NEET 2026 — Last-Day Revision for PP-04
SECTION A: WATER TRANSPORT RAPID REVIEW
Ψw = Ψs + Ψp | Ψs ≤ 0 | Pure water Ψw = 0
Water: HIGH Ψw → LOW Ψw
At incipient plasmolysis: Ψp = 0, so Ψw = Ψs
Hypertonic → water exits → plasmolysis
Hypotonic → water enters → turgidity
| Apoplast | vs | Symplast |
|---|---|---|
| Cell walls | Route | Plasmodesmata |
| Fast | Speed | Slow |
| Non-selective | Selectivity | Selective |
| BLOCKED at endodermis | Barrier | Continuous |
Casparian Strip: SUBERIN | ENDODERMIS | Blocks APOPLAST
SECTION B: WATER ASCENT RAPID REVIEW
| Mechanism | Force | Sufficiency |
|---|---|---|
| Root pressure | Positive (push) | Only short distances (guttation) |
| Cohesion-tension (Dixon & Joly) | Negative (pull) | All heights — PRIMARY |
| Capillary action | Surface tension | ~1 m only |
Guttation = LIQUID + HYDATHODES + ROOT PRESSURE + NIGHT Transpiration = VAPOUR + STOMATA + COHESION-TENSION + DAY
Transpiration: Stomatal 90-95% | Cuticular 5-10% | Lenticular <1% Increases with: High light, high temp, high wind, LOW humidity
SECTION C: MINERAL NUTRITION RAPID REVIEW
9 MACRO: C H O N P K Ca Mg S 8 MICRO: Fe Mn Zn Cu Mo B Cl Ni
| Mobile (OLD leaf first) | Immobile (YOUNG leaf first) |
|---|---|
| N, P, K, Mg | Ca, Fe, S, Mn, B |
Named Diseases:
- Whiptail = Mo (cauliflower)
- Little leaf = Zn
- Stout stalk = B (celery)
- Leaf tip necrosis = Ni
- Cu → dieback of shoots
Functions:
- Mg = CHLOROPHYLL centre
- Mn = PS II WATER PHOTOLYSIS
- Mo = nitrogenase + nitrate reductase
- B = pollen germination
- Zn = auxin synthesis
- Ni = urease
SECTION D: NITROGEN FIXATION RAPID REVIEW
Nitrogenase: Mo-Fe protein | 16 ATP | 8$e^{-}$ | IRREVERSIBLY $O_{2}$ inhibited
Reaction: $N_{2}$ + 8$H^{+}$ + 8$e^{-}$ + 16ATP → $2NH_{3}$ + $H_{2}$ + 16ADP + 16Pi
| Organism | Type | Host/Habit |
|---|---|---|
| Rhizobium | Symbiotic | Legume root nodules |
| Frankia | Symbiotic | Alnus, Casuarina (non-legume) |
| Azotobacter | Free-living AEROBIC | Soil |
| Clostridium | Free-living ANAEROBIC | Soil |
| Anabaena/Nostoc | Free-living/Symbiotic | Heterocysts; Azolla |
| Azospirillum | Associative | Grass rhizosphere |
Leghemoglobin: scavenger | MICROAEROBIC (not anaerobic) | PINK colour = active
SECTION E: NITROGEN CYCLE RAPID REVIEW
$N_{2}$ → [Fixation: Rhizobium, Azotobacter] → $NH_{3}$
$NH_{3}$ → [Nitrosomonas] → $NO_{2}^{-}$ → [Nitrobacter] → $NO_{3}^{-}$
$NO_{3}^{-}$ → [Pseudomonas/Thiobacillus: Denitrification] → $N_{2}$
Dead organic N → [Decomposers: Ammonification] → $NH_{3}$
TOP NEET TRAPS:
- Guttation ≠ transpiration (root pressure vs cohesion-tension)
- Nitrosomonas = step 1 (→); Nitrobacter = step 2 (→)
- Fe is MICRO not macro
- Mg = MOBILE (old leaves); Fe = IMMOBILE (young leaves)
- Nitrogenase = 16 ATP (not 8)
- Leghemoglobin = MICROAEROBIC (not zero )
- Frankia = non-legume; Rhizobium = legume