Biology 20: Unit A Notes
Energy Flow in Ecosystems
 Biomass is the total mass of all living things in a given area.

Biomass can also refer to the mass of a particular type of matter, such as organic materials
used to produce biofuels.

Biomass is generally measured in g/m2 or kg/m2 .
 Within an organism’s niche, the organism interacts with the ecosystem by:
1. Obtaining food from the ecosystem
2. Contributing energy to the ecosystem
 Plants are called producers because they produce carbohydrates from carbon dioxide, water,
and the Sun’s energy.

Consumers get their energy by feeding on producers or other
consumers.

Decomposition is the breakdown of wastes and dead organisms
by organisms called decomposers through the process of
biodegradation.
Energy Flow and Energy Loss in Ecosystems: Food Chains
 Scientists use different methods to represent energy moving through ecosystems.

Food chains

Food webs

Food pyramids
 Food chains show the flow of
energy in an ecosystem.
Each step in a food chain is a trophic level

Producers = 1st trophic level

Primary consumers = 2nd
trophic level

Secondary consumers = 3rd
trophic level
Biology 20: Unit A Notes

Tertiary consumers = 4th trophic level
Consumers in a food chain can be classified as:
1. Detrivores – consumers that obtain energy and nutrients from dead organisms and waste
matter
Examples include earthworms, bacteria and fungi.
Detrivores feed at every trophic level.
Detrivores have their own, separate food chains
and are very numerous.
2. Herbivores – primary consumers
Herbivores eat plants (producers) only.
3. Carnivores – secondary or tertiary consumers
Secondary consumers eat non-producers, such
as herbivores.
Tertiary consumers eat secondary consumers. - Also called top consumers or top
carnivores.
4. Omnivores – consumers that eat both plants and animals
Examples include humans and bears.
Most organisms are part of many food chains.

Food webs represent interconnected food chains.

Food webs are models of the feeding relationships in an ecosystem.

Arrows in a food web represent the flow of energy and nutrients.

Following the arrows leads to the top carnivore(s).
Biology 20: Unit A Notes
This food web represents a
terrestrial ecosystem that could
be found in British Columbia
Energy Flow and Energy Loss in Ecosystems: Food Pyramids
 Food pyramids show the changes in available energy from one trophic level to another in a food
chain.
 Energy enters at the first trophic level (producers), where there is a large amount of biomass and
therefore much energy.
 It takes large quantities of organisms in one trophic level to meet the energy needs of the next
trophic level.

Each level loses large amounts of the energy it gathers through basic processes of living.

80 – 90 percent of energy taken in by consumers is used in chemical reactions in the body and
is lost as thermal energy.

There is very little energy left over for growth or increase in biomass.
Biology 20: Unit A Notes
Ninety percent of this mouse’s food energy is used to maintain its life functions
 Food pyramids are also known as ecological pyramids.

Ecological pyramids may show biomass, population, or energy numbers.

The amount of life an ecosystem can contain is based on the bottom level of the ecological
pyramid, where producers capture energy from the Sun.

Each level in the energy pyramid = a loss of 90 percent of total energy available.

Lower trophic levels have much larger populations than upper levels.

This shows the importance of maintaining large, biodiverse populations at the
lowest levels of the food pyramid.
Biology 20: Unit A Notes
READ THE FOLLOWING INFORMATION…
Then answer the following questions from your textbook from what you have
learned.
Page 64-65 #3, 6*, 7, 10*, 11*, 20*.
2.2 Nutrient Cycles in Ecosystems
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•
•
Nutrients are chemicals required for growth and other life processes.

Nutrients move through the biosphere in nutrient cycles or exchanges.

Nutrients often accumulate in areas called stores.

Without interference, generally the amount of nutrients flowing into a store equals the
amount of nutrients flowing out.
Human activities can upset the natural balance of nutrient cycles.

Land clearing, agriculture, urban expansion, mining, industry, and motorized
transportation can all increase the levels of nutrients more quickly than the stores can
absorb them.

Excess nutrients in the biosphere can have unexpected consequences.
There are five chemical elements required for life.

Carbon, hydrogen, oxygen, and nitrogen cycle between living things and the atmosphere.

Phosphorus cycles in from sedimentary rock.
Nutrient Cycles:
The Carbon Cycle
•
Carbon atoms are a fundamental unit in cells of all living things.

•
•
Carbon is also an essential part of chemical processes that sustain life.
Carbon can be stored in many different locations.

Short-term shortage is found in aquatic and terrestrial organisms, in CO2 in the
atmosphere and in the top layers of the ocean.

Long-term storage is found in middle and lower ocean layers as dissolved CO2 and in coal,
oil, and gas deposits in land and ocean sediments.
Sedimentation traps many long-term stores of carbon.

Layers of soil and decomposing organic matter become buried on land and under the
oceans.
Biology 20: Unit A Notes

Slowly, under great pressure over many years, coal, oil, and gas form.

Layers of shells also are deposited in sediments on the ocean floor, forming carbonate
rocks like limestone over long periods of time.
•
Carbon stores are also known as carbon sinks.
•
Carbon is cycled through ecosystems in a variety of ways.
•
•
•
Photosynthesis: energy from the sun allows CO2 and H2O to react
•
6CO2 + 6H2O + sunlight
•
Carbon in the atmosphere is transformed by plants into carbohydrates.
•
Photosynthesis also occurs in cyanobacteria and algae in oceans.
Cellular respiration: carbohydrates release energy in consumers
•
C6H12O6 + O2
•
The energy released is used for growth, repair, and other life processes.
•
6CO2 + 6H2O + energy
Decomposition: decomposers break down large quantities of cellulose
•
•
C6H12O6 + 6O2
Cellulose is a carbohydrate most other organisms cannot break down.
Ocean processes: CO2 dissolves in cold, northern waters and sinks
•
Ocean currents flow to the tropics where the water rises and releases CO 2.
•
This process is called ocean mixing.
Eruptions and fires – volcanic eruptions can release CO2.
•
Forest fires also release CO2.
Biology 20: Unit A Notes
•
Many human activities can influence the carbon cycle.
•
Since the start of the Industrial Revolution (160 years ago), CO2 levels have increased by 30
percent due to the increased burning of fossil fuels.

The increase in CO2 levels in the previous 160 000 years was 1 - 3 percent

Carbon is being removed from long-term storage more quickly than it naturally would as
we mine coal and drill for oil and gas.

CO2 is also a greenhouse gas, which absorbs heat in the atmosphere.

Clearing land for agriculture and urban development reduces plants that can absorb and
convert CO2.

Farmed land does not remove as much CO2 as natural vegetation does.
Biology 20: Unit A Notes
The Nitrogen Cycle

Nitrogen is very important in the structure of DNA and proteins.
•
•

In animals, proteins are vital for muscle function.

In plants, nitrogen is important for growth.
The largest store of nitrogen is in the atmosphere in the form N2.

Approximately 78 percent of Earth’s atmosphere is N2 gas.

Nitrogen is also stored in oceans, and as organic matter in soil.

Smaller nitrogen stores are found in terrestrial ecosystems and waterways.
Nitrogen is cycled through processes involving plants.
1. Nitrogen fixation
2. Nitrification
3. Uptake
•
Nitrogen fixation is the conversion of N2 gas into compounds containing nitrate (NO 3–) and
ammonium (NH4+).
1. Both nitrate and ammonium compounds are usable by plants.
2. Nitrogen fixation occurs in one of three ways.
•
In the atmosphere – lightning provides the energy for N2 gas to react with O2
gas to form nitrate and ammonium ions.
•
Compounds formed by these ions then enter the soil via precipitation.
•
This provides only a small amount of nitrogen fixation.
•
In the soil – nitrogen-fixing bacteria like Rhizobium convert N2 gas into
ammonium ions
•
•
These bacteria grow on the root nodules of legumes like peas.
•
The plants provide sugars, while bacteria provide nitrogen ions.
In the water – some cyanobacteria convert N2 into ammonium during the
process of photosynthesis.
• Nitrification occurs when certain soil bacteria convert ammonium. (CALLED NITROGEN
FIXATION)
Biology 20: Unit A Notes
•
•
•

Ammonium is converted into nitrates (NO 3–) by nitrifying bacteria. (CALLED NITRIFICATION)


Ammonium is converted to nitrite (NO 2–), which is then converted to nitrate.
Plants and animal decay and decomposers convert their waste into Ammonia (CALLED
AMMONIFICATION)
Nitrates enter plant roots through the process of uptake.

These nitrogen compounds compose plant proteins.

Herbivores then eat plants and use nitrogen for DNA and protein synthesis.
Nitrogen is returned to the atmosphere via DENITRIFICATION.

Nitrates are
converted back to N2
by denitrifying
bacteria.

N2 is also returned
to the atmosphere
through volcanic
eruptions.
Excess nitrogen dissolves in water, enters the waterways, and washes into lakes and oceans.
Biology 20: Unit A Notes
The nitrogen compounds eventually become trapped in sedimentary rocks and will not be released
again until the rocks undergo hundreds of years of weathering.
•
Human activities can also affect the nitrogen cycle.

Due to human activities, the amount of nitrogen in the ecosystem has doubled in the last
50 years.

Burning fossil fuels and treating sewage releases nitrogen oxide (NO) and nitrogen dioxide
(NO2).

Burning also releases nitrogen compounds
that increase acid precipitation in the form
of nitric acid (HNO3).

Agricultural practices often use large amounts of nitrogen-containing fertilizers.

Excess nitrogen is washed away, or leaches, into the waterways.
Biology 20: Unit A Notes

This promotes huge growth in aquatic algae called algae blooms.

Algae blooms use up all CO2 and O2 and block sunlight, killing many aquatic organisms.
•
Algae blooms can also produce neurotoxins that poison animals.
The Phosphorous Cycle
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Phosphorus is essential for life processes in plants and animals.

Phosphorus is a part of the molecule that carries energy in living cells.

Phosphorus promotes root growth, stem strength, and seed production.

In animals, phosphorous and calcium are important for strong bones.
Phosphorus is not stored in the atmosphere.

•
•
Instead, it is trapped in phosphates (PO 43– , HPO42–, H2PO4–) found in rocks and in the
sediments on the ocean floor.
Weathering releases these phosphates from rocks.

Chemical weathering, via acid precipitation or lichens, releases phosphates.

Physical weathering, including wind, water and freezing, releases phosphates.

Phosphates are then absorbed by plants, which are then eaten by animals.

Weathering does not occur until there is geologic uplift, exposing the rock to chemical
and physical weathering.
Humans add excess phosphorus to the environment
through mining for fertilizer components.

Extra phosphorus, often along with potassium, then enters the ecosystems faster than
methods can replenish the natural stores.
Biology 20: Unit A Notes
•
Humans can also reduce phosphorus supplies.
•
Slash-and-burning of forests removes phosphorus from trees, and it then is deposited as ash
in waterways.
How Changes in Nutrient Cycles Affect Biodiversity
•
Any significant changes to any of these nutrients (C, H, O, N, or P) can greatly affect
biodiversity.

Carbon cycle changes contribute to climate change
and global warming.

Slight temperature fluctuations and changes in water levels can drastically change
ecosystems.

Changes influence other organism in the food webs.
Biology 20: Unit A Notes

Increased levels of nitrogen can allow certain plant species to outcompete other
species, decreasing resources for every species in the food webs.

Decreased levels of phosphorus can inhibit the growth of algae that are very
important producers in many food chains.
2.3 Effect of Bioaccumulation on Ecosystems
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•
Amphibians live on both land and in the water.

Amphibians are sensitive to chemical changes in the environment.

They are therefore valuable indicators of environmental health.

Since the 1980s, many of the world’s amphibian species have suffered declines in
population.

There also have been alarming increases in amphibian birth deformities.

Many theories attempt to explain these changes, including drought, increased UV rays,
pollution, habitat loss, parasites, and diseases.
Bioaccumulation refers to the gradual buildup of
chemicals in living organisms.

Many harmful chemicals cannot be decomposed naturally.

These chemicals can be eaten or absorbed and sometimes cannot be removed from the
body of the organism effectively.

If a keystone species suffers a chemical bioaccumulation, it can affect every other organism in
its far-reaching niches.

A keystone species is a vital part of an ecosystem.
•
Biomagnification is the process by which chemicals become more concentrated at
each trophic level.
•
At each level of the food pyramid, chemicals that do not get broken down build up in
organisms.
•
When a consumer in the next trophic level eats organisms with a chemical accumulation, it
receives a huge dose of the chemical(s).
•
An example of bioaccumulation in British Columbia
is the effect of PCBs on the Orca.
Biology 20: Unit A Notes
•
PCBs are chemicals that were used for many industrial and electrical applications in the mid20th century.
•
PCBs were banned in 1977 because of their environmental impact.


PCBs bioaccumulate and have a long half-life (they break down very slowly).
PCBs will affect the reproductive cycles of orcas until at least 2030.
The bioaccumulation
of PCBs begins with
the absorption of the
chemicals by
microscopic plants
and algae
•
Chemicals like PCBs and DDT are called persistent organic pollutants (POPs).

POPs contain carbon, like all organic compounds, and remain in water and soil for many years.

Many POPs are insecticides, used to control pest populations.

DDT was introduced in 1941 to control mosquito populations, and is still used in some places
in the world.

Like PCBs, DDT also bioaccumulates and has a long half-life.

Even at low levels (5 ppm), DDT in animals can cause nervous, immune,and
reproductive system disorders.
•
ppm = parts per million
•
Heavy metals are metallic elements that are toxic to organisms.
•
Levels of lead in the soil have increased due to human activities.
Biology 20: Unit A Notes



Lead is not considered safe at any level.

Many electronics contain lead and must be recycled carefully.

Lead can cause anemia and nervous and reproductive system damage.
Cadmium is also found in low levels naturally.

Cadmium is used in the manufacture of plastics and nickel-cadmium batteries.

It is toxic to earthworms and causes many
health problems in fish.

In humans, the main source of cadmium is
exposure to cigarette smoke.

Cadmium causes lung diseases, cancer, and nervous and immune system damage.
Mercury also is found naturally.

Mercury has entered ecosystems through the burning of fossil fuels, waste
incineration, mining, and the manufacture of items like batteries.

Coal burning accounts for 40 percent of the mercury released into the atmosphere.

Mercury bioaccumulates in the brain, heart and kidneys of many animals.

Mercury compounds bioaccumulate in fish, adding risk for any organisms eating fish.
Reducing the effects of chemical pollution
•
Bioremediation is the use of micro-organisms or plants to help clean up toxic chemicals.

•
Example: the oil industry uses bacteria to “eat” oil spills.
By trapping chemicals in the soil, they cannot enter the food chains as easily.