyanin
D. Myoglobin
Answer: B
Solution: Leghaemoglobin (plant protein + haem) buffers O₂ for nitrogenase enzyme.
Shortcut tip: “Leg-haemo” → Legume + blood-like.
Concept tag: Nitrogen fixationThe closing of stomata is triggered by: A. Cytokinin
B. Gibberellin
C. Abscisic acid (ABA)
D. Auxin
Answer: C
Solution: ABA is stress hormone; causes K⁺ efflux → guard cells lose turgor → stomata close.
Shortcut tip: “ABA—Avoid Being Arid”.
Concept tag: Stomatal movementOptimum wavelength for photosynthesis is: A. 400–450 nm
B. 450–550 nm
C. 650–700 nm
D. 700–800 nm
Answer: C
Solution: Red light (650–700 nm) is maximally absorbed by chlorophyll-a.
Shortcut tip: “Red-Read” → red light gives max yield.
Concept tag: Light reactionWhich cell organelle is responsible for photorespiration? A. Chloroplast only
B. Mitochondrion only
C. Peroxisome and chloroplast
D. Chloroplast, peroxisome & mitochondrion
Answer: D
Solution: Glycolate pathway involves three organelles; RuBP-oxygenase starts in chloroplast.
Shortcut tip: “CPM” → Chloroplast → Peroxisome → Mitochondrion.
Concept tag: PhotorespirationA plant flowers when exposed to 14 h dark & 10 h light. It is: A. Day-neutral
B. Long-day
C. Short-day
D. Medium-day
Answer: C
Solution: Critical dark period >12 h → short-day plant (e.g., chrysanthemum).
Shortcut tip: “Dark dominates” → longer dark = short-day.
Concept tag: Photoperiodism
5 Previous Year Questions
The enzyme that fixes atmospheric CO₂ in C4 plants is: [RRB NTPC 2021] A. RuBisCO
B. PEP carboxylase
C. Malate dehydrogenase
D. Pyruvate kinase
Answer: B
Solution: PEPcase has high affinity for CO₂, no oxygenase activity → avoids photorespiration.
Shortcut tip: “PEP—Primary Entry of CO₂ in C4”.
Concept tag: C4 pathwayWhich of the following is NOT a micronutrient for plants? [RRB Group-D 2019] A. Zinc
B. Boron
C. Magnesium
D. Molybdenum
Answer: C
Solution: Mg is a macronutrient (component of chlorophyll).
Shortcut tip: “Mg—Macro-green”.
Concept tag: Mineral nutritionThe pigment involved in flowering based on photoperiod is: [RRB NTPC 2020] A. Cytochrome
B. Phytochrome
C. Chlorophyll
D. Anthocyanin
Answer: B
Solution: Phytochrome (Pᵣ ↔ Pᶠᵣ) senses red/far-red ratio to induce flowering.
Shortcut tip: “Phy-to” → “Physically tells flowering”.
Concept tag: PhotoperiodismOpening of stomata in daylight is due to: [RRB ALP 2018] A. Endosmosis of guard cells
B. Exosmosis of guard cells
C. Plasmolysis
D. Guttation
Answer: A
Solution: K⁺ influx → water enters → turgor ↑ → stomata open.
Shortcut tip: “Open = In”.
Concept tag: Stomatal physiologyWhich plant is associated with symbiotic nitrogen fixation? [RRB NTPC 2017] A. Rice
B. Wheat
C. Gram
D. Maize
Answer: C
Solution: Gram (legume) has Rhizobium in root nodules.
Shortcut tip: “Gram—Ground with Rhizo”.
Concept tag: Biological N₂ fixation
Speed Tricks & Shortcuts
| Situation | Shortcut | Example |
|---|---|---|
| C3 vs C4 examples | “CRWM” – C4: Corn, R-Sugarcane, Wheat (some), Millet | Remember 4 letters → C4 |
| Plant hormone function | “ACGEE” – Auxin (Apical), Cytokinin (Cell division), Gibberellin (Growth & bolting), Ethylene (Eating ripe), ABA (Away water stress) | First letters match key action |
| Photoperiod plants | “SRL” – Short-day: Rice, Chrysanthemum; Long-day: Radish, Wheat; Day-neutral: Tomato, Cotton | Short = long night; Long = short night |
| Nutrient type | “C.HOPKiN’S CaFe Mg” – All macro; rest micro | 6+3 = 9 macronutrients |
| Stomata open/close | “Light-Open, ABA-Close” – daylight & low CO₂ → open; drought → ABA → close | Instant recall in situation questions |
Common Mistakes to Avoid
| Mistake | Why Students Make It | Correct Approach |
|---|---|---|
| Confusing C4 first product with that of C3 | Memory lapse in cycle sequence | Always write Calvin = C3 = 3-PGA; C4 = 4-C = OAA |
| Calling leghaemoglobin a bacterial pigment | Pink colour misattributed | Remember it is plant-derived, only present in nodules |
| Mixing micronutrients & macronutrients | Mn, Mo, Mg sound similar | Use mnemonic “C.HOPKiN’S CaFe Mg” for macros; rest micro |
| Reversing short-day & long-day definitions | Focus on light instead of dark | Count critical DARK period: >12 h dark = short-day plant |
Quick Revision Flashcards
| Front | Back |
|---|---|
| C4 first CO₂ acceptor | Phosphoenol pyruvate (PEP) |
| Photosynthesis equation (balanced) | 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ |
| Site of photorespiration | Chloroplast + Peroxisome + Mitochondrion |
| Hormone for fruit ripening | Ethylene |
| Nitrogenase requirement | Anaerobic condition; protected by leghaemoglobin |
| Stomata close signal | Abscisic acid (ABA) |
| C3 plants examples | Rice, Wheat, Cotton (RWC) |
| Maximum absorption peak of chlorophyll-a | Red ~663 nm & blue ~430 nm |
| Kranz anatomy | Large bundle sheath cells with chloroplasts; seen in C4 leaves |
| Guttation occurs through | Hydathodes (when root pressure high & transpiration low) |
BETA
