| # |
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
1. 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 pigments2. The 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 cycle3. Which 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 hormones4. Water 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 plants5. Which 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 pathway6. Pink 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 fixation
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 movement
8. Optimum 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 reaction9. Which 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:** Photorespiration10. A 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:** Photoperiodism5 Previous Year Questions
1. 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 pathway2. Which 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 nutrition3. The 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:** Photoperiodism4. Opening 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 physiology5. Which 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 fixationSpeed 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
