The Biosphere
Standard Grade Biology
What is an Ecosystem?
Investigating an Ecosystem
3 Stages
• Collecting and counting samples of
organisms
• Correct identification of organisms
• Measuring the physical conditions
present in the environment
Keys
Biotic factors
(Presence of Living Factors)
• Presence or absence of predators
• Competition
• Consumers
Abiotic factors
(Non living factors which affect the organisms living in a
particular place)
•
•
•
•
•
pH (acidity or alkalinity)
Moisture
Light intensity
Temperature
Oxygen concentration etc
Sources of Error
Effect of Abiotic Factors
• Green plants need light for
photosynthesis and will not grow where
light levels are low
• Most organisms will not survive
extremes of temperature, enzymes will
not function at low temperatures and
are denatured at high temperatures
• Water freezes at 0ºC and living
processes depend on liquid water.
Food and Energy in an Ecosystem
• Green plants are called producers
because they use light energy from the
sun to make their own food
• This process is called photosynthesis
• Other organisms are called consumers
because the get energy by eating plants
or animals that eat plants
Types of Consumers
• Herbivores eat plants
• Carnivores eat other animals
• Omnivores eat plants and animals
Producers
Consumers
Herbivores
Carnivores
Omnivores
Feeding Relationships
• Living things need food
• They can either make their own food
from raw materials
• Or they can get it by eating other
organisms
• Green plants make their own food
• Animals get their food by eating plants
or other animals
Food Chains
• Energy in the form of chemical energy is
transferred from one organism to another
• The primary consumer in a food chain is
always a herbivore (or omnivore) because it
consumes the energy produced by the plant
• The secondary consumer is always a carnivore
(or omnivore) because it eats the herbivore
• This information can be used to make a food
chain
• The arrows in a food chain show the direction
of energy flow in the chain
Food Webs
• Most animals eat more than one thing
• It is better to show energy flow as a
food web
• A food web is made up of several food
chains linked together
Upsetting a Food Web
• If a plant or animal is removed from a
food web its consumers just eat
something else
• In exams you may be asked what the
effect on one species will be if another
dies out
• You must be able to justify or explain
why you think the 2nd species will
increase or decrease
Pyramids
• As you move along a food chain the size of the organ
isms increases but their number decreases
GRASS
(very large no. of
small organisms)
RABBIT
(fewer larger
organisms)
FOX
(few, even larger
organisms)
Pyramid of Numbers
• Food chains and webs do not tell us how
many organisms are eaten
• A fox eats more than one rabbit in its
lifetime
• We can draw a special diagram called a
Pyramid of Numbers to show how many
organisms are eaten
Leaves → caterpillar → shrew → owl
Problems with the Pyramid of Numbers
• Does not take account
of the size of the
organisms at each stage
• E.g. an oak tree and a
daisy each count as one
plant
• But the oak tree can
support many more
consumers than a daisy
can
• This can result in a
strange pyramid of
numbers
Pyramid of Biomass
• A better way of
showing a food chain
is to use a pyramid
of biomass
• This takes account
of the mass of all
the organisms at
each stage of the
chain
Oak tree → caterpillar → blackbird →
flea
• Pyramid of numbers
• Can be an inverted
shape
• Pyramid of biomass
• Always a pyramid
shape
Loss of Energy in Food Chains
• As you go along a food chain there are
fewer but bigger organisms
• This is because when energy is passed
along 90% is lost as
1. Heat
2.Movement
3.Un-digestible bits like bones, hair,
horns
4.Only 10% is passed on to the next stage
Food for Thought
• If 90% of the available energy is lost at
each link of the food chain it means
that shorter chains lose less energy
• This loss of energy is the reason why
very few chains are longer than 4 links
• The more meat a society eats the less
efficient its food chain
Population Growth
•
•
1.
2.
3.
4.
5.
Populations grow when the birth rate is
greater then the death rate.
Populations stop growing when growth
limiting factors come into play:lack of space (prevents breeding),
disease,
shortage of water or food,
predators,
build up of toxic waste.
World Population
Population Growth Curve
a.
b.
c.
d.
Growth in numbers is slow as individuals grow in size
As individuals mature and reproduce the rate of increase in numbers is at
a maximum
As food begins to run out and waste (toxins) build up the rate of
population growth slows down
Birth rate = Death rate, numbers are steady
Competition
•
•
Plants compete for
space, water, light,
minerals
Animals compete
for food, water,
shelter, mates
Effects of competition
• The stronger competitor gets all the
food and the weaker competitor can die
out.
• The stronger competitor can also die
out if it runs out of food, water, space
or toxic waste builds up.
Recycling of nutrients
• overview
Death + excretion
Nutrients in
living
organisms
Absorption
by living
things
Nutrients in dead
bodies + waste
Nutrients freed and
in environment e.g
in soil
Decomposition by
bacteria + fungi
Nitrogen
• Nitrogen is a nutrient
• It is used to make protein by animals
and plants
• It is constantly recycled in the nitrogen
cycle
• The nitrogen cycle is possible because
of the action of bacteria.
Nitrogen
fixed by
lightning
Animal protein
Excretion
& death
Plant
protein
Nitrogen fixing
bacteria (legumes)
Plant protein
Soil nitrates
Nitrifying
bacteria
Decomposition by
fungi & bacteria
Ammonia compounds
Nitrifying bacteria
Denitrifying
bacteria in
waterlogged soil
Core Nitrogen Cycle
• Go over the full version in your notes.
Dead plants,
animals
Urine & faeces
Plants make
protein
Ammonium
Compounds
Plants absorb
Nitrates through
their roots
Nitrites
Nitrates
Nitrogen Fixing Bacteria in the root Nodules of Peas, Beans and
Clover
Types of bacteria
• Nitrogen fixing (root
nodules of peas, beans
,clover)
• Fix nitrogen gas from air into
nitrates
• Nitrifying (soil)
• Change ammonia into nitrites
and nitrites into nitrates
• Denitrifying (soil)
• Change nitrates back to
nitrogen gas
• Decomposers (bacteria and
fungi)
• Bacteria + fungi which
decompose dead plants +
animals into ammonia
Effect of Pollution on the Number of Species
Organic pollutant enters water
No of bacteria increases
Dissolved oxygen used up
Less oxygen available to other species
Most organisms
cannot tolerate
lack of oxygen so die
A few organisms can
tolerate lack of
oxygen and survive
No of species reduced
Indicator species
A species whose presence or absence tells us about the
conditions present in the ecosystem
• Mayfly + stonefly - found in
unpolluted water
• Sludge worms + rat tailed maggots
- can be found in polluted water
• Lichens found in areas with low levels
of air pollution
Control and Management
Management of Resources
• The earth’s resources will not last
forever
• Solutions must be found to halt and
then reverse damage
Management of Resources
Poor Management
Possible Solution
Over-fishing in North
Sea
Larger mesh in nets allows small
fish to escape
Fishing quotas
Destruction of
rainforests
Managed timber production
Efficient food production
Overgrazing leading to Changing farming practices (crop
desertification
rotation, natural fertilisers)
Overuse of chemicals
Poor
Reason for
management practice
practice
Effect of
Possible
bad
solution
management
Overuse of
fertilizers and
pesticides
Chemicals
washed into
rivers,
fertilizers
allow algae to
breed, when
they die and
rot the
bacteria use up
oxygen, fish
die
Harvesting
removes
minerals
Cultivation of a
single type of
crop allows
disease to
spread
Pesticides
enter food
chain e.g. DDT
Use minimum
fertilizer,
develop
biodegradeable pesticides
Use more
biological
controls
Rotate crops
Poor
management
practice
Use of grain
to feed
cattle for
meat
Reason for
practice
Rich nations
like to eat
meat and
dairy
products
Effect of
bad
management
This diet
leads to
obesity and
heart
disease,
The longer
the food
chain the
less
efficient it
is
Possible
solution
It is better
to use the
land to grow
crops that
people can
eat rather
than to grow
crops to
feed cattle
Poor
management
practice
Growth of
cash crops
by poor
nations
Reason for
practice
Poor nations
without
reserves of
fossil fuels
grow crops
such as tea
and coffee
to sell to
rich nations
so they can
get the
money to buy
tools and
technology
Effect of
bad
management
Less food
grown so
people
starve
Possible
solution
More
support
should be
given to poor
countries,
allow them
to grow more
food
Poor
management
practice
Overgrazing
of grassland
Reason for
practice
Livestock
seen as a
source of
wealth in
some
societies
Effect of
bad
management
Kills grass
plants , leads
to soil
erosion and
expansion of
deserts, land
able to
support even
fewer cattle
and people
Possible
solution
Plant trees
and grass
varieties
that can
withstand
intense
grazing