Download Ch40_Humans & Environment

Ch40: Human Population Effects on
Environment
Higher Human Biology
Food Chains
Energy
from the
Sun
Green plants
make their own
food by
photosynthesis –
producing
carbohydrates
Animals
depend on
plants for
energy
Some animals eat
other animals for
food – so
indirectly rely on
plants for energy
Transfer of
energy along
food chain
Food Webs
Food webs are made up of interconnecting food chains.
Most animals eat more than one type of food , so if
one kind of food runs out they survive by eating
something else.
Disruption of Food Webs
Factors that affect one species in a food web will
have a knock-on effect for other species in the
food web.
e.g. Chemicals
Fertilisers
to improve soil fertility
Pesticides
to limit crop damage
Effects of chemicals on wildlife
When using chemicals the following questions
should be considered:
Is it biodegradable
or does it stay in
Is it specific or is it
the environment for
poisonous to other
a long time?
organisms?
Is the minimum
concentration &
frequency used?
If these issues are not considered there can be
disastrous consequences!!
Increase in Concentration of Chemical
e.g. DDT
In 1950s & 1960s…
Tertiary consumers at
the top suffered severe
poisoning
More concentrated as moved
up the food chain
Passed easily through
food chains
DDT
An insecticide
Increase in Concentration of Chemical
e.g. DDT
Despite the dilution
of the sea DDT has
been found in
marine ecosystems
Traces have even been
found in penguins in the
Antarctic!
In female birds at the
top of the food chain
the hormones that
control the
Thinner
development of
egg
strong egg shells
shells
were affected by
the DDT
Broken
eggs
Less young
– so a
decrease in
reproductive
success
Resistance to chemicals
DDT used to kill disease-causing insects…
e.g.
Mutants
developed
resistance to
DDT
Tse-tse fly
Mosquitoes (sleeping sickness)
No competition
(Malaria &
so multiplied
Yellow-fever)
rapidly
Level of diseases
high again
Control of Chemicals
Because of :
• Persistence
• Resistance
Non-biodegradable
pesticides
e.g. DDT
(don’t decompose in
organisms or
environment)
In developed
countries all
pesticides are now
subject to strict
controls
Banned
since
1980s
But many are
still being used
in developing
countries!
Disturbing the Balance:
In tropical climates – they don’t
have cold winters as a natural
control against pests, instead
they rely on the natural control
of predatory insects e.g.
ladybirds to eat the pests.
If pesticides were used they would
also kill the useful insects too!
Those sprayed with
e.g. Banana insecticides found more
Plantations damage when insecticide
was used because it
in 1960s
killed predatory wasps.
Interdependence of a Community
Community = all the living organisms (plants &
animals) in an ecosystem
Green Plants
Producers
= produce
their own
food
Animals
Consumers
= consume
food for
energy
Micro-organisms
Decomposers
= breakdown
dead organic
matter
Interdependence of a Community
Plants
Micro-organisms
Depended on to
Depended on
Animals
decompose wastes and
for food &
Needed for
release chemicals into
oxygen
pollination &
ecosystem for
seed dispersal
re-use
Natural ecosystem = a delicately balanced biological
unit of interdependent living things in a state of
dynamic equilibrium.
Ecosystem Instability
The more easily an ecosystem recovers from a
disturbance the more stable it is.
The more drastic the effect, the
more unstable it becomes & the less
likely it is to recover.
Most unstable ecosystems are
due to human activities
NITROGEN CYCLE
The nitrogen cycle is an example of nutrient
recycling………….
• 80% of the air consists of nitrogen gas.
• Nutrients must be recycled because they have a
limited supply and so need to be used again and again
• All living things need nitrogen to make protein but
plants and animals cannot make use of the nitrogen gas
directly.
• Animals must eat plant or animal protein to obtain
their supply of nitrogen.
• Plants absorb nitrogen from the soil in the form of
nitrate.
Denitrification
Nitrogen fixation
Decomposition
Nitrification
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Nitrogen fixation
How does the nitrogen gas get
from the air into the soil?
The nitrogen gas is absorbed
by bacteria (often found in
the root nodules of
leguminous plants e.g. clover).
The bacteria convert the the
nitrogen into ammonia.
This is called…. Nitrogen
Fixation
Root nodules
What happens to the ammonia in the
soil?
Bacteria convert the ammonium compounds
in the soil into nitrites and then to nitrates.
This is called…. Nitrification
What happens to the nitrogen once
its in the plants?
The plants then absorb the nitrates
through their roots to make use of the
nitrogen.
The plants need the nitrogen, to make
proteins.
What happens to the nitrogen in
plants and animals?
When plants and animals die, bacteria and fungi
(micro-organisms) break them down causing
them to decompose.
Decomposition of dead organisms and animal
waste containing nitrogen forms ammonium
compounds.
How does the nitrogen get from the
soil back into the air?
The nitrates in the soil mix with water and
turn into a solution.
Bacteria break down the nitrates and
release nitrogen gas.
This is called…. Denitrification
Disruption of nitrogen cycle:
Algae
Algae
• simple photosynthetic
plants that lack roots
• most live in water
• many are microscopic
(phytoplankton)
Growth requires:
• Light
• Carbon dioxide
• Warmth
• Mineral nutrients
(nitrate & phosphate)
If one factor becomes limited, algal growth is held in check
Disruption of nitrogen cycle:
Algal Blooms
If algae have the right conditions
they multiply rapidly forming an
algal bloom.
Naturally occur – common
in spring due to:
• warmer temperatures
• increased daylength
• rich nutrients
Disruption of nitrogen cycle:
Eutrophication
Eutrophication is the enrichment of water systems
by nutrients (nitrates & phosphates).
Naturally this occurs very slowly, but this process
occurs more quickly because of:
Fertiliser
run-off
Sewage
effluent
Livestock
sewage
Detergents
(rich in
phosphates)
1
4
2
3
Sewage
If raw or inadequately
treated sewage
escapes into a river
bacteria feed on the
sewage and rapidly
multiply causing a
decrease in oxygen
and the death of
animal and plant life.
Bacteria
population
multiplies
Presence of sewage &
millions of bacteria causes
water to become cloudy so
reduces photosynthesis
O2
Concentration
Bacteria decompose
sewage and use up
the oxygen
(for
respiration)
Bacteria
population
Entry of
sewage
Distance downstream
Organic
waste
containing
nitrogen
by bacteria
Ammonium
compounds
by bacteria
Nitrate
compounds
Increase in algae
causing eutrophication
OXYGEN
CONTENT
BIODIVERSITY
LEVEL OF
POLLUTION
HIGH
HIGH
LOW
VERY
LOW
VERY
LOW
VERY
HIGH
LOW
LOW
HIGH
QUITE
HIGH
QUITE
HIGH
QUITE
LOW
HIGH
HIGH
LOW
SEWAGE
WORKS
INDICATOR
SPECIES
their
presence
shows the
water is
very clean
Their absence
shows the
water is
polluted
Once the river
recovers they
are found again
STONEFLY
LARVAE
MAYFLY LARVAE
SEWAGE
WORKS
The greater the level of organic waste pollution in a
river, the greater the numbers of micro-organisms
and the lower the oxygen available to other
organisms.
High level of pollution – organic waste level _____.
high
Micro-organisms feed on the waste using up the
_________.
Numbers of species ________
due to
oxygen
low
lack of oxygen.
Low level of pollution – organic waste level low
_____.
Few micro-organisms in the river due to lack of food
high
so oxygen content _____.
Numbers of species
high due to abundance of oxygen.
_____
Problem of sewage disposal
As the population increases – what should we do
with the sewage sludge?
Out to sea?
Landfill?
WHO guidelines
Increasing concentration of nitrate
50 ppm
100 ppm
Recommended Safe
upper
upper limit
limit
Reduces O2
carrying
capacity of
blood in
babies
e.g.
Blue-baby
syndrome
Fetal
100+ ppm
abnormalities
Unfit
for human
consumption
Gastric
ulcers
Carbon Cycle
• Before the industrial revolution the carbon cycle
maintained a fairly constant atmospheric CO2
concentration.
• Increasing human
population causes an
increased energy demand
 met by combustion of
fossil fuels
• Forests & oceans act as
carbon sinks but can’t
absorb extra CO2
CARBON CYCLE
The Carbon cycle is an example of this
recycling………….
• Bacteria release CO2 into the air.
• Plants use CO2 from the air for
photosynthesis
• Animals uptake Carbon when they eat
plants
• Carbon is released into the air during
combustion processes and the burning of
fossil fuels
CARBON
CYCLE….
More
detail
Human intervention on the
Carbon Cycle
• Burning of fossil fuels –
releases Carbon compounds
into atmosphere, leading to
enhanced greenhouse effect
(& global warming)
•Depletion of reserves of coal,
oil, peat – depletion of a natural
carbon sink
• Deforestation:
depletion of a
natural carbon
sink
Deforestation effect on CO2
Less trees to
absorb CO2 from
the atmosphere
(by
photosynthesis)
Burning the cut-down trees adds
CO2 to the atmosphere
Greenhouse Gases
Gases that trap Infra-red
radiation (heat) from the sun
are known as
greenhouse gases.
Without the natural greenhouse
effect the Earth would be too
cold to support life.
However the an increase in
greenhouse gases in the Earth’s Increased global
atmosphere is causing the
temperatures
‘Enhanced Greenhouse Effect’.
Increase in Global CO2
As the
human
population
increases,
more
energy is
needed, so
more CO2
is
released
as fossil
fuels are
burned.
CO2 concentration changes due to change in rate of
photosynthesis / seasonal changes in plant activity
Increase in Methane (CH4)
Methane production occurs naturally when plants &
animals remains decay in the absence of oxygen.
Increasing
due to …
burning
tropical
forests
Waste gas
from cows
etc.
Landfill
rubbish dumps
Anaerobic
bacteria in
rice paddies
Chloroflurocarbons (CFC’s)
Before industrialisation there were no CFCs in the
Earth’s atmosphere.
Used as…
propellants in
aerosols
Banned in the UK since 2000
coolants
in
fridges
blowing
agents in
foam
production
Effects of increased greenhouse
gases - CO2, CFC’s & methane
Melting polar ice
Rise in
sea level
Contribution of Greenhouse Gases
Molecule for
molecule…
• Methane is 30x
• CFC’s are 10,000x
…as efficient at
absorbing the
sun’s radiation as
CO2
Rise in Global Temperatures
Predicted increase of
4-5 °C by 2050
but average temperatures in
the last ice age (16 000 BC)
were only 4-5 °C lower than
today
So a small change in temperature can have a
large impact on the global climate
Global Shift in Climate
Will lead to:
Desertification
Food shortages
Drought
Shift in
agriculture
towards
the poles
Extinction of plant &
animal species
Global Warming:
Natural or mad-made?
…it’s must be due to
human activity, I
saw a TV program
about it!!
Scientific climate
change models can’t
take everything into
account
It could be due to natural
variation in the Earth’s climate
– The Earth has experienced
extreme temperatures before,
why not again?
There is no clear explanation
because other factors
(pollution, ozone hole, Earth’s
albedo) complicate it
What can be done to help?
Reduce greenhouse gas emissions….
• energy
efficiency
• using
renewable
energy
• Capture & use
methane from landfill
& agriculture
• discourage
deforestation & the
burning of tropical
biomass  Debt relief
• Strict
control
• Phase out
use
• Use
harmless
substitutes
A long-term solution needs
international co-operation