Transcript MONITORING THE ENVIRONMENT ENERGY FLOW NUTRIENT

MONITORING THE
ENVIRONMENT
ENERGY FLOW
NUTRIENT TRANSFER
Energy Flow
Learning Outcomes
• understand that radiation from the Sun
is the source of energy for most
ecosystems / communities of living
organisms and that green plants, and
other photosynthetic organisms such
as algae, capture a small percentage
of the solar energy which reaches
them.
Food Chains
• Food chains are one way of showing
how organisms interact.
Grass Rabbit

Fox
• The arrows represent the transfer of
energy between organisms.
Food Chains
• Plants are producers because they
make their own food
• Animals are consumers because they
eat food to obtain energy.
Consumers and Decomposers
• There are 3 types of consumer
– Herbivores eat plants
– Carnivores eat other animals
– Omnivores eat plants and animals
• Organisms that breakdown dead
plants and animals are called
decomposers
– e.g. fungi and bacteria
Producer
 primary
consumer

secondary
consumer

• Each feeding level is known as a
trophic level
tertiary
consumer
Energy in the Ecosystem
• The sun is the main source of energy
for food chains
• Photosynthetic organisms capture a
small percentage of the solar energy
which reaches them and convert this
into chemical energy.
• This chemical energy is then available
to other organisms.
Light energy available to the
plant
• Of the 100% solar energy reaching the
Earth only some is trapped by
chlorophyll
• What happens to the rest?
–
–
–
–
Reflected by clouds or dust in the air
Reflected by plants
Does not fall on leaves
Wrong wavelength for chlorophyll to trap
– Pass through leaves
Energy Flow through an
ecosystem
• Energy is transferred from one
organism to another.
• This is shown in food chains and food
webs
• Energy given out by organisms is lost to
the environment.
Pupil Activity
Food Chains and energy in living systems
• Colour in the handout
• Answer the questions below in full
sentences
1. In a cool, wet summer the hedgerow insect
population is low. Why will fewer young
weasels be born that spring survive?
2. Simple food chains of the type shown, are
uncommon, why?
3. Why does the amount of energy flowing
through the food chain fall so much between
each level?
Prep: Food Chains and Energy
Flow
• Read all the information provided
• Answer questions 1 – 7
• This is due in on Wednesday 18th May
2011
Learning Outcomes
• Investigate data about food chains
and food webs and understand that
they show the transfer of energy
between organisms and involve
producers; first, second and third stage
consumers; herbivores and carnivores.
Energy Flow – Progress question
• What is the source of energy for
ecosystems?
• How does energy from that source
become available to a predator like a
tiger?
Food chains show the flow of
energy through an ecosystem
Plants are at the start of every
food chain
Food Webs
• If food chains in a habitat are linked,
they form a FOOD WEB.
Food web for a single tree
Changing Food Webs
• Look at the two examples of
ecosystems given.
• For each question give a suggestion of
what might happen to the populations
of organisms and explain why you
think this.
Changing food webs
Changing food webs
Food Webs
• Food webs are easily unbalanced if
one population of organisms in the
web disappears due to:
–
–
–
–
–
–
Over-predation or hunting
Disease
Pollution
Use of pesticides
Lack of food
emigration
Past Paper Question (grade B)
• Answer the question on Sandeels
• 4. (a)
– decrease the numbers (of sandeels) [1]
– sandeels are eaten by herring [1]
– herring compete with sandeels for
(animal) plankton/feed on plankton [1]
• (b) 3 effects are looked for in the answer from:
– herring compete with birds for sandeels/reduce number of
sandeels;
– sandeels do not have enough food / (animal) plankton;
– rise in sea temp (global warming) affect plankton
distribution or numbers;
– fishing for sandeels;
– Not enough food for birds as numbers of sandeels
dropping.
– (not: ref. bird breeding rate unqual./ref. herring killing
sandeels)
• (c) quotas for sandeel fisheries /
sandeel fishing ban or protected
species/ marine or nature reserves [1]
• (not: captive breeding/increase
number of seals/fishing ban unqual.)
Learning Outcomes
• understand that at each stage in the
food chain energy is used in repair and
in the maintenance and growth of
cells whilst energy is lost in waste
materials and as heat during
respiration.
Energy Loss in a food chain
• Energy is lost at each level in the food
chain
–
–
–
–
–
Respiration (lost as heat)
Used up in movement
Maintaining constant body temperature
Faeces and urine (lost as heat)
Some material not being eaten by the
consumer
Energy loss in a food chain
• 90% of energy is lost at each level in a food
chain
Tree  aphid  ladybird  little bird  big bird
100
10
1
0.1
0.01
Energy units
• In long food chains, very little energy is left
for the top carnivore
• In short food chain, less energy is lost.
Energy losses from an animal
• Herbivore
Energy losses from an animal
• Carnivore
Shortening the food chain
• The fewer the trophic levels, the less
food energy is lost so the more food is
available to consumers.
Shortening the food chain
• Energy transfer between producers and
consumers is inefficient because:
– Some plant material is not digested and passes
out of the herbivore body as faeces
– The herbivore uses energy to stay alive
– When the herbivore dies, its body represents
“locked up” energy, which transfers to
decomposers
Pupil Activity
• Practice question on food chains and
energy flow.
Learning Outcome
• use data to construct and interpret
pyramids of numbers and biomass.
Food Pyramids
• Each trophic level is represented by a
horizontal bar
• The width of the bar represents
– The number of organisms
– The amount of biomass
• The base of the pyramid represents the
producer
• The second level is the primary
consumer, etc
Pyramids of number
• This represents the relative number of each
type of organism at each trophic level.
• Draw a pyramid of number for each of the
three food chains below:
– Grass  antelope  lion
– Oak tree  caterpillar  blue tits  owl  fleas
– Rose bush  aphid  ladybird  blackbird
Pyramids of number
• Pyramids of number can be inverted
as they do not take into account the
size of the organism.
• Pyramids of Biomass take into account
the number of organisms and their size.
• Pyramids of biomass are never
inverted.
Pyramids of Biomass
• This represents the amount of living material
(biomass) at each level.
• Draw a pyramid of biomass for each of the
three food chains below:
Grass  antelope  lion
Oak tree  caterpillar  blue tits  owl  fleas
Rose bush  aphid  ladybird  blackbird
Practice Questions on
Pyramids
• Collect
– a question sheet
– A sheet of A4 paper
– Graph paper
Nutrient Transfer
Learning Outcomes
• understand that carbon is constantly
cycled in nature by the carbon cycle
via photosynthesis which incorporates
it and respiration which releases it.
Nutrient Cycling
• Materials are returned to the environment in
waste materials or when living things die and
decay.
• We say that they are recycled.
• This decay is caused by organisms:
– Detritivores e.g. worms
– Decomposers e.g. bacteria and fungi
• These release enzymes which are adapted to
breakdown material
• For decay to be successful the following
conditions are required.
– Oxygen – for respiration
– Warmth – bacteria will reproduce more quickly,
increasing the number of decomposers.
– Water
• For normal life processes
• To secrete solutions of digestive enzymes
• To absorb the products of digestion
• Most living matter is made up of just 6
elements; carbon, hydrogen, oxygen,
nitrogen, phosphorous and sulphur.
• Living things need these elements to
make proteins, carbohydrates and
fats.
The carbon cycle
Carbon dioxide
In the air (CO2)
photosynthesis
respiration
Combustion
(burning)
Fossil fuels
Coal, oil, gas,
peat
feeding
Carbon compounds
in plants
Carbon
compunds
in animals
decay
Past Paper Questions
•2
• (a)
– (i) Two from: leaves, grass, twigs [1]
– (ii) Compost [1]
– (iii) Improve soil (not: fertiliser) [1]
• (b)
– (i) Bacteria/fungi (not: mould) [1]
– (ii) Oxygen [1]
– (iii) heat from respiration
Past Paper Questions
•5
• (a) A burning [1] B photosynthesis [1]
• (b)
– (i) Increase/rise [1]
– (ii) Global warming / acid rain (spec) / accept
greenhouse effect [1]
(not: pollution/greenhouse gas/specific
examples e.g. melting ice caps/ increase in
temperature)
Past Paper Questions
• 5.
– (a) (i) Clockwise – burning, respiration, feeding,
photosynthesis [4 × 1]
– (b) bacteria / fungi / decomposers [1]
(not: microbes/worms)
– (c) deforestation / increase burning fossil fuels / increase in
traffic / increase in power stations [1] (not: cutting down
trees)
• (d)
– (i) killing fish / trees/ tops of pine trees turn yellow [1]
– (ii) lung disease [1
Past Paper Questions
•4
– (a)
• bacteria and fungi 1 mark each [2]
• (allow: decomposers for 1 mark, no mark for
bacteria/fungi as well)
• (b)
– (i)
• Respiration 2 [1]
• Combustion 1 [1]
• Photosynthesis 3 [1]
– (ii) feeding/ingestion [1]
(not: digestion/food chain/nutrition)
Learning outcomes
• know that microorganisms, bacteria
and fungi, feed on waste materials
from organisms and that when plants
and animals die their bodies are
broken down by microorganisms
bringing about decay. These
microorganisms respire and release
carbon dioxide into the atmosphere.
• Understand what happens when
decay is prevented. Burning fossil fuels
releases carbon dioxide.
• Microorganisms digest materials from
their environment for growth and other
life processes.
• These materials are returned to the
environment either in waste products
or when living things die and decay.
• When decay is prevented substances
such as peat, coal, oil and gas are
formed and these store energy in
carbon compounds (Fossil Fuels)
• Energy and carbon dioxide are
released when these fossil fuels are
burnt
• In the last 200 years, humans have
extracted and burnt fossil fuels,
increasing the levels of carbon dioxide
in the atmosphere.
Possible investigations:
• Investigate the decay of leaves in
different environmental conditions e.g.
soil pH, temperature and in bags of
different mesh size.
• Experiments to investigate the
microbial decay of fruit or vegetables.
Nitrogen Cycle
Learning Outcomes
• understand that nutrients are
released in decay, e.g. nitrates and
phosphates, and that these nutrients
are then taken up by other organisms
resulting in nutrient cycles. In a stable
community the processes which
remove materials are balanced by
processes which return materials. .
Decay and Recycling
• All minerals in living things are
recycled.
– Plants take these minerals from their environment
– Animals take them in as food
– These minerals are recycled when dead plants
and animals decay.
• This maintains a balance between
living things and the environment.
• Nitrates and phosphates are important
substances to living things
• The nitrogen cycle and the
phosphorous cycle ensure that the
minerals are recycled.
Learning outcomes
• understand that nitrogen is also
recycled through the activity of soil
bacteria and fungi acting as
decomposers, converting proteins and
urea into ammonia. This is converted
to nitrates which are taken up by plant
roots and used to make new protein.
The Nitrogen Cycle
• Plants and animals need nitrogen to
make proteins.
• Nitrogen gas is unreactive and can not
be used by living things
• Nitrogen gas must be changed to
nitrates before it can be used by
plants.
• Animals then eat plants
The nitrogen cycle
Denitrifying bacteria
Nitrogen gas in the air
Nitrogen fixation
Animal protein
Plant protein
Animal wastes
Decay bacteria break
down proteins and
release ammonia
Nitrifying bacteria
Nitrates in soil
Nitrogen fixing
bacteria in the
soil
Nitrogen fixing
bacteria in
root nodules
Nitrogen fixation
• Making nitrates from the nitrogen gas
in the air
• Nitrogen-fixing bacteria found in the
soil and in the root nodules of
leguminous plants, such as peas,
beans and clover
Nitrogen Fixation
Feeding
Decay
• Nitrogen compounds in living things
are returned to the soil as ammonium
compounds through:
– excretion and egestion by animals
– the breakdown of dead plants and animals by decay
bacteria
Nitrifying bacteria
• Change ammonium compounds to
nitrates
decay
decay
Denitrifying bacteria
• Denitrifying bacteria live in water
logged soils.
• They change nitrates back into
nitrogen gas.
denitrification
The bacteria
• The nitrogen cycle involves four
different types of bacteria
–
–
–
–
decay
Nitrifying
Denitrifying
Nitrogen-fixing
• In an exam, you will need to be able
to describe the roles of these bacteria
Leaching
• Some nitrates may be washed out of
the soil by rainwater, this is called
leaching.
• Leaching can lead to the
eutrophication of lakes
Learning Outcome
• investigate the action of urease on
urea.
Urease and decay
• Decomposers secrete enzymes into
the soil to breakdown waste.
• The enzyme urease can cause decay
by breaking down urea to form
ammonia and carbon dioxide
• Ammonia dissolves in water to form an
alkaline solution.
• In an experiment the action of urease
can be investigated using universal
indicator paper
How does urine help keep the
nitrogen cycle going?
• This practical is designed to help you
– Draw conclusions
– Judge the strength of evidence
– Understand control experiments
How does urine help keep the
nitrogen cycle going?
• Alternative name to practical
– Investigating the effect of the action of urease
on urea.
• Collect the instruction sheet
• Read through all instructions
• Draw a results table
• Collect your equipment
• Start the investigation
Analysis of Investigation
• What are your conclusions from this experiment?
• How certain are you of these conclusions? Give
reasons for your answers.
• Why do you think that ethanoic acid was added to
the tubes?
• What was the point of tube D?
• How could you have improved the reliability of your
results?
• In this experiment, different volumes were used to
vary the concentration of urease. Suggest how this
method could be improved.
Monitoring the Environment
Learning Outcomes
• understand the issues surrounding the
need to balance the human
requirements for food and economic
development with the needs of
wildlife.
The Environment
• The environment includes
– All living things
– All habitats
• place where living things live
– The climate
• The physical factors
• All of these things are interlinked
• A change in one factor can have
effects on the others
Conservation of Wildlife
• Is this a good thing?
– In pairs discuss the conservation of wildlife
– List the possible advantages and
disadvantages of conserving wildlife
Conservation of wildlife
• Conflicts can arise when
– Conservation measures means a
disadvantage for the human population
– Conserving one species means another
suffers
• Example
– Humans need housing
– Building houses will destroy animal and
plant habitats
Learning Outcomes
• Discuss how the collection of detailed,
reliable scientific information and
monitoring by biologists could help to
inform, manage and reduce the
impact of development on the
environment e.g. the role of the
Environment Agency.
Conflicts between humans and
conservation
• Humans need food
– Habitats are
converted into
farmland, which
reduces the number
of species that can
live there
• Humans need
alternative energy
sources
– Structures built can
destroy or alter
natural habitats
Getting the balance right
• Environments are constantly changing
– they are dynamic
• The Environment Agency monitors the
environment and the human impact.
• The Environment Agency has an
important role in
– monitoring, protecting and improving the
environment,
– promoting sustainable development.
Monitoring the environment
• Before any development, scientific
information must be collected on
– The state of the environment
– What changes could occur
– The impact of these changes on the species
• This is presented in a document called
an Environmental Impact Assessment.
E.I.A
• EIA
– assessment of potential environmental
damage
Cardiff Bay Barrage
• Read through the information
provided
– Summarise the benefits and
disadvantages of the barrage
– In pairs, discuss whether or not it was right
to build a barrage across Cardiff bay.
How Science Works Task
• Since moving their feeding ground,
survival rate of the common redshank
has gone down from 85% to 78%.
• It is possible that this is because the
food supply on the new feeding
ground is not as good as in Cardiff Bay.
• What information would scientists need
to collect before they could confirm
this hypothesis?
Redshank
Research and use of information
PREP TASK
• Research information on the Allt Duine Wind
Farm
– Use a google search
– Bring the information to lesson with you next
week
– You will be given 45 minutes in lesson time next
week to write a report
– There is information on the students P Drive (for
emergency use)
– Do not bring in too much information – although
you do not know the question you are going to
have to research you can sieve through
information and bring in relevant unbiased
information.
Research and use of information
Class Task
• Part A
– Using the information which you found, write a
brief report about the proposed development of
a wind farm at Allt Duine
• Part B
– Devise a method to find out how many people
who live or use the area support the proposed
development.
Learning Outcomes
• discuss the advantages and
drawbacks of intensive farming
methods, such as using fertilisers,
pesticides, disease control and battery
methods to increase yields.
Intensive Farming Methods
Intensive Farming Methods
•Modern farming is intensive
– This means that farmers produce as
much food as possible by making
the best use of available land, plants
and animals
Battery farming
•Animals are reared in controlled
conditions
– Amount and type of food
• High protein diets with additives
– Temperature of surroundings kept constant
– Restrict movement
– Antibiotics put in food to control disease
Advantages
• Produces more food on available land
• Huge variety of top quality foods
• Production of foods all year round
• Cheap prices
• No longer the risk of having to ration
food
Drawbacks
• Habitat destruction
– Remove hedgerows to make large fields to maximise efficiency
• Soil erosion
• Use of fertilisers
– Eutrophication
• Use of pesticides
– Disrupt food chains
• Battery farming, such as hens and
crated veal calves
– Ethics – is this humane?
Fertilisers
Learning Outcomes
• understand that untreated sewage
and fertilisers may cause rapid growth
of photosynthesisers, plants and algae,
in water. When the plants and algae
die, the microbes, which break them
down, increase in number and further
use up the dissolved oxygen in the
water. Animals, including fish, which
live in the water may suffocate
Fertilisers
•Fertilisers containing nitrates wash into
rivers and streams
•The result is a river enriched with
nutrients, this is known as
eutrophication
The stages that follow
eutrophication
• rapid plant growth
• plant death
• increase in microbes
• Decrease in oxygen as microbes
respire
• Death of fish and invertebrates
Pesticides
Pesticides
•used to kill insect pests to reduce
damage to crops
•Also kills non target insects, which may
have been useful
•Shortage of food for insect eating birds
•Pesticides can enter the food chain
Pesticides and Food Chains
• Pesticides are used to kill pest species
– Insecticides kill insects
– Herbicides kill weeds
• Pesticides stay in the ecosystem for a
long time, they are not biodegradable
• This can have a devastating effect on
wildlife.
Bioaccumulation
• pesticides are poisonous to other animal life.
• If the animals at the start of a food chain
take up small amounts it becomes more
and more concentrated higher up until it
can kill the animals at the top
For information only
• One example was the use of a pesticide called DDT
used in the 1960's.
• It was used to kill insects (an insecticide) that were
damaging crops but it leaked into rivers and
contaminated plants.
• The small animals and fish further up the food chain
collected more and more because it wasn't lost
(not excreted) from their bodies.
• Eventually, otters ate the fish and were killed. Otters
were virtually made extinct in Southern England.
TB in Cattle
Learning Outcomes
• Investigate the issues surrounding the
question of the source of TB infection in
cattle, including the role of the
scientific community in planning valid
experiments in order to inform policy
decisions and how different
interpretations can be applied to
reach various possible outcomes.
Badgers and Bovine Tuberculosis
• The facts
– Badgers carry Bovine TB and pass it on to
cattle
– If badgers in an area are culled, bovine TB
is significantly reduced
– It’s difficult to kill every badger in an area
– Badgers can move to surrounding areas
increasing bovine TB in those areas.
Culling Badgers
• Is it possible to obtain evidence about
the source of infection?
• Is it proven that badgers are
responsible for TB in cattle?
• If badgers are culled would new
populations fill the vacant niches?
• If badgers are culled would TB actually
spread to new areas?
• Is vaccination of cattle and or badgers
a possible method of control?
Exam Question bTB
• (a) (i)
– because badgers could move into the area/new
areas (to fill vacant niches)
– because of the movement of cattle between
herds/one farm to another. [1]
• (ii)
– because it would remove a possible source of
the infection in cattle
– cattle can be infected by badgers. [1]
• (b)
–
–
–
–
–
–
badgers are protected by law
they consider the evidence is unreliable
Culling doesn’t control bTB
farmers could do more to protect their herds
Vaccination
ref. animal rights or inhumane [1
• not:
– ref. endangered species /
– extinction of badgers /
– cruelty
• (c)
–
–
–
–
–
vaccination
more reliable (tuberculin) testing
check cattle when sold
More control on cattle movement
culling infected herds. [1]
• not:
– killing cattle
RESEARCH AND USE OF
INFORMATION
• Farmers can not kill badgers unless they get a
licence from the Government. In 2010 farmers in
some areas of Wales were licensed and there was a
proposal to allow English farmers to cull badgers,
too.
• On the basis of scientific evidence, what do you
think the UK government’s policy on badger culling
should be?
• Use the internet to research Bovine TB and badgers
– bring any print outs with you to the next lesson.
Pollution
Pollution
• Pollutant
– Substance added to environment which
damages it in some way
– Can be natural or unnatural
Common pollutants
•
•
•
•
•
•
•
•
Oil
Detergents
Fertilisers
Pesticides
Heavy metals
Carbon dioxide
Methane
CFCs
• Sulfur dioxide
• Nitrous oxides
• Human and animal
sewage
• Noise
• Heat
• Non-recyclable
household waste
Indicator Species
Learning Outcomes
• investigate using suitable data, how
indicator species and changes in pH
and oxygen levels may be used as
signs of pollution in a stream
Pollution Indicating Species
• A Pollution Indicator is any living organism
that shows the presence of environmental
pollution.
• Species vary significantly between clean
and polluted areas.
• Pollution levels in a river can be monitored
by looking at the species of organisms living
there.
Freshwater indicator species
red tubeworms
• A large population of
tubeworms in a river
tells us that there are
low oxygen levels.
• They are red in colour
because they contain
haemoglobin
• This helps them to
absorb dissolved
oxygen from the water.
Chemical Indicators
• Oxygen levels can
be a measure of
pollution.
• pH is also measured
to find out how
clean water is.
• A data logger can
be used to measure
these things.
Data logger
Trent Biotic Index
This is a standard method of measuring pollution. It is based on the
fact that different organisms can resist different degrees of
pollution.
The table shows an interpretation of Trent Biotic Index results.
Index
State
Typical Animals
XI-X
Very clean
VII-X
Clean
Fish and various arthropods
VI-VII
Clean
As above but fewer species
V-VI
Fairly clean
III-IV
Dubious
As above but fewer species
II-IV
Dubious
As above but only fish
I-III
Poor
Insect larvae and tubeworms
0-I
Poor
Anaerobic organisms only
Trout, salmon
A few fish, freshwater fleas
The case of a polluted river
Click the numbers on the river to see the effect of the pollution which has
happened between locations  and  on the population of different
organisms.
Use this data to plot a graph and write a conclusion.
Click on the
graph icon above
to plot a graph
1
2
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12
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12
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8
16
5
14
2
6
2
0
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4
Bar graph to show the effect of the pollution on
the population of different river organisms.
Number
20
19
18
17
16
15
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9
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7
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1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
1 2 3 4
Click the numbers in order to record the number of organisms
1 2 3 4
Back to
the data
Practical
testing water for organic pollutants
• Sewage or fertiliser pollution causes an
increase in the number of bacteria in water.
• These bacteria produce an enzyme, catalase,
which breaks down hydrogen peroxide in
their cells into water and oxygen.
• Polluted water, with more bacteria, will break
down hydrogen peroxide faster than clean
water will.
• The breakdown can be measured by the
oxygen produced.
Analysing your results
• Draw a graph of your results.
• What are your conclusions from your
results?
• Why is it better to use capillary tubing
in this experiment rather than normal
glass tubing?
Prep Task
• How can we tell how polluted the
environment is?
– Read through the task on pages 22 &23 in
the textbook
• Write a report of the pollution of the
stream and its likely causes.
Learning Outcomes
• investigate how lichens can be used
as indicators of air pollution
Lichens and Air pollution
• Lichens are used are indicators of air
pollution
• Different lichens have different
sensitivities to sulphur dioxide in the air.
Lichen
Plants can also be good indicators of pollution. Lichen are
very sensitive to sulphur dioxide in the air. They do not grow
well in areas with air pollution.
Lichen growing on a
tree in a clean air
area.
Click the trees to change
their colour to show the
polluted areas
Trees with lichen
Trees without lichen
Learning Outcomes
• Understand that mathematical
modelling can be used to analyse and
predict effects.
Modelling
• Mathematical modelling can be used
to predict and analyse the effects of
pollutants in the environment.
Learning Outcomes
• Discuss and understand that the
effects of pesticides, such as DDT,
became apparent in the early 1960s
and the initial observation,
accumulation and interpretation of
scientific evidence emphasised the
need to monitor the effects and
control the use of these chemicals
Learning Outcomes
• explore information about the heavy
metals which may be present in
industrial waste and the types of
pesticides used on crops. Some of
these chemicals enter the food chain,
accumulate in animal bodies and may
reach a toxic level and so have
harmful effects.
Chemicals and food chains
• Heavy metals and pesticides are two
types of chemical that can enter the
food chain.
• Heavy metal pollution includes lead
and mercury
Minemata Bay
• Mercury released into the bay from a
factory
• Phytoplankton absorb mercury from the
water
• Zooplankton eat the phytoplankton
• Fish eat the phytoplankton and the
zooplankton
• Mercury builds up to high levels in the fish
making them poisonous
• Humans ate the fish