Carbon and Chemicals
in Food Chains
Page 22
. THE CARBON CYCLE

Carbon is the key element of life

Carbon does not decrease as it moves up a
food chain, rather it is changed and
recycled
CARBON CYCLE:

CO2
Photosynthesis
+
carbon dioxide

Two key steps
H2O
light

water
C6H12O6
+
O2
glucose
oxygen
Respiration
C6H12O6 +
glucose
O2
oxygen
 CO2
carbon dioxide
+ H2O
water
Only plants do photosynthesis
All cells must do respiration
Decomposers break down dead plants
& animals, releasing CO2 into the air
Fungi decomposing a log.
Bacteria decomposing a
tomato.
Humans
burn fossil fuels and release
ever more CO2 into the air
Car exhaust
Industrial fumes
Other cycles:
There is a nitrogen cycle that includes: (tomorrow)
proteins, muscles, wastes and bacteria decomposers
There is a slow phosphorus cycle that includes: (tomorrow)
bones & teeth, rocks and weathering
BIOAMPLIFICATION

This refers to an increase in levels of a
chemical as you move up a food chain
Fish provides a heart-healthy source of protein and contains a host
of nutrients including omega-3 fatty acids and vitamin B12.
Mercury exists in our waters and subsequently in fish eat.
The concentration of mercury in local-waters varies, and
therefore, the content in any given fish.
Due to bioamplification, fish at the top of the predator chain are
far more likely to contain high amounts of mercury than smaller
fish.
BIOAMPLIFICATION

The chemical must be fat soluble,
otherwise it is simply urinated out

If a carnivore eats an animal, it accumulates
all of the chemical in that animal’s fat
and retains it for its whole life

Animals high in the food chain may
accumulate lots of chemical
BIOAMPLIFICATION: Example

The chemical DDT was sprayed to kill
mosquitoes

It did kill the mosquitoes, but some
chemical ended up on leaves & grass

That chemical could enter food chains
such as the one on the next slide
snake
hawk
grass
frog
cricket

1 hawk eats 10 snakes
each with 50000 unit
• 1 snake eats 20 frogs
each with 2500 units
• 1 frog eats 25 cricket
each with 100 units
 500000 units in hawk
NO
HARM
 50000 units in snake
NO
HARM

2500 units in frog
NO
HARM
100 units in cricket
NO
HARM
• 1 cricket eats 100 blades of grass
each with 1 unit DDT 
• some blades of grass gets 1 unit DDT when we spray an area
Effect of DDT

If DDT at 500,000 units does NOT harm hawks, why are
we concerned?
•
DDT above 100,000 units makes egg shells thinner
•
When the adult sits on these eggs, they break
• As a result, hawk and eagle populations dropped
greatly in the 50’s, 60’s and 70’s
when DDT was used
Banning DDT

Canada, U.S. and Europe have banned
DDT and bird populations have recovered

but South America and Africa still use
DDT because it is cheap and effective at
killing mosquitoes [which carry disease
that kills millions of people each year]
Other chemicals

Other fat soluble chemicals
may cause sperm problem
in mammals
Some chemicals
cause baby whales to
refuse mother’s milk

• New pesticides are not fat soluble and so
cause fewer problems.
In India, vultures clean-up
the carcasses of the dead
cows
But, 97% of all Indian
vultures died between 2002
and 2006
The question was, what can be
killing the vultures?
The first thing they noticed
was that the vultures were
sick for only a short time
before death
Autopsies showed kidney
failure.
Originally they thought it was a virus, but it did not
spread when healthy birds were put with sick birds.
They then looked at what
vultures ate, and concluded it
was a cattle problem.
Diclofenac – is an antiinflammatory drug used on
cattle
Researchers were able to
show that Diclofenac shuts
down the vulture’s kidneys
and in late 2006 they banned
the drug