PROTISTS.
The earliest forms of life appeared about 3,500 to 3,800 mya (million years ago).
These Prokaryotes are microscopic, unicellular organisms with no nuclear membrane or mitochondria.
They also have circular DNA and reproduce asexually by binary fission (mitosis).
Mainly bacteria and blue-green algae (Cyanobacteria) they are still the most abundant form of life.
Eukaryotes evolved from prokaryotes about 2000 mya.
A protist or protoctist is any eukaryotic organism that is not an animal, plant or fungus.
They have a membrane enclosing the nucleus, cell organelles and linear DNA.
They show asexual and sexual reproduction (mitosis and meiosis).
A few years ago Protists were in Kingdom Protoctista then Kingdom Protista.
They are now in the Domain Eukaryota.
They are a huge diverse group with members in several supergroups or Clades.
They vary widely in their genetic makeup, morphology, habit, nutrition and reproduction.
There is no single feature that is common to them all.
Examples include:
- Amoebae use pseudopodia (false feet) to move along surfaces.
- Slime moulds that developed from the amoeba and
- Algae that can photosythesise and live in watery environments.
J.F.
