Role of Macro and Micro-nutrients Questions in English

(C) The element related to energy in plants is $Magnesium$ $(Mg^{2+})$.
$1$. $Magnesium$ is a crucial component of the chlorophyll molecule, which is essential for photosynthesis (energy production).
$2$. It is also required for the binding of the subunits of ribosomes, which are the sites of protein synthesis.
$3$. Therefore, $Magnesium$ is required for the maintenance of ribosome structure.
$4$. Option $A$ refers to $Sulfur$, option $B$ refers to $Iron$, and option $D$ refers to $Boron$.

(C) The correct matches are as follows:
$(a)$ Calcium: Required for the formation of the middle lamella in cell walls and is essential for the growth of meristematic tissues. Thus,$(a-r)$.
$(b)$ Phosphorus: $A$ major constituent of cell membranes,nucleic acids,and proteins. Thus,$(b-s)$.
$(c)$ Iron: It is a component of ferredoxin and cytochromes,which are involved in electron transport. Thus,$(c-p)$.
$(d)$ Manganese: It plays a crucial role in the splitting of water to liberate oxygen during photosynthesis and is also involved in $N_2$ metabolism. Thus,$(d-q)$.
Therefore,the correct sequence is $(a-r), (b-s), (c-p), (d-q)$.

(C) Calcium $(Ca^{2+})$ is an essential mineral nutrient for plants.
$(1)$ It is required for the formation of the mitotic spindle during cell division,but it is not the primary component of the spindle fibers themselves (which are made of tubulin protein). However,it is involved in the regulation of spindle formation.
$(2)$ This statement is incorrect as calcium is often a cofactor or activator for enzymes,not a barrier to their activity.
$(3)$ Calcium is essential for the synthesis of the cell wall,particularly as calcium pectate in the middle lamellae,which acts as a cementing material between cells.
$(4)$ It is required by meristematic and differentiating tissues for cell division and cell wall formation.
Therefore,statements $(3)$ and $(4)$ are correct.

(D) The correct matches are as follows:
$(a)$ Nitrogen is a major component of vitamins (e.g.,thiamine,biotin),thus $(a-4)$.
$(b)$ Potassium is essential for maintaining the ionic balance in cells,thus $(b-3)$.
$(c)$ Phosphorus is a component of $ATP$,which is required for the work done by $F_1$ (part of $ATP$ synthase),thus $(c-2)$.
$(d)$ Calcium is required for the activation of several enzymes,such as those involved in the hydrolysis of $ATP$ and phospholipids,thus $(d-1)$.
Therefore,the correct sequence is $(a-4), (b-3), (c-2), (d-1)$.

(C) The essential elements are classified based on their functions in plants.
$(1)$ Magnesium $(Mg^{2+})$ is a critical component of the ring structure of chlorophyll,which is the primary pigment involved in photosynthesis.
$(2)$ Phosphorus $(P)$ is a vital component of energy-related compounds such as $ATP$ $(Adenosine \ Triphosphate)$,$ADP$,and nucleic acids,which are essential for energy transfer and storage in cells.
Therefore,the correct pair is $(1) Mg$ and $(2) P$.

(C) Calcium $(Ca^{2+})$ is an essential mineral nutrient for plants. Let's analyze the statements:
$(i)$ Calcium is required during the formation of the mitotic spindle,which is correct.
$(ii)$ Calcium is not essential for auxin synthesis; Zinc is required for auxin synthesis. Thus,this statement is incorrect.
$(iii)$ Calcium is a structural component of the cell wall (calcium pectate) and is relatively immobile in plants. Therefore,it does not accumulate in older leaves; rather,it is found in younger tissues. This statement is incorrect.
$(iv)$ It is required by differentiating tissues,which is correct.
$(v)$ Calcium is not directly involved in the synthesis of nucleic acids. This statement is incorrect.
Therefore,statements $(ii), (iii),$ and $(v)$ are incorrect. However,based on the provided options,the most appropriate choice identifying the incorrect statements is $(ii)$ and $(v)$.

(B) The correct matches are as follows:
$a$. Magnesium $(Mg^{2+})$ is essential for maintaining the structure of ribosomes by binding to the ribosomal subunits.
$b$. Potassium $(K^+)$ plays a vital role in maintaining the anion-cation balance in cells.
$c$. Boron is involved in the translocation of carbohydrates within the plant.
$d$. Sulphur is a key constituent of amino acids like cysteine and methionine,and vitamins such as biotin and thiamine.
Therefore,the correct sequence is $a-ii, b-iv, c-i, d-v$.

(A) The toxicity of manganese in plants is characterized by the appearance of brown spots surrounded by chlorotic veins.
Excess manganese competes with iron and magnesium for uptake and with magnesium for binding with enzymes.
Manganese also inhibits calcium translocation in the shoot apex.
Therefore,excess manganese may induce deficiencies of iron,magnesium,and calcium.

(D) Option $D$ is correct. $Zn^{+2}$ acts as an essential cofactor or activator for the enzyme alcohol dehydrogenase.
Option $A$ is incorrect because Magnesium $(Mg^{+2})$,not Phosphorus,is the central constituent of the ring structure of chlorophyll.
Option $B$ is incorrect because $Mg^{+2}$ is the activator for $RuBisCO$,not $Ca^{+2}$.
Option $C$ is incorrect because Manganese $(Mn^{+2})$ and Chloride $(Cl^-)$ ions are involved in the splitting of water to liberate oxygen,not Nitrogen.

(A) Sulphur is a macronutrient found in amino acids like cysteine and methionine. It is a structural component of many coenzymes,vitamins (thiamine,biotin,coenzyme $A$),and ferredoxin. However,the formation of the mitotic spindle is primarily associated with calcium and other factors,not sulphur. Furthermore,boron is the element specifically required for carbohydrate translocation,not sulphur. Therefore,options $A$ and $C$ are technically incorrect statements regarding the role of sulphur. In the context of standard biology curriculum,boron's role in carbohydrate translocation is a classic point of distinction.

(D) Zinc $(Zn^{2+})$ is an essential micronutrient for plants. It is known to activate various enzymes,especially carboxylases,such as carbonic anhydrase. It is also required in the synthesis of auxin.

(A) Iron $(Fe)$ is an essential micronutrient for plants.
It is a vital component of ferredoxin and cytochromes,which are involved in electron transport.
It is essential for the formation of chlorophyll.
Crucially,it activates the enzyme catalase,which is responsible for the breakdown of hydrogen peroxide $(H_2O_2)$ in cells.
Therefore,option $A$ is correct.

(D) Molybdenum $(Mo)$ is an essential micronutrient for plants.
It is a critical component of two key enzymes involved in nitrogen metabolism: nitrogenase and nitrate reductase.
Nitrogenase is responsible for biological nitrogen fixation,while nitrate reductase is involved in the reduction of nitrate to nitrite during nitrogen assimilation.
Therefore,the correct option is $D$.

(B) Manganese $(Mn^{2+})$ has a complex interaction with other mineral nutrients.
$1$. It competes with iron $(Fe^{2+})$ and magnesium $(Mg^{2+})$ for uptake by the roots.
$2$. Furthermore,an excess of manganese inhibits the translocation of calcium $(Ca^{2+})$ to the shoot apex.
$3$. Therefore,symptoms of manganese toxicity may actually be caused by deficiencies of iron,magnesium,or calcium.

(C) The characteristics described are specific to the element Potassium $(K^+)$.
$(i)$ Potassium plays a vital role in maintaining the anion-cation balance within the cell.
$(ii)$ It is essential for protein synthesis and the activation of various enzymes.
$(iii)$ The opening and closing of stomata are regulated by the influx and efflux of $K^+$ ions in guard cells.
$(iv)$ Potassium is crucial for maintaining the turgidity of cells by regulating osmotic potential.
Therefore,the correct option is $C$.

(A) Iron $(Fe)$ is classified as a micronutrient because it is required by plants in small amounts compared to macronutrients. However,among all micronutrients,it is required in the largest quantity.
Iron is an essential component of proteins involved in electron transport,such as ferredoxin and cytochromes. It undergoes reversible oxidation $(Fe^{2+} \leftrightarrow Fe^{3+})$ during electron transfer.
Therefore,the correct option is $A$.

(C) Plants require mineral elements in varying amounts. Based on their quantitative requirements, they are divided into two categories: macronutrients and micronutrients.
Macronutrients are generally present in plant tissues in large amounts (in excess of $10 \text{ mmol kg}^{-1}$ of dry matter). Examples include Carbon, Hydrogen, Oxygen, Nitrogen $(N)$, Phosphorus $(P)$, Potassium $(K)$, Calcium $(Ca)$, Magnesium $(Mg)$, and Sulphur $(S)$.
Micronutrients or trace elements are needed in very small amounts (less than $10 \text{ mmol kg}^{-1}$ of dry matter). Examples include Iron $(Fe)$, Manganese $(Mn)$, Copper $(Cu)$, Molybdenum $(Mo)$, Zinc $(Zn)$, Boron $(B)$, Chlorine $(Cl)$, and Nickel $(Ni)$.
Therefore, among the given options, $Mn$ (Manganese) is a micronutrient, while $P$, $Ca$, and $N$ are macronutrients.

(D) Cytochromes are iron-containing hemoproteins that act as electron carriers in the electron transport chain. The central metal ion in the heme group of cytochromes is $Fe$ (Iron). While copper $(Cu)$ is present in cytochrome c oxidase (Complex $IV$),the fundamental prosthetic group of all cytochromes is the iron-porphyrin complex. Therefore,$Fe$ is the primary mineral associated with cytochromes.

(A) The middle lamella is a layer that cements the cell walls of two adjoining plant cells together.
It is primarily composed of calcium pectate and magnesium pectate.
Calcium $(Ca^{2+})$ ions are essential for the formation of these pectate salts,which provide structural stability to the middle lamella.
Therefore,$Ca$ is the essential element for the middle lamella.

(C) Plant nutrients are classified into two categories based on their quantitative requirements: macronutrients and micronutrients.
$1$. Macronutrients are required in large amounts (usually $ > 10 \text{ mmol kg}^{-1}$ of dry matter). Examples include Carbon, Hydrogen, Oxygen, Nitrogen, Phosphorus, Sulphur, Potassium, Calcium, and Magnesium.
$2$. Micronutrients or trace elements are required in very small amounts (usually $ < 10 \text{ mmol kg}^{-1}$ of dry matter). Examples include Iron, Manganese, Copper, Molybdenum, Zinc, Boron, Chlorine, and Nickel.
Among the given options, Calcium, Magnesium, and Nitrogen are macronutrients, whereas Manganese $(Mn)$ is a micronutrient.

(A) Boron is essential for the uptake and utilization of $Ca^{2+}$,membrane functioning,pollen germination,cell elongation,cell differentiation,and carbohydrate translocation.
Specifically,boron facilitates the transport of sugars (carbohydrates) across the cell membrane in the form of sugar-borate complexes.

(B) Micronutrients,also known as trace elements,are required in very small amounts by living organisms. Their primary biological role is to act as cofactors for various enzymes. Many enzymes require these metal ions (e.g.,$Zn^{2+}$,$Fe^{2+}$,$Mn^{2+}$,$Mo$) to function correctly,facilitating biochemical reactions within the cell. Therefore,they are essential for metabolic processes.

(B) Magnesium $(Mg^{2+})$ is an essential macronutrient for plants.
It is a central constituent of the chlorophyll molecule,which is the primary pigment responsible for photosynthesis.
Without magnesium,plants cannot synthesize chlorophyll,leading to chlorosis (yellowing of leaves).
Additionally,it acts as a cofactor for many enzymes involved in phosphate metabolism and $DNA$/$RNA$ synthesis.

(B) Manganese $(Mn^{2+})$ plays a crucial role in the process of photosynthesis. Its primary function is to act as a cofactor for the oxygen-evolving complex,which is responsible for the photolysis (splitting) of water molecules into oxygen,protons,and electrons. This reaction is essential for providing electrons to the electron transport chain in photosystem $II$.

(A) Calcium $(Ca^{2+})$ is essential for the formation of the cell wall,particularly as calcium pectate in the middle lamella. It is also required for the normal functioning of the cell membrane and is involved in the mitotic division of cells. Since the root apex is a region of active cell division (meristematic tissue),calcium is crucial for its growth and elongation.

$(C)$ Macronutrients are essential elements required by plants in large amounts (generally $10 \text{ mmol kg}^{-1}$ of dry matter).
These include Carbon,Hydrogen,Oxygen,Nitrogen,Phosphorus,Sulphur,Potassium,Calcium,and Magnesium.
Option $C$ contains Nitrogen,Potassium,and Phosphorus,all of which are macronutrients.
Iron,Copper,Molybdenum,Manganese,Boron,and Zinc are micronutrients.

(C) $Potassium$ $(K^+)$ is the most abundant cation in the cell and plays a crucial role in maintaining the turgor pressure of cells.
It regulates the opening and closing of stomata by changing the osmotic potential of guard cells.
It is also involved in protein synthesis, activation of enzymes, and maintenance of the anion-cation balance in cells.

(B) Essential elements are classified into macronutrients and micronutrients based on the quantity required by plants.
Micronutrients (trace elements) are required in very small amounts (less than $10 \text{ mmol kg}^{-1}$ of dry matter).
The micronutrients include Iron $(Fe)$, Manganese $(Mn)$, Copper $(Cu)$, Molybdenum $(Mo)$, Zinc $(Zn)$, Boron $(B)$, Chlorine $(Cl)$, and Nickel $(Ni)$.
Macronutrients are required in larger amounts and include Carbon $(C)$, Hydrogen $(H)$, Oxygen $(O)$, Nitrogen $(N)$, Phosphorus $(P)$, Sulfur $(S)$, Potassium $(K)$, Calcium $(Ca)$, and Magnesium $(Mg)$.
Option $B$ contains $Cu, Fe, Zn, B, Mn$, all of which are micronutrients.

(A) Essential elements are divided into macronutrients and micronutrients based on their quantitative requirements.
Macronutrients are required in large amounts (e.g.,$C, H, O, N, P, K, S, Mg, Ca$).
Micronutrients are required in very small amounts (trace amounts). These include $Fe, Mn, Cu, Mo, Zn, B, Cl,$ and $Ni$.
Among the given options,$Ca$ (Calcium) is a macronutrient,while $Mn, Zn,$ and $Cu$ are micronutrients.
Therefore,$Ca$ is not a micronutrient.

(A) Magnesium $(Mg^{2+})$ is the central structural component of the chlorophyll molecule's porphyrin ring.
Manganese $(Mn^{2+})$ is involved in the photolysis of water during photosynthesis and acts as an enzyme activator,but it is not a structural component of chlorophyll.
Calcium $(Ca^{2+})$ is required for the formation of calcium pectate in the middle lamella of cell walls.
Zinc $(Zn^{2+})$ acts as an activator for various enzymes,such as alcohol dehydrogenase and carbonic anhydrase.
Iron $(Fe)$ is a vital component of ferredoxin and cytochromes,which are involved in electron transport.
Therefore,the match in option $A$ is incorrect.

(N/A) Essential mineral elements play diverse roles in plant metabolism,which include:
$\Rightarrow$ Maintaining the permeability of the cell membrane.
$\Rightarrow$ Regulating the osmotic concentration of the cell sap.
$\Rightarrow$ Functioning as components of electron transport systems.
$\Rightarrow$ Acting as buffers to maintain cellular $pH$.
$\Rightarrow$ Serving as cofactors or activators for enzymatic activity.
$\Rightarrow$ Acting as major structural constituents of biological macromolecules (like proteins,nucleic acids) and co-enzymes.

(N/A) $\Rightarrow$ Nitrogen: Absorbed as $NO_{3}^{-}, NO_{2}^{-}, NH_{4}^{+}$. Required in meristematic tissues and metabolically active cells. Major constituent of proteins,nucleic acids,vitamins,and hormones.
$\Rightarrow$ Phosphorus: Absorbed as $H_{2}PO_{4}^{-}$ or $HPO_{4}^{2-}$. Constituent of cell membranes,nucleic acids,and nucleotides. Required for all phosphorylation reactions.
$\Rightarrow$ Potassium $(K^{+})$: Absorbed as $K^{+}$. Required in meristematic tissues,buds,leaves,and root tips. Maintains anion-cation balance,protein synthesis,stomatal opening/closing,and cell turgidity.
$\Rightarrow$ Calcium $(Ca^{2+})$: Absorbed as $Ca^{2+}$. Required by meristematic and differentiating tissues. Used in cell wall synthesis (calcium pectate in middle lamella) and mitotic spindle formation. Involved in membrane functioning and enzyme activation.
$\Rightarrow$ Magnesium $(Mg^{2+})$: Absorbed as $Mg^{2+}$. Activates enzymes of respiration and photosynthesis. Involved in $DNA$ and $RNA$ synthesis. Constituent of chlorophyll ring structure and maintains ribosome structure.
$\Rightarrow$ Sulphur: Absorbed as $SO_{4}^{2-}$. Present in amino acids (cysteine,methionine). Constituent of coenzymes,vitamins (thiamine,biotin,Coenzyme $A$),and ferredoxin.
$\Rightarrow$ Iron: Absorbed as $Fe^{3+}$. Constituent of proteins involved in electron transfer (ferredoxin,cytochromes). Reversibly oxidized between $Fe^{2+}$ and $Fe^{3+}$. Activates catalase and essential for chlorophyll formation.
$\Rightarrow$ Manganese: Absorbed as $Mn^{2+}$. Activates enzymes in photosynthesis,respiration,and nitrogen metabolism. Essential for water-splitting reaction to liberate oxygen.
$\Rightarrow$ Zinc: Absorbed as $Zn^{2+}$. Activates carboxylases and required for auxin synthesis.
$\Rightarrow$ Copper: Absorbed as $Cu^{2+}$. Essential for overall metabolism and redox reactions. Reversibly oxidized between $Cu^{+}$ and $Cu^{2+}$.
$\Rightarrow$ Boron: Absorbed as $BO_{3}^{3-}$ or $B_{4}O_{7}^{2-}$. Required for $Ca^{2+}$ uptake/utilization,membrane functioning,pollen germination,cell elongation,and carbohydrate translocation.
$\Rightarrow$ Molybdenum: Absorbed as $MoO_{2}^{2+}$. Component of nitrogenase and nitrate reductase,involved in nitrogen metabolism.
$\Rightarrow$ Chlorine: Absorbed as $Cl^{-}$. Along with $Na^{+}$ and $K^{+}$,helps determine solute concentration and anion-cation balance. Essential for water-splitting reaction in photosynthesis.

(N/A) $\Rightarrow$ The requirement of micronutrients is always in low amounts.
$-\quad$ Their moderate decrease causes deficiency symptoms.
$\Rightarrow$ Their moderate increase causes toxicity.
$\Rightarrow$ Any mineral ion concentration in tissues that reduces the dry weight of tissues by about $10\%$ is considered toxic.
$\Rightarrow$ Such critical concentrations vary widely among different micronutrients.
$\Rightarrow$ Toxicity symptoms are often difficult to identify.
$\Rightarrow$ Toxicity levels for any element also vary among different plants.
$\Rightarrow$ Many times,an excess of one element may inhibit the uptake of another element.
$\Rightarrow$ Example: Toxicity of Manganese $(Mn)$:
$\Rightarrow$ The appearance of brown spots surrounded by chlorotic veins.
$\Rightarrow$ Manganese competes with Iron $(Fe)$ and Magnesium $(Mg)$ for binding with enzymes.
$\Rightarrow$ Manganese inhibits Calcium $(Ca)$ translocation to the shoot apex.
$\Rightarrow$ Therefore,an excess of Manganese may,in fact,induce deficiencies of Iron,Magnesium,and Calcium.
$\Rightarrow$ Thus,what appears as symptoms of Manganese toxicity may actually be the deficiency symptoms of Iron,Magnesium,and Calcium.

(D) Potassium $(K^+)$ is an essential macronutrient for plants. Its primary functions include:
$1$. It helps in maintaining the turgidity of cells by regulating osmotic potential.
$2$. It is involved in the activation of many enzymes,which are crucial for metabolic processes.
$3$. It plays a vital role in protein synthesis.
$4$. It regulates the opening and closing of stomata,which is essential for gas exchange and transpiration.
Therefore,all the given options are correct functions of $K^+$.

(D) Calcium $(Ca^{2+})$ is an essential macronutrient for plants. Its importance includes:
$1$. It is required by meristematic and differentiating tissues.
$2$. During cell division,it is used in the synthesis of the cell wall,particularly as calcium pectate in the middle lamella.
$3$. It is also needed during the formation of the mitotic spindle.
$4$. It accumulates in older leaves and is involved in the normal functioning of cell membranes.
$5$. It activates certain enzymes and plays an important role in regulating metabolic activities.

(D) The usefulness of $Mg^{2+}$ in plants includes:
$1$. It acts as a constituent of the ring structure of chlorophyll,which is essential for photosynthesis.
$2$. It activates many enzymes involved in respiration and photosynthesis.
$3$. It is involved in the synthesis of nucleic acids like $DNA$ and $RNA$.
$4$. It helps in maintaining the structure of ribosomes by binding the two subunits together.

(B) $\Rightarrow$ It is required in larger amounts in comparison to other micronutrients.
$\Rightarrow$ It is an important constituent of proteins involved in the transfer of electrons like ferredoxin and cytochromes.
$\Rightarrow$ It is reversibly oxidised from $Fe^{+2}$ to $Fe^{+3}$ during electron transfer.
$\Rightarrow$ It activates the catalase enzyme.
$\Rightarrow$ It is essential for the formation of chlorophyll.

(A) $1$. $Zn^{2+}$ (Zinc): It activates various enzymes,especially carboxylases. It is also essential for the synthesis of auxin,a plant growth hormone.
$2$. $Cu^{2+}$ (Copper): It is essential for the overall metabolism in plants. Like iron,it is associated with certain enzymes involved in redox reactions and is reversibly oxidized from $Cu^{+}$ to $Cu^{2+}$.

(D) Boron is an essential micronutrient for plants. Its primary roles include:
$1$. $Boron$ is required for the uptake and utilization of $Ca^{2+}$.
$2$. It plays a crucial role in pollen germination and tube growth.
$3$. It is essential for cell elongation and cell differentiation.
$4$. It facilitates the translocation of carbohydrates.
Deficiency symptoms include the death of root and shoot tips,and the inhibition of pollen germination.

(B) $\Rightarrow$ It is absorbed by plants in the form of chloride ions $(Cl^{-})$.
$\Rightarrow$ Along with $Na^{+}$ and $K^{+}$,it plays a crucial role in determining the solute concentration and maintaining the anion-cation balance within the cells.
$\Rightarrow$ It is essential for the water-splitting reaction in photosynthesis,which leads to the evolution of oxygen.

(C) Nitrogen $(N)$ is considered a marginal factor because it is required by plants in large quantities for the synthesis of proteins,nucleic acids,vitamins,and enzymes.
Although $N$ is abundant in the atmosphere as $N_2$ gas,plants cannot utilize it directly.
In the soil,nitrogen is often present in limited amounts or in forms that are not easily accessible to plants.
Due to this high demand for growth and its frequent scarcity in the soil,nitrogen often acts as a limiting factor,thereby restricting the overall productivity of the plant.

(N/A)

Macronutrients	Micronutrients
They are present in plant tissues in large amounts (in excess of $10 \text{ mmol kg}^{-1}$ of dry matter).	They are present in plant tissues in very small amounts (less than $10 \text{ mmol kg}^{-1}$ of dry matter).
Examples: $C, H, O, N, P, K, S, Ca, Mg$.	Examples: $Fe, Mn, Cu, Mo, Zn, B, Cl, Ni$.

(N/A) $(1)$ Macronutrients: These are elements present in plant tissues in large amounts,typically in excess of $10 \text{ mmol } kg^{-1}$ of dry matter.
$(2)$ Micronutrients: These are elements required by plants in very small amounts,typically less than $10 \text{ mmol } kg^{-1}$ of dry matter.

(N/A) $\Rightarrow$ Sulphur is a macronutrient. It is absorbed by plants in the form of $SO_{4}^{2-}$ ions.
$\Rightarrow$ It is a structural component of vitamins (biotin and thiamine),coenzyme $A$,and ferredoxin.
$\Rightarrow$ It is essential for the synthesis of specific amino acids and is involved in the formation of secondary metabolites like sinigrin.
$\Rightarrow$ Deficiency of sulphur leads to chlorosis,particularly in younger leaves,and can cause stems to become hard and woody. It also affects the quality of fruits and causes yellowing in tea leaves.
$\Rightarrow$ Sulphur is present in the amino acids $Cysteine$ and $Methionine$.

(N/A) $(1)$ Major constituent elements: Essential elements that act as components of biomolecules and are structural elements of the cell. For example,$C$,$H$,and $O$ are major constituent elements found in the composition of carbohydrates and are also present in the cell wall.
$(2)$ Cell membrane and plasma-based elements: $N$,$P$,and $S$ are constituent elements of the cell membrane and plasma. These form the plasma along with $C$,$H$,and $O$.
$(3)$ Elements for enzyme activity: Some enzymes do not function without the presence of mineral elements. For example,$RuBisCO$ functions in the presence of $Mg^{2+}$,and the presence of $Mg^{2+}$ is also necessary for $PEP$ carboxylase.
$(4)$ Elements for osmotic potential maintenance: Potassium $(K^{+})$ plays an important role in the opening and closing of stomata.
$(5)$ Elements for ionic balance: They help in maintaining the ionic balance or equilibrium of the cell,for example,$Ca^{2+}$,$Mg^{2+}$,and $K^{+}$.

(N/A) $\Rightarrow$ Each plant has a requirement for micronutrients in very low amounts. $A$ moderate decrease causes deficiency symptoms,while a moderate increase causes toxicity.
$\Rightarrow$ Any mineral ion concentration in tissues that reduces the dry weight of tissues by about $10 \%$ is considered toxic.
$\Rightarrow$ Toxicity levels vary for different micronutrients and different plant species. For example,$Mn^{+2}$ toxicity is a common issue. Concentrations above $600 \mu g g^{-1}$ are toxic for many plants,while $300 \mu g g^{-1}$ is toxic for soybean and sunflower.
$\Rightarrow$ Toxicity symptoms are often difficult to identify because the excess of one element may inhibit the uptake of other nutrients.
$\Rightarrow$ For example,the prominent symptom of manganese toxicity is the appearance of brown spots surrounded by chlorotic veins.
$\Rightarrow$ Manganese toxicity occurs because:
$(i)$ It competes with $Fe^{+2}$ and $Mg^{+2}$ for uptake.
$(ii)$ It inhibits the binding of $Mg^{+2}$ to enzymes.
$(iii)$ It inhibits the translocation of $Ca^{+2}$ to the shoot apex.
$\Rightarrow$ Thus,excess $Mn^{+2}$ induces deficiencies of iron,magnesium,and calcium.

(A) $(1)$ Micronutrients are essential elements required in small amounts by plants. Manganese $(Mn)$ is a classic example of a micronutrient.
$(2)$ Nitrogenase is an enzyme involved in biological nitrogen fixation,and it requires Molybdenum $(Mo)$ as a cofactor for its activity.

(MAGNESIUM, BORON) $(1)$ Magnesium is a central atom in the porphyrin ring of the chlorophyll molecule.
$(2)$ Boron is essential for the translocation of carbohydrates (sugars) through the phloem.