All living organisms are made of cells.
Each cell contains several types of organelles.
Each cell is surrounded by a membrane.
The hereditary information of a cell consists of DNA contained in chromosomes.
- Procaryotic cells:
Bacteria, Cyanobacteria, and Archaea have simple (procaryotic) cells
without a well-defined nucleus. These procaryotic cells have:
- small sizes (1-10 micrometers across);
- no internal membranes or membranous organelles
(endoplasmic reticulum, Golgi apparatus, mitochondria, plastids,
lysosomes, vacuoles, or vesicles)
- no well-defined nucleus;
- no microtubules, cilia, centrioles, spindle fibers, or true mitosis;
- only one closed-loop chromosome (and possibly circular plasmids as well);
- no multicellular organization.
- Eucaryotic cells:
All other organisms, including animals, plants, fungi, and more, have
larger and more complex (eucaryotic) cells which have:
- larger sizes (10-100 micrometers across);
- many organelles with membrane parts (including endoplasmic reticulum,
Golgi apparatus, mitochondria, plastids, lysosomes, vacuoles, vesicles).
- energy-producing mitochondria
- a well-defined nucleus, bounded by a double membrane ("envelope");
- microtubular organelles, including centrioles (with "9+2" internal structure), spindle fibers, and,
in some cells, cilia and/or flagella;
- multiple linear chromosomes, containing proteins (histones) in addition to DNA;
- no plasmids;
- true mitosis and meiosis, using spindle fibers;
- frequent multicellular organization and cell specialization.
Major types of eucaryotic cells include:
- Animal cells: No cell wall; many small vacuoles; nucleus in center;
centrioles present; usually some cells motile in each animal.
- Plant cells: Surrounded by a cell wall containing cellulose; often one
large vacuole; nucleus often pushed to one side; chloroplasts (containing chlorophyll)
and other plastids; usually no centrioles; motility generally absent or confined to male gametes.
- (Fungi and Protista also)
Cell theory (originated in 1830s by Schleiden and Schwann):
- All organisms are made of cells (units of structure);
- All substances produced by organisms are made by cells;
- All major body functions are carried out at the cell level;
- All cells come from pre-existing cells.
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