1.1Free
Your guide: Miss AimanThinks the human body is the best-designed machine in the syllabus.
Life has millions of kinds. Scientists sort them into three big groups.
Let us see how.
First the history, then two prokaryotic domains.
1969: Robert Whittaker proposed five kingdoms. They are Monera, Protista, Fungi, Plantae and Animalia.
Monera held the prokaryotes. The other four were eukaryotes.
1990: Carl Woese split the prokaryotes into two groups. They are Archaea and Bacteria.
He placed all life in three domains: Archaea, Bacteria and Eukarya.
A diagram of evolutionary relationships is a phylogenetic tree. The three domains branch from a common ancestor.
Archaea are prokaryotes. The name comes from Greek archaios, meaning ancient.
Size runs from 0.1 μm to over 15 μm. Some filaments reach 200 μm.
They reproduce asexually. They do not undergo mitosis or meiosis.
Membrane lipids: ether linkage and branched fatty acid chains. Bacteria and Eukarya have ester linkage and unbranched chains.
Cell wall: no cellulose and no peptidoglycan. Some have pseudopeptidoglycan.
Only archaea make methane (methanogenesis). Groups: methanogens, halobacteria, thermococci, thaumarchaeota.
Bacteria are the true bacteria. They have no true nucleus and no membrane-bound organelles.
The cell wall is peptidoglycan. The DNA is one circular chromosome in the nucleoid. Small circular DNA pieces are plasmids.
They divide by binary fission. They can be autotrophs or heterotrophs.
Shapes: cocci (spherical), bacilli (rod), spirilla (spiral), vibrios (comma).
Pairs are diplococci, chains are streptococci, clusters are staphylococci.
Step 1 / 7
Life has millions of kinds. Scientists sort them into three big groups.
Let us see how.
First the history, then two prokaryotic domains.
1969: Robert Whittaker proposed five kingdoms. They are Monera, Protista, Fungi, Plantae and Animalia.
Monera held the prokaryotes. The other four were eukaryotes.
1990: Carl Woese split the prokaryotes into two groups. They are Archaea and Bacteria.
He placed all life in three domains: Archaea, Bacteria and Eukarya.
A diagram of evolutionary relationships is a phylogenetic tree. The three domains branch from a common ancestor.
Archaea are prokaryotes. The name comes from Greek archaios, meaning ancient.
Size runs from 0.1 μm to over 15 μm. Some filaments reach 200 μm.
They reproduce asexually. They do not undergo mitosis or meiosis.
Membrane lipids: ether linkage and branched fatty acid chains. Bacteria and Eukarya have ester linkage and unbranched chains.
Cell wall: no cellulose and no peptidoglycan. Some have pseudopeptidoglycan.
Only archaea make methane (methanogenesis). Groups: methanogens, halobacteria, thermococci, thaumarchaeota.
Bacteria are the true bacteria. They have no true nucleus and no membrane-bound organelles.
The cell wall is peptidoglycan. The DNA is one circular chromosome in the nucleoid. Small circular DNA pieces are plasmids.
They divide by binary fission. They can be autotrophs or heterotrophs.
Shapes: cocci (spherical), bacilli (rod), spirilla (spiral), vibrios (comma).
Pairs are diplococci, chains are streptococci, clusters are staphylococci.
Q1. Book MCQ 1: which domain lives in extreme places and has ether-linked membrane lipids?
Archaea. Ether-linked lipids with branched chains make the membrane resist extreme conditions.
Q2. Book MCQ 2: a key difference between Bacteria and Archaea.
Bacterial cell walls have peptidoglycan. Archaeal cell walls do not.
✗ “Archaea are a kind of bacteria.”
✓ Since Woese (1990) they are a separate domain. The old name archaebacteria is no longer used as a group name.
1. Who proposed the three domains?
(a) 1990, from the book.
2. Which cell wall polymer is found in bacteria?
(a) Cellulose is in plants, chitin in fungi.
3. Which process is found only in archaea?
(a) The book: methanogenesis is absent in bacteria and Eukarya.
4. A comma-shaped bacterium is called:
(a) Cocci are spheres. Bacilli are rods. Spirilla are spirals.
Free right now. No ads. Tell us what to fix.