SPECIES, COMMUNITIES AND ECOSYSTEMS
Species
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A ​species ​is a group of organisms that can potentially interbreed to produce fertile
and viable offspring.
● Members of a single species are unable to produce fertile and viable offspring
with members from a different species
● When 2 different species do produce offspring by crossbreeding, these offspring
are called ​hybrids ​and they are reproductively sterile (e.g. liger, mule)
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A ​population ​is a group of organisms of the same species that are living in the same
area at the same time
● Organisms that live in different regions, different populations, are
reproductively isolated and unlikely to interbreed, however are classified as
the same species if interbreeding is functionally possible
Ecology Terms
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Species - ​a group of organisms that can potentially interbreed to produce fertile and
viable offspring.
Population - ​a group of organisms of the same species, living in the same area at the
same time.
Community - ​a group of populations living together and interacting with each other
within a given area.
Habitat - ​the environment in which a species normally lives, or the location of a
living organism.
Ecosystem - ​a community and its abiotic environment (i.e habitat)
Ecology - ​the study of the relationship between living organisms, or the relationship
between living organisms and their environment.
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🐻🐰🥕
⛰🏝
🐻🐰🥕➕🌲🌲🌦
Modes of Nutrition
Living organisms obtain chemical energy in one of 2 ways. Some species have either an
autotrophic or heterotrophic method of nutrition, but some may have both!
🌳🌻
Autotrophs​
● Autotrophs synthesise their own organic molecules from simple inorganic
substances e.g. carbon dioxide
● Energy for this process is derived from sunlight (photosynthesis) or via the
oxidation of inorganic molecules (chemosynthesis)
● Because autotrophs synthesise their own organic molecules they are commonly
referred to as ​producers
🐯🐻🐰
Heterotrophs​
● Heterotrophs obtain organic molecules from other organisms, either living,
recently killed, or their nonliving remains and detritus (organic waste of dead
organisms)
● Because heterotrophs cannot produce their own organic molecules and obtain it
from other sources, they are called ​consumers
Mixotrophs
● Certain unicellular organisms may on occasion use both forms of nutrition,
depending on resource availability
● Euglena gracilis​ possess chlorophyll for photosynthesis but may also feed on
detritus
Further classification of species based on their mode of nutrition
● Autotrophs produce their own organic molecules using either light energy or
energy derived from the oxidation of chemicals
○ Photoautotrophs ​use photosynthesis to make organic compounds using energy
derived from the sun
○ Chemoautotrophs ​use chemosynthesis to make organic compounds using energy
derived from the oxidation of chemicals
● Heterotrophs obtain organic molecules from other organisms via one of three
methods
○ Consumers ​ingest organic molecules from living or recently killed
organisms
○ Detritivores ​ingest organic molecules found in the non-living remnants of
organisms (detritus, humus)
○ Saprotrophs ​release digestive enzymes and then absorb the external
products of digestion (decomposers)
Autotrophs
Autotrophs synthesise organic molecules from simple inorganic substances
● Most autotrophs derive the energy for this process from sunlight via
photosynthesis ☀
● Some may derive the needed energy from the oxidation of inorganic molecules via
chemosynthesis
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🌨🌲
Autotrophs obtain the simple inorganic substances required for this process from the
abiotic environment ​(air, water, soil… non living)
● These nutrients include carbon, nitrogen, hydrogen, oxygen and phosphorus, and
they are obtained from the air, water or soil
Heterotrophs may also obtain some simple inorganic substances from the environment,
but principally obtain their carbon and nitrogen from the organic molecules produced
by autotrophs.
Heterotrophs
Heterotrophs obtain organic molecules from other organisms via different feeding
mechanisms and different food sources. Consequently, heterotrophs can be
differentially classified according to their feeding pattern.
🥩🥦
Consumers​
● Consumers are heterotrophs that feed on ​living organisms​ by ingestion
● Herbivores are consumers that feed on plant matter (cows, sheep, rabbit)
● Carnivores are consumers that feed on animal matter (tiger, beary)
● Omnivores are consumers that have a diet composed of both plant and animal
matter (humans, pandas)
​
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💀👻🥩🦅
Scavengers​
​(pretend this is a vulture)
● Scavengers are a type of consumer that feed on ​dead​ and decaying carcasses
rather than hunting live prey
● E.g. hyenas, carrion birds such as crows, vultures
💀👻💩🦀🐌
Detritivores​
● Detritivores are a type of heterotroph that obtains nutrients from ​non-living
organic sources​, such a as detritus (waste or debris) and humus (organic
components of soil, formed by the decomposition of leaves and other plant
material by soil microorganisms)
● Detritus is dead, particulate organic matter, such as decaying organic material
and fecal matter POO
● Humus is the term given to the decaying leaf litter intermixed within the
topsoil
● Detritivores include, earthworms, snails, crabs, dung beetles
🍄🦠🧪
Saprotrophs​
● Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms
by external digestion, so they ​don’t ingest​ it!
● They live on, or in, non-living organic matter
● They secrete digestive enzymes into it and absorbs the products of digestion
● Unlike other types of heterotrophs, saprotrophs do not ingest food, but use
enzymatic secretion to facilitate external digestion
● Because saprotrophs facilitate the breakdown of dead organic material, they are
commonly referred to as decomposers
● Examples of saprotrophs include bacteria and fungi, mushroom, mold
● Bonus notes: So you know how viruses make u sick right? Well bacteria make u
sick differently, they digest things right so they release a lot of chemicals,
which may damage tissues in your body, those chemicals might be toxic.
Nutrient Cycling
Nutrients ​are the materials required by an organism. It includes elements such as
carbon, nitrogen and phosphorus. The supply of inorganic nutrients on Earth is
finite, new elements cannot simply be created and so are in limited supply.
Chemical elements are constantly recycled after they are used, since there is a
limited supply
● Autotrophs ​obtain inorganic nutrients from the air, water and soil and convert
them into organic compounds
● Heterotrophs ​ingest these organic compounds and use them for growth and
respiration, releasing inorganic byproducts
● When organisms die, ​saprotrophs​ decompose the remains and free inorganic
materials into the soil
● The return of organic nutrients to the soil ensures the continual supply of raw
materials for the autotrophs
Mesocosms
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🐻🐰🥕) and
Ecosystems ​describe the interaction between biotic components (community
abiotic components (habitat
)
● Ecosystems are largely self contained and have the capacity to be self
sustaining over long periods of time
3 components are required for sustainability in an ecosystem:
1. Energy availability​ - light from the sun provides the initial energy source for
almost all communities
2. Nutrient availability ​- saprotrophic decomposers ensure the constant recycling
of inorganic nutrients within an environment
3. Recycling of wastes ​- certain bacteria can detoxify harmful waste byproducts,
for example, denitrifying bacteria such as N
​ itrosomonas
Mesocosms ​are enclosed environments that allow a small part of a natural environment
to be observed under controlled conditions.
A ​terrarium ​is a small transparent container, either plastic or glass, in which
selected plants or animals are kept and observed.
You need to know how to make a self-sustaining terrarium!
You can make one using a glass or plastic bottle with a lid.
1. Building a verdant foundation
a. Add a bottom layer of pebbles, gravel or sand - this layer exists for
drainage. The smaller the vessel the thinner rock layers required.
b. Add a second thin layer of activated charcoal, this will prevent mold and
help to aerate the soil
c. Spread a thin cover of sphagnum moss, or organic coffee filter, to create
a barrier between the lower layers and soil
d. The final layer is the pre-moistened growing medium, such as soil potting
mix
2. Select the right plants
a. Choose plants that are slow growing and thrive in a bit of humidity, such
as ferns, club moss
b. Inspect the plant thoroughly for any signs of disease or insects before
introducing to the terrarium
3. Maintaining appropriate conditions
a. Ensure the terrarium is placed in a location that provides a continuous
source of light
b. Locate the terrarium in a place that does not experience fluctuating
temperature conditions (avoid direct sunlight!)
c. Do not initially over water the plants, once the right humidity is
established, a terrarium can go months without watering!
d. Occasional pruning (trim plants) may be required, but then, as level of
soil nutrients decrease, plant growth should slow down
😳)
Chi-Squared Test (again?
The presence of two species within a given environment will be dependent upon
potential interactions between them.
If two species are typically found within the same habitat, they show a ​positive
association​.
● Species that show a positive association include those that exhibit
predator-prey​ or ​symbiotic relationships
If two species tend not to occur within the same habitat (react less), they show a
negative association
● Species will typically show a negative association if there is competition for
the same resources
● One species may utilise the resources more efficiently, precluding survival of
the other species (​competitive exclusion)
● Both species may alter their use of the environment to avoid direct competition
(​resource partitioning​)
If two species do not interact, there will be ​no association ​between them and their
distribution will be independent of one another.
Quadrat Sampling
The presence of two species within a given environment can be determined using
quadrat sampling.
A quadrant is a rectangular frame of known dimensions that can be used to establish
population densities.
● Quadrats are placed inside a defined area in either a random arrangement or
according to a design
● The number of individuals of a given species is either counted or estimated via
percentage coverage
● The sampling process is repeated many times in order to gain a representative
data set
Quadrat sampling is not an effective method for counting motile organisms, it is used
for counting plants and sessile animals
● In each quadrat, the presence or absence of each species is identified
● This allows for the number of quadrats where both species were present to be
compared against the total number of quadrats
Chi-Squared Test
A chi-squared test can be applied to data generated from quadrat sampling to
determine if there is a statistically significant association between the
distribution of two species.
The presence or absence of two species of scallop was recorded in fifty quadrats (1m​2
sized quadrat) on a rocky seashore.
The following distribution pattern was observed:
● 6 quadrats had both species
● 15 quadrats had king scallop only
● 20 quadrats had queen scallop only
● 9 quadrats had neither species
QUEEN SCALLOP
KING SCALLOP
Present
Absent
Total
Present
6
15
21
Absent
20
9
29
Total
26
24
50
Step 1 - Set up a hypothesis
● Null hypothesis (H​0​): there is no significance difference between the
distribution of two species (​distribution is random)
● Alternative hypothesis (H​1​): there is a significant difference between the
distribution of species (​the species are associated​)
Step 2 - Construct a table of frequencies
Times the totals (we are finding the expected values! E)
QUEEN SCALLOP
KING SCALLOP
Present
Absent
Total
Present
26 x 21 / 50
= ​10.9
24 x 21 / 50
= ​10.1
21
Absent
26 x 29 / 50
= ​15.1
24 x 29 / 50
= ​13.9
29
Total
26
24
50
Apply the Chi-squared formula
Where ​∑ = Sum​, ​O = Observed frequency​, ​E = Expected frequency
QUEEN SCALLOP
KING SCALLOP
PRESENT
PRESENT
ABSENT
OBSERVED
6
15
EXPECTED
10.9
10.1
ABSENT
(O−E)2
E
2.20
2.38
OBSERVED
20
9
EXPECTED
15.1
13.9
(O−E)2
E
1.59
1.73
X​2​ = 2.20 + 2.38 + 1.59 + 1.73 = 7.90
Determine the degree of freedom
2 species - 1 = 1
Degree of freedom is 1
Look at table of critical values (given)
Always look at 0.05 (5%)
● If the X​2 ​value is equal or greater than the critical value, reject the null
hypothesis H​0
● Ok the critical value is 3.841.
● 7.90 > 3.841, hence we reject H​0 and
accept H​1 ​which states that there is a
​
significant difference between observed and expected frequencies
● So it means that these two species do not tend to be present in the same area,
so we infer that there is a ​negative association ​between them
Energy Flow
Energy Source
All green plants, and some bacteria, are ​photoautotrophic☀, meaning they use sunlight
as a source of energy.
● As a result, light is the initial source of energy for almost all communities
● In a few ecosystems the producers are chemoautotrophic bacteria, which use
energy derived from chemical processes
Light energy is absorbed by photoautotrophs and is converted into chemical energy via
photosynthesis.
● This light energy is used to make organic compounds (e.g sugars) from inorganic
sources (e.g CO​2​)
● Heterotrophs ingest these organic compounds in order to derive their chemical
energy (ATP)
● When organic compounds are broken down via cell respiration, ATP is produced to
fuel metabolic processes
Energy Flow
Energy enters most ecosystems as sunlight, where it is converted into chemical energy
by producers via photosynthesis. This chemical energy is stored in carbon compounds
(organic molecules) and is transferred to heterotrophs via feeding.
Trophic Levels
The position an organism occupies within a feeding sequence is known as a trophic
level.
● Producers ​always occupy the 1st trophic level in a feeding sequence
● Primary consumers ​feed on producers, so they occupy the 2nd trophic level
● Secondary consumers ​feed on primary consumers occupy the 3rd trophic level
●
Tertiary consumers ​feed on secondary consumers so they occupy the 4th trophic
level
Food Chains
A food chain shows the ​linear ​feeding relationships between species in a community
● Arrows represent the transfer of energy and matter as one organism is eaten by
another (arrows point in the direction of energy flow)
● The first organism in a food chain is always a producer, followed by the
consumers (primary, secondary, tertiary)
●
→ → →
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Energy Loss
Energy stored in organic molecules, such as sugars and lipids, can be released by
cell respiration to produce ATP.
● This ATP is then used to fuel metabolic reactions required for growth and
homeostasis
● A by-product of these chemical reactions is heat (thermal energy), which is
released from the organism
Not all energy stored in organic molecules is transferred via heterotrophic feeding,
some of the chemical energy is lost by:
● Being excreted as part of the organism’s faces
● Remaining unconsumed as the uneaten portions of the food
Living organisms cannot convert heat to other forms of energy, and Heat is lost from
ecosystems
The chemical energy produced by an organism can be
converted into a number of forms, including:
● Kinetic energy during muscular contractions
● Electrical energy during the transmission of
nerve impulses
● Light energy when producing bioluminescence
(lantern fish)
All of these reactions are ​exothermic​ and release
thermal energy (heat) as a by-product
● Living organisms cannot turn this heat into
other forms of usable energy
● This heat energy is released from the organism
and is lost from the ecosystem, unlike
nutrients, which are recycled
●
Hence, ecosystems require a continuous influx of energy from an external source,
such as the sun
Energy Efficiency
When energy transformations take place in living organisms the process is never 100%
efficient
● Most of the energy is lost to the organism, either used in respiration, released
as heat, excreted in faeces, or unconsumed
● Typically, energy transformations are about ~10% efficient, with about 90% of
available energy lost between trophic levels
● The amount of energy transferred depends on how efficiently organisms can
capture and use energy (usually between 5-20%)
As energy is lost between trophic levels, higher trophic levels store less energy as
carbon compounds, and so higher trophic levels have less biomass
● Biomass ​is the total mass of a group of organisms, consisting of the carbon
compounds contained in the cells and tissues
● Because carbon compounds store energy, scientists can measure the amount of
energy added to organisms as biomass
● Biomass diminishes along food chains with the loss of carbon dioxide, water and
waste products (e.g urea) to the environment
Because energy and biomass is lost between each level of a food chain, the number of
potential trophic levels are limited.
● Higher trophic levels receive less energy/biomass from feeding and so need to
eat larger quantities to obtain sufficient amounts
● Because higher trophic levels need to eat more, they expend more energy and
biomass hunting for food
● If the energy required to hunt food exceeds the energy available from the food
eaten, the trophic level becomes unviable
Pyramids of Energy
A pyramid of energy is a graphical representation of the amount of energy at each
trophic level of a food chain.
● They are expressed in units of energy per area per time (kJ m​–2​ year​–1​)
Pyramids of energy will never appear inverted as some of the energy stored in one
source is always lost upon transfer
● Each level should be roughly one tenth of the size of the preceding level, as
energy transformations are ~10% efficient
●
The bottom level will always represent the producers, with subsequent levels
representing consumers (primary, secondary, etc)
Carbon Cycling
The Carbon Cycle
The carbon cycle ​is a biogeochemical cycle whereby carbon is exchanged between the
different spheres of the Earth
● There are 4 spheres
○ Atmosphere (air)
○ Lithosphere (ground)
○ Hydrosphere (water/oceans)
○ Biosphere (living things
● These 4 spheres are also known as carbon sinks (reservoirs), so in the diagram
you should label the sinks.
Carbon is exchanged between a variety of forms, including
● Atmospheric gases, mainly carbon dioxide and also methane
● Oceanic carbonates, including bicarbonates dissolved in water, and calcium
carbonate in corals and shells
● Organic materials, including the carbohydrates, lipids and proteins found in all
living things
● Non living remains, such as detritus and fossil fuels
Different processes facilitate the cycling of carbon between the different forms e.g.
feeding, combustion.
Drawing the carbon cycle
Carbon Source 1: Carbon Compounds
Carbon is found in the form of organic molecules in producers and consumers
Autotrophs, such as all plants and algae, convert inorganic carbon dioxide into
organic compounds via ​photosynthesis
● These organic compounds include the carbohydrates, lipids and proteins required
by the organism for survival
Since autotrophs use carbon dioxide for photosynthesis, the levels of carbon dioxide
within the organism should always be low
● In other words, carbon dioxide should always be at a higher concentration in the
atmosphere, or water
● This concentration gradient ensures that carbon dioxide will passively diffuse
into the autotrophic organism as required
● In aquatic producers, carbon dioxide can usually diffuse directly into the
autotroph, whereas in terrestrial plants, diffusion occurs at stomata
Heterotrophs cannot synthesise their own organic molecules and instead obtain carbon
compounds via ​feeding.
Role of cell respiration
All organisms may produce the chemical energy, ATP, required to power metabolic
processes via the process of ​cell respiration.
● So, cell respiration produces ATP, which is used to power metabolic processes
● Cell respiration involves the breakdown of organic molecules (carbon compounds)
and produces carbon dioxide as a by-product
● The buildup of carbon dioxide in respiring tissues creates a concentration
gradient, allowing it to be removed by passive diffusion
In autotrophs, the uptake of carbon dioxide by photosynthesis may at times be
balanced by the production of carbon dioxide by respiration
● This is known as the ​compensation point​, at which the net carbon dioxide
assimilation is zero (intake = output)
Similarly, the amount of carbon dioxide in the environment will be determined by the
level of respiration and photosynthesis
● If there is more net photosynthesis than cell respiration occuring in the
biosphere, atmospheric carbon dioxide levels should drop, and vice versa!
Carbon Source 2: Calcium Carbonate (Aquatic Conversions)
Carbon dioxide dissolves in water and some of it will remain as a dissolved gas,
however the remainder will combine with water to form carbonic acid
●
●
●
●
●
●
CO​2​ + H​2​O ⇄ H​2​CO​3 (carbonic acid)
Carbonic acid will then dissociate to form hydrogen carbonate ions
H​2​CO​3​ ⇄ HCO​3​–​ + H​+ ​(bicarbonate ion)
This conversion also releases hydrogen ions (H​+​), which is why pH changes when
carbon dioxide is dissolved in water, more acidic
The bicarbonate ion also likes to dissociate into carbonate ions
HCO​3​– ​⇄ CO​3​2- ​(carbonate ion) + H​+
Aquatic autotrophs absorb both dissolved carbon dioxide and hydrogen carbonate ions
and use them to produce organic compounds.
When the carbonate ions come into contact with the rocks and sediments on the ocean
floor, they acquire metal ions. This commonly results in the formation of calcium
carbonate and the subsequent development of limestone.
● CO​3​2-​ + Ca​2+​ ⇄ CaCO​3​ (calcium carbonate)
Living animals may also combine the hydrogen carbonate ions with calcium to form
calcium carbonate
● This calcium carbonate forms the hardered exoskeletons of coral, as well as
forming the main component of mollusca shells
● When the organism dies and settles to the sea floor, these hard components may
be fossilised in the limestone
Carbon Source 3: Methane
Methane is produced from organic matter in anaerobic conditions by methanogenic
archaeans and some diffuses into the atmosphere or accumulates in the ground.
Methanogens are​ archaea microorganisms (look like bacteria but not bacteria, another
type) that produce methane (CH​4​) as a metabolic by-product in anaerobic conditions.
Anaerobic (no oxygen) conditions where methanogens may be found include:
● Wetlands, e.g. swamps and marshes
● Marine sediments e.g. in the mud of lake beds
● Digestive tract of ruminant animals (funny shape stomach) e.g. cow, sheep, goat
Methanogens produce methane from the by-products of anaerobic digestion, principally
acetic acid and carbon dioxide
● So then when methanogens respire anaerobically, they produce acetic acid, carbon
dioxide and hydrogen. These 3 products undergo some further change to produce
methane.
● Acetic acid → Methane and Carbon Dioxide (CH​3​COO​–​ + H​+​ → CH​4​ + CO​2​)
● Carbon Dioxide and Hydrogen → Methane and Water (CO​2​ + 4H​2​ → CH​4​ + 2H​2​O)
Methane may either accumulate under the ground, or diffuse into the atmosphere.
●
●
When organic matter is buried in anoxic conditions (no oxygen), such as seabeds,
then deposits of methane as a form of natural gas may form underground
○ Decomposing bodies, some bacteria or methanogens ?? may release methane
also
Rising global numbers of domesticated cattle may be increasing the levels of
methane being released into the atmosphere
Oxidation of methane into carbon dioxide and water in the atmosphere
When methane is released into the atmosphere as a result of anaerobic reactions, it
only persists for ~12 years.
Methane will be naturally oxidised to form carbon dioxide and water, in vapor form
(CH​4​ + 2O​2​ → CO​2​ + 2H​2​O)
● This is why methane levels in the atmosphere are not very large, even though
significant quantities are being produced.
Carbon Source 4: Fossil Fuels
Plants and animals may decompose via soil bacteria, and then they may be fossilised
into fossils, and then extracted into fuels.
Partial Decomposition
In many soils, saprotrophic bacteria and fungi, and detritivores, will decompose dead
organisms and return nutrients to the soil for cycling.
● This decomposition process requires oxygen, as cell respiration is required to
fuel digestive reactions
Water logged regions may lack oxygenated air spaces within the soil and thus possess
anaerobic conditions
● Anaerobic respirations by organisms in these regions produces organic acids,
such as acetate acid (methanogens), resulting in acidic conditions
● Saprotrophic bacteria and fungi cannot function effectively in anaerobic and
acidic conditions, preventing decomposition
And since this organic matter is not fully decomposed in waterlogged soils, carbon
rich molecules remain in the soil and form ​peat
● When deposits of peat are compressed under sediments, the heat and pressure
force out impurities and remove moisture
● The remaining material has high carbon concentration and undergoes a chemical
transformation to produce ​coal
● Strange peat question: so apparently, acidic conditions, anaerobic conditions
and the presence of organic matter favours the production of peat
So coal only forms in marshy areas, waterlogged anaerobic conditions! Remember.
oil/natural gas formation
Partially decomposed organic matter from past geological eras was converted into
either coal, or oil, or gas, which accumulates in porous rocks
Oil, i.e. petroleum, and natural gas, form as the result of the decay of marine
organisms on the ocean floor.
● Sediments, such as clay and mud, are deposited on top of the organic matter,
creating anoxic conditions that prevent decomposition
● As a result of the burial and compaction, the organic material becomes heated
and hydrocarbons are formed
●
The hydrocarbons form oil and gas, which are forced out of the source rock and
accumulate in porous rocks, e.g. sandstone
Carbon Source 5: Pollution (Combustion)
When organic compounds rich in hydrocarbons are heated in the presence of oxygen,
they undergo a ​combustion ​reaction.
● This reaction is exergonic, it produces energy, and releases carbon dioxide and
water as by products
● The carbon dioxide is typically released into the atmosphere, increasing the
concentration of the gas in the air
● For example, complete combustion of propane (refer to chemistry)
Combustion Source 1: Fossil Fuels
Organic compounds can become rich in hydrocarbons when compacted underground for
millions of years
● The heat and pressure over time, triggers a chemical transformation that results
in the compaction of the organic matter
● The resulting products of this process are fossil fuels (coal, oil and natural
gas)
● Because this geological process takes millions of years to occur, fossil fuels
are a non-renewable energy source
Combustion Source 2: Biomass
An alternative to relying on fuels produced by geological processes is to manufacture
fuels from biological processes. You can produce some renewable energy from biomass.
● Living organisms produce hydrocarbons as part of their total biomass, either for
use, or as a waste product
● These hydrocarbons can be extracted and purified to produce an alternative fuel
source, e.g bioethanol and biodiesel
● Provided new raw materials are provided and waste products are removed, this
source of energy is renewable
Carbon Fluxes
Carbon fluxes​ describe the rate of exchange of carbon between the various carbon
sinks / reservoirs.
● There are 4 main carbon sinks:
○
○
○
○
Lithosphere (earth crust)
Hydrosphere (oceans)
Atmosphere (air)
Biosphere (organisms)
The rate at which carbon is exchanged between these reservoirs, or ​carbon fluxes​,
depend on the conversion processes involved:
● Photosynthesis ​- removes carbon dioxide from the atmosphere and fixes it in
producers as organic compounds
● Respiration ​- releases carbon dioxide into the atmosphere when organic compounds
are digested in living organisms
● Decomposition ​- releases carbon products into the air or sediment when organic
matter is recycled after the death of an organism
● Gaseous dissolution ​- the exchange of carbon gases between the ocean and
atmosphere
● Lithification ​- the compaction of carbon-containing sediments into fossils and
rocks within the Earth’s crust (e.g. limestone)
● Combustion ​- releases carbon gases when organic hydrocarbons (coal, oil and gas)
are burned as a fuel source
It is ​impossible ​to directly measure the size of the carbon sinks or the fluxes
between them - instead estimates are made.
● Global carbon fluxes are very large, and are therefore measured in ​gigatonnes
○ 1 gigatonne of carbon = 1 billion metric tonnes
● Because carbon fluxes are large and based on measurements from many different
sources, estimates have large uncertainties
Fluxes are in red*
Estimating Carbon Fluxes
Estimating carbon fluxes requires an understanding of the factors that can affect the
exchange of carbon between different sinks.
● Some of the main causes for flux change include climate conditions, natural
events and human activity
● 1. Climate conditions
○ Rates of photosynthesis will likely be higher in summer seasons, as there
is more direct sunlight and longer days
○ Oceanic temperatures also determine how much carbon is stored as dissolved
CO​2​ or as hydrogen bicarbonate ions
○ Climate events like El Nino and La Nina will change the rate of carbon
flux between ocean and atmosphere
○ Melting of polar ice caps will result in the decomposition of frozen
detritus
● Natural events
○
●
Forest fires can release high levels of carbon dioxide when plants burn,
loss of trees also reduces photosynthetic carbon uptake
○ Volcanic eruptions can release carbon compounds from the Earth’s crust
into the atmosphere
Human Activity
○ Clearing of trees for agricultural purposes (deforestation) will reduce
the removal of atmospheric CO​2​ via photosynthesis
○ Increased numbers of ruminant livestock ( ) will produce higher levels of
methane
○ The burning of fossil fuels will release carbon dioxide into the
atmosphere
🐮
Application: Analysis of data from air monitoring stations to explain annual
fluctuations
Atmospheric CO​2​ concentrations have been measured at the Mauna Loa Observatory (in
Hawaii) since 1958 by Charles Keeling.
From these continuous and regular measurements a clear pattern of carbon flux can be
seen:
● CO​2​ levels fluctuate annually, lower in the summer months when long days and
more light increase photosynthetic rates
● Global CO​2​ trends will conform to northern hemisphere patterns as it contains
more of the planet’s land mass (i.e more trees)
● CO​2​ levels are steadily increasing year on year since the industrial revolution,
due to increased burning of fossil fuels
● Atmospheric CO​2​ levels are currently at the highest levels recorded since
measurements began
Data is now being regularly collected at a variety of field stations globally, using
standardised measurement techniques
● All station show a clear upward trend in atmospheric CO​2​ concentrations year on
year, with annual fluctuations
● Different monitoring stations may have slightly different trends due to seasonal
variations and the distribution of local vegetation
Climate Change
Greenhouse Gases
Greenhouse gases absorb and emit long-wave infrared radiation, thereby trapping and
holding heat within the atmosphere.
● Greenhouse gases collectively make up less than 1% of the Earth’s atmosphere
The greenhouse gases which have the largest warming effect within the atmosphere are
water vapour ​(clouds) and ​carbon dioxide
● These 2 are the worst!!!
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Water vapour is created via evaporation of water bodies, like oceans, and
transpiration
Water vapour is removed via precipitation (rain)
Carbon dioxide is made by cell respiration and burning fossil fuel
It is removed via photosynthesis and absorption by ocean
Other greenhouse gases include methane and nitrogen oxides - these have less impact
on the overall warming effect
● Methane ​is emitted from waterlogged habitats, such as marshes, and landfills!!!
It is also a gaseous waste produced by ruminants (cow cow)
● Nitrogen oxides ​are released naturally by certain bacteria and also emitted in
the exhaust by certain vehicles
The most abundant greenhouse gas in the atmosphere is water vapour, but is not
produced as a product of human activity
The greenhouse gases: water vapour, carbon dioxide, methane, nitrogen oxides
The impact of a greenhouse gas (warming the atmosphere)
There are 2 factors which determine how much of an impact a greenhouse gas will have
in warming the atmosphere
1. Ability to absorb long-wave radiation
a. Gases that have a greater capacity to absorb long-wave radiation will have
a greater warming impact (per molecule)
2. Concentration within the atmosphere
a. The greater the concentration of the gas, the greater its warming impact
will be within the atmosphere
b. The concentration of a gas will be determined by both its rate of
persistence and release within the atmosphere
The overall impact of a greenhouse gas will be determined by the combination of both
these factors
● Methane has a larger capacity to absorb long wave radiation than carbon dioxide,
but is significantly less abundant
● Water vapour enters the atmosphere rapidly but only remains for short periods,
while carbon dioxide persists for years
● Human activity is increasing the amount of greenhouse gases (except water
vapour) and hence increasing their impact
The greenhouse effect is naturally occurring but then anthropomorphic activity
amplifies it.
Carbon Dioxide Concentrations
While greenhouse gases occur naturally, man is increasing greenhouse gas emission via
a number of activities, including:
● Deforestation ​- the removal of trees means that less carbon dioxide is removed
from the atmosphere via photosynthesis
● Increased farming and agriculture ​involves land clearing for cattle grazing,
also ruminant cattle produce methane
The greenhouse gas that is increasing most rapidly in the atmosphere is carbon
dioxide, and the main cause is ​combustion
● When fossil fuels, such as coal, oil and gas, are combusted to release energy,
carbon dioxide gas is released as a by-product
● The increased reliance on fossil fuels following the industrial revolution has
increased in a ~38% increase in CO​2​ levels
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There are now efforts to reduce our reliance on fossil fuels by exploiting
alternative energy sources, such as solar power
Climate Changes
Global temperatures and climate patterns are influenced by concentration of
greenhouse gases
Greenhouse gases play a pivotal role in determining global temperatures and climate
patterns due to their capacity to retain heat
● As these gases trap heat, increases in greenhouse gas concentrations should
correlate with an increase in global temperature
● Long term weather patterns (climate) may also be influenced by greenhouse gas
concentrations
Scientists predict that increases in greenhouse gas concentrations will lead to an
enhanced greenhouse effect, resulting in:
● More frequent extreme weather conditions (heat waves, cyclones, more powerful
tropical storms)
● Some areas to become more drought affected, while other areas become more prone
to periods of heavy rainfall
● Changes to circulating ocean currents - which may cause longer EL NINO (warming)
and LA NINA (cooling) events
Correlations between global temperatures and carbon dioxide concentrations on Earth
The link between global temperatures and carbon dioxide concentrations was
established by analysing data over a long time period
● Ice cores taken from the Vostok station in antarctica provide evidence of
environmental conditions at the time of freezing
● The Vostok ice core is one of the longest drilled, reaching back 420, 000 years
and covering the past four glacial cycles
● By analysing the gas bubbles trapped in ice, historical CO​2​ levels and air
temperatures (via oxygen isotopes) can be deduced
Data collected from the Vostok ice core demonstrates that:
● There is a strong positive correlation between carbon dioxide concentrations and
temperature (↑ CO​2​ levels ↑ temperature)
● There have been fluctuating cycles of CO​2​ concentrations which appear to
correlate with global warm ages and ice ages
● Current concentrations of CO​2​ are higher than at any time recorded in the last
400,000 years
Industrial revolution
The industrial revolution introduced new manufacturing processes which significantly
increased mankind’s use of fossil fuels. The burning of fossil fuels releases carbon
dioxide as a by product, leading to a steady increase in its atmospheric
concentration.
When fuel emissions, atmospheric CO​2​ concentrations and global temperatures are
compared, the following trends are revealed:
● There is a strong positive correlation between increasing fossil fuel emissions
and rising atmospheric concentrations of CO​2
● Atmospheric CO​2​ concentrations have increased ~38% since pre-industrial times
(1800: ~ 280 ppm ; 2010: ~ 380 ppm)
● About 40% of CO​2​ emissions have remained in the atmosphere, the rest has been
absorbed by carbon sinks (mainly oceans)
● This increase in atmospheric carbon dioxide concentration correlates with an
increase in average global temperature
● While correlation doesn't equal causation, there is mounting evidence to suggest
that CO​2​ emissions are linked to global temperature changes (although other
factors likely also contribute)
Ocean Acidification
The oceans are a major carbon sink and absorb roughly a third of all human produced
(anthropomorphic) CO​2​ emissions
● CO​2​ solubility is temperature dependent, they are more soluble when cooler, so
less CO2 will be absorbed as temperature rises
When oceans absorb atmospheric CO​2​ some of it will remain dissolved in a gaseous state
but most will be chemically modified
● Carbon dioxide will combine with water to form carbonic acid, which dissociates
into hydrogen ions and hydrogen carbonate
● H​+​ ions will lower the ocean PH (acidification) and will also combine with free
carbonate ions to form more hydrogen carbonate
● With less free carbonate ions in the water, marine organisms are less able to
produce calcium carbonate via calcification
● Calcium carbonate is used to form the hard exoskeleton of coral and is also
present in the shells of certain molluscs
● Hence increasing concentrations of dissolved carbon dioxide threatens the
viability of coral reefs and certain molluscs
● You should see above notes^^^
Carbon Dioxide emissions and ocean acidification
Rising levels of atmospheric carbon dioxide are causing a decrease in the pH of ocean
water (ocean acidification)
● Since the start of the industrial revolution ocean pH has dropped from ~8.2 to
~8.1, which is roughly a 30% increase in acidity
● It is predicted that if current conditions continue, oceanic pH could fall to
roughly 7.8 by the turn of the century 2100
The decrease in ocean pH is predicted to threaten the survival of marine organisms
that require calcium carbonate
● An increase in the concentration of H+ ions means there are less free carbonate
ions available for calcification
● Shells and coral exoskeletons are also likely to begin to dissolve when ocean
conditions are more acidic
● Experiments have shown that increasing water acidity correlates with the
significant thinning of shells over several weeks
● Corals, sea urchins and shelled molluscs do not exist in regions with high
levels of dissolved CO​2​ (like hydrothermal vents)
Consequences of ocean acidification
An increase in ocean acidification as a result of elevated anthropomorphic CO​2
emissions could have several consequences:
● The disappearance of coral reefs could result in a loss of shoreline protection
and habitat, altering coastal ecosystems
● The loss in revenue from tourism and food industries is predicted to cost
economies upwards of $1 trillion by 2100
● Increasing the dissolved CO​2​ levels in oceans would cause invasive species of
algae to flourish (more photosynthesis)
Greenhouse Debate
Many claims have been made regarding the impact of human
activities on climate change - not all are supported by
evidence.
● Many arguments are not backed by reliable
scientific data or are made by entities with vested
interests, such as oil companies
Here are some false claims:
Claim 1: Climate change has changed in the past and current trends merely reflect the
Earth’s natural climatic cycle
● Supporting argument:
○ Data collected from the vostok ice core shows several changes in climate
over the last 400, 000
○ At several points in history, global average temperatures have been warmer
than those currently observed
● Counter argument:
○ Climate changes do occur naturally, but usually not as abruptly as what is
seen currently
○ When global warming occurred abruptly in the past, it was always highly
destructive to life for example mass extinctions
○ Atmospheric CO​2​ levels positively correlate to average global temperatures
and are currently at the highest levels ever recorded
Claim 2: Climate change is being caused by solar activity and the effect of
greenhouse gas emissions is negligible
● Supporting argument:
○ Temperatures on earth are influenced by the amount of solar radiation from
the sun, more radiation = warmer temperatures
○ Warmer temperatures may be caused by an increase in solar irradiance by
the sun, as determined by the number of sunspots
● Counter argument:
○ Over the last 35 years the sun has shown a slight cooling trend, however
average global temperatures have increased
○ There is no evidence to support a correlation between solar irradiance and
current global temperature trends
Claim 3: Certain changes in climate conditions cannot be linked to greenhouse gas
emissions
● Supporting argument:
○ Global sea levels began to increase before greenhouse gas emissions
significantly increased following the industrial revolution
○ Therefore climate changes like rising sea levels are unrelated to
greenhouse gas emissions
● Counter argument:
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The overall pattern of change in sea levels will be influenced by the time
over which the data is collected
While sea levels did increase preceding the industrial revolution, this
rise in sea levels followed a preceding period of decrease
The rate at which sea levels have risen in the past 30 years is greater
than that seen in the last 200 years
Claim 4: Variability between predicted climate change models means that such models
are unreliable
● Supporting argument:
○ Three different models of predicted climate change commissioned by the
IPCC show variation of more than 5ºC
○ Climate change models are based on assumptions and if those assumptions
are false, the predictions will be incorrect
● Counter Argument:
○ The assumptions made by the different models relate to the extent of human
activity predicted over the next 100 years
○ Model A1B predicts a continued reliance on fossil fuels while model B1
predicts a reduction in the current use of raw materials
○ All three models still predict an increase in average global temperatures
over the next 100 years
Claim 5: Increases in greenhouse gas concentrations in the atmosphere will not be
enough to cause significant climate change
● Supporting argument:
○ As of 2009, there were only ~39 molecules of carbon dioxide per 100,000
molecules in the atmosphere
○ At our current rate of CO​2​ emission, it will take mankind another 5 years
to raise that level by 1 molecule (to 40 per 100,000)
○ While we may double atmospheric CO​2​ levels by the end of the century,
doubling a small number still produces a small number
● Counter Argument:
○ The reason why carbon dioxide is so important to the environment is
because there is so little of it
○ Living things require constant internal environments (homeostasis) – small
external changes can have big impacts on viability