Biology 1406 Exam 6 History of Life - The Early Years
Living organisms have common structure (cells and cell structures)
1.3
Genetic information (DNA) determines structure
1.5, Ch 10
DNA → RNA → proteins ↓→ cell structure
→ enzymes control cell chemistry ( metabolism )
Mutations in DNA produce variation in living organisms of many traits - random
events, chance
Variation allows →↓ →
adaptation by natural selection
1.7, Ch 13
↓ [variations that increase reproductive success accumulate,
↓ other variations decrease - not chance ]
↓
→ speciation - populations that are isolated accumulate different
mutations; genetic differences increase through time prevent inter-reproduction Ch 14
- therefore life has a history of change
Ch 15
- well documented in fossil record, the “archive of living history”
13.4
What are fossils?
History of life closely intertwined with history of the earth - geology
15.7
- very dynamic system, life responds to change
- continental drift (Alfred Wegener, 1912)
- plate tectonics explains continental drift and most geological processes
Radiometric dating gives accurate time spans
15.5
- based on decay of naturally occurring radioactive elements
- halflife is time for 50% of atoms to decay - constant for atom
- while rock is molten crystals form with radioactive atom, not product
- crystal becomes “time capsule” trapping parent atom and daughter product
- strongly correlated to geological features
- accurate in rock of single age - volcanic ash and igneous (molten) rocks
- sedimentary rocks not reliable
Radioactive Parent Stable Product Half-life
uranium-238
lead-206
uranium-235
lead-207
thorium-232
lead-208
rubidium-87
strontium-87
potassium-40
argon-40
carbon-14
nitrogen-14
4,500 million
713
“
14,100 “
47,000 “
1,300 “
5,730 years
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↓↓ 10 million years
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↓↓
10 million years
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↓↓
10 million years
OOOOOOXXXXXX
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↓↓
10 million years
OOOOOOOOOXXX
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parent all
daughter none
parent 1/2
daughter 1/2
parent 1/4
daughter 3/4
parent 1/8
daughter 7/8
parent 1/16
daughter 15/16
History of Earth
15.1, 15.4
- formed about 4,600 mya (million years ago), with dense iron/nickel sinking to
form core, less dense mantle and even less dense crust
- cool enough by 3,900 mya for seas to form and gaseous atmosphere (CO2, N2,
H2S, H2; some CH4, NH3; no oxygen)
- oldest exposed rocks about 3,800 mya
- rocks from 3,500 mya contain fossils of several types of primitive bacteria
including stromatolite-forming cyanobacteria
- life probably arose between 3,900 and 3,500 mya
Formation of living system involves several steps:
15.1 - 15.3
- synthesis and accumulation of small organic molecules (A. Oparin 1920’s and
experiments of Stanley Miller and Harold Urey 1953)
- polymers (chains) from small molecules
- aggregation of molecules in a membrane
- self replication of the system (probably RNA)
- simple metabolism to gain energy
- any system like this could accumulate improvements through natural selection
- these steps very likely in reducing environment (electron giving) without oxygen
- in oxidizing environment organic molecules would break down quickly
What are ribozymes and why are they important ?
Modes of nutrition: prokaryotes have all variations
16.4
- all living organisms must obtain 2 resources: energy and nutrients to build new
molecules
- energy from several sources:
- simple inorganic reactions ex. H2S ---> H2 +S
(these compounds common in volcanic vents)
- breakdown of organic molecules
- light energy using photopigments
- nutrients from several sources:
- inorganic carbon dioxide (CO2)
- organic molecules (“fixed”, CHx )
- nitrogen is another important nutrient, but most organism can use only
fixed nitrogen (N-H or N-O), not N2
32.13
List the energy source and the nutrient source for each of the following modes of
nutrition. Include the organisms that use each mode.
chemoautotrophs chemoheterotrophs photoautotrophs photoheterotrophs -
One group of prokaryotes have outstanding history:
- cyanobacteria (blue-green bacteria) among oldest fossils, formed structures
called stromatolites
- photoautotrophs that can fix their own nitrogen (have two different type cells,
one photosynthesizing and the other fixing nitrogen)
- extremely common until about 1,000 mya; extensive fossil beds
- oxygen produced as byproduct of photosynthesis using water as an electron
source
- iron in solution until about 3,750 mya, then from 3,750 to about 2,000 mya
massive deposits of iron oxides (“rusting of the earth”) - thick banded iron
deposits found world wide
- indicates that large quantity of oxygen produced during this time period, most
absorbed in iron oxides (20 times as in atmosphere today)
- about 2,000 mya oxygen began accumulating in the atmosphere (iron depleted)
- cyanobacteria closely related to chloroplasts in plant and algae cells
Oxygen environment major catastrophe for life:
- deadly to most primitive bacteria
- allows more efficient metabolism - aerobic respiration 20 times more energy
than anaerobic respiration
- 1-2 levels in anaerobic food chain, 5-6 levels in aerobic food chain
- some primitive bacteria adapted to use oxygen
- ozone, O3, produced as byproduct of oxygen atmosphere, blocks ultraviolet
radiation
Living organisms divided into 3 domains
- Bacteria - (eubacteria)
- Archaea - (archaeabacteria)
- Eukarya - "protists", fungi, plants and animals
15.19
Prokaryotic cells: (Bacteria and Archaea)
16.1-12
- small (diameter 1-5 m)
- simple structure with no nucleus and generally little internal membranes
- have cell wall (chemically different from plants)
- many move by rotary flagellum, different from eukaryotic flagellum
- first fossils from 3,500 mya and numerous fossils to present
- only prokaryotes until about 2,200 mya, when eukaryotes appear and about 600
mya when multicellular organisms appear
- extremely common - anywhere there is life
- collective biomass of prokaryotes 10 times biomass of eukaryotes
- can accumulate DNA from other bacteria (horizontal gene transfer)
- complexes of interdependent bacteria develop, especially in anaerobic
environments; called biofilms or "consortium"
- more complex metabolism
- ex. sulfur consuming bacteria and methane consuming archaea
Archaea
- very common in anaerobic (without oxygen) environments similar to early earth:
“extremophiles”
- extreme halophiles live in high salt environments
- extreme thermophiles live in high temperature environments (boiling and above)
- acidophiles live in very acidic environments
- “lithophiles” in deep rock strata
- methanogens get energy by combining CO2 and H into methane in anaerobic
environment
- radiophiles can withstand extreme levels of radiation
- many species in non-extreme environments
Bacteria (eubacteria)
- most abundant group of living organisms on earth
- “gram-negative” and “gram-positive”
- some cause disease - toxins
- many harmless and symbiotic forms
- every form of nutrition
Eukaryotes
16.13 - .20
- larger cells with nucleus and internal membranes
- oldest fossils about 2,100 mya, common by 1,200 mya
- probably related to higher oxygen levels
- membrane infolding in “protoeukaryote”
- endosymbiosis with bacteria that could use oxygen for energy production
(became mitochondria); related to group of eubacteria
- then later with bacteria that could use light energy to fix carbon (became
chloroplast); related to cyanobacteria
- several features of mitochondria and plastids link them to primitive bacteria
- genetically similar: DNA, RNA and ribosomes
- method of division
- size and cell structure
- secondary endosymbiosis
- movement with cilia and flagella - “9 + 2” pattern
"Protists" - very diverse group of mostly single cell eukaryotes
- secondary endosymbiosis important in protist evolution
- several modes of nutrition in different groups
- different groups ancestors to multicellular groups (plant, animals and fungi)
- multicellular algae by 1.2 bya and soft body animals by 600 mya
- mass extinctions about 600 mya, then rapid expansion of multicellular forms
Biology 1406 Exam 6 Review
What are fossils?
Describe the process of plate tectonics and explain how this is related to continental drift.
Why is understanding plate tectonics important to understanding the history of life?
Describe the process of radiometric dating. What is the half-life for radioactive elements?
How can this process be used to date rocks? Why can this technique not be used with
sedimentary rocks?
How long ago do scientists think the Earth was formed?
When did the Earth cool enough to support liquid seas and an atmosphere?
What gasses composed the atmosphere during this time period?
How old are the oldest fossils of living organisms that have been found so far?
List the four steps that biologist think occurred in the formation of living cells.
What conditions were necessary for this to occur; what could not have been present?
Describe the modes of nutrition in living organisms.
What are the two things that organisms obtain from their food?
What are the three sources of energy?
What are the two sources of carbon (and other nutrients)? What is “fixed” nitrogen?
List the modes of nutrition in organisms. For each mode list the energy source, the carbon
source and some examples of organisms that use this mode.
Describe the history of cyanobacteria (blue-green bacteria). How have they changed the
world? What metabolic process is responsible for this change?
How do the banded iron deposits help us understand this change?
Explain the endosymbiotic hypothesis that involves a group of cyanobacteria.
List some of the positives and negatives of having an oxygen environment.
What is ozone and why is it important to life, especially for life out of water?
List several characteristics of prokaryotes.
What occurs in prokaryotes that make it difficult to trace their genetic relationships?
What is a biofilm or consortium?
List the kinds of habitats that “extremophiles” Archaea live in.
What do these habitats have in common?
What is the other domain of prokaryotic organisms besides Archaea?
Which is most closely related to eukaryotes? Which is the most abundant?
Describe the features of eukaryotes.
How old are the oldest fossils of eukaryotes found so far?
Describe the two stages that biologists think “protoeukaryotes” went through in
becoming eukaryotes.
Which two cell organelles of eukaryotes today are thought to have originated this way?
What is secondary endosymbiosis and how important is it in the evolution of eukaryotes?
What is the common feature of eukaryotes flagella and cilia?
Describe the features of protists.
How are protists related to plants, animals and fungi?
.