NEET 2025 Botany: Cell - The Unit of Life Notes

Overview of Cells

  • Cell Types:
    • Prokaryotic
    • Eukaryotic

Cytoplasm

  • Semifluid substance in cells
  • Site for cellular activities (protein synthesis)
  • Maintains cell in a living state
  • Present in both prokaryotes and eukaryotes

Ribosomes

  • Smallest organelle, non-membrane bound
  • Function: Protein synthesis
  • Ribosome sizes:
    • Prokaryote: 70S70S
    • Eukaryote: 80S80S (cytoplasm), 70S70S (mitochondria and chloroplast)

Centrosome

  • Composed of two centrioles
  • Present only in animal cells
  • Important for cell division

Characteristics of Prokaryotes vs. Eukaryotes

  • Prokaryotes:
    • Size: Small
    • Multiplication: Fast
    • No true nucleus or membrane-bound organelles
    • DNA: Circular and naked
  • Eukaryotes:
    • Size: Large
    • Multiplication: Slow
    • Well-defined nucleus and membrane-bound organelles present
    • DNA: Linear and organized in chromosomes

Cell Size and Shape

  • Varies greatly among organisms:
    • Smallest: Mycoplasma (0.3m)
    • Largest: Ostrich egg
    • RBC: Approximately 7.0 extμm7.0 \, ext{μm}
  • Shapes: Irregular, disc, cuboidal, columnar

Prokaryotic Cell Structure

  • Common shapes: Bacillus (rod), coccus (spherical), vibrio (comma), spirillum (spiral)
  • All prokaryotes have a cell membrane, ribosome, and naked DNA except mycoplasma which lacks a cell wall

Plasmids

  • Extra-nuclear circular DNA in bacteria
  • Can carry antibiotic resistance genes
  • Used in genetic engineering for transformation of foreign DNA

Inclusions in Prokaryotes

  • Cytoplasmic structures for storage (e.g., phosphate granules, glycogen)
  • Membranless and lie freely within the cytoplasm

Summary of Key Concepts

  • Prokaryotic cells multiply rapidly and are smaller than eukaryotic cells
  • Different organelles serve distinct functions and are defined by whether they have membranes
  • Shapes of cells reflect their functions

Important Assertions

  • Cytoplasm acts as the main site for metabolic reactions in cells
  • Different cell shapes are adaptations for their specific functional roles.