Download Ecological relationships and energy flow

Ecology
is the study
of living things
in their environment
Ecosystem =
community + environment
(all the living things)
(all the surroundings)
An ecosystem is the
name given to all
the living things,
community, and
their non-living
environment in a
particular area.
The living organisms
are all dependent
on each other
through feeding
relationships.
What
is an
Ecosystem?
How does life on Earth rely
on energy from the Sun?
Energy flow
• Life can exist on Earth
because of sunlight
energy.
• Plants capture light
energy through the
process of
photosynthesis.
• And make organic
compounds such as
carbohydrates
• Energy is transferred through the ecosystem
by feeding relationships.
Finding out about
populations in a habitat
Fieldwork provides information about what
plants and animals live in a particular habitat and
their numbers.
It is therefore necessary
•
to be able to identify organisms, using keys
•
and understand the different sampling
techniques used to count them.
We cannot actually count
every plant or animal in a
particular place, so
we count a sample of the
population to calculate
an estimated population size.
Sampling populations
You should understand the importance of
random sampling.
This is essential to avoid observer bias.
WHAT DOES THIS MEAN?
This means that the person collecting the data
does not affect the result deliberately, e.g. by
only counting in one part.
Quadrats are usually used
to count plants,
but can also be used
to count slow moving
animals
such as snails.
1. Lay out two tapes at right-angles in the area you
want to sample.
2. Use random number tables to pick co-ordinates:
• quadrats should be placed randomly so that a
representative sample is taken.
3. Place a quadrat (of suitable size) at that point and
count the organisms within it.
4. Repeat using using at least 20 quadrats, at other
random coordinates across the grid:
• repeating increases the reliability.
• collecting across the whole grid area reduces the
effect of an unusual distribution
5. Calculate the average number of organisms in each
quadrat
6. Use the average to calculate an estimated total
number of organisms in the grid area.
Quadrats can be used to estimate a population in
an area which is fairly uniform. Examples include
lawns, woods and open ground.
There are three ways to count organisms to
estimate population size:
• 1. Density
(calculating the number of organisms per m2);
• 2. Frequency
(number of number of quadrats that contain the
organism)
• 3. Percentage cover
(estimating the percentage of the grid area that
contains the organism)
Percentage cover – do you agree with
the estimates?
• Percentage cover is an easy way to estimate
population size.
• However, a disadvantage is that it is difficult
to estimate exactly what percentage of the
quadrat is actually covered by a particular
type of plant, so it is normal to round up to
the nearest 10%. An exception is if there are
any plants with a percentage cover of 1 -5% this is recorded as 1 and not 0.
• This makes the results less reliable than
estimating the density.
Belt transects can be used to
investigate
changes in the distribution
of organisms along a
particular habitat,
e.g. due to changing abiotic
factors such as light intensity
Sampling animal populations
How do we know that the invasive
harlequin ladybird is affecting the
populations of native ladybirds?
used to collect
small
invertebrates.
• Sweep nets allow you
to collect large
numbers of
invertebrates that live
in low vegetation
(stems, tall grasses,
flowers etc) or in rivers
and ponds
• Sweep netting involves
making a large rapid
sweep with a net in
between large paces.
• The invertebrates can
be collected in a tray
and counted
Stones to prevent rain flooding
the trap or birds or other
predators from removing the
trapped animals
jar sunk in a hole
in the ground
Pitfall traps must be properly set up:
• the top of the jar should be level with the soil
surface
• cover the trap with a stone or piece of wood to
keep out the rain, to make it dark and to stop
birds eating your catch
• the traps must be checked often to avoid the
animals escaping or being eaten before they are
counted
• as with most methods a large number of traps
makes results more reliable and minimises the
effects of unusual results
• http://www.bbc.co.uk/scotland/learning/bites
ize/standard/biology/biosphere/investigating_
an_ecosystem_rev5.shtml
These are the non-living, physical parts of the
environment, including:
• Wind
• Water
• pH
• Light
• Temperature
These are the living parts of the environment,
including:
• Predators
• Disease
• Waste produced by living organisms
See worksheet (pages 54 -55 textbook)
Each organism is adapted (suited) to the
environment in which it lives.
This case study tries to explain why specific plants live
at different distances from the seashore.
1. Describe the area that was being studied.
• 1km sand dune, divided into 3 sections.
• Section 1 from the start of the first sand
dune inshore.
• Section 2 half way between 1 and 3.
• Section 3 from the end of the last dune to
to the start of the woodland.
2. What sampling method was used to study the
distribution of plants along the sand dunes?
• 3 interrupted belt transects
3. How many samples were taken?
• 20 at each site
4.
•
•
•
Name the biotic data collected.
the average percentage cover
of marram grass, common heather and gorse
along each transect
5. Name the abiotic data collected
• average light intensity reaching the ground
• Average soil moisture
• Average pH
6. Describe the conditions in which each of the
plants prefers to grow.
• Marram grass: can grow in very unstable
conditions such as those found near the shore,
where the sand is constantly moving in the
wind. It helps to stabilise the dunes, by
holding the sand together for other plants to
grow in.
• Heather: small shrub, prefers stable moist soil
• Gorse: large shrub, prefers very stable soil with
lots of moisture and nutrients
7. Describe the trends shown by the graphs.
• Marram grass is only common in transect 1
• Heather is not found in transect 1 but is found
in transect 2
• Gorse is most common in transect 3, but
uncommon or absent at transects 1 and 2.
8. Use the biological knowledge about the 3
plants and the abiotic data to explain the
trends.
• Marram grass can grow at the beginning of the
dunes where there is not much water available
in the sand, 20%.
• It needs high light intensity to grow, 95%.
• Further inland, where the conditions are more
stable, there is less light and there is more
moisture, so the other plants out-compete the
marram grass.
• Heather cannot grow in transect 1 because
there is not enough moisture.
• Gorse grows best in transect 3 where there is
most water, 60%.
• Gorse is a large shrub and creates shade,
preventing the marram grass and heather
from growing.
9. What features of this investigation make the
results reliable?
• The plants were counted in 20 quadrats at
each transect and an average was calculated.
10. How could the reliability be increased further?
• ******
11. Explain why you think this a fair test?
• Only one thing was being changed.
12. State the following:
the independent variable
• The position of the transect along the dune.
the dependent variable
• Percentage plant cover in each quadrat
the controlled variables
• Size of the quadrat
• Time of the year the measurements were
taken.
It was not possible to keep the wind, light
intensity, soil moisture or pH controlled.
However these factors were measured and
helped to explain the presence or absence of
the plants at the different transects.
• Keys are used to identify unknown
organisms. Dichotomous keys, used in
biology, consist of a series of two part
statements that describe observable
features of organisms.
• At each step of a dichotomous key you are
presented with two choices. As you make a
choice about a particular feature or
characteristic of an organism you are led to
a new branch of the key. Eventually you will
be led to the name of the organism that you
are trying to identify.
Constructing a key for objects in a pencil case
1. Look at the group of
objects and separate
them into two groups
based on a single
observable feature.
2. Look at each group separately and again separate
each into two groups based on a single observable
feature.
3. Continue until each group has only one object.
A dichotomous key may be shown as a branching
diagram or as a numbered key.
A branching key:
A numbered key:
• Carefully examine and think about the observable
features of the 8 aliens and create a dichotomous
key using some of these characteristics.
Broad leaved trees
This trees leaves are green all over and
have a hairy upper surface. They are
rounded with a pointed tip and they are
larger on one side of the midrib than the
other. The edges of the leaves are
toothed, but they have no lobes or
prickles. The stalk is short and rounded
and bears a single leaf.
LEAF LITTER
This wingless invertebrate has a waistless
segmented body with 3 pairs of legs. It
uses a spring under its abdomen to move
by jumping.
Grassland
This 6 legged invertebrate has a broad
body with a triangle shape on its back. It
has 2 pairs of wings; one pair forms a
protective case. It moves by flying or
walking and has no obvious snout.
Garden weeds
This spineless weed has smooth edged,
arrow shaped leaves. The stem trails
along the ground and produces pink and
white trumpet shaped flowers.
All living organisms are divided into five large
groups called Kingdoms.
The 5 kingdoms are:
All the organisms in each kingdom have
specific features in common.
These include:
(1) their mode of nutrition (how they feed)
(2) whether they have a cell wall
(3) cellular organisation;
Group
Nutrition
Cell wall
Cellular organisation
Protoctista
Saprophytic or
photosynthetic
Cellulose cell wall
or none
Single celled with nucleus
or algae that are not truly
multicellular
Bacteria
Saprophytic
Non-cellulose
Single celled with no
nucleus
Fungi
Saprophytic or
parasitic
Non-cellulose
Single or multicellular –
can be ‘acellular’ with it
being difficult to
distinguish individual
cells and nuclei scattered
throughout the organism
Plants
Photosynthesis
Cellulose
Single or multicellular –
‘typical’ cell arrangement
with a nucleus
Animals
Eating organic food
None
Single or multicellular –
‘typical’ cell arrangement
with a nucleus
fungal cell
dead food
1. Enzymes released
onto food
3. Soluble
products
absorbed
2. Enzymes digest food
1. Some organisms are difficult to classify e.g.
Euglena, which has both plant and animal
characteristics. This is why single-celled plants
and animals are classified in a separate group
called the Protoctista.
2. Sometimes it is difficult to identify which species
an organism belongs to or where one species
merges into another. Definition – a species is a
group of organisms, with shared features,
which can breed together to form fertile
offspring.
3. Viruses are a complex group and are very
difficult to classify. All viruses, e.g. the HIV
virus that causes AIDS, lack proper cellular
organisation. They have a DNA/RNA core (DNA
and RNA are nucleic acids – the building
blocks of chromosomes) and an outer protein
coat without the typical cytoplasm of other
cells. They can only live if they gain access to
other cells and many biologists therefore
regard them as non-living.
Read through your notes on
classification before answering
question 3 (p71) in the
GCSE Biology textbook.
Classification using observable
features
• Construct a table to classify the sample of
organisms into vertebrates and invertebrates.
Mr D’s table….
Ecological terms
biodiversity, population, habitat, environment,
community and ecosystem
Match the terms with the definitions and write
them into your notes.
[Answers on next slide ]
TERM
DEFINITION
Biodiversity
A measure of the number of different
types of plant and animal species in an
area
Population
The number of one type of organism
(species) in an area
Habitat
The place where an organism lives
Environment
The factors, both physical (abiotic) and
living (biotic), that affect organisms in a
habitat
Community
The total number of organisms from all
the populations in an area
Ecosystem
The community of organisms that are
interdependent on each other and the
environment in which they live
Population changes
• Population numbers change over time.
• Many factors can contribute to population
change but they can be summarised by:
Consider how each of these factors contributes to
population growth:
• Birth rate
• Death rate
• Immigration
• Emigration
They can be summarised by the equation:
Population growth = (birth rate + immigration) –
(death rate + emigration)
The Sun as Energy Source
The Sun is the energy source for most
ecosystems on Earth and green plants play a
vital role as ‘producers’ in capturing this
energy through the process of photosynthesis.
The plants make sugars and other organic
compounds that are then eaten by other
organisms, so:
plants make the sunlight energy available to
other organisms.
The sequence of producers trapping the Sun’s
energy and this energy then passing on to
other organisms as they feed is known as
energy flow.
The different stages in the feeding sequence are
called trophic levels (or ‘feeding levels’). The
sequence can be drawn as arrows from
producer to consumers, the arrows
representing energy flow.
The sequence of energy flow from producer to
consumers is known as a food chain.
FOOD CHAINS
Food chains show the
feeding relationships and
energy transfer between a
number of organisms.
Draw a food chain from the
food web shown opposite
and identify:
(a) The trophic levels
(b) Producers and
consumers.
In all food chains the first organism (at trophic level 1) is
the producer (a plant) and it provides food and energy
for primary consumers.
Note that in reality very few animals have only one food
source, so energy flow in an ecosystem is more
accurately represented by a food web, not a simple
chain.
Food webs show how a number of food chains are
interlinked and they give a more realistic picture of
feeding relationships.
Pyramids of number and biomass
• The number of organisms at each stage of a
food chain (i.e. at each trophic level) can be
represented by a pyramid of numbers.
The problem with a pyramid of numbers is that
it is not always pyramid-shaped, as it does not
take into account the size of the organisms
involved, e.g. one oak tree will support many
more organisms than one grass plant
And also …. Pyramids may appear top heavy if
we include parasites, as many parasites will
feed on one consumer.
Advantages/disadvantages
Advantages of pyramid of numbers
Disadvantages of pyramid of numbers
Easy to count
Ignores sizes of organisms
No organisms get killed
Difficult to convert e.g. grass plant leaves
to numbers which can be worth
comparing with others
When representing energy flow through a food
chain it is sometimes more accurate to use a
pyramid of biomass.
These diagrams represent
the mass of living tissue
in the organisms.
Advantages/disadvantages
Advantages of pyramid of
biomass
Disadvantage of pyramid of
biomass
Amount of energy in trophic
level more accurately
represented
Organisms must be collected
and killed in order to measure
biomass (usually dry weight of
organisms).
Difficult to catch/weigh all
organisms
The biomass of an individual
can vary through the year, e.g.
an oak tree will have a much
greater biomass in June than
in December
Another difficulty in producing both pyramids of
number and biomass arises if organisms feed
at two different trophic levels e.g. an organism
that eats both plants and animals.
Review
Complete questions 1, 2 and 4 from GCSE
textbook p70 – 71
[Note that this may take up to 30 minutes]
Decomposition
What happens to the energy available in dead
organisms? Decomposers break down dead
organisms-plants and animals. Decomposers
are important to an ecosystem because they
return nutrients to the environment.
Bacteria and fungi are examples
of decomposers – they are
saprophytes.
Decomposing action of saprophytic
fungi and bacteria
• A saprophyte is an organism that feeds on
dead or decaying organic matter. Saprophytic
bacteria and fungi secrete enzymes into the
soil or dead organism. The enzymes break
down (digest) the organic material and then it
is absorbed by the bacteria or fungi. This is
known as extracellular digestion.
Extracellular digestion – a reminder
Formation of humus
Humus is the organic content of the soil formed
from decomposing plant and animal material.
Decomposition takes place more quickly when
conditions are optimum. These include:
A warm temperature
Adequate moisture
A large surface area in the decomposing
organism.
Give two reasons why large, flat tropical plant
leaves will decompose much more quickly
than Norwegian pine needles.
Energy loss and trophic levels
Most food chains are relatively short, with just four
organisms. This is because at each stage of energy
transfer (including trophic level 1), some energy is
lost.
5 minute task:
In pairs, list as many reasons as you can for energy loss
within organisms and between organisms on
different trophic levels.
Review the different reasons identified by the class.
Even at the first trophic level, the absorption of light
energy by plants is not efficient e.g. energy is lost:
• as light is reflected from leaves
• as light passes through leaves and misses
chloroplasts
• light energy is used to evaporate water from leaves.
However this loss of energy is not significant as so
much light energy comes from the Sun.
The transfer of energy between plants and
animals and between animals of different
trophic levels is usually 10 – 20%.
This means that for every 100g of plant material
available, only between 10 and 20g is built up
as a tissue (as ‘biomass’) in the herbivore’s
body. The same applies when carnivores eat
herbivores.
The loss of energy is due to three main
reasons:
1. Not all the available food is eaten. Most carnivores
do not eat the skeleton or fur of their prey, for
example.
2. Not all the food is digested; some is lost as faeces
in egestion.
3. A lot of energy is lost as heat in respiration.
Respiration provides the energy for movement,
growth, reproduction etc. Heat is produced as a byproduct of respiration. Heat is lost and cannot be
passed on to the next trophic level.
See sheet ‘Energy loss and trophic
levels’
Nutrient cycles
The flow of nutrients in ecosystems differs from the
flow of energy in important ways. In a stable
ecosystem the overall gain or loss of nutrients
from the system will be small and, unlike energy,
the nutrients can be recycled as part of a
nutrient cycle.
Remember that decomposers can break down
organic compounds, and nutrient cycling
involves the processes of decay and
decomposition.
For recycling to take place, dead organisms must first
be broken down during the decay process.
Organisms involved in this process include earthworms,
woodlice and various types of insect – these
organisms are known as ‘detrivores’.
Fungi and bacteria are the decomposers that break
down the organic compounds into their simplest
components.
• The decomposing action of saprophytic fungi
and bacteria also helps in the formation of
humus, the organic substance in soil that
makes it more fertile and produces good
‘crumb structure’.
• Recall the previous notes made on the
formation of humus that included the key
features of the decay process - a warm
temperature, adequate moisture and a large
surface area in the decomposing organism.
• Read information sheet ‘Soil microorganisms’
The Carbon Cycle
From our study of diet and nutrition we know already
that carbon is an essential element in many
important biological molecules e.g.
………………………………………
Using the cards supplied, identify the definition to
explain each of the main processes in the carbon
cycle – photosynthesis, feeding, respiration,
decomposition and combustion.
Write the definitions into your notes.
Design a Carbon Cycle poster
Using diagrams from GCSE textbooks and the
key terms from matching activity, create a
poster on the carbon cycle that includes an
annotated diagram.
The Carbon Cycle and Global Warming
Carbon dioxide gas is one of the gases present in
the Earth’s atmosphere. It has been present
for millions of years, but recent evidence has
shown that the level of carbon dioxide in the
atmosphere is rising. There is also evidence
that humans are responsible for the increase
in carbon dioxide levels.
Two main changes have contributed to the rise in
carbon dioxide levels and therefore carbon cycling
on Earth:
1. Increased combustion of fossil fuels has added
more carbon dioxide to the atmosphere;
2. Increased deforestation has removed many
forests, meaning that less carbon dioxide is taken
out of the atmosphere by the process of
photosynthesis.
The changes mean that the carbon cycle has become
unbalanced.
The link between carbon dioxide levels
and global warming
The atmosphere that surrounds the Earth acts as
an insulator – trapping heat from the Sun’s
radiation to produce a temperature suitable
for life on our planet. Without carbon dioxide
and water vapour, the surface of the Earth
would be at -40oC. The ‘greenhouse effect’ is
necessary for life as we know it, but the
problem in recent years has been an increase
in the concentration of gases that contribute
to the greenhouse effect.
Increasing carbon dioxide levels
However, some gases add to this ‘greenhouse
effect’ more than others, for example carbon
dioxide, methane and water vapour. It is
thought that the increase in carbon dioxide
due to human activity is in turn increasing the
greenhouse effect, that is, an enhanced
greenhouse effect. The enhanced effect is
leading to ‘global warming’.
Evidence for global warming
Scientists have been highlighting the increase in
carbon dioxide levels for many years and have
been attempting to persuade Governments to
take global warming seriously. It is only
recently that many politicians and people
have accepted that it is the increase in carbon
dioxide levels that are causing global warming.
It is difficult for some nations to accept the link
because that also means accepting that
human beings are responsible and that we
must change our lifestyle to try to reduce our
dependence on fossil fuels.
Effects of global warming
The warming of the atmosphere causes:
• Climate change – more weather extremes
such as droughts and severe storms;
• Polar ice-caps to melt;
• Increased flooding;
• More land to become desert.
Reducing global warming
Explain in your own words how the following
actions could reduce global warming:
Planting more trees
Reducing deforestation
Burning less fossil fuels by using alternative fuels
and/or becoming more energy efficient.
Reducing carbon emissions
• Agenda 21 is an action plan of the United
Nations (UN) related to promoting sustainable
development and was an outcome of a
conference on the environment held in Rio de
Janeiro, Brazil, in 1992. It is a recommendation
for action to be taken globally, nationally, and
locally by organizations of the UN,
governments, and major groups in every area
in which humans directly affect the
environment.
North Down Borough Council
Scientific evidence of human effects on the environment
informs our local government about the need to implement
policies such as:
- Reductions in carbon emissions;
- Increases in renewable energy; and
- Changes in agricultural practices (see later notes following
eutrophication).
[Read information sheet ‘Local Agenda 21 in North Down’. From
the information provided identify two questions you could ask
environmental staff from NDBC regarding Council policies ]
Changes brought about by local councils in
recent years include providing ‘brown bins’ to
households to increase composting and ‘blue
bins’ for recycling paper, some plastics and
metal cans.
The recycling Centre at Balloo has a wind
turbine.
Acid Rain
Using the textbook p66 – 67, create an
annotated diagram/poster about:
1. the causes and
2. effects of acid rain and
3. strategies to reduce acid rain.
Make sure you include detail.
The Nitrogen cycle
[Use the accompanying worksheet to ‘fill in the blanks’
about the nitrogen cycle]
• Most of the nitrogen in plants and animals is in the
form of amino acids and protein . The nitrogen cycle
can be split into three phases:
1. The build-up of nitrogen into amino acids and
protein in plants and animals and the eventual
breakdown of these compounds into nitrates.
Plants absorb nitrogen as nitrates and use them to
make proteins . As plants (and animals) are eaten
the proteins are eaten, digested and then built up
into other proteins in sequence.
Eventually the nitrogen is returned
to the ground as urine or through
the process of death and decay.
Decay or putrefying () bacteria and fungi
break down proteins to release ammonia. A
second very important group of bacteria,
nitrifying bacteria, convert the ammonia or
ammonium compounds into nitrates
(nitrification).
2. Nitrogen-fixing bacteria are a special group of bacteria that
can convert nitrogen gas into nitrates. These bacteria can
be found in the soil or frequently in small swellings (root
nodules) in the roots of a group of plants called legumes.
•
Legumes include peas, beans and clover. The relationship
between the legumes and bacteria is beneficial for both
organisms; the bacteria gain carbohydrates from the
legumes and they in turn provide a source of nitrates for
the plants. The process of converting nitrogen from the
atmosphere into nitrates is called nitrogen fixation.
3. Denitrifying bacteria convert nitrates into
atmospheric nitrogen. This is a wasteful and
undesirable process.
Denitrifying bacteria are anaerobic and are most
commonly found in waterlogged soils. Their effect
in well-drained soils is much reduced. The process
of converting nitrates into nitrogen is called
denitrification ().
Consider: Why might ploughing a field be
advantageous to a farmer growing crops?
Happy farmer with no
denitrifying bacteria
in his fields
Root hair cells and active uptake
Plants need nitrates to form proteins and they
obtain these from the soil through root hair
cells by active uptake.
The diagram of a root hair cell shows the
adaptations of the cell:
• An extended shape (a ‘cytoplasmic extension’)
• Providing an increase in cell surface area for
increased uptake of water and minerals.
Active uptake is a process that
requires energy to transport
minerals against a concentration
gradient.
This is because there are more nitrate ions inside the
cell compared with outside in the soil. This process
requires oxygen for aerobic respiration to produce
the energy needed to transport the nitrates against
the concentration gradient.
Review: what is meant by ‘concentration gradient’?
Replacing lost nitrogen – the use of
fertilisers
When farmers harvest crops, or animals are
taken to the abattoir, the nutrients they took
from the soil are not replaced. The crops do
not decay and decompose back into the soil to
recycle the nutrients. For this reason, soil
needs to be fertilised on a regular basis.
Important minerals
Calcium – needed for plant cell walls.
Magnesium – needed for chlorophyll.
Nitrogen – needed to make amino acids and
protein for growth.
All these minerals must be replaced in the soil to
maintain plant growth.
Natural and Artificial Fertilisers
Both natural fertilisers (farmyard manure and
compost) and artificial fertilisers may be used
to replace nitrates and other minerals in soil.
Comparing natural and artificial
fertilisers
Eutrophication
The problem with using fertilisers is that not all
the nutrients sprayed onto fields gets used by
plants. Both sewage and fertiliser ‘run-off’
can cause eutrophication.
Key points:
Nitrates from sewage and fertiliser cause an increase in
the growth of aquatic plants and algae;
The plants die due to shading (as they cannot
photosynthesise) and both plants and algae die to
due the eventual decrease in concentration of
nitrates available (nitrate depletion);
The dead organisms are broken down by decomposers,
which further depletes oxygen levels in the water;
Other aquatic vertebrates and invertebrates die due to
oxygen depletion.
Using the information in the previous slide, plus
Figure 7.21, p66 in GCSE textbook,
design a summary poster
to explain how
eutrophication is a
consequence of water pollution.
Include in your poster the ways that this type of
pollution can be reduced (read section on
‘Water pollution’ p66).
Summer extended writing task
Choose one of the following topics to research over the
holiday, giving details/examples of how the local
environment has been impacted.
1. Methods of monitoring change in the environment
2. The role of the Government in conserving the
environment
3. Changes in agriculture (including EU Nitrates
Directive)
4. International co-operation and legislation.