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Plant Physiology - Mineral Nutrition (Essential Minerals, Nitrogen Cycle)

Grade 11ICSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Criteria for Essentiality: An element is essential if the plant cannot complete its life cycle without it, the requirement is specific (not replaceable by another element), and it is directly involved in plant metabolism.

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Macronutrients: These are required in large amounts (more than 10 mmole kg−110\text{ mmole } kg^{-1} of dry matter). They include C,H,O,N,P,K,S,Ca,C, H, O, N, P, K, S, Ca, and MgMg.

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Micronutrients: These are trace elements required in very low amounts (less than 10 mmole kg−110\text{ mmole } kg^{-1} of dry matter), including Fe,Mn,Cu,Mo,Zn,B,Cl,Fe, Mn, Cu, Mo, Zn, B, Cl, and NiNi.

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Biological Nitrogen Fixation: The conversion of atmospheric N2N_2 to NH3NH_3 by living organisms using the enzyme NitrogenaseNitrogenase. This process is highly energy-consuming, requiring 88 ATP for every one NH3NH_3 produced.

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Nitrification: The two-step biological oxidation of ammonia to nitrate. NH3NH_3 is first converted to NO2−NO_2^- (Nitrite) by NitrosomonasNitrosomonas or NitrococcusNitrococcus, and then to NO3−NO_3^- (Nitrate) by NitrobacterNitrobacter.

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Leghemoglobin: A pink-colored pigment found in the root nodules of leguminous plants that acts as an oxygen scavenger, protecting the oxygen-sensitive NitrogenaseNitrogenase enzyme.

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Ammonification: The process of decomposition of organic nitrogen (from dead plants and animals) into ammonia (NH3NH_3) by soil microbes.

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Denitrification: The process where soil nitrates (NO3−NO_3^-) are reduced back into atmospheric nitrogen (N2N_2) by bacteria like PseudomonasPseudomonas and ThiobacillusThiobacillus.

📐Formulae

N2+8e−+8H++16ATP→2NH3+H2+16ADP+16PiN_2 + 8e^- + 8H^+ + 16ATP \rightarrow 2NH_3 + H_2 + 16ADP + 16P_i

2NH3+3O2→2NO2−+2H++2H2O2NH_3 + 3O_2 \rightarrow 2NO_2^- + 2H^+ + 2H_2O

2NO2−+O2→2NO3−2NO_2^- + O_2 \rightarrow 2NO_3^-

α-ketoglutaric acid+NH4++NADPH→Glutamate DehydrogenaseGlutamate+H2O+NADP+\alpha\text{-ketoglutaric acid} + NH_4^+ + NADPH \xrightarrow{\text{Glutamate Dehydrogenase}} \text{Glutamate} + H_2O + NADP^+

Amino donor+Keto acceptor→TransaminaseAmino product+Keto product\text{Amino donor} + \text{Keto acceptor} \xrightarrow{\text{Transaminase}} \text{Amino product} + \text{Keto product}

💡Examples

Problem 1:

Calculate the total number of ATPATP molecules required to fix 33 molecules of N2N_2 into NH3NH_3 during biological nitrogen fixation.

Solution:

The production of 22 molecules of NH3NH_3 from 11 molecule of N2N_2 requires 1616 ATPATP. Therefore, to fix 33 molecules of N2N_2, the ATPATP required is 3×16=483 \times 16 = 48 ATPATP.

Explanation:

According to the balanced equation for nitrogen fixation, 88 ATPATP are consumed for every 11 NH3NH_3 produced. Since 11 N2N_2 yields 22 NH3NH_3, 1616 ATPATP are needed per N2N_2 molecule.

Problem 2:

A plant shows interveinal chlorosis in young leaves. Identify the likely deficient mineral and explain why symptoms appear in young leaves first.

Solution:

The deficiency is likely FeFe (Iron). Symptoms appear in young leaves because FeFe is relatively immobile within the plant tissue.

Explanation:

Elements like N,P,KN, P, K are mobile and are exported to young developing tissues from old senescing leaves. However, immobile elements like Fe,Ca,Fe, Ca, and SS are not transported out of mature organs, so deficiency symptoms appear first in young tissues.

Problem 3:

Identify the bacteria responsible for the following conversion: 2NO2−+O2→2NO3−2NO_2^- + O_2 \rightarrow 2NO_3^-.

Solution:

NitrobacterNitrobacter.

Explanation:

This is the second step of nitrification where nitrites are oxidized to nitrates. This chemoautotrophic process is mediated by NitrobacterNitrobacter.

Mineral Nutrition (Essential Minerals, Nitrogen Cycle) Revision - Class 11 Biology ICSE