General Q&A for Class 12 · Page 245
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
What are inclusion bodies?
Inclusion bodies are: Non-membrane-bound granular structures Store reserve materials in prokaryotic cytoplasm Types: Phosphate granules (polyphosphate/volutin granules) Glycogen granules (energy storage) Cyanophycean granules (cyanophycin) – nitrogen reserve in cyanobacteria Gas vacuoles
- GeneralClass 12All
Explain the ribosomes found in prokaryotic cells.
Prokaryotic ribosomes characteristics: Type: 70S ribosomes (Svedberg units) Large subunit: 50S Small subunit: 30S Location: Free in cytoplasm Attached to plasma membrane (in some species) Form polyribosomes (polysomes) when multiple ribosomes attach to
- GeneralClass 12All
Write a short note on nuclear material of prokaryotes.
In prokaryotic cells: Nuclear membrane is absent; genetic material lies in the nucleoid region DNA is: Circular (not linear) Double-stranded Not associated with histone proteins (except in some Archaea) Equivalent to a single chromosome containing essential genes <strong
- GeneralClass 12All
Cells show great variation in their shape and size. Explain.
Cellular morphology varies based on function, location, and organism type: Shape/Type Description Examples Spherical Minimal surface area-to-volume ratio <td w
- GeneralClass 12All
Are organelles without membrane present? Comment.
Yes, non-membrane-bound organelles exist and include: Ribosomes: Found in prokaryotes (70S) and eukaryotes (80S) Also present in mitochondria and chloroplasts (70S type) Composed of rRNA and ribosomal proteins Function: Protein synthesis Centrioles</strong
- GeneralClass 12All
Define the two types of cells on the basis of organisation of their nucleus.
Feature Prokaryotic Cells Eukaryotic Cells Nuclear membrane Absent Present (double membrane) Genetic material <td width="2
- GeneralClass 12All
Mention the postulates of the theory given by Schleiden and Schwann in 1839.
The Cell Theory formulated by Matthias Schleiden (botanist) and Theodor Schwann (zoologist) established: All living organisms are composed of cells and products of cells – Cells are the fundamental structural units of life All cells arise from pre-existing cells (Omnis cellula e cellula) – Added later by Rudolf Virchow (1855)
- GeneralClass 12All
How was the study of cell and its detailed structure made possible?
Advancement in microscopy revolutionized cytology: Light Microscopy (17th century): Robert Hooke (1665) first observed dead cork cells; Anton van Leeuwenhoek examined living microorganisms Improved Staining Techniques: Differential staining revealed cellular components Electron Microscopy (1930s-1940s): Transmission Electr
- GeneralClass 12All
Explain the type of organisms on the basis of number of cells present in their body.
Organisms are classified based on cellular organization: Type Definition Examples Unicellular Body consists of a single cell performing all life functions Amoeba,
- GeneralClass 12All
Briefly describe hub in the structure of centriole.
The hub is a central, proteinaceous mass located at the core of the centriole. It anchors nine radial spokes that connect to the peripheral triplet microtubules, forming the characteristic cartwheel structure visible in transverse section of centrioles.
- GeneralClass 12All
Which stain is used to observe mitochondria?
Janus Green B is a vital stain that selectively colors mitochondria blue-green in living cells. This supravital dye is reduced by cytochrome oxidase in the mitochondrial electron transport chain, making mitochondria visible under light microscopy.
- GeneralClass 12All
In which medium do the enzymes of lysosomes work?
Lysosomal enzymes (hydrolases) function optimally in an acidic medium (pH ~4.5–5.0). The lysosomal membrane contains proton pumps that actively transport H⁺ ions into the lumen, maintaining this acidic environment necessary for enzymatic digestion of macromolecules.
- GeneralClass 12All
Which type of ER is involved in steroid and lipid synthesis?
Smooth Endoplasmic Reticulum (SER) lacks ribosomes and specializes in: Lipid biosynthesis (phospholipids, cholesterol) Steroid hormone synthesis (e.g., in adrenal cortex, gonads) Detoxification of drugs and toxins (especially in liver hepatocytes) Calcium ion storage (in muscle cells)
- GeneralClass 12All
What is the shape of kinetochore?
The kinetochore is a disc-shaped protein structure assembled on the centromere region of each chromatid during cell division. It serves as the attachment site for spindle microtubules, enabling chromosome segregation during mitosis and meiosis.
- GeneralClass 12All
Which part of a lipid molecule is hydrophilic in nature?
The polar head (or phosphate group) of a phospholipid molecule is hydrophilic (water-loving). It contains charged or polar functional groups that interact favorably with aqueous environments, while the fatty acid tails are hydrophobic (water-repelling).
- GeneralClass 12All
Which is the innermost component of the cell envelope of bacteria?
The plasma membrane (also called the cell membrane) is the innermost layer of the bacterial cell envelope. This selectively permeable, phospholipid bilayer regulates the transport of substances and houses proteins involved in respiration and DNA replication.
- GeneralClass 12All
Which structure provides some extra properties to bacteria like resistance to antibiotics?
Plasmids are extra-chromosomal, circular DNA molecules found in the cytoplasm of bacterial cells. They carry genes conferring advantageous traits such as antibiotic resistance, virulence factors, and metabolic capabilities. Plasmids replicate independently of chromosomal DNA.
- GeneralClass 12All
Where do almost all cellular activities occur in a cell?
The cytoplasm is the primary site for most cellular activities. This semi-fluid matrix contains dissolved nutrients, enzymes, and organelles (both membrane-bound and non-membrane-bound), facilitating metabolic reactions, protein synthesis, and energy production.
- GeneralClass 12All
Who expanded the cell theory and gave the statement Omnis cellula e cellula?
Rudolf Virchow (1855) expanded the cell theory by proposing the principle Omnis cellula e cellula, which translates to "all cells arise from pre-existing cells". This postulate challenged the theory of spontaneous generation and established that cellular continuity occurs through cell division.
- GeneralClass 12All
Write short notes on the following:
(a) Lateral meristems(b) Vessels(c) Subsidiary cells(d) Ground tissue Solution: (a) LATERAL MERISTEMS: Definition: Lateral meristems are cylindrical meristems located in the mature regions of roots and stems, responsible for secondary growth (increase in girth). Types: <ol