Question

how we organize life?

define and then explain the similarities and differences between the three domains of life

archaea only

bacteria only

eukarya only

similarities/differences of all three domains.

Explanation:

Define the three domains of life

Using the Domains of Life knowledge point, we define the three primary evolutionary branches:

• Archaea: Single-celled prokaryotic organisms lacking a nucleus, often living in extreme environments.
• Bacteria: Single-celled prokaryotic organisms lacking a nucleus, with peptidoglycan cell walls, found everywhere.
• Eukarya: Organisms containing complex cells with a membrane-bound nucleus and organelles.

Identify characteristics unique to Archaea

Using the Domains of Life and Prokaryotic Cells knowledge points:

• Archaea possess unique membrane lipids with ether linkages instead of ester linkages.
• Their cell walls lack peptidoglycan.
• They have unique ribosomal RNA (rRNA) sequences and RNA polymerases that resemble eukaryotic machinery.

Identify characteristics unique to Bacteria

Using the Domains of Life and Prokaryotic Cells knowledge points:

• Bacteria have cell walls containing peptidoglycan.
• They possess membrane lipids with ester linkages.
• They have unique RNA polymerases and are sensitive to traditional antibacterial antibiotics.

Identify characteristics unique to Eukarya

Using the Eukaryotic Cells knowledge point:

• Eukarya possess a membrane-bound nucleus and membrane-bound organelles (e.g., mitochondria, chloroplasts).
• They can be multicellular (animals, plants, fungi) or unicellular (protists).
• They have linear chromosomes and undergo mitosis and meiosis.

Compare similarities and differences of all three

Using the Domains of Life knowledge point:

• Similarities: All three domains share a common ancestor, use DNA as genetic material, have ribosomes for protein synthesis, and possess a cell membrane.
• Differences: Archaea and Bacteria are prokaryotic (no nucleus), while Eukarya are eukaryotic. Archaea share more molecular and genetic similarities (like transcription machinery) with Eukarya than with Bacteria.

Answer:

Archaea Only

• Cell walls lack peptidoglycan.
• Membrane lipids contain ether linkages with branched hydrocarbons.
• Genetically and biochemically more similar to Eukarya (e.g., translation and transcription machinery).
• Often inhabit extreme environments (extremophiles).

Bacteria Only

• Cell walls contain peptidoglycan.
• Membrane lipids contain ester linkages with unbranched hydrocarbons.
• Possess unique RNA polymerase distinct from Archaea and Eukarya.
• Sensitive to traditional antibiotics.

Eukarya Only

• Cells contain a membrane-bound nucleus and membrane-bound organelles.
• Genetically organized into linear chromosomes.
• Includes multicellular organisms (Fungi, Plantae, Animalia) as well as unicellular protists.

Similarities and Differences of All Three Domains

• Similarities: All three domains share a common evolutionary origin, use double-stranded DNA as their genetic material, utilize ribosomes to synthesize proteins, and possess a plasma membrane.
• Differences: Archaea and Bacteria are prokaryotic (lacking a nucleus and membrane-bound organelles), whereas Eukarya are eukaryotic. Archaea and Eukarya share a more recent common ancestor with each other than either does with Bacteria, as evidenced by their similar replication, transcription, and translation machinery.