Subtopics - Mineral Nutrition (NEET)
Ten major content blocks: essential mineral elements and their classification, roles of macro- and micronutrients, plant analysis methods, mineral absorption mechanisms, mineral translocation, soil as mineral reservoir, nitrogen metabolism with biological nitrogen fixation, and special modes of nutrition in plants.
1) Essential mineral elements
Covers the fundamental classification of mineral elements required by plants. Arnon and Stout (1939) established three criteria of essentiality: the element must be absolutely essential for normal growth and reproduction, its requirement must be specific and not replaceable by another element, and the element must be directly involved in the metabolism of the plant. Based on quantitative requirements, essential elements are classified into macronutrients (present at 1-10 mg per gram dry matter) including C, H, O, N, P, K, S, Ca, and Mg, and micronutrients (equal to or less than 0.1 mg per gram dry matter) including Fe, Mn, Cu, Zn, Mo, B, Cl, and Ni. Macroelements are usually involved in synthesis of organic molecules and development of osmotic potential, while microelements mostly function as enzyme cofactors or metal activators. Cobalt, vanadium, aluminium, and nickel may be essential for certain plants. Ash analysis at 550-600 degrees C in an electric muffle furnace reveals about 92 mineral elements, of which 30 are found in every plant and 16 are classified as essential.
2) Major role of nutrients
Covers the six broad functional categories in which mineral nutrients participate within the plant body. Framework elements (C, H, O) construct the plant body by entering cell wall and protoplasm constitution, along with N, P, S, Mg, and Fe as protoplasmic elements. Minerals maintain osmotic pressure of cells through organic and inorganic forms in cell sap. Calcium, potassium, and sodium ions maintain permeability of cytomembranes. Different cations and anions influence the pH of cell sap. Several elements (Fe, Ca, Mg, Mn, Zn, Cu, Cl) act as metallic catalysts in biochemical reactions. Some minerals like Cu and As impart toxic effects on protoplasm under specific conditions. Certain minerals or their salts act against harmful effects of other nutrients, providing a balancing function essential for metabolic homeostasis.
3) Plant analysis
Describes the experimental methods used to determine the mineral requirements of plants. Ash analysis involves subjecting plant tissue to 550-600 degrees C in an electric muffle furnace; the residual ash reveals approximately 92 mineral elements, 30 of which occur in every plant and 16 are classified as essential elements. Hydroponics (soilless culture developed by Gericke) involves growing plants in a defined mineral nutrient solution, allowing researchers to add or omit specific elements to determine essentiality. Sand culture grows plants in inert sand irrigated with nutrient solution, providing roots with natural support and proper aeration. Aeroponics suspends roots in air and bathes them in nutrient mist, successfully used for growing Citrus and olive plants. These techniques collectively enabled the identification and confirmation of essential mineral elements.
4) Specific role of macronutrients
Details the individual functions and deficiency symptoms of each macronutrient. Nitrogen is a constituent of proteins, nucleic acids, vitamins, chlorophyll, hormones, coenzymes, and ATP; its deficiency causes chlorosis in older leaves first, anthocyanin pigmentation, and suppressed flowering. Phosphorus is abundant in growing organs and seeds, essential for energy metabolism and phosphorylation reactions; deficiency causes dark green or purplish leaves, necrosis, sickle leaf disease. Sulphur is part of amino acids (cystine, cysteine, methionine), vitamins (biotin, thiamine), and coenzyme A; deficiency causes chlorosis in young leaves and tea yellow disease. Potassium is the only monovalent essential cation, activates DNA polymerase and enzymes for translocation and stomatal movement; deficiency causes mottled chlorosis and bushy growth. Calcium forms middle lamella as calcium pectate and is needed for meristem growth; deficiency kills meristems. Magnesium is a central constituent of chlorophyll, activates several enzymes, and is required for ribosome subunit binding; deficiency causes interveinal chlorosis in mature leaves first due to high mobility.
5) Specific role of micronutrients
Details the specific functions and deficiency diseases of each micronutrient. Iron is a structural component of ferredoxin, cytochromes, peroxidases, and catalases; activates nitrate reductase; essential for chlorophyll synthesis; deficiency causes interveinal chlorosis in younger leaves. Manganese activates respiratory enzymes and nitrite reductase; required for photolysis of water in photosynthesis; deficiency causes grey speck disease in oat and marsh spot in pea. Copper is found in plastocyanin and is a constituent of tyrosinase and ascorbic acid oxidase; deficiency causes die-back disease in Citrus. Molybdenum activates nitrate reductase (crucial for nitrogen fixation); deficiency causes whiptail disease in cauliflower and cabbage. Zinc is required for tryptophan synthesis (auxin precursor); constituent of carbonic anhydrase and alcohol dehydrogenase; deficiency causes little leaf disease and khaira disease of rice. Boron facilitates sugar translocation and pectin formation; deficiency kills shoot tips and causes internal cork of apple and heart rot of sugar beet. Chlorine is involved in photolysis of water. Toxicity of micronutrients occurs at a narrow concentration range, and excess manganese can induce deficiencies of iron, magnesium, and calcium.
6) Mechanism of absorption of mineral elements
Explains how roots take up mineral ions from the soil solution through passive and active mechanisms. Mineral salt absorption is independent of water absorption and occurs maximally in the zone of elongation (not root hair zone). Passive absorption (without metabolic energy, demonstrated by Briggs and Robertson 1957) includes mass flow hypothesis (Hylmo, 1953), simple diffusion, facilitated diffusion via carrier proteins, and ion exchange hypothesis (contact exchange theory and carbonic acid exchange theory where CO2 from root respiration forms H2CO3 that dissociates and exchanges ions with clay colloids). Donnan equilibrium (F.G. Donnan, 1927) accounts for non-diffusible fixed ions across membranes. Active absorption (Hoagland, 1944) is supported by evidence that respiratory inhibitors check salt uptake and that higher respiration increases salt accumulation. Active transport theories include the carrier concept (Van den Honert, 1937, with kinase and phosphatase enzymes mediating carrier cycling using ATP), cytochrome pump hypothesis (Lundegardh, 1950, explaining salt/anion respiration), and protein-lecithin carrier concept (Bennet-Clark, 1956, using lecithin as an amphoteric carrier). Factors affecting absorption include temperature, light, oxygen, pH, interaction with other minerals, and growth.
7) Translocation of mineral ions
Explains how absorbed mineral ions move from roots to the rest of the plant. P.R. Stout and D.R. Hoagland (1939) proved that mineral salts are translocated through xylem. Two pathways exist: the apoplast pathway where ions move through cell wall spaces (polysaccharides) from epidermis through cortex to xylem traversing endodermis cytoplasm, and the symplast pathway where ions move through cytoplasm via plasmodesmata from epidermis through cortex, endodermis, pericycle, and into xylem. Once in the xylem, minerals are carried along with water to other parts of the plant via the transpiration stream. Minerals reaching leaves participate in the assimilation of organic compounds and are then transported to other parts of the plant through phloem sieve tubes. The redistribution through phloem is particularly important for mobile elements like nitrogen, phosphorus, potassium, and magnesium.
8) Soil as reservoir of mineral elements
Covers how soil functions as the primary source of mineral nutrients for plants. Mineral salts exist in soil solution dissolved in water and are also adsorbed onto colloidal clay particles (clay micelles). Leaching is the phenomenon where mineral salts dissolved in soil solution constantly pass downwards with percolating gravitational water, and it is more pronounced for anions than cations. The soil pH influences mineral availability: acidic pH favours availability of micronutrients like Fe, Mn, and Zn but reduces availability of Mo, while alkaline conditions increase P and Mo availability. Cation exchange capacity of clay particles determines how well soils retain nutrient cations. Sandy soils have lower retention capacity and are prone to nutrient depletion through leaching, particularly during rainy seasons. Constant agricultural cultivation depletes critical elements (N, P, K) which must be replenished through fertilisers. NPK fertilisers include ammonium chloride, ammonium sulphate, ammonium nitrate, bone meal, calcium magnesium phosphate, and nitrate of soda.
9) Nitrogen metabolism
Covers the entire nitrogen utilisation pathway in plants, from atmospheric fixation to assimilation into organic molecules. Nitrogen fixation occurs by abiological methods (atmospheric through lightning accounting for 10% of total, and industrial via Haber-Bosch process converting N2 + H2 to NH3) and biological methods (asymbiotic by free-living bacteria such as Azotobacter aerobic, Clostridium anaerobic, Chlorobium photosynthetic, cyanobacteria like Anabaena and Nostoc; and symbiotic by Rhizobium in legume root nodules and Frankia in non-legumes like Casuarina, Cycas, Alnus). The nitrogenase enzyme complex has two subunits: Fe protein (dinitrogen reductase, component I) and MoFe protein (dinitrogenase, component II). Leghaemoglobin acts as an oxygen scavenger to protect anaerobic nitrogenase. The equation is N2 + 8e- + 8H+ + 16ATP yields 2NH3 + H2 + 16ADP + 16Pi. Ammonification converts dead organic nitrogen to ammonia. Nitrification by Nitrosomonas (NH3 to NO2-) and Nitrobacter (NO2- to NO3-) as chemoautotrophs. Denitrification by Thiobacillus and Micrococcus converts nitrates back to N2. Nitrate assimilation proceeds through nitrate reductase (flavoprotein with FAD and Mo) reducing NO3- to NO2-, then nitrite reductase (needs Fe and Cu) reduces NO2- to NH3 via hyponitrite and hydroxylamine intermediates. Ammonia is immediately converted to glutamate using alpha-ketoglutarate and NADH.
10) Biological nitrogen fixation
Provides detailed mechanistic understanding of how living organisms convert atmospheric N2 into usable forms. The conversion of atmospheric nitrogen into inorganic or organic usable forms through the agency of living organisms is called biological nitrogen fixation. Symbiotic nitrogen fixation in legumes involves Rhizobium penetrating root cortex through infection threads, stimulating cortical cells to form root nodules. The pinkish colour of nodules is due to leghaemoglobin, which is closely related to haemoglobin and acts as an oxygen scavenger to maintain anaerobic conditions required by nitrogenase. The nitrogenase complex consists of Fe protein (dinitrogen reductase, component I) and MoFe protein (dinitrogenase, component II). Pyruvate acts as both ATP donor and electron donor via NADH2 and ferredoxin. Electrons flow from reducing agent to Mg-ATP-Fe protein complex, then to MoFe protein, and finally to N2. Free-living nitrogen fixers (Azotobacter, Clostridium, cyanobacteria) contribute 10-25 kg N per hectare per annum in soil, while cyanobacteria add 20-30 kg N2 per hectare. Ammonia produced is immediately converted to glutamate to avoid toxicity. Symbiotic associations also include Frankia with Casuarina and Alnus, and cyanobacteria with Azolla and Anthoceros.
Subtopics - Mineral Nutrition (NEET)
Ten major content blocks: essential mineral elements and their classification, roles of macro- and micronutrients, plant analysis methods, mineral absorption mechanisms, mineral translocation, soil as mineral reservoir, nitrogen metabolism with biological nitrogen fixation, and special modes of nutrition in plants.
11) Special modes of nutrition
Covers heterotrophic nutritional strategies in plants that cannot fully manufacture their own food. Parasites obtain organic food or water and minerals from a host using haustoria (specialised absorbing organs). Total stem parasite Cuscuta is rootless and yellow, twining around host with haustorial connections to xylem and phloem. Total root parasites include Orobanche (on brinjal and tobacco), Rafflesia (stinking corpse lily with the largest flower), and Balanophora. Partial parasites have chlorophyll and only take water and minerals: Viscum album (mistletoe) and Loranthus are partial stem parasites; Santalum album (sandalwood) and Striga are partial root parasites. Saprophytes like Monotropa (Indian pipe) and Neottia (bird's nest orchid) obtain nutrients through mycorrhizal associations. Symbiotic plants include lichens (phycobiont + mycobiont), root nodule legumes with Rhizobium, and myrmecophily (ants + Acacia sphaerocephala). Insectivorous plants grow in nitrogen-deficient marshy soils: Drosera (sundew, thigmonasty), Utricularia (bladderwort, bladder trap), Nepenthes (pitcher plant, N. khasiana endangered in Assam/Meghalaya), Dionaea (Venus fly trap, bilobed lamina), Sarracenia (trumpet pitchers, bacterial digestion), Pinguicula (butterwort, stalked and sessile glands), and Aldrovanda (rootless aquatic, bilobed leaves).
Mineral Nutrition Download Notes & Weightage Plan
For each topic in the Mineral Nutrition chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
Classification of elements into macronutrients and micronutrients based on Arnon and Stout criteria of essentiality. Quantitative thresholds, functional roles, and the 16 essential elements.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Direct questions on classification (macro vs micro), criteria of essentiality, and concentration thresholds appear frequently in NEET.
- High-risk Area: Confusing borderline elements: iron is intermediate between macro and micro; nickel is sometimes considered essential. Silicon and sodium are non-essential but occur in macronutrient range.
- Best Practice Style: Table-based recall with mnemonic: C HOPK N S CaMg (macronutrients) and FeMnCuZnMoBCl (micronutrients).
Specific role of macronutrients and micronutrients
Individual functions, sources, and deficiency symptoms of all 16 essential elements. Covers deficiency diseases with named symptoms for each element.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Named deficiency diseases are the most commonly tested aspect. Also frequently tested: which element activates which enzyme, and mobile vs immobile element symptom patterns.
- High-risk Area: Manganese toxicity mimics iron, magnesium, and calcium deficiency because Mn competes with these elements for uptake. Brown spots surrounded by chlorotic veins is Mn toxicity, not Mn deficiency.
- Best Practice Style: Disease-to-element matching drills. Practice MCQs that give deficiency symptoms and ask for the element.
Mechanism of absorption and translocation
Passive and active mechanisms of mineral absorption. Carrier concept, cytochrome pump hypothesis, protein-lecithin carrier. Apoplast and symplast translocation pathways through xylem.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Carrier concept (Van den Honert) and cytochrome pump (Lundegardh) with salt/anion respiration are most tested. Also tested: mineral absorption is independent of water absorption.
- High-risk Area: Lundegardh's hypothesis explains only anion absorption actively, with cations moving passively along the electrical gradient. Students often wrongly state both ions are actively absorbed.
- Best Practice Style: Theory comparison tables with one distinguishing feature highlighted for each.
Nitrogen metabolism and biological nitrogen fixation
Complete nitrogen cycle coverage: biological nitrogen fixation (symbiotic and asymbiotic), nitrogenase mechanism, leghaemoglobin, ammonification, nitrification, denitrification, and nitrate assimilation pathway.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Nitrogenase equation (16 ATP requirement), leghaemoglobin function, Nitrosomonas vs Nitrobacter distinction, and symbiotic vs asymbiotic examples are the most frequently tested.
- High-risk Area: Students confuse Nitrosomonas (NH3 to NO2-) with Nitrobacter (NO2- to NO3-). Also: nitrogenase needs anaerobic conditions (leghaemoglobin protects it), but nitrifying bacteria are aerobic chemoautotrophs.
- Best Practice Style: Draw the nitrogen cycle as a flow diagram with all organisms placed at their correct conversion step. Self-test by covering organism names.
Parasitic plants (total and partial, stem and root), saprophytes with mycorrhiza, symbiotic plants (lichens, root nodules, myrmecophily), and insectivorous plants with their trapping mechanisms.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Cuscuta (total stem parasite, haustoria to xylem and phloem), Nepenthes khasiana (endangered, Assam/Meghalaya), Rafflesia (largest flower), and Drosera (sundew) are most tested.
- High-risk Area: Sarracenia uses bacterial digestion (no digestive enzymes) while all other insectivorous plants use enzymatic (pepsin hydrochloride) digestion. Students often assume all use enzymes.
- Best Practice Style: Categorisation tables with one unique identification feature per organism.
Mineral Nutrition Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the Mineral Nutrition chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Assuming all deficiency symptoms appear in younger leaves: Mobile elements (N, Mg, K, P) are translocated from older to younger tissues, so their deficiency symptoms appear in <b>older leaves first</b>. Only immobile elements (Ca, S, Fe, B) show symptoms in younger leaves.
- Confusing iron and magnesium chlorosis patterns: Both cause interveinal chlorosis, but iron deficiency affects <b>younger</b> leaves (immobile) while magnesium deficiency affects <b>older</b> leaves (mobile). This distinction is a direct NEET trap.
A student sees 'interveinal chlorosis in younger leaves' and marks magnesium, but the correct answer is iron because younger leaf involvement indicates an immobile element.
How NEET Frames The Trap
NEET presents chlorosis symptoms and asks which element is deficient. The age of the affected leaf (younger vs older) is the critical differentiator that students overlook.
Q. Interveinal chlorosis appearing first in younger leaves is a characteristic deficiency symptom of:
A. Magnesium B. Nitrogen C. Iron D. Potassium
Trick: Iron is immobile so its deficiency appears in younger leaves. Magnesium is mobile so its chlorosis appears in older leaves first. The word 'younger' is the key differentiator.
Mistake Snapshot (What Students Do Wrong)
- Incorrectly recalling ATP requirement as 8 instead of 16: The nitrogenase equation requires <b>16 ATP</b> molecules to reduce one N2 to 2NH3. Students often confuse 8 (the number of electrons and H+ ions) with the ATP count.
- Thinking nitrogenase works in aerobic conditions: Nitrogenase functions only under <b>anaerobic conditions</b>. Leghaemoglobin acts as an oxygen scavenger to protect it. Students confuse Rhizobium (aerobic bacterium) with nitrogenase (anaerobic enzyme).
A student selects '8 ATP' because 8 appears twice in the equation (8e- and 8H+), missing that ATP requirement is separately 16.
How NEET Frames The Trap
NEET gives the nitrogenase reaction and asks for the number of ATP molecules consumed, or asks about the conditions required for nitrogenase activity.
Q. How many ATP molecules are required by nitrogenase to reduce one molecule of nitrogen to two molecules of ammonia?
A. 8 B. 12 C. 16 D. 32
Trick: The answer is 16 ATP. Students confuse 8 (electrons and H+ count) with ATP count. The complete equation is N2 + 8e- + 8H+ + 16ATP = 2NH3 + H2 + 16ADP + 16Pi.
Mistake Snapshot (What Students Do Wrong)
- Swapping the roles of Nitrosomonas and Nitrobacter: <b>Nitrosomonas</b> (and Nitrosococcus) convert ammonia to nitrite (NH3 to NO2-). <b>Nitrobacter</b> converts nitrite to nitrate (NO2- to NO3-). Students frequently reverse these.
- Classifying nitrifying bacteria as heterotrophs: Both Nitrosomonas and Nitrobacter are <b>chemoautotrophs</b> that derive energy from oxidation reactions to perform chemosynthesis. They are not heterotrophs.
A student attributes ammonia-to-nitrate conversion to a single organism, not realising it is a two-step process by two different bacterial genera.
How NEET Frames The Trap
NEET presents the nitrification pathway and asks which bacterium catalyses a specific step, or asks about the trophic mode of nitrifying bacteria.
Q. During nitrification, the conversion of ammonia to nitrite is carried out by:
A. Nitrobacter B. Nitrosomonas C. Rhizobium D. Thiobacillus denitrificans
Trick: The answer is Nitrosomonas. The mnemonic 'NitrosoMONAS handles aMMonium' helps. Nitrobacter handles the second step (nitrite to nitrate). Thiobacillus is a denitrifier.
Mistake Snapshot (What Students Do Wrong)
- Diagnosing brown spots with chlorotic veins as manganese deficiency: Brown spots surrounded by chlorotic veins are a symptom of <b>manganese toxicity</b> (excess), not deficiency. Manganese excess inhibits uptake of iron, magnesium, and calcium, so the visible symptoms may actually reflect secondary deficiencies.
- Ignoring element interaction effects: Excess manganese competes with iron and magnesium for uptake and inhibits calcium translocation. What appears as Mn toxicity may actually be Fe, Mg, or Ca deficiency symptoms.
A NEET question describes brown spots surrounded by chlorotic veins. Students mark iron or magnesium deficiency, but the correct answer is manganese toxicity.
How NEET Frames The Trap
The question describes classical Mn toxicity symptoms and asks to identify the condition, testing whether students recognise excess vs deficiency and inter-element competition.
Q. Appearance of brown spots surrounded by chlorotic veins is a prominent toxicity symptom of:
A. Iron B. Zinc C. Manganese D. Molybdenum
Trick: The answer is Manganese. This is a toxicity symptom, not deficiency. Mn competes with Fe, Mg for uptake and inhibits Ca translocation. Students confuse toxicity with deficiency.
Mistake Snapshot (What Students Do Wrong)
- Confusing whiptail (Mo) with little leaf (Zn): Whiptail disease of cauliflower and cabbage is caused by <b>molybdenum</b> deficiency. Little leaf disease is caused by <b>zinc</b> deficiency (due to reduced auxin from less tryptophan synthesis).
- Forgetting which disease belongs to which crop-element pair: Grey speck = Mn deficiency in oat. Khaira = Zn deficiency in rice. Die-back = Cu deficiency in Citrus. Internal cork = B deficiency in apple. Sickle leaf = P deficiency. Students mix these pairs.
A student sees 'whiptail disease in cauliflower' and selects zinc instead of molybdenum, confusing it with little leaf disease.
How NEET Frames The Trap
NEET gives a named deficiency disease and crop, asking which mineral element is responsible. The large number of disease-element-crop combinations creates frequent confusion.
Q. Whiptail disease of cauliflower is caused by the deficiency of:
A. Zinc B. Boron C. Molybdenum D. Manganese
Trick: The answer is Molybdenum. Students confuse this with zinc (which causes little leaf disease). Mo activates nitrate reductase and its deficiency causes leaf margins to become grey and flaccid in cauliflower (whiptail).
Mistake Snapshot (What Students Do Wrong)
- Assuming all insectivorous plants use enzymatic digestion: <b>Sarracenia</b> lacks digestive enzymes and uses <b>bacterial decomposition</b> for digestion. Most other insectivorous plants (Drosera, Dionaea, Nepenthes) use pepsin hydrochloride for enzymatic digestion.
- Confusing Nepenthes with Sarracenia pitcher type: Nepenthes has a <b>stalked pitcher with lid</b> (lamina modified) and uses enzymatic digestion. Sarracenia has <b>trumpet-shaped sessile pitchers</b> with bacterial digestion. Both are pitcher plants but differ in mechanism.
A student states Sarracenia secretes digestive enzymes like Nepenthes, not realising Sarracenia relies on bacterial decomposition.
How NEET Frames The Trap
NEET asks which insectivorous plant does NOT secrete digestive enzymes, or asks about the digestion mechanism in a specific pitcher plant.
Q. Which insectivorous plant digests trapped insects through bacterial decomposition rather than secreting its own digestive enzymes?
A. Drosera B. Dionaea C. Sarracenia D. Nepenthes
Trick: The answer is Sarracenia. It has trumpet-shaped sessile pitchers but lacks digestive enzymes, unlike Nepenthes which secretes pepsin. Drosera and Dionaea both use enzymatic digestion.
Mistake Snapshot (What Students Do Wrong)
- Claiming both anions and cations are actively absorbed in Lundegardh theory: In Lundegardh's cytochrome pump hypothesis, only <b>anions are actively absorbed</b>. Cations move <b>passively</b> along the electrical gradient created by anion accumulation at the inner membrane surface.
- Not knowing the term salt respiration: The increased respiration observed when a plant is transferred from water to salt solution is called <b>salt respiration or anion respiration</b>. This is the key evidence for Lundegardh's hypothesis.
A student states that Lundegardh's theory explains active absorption of all ions, but it only accounts for active anion transport with passive cation movement.
How NEET Frames The Trap
NEET asks about the limitation of Lundegardh's hypothesis or which ions are actively absorbed according to this theory.
Q. According to Lundegardh's cytochrome pump hypothesis, which of the following is correct?
A. Both cations and anions are actively absorbed B. Only cations are actively absorbed C. Only anions are actively absorbed and cations move passively D. Neither cations nor anions require energy
Trick: The answer is only anions are actively absorbed and cations move passively. The electrical gradient from accumulated anions pulls cations inward. This is both the core mechanism and the main limitation of the theory.