Phylogeny Review and Origins of Photosynthetic Life

Practice flashcards covering the concepts of phylogeny, taxonomic classification, the three domains of life, and the origins of photosynthesis and oxygen-rich environments.

Why does a phylogenetic tree reflect a nested hierarchy?

It reflects the diversification of life through evolution, specifically through the process of speciation.

What are the three principal domains of life?

Bacteria, Archaea, and Eukarya.

What is the chemical equation for the photosynthesis reaction according to the lecture?

$CO_2 + H_2O \rightarrow \text{glucose} + O_2$ in the presence of sunlight.

Which two metabolic reactions of cyanobacteria make them valuable symbionts for eukaryotes?

Oxygenic photosynthesis and the ability to fix nitrogen gas from the atmosphere.

How is a vertebrate defined in the taxonomic classification system?

An animal with a rigid backbone.

What traits define the category of mammals?

The possession of mammary glands and a body covered with hair.

In phylogenetic terms, what is the 'root' of a tree?

The original common ancestor for the group being studied.

What do 'branches' represent in a phylogenetic tree?

The lineages leading from an ancestor.

What is a clade?

A lineage consisting of an ancestor and all of its descendants.

How are 'sister groups' defined in a phylogeny?

The two branches and their descendant species that diverged from a common ancestor; they are each other's closest biological relatives.

What is the 'Tree of Life'?

A reconstruction of the history of branching in all lineages of life using the patterns of homologous characters, particularly from DNA sequences.

What is the defining characteristic of the domain Eukarya?

They are eukaryotes, which are cells containing nuclei.

What is the defining characteristic of the domains Bacteria and Archaea?

They are prokaryotes, which are cells without nuclei.

What distinguishes cyanobacteria as the first organisms to perform oxygenic photosynthesis?

They were the first to perform the typical carbon-fixing type of photosynthesis prevalent today, despite being prokaryotes with circular chromosomes and no nucleus.

What are stromatolites and how old are the oldest fossils?

They are bacterial mats with layers of precipitated minerals. Fossil stromatolites are up to $3.4$ billion years old.

What does the abbreviation 'Ga' stand for?

Billion years ago.

What was the significance of the Great Oxygenation Event?

It favored organisms that could withstand and utilize oxygen, setting the stage for the rise and diversification of eukaryotes.

What is the chemical product of nitrogen fixation by cyanobacteria?

$N_2\,\text{(gas)} \rightarrow NH_4$, $NO_2^-$, and $NO_3^-$ (ammonia, nitrite, and nitrate).

Why is the ammonia, nitrite, and nitrate produced by cyanobacteria important for life?

They act as fertilizer needed for the synthesis of amino acids (proteins) and nucleic acids (DNA and RNA).

What are heterocysts in the context of cyanobacteria like $Anabaena$?

Specialized cells used to 'fix' nitrogen gas from the atmosphere.