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Biology AS CIE

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  1. 1-cell-structure
    10 主题
  2. 2-biological-molecules
    19 主题
  3. 3-enzymes
    13 主题
  4. 4-cell-membranes-and-transport
    16 主题
  5. 5-the-mitotic-cell-cycle
    8 主题
  6. 6-nucleic-acids-and-protein-synthesis
    9 主题
  7. 7-transport-in-plants
    11 主题
  8. 8-transport-in-mammals
    16 主题
  9. 9-gas-exchange
    6 主题
  10. 10-infectious-diseases
    6 主题
  11. 11-immunity
    10 主题
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1-2-cells-as-the-basic-units-of-living-organisms AS prokaryotic-v-eukaryotic-cells

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Exam code:9700

Structural features of typical prokaryotic cells

  • Animal and plant cells are eukaryotic cells, whereas bacterial cells are prokaryotic

  • Prokaryotes have a cellular structure that is distinct from eukaryotes:

    • Their genetic material is free in the cytoplasm and is circular

      • Eukaryotic genetic material is packaged as linear chromosomes in the nucleus

    • Prokaryotes lack membrane-bound organelles

      • This means that they do not have any internal structures surrounded by membrane, e.g. a nucleus or mitochondria

    • They are many times smaller than eukaryotic cells

      • Prokaryotic cells are usually 1-5 μm in diameter, while eukaryotic plant cells can be 10-100 μm across

    • Their ribosomes are structurally smaller (70 S) in comparison to those found in eukaryotic cells (80 S)

    • Their cell walls are made of peptidoglycan rather than cellulose or chitin

  • Prokaryotes are always unicellular, while eukaryotic animal and plant cells can function together in multicellular organisms

Diagram of a bacterial cell showing flagellum, capsule, cell wall, surface membrane, cytoplasm, circular DNA, ribosomes, plasmid, pili, and infolding.
Prokaryotic cells have no internal membrane-bound structures, and are smaller than eukaryotic cells

Prokaryotic v eukaryotic cell structures

Feature

Prokaryotes

Eukaryotes

Size

0.5-5 μm

Up to 100 μm

Genetic material

Circular chromosome in the cytoplasm

Not associated with proteins

Linear chromosomes in the nucleus

Associated with histone proteins

Cell division

Binary fission

No spindle fibres involved

Mitosis or meiosis

Chromosomes are separated by spindle fibres

Ribosomes

70S

80S

Organelles

No membrane-bound organelles

Multiple membrane-bound organelles, e.g. a nucleus, mitochondria, chloroplasts

Cell wall

Made of peptidoglycan

Made of cellulose in plants, or chitin in fungi

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