Definition: Cell theory is a fundamental scientific theory that defines the properties of cells.
Key Principles:
The cell is the fundamental unit of structure and function in living things.
All known living things are made up of cells.
All cells are basically the same in chemical composition.
Organisms can be unicellular (one cell) or multicellular (multiple cells).
Origin of Cells:
All cells arise from pre-existing cells through the process of division.
Hereditary Material:
Cells contain hereditary information (DNA) which is passed down during cell division.
Metabolism:
Energy flow (metabolism and biochemistry) occurs within cells.
Organism Activity:
An organism's activity relies on the collective activity of its cells.
General Categories:
There are two main types of cells: prokaryotic and eukaryotic.
Prokaryotic cells: Found in organisms of domains Bacteria and Archaea.
Etymology: From Greek πρό (pró) 'before' and κάρυον (káruon) 'nut, kernel'.
Eukaryotic cells: Found in protists, fungi, animals, and plants.
Etymology: From Greek eu, "well," and káruon "karyon".
Size:
Eukaryotic cells are generally larger than prokaryotic cells.
Typical sizes:
Prokaryotic: 1–5 μm
Eukaryotic: 10–100 μm
Nuclear Structure:
Eukaryotic cells have a nucleus enclosed by a double membrane.
Prokaryotic cells lack a nucleus; their DNA is in an unenclosed region called the nucleoid.
Organelles:
Prokaryotic cells do not have membrane-bound organelles.
Eukaryotic cells contain membrane-bound organelles.
Lack of Nucleus: Prokaryotic cells do not have a membrane-bound nucleus.
Intracellular Structures: They lack many intracellular structures, making them simpler in organization.
Key Features:
Plasma Membrane: Encloses the cytoplasm.
Ribosomes: Sites for protein synthesis.
Cell Wall: Rigid structure outside the plasma membrane.
Glycocalyx: Outer coating, which may be a capsule or slime layer.
Flagella: Locomotion organelles found in some prokaryotes.
Nucleoid: Site of DNA; not membrane-bound.
Plasmids: Small, circular DNA molecules, extra-chromosomal.
Fimbriae: Attachment structures on some prokaryotes.