History of Life on Earth; Phylogeny
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| Key events in life's history include the origin of ___ and ___ organisms and the colonization of ___. | - single-celled
- multi-celled
- land
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| ___ show evolutionary relationships. | Phylogenies
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| Phylogenies are inferred from ___ and ___ data. | - morphological (form and structure of organisms)
- molecular (DNA)
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| The first sing-celled organisms appeared on Earth approximately ___ billion years ago. About 3 billion years elapsed before the ___ occurred (~500 million years ago). | - 3.5
- colonization of land
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| phylogeny | the evolutionary history of a species or group of species
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| To construct phylogenies, biologists use systematics. What is that? | a discipline focused on classifying organisms and determining their evolutionary relationships
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| The study of ___ has helped geologists establish a geologic record of Earth's history. | fossils
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| What were the first single-celled organisms, and where does the earliest evidence of their origin come from? | - prokaryotes (heterotrophic, anaerobic)
- stromatolites
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| What are stromatolites? | layered rocks that form when certain prokaryotes bind thin films of sediment together
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| For how long were prokaryotes the only life forms on Earth? | from 3.5 to 2.1 billion years ago, so about 1.4 billion years
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| What's the relationship between the evolution of photosynthesis and the appearance of atmospheric oxygen? | - photosynthesis evolved (light energy from the sun used to synthesize sugars from CO2; released oxygen as a waste product)
- carried out by autotrophs
- oceans became saturated with oxygen, so it started releasing into the atmosphere
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| What were cyanobacteria and what was their role? | - the first oxygen releasing, photosynthetic bacteria (autotrophic, aerobic)
- saturated the ocean with oxygen, which then led to oxygen being released into the atmosphere
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| autotroph | an organism that obtains organic food molecules without eating other organisms or substances derived from other organisms; autotrophs use energy from the sun or from oxidation of inorganic substances to make organic molecules from inorganic ones
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| heterotroph | an organism that obtains organic food molecules by eating other organisms or substances derived from them
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| anaerobic organism | - an organism that does not require oxygen for growth
- may react negatively or even die if oxygen is present
- may be unicellular (e.g. protozoans, bacteria) or multicellular
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| aerobic organism | - an organism that can survive and grow in an oxygenated environment
- some need oxygen, others can go without if necessary
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| What did this increase in atmospheric oxygen mean for the evolution of prokaryotic organisms? | - (oxygen can attack chemical bonds, inhibit enzymes, and damage cells)
- rising O2 meant that many prokaryotic groups died out
- Some survived in anaerobic environments, others w/ adaptations (cellular respiration: glucose+O2+ADP+phos. → CO2+H2O+ATP)
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| The first single-celled eukaryotes appeared about ___ years ago. | 2.1 billion
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| What are the defining features of eukaryotic cells? | - nuclear envelope (w/ linear DNA)
- mitochondria and other internal structures
- cytoskeleton
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| What is the endosymbiont theory of how eukaryotic features evolved from prokaryotic cells? | mitochondria and plastids (general term for chloroplasts and related organelles) were formerly small prokaryotes that began living within larger (host) cells
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| What is the hypothesis of serial endosymbiosis? | mitochondria evolved before plastids through a sequence of endosymbiotic events
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| What is the evidence for the endosymbiotic origin of mitochondria and plastids? | - inner membranes of both are homologous to the plasma membranes of living prokaryotes
- both replicate similarly to certain prokaryotes
- each contain a circular DNA molecule not assoc. w/ large amounts of proteins
- similar cellular machinery
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| What did the evolution of multicellularity make possible? | greater morphological diversity (a single cell can't specialize...it is what it is)
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| Why were multicellular eukaryotes limited in size and diversity until the late Proterozoic (ca. 570 MYA)? | severe ice ages
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| What is the “snowball Earth” hypothesis? | suggests that most life would have been confined to areas near deep-sea vents and hot springs or to equatorial regions of the ocean that lacked ice cover
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| What was the Cambrian explosion (535 to 525 MYA)? | - a relatively brief time in geologic history when many present day phyla of animals first appeared in the fossil record
- emergence of the first large, hard-bodied animals
- major lineages of all animals were established
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| There is fossil evidence that cyanobacteria and other photosynthetic prokaryotes coated damp territorial surfaces well over a billion years ago. However, larger forms of life did not begin to colonize land until about ___ years ago. | 500 million
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| The gradual evolutionary venture out of aquatic environments was associated with adaptions that ___ and ___. | - made it possible to reproduce on land
- helped prevent dehydration
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| What sorts of adaptations were associated with the colonization of land by plants? | - vascular systems (for transporting materials internally)
- leaves with a waxy coating
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| (Colonization of land) What was the deal with fungi? | - roots of most plants were associated with fungi
- fungi helped plants absorb water and nutrients from the soil
- in turn, the fungi would obtain their organic nutrients from the plants
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| (Colonization of land) What was the deal with arthropods such as insects and spiders? | - the first animals to colonize land
- had hard outer coverings to retain moisture
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| (Colonization of land) What was the deal with tetrapods? | - evolved from a group of lobe-finned fishes
- humans arrived late in the scene
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| When did humans show up? | 195,000 years ago (so not long ago at all in the grand scheme of things)
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| taxonomy | a scientific discipline concerned with naming and classifying the diverse forms of life
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| systematics | - a discipline used by biologists to construct phylogenies
- focused on classifying organisms and determining their evolutionary relationships
- use info from fossils, genes, molecules, etc.
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| Phylogenies show ___ relationships. | evolutionary
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| binomial nomenclature | a two-part, latinized format for naming a species, consisting of the genus and specific epithet (which is unique for each species within the genus)
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| What is the first part of a binomial? | - the genus
- (what different species belong to)
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| What is the second part of a binomial? | - the specific epithet
- (unique to each species)
- (usually a description of the species)
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| What are the advantages of using Latin or Latinized names? | - avoids ambiguity when communicating about research
- latin was the scientific language
- standardization
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| What is the order of Linnaean classification? (Remember the mnemonic!) | - domain, kingdom, phylum, class, order, family, genus, species
- (Dirty King Phillip Came Over From Great Spain)
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| taxon | - a named taxonomic unit at ANY given level of classification
- (ex. Panthera pardus...Panthera is the taxon at the genus level, pardus at the species...mammalia would be the taxon at the class level)
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| Why do we classify organisms at all? | - recognition
- it's a way to structure our human view of the world
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| How was this type of hierarchical classification done classically? | people grouped species based on their morphological characters (so, what they looked like)
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| Classifying organisms based on their morphological characters may reflect relatedness, but does it necessarily reflect evolutionary history? | no, its just categorizing...it has nothing to do with history
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| What do phylogenetic trees purport to show? | - the evolutionary history of a group of organisms
- shows common ancestry
- the branching pattern of these trees often match how taxonomists have classified groups of organisms nested within more inclusive groups
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| A phylogenetic tree represents a hypothesis about evolutionary relationships. Why would we call this a hypothesis? | - because a lot of common ancestors are extinct
- DNA analyzed on things existing today are used to hypothesize with phylogenetic trees
- things that have been separated for less time have less genetic differences...greater time, more differences
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| branch point | where lineages diverge (on a phylogenetic tree)
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| polytomy | an unresolved pattern of divergence (on a phylogenetic tree)
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| sister taxa | - groups of organisms that share an immediate common ancestor (branch point)
- located at the tip ends of branches on a phylogenetic tree
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| basal taxon | - a lineage that diverges early in the history of a group
- originates near the common ancestor
- (basal...base...=thing that split off first)
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| What does it mean when a phylogenetic tree is rooted? | a branch point within the tree (often drawn furthest to the left or bottom) is included that represents the most recent common ancestor of all taxa in the tree
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| Phylogenetic trees are intended to show patterns of ___. | descent
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| Although closely related organisms often resemble one another due to their common ancestry, they may not if ___ or ___. | - their lineages have evolved at different rates
- they faced very different environmental conditions
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| On a phylogenetic tree, crocodiles, lizards/snakes, and birds share a common ancestor. However, crocodiles and birds share an additional branching point. What does this mean? | crocodiles are more closely related to birds than to snakes and lizards (since the crocs and birds share a more recent common ancestor)
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| The sequence of branching in a tree does not necessarily indicate the actual (absolute) ___ of the particular taxa. | ages
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| Unless given specific information about what the branch lengths in a phylogenetic tree mean, we should interpret the diagram solely in terms of ___. | patterns of descent
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| Two taxa on a phylogenetic tree are next to each other. Does this mean that one of them evolved from the other? | no (remember that branching points can be flipped, so that will change the order of taxa)
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| A person collects plants for pharmaceutical testing looking for natural products with anti-cancer activity. When the National Cancer Institute gets a “hit” on an extract from a particular plant, how do you think that person proceeds from there? | - they grab that sample, find its sister taxa, and test those for anti-cancer activity too
- one of them might work better than the first sample did
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| Phylogenies are inferred from morphological and molecular data. These analyses can reflect evolutionary relationships only if the characters used result from common ancestry. What does that mean? | it is important to focus on features that result from common ancestry because only those reflect evolutionary relationships
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| What does it mean when we say that the limbs of humans, cats, whales, and bats are morphologically homologous? | - they may have different functions (flying vs. swimming, etc.), but the underlying anatomy is similar
- this is due to a common ancestor with the same bone structure
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| If you were to look at genes sequences and other DNA sequences from morphologically homologous organisms, what would you find? | that their DNA would be more similar compared to other organisms (ex. mammals vs. reptiles/insects/etc.)
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| What do you think we would find if we were to compare DNA sequences from bats to DNA sequences from birds? | - there would be a larger difference between bats and birds than between bats and humans/cats/whales
- both are tetrapods and their wings are homologous as limbs, but bats are mammals, birds are not; so, they are not as closely related
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| As swimming organs, what’s the deal with whale fins and shark fins? | - the swimming organs have the same function, but they evolved independently (not from a common ancestor)
- the swimming limbs are analogous
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| As swimming organs, whale fins and shark fins are _____________ and the result of ________________. | - analogous structures
- convergent evolution
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| As flying organs, bat wings, bird wings, and butterfly wings are _____________ and the result of ________________. | - analogous structures
- convergent evolution
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| analogous | - having characteristics that are similar because of convergent evolution, not homology
- they evolved independently
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| convergent evolution | the evolution of similar features in independent evolutionary lineages
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| homology | phenotypic and genetic similarities due to common ancestry
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| Bat wings and bird wings are ___ as limbs, but they are ___ as flying organs. | - homologous
- analogous
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| homoplasies | analogous structures that arose independently; same as analogy
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| When are morphological structures more likely to be homologous? | - when the common ancestor is more recent
- (the more elements that are similar in two complex structures, the more likely it is that they evolved from a common ancestor)
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| When are genes more likely to be homologous? | - when the common ancestor is more recent
- (if genes in two organisms share many portions of their nucleotide sequences, it is likely that the genes are homologous)
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| nucleotide sequence alignment | - a way of arranging the sequences of DNA/RNA/protein to identify regions of similarity that may be a consequence of functional, structural, or evolutionary relationships between the sequences
- done with a computer; gaps are added so sequences align
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| What would you call two DNA sequences (from two diff. organisms not closely related) that coincidentally share 25% of their bases? | a molecular homoplasy
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