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Biology
Preliminary Course
Stage 6
Life on Earth
Part 3: Early life
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Contents
Introduction ............................................................................... 2
Studying groups of bacteria....................................................... 4
Technological advances ......................................................................5
Archaea and Eubacteria ......................................................................5
Ancient and present day bacteria ............................................ 12
Evidence for Archaea ........................................................................12
Additional resources................................................................ 14
Suggested answers................................................................. 17
Exercises – Part 3 ................................................................... 19
Part 3: Early life
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Introduction
Further developments in our knowledge of present day organisms and
the discovery of new organisms allows for better understanding of the
origins of life and the processes involved in the evolution of
living things.
Part 3 will provide you with opportunities to learn to:
•
describe technological advances that have increased knowledge of
procaryotic organisms
•
describe the main features of the environment occupied by one of the
following and identify the role of this organism in its ecosystem:
–
Archaea
–
Eubacteria
–
Cyanobacteria, including those that form stromatolites
–
nitrogen-fixing bacteria
–
methanogens
–
deep sea bacteria
Part 3 will provide you with opportunities to:
•
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use the available evidence to outline similarities in the environments
past and present for one of the following:
–
Archaea
–
Eubacteria
–
Cyanobacteria, including those that form stromatolites
–
nitrogen-fixing bacteria
–
methanogens
Life on Earth
•
analyse information from secondary sources to discuss the diverse
environments that living things occupy today and use available
evidence to describe possible alternative environments in which life
may have originated.
Extracts from Biology Stage 6 Syllabus © Board of Studies NSW, originally
issued 1999. Revised October 2002. The most up-to-date version can be
found on the Board’s website at
http://www.boardofstudies.nsw.edu.au/syllabus_hsc/index.html.
Part 3: Early life
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Studying groups of bacteria
In the previous two parts you have become familiar with evidence for the
origin and evolution of life. Evidence suggests that the first organisms
were procaryotic and this is the topic of this part. You will recall
investigating the differences between procarotic and eucaryotic
organisms in the previous module, Patterns in nature.
cell membrane
specialised
cell
structures
(organelles)
scattered
nuclear
material
nuclear
material
surrounded
by nuclear
membrane
procaryotic cell
eucaryotic cell
What are the main differences between eucaryotic and procaryotic cells?
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_________________________________________________________
_________________________________________________________
Check your answers.
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Life on Earth
What are procaryotic organisms?
Procaryotic organisms are usually microscopic, free living and
unicellular, although some may be found as colonies or long filaments.
They may have structures such as cilia or flagella attached to the surface
for locomotion. They are thought to be the first form of life on Earth and
are still the most abundant life form on the planet.
Technological advances
The internal structure of procaryotes was unknown until technology
became available. This then lead to the separation of the procaryotes
from other living organisms. One of the major advances that first
distinguished procaryotic from eucaryotic cells was the electron
microscopes, in the 1970s. There are two main types of electron
microscopes:
•
scanning electron microscope (SEM)
•
transmission electron microscope (TEM)
As more technology has become available, such as protein synthesis
analysis, other molecular features have been used to further classify
procaryotes. Today DNA sequencing is used to classify the procaryotes.
Further information has become available through the technological
advances that have occurred in deep-sea exploration and deep-sea drilling.
Complete Exercise 3.1: Technological advances
Archaea and Eubacteria
One method of classification divides procaryotes into two groups:
Archaea and Eubacteria. Archaea (archaeo means ancient) are
considered the more primitive group as they do not possess molecular
features present in Eubacteria.
The most significant difference between those two groups is in the
molecular structure. For example, the cell walls of the Eubacteria are
made from a substance called murein. The structure of the lipids within
the cell membrane is not branched. Eubacteria are sensitive to antibiotics
such as penicillin, streptomycin and chloramphenicol. The Archaea do
not possess these features.
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Archaea
Carl Woese and a team of scientists identified the existence of the
Archaebacteria in the 1970s based on vast differences in genetic makeup. He also suggested that the bacteria be removed from the end of the
original name, so you may find this group referred to as the ‘Archaea’.
Archaea are unique and are thought to be very rare. It is possible that
they are relics of the earliest forms of bacterial life. Evidence to support
this comes from their anaerobic nature and ability to survive in odd
places such as swamps, near-boiling hot springs, salt marshes and the
digestive tracts of herbivores. They all carry our unusual metabolic
pathways and live in extreme environments.
Archaea can be subdivided into three groups:
•
methanogens
•
halophiles and
•
thermophiles.
Methanogens
These organisms produce methane as a waste product of cellular
metabolism ( methano refers to methane; gen means causing).
Methanogens are found in places where there is little or no available
oxygen, such as deep in the soil, swamp mud, animal digestive tracts
(including humans) and any sewage treatment plant.
The methanogens make up the largest group of the Archaea. They are
anaerobic, which means that they do not use oxygen as an energy
source, utilising hydrogen instead. The carbon required for growth is
obtained from carbon dioxide that is reduced by the fermentation of
carbohydrates, releasing methane gas.
Halophiles
These organisms live in places with very high salt concentration (halo
refers to salt; phile means loving). The halophiles get their name from
their tolerance of extreme levels of salt. They can be found in the Middle
East in the Dead Sea and the Great Salt Lake in the USA or in any large
scale saline evaporation pond such as a saltern, sometimes at near
saturation levels. They do not use chlorophyll but a different substance
called bacteriorhodopsin to harness the Sun’s energy for
photosynthesis. This pigment makes the cells appear purple.
The halophiles are thought to be aerobic.
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Life on Earth
Thermophiles
These organisms live in hot places such as near-boiling springs (thermo
refers to heat). The thermophiles are found in areas of volcanic activity
where the temperatures are high. The sulfur produced is utilised as an
energy source. There is a group called the thermoacidophiles that are
able to survive under extreme conditions such as 90°C and strong acidity.
These Archaea may be found in volcanic or thermal vents and geysers.
With advanced technology available to explore the extreme depths of the
ocean, it has been possible to identify deep sea bacteria that thrive near
the vents along mid-ocean ridges where rock is being formed by
volcanic activity.
Describe the places where it would be possible for each of the Archaea
groups to exist.
Methanogens ______________________________________________
_________________________________________________________
_________________________________________________________
Halophiles ________________________________________________
_________________________________________________________
_________________________________________________________
Thermophiles______________________________________________
_________________________________________________________
_________________________________________________________
Check your answers.
If you have access to the Internet go to the science page for some suggested
websites to find some more information about the procaryotes.
http://www.lmpc.edu.au/science
Eubacteria
Eubacteria is a large group containing organisms usually thought of as
bacteria. These organisms thrive in many environments. Most bacteria
live in air, soil and water. Disease-causing bacteria are
usually Eubacteria.
The Eubacteria contain groups that you may have come across previously
in your studies such as the nitrogen-fixing bacteria found in the soil,
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disease-causing bacteria including diphtheria, tuberculosis, tetanus and
syphilis in humans. They are often about one-tenth of the size of
eucaryotic cells. The Eubacteria can be classified into a number of
specialised groups. The phototrophs and chemotrophs will be described
here for you.
The phototrophs
One group of phototrophs is the Cyanobacteria. These organisms can
live in colonies or singly. The Cyanobacteria contain chlorophyll and are
photosynthetic. It is because of this photosynthetic nature that these
simple bacteria have sometimes been incorrectly referred to as bluegreen algae.
Stromatolites
The oldest known fossils formed by cyanobacteria are the stromatolites.
They have been found in the Pilbara region in Western Australia and
have been dated at 3450 million years old.
What do you think is the significance of the stromatolites for the
atmosphere. Think about the early atmosphere, as described in Part 1.
Can you suggest the major implications of the presence of stromatolites
might have had on the atmosphere?
Hint: think about the photosynthesis equation and the gases present in the
early atmosphere.
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Check your answers.
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Life on Earth
A cross-section of a fossilised stromatolite. This sample is on display at
Macquarie University. (Photo: T Reid ©LMP)
Stromatolites are layered structures, thought to have resulted from the
activities of ancient bacteria that produce lime (calcium rich salts) and
trap silt (very fine mud). The photograph above is a cross section of a
fossilised stromatolite, placed on its side. Modern day stromatolites can
be found in Hamelin Pool, Shark Bay in Western Australia.
Formation of ancient stromatolites has been inferred from modern day
stromatolites such as those found in Shark Bay.
Present day stromatolites are found in environments in which other
organisms find it very difficult to survive. These environments include
saline lakes and near hot springs.
The chemotrophs
The chemotrophs are bacteria that utilise inorganic substances, such as
iron and sulfur compounds from the Earth’s crust in their metabolic
processes. This results in the production of sulfuric acid, which can be
utilised by plants in the form of sulfate and hydrogen ions to produce
amino acids. Other chemotrophic bacteria are able to produce nitrates
and nitrites from ammonia, these compounds are utilised by plants as a
source of nitrogen. These organisms can exist in the absence of light.
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Soil and water bacteria
Soil and water bacteria include those that play an important role in the
recycling of matter. One such group includes the nitrogen-fixing
bacteria. These are found in the soil, sometimes in symbiotic
relationships with the roots of some flowering plants. These bacteria
take nitrogen from the atmosphere and convert it to ammonia and
ammonium ions.
What role do nitrogen-fixing bacteria play in the environment?
_________________________________________________________
_________________________________________________________
Check your answers
An example of an important nitrogen-fixing bacteria is Rhizobium.
This is a symbiotic bacteria found in nodules on the roots of legumes,
such as beans, lucerne and peas. These plants are able to survive in soils
low in nitrogen because the bacteria in their root nodules help to fix the
available nitrogen (atmospheric) into a form that is usable by the plants.
The bacteria are then supplied with sugar (from photosynthesis) by
the plant.
Root nodules of clover contain nitrogen-fixing bacteria. (Photo Jane West)
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Life on Earth
Complete the table to summarise the types of environments these organisms
occupy and the role they play in it.
Organisms
Examples
Environment
Role in environment
Archaea
Eubacteria
Complete Exercise 3.2: Groups of bacteria.
Part 3: Early life
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Ancient and present day bacteria
Procaryotic organisms have very specific environmental conditions in
which they live. The physical requirements of the Archaea and the
Eubacteria will now be investigated.
Evidence for Archaea
The evidence that these organisms existed can be found in the Earth’s
oldest sedimentary rocks, dating back more than 3800 million years.
This evidence has been obtained from stable carbon isotopes and not
fossils. Therefore, it is difficult for scientists to conclusively determine
what the organisms actually looked like.
The best way of understanding these early forms of life comes from the
ability to study present day Archaea. Modern day Archaea have been
found living in high temperature, deep marine environments such as
those associated with submarine volcanic vents.
Approximately 4000 million years ago, the Earth had a completely
different atmosphere as mentioned previously. The atmosphere did not
contain any free oxygen, the surface of the Earth being made up of only
volcanic island chains. Today the majority of cells have evolved in an
oxygen rich atmosphere, utilising sugars to obtain energy.
What is the name of the process in which oxygen and sugars are used to
produce energy? Did you remember that the process is called respiration.
Those cells that do not exist in an environment in which respiration is
possible need to use other methods of obtaining their energy.
Environments that do not contain oxygen are called anaerobic.
There are organisms that can exist in the absence of sunlight and are
capable of manufacturing organic molecules from elements other than
oxygen in their environment. This is known as chemosynthesis.
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Life on Earth
Organisms that chemosynthesise are found in locations associated with
submarine volcanic vents, where water can reach temperatures exceeding
300°C. Under these conditions sulfates are converted into hydrogen
sulfide, which is utilised as an energy source instead of obtaining energy
from the Sun. The water remains liquid at these temperatures due to the
great pressure at such depths, approximately 2.5 km.
Bacteria living in anaerobic environments can generate energy through
anaerobic fermentation. This involves the decomposition of a sugar into
alcohol and carbon dioxide. This process occurs through a number of
stages. Fossil evidence shows that bacteria, similar to present day
bacteria, lived on Earth millions, even billions, of years ago.
Information about the environments and roles of present day bacteria
assists in predicting and understanding the environments and roles of
ancient bacteria.
Diverse environments of procaryotes
Procaryotes are found in nearly every ecosystem on Earth. They play
important roles in the recycling of materials in the nitrogen, carbon,
oxygen and sulfur cycles.
Decomposers play a large role in recycling material between the living
and the non-living world. Nitrogen-fixing bacteria in the roots of plants
change atmospheric nitrogen into a form that plants can utilise.
Cyanobacteria are responsible for producing large amounts of oxygen
especially from the oceans of the world.
The prokaryotes are the most abundant life form and can live in the most
extreme environments on Earth. It is for this reason that it is thought that
when life is found on other worlds they may be similar to procaryotes.
In this exercise, you will research and present information about the
present and past environments of one of the following:
•
Archaea
•
Eubacteria.
You can find information about some of these organisms in the Additional
resources. Other information is available from the science website.
http://www.lmpc.edu.au/science
Complete the Exercise 3.3: Past and present environments.
Part 3: Early life
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Additional resources
The earliest cellular fossil
The earliest cellular fossils now known, are the filamentous microfossils
from the Apex chert (chert is a silica rich sedimentary rock) near Marble
Bar in northwestern Australia. These fossils were discovered by the
palaeobiologist J W Schopf in 1992, and have been dated at
approximately 3465 million years.
These fossils have been described as being ‘cyanobacterium-like’,
implying that they may have been able to photosynthesise. If these
organisms were a type of photosynthetic bacteria, then this would be the
earliest evidence of oxygen being produced by organic means.
Present day Archaea
Is there life existing on Earth today that does not need oxygen to survive?
There are a number of areas where very simple microscopic bacteria
flourish in the absence of oxygen.
What do you think of when someone says to you, ‘you need to do more
aerobic exercise’? You should be thinking in terms of exercise that
involves a high heart rate and lots of breathing such as running, boxercise
and swimming. The term ‘aerobic’ means in the presence of free
oxygen. We are therefore considered aerobic organisms, since we need
oxygen to extract the energy necessary for living.
What therefore, do you think the term anaerobic organisms means?
An environment, which has very little to no oxygen, is said to be
anaerobic. There are a number of anaerobic environments such as
anaerobic marshes, sewage treatment plants and the digestive tract of
animals including humans. In each of these environments Archaea
happily exists. These bacteria are known as anaerobic organisms.
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Life on Earth
Modern day Archaebacteria have also been found living in hightemperature, deep marine environments such as those associated with
submarine (beneath the water) volcanic vents known as fumaroles.
These present day Archaea, due to their very simple structure and their
ability to live in very harsh, hot and oxygen-depleted environments are
thought to be related to the very first life forms on Earth.
Archaea can be found underwater around volcanic vents known as black
smokers. You can see the presence of organisms on the photograph on the
left. The photograph on the right shows the sulfides being emitted as ‘smoke’.
(Photo courtesy of Dr Ray Binns. CSIRO.)
The best way of understanding these early life forms is to study present
day Archaea. The volcanic vents referred to above, produce structures
known as black smokers.
Part 3: Early life
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The name black smoker is derived from the way sulfides are emitted into
the ocean when hot lava from the submarine volcanic vent, comes into
contact with the surrounding seawater. The result is a black cloud of
sulfides and sulfates, which become deposited around the vent itself and
eventually form a submarine ‘chimney stack’. All this volcanic activity
produces temperatures in excess of 300∞C.
If you can obtain access to the video The Living Machine, from the Planet
Earth series, it has some vary rare footage of these black smokers in action.
This is an excellent film.
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Life on Earth
Suggested answers
Studying groups of bacteria
In a eucaryotic cell, the nucleus is bound by a nuclear membrane, as are
the mitochondria, chloroplasts, Golgi bodies, endoplasmic reticulum and
ribosomes. The chromosomes usually occur in linear pairs.
In a procaryotic cell, there is a nuclear region but there is no membrane
around it. The nuclear region or nucleoid, is not regarded as a nucleus.
Within the nucleoid, there is a single chromosome that is usually circular.
Archaea
•
Methanogens can be found in soil, swamps, salt marshes, digestive
tracts of animals, sewerage treatment plants. All these environments
have little available oxygen.
•
Halophiles can be found in salterns and salt lakes. These are very
salty environments.
•
Thermophiles can be found in volcanic or thermal vents and deep
sea mid-ocean ridges. These environments have a very high
temperature.
Stromatolites
Carbon dioxide was present in large quantities in the early atmosphere.
The presence of photosynthetic stromatolites would cause the production
and build up of oxygen in the atmosphere. This was thought to have
caused the gradual change from an anoxic to an oxic environment.
Soil and water bacteria
Nitrogen fixing bacteria assist in the recycling of matter and fixing of
atmospheric nitrogen into nitrate compounds in the soil.
Part 3: Early life
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Organisms
Examples
Environment
Role in
environment
Archaebacteria
Halophiles
places with a high
salt concentration
eg. Dead Sea
photosynthetic
producing oxygen
Eubacteria
Phototrophs
such as
Cyanobacteria
warm shallow
seas such as
Hamelin Pool, WA
photosynthetic
adding oxygen to the
atmosphere.
Life on Earth
Exercises – Part 3
Exercise 3.1 to 3.3
Name: _________________________________
Exercise 3.1: Technological advances
Describe two technological advances that have increased knowledge of
procaryotic organisms.
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
_________________________________________________________
Exercise 3.2: Archaea and Eubacteria
Complete a summary of the present environments and roles of the
bacteria listed in the table below. If you prefer you may prepare your
summary in point form rather than completing the table. You will need
to redraw the table before completing it.
Part 3: Early life
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Type of Bacteria
Eubacteria
Example
phototrophs
Environment(s)
occupied
Role in
ecosystem(s)
where found
cyanobacteria
stromatolites
chemotrophs
Archaea
nitrogen -fixing
bacteria
methanogens
halophiles
thermophiles
deep-sea
bacteria
Exercise 3.3: Past and present environments
Evidence of procaryotes occurs as fossils in sedimentary rocks.
Discuss how information about the present day environment(s) of
your selected organism assists in understanding environments of
the past.
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
______________________________________________________
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Life on Earth