Part 1 — Methods to Study Mineral Requirements, Essentiality, Macronutrients & Micronutrients (Q1–25)

Part 1 — Methods to Study Mineral Requirements, Essentiality, Macronutrients & Micronutrients (Q1–25)

Q1.

What is hydroponics?
A. Growing plants in soil with added organic manure
B. Growing plants in nutrient solution without soil ✅
C. Growing plants in sand only
D. A technique for sterilizing soil

Explanation:

• A. This is conventional soil culture with organic amendment, not hydroponics.
• B. (Correct) Hydroponics is a soilless culture technique in which plant roots are supplied with an aqueous solution containing all required mineral nutrients — widely used to study mineral nutrition because the nutrient environment can be precisely controlled.
• C. Growing in sand is a medium-based culture but not the complete definition of hydroponics (hydroponics uses nutrient solutions; an inert medium may be used only to support roots).
• D. Hydroponics is not a sterilization technique.

Q2.

Why is hydroponics particularly useful to determine essentiality of mineral elements?
A. It mimics natural soil microbes exactly
B. It allows precise omission and control of individual nutrients ✅
C. It only provides organic nutrients
D. It increases atmospheric CO₂ for plants

Explanation:

• A. Hydroponics does not necessarily mimic soil microbial complexity; in fact, it often excludes microbes.
• B. (Correct) Because plants are grown in defined nutrient solutions, researchers can omit a single element and observe whether the plant cannot complete its life cycle — a key experimental test of essentiality.
• C. Hydroponic solutions supply inorganic mineral ions, not just organics.
• D. Hydroponics doesn’t inherently change atmospheric CO₂; that is unrelated to essentiality testing.

Q3.

Which of the following is commonly used as an inert support medium in hydroponic culture?
A. Peat soil (rich organic soil)
B. Perlite or rockwool ✅
C. Compost with high microbial load
D. Fertile loam

Explanation:

• A/C/D. Organic soils and compost contain nutrients and microbes which confound controlled nutrient studies.
• B. (Correct) Perlite, rockwool, and washed sand are inert supports often used in hydroponics so roots are supported while nutrients are supplied solely by the solution — allowing precise control of mineral supply.

Q4.

Which experimental approach was classically used to demonstrate that a particular element is essential for plant growth?
A. Increasing light intensity only
B. Omitting the element from a defined nutrient solution and observing failure to complete life cycle ✅
C. Growing plants in different soil textures keeping nutrient supply same
D. Measuring soil pH changes

Explanation:

• A. Light manipulation alone does not address mineral essentiality.
• B. (Correct) The standard experimental criterion: when a plant grown in otherwise complete defined solution fails to complete its life cycle (e.g., cannot flower/produce viable seeds) in the absence of a specific element, that element is considered essential. Hydroponics enables this omission test.
• C/D. Soil texture/pH studies are useful but don’t directly demonstrate essentiality of a specific element.

Q5.

Which of these is NOT part of the classical criteria for an element to be considered essential for plant growth?
A. The plant cannot complete its life cycle without the element
B. The element is directly involved in plant metabolism (not replaceable by any other element)
C. The element is required in a larger amount than all others ✅
D. No other element can replace its function

Explanation:

• A/B/D. These are classical criteria: inability to complete life cycle without it; direct role in metabolism; and irreplaceability by another element.
• C. (Correct) The amount required (larger or smaller) is not a criterion of essentiality — an element can be essential even in trace amounts. Essentiality concerns necessity and irreplaceability, not relative quantity required.

Q6.

Which scientist’s law is most closely associated with the concept that plant growth is limited by the scarcest nutrient?
A. Darwin’s law
B. Liebig’s law of the minimum ✅
C. Mendel’s law
D. Hooke’s law

Explanation:

• A/C/D. Not relevant.
• B. (Correct) Liebig’s law of the minimum states that plant growth is controlled not by the total resources available, but by the scarcest (limiting) resource — a principle central to mineral nutrition.

Q7.

Which of the following is a macronutrient (required in relatively large amounts) for plants?
A. Iron (Fe)
B. Zinc (Zn)
C. Magnesium (Mg) ✅
D. Molybdenum (Mo)

Explanation:

• A/B/D. Fe, Zn, and Mo are micronutrients (required in trace amounts).
• C. (Correct) Magnesium is a macronutrient — needed in relatively larger quantities (component of chlorophyll, cofactor for many enzymes).

Q8.

Which of the following is typically classified as a micronutrient (essential in trace amounts)?
A. Nitrogen (N)
B. Potassium (K)
C. Phosphorus (P)
D. Manganese (Mn) ✅

Explanation:

• A/B/C. N, P, and K are macronutrients (primary nutrients).
• D. (Correct) Manganese is a micronutrient required in small amounts as a cofactor in photosynthetic and enzymatic reactions.

Q9.

Which element is commonly considered a beneficial (not strictly essential) element for many plants, especially grasses?
A. Boron (B)
B. Sodium (Na) ✅
C. Nitrogen (N)
D. Phosphorus (P)

Explanation:

• A/C/D. B is an essential micronutrient for many plants; N and P are essential macronutrients.
• B. (Correct) Sodium is considered a beneficial element for some plants (e.g., certain C4 or halophytic species) — it can substitute partially for K in osmotic functions or be used metabolically by some species, but is not universally essential.

Q10.

Calcium’s primary role in plants is best described as:
A. Central atom of chlorophyll molecule
B. Structural component of cell walls and membranes ✅
C. Main osmoticum in guard cells
D. Major component of ATP

Explanation:

• A. Magnesium (Mg) is central in chlorophyll.
• B. (Correct) Calcium (Ca²⁺) stabilizes cell wall (pectate cross-linking) and membrane integrity; it’s relatively immobile and deficiency affects growing tips.
• C. Potassium (K⁺) is the major osmotic regulator in guard cells.
• D. Phosphorus is the key component of ATP.

Q11.

Magnesium is essential in plants mainly because it:
A. Activates many enzymes and is central in chlorophyll ✅
B. Carries oxygen in plant blood
C. Is the main building block of cellulose
D. Is required for nodule formation only

Explanation:

• A. (Correct) Mg²⁺ is the central atom in chlorophyll and acts as a cofactor/activator for many enzymes (notably those involved in photosynthesis and carbohydrate metabolism).
• B. Plants do not have blood; oxygen transport is not by Mg.
• C. Cellulose is composed of glucose polymers (C, H, O).
• D. Nodule formation involves other elements (e.g., Mo, Fe); Mg is not uniquely required for nodulation.

Q12.

Which nutrient is most directly required for ATP and nucleic acid synthesis?
A. Nitrogen (N)
B. Sulfur (S)
C. Phosphorus (P) ✅
D. Calcium (Ca)

Explanation:

• A/B/D. Important for proteins, sulphur-containing amino acids, and structure, respectively.
• C. (Correct) Phosphorus is a component of ATP, ADP, nucleic acids (DNA/RNA), phospholipids — central to energy transfer and genetic material.

Q13.

Which of the following elements is a constituent of some amino acids (e.g., cysteine, methionine) and is essential for protein synthesis?
A. Boron (B)
B. Sulphur (S) ✅
C. Iron (Fe)
D. Chlorine (Cl)

Explanation:

• A/C/D. Not constituents of amino acids in the same way.
• B. (Correct) Sulphur is present in cysteine and methionine and thus essential for protein structure and function.

Q14.

Potassium (K) is crucial in plants primarily because it:
A. Forms the backbone of DNA
B. Regulates stomatal movement and osmotic balance ✅
C. Binds oxygen in chloroplasts
D. Is the central atom of chlorophyll

Explanation:

• A. DNA backbone is phosphodiester bonds with phosphorus.
• B. (Correct) K⁺ is a major osmoticum controlling turgor in guard cells and many cells — it plays key roles in stomatal regulation, enzyme activation, and ionic balance.
• C/D. Incorrect — Mg is central in chlorophyll, not K.

Q15.

Which of these is a typical symptom of nitrogen deficiency in plants?
A. Interveinal chlorosis in young leaves
B. General chlorosis and stunted growth, starting in older leaves ✅
C. Necrotic leaf margins
D. Deformation of new leaves only

Explanation:

• A. Interveinal chlorosis in young leaves usually indicates iron deficiency (immobile element).
• B. (Correct) Nitrogen is mobile; when deficient, older leaves show yellowing (chlorosis) first as N is translocated to growing tissues — overall stunting and pale green color are classic symptoms.
• C. Necrotic margins are commonly K deficiency.
• D. New-leaf deformation suggests immobile element deficiency (e.g., Ca).

Q16.

An interveinal chlorosis of young leaves (veins remain green) typically indicates deficiency of:
A. Nitrogen (N)
B. Iron (Fe) ✅
C. Potassium (K)
D. Magnesium (Mg)

Explanation:

• A. Nitrogen leads to uniform chlorosis starting in older leaves.
• B. (Correct) Iron deficiency causes interveinal chlorosis particularly in new leaves because Fe is relatively immobile. Veins often stay green while interveinal areas turn yellow.
• C/D. K and Mg deficiencies show different symptoms (Mg deficiency is interveinal chlorosis but often starts on older leaves; context differentiates Fe vs Mg).

Q17.

Which nutrient’s deficiency symptoms typically appear first in older leaves, indicating its mobility in the plant?
A. Calcium (Ca)
B. Nitrogen (N) ✅
C. Iron (Fe)
D. Boron (B)

Explanation:

• A/C/D. Ca, Fe, B are relatively immobile — deficiencies show in young tissues first.
• B. (Correct) Mobile nutrients like nitrogen are remobilized from older to younger tissues; thus deficiency symptoms commonly appear first in older leaves.

Q18.

Excess of which micronutrient is most commonly associated with copper toxicity symptoms like stunted roots and chlorosis?
A. Zinc (Zn)
B. Copper (Cu) ✅
C. Boron (B)
D. Molybdenum (Mo)

Explanation:

• A/C/D. Excess of other micronutrients causes other symptoms (e.g., B toxicity causes necrosis at tips).
• B. (Correct) Copper in excess is phytotoxic — causes root growth inhibition, chlorosis, and necrosis due to interfering with normal metabolic processes.

Q19.

Which process among the following is an example of active absorption of mineral ions by root cells?
A. Movement of water down a concentration gradient by osmosis
B. Uptake of NO₃⁻ via H⁺-NO₃⁻ symporter using proton gradient generated by H⁺-ATPase ✅
C. Diffusion of O₂ into root cells
D. Capillary movement of nutrient solution in soil

Explanation:

• A. Osmosis is passive.
• B. (Correct) Active uptake often involves proton pumps generating H⁺ gradients; secondary active transporters (symporters/antiporters) use that gradient to drive uptake of ions like nitrate against their concentration gradient. This exemplifies active absorption.
• C/D. Passive processes or physical phenomena, not active ion uptake.

Q20.

Root hairs enhance mineral absorption mainly by:
A. Increasing photosynthesis rate
B. Increasing root surface area for uptake ✅
C. Producing hormones to attract microbes
D. Storing excess nutrients

Explanation:

• A. Photosynthesis occurs in leaves.
• B. (Correct) Root hairs are tubular extensions that greatly increase the root surface area and thus the contact with soil solution — facilitating water and mineral uptake.
• C/D. Not primary functions of root hairs.

Q21.

Which pathway of ion/water movement in root cortex involves successive crossing of plasma membranes (in and out) of cells?
A. Apoplast pathway
B. Symplast pathway
C. Transmembrane pathway ✅
D. Xylem flow pathway

Explanation:

• A. Apoplast = movement through cell walls and intercellular spaces without crossing membranes (until endodermis).
• B. Symplast = movement through cytoplasm via plasmodesmata (crosses plasma membrane once to enter symplast).
• C. (Correct) Transmembrane route involves repeated movement across membranes and cell walls (into and out of cells), i.e., crossing plasma membrane multiple times.
• D. Xylem is long-distance transport, not a root cortical pathway.

Q22.

The Casparian strip in the endodermis functions to:
A. Allow free apoplastic flow into the stele
B. Block apoplastic flow forcing selective uptake via symplast ✅
C. Produce root hairs
D. Store mineral ions in vacuoles

Explanation:

• A. Casparian strip prevents free apoplastic flow.
• B. (Correct) The suberin-rich Casparian strip blocks the apoplast at the endodermis, forcing water and solutes to cross plasma membranes (enter symplast) — enabling selective uptake and regulation before minerals enter the vascular stele.
• C/D. Not functions of Casparian strip.

Q23.

Mineral ions absorbed by roots are mainly translocated to aerial parts through:
A. Phloem by mass flow
B. Xylem in the transpiration stream ✅
C. Cortex symplast only
D. Root hair exudation

Explanation:

• A. Phloem transports organic solutes (sugars), not bulk mineral upward movement.
• B. (Correct) Minerals travel with water in the xylem sap (transpiration stream) to stems and leaves — xylem is the primary pathway for mineral translocation upward.
• C/D. Not major long-distance routes.

Q24.

Biological nitrogen fixation by symbiotic bacteria (e.g., Rhizobium) converts atmospheric N₂ into:
A. NO₃⁻ (nitrate) directly
B. NH₃ / NH₄⁺ (ammonia/ammonium) via nitrogenase ✅
C. N₂O only
D. Amino acids inside plant nucleus

Explanation:

• A. Nitrogenase first reduces N₂ to ammonia (NH₃), which is then converted to ammonium and incorporated into organic forms; nitrification to NO₃⁻ is a separate microbial process in soil.
• B. (Correct) Symbiotic nitrogen fixation produces ammonia/ammonium via the enzyme nitrogenase in bacteroids within nodules.
• C. N₂O can be a by-product of denitrification, not the primary fixed product of nitrogenase.
• D. Amino acid synthesis occurs later in plant metabolism, not a direct immediate product in the nucleus.

Q25.

Which micronutrient is a cofactor for the nitrogenase enzyme complex and is therefore essential for biological nitrogen fixation?
A. Boron (B)
B. Molybdenum (Mo) ✅
C. Sodium (Na)
D. Silicon (Si)

Explanation:

• A/C/D. Not the primary cofactor for nitrogenase.
• B. (Correct) Molybdenum is a crucial component of the nitrogenase enzyme (Fe–Mo cofactor) required for N₂ reduction — deficiencies impair nitrogen fixation in nodules.

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