Organization and Diversity of Life — Quick Review

Functions: holds cell contents in place; takes in nutrients; helps build/export molecules; allows interactions with environment and neighboring cells
Embedded molecules: proteins, carbohydrates, lipids; many are mobile across the membrane
Carbohydrate chains: provide a fingerprint for cell identification
Cholesterol: helps membrane retain flexibility
Membrane proteins types:
- Receptor proteins
- Recognition (identification) proteins
- Transport proteins
- Membrane enzymes
Glycolipids and glycoproteins contribute to external face recognition

Diffusion: movement of solute from higher to lower concentration; passive
- Can be simple or facilitated
Osmosis: diffusion of water across a membrane
Key idea: passive processes do not require cellular energy

Prokaryotes: nucleoid, cell wall (in some), capsule (some), flagellum, cell membrane
Eukaryotes: nucleus with nuclear membrane; endoplasmic reticulum; ribosomes; Golgi; mitochondria/chloroplasts
How eukaryotic organelles evolved (two theories):
- Invagination Theory
- Endosymbiotic Theory

Taxonomy: classification/organization of living things
Hierarchical levels (in order): Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
Common mnemonic (example): Dear Kingdom Phylum… to help remember order; your own fun acronym is fine (e.g., Keeping Precious Creatures Organized For Grumpy Scientists)
Reference concept: 12.12

Species names are Latin, using genus and specific epithet
Genus name: capitalized; species epithet: lowercase
Full species name: italicized
Example: Homo sapiens (genus Homo; epithet sapiens; Latin origins: man and wise)
Rules: include genus and species; genus first and capitalized; epithet second and lowercase; written in italics
Reference concept: 12.12

Phylogeny: evolutionary history of organisms; often shown as a phylogenetic tree
Node = common ancestor; represents a speciation event
More recent common ancestor implies closer relationship
Humans share a more recent ancestor with rats/mice than with fish
Darwin’s finches as example of speciation and branching
Reference concept: 12.6, 12.7

What is a species? “Species is a human construct”
Morphological, Biological, and Phylogenetic species concepts exist
Biological Species Concept: species are populations that interbreed (or could) under natural conditions and cannot interbreed with other such groups; centers on reproductive isolation, not appearance or genetics
Barriers to interspecies reproduction:
- Prezygotic barriers: before zygote formation; prevent fertilization
- Postzygotic barriers: after fertilization; prevent fertile offspring; hybrids may be sterile or non-viable
Acknowledgement: some species concepts struggle with asexual organisms and fossils
Reference concepts: 12.3, 12.4

Six characteristics of living things (as a baseline):
- Made up of cells; viruses are not
- Use/transform energy; viruses rely on host metabolism
- Respond to environment; regulation/homeostasis; growth/reproduction; evolution
Viruses lack a cell membrane and organelles; have a protein coat enclosing genome
They replicate only inside a host cell; do not have independent metabolism or homeostasis
They can evolve, but not independently;
many scientists do not consider viruses alive or part of the tree of life
Conclusion: viruses are debated; generally not classified within the three domains
Reference concepts: 12.12

Domain and Kingdoms: Bacteria, Archaea, Eukarya; kingdoms within each domain (Eukarya has four kingdoms)
Fossil and lineage notes: origin of organelles, speciation, and phylogenetic relationships are central to organization of life
Remember: key mechanisms (diffusion, osmosis, diffusion types; barriers to reproduction; binomial nomenclature rules) are essential for quick recall