2.7

• What is the definition of speciation?

  Speciation is the process by which one species splits into two or more species.
• How does speciation contribute to biodiversity?

  It explains how new organisms arise from pre-existing ones, leading to diversity.
• What does the biological species concept define?

  A species is defined as a group of populations whose members can potentially interbreed and produce fertile, viable offspring.
• What is the morphological species concept based on?


  It groups organisms as separate species based on similarities in their morphology or body structure.
• How does the ecological species concept classify organisms?

  It groups organisms as separate species based on their ecological niche or role in the ecosystem.
• What does the phylogenetic species concept focus on?

  It groups organisms as separate species if they form one branch in the tree of life.
• What is allopatric speciation?

  Allopatric speciation occurs when two groups of organisms are separated by geographic barriers preventing gene flow.
• What is sympatric speciation?

  Sympatric speciation occurs when two groups separate into two species while living in the same geographical area.
• What is the geologic time scale?

  The geologic time scale is a record of Earth’s history built by geologists through paleontology.
• How is the geologic time scale divided?

  It is divided into three eons, with the third eon characterized by major evolutionary events in the animal kingdom.
• When did the first single-celled organisms exist?

  They existed about 3.5 billion years ago.
• What are stromatolites?


  Stromatolites are layered rocks that form when certain prokaryotes bind thin films of sediment together.
• When did the first photosynthetic organisms appear?

  They appeared around 2.7 billion years ago.
• What evidence supports the appearance of the first photosynthetic organisms?

  The presence of iron-rusted rocks dated around 2.7 billion years ago supports this evidence.
• What was the impact of increased oxygen concentration in the atmosphere?

  It caused a wave of extinction among anaerobic single-celled organisms and favored aerobic cellular respiration.
• When did the first eukaryotic organisms appear?

  They appeared around 2.1 billion years ago.
• What does the endosymbiotic theory describe?

  It postulates that the organelles of eukaryotes were once engulfed prokaryotes that mutually lived inside eukaryotic cells.
• When did the earliest ancestors of multicellular eukaryotes appear?

  They appeared approximately 1.2 billion years ago.