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General BiologyIAnswers to FAQ
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The Tree of LifeChapter 26
5
Origins of LifeThe Earth formed as a hot mass of molten
rock about 4.5 billion years ago (BYA)
-As it cooled, chemically-rich oceans were formed from water condensation
Life arose spontaneously from these early waters (@ about 49-88 Celsius)
Or life may have infected Earth from some other planet (via meteors or cosmic dust)
-This hypothesis is termed Panspermia
6
Fundamental Properties of Life
Cellular organization
Sensitivity
Growth
Development
Reproduction
Regulation
Homeostasis
Heredity
Paramecia (protists) “eating” yeast
7
Environmental Conditions on Early
EarthEarth’s Early atmosphere had
CO2, N2, H2O and H2
Carbon-Rich Reducing atmosphere...energetically easier
to form carbon-rich molecules
8
First Organisms
May have been born in Earth’s crust, in clay, or at deep-sea vents
3.5BYA We have Oldest fossils of prokaryotes.
2.5-2BYA Cyanobacteria...Appearance of oxygen in atmosphere
1.5BYA Oldest definite fossils of eukaryotes
9
Miller-Urey Experiment (1953)
Reproduced Earth’s early atmosphere
Prebiotic
Chemistry
10
Evolution of Cells*Self replicating RNA may have been first genetic
material
*Amino acids polymerized into proteins
*Metabolic pathways emerged
*Lipid bubbles became living cells with cell membranes-CONCENTRATED MOLECULES
*Several innovations contributed to diversity of life
-Eukaryotic cells
-Sexual reproduction
-Multicellularity
11
Classification of OrganismsMore than 2000 years ago, Aristotle divided living
things into animals and plants
Greeks and Romans later grouped plants and animals to basic units called genera
Felis (cats) and Equus (horses)
In the 1750s, Carolus Linnaeus instituted the use of two-part names, or binomials
-Homo sapiens (Genus and Species name)
12
Classification of Organisms
Taxonomy is the science of classifying living things
*A classification or organization is called a taxon
*Scientific names avoid confusion
caused by common names
13
The Linnaean Hierarchy
Taxa are based on shared characteristics
-Domain (most inclusive)
-Kingdom
-Phylum
-Class
-Order
-Family
-Genus
-Species (least inclusive)
14
Eukaryotic Cells
Heterotrophs w/ no cell wall
Mammary Glands
Gnawing teeth
4 front toes 5 back toes
Morphological Differences
Arboreal
Vertebrates
Hierarchical System
Notocord
Chapter 23Linnaean Hierarchy may represent Convergent Evolution
and NOT COMMON ANCESTRY...(this is relative to ahypothesized recent ancestor)
Everybody in the shown animal group has an ancestral trait from this animal here
Some in the shown animal group have a
derived trait from this animal here
We would have a polyphyletic group if we said all the animals in this group Descended from here
18
Limitations of the HierarchyHierarchies are being re-examined based on
molecular analysis
Do not accurately correspond to evolutionary relationships amongst animals
Hiearchies may suggest 2 animals came from the same predecessor (monophyletic) but in fact don’t (polyphyletic).
Linnaean ranks (listed in the hierarchy) do not give strict inheritance information of the members in a rank
19
Grouping Organisms
Biologists are increasingly adopting a three-domain phylogeny based on rRNA studies
-Domain Archaea
-Domain Bacteria
-Domain Eukarya
Each of these domains forms a clade
Archaea and Eukarya are more closely related to each other than to bacteria
21
Grouping Organisms
Carl Woese proposed a six-kingdom system
Prokaryotes Eukaryotes
22
Grouping Organisms via Molecular Analysis
• Since all life has genetic material in common we can group each life form according to differences and similarities in genetic material.
• The sequenced genetic material is usually rRNA.
• Two organisms that inherit similar rRNA sequence are closer related than two organisms with a dissimilar sequence--NO MATTER HOW THEY LOOK LIKE.
23
Phylogeny prepared from rRNA analyses. During evolution, microbes swapped genetic
information via horizontal gene transfer (HGT)
24
Bacteria*Most abundant organisms on Earth...more in
your mouth than mammals on Earth*Extract nitrogen from the air, and recycle
carbon and sulfur *Perform much of the world’s photosynthesis*Responsible for many diseases*Make up our natural intestinal flora*Most taxonomists recognize 12-15 different
groups
25
ArchaeaProkaryotes that are more closely related to
eukaryotesCharacteristics
-Cell walls lack peptidoglycan-Membrane lipids are branched-Distinct rRNA sequences
Divided into three main groups
26
Methanogens
-Use H2 to reduce CO2 to CH4
-Strict anaerobes that live in swamps
Extremophiles
-Thermophiles – High temperatures
-Halophiles – High salt
-Acidophiles – Low pH
Nonextreme archaea
-Grow in same environments as bacteria
-Nanoarchaeum equitans – Smallest cellular genome
27
28
EukaryaProkaryotes ruled the earth for at least one
billion years
Eukaryotes appeared about 2.5 BYA
Their structure and function allowed multicellular life to evolve
Eukaryotes have a complex cell organization
-Extensive endomembrane system divides the cell into functional compartments
29
Mitochondria and chloroplasts most likely gained entry by endosymbiosis
-Mitochondria were derived from purple nonsulfur bacteria
-Chloroplasts from cyanobacteria
30
The Four Eukaryotic Kingdoms
Protista
-Unicellular with few multicellular organisms
-Not monophyletic
Fungi
Plantae
Animalia
-Largely multicellular organisms
-Each is a distinct evolutionary line derived from a unicellular protist
31
Symbiotic Events
32
Key Eukaryotic Characteristics
Compartmentalization
-Allows for increased subcellular specialization
Multicellularity
-Allows for differentiation of cells into tissues
Sexual reproduction
-Allows for greater genetic diversity
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34
35
Making Sense of the Protists
Protists are a paraphyletic group
-Catchall for eukaryotes that are not plant, fungus or animal
Divided into six groups
-However, at least 60 protists do not fit into any of these groups
36A new kingdom, Viridiplantae, has been suggested
-Plants + green algae(Chlorophyta)
Notice that Protists (olive green color) are not monophyletic
37
Origin of Plants
38Land plants arose from an ancestral green alga,
and only once during evolution
Streptophyta has 7 clades, including land plants
Sister clades
Green alga consist of 2 monophyletic groupsChlorophyta and Streptophyta
39
Some land plants show evidence of horizontal gene transfer
The flowering plant Amborella acquired three moss genes
Close contact increases the probability of HGT
40
Modeling evolutionary relationships provides...
An orderly and logical way to name organisms
Insights in understanding the history of major features and functions--Gather clues about the genes involved in speciation and trait formation
41
Segmentation is regulated by the Hox gene family
Segmentation has been used in the past to group
arthropods and annelids close together
rRNA sequences now suggest they’re distantly related