๐ฑ Plant Physiology: One Night Revision & Cram Sheet
Explain how a plant moves water and mineral nutrients, converts light into carbohydrate, distributes that carbohydrate, and uses hormones, photoreceptors, and stress responses to control growth, flowering, germination, and senescence.
๐ Core Axioms & High-Yield Golden Rules
8 Core PrinciplesNon-negotiable foundational truths frequently tested in direct conceptual and numerical exam questions. Click checkbox to mark as mastered.
Water potential equation: Psi_w = Psi_s + Psi_p (water potential = solute/osmotic potential + pressure potential). Pure water has Psi_w = 0 MPa at atmospheric pressure; adding solute makes Psi_s negative.
๐ก Water flows from higher to lower Psi_wPhotosystem II (P680) oxidizes water at the oxygen-evolving complex (Mn4CaO5 cluster), releasing 4 H+ and O2; Photosystem I (P700) reduces NADP+ to NADPH via Ferredoxin-NADP+ reductase.
๐ก PSII splits water -> PSI makes NADPHCyclic photophosphorylation involves only Photosystem I and cytochrome b6f, producing ATP without producing NADPH or releasing oxygen.
๐ก Cyclic = ATP only, no NADPHRubisco oxygenase activity initiates photorespiration (C2 oxidative photosynthetic carbon cycle): 2-phosphoglycolate processed across Chloroplast -> Peroxisome -> Mitochondrion.
๐ก Photorespiration: Chl -> Perox -> MitoC4 pathway (Kranz anatomy) eliminates photorespiration: PEP Carboxylase fixes HCO3- in mesophyll to form Oxaloacetate; malate transported to bundle sheath where Rubisco operates under high CO2.
๐ก C4 = Spatial separation of CO2 fixationCAM photosynthesis uses temporal separation: Stomata open at night to fix CO2 via PEP carboxylase into vacuolar malic acid; daytime stomatal closure prevents transpiration while Calvin cycle runs.
๐ก CAM = Night fixation, Day Calvin cycleAuxin (IAA) promotes apical dominance, cell elongation via acid growth hypothesis (proton pump activation -> expansins), and root initiation.
๐ก Auxin = Elongation & Apical DominanceAbscisic acid (ABA) is the plant stress hormone: induces stomatal closure during drought via Ca2+ influx and K+ efflux from guard cells; promotes seed dormancy.
๐ก ABA = Closes Stomata & Enforces Dormancy๐ Chapter-by-Chapter Rapid Cram Breakdown
8 ModulesHigh-density review of every curriculum chapter. Click any chapter title to view full in-depth lecture notes.
Water relations →
- Master Water potential: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master turgor and plasmolysis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master aquaporins: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master cohesionโtension: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master root pressure: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Mineral nutrition →
- Master Essentiality: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master deficiency: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pH and iron: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master uptake: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Casparian strip: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Photosynthesis →
- Master Light reactions: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master photophosphorylation: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Calvin cycle: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master photorespiration: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master C4 and CAM: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Alternative oxidase: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master sucrose: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master phloem loading: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master pressure flow: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master sources and sinks: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Plant hormones →
- Master Auxin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master cytokinin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master gibberellin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ethylene: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ABA: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Light and time →
- Master Phytochrome: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master blue-light receptors: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master phototropism: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master photoperiodism: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master florigen: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
Stress physiology →
- Master Drought: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master salinity: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master heat and cold: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master flooding: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ROS: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master Seed parts: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master dormancy: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master ABA and gibberellin: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master aleurone: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
- Master senescence versus necrosis: understand underlying structural mechanisms, biochemical pathways, and diagnostic indicators.
โ๏ธ Must-Know Comparison & Distinction Tables
1 TablesSide-by-side matrices comparing commonly confused biological mechanisms, kinetic types, and pathways.
Comparison of C3, C4, and CAM Photosynthetic Pathways
| Feature | C3 Plants (e.g. Wheat, Rice) | C4 Plants (e.g. Maize, Sugarcane) | CAM Plants (e.g. Pineapple, Cactus) |
|---|---|---|---|
| Primary CO2 Acceptor | Ribulose-1,5-bisphosphate (RuBP) | Phosphoenolpyruvate (PEP) | Phosphoenolpyruvate (PEP) |
| Primary Carboxylating Enzyme | Rubisco | PEP Carboxylase (mesophyll) | PEP Carboxylase (night) |
| First Stable Product | 3-Phosphoglycerate (3-PGA, 3C) | Oxaloacetate (OAA, 4C) | Oxaloacetate (OAA, 4C) |
| Leaf Anatomy | Mesophyll only (no Kranz anatomy) | Kranz anatomy (distinct bundle sheath) | Succulent mesophyll with large vacuoles |
| Photorespiration Rate | High (up to 25-40% carbon loss) | Negligible / Suppressed | Negligible |
| CO2 Fixation Separation | None | Spatial (Mesophyll vs Bundle Sheath) | Temporal (Night vs Day) |
โ ๏ธ Examiner Traps & Common Student Mistakes
1 PitfallsClassic trap questions designed by examiners to catch uncritical students. Don't lose easy marks here!
Substrate of PEP Carboxylase in C4 Plants
Thinking PEP carboxylase fixes dissolved CO2 gas.
PEP carboxylase uses BICARBONATE (HCO3-), formed from CO2 by carbonic anhydrase, NOT molecular CO2. It has zero affinity for oxygen.
๐ Key Formulas & Numerical Constants
2 FormulasWater Potential Equation
ฮจw = ฮจs + ฮจp + ฮจgDetermines direction of water transport in xylem and cell turgor.
Van 't Hoff Equation for Solute Potential
ฮจs = -i * C * R * TCalculates osmotic potential: i = ionization constant, C = molar concentration, R = gas constant, T = absolute temp.
๐๏ธ Landmark Scientists & Nobel Discoveries
5 PioneersFrequently tested in historical milestone and match-the-following exam questions.
Katherine Esau
๐ National Medal of Science (1989)Major landmark discoveries
Jan Ingenhousz
Major landmark discoveries
Melvin Ellis Calvin
๐ Nobel Prize in Chemistry (1961) for his research on the carbon dioxide assimilation in plantsMajor landmark discoveries
Julius von Sachs
Major landmark discoveries
Folke Karl Skoog & Carlos O. Miller
๐ National Medal of Science (1991)Major landmark discoveries
๐ฏ Rapid-Fire Active Recall Checklist
3 QuestionsTest your memory before stepping into the exam hall. Try to answer mentally, then tap "Reveal Answer" to verify!