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Prokaryotic Cells: Bacteria Structure and Functions

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Bacteria are the simplest and oldest living cells. They are prokaryotic cells — cells without a true nucleus. Despite tiny size, they live everywhere: soil, water, air and our gut.

Prokaryotic cells matter because bacteria help in digestion, nitrogen fixation, food making and medicine production, while some also cause diseases. Understanding their structure helps us control both benefits and harm.

Key Concepts

Prokaryotic cell size is usually 1-5 micrometres. It has cell wall, plasma membrane, cytoplasm, nucleoid (single circular DNA without membrane), ribosomes (70S) for protein synthesis, and sometimes plasmids (extra DNA). Outer structures: capsule for protection, flagella for movement, pili/fimbriae for attachment. No membrane-bound organelles like mitochondria or ER. Mesosomes are membrane folds (earlier thought important; now considered artifacts in many preparations). Cell wall in bacteria contains peptidoglycan.

How It Works

  1. Plasma membrane controls entry and exit and carries respiration enzymes.
  2. DNA in nucleoid controls all activities without nuclear membrane.
  3. Ribosomes make proteins needed for growth.
  4. Flagella rotate and push bacterium through liquid.
  5. Under harsh conditions, some bacteria form tough endospores to survive.
  6. Reproduction is mainly by binary fission — one cell splits into two.

Worked Example

A bacterium divides every 20 minutes in good conditions. Starting from 1 cell: after 1 hour (3 divisions) = 2^3 = 8 cells; after 3 hours (9 divisions) = 2^9 = 512 cells; after 6 hours (18 divisions) = 2^18 = 262,144 cells. This step-by-step exponential growth explains why bacterial infections and food spoilage can increase so fast.

Common Misconceptions

  • Bacteria have a true nucleus. They have nucleoid DNA without nuclear membrane.
  • All bacteria are harmful. Most are harmless or useful; only some are pathogenic.
  • Bacteria have mitochondria. They lack membrane organelles; membrane does respiration work.

Real-World Applications

Useful bacteria make curd, antibiotics, vaccines, biogas and fix nitrogen in legume roots. Harmful bacteria cause TB, cholera and typhoid, treated with antibiotics and hygiene. Genetic engineering uses plasmids as vectors to produce insulin.

Prokaryotic cells are simple but highly successful. Their compact structure and fast division let bacteria survive and influence life everywhere.

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