General Q&A for Class 12 · Page 243
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Which type of proteins are formed by free and attached ribosomes?
Ribosome Location Proteins Synthesized Destination Free ribosomes (in cytosol) Structural proteins, enzymes for cytoplasmic functions Cytoplasm, nucleus, mitochond
- GeneralClass 12All
Why are mitochondria known as semi-autonomous organelles?
Mitochondria are semi-autonomous because: Autonomous features: Own DNA: Circular, double-stranded mtDNA (16.5 kb in humans) Own ribosomes: 70S type (prokaryotic, not 80S eukaryotic) Self-replication: Divide by binary fission independent of cell cycle Protein synthesis: Synthesize ~13 proteins encoded by m
- GeneralClass 12All
X' is a type of cell organelle found in plant cells. One of its type 'Y' gets converted into another type 'Z' that provides colour to plant products like fruits. Identify X, Y and Z. Give one common feature of 'X' and mitochondria.
Answer: (a) Identification: X = Plastid (family of plant organelles) Y = Chloroplast (photosynthetic plastid) Z = Chromoplast (pigmented plastid) Interconversion: During fruit ripening, chloroplasts lose chlorophyll and accumulate carotenoids (red, or
- GeneralClass 12All
How are chromosomes formed from chromatin?
Chromatin condensation process: Interphase chromatin: Extended, loosely packed Composition: DNA + histone proteins (H1, H2A, H2B, H3, H4) + non-histone proteins + RNA Nucleosome formation: DNA (147 bp) wraps around histone octamer (2 copies each of H2A, H2B, H3, H4) "Beads-on-string" structu
- GeneralClass 12All
What are plasmids? Where are they present?
Plasmids are extra-chromosomal, circular, double-stranded DNA molecules in prokaryotic cells. Location: Bacterial cytoplasm, independent of chromosomal DNA Characteristics: Size: 1–200 kb (kilobases) Self-replicating (autonomous replication) Carry non-essential genes: antibiotic resistance (R-plasmids),
- GeneralClass 12All
Write two postulates of the cell theory.
All living organisms are composed of cells and products of cells – Cells are the basic structural and functional units of life All cells arise from pre-existing cells (Omnis cellula e cellula) – Continuity of life through cell division; no spontaneous generation Additional classical postulate: New cells are formed through division of existing cells (binary fission, mitosis, meiosis)
- GeneralClass 12All
Which type of arrangement of fibrils is found in centrioles?
9+0 arrangement – nine triplet microtubules arranged in a cylindrical pattern with no central microtubules. Each triplet consists of A, B, and C tubules joined together.
- GeneralClass 12All
Mention the two subunits of ribosome of eukaryotic cell.
Eukaryotic 80S ribosomes consist of: 60S large subunit (contains 28S, 5.8S, 5S rRNA + ~49 proteins) 40S small subunit (contains 18S rRNA + ~33 proteins)
- GeneralClass 12All
What are stroma lamellae?
Stroma lamellae (also called intergranal lamellae or frets) are flat, membranous tubules connecting grana (thylakoid stacks) in chloroplasts. They ensure structural continuity of the thylakoid system and house some photosynthetic proteins.
- GeneralClass 12All
Which cell organelle synthesises the enzymes of lysosomes?
Rough Endoplasmic Reticulum (RER). Lysosomal hydrolytic enzymes are synthesized on RER-bound ribosomes, then transported to the Golgi apparatus for processing and packaging into lysosomes.
- GeneralClass 12All
Which membrane protein is involved in facilitated diffusion?
Carrier proteins (also called permeases or transporter proteins) and channel proteins facilitate the diffusion of polar molecules and ions across the membrane without energy expenditure.
- GeneralClass 12All
Define gram negative bacteria.
Gram-negative bacteria are prokaryotes that do not retain the crystal violet stain in the Gram staining procedure and appear pink/red after counterstaining with safranin. They possess a thin peptidoglycan layer (2–3 nm) and an outer lipopolysaccharide membrane. Examples: E. coli, Salmonella, Vibrio cholerae
- GeneralClass 12All
What is a nucleoid?
Answer: The nucleoid is the irregularly-shaped, non-membrane-bound region in prokaryotic cells where the circular chromosomal DNA is located. Unlike the eukaryotic nucleus, it lacks a surrounding membrane and the DNA is not associated with histone proteins.
- GeneralClass 12All
Who gave the statement Omnis cellula e cellula? What does it mean?
Answer:Rudolf Virchow (1855). Meaning: "All cells arise from pre-existing cells" – established that cells cannot originate spontaneously but only through cell division from parent cells.
- GeneralClass 12All
Write a short note on nuclear envelope.
Nuclear Envelope (Nuclear Membrane): Structure: (i) Double Membrane System: Outer membrane: Continuous with rough ER; may bear ribosomes Inner membrane: Smooth; associated with nuclear lamina (intermediate filament network) Perinuclear space: 10–50 nm gap between membranes; continuous
- GeneralClass 12All
Explain the structure of cilia and flagella.
Structure: (i) Origin and Attachment: Arise from basal bodies (modified centrioles) Basal bodies anchor structures and control movement Membrane-bound extensions of plasma membrane (ii) Axoneme (Core Structure): Central cylinder running length of cilium/flagellum "9+
- GeneralClass 12All
Draw a well-labelled diagram of mitochondrion.
[Refer to diagram in PDF showing]: Outer membrane (smooth, permeable) Inner membrane (cristae - infoldings) Inter-membrane space (between membranes) Cristae (shelf-like projections) Matrix (inner fluid compartment) Additional labels should include: ATP synthase (on cristae) <strong
- GeneralClass 12All
Explain the following vacuoles: (a) Sap vacuoles (b) Contractile vacuoles (c) Food vacuoles
(a) Sap Vacuoles (Plant Vacuoles) Structure: Large, membrane-bound (tonoplast) organelle occupying up to 90% of cell volume Contents (Cell sap): Water (main component) Mineral salts (K⁺, Na⁺, Cl⁻, NO₃⁻) Sugars, amino acids Organic acids (malic, citric)
- GeneralClass 12All
Mention the functions of Golgi apparatus.
The Golgi apparatus performs critical post-translational and secretory functions: Primary Functions: (i) Packaging and Secretion: Receives proteins/lipids from ER via transport vesicles Modifies, sorts, and packages materials into secretory vesicles Materials delivered to: Intracellular targets: Lysosomes, vacuol
- GeneralClass 12All
Describe the structure of Golgi apparatus.
Structure: (i) Basic Organization: Composed of flattened, membrane-bound cisternae (sac-like structures) Stacked arrangement: Usually 4–8 cisternae per stack (may vary: 3–20) Resembles smooth ER in membrane structure (ii) Spatial Arrangement: Forms concentric network near