Principles of Phylogeny and Evolution of Photosynthetic Life

Principles of Phylogeny

Understanding Phylogenetic Trees

Phylogenetic trees are diagrammatic representations that illustrate the evolutionary relationships among various biological species based on similarities and differences in their physical or genetic characteristics. These trees reflect the nested hierarchy resulting from the process of evolution.

• Phylogenetic Tree: A branching diagram showing the inferred evolutionary relationships among species.

• Common Ancestry: The concept that all organisms share a common ancestor at some point in their evolutionary history.

• Synapomorphy: A shared, derived trait that is used to determine evolutionary relationships.

• Clade: A group consisting of an ancestor and all its descendants.

• Sister Taxa: Two groups that are each other's closest relatives.

Example: Birds and crocodiles are sister taxa within the clade Archosauria, sharing a more recent common ancestor with each other than with other reptiles.

Reading and Interpreting Phylogenetic Trees

Phylogenetic trees can be read to determine evolutionary relationships, identify clades, and understand trait evolution.

• Root: The most ancestral branch of the tree, representing the common ancestor of all taxa in the tree.

• Branches: Lineages leading from ancestors to descendants.

• Node: A point where a branch splits, representing a common ancestor.

• Homology: Traits inherited from a common ancestor.

• Homoplasy: Similar traits that evolved independently, often due to convergent evolution.

Additional info: Phylogenetic trees can be drawn in multiple ways but represent the same relationships as long as the branching order is preserved.

Domains of Life

The Three Principal Domains

All living organisms are classified into three principal domains based on cellular organization and genetic differences.

• Bacteria: Prokaryotic cells without a nucleus; includes cyanobacteria and many other groups.

• Archaea: Prokaryotic cells distinct from bacteria, often found in extreme environments.

• Eukarya: Organisms with eukaryotic cells (cells containing a nucleus), including plants, animals, fungi, and protists.

Domain	Cell Type	Examples
Bacteria	Prokaryotic	Cyanobacteria, E. coli
Archaea	Prokaryotic	Halophiles, Thermophiles
Eukarya	Eukaryotic	Plants, Animals, Fungi

Photosynthesis

Inputs and Outputs of Photosynthesis

Photosynthesis is the process by which photoautotrophic organisms convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.

• Inputs: Carbon dioxide (CO2), water (H2O), and sunlight.

• Outputs: Glucose (C6H12O6) and oxygen (O2).

Photosynthesis Equation:

$6CO_2 + 6H_2O \rightarrow C_6H_{12}O_6 + 6O_2$

Example: Plants, algae, and cyanobacteria perform photosynthesis, contributing to the oxygen content of Earth's atmosphere.

Metabolic Reactions of Cyanobacteria

Cyanobacteria are among the first organisms to perform oxygenic photosynthesis, playing a crucial role in the evolution of Earth's oxygen-rich atmosphere.

• Oxygenic Photosynthesis: Production of oxygen as a byproduct of photosynthesis.

• Nitrogen Fixation: Conversion of atmospheric nitrogen (N2) into ammonia (NH3), which can be used to synthesize amino acids and nucleic acids.

• Ecological Importance: Cyanobacteria are primary producers in aquatic ecosystems and contributed to the Great Oxygenation Event.

Additional info: The metabolic versatility of cyanobacteria makes them valuable for biotechnological applications, such as biofuel production and bioremediation.

Evolutionary Impact of Photosynthesis

Photosynthesis and Earth's Atmosphere

The origin of photosynthesis drastically influenced the composition of Earth's atmosphere and the course of biological evolution.

• Great Oxygenation Event: The rise of oxygen in Earth's atmosphere due to photosynthetic activity, enabling the evolution of aerobic organisms.

• Diversification of Eukaryotes: Increased oxygen levels allowed for the evolution and diversification of complex eukaryotic life forms.

Example: The appearance of oxygen-dependent organisms and the development of multicellular life are linked to the evolution of photosynthetic cyanobacteria.