GK: Class 12 General Q&A · Page 164
3,658 free answers on GK (General) for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What is the difference between S phase and G₂ phase?
Feature S Phase G₂ Phase Primary activity DNA replication Protein synthesis (tubulin, enzymes) Duration (humans) <td width
- GeneralClass 12All
Mention the significance of crossing over phenomenon occurring during meiosis I.
Crossing over introduces genetic recombination by exchanging DNA segments between non-sister chromatids of homologous chromosomes, generating genetic variation in offspring. Explanation: Occurs during pachytene of prophase I Chiasmata mark crossover sites Produces recombinant chromatids with new allele combinations Essential for evo
- GeneralClass 12All
Differentiate between anaphase I and anaphase II of meiosis.
Feature Anaphase I Anaphase II What separates Homologous chromosomes (bivalents) Sister chromatids Centromere behavior <td
- GeneralClass 12All
Why is DNA duplicated well before cell division?
Solution: DNA duplication during S phase ensures that both daughter cells receive identical genetic information necessary for proper structure and function, maintaining genomic integrity. Explanation: S phase occurs during interphase (before M phase) DNA replication produces sister chromatids joined at the centromere <li
- GeneralClass 12All
Which type of cell division produces new cells for regeneration?
Mitosis Explanation: Mitosis is responsible for: Tissue repair (wound healing) Regeneration (e.g., lizard tail regrowth) Asexual reproduction (unicellular organisms) Growth (increase in cell number) Example: When a lizard's tail is severed, somatic cells at the amputation site undergo rapid mitotic d
- GeneralClass 12All
Name the three sub-stages of interphase.
G₁ phase, S phase, G₂ phase Explanation: Sub-stage Duration (humans) Key Events G₁ (Gap 1) 8-10 hours RNA/protein synthesis, organelle duplication</p
- GeneralClass 12All
How does the cell plate divide the plant cell into two daughter cells?
The cell plate forms at the centre of the cell and grows centrifugally (outward) toward the lateral walls, ultimately dividing the cell into two halves. Explanation: In plant cytokinesis: Phragmoplast (microtubule structure) forms at the equator Golgi-derived vesicles carry cell wall materials (pectin, cellulose) Vesicles fuse to form the cel
- GeneralClass 12All
Which process changes the long, fine chromatin fibres into chromosomes?
Chromosome condensation (chromatin condensation) Explanation: During early prophase, loosely packed chromatin undergoes: Coiling and supercoiling mediated by condensin proteins Histones facilitate compaction Chromatin transforms into visible, distinct chromosomes This condensation ensures accurate chromosome segregati
- GeneralClass 12All
Name the phase in which the chromatids move apart in mitosis and meiosis.
Solution: Mitosis: Anaphase Meiosis: Anaphase II Explanation: Division Type Phase What Separates Mitosis Anaphase</
- GeneralClass 12All
Name the last stage of prophase I.
Diakinesis Explanation: Diakinesis is the final substage of prophase I characterized by: Terminalisation of chiasmata (chiasmata move toward chromosome ends) Maximum chromosome condensation Nucleolus and nuclear envelope disintegration Preparation for metaphase I alignment
- GeneralClass 12All
What percentage of duration of cell cycle does interphase last?
More than 95% Explanation: The cell cycle consists of: Phase Duration (%) Key Events Interphase (G₁, S, G₂) >95% DNA replicatio
- GeneralClass 12All
Name the first stage of the interphase in which active synthesis of RNA and protein occurs.
Solution:G₁ phase (Gap 1 phase) Explanation: During the G₁ phase, the cell exhibits: Active transcription of RNA Protein synthesis (enzymes, histones) Organelle replication (mitochondria, ribosomes) Cell growth in preparation for S phase This phase accounts for the majority of interp
- GeneralClass 12All
Name the stage which connects meiosis I and meiosis II.
Explanation: Interkinesis is a brief resting phase between meiosis I (reductional division) and meiosis II (equational division). Unlike interphase, interkinesis does not involve DNA replication. The cell prepares for the second meiotic division, where sister chromatids separate.
- GeneralClass 12All
How many meiotic divisions are required to produce 32 microspores?
Eight meiotic divisions are required. Explanation: Each meiotic division produces four haploid microspores from one diploid microspore mother cell (MMC). To calculate the number of divisions needed: 32 microspores ÷ 4 microspores per division = 8 meiotic divisions This principle is fundamental in understanding microsporogenesis in flowering plants
- GeneralClass 12All
(i) Draw a well-labelled diagram of T.S. of centriole. (ii) Give the functions of centriole.
Answer: (i) T.S. (Transverse Section) of Centriole [Diagram in PDF shows]: 9 triplet fibrils arranged radially (9+0) Each triplet: A, B, C tubules (A-tubule complete, B and C incomplete) Central hub (proteinaceous mass) 9 radial spokes (cartwheel structure) C-A connectives linking triplets Perice
- GeneralClass 12All
Differentiate between prokaryotic and eukaryotic cells on the basis of: (a) Nucleus (b) Membrane-bound organelles (c) Nucleolus (d) Ribosomes (e) Plasmids
[Comprehensive table previously provided in question 22 - Section A] Additional distinctions: Feature Prokaryotic Eukaryotic Cell division Binary fission, budding M
- GeneralClass 12All
(a) What is the composition of chromatin? (b) What is the function of histone proteins?
(a) Chromatin composition: DNA (30–40%): Genetic material Histone proteins (50–60%): 5 types Core histones: H2A, H2B, H3, H4 (form nucleosome octamer) Linker histone: H1 (stabilizes higher-order structure) Non-histone proteins (10%): Structural (scaffolding), regulatory (transcription factors), enzymatic (polyme
- GeneralClass 12All
Give three differences between cilia and flagella.
[Comprehensive table previously provided in question 44] Brief comparison: Feature Cilia Flagella Number 300–14,000 per cell 1–4 per cell </tr
- GeneralClass 12All
Explain the structure of protein factories.
Ribosomes – "Protein Factories" Structure: (i) Composition: Non-membrane-bound organelles rRNA (60%) + ribosomal proteins (40%) Chemically: Ribonucleoprotein complex (ii) Two Subunit Organization: Type <td width="
- GeneralClass 12All
Write the chemical composition of cell wall of: (a) Bacteria (b) Fungus (c) Alga
[Previously answered in question 39 - refer to detailed table] Brief summary: (a) Bacteria: Peptidoglycan (NAG-NAM cross-linked by peptides) (b) Fungus: Chitin (β-1,4-linked N-acetylglucosamine) + glucans (c) Alga: Cellulose + galactans, mannans, minerals (calcium carbonate); some with silica (diatoms)