General Q&A for Class 12 · Page 238
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
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Questions
- GeneralClass 12All
Site, biochemical events, end product, and fate of nitrogen fixation.
Site:Root nodules of leguminous plants Biochemical Events: Enzyme:Nitrogenase (Mo-Fe protein complex) catalyzes N₂ reduction Nitrogen binding: N₂ binds to Mo-Fe component Sequential reduction: NADPH provides hydrogen atoms: N₂ → N₂H₂ (dimide) N₂H₂ → N₂H₄ (hydrazine) N₂H₄ → 2NH₃ (ammonia)<
- GeneralClass 12All
Formation of root nodules (ii) Significance of leghaemoglobin
(i) Root Nodule Formation: Steps in Nodulation: Chemotaxis: Legume roots secrete flavonoids that attract Rhizobium Attachment: Bacteria adhere to root hair epidermal cells. Infection Thread Formation: Bacteria release Nod factors causing root hair curling. An infection thread</strong
- GeneralClass 12All
Match elements with roles:
Element Role a. Boron (iv) Pollen germination b. Manganese (i) Splitting of H₂O to liberate O₂ during photosynthesis <td widt
- GeneralClass 12All
Short notes: (i) Symbiotic nitrogen fixation (ii) Ammonification
(i) Symbiotic Biological Nitrogen Fixation: This refers to mutualistic associations between nitrogen-fixing microbes and host plants. The most prominent example is the legume-Rhizobium relationship. Mechanism: Rhizobium bacteria colonize legume roots and induce formation of root nodules Nodules provide anaerobic conditions (via leghaem
- GeneralClass 12All
Element mobility—older vs. younger leaves, examples, importance.
Mobile vs. Immobile: If deficiency symptoms appear first in older leaves, the element is actively mobile. Mobile elements can be remobilized from older tissues and translocated to younger, growing tissues. As deficiency persists, younger leaves eventually show symptoms too. (ii) Examples: Mobile Elements: Potassium (K), Zinc (Zn) Immobile Elements:</stron
- GeneralClass 12All
Four deficiency symptoms with responsible elements.
Deficiency Symptom Deficient Elements 1. Chlorosis N, K, Mg, S, Fe 2. Necrosis Ca, Mg, Cu, K 3. Delay in flowering <
- GeneralClass 12All
Ionic form and functions of manganese and zinc.
(i) Manganese (Mn): Ionic Form:Mn²⁺ (manganous ion) Functions: Enzyme activation: Activates enzymes in photosynthesis, respiration, and nitrogen metabolism. Photolysis of water: Plays a major role in splitting water molecules to liberate O₂ during the light reactions of photosynthesis. (ii) Zinc (Zn):</stro
- GeneralClass 12All
(i) Why is an element essential? (ii) How many elements are essential? Name them. (iii) Classify as macro and micronutrients. (iv) Name two non-mineral elements.
(i) Criteria of Essentiality: An element is essential if it has a specific structural or physiological role and without it, plants cannot complete their life cycle. (ii) Essential Elements: 17 elements are essential: C, H, O, N, P, K, Ca, Mg, S, B, Mo, Mn, Ni, Cl, Fe, Cu, Zn (iii) Classification: Macronutrients
- GeneralClass 12All
Classification of essential elements based on function with examples.
Essential elements are classified into four functional categories: Structural Elements: Components of biomolecules forming cell structure: C, H, O: Constituents of cellulose, proteins, lipids, nucleic acids N: Component of proteins, nucleic acids, chlorophyll Components of Energy-Related Compounds:
- GeneralClass 12All
Fill in the blanks:
(i) Phosphorus is a macronutrient while chlorine is a micronutrient. (ii) In plants, sodium is a non-essential element. (iii) The mineral element which is a constituent of middle lamella is calcium. (iv) Any mineral ion concentration that reduces dry weight by about 10% is said to be toxic. (v) Xylem is the path of translocation of minerals.
- GeneralClass 12All
State three physiological roles and two deficiency symptoms of potassium.
Physiological Roles: Anion-cation balance: Maintains ionic equilibrium and electrical neutrality in cells. Protein synthesis: Activates enzymes involved in protein biosynthesis pathways. Stomatal regulation: Essential for guard cell turgor changes controlling stomatal opening/closing. Deficiency Symptoms: Chlorosis: Yellowing o
- GeneralClass 12All
Hydroponics Setup—Technique, Scientist, Significance of Components, Applications
(i) Technique & Scientist: The technique shown is Hydroponics (also called Solution Culture), first demonstrated by Julius von Sachs in 1860. This revolutionary technique enabled controlled studies of plant mineral nutrition. (ii) Significance of Components: Aerating Tube: Supplies oxygen to the nutrient solution</li
- GeneralClass 12All
Briefly describe the mechanism of nitrogen fixation.
Answer: Nitrogen fixation is catalyzed by the enzyme nitrogenase under anaerobic conditions: Steps: Substrate Binding: A nitrogen molecule (N₂) binds to the Mo-Fe component of nitrogenase. Reduction: The N≡N triple bond is sequentially reduced by addition of hydrogen atoms supplied by NADPH.
- GeneralClass 12All
What is denitrification? Give two microbes responsible.
Denitrification is the microbial reduction of soil nitrates (NO₃⁻) to gaseous forms of nitrogen (N₂, N₂O), which are released into the atmosphere. This process reduces soil fertility by depleting available nitrogen. Microbes Responsible: Pseudomonas denitrificans Thiobacillus denitrificans Denitrification typically occurs under anaerobi
- GeneralClass 12All
(i) Identify A and B in the equation. (ii) What is its significance? Equation: α-Ketoglutaric acid + [A] + NADPH → [B] + H₂O + NADP⁺
(i) Identification: [A] = NH₄⁺ (ammonium ion) [B] = Glutamate (glutamic acid) (ii) Significance: This equation represents reductive amination—a pathway of ammonia assimilation where an ammonium ion is directly incorporated into an organic acid (α-ketoglutarate) to form an amino acid (glutamate). This is catalyzed by
- GeneralClass 12All
Give reasons for the following:
(i) Iron is not a constituent of chlorophyll but its deficiency causes chlorosis. Answer: Though iron (Fe) is not a structural component of chlorophyll, it is essential for chlorophyll biosynthesis. Iron activates several enzymes involved in chlorophyll synthesis pathways. Therefore, iron deficiency impairs chlorophyll production, leading to chlorosis (yellowing of leaves). <s
- GeneralClass 12All
Name at least two mineral elements responsible for deficiency symptoms.
Deficiency Symptom Responsible Elements (i) Inhibition of cell division N, K, S, Mo (ii) Late flowering N, S, Mo <td width="2
- GeneralClass 12All
Give three functions of potassium in plants.
Potassium (K) performs several critical physiological roles: Maintains anion-cation balance: Regulates ionic equilibrium in cells and maintains electrical neutrality. Stomatal movement: Essential for opening and closing of stomata—K⁺ influx into guard cells causes stomatal opening. Cell turgidity: Helps maintain turgor pressure in cells, essential for
- GeneralClass 12All
What are amides? Give two examples.
Answer: Amides are nitrogen-rich organic compounds derived from amino acids where the hydroxyl group (-OH) of the carboxyl group (-COOH) is replaced by another amino group (-NH₂). Structural Significance: Amides contain more nitrogen than their parent amino acids, making them efficient for nitrogen storage and transport. Examples: <stron
- GeneralClass 12All
Draw a well-labelled diagram of the nitrogen cycle.
The nitrogen cycle illustrates the transformation of nitrogen through various forms in the ecosystem: Key Processes: Nitrogen Fixation: Atmospheric N₂ → NH₃ (biological, industrial, electrical) Ammonification: Organic nitrogen → NH₃ Nitrification: NH₃ → NO₂⁻ → NO₃⁻ Uptake: NO₃⁻ → Plant biomass → Animal biomass<