Download Page of 12 A2 U4 Biology Notes – HM Ecology 5.10 – 5.12

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Disclaimer:
These notes are to be taken as a guide only. They are from when I personally did A-level, and
there’s some additional things I added. Essentially the information is taken from the Edexcel
A-level books mentioned on page 8, and I’ve tried to make it as concise and as complete as
possible; it should have the essential bits anyway. But it’s vital that you make sure to edit
these with your own notes / Mrs Crouch’s notes, which are more important.
If you want me to talk you through any of this, I am at school on a weekly basis for now, let
me know on my new site www.qegshm.webs.com and go to the ‘Forums’ or ’Contact Me’
section. (or use QEGS HM on facebook or [email protected])
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5.10. Explain that the numbers and distribution of organisms in a
habitat are controlled by biotic and abiotic factors.
Difficulty **
5.11. Describe how to carry out a study on the ecology of a
habitat to produce valid and reliable data (including
the use of quadrats and transects to assess abundance
and distribution of organisms and the measurement
of abiotic factors, eg solar energy input, climate,
topography, oxygen availability and edaphic factors).
Difficulty ***
5.12. Explain how the concept of niche accounts for distribution and
abundance of organisms in a habitat.
Difficulty **
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Background information
During AS, we look at biodiversity and the variety of genotypes and phenotypes that exist
between and within species, as well as the basic principles of evolutionary biology.
Here are introductory terms to be familiar with:
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Abundance (population size) - the number of individuals of one species in a particular
area
Distribution - where a species is within a particular area (proportional abundance
relative to geographical location)
Habitat – the place where an organism lives
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Population – all the selected organisms of one species in a habitat
Community – all the populations of the different species in a habitat at any one time
Ecosystem – the set of all biotic and abiotic factors in one or more particular location(s)
Biomes – large ecosystems
For A2 Topic 5, we take this further by showing that biotic and abiotic factors define the
niche of a species and these factors also affect the:
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Abundance and distribution of organisms 5.10-5.12
Stages of succession and climax communities 5.13
Developmental and physiological adaptations 5.15-5.17 (and behavioural)
Evolved adaptations by means of natural selection 5.22 (there are also other
selection processes like sexual selection)
Speciation (evolutionary event) by reproductive isolation (a process and consequence
of natural selection) 5.21
The factors are also relevant when we look at forensics and factors affecting the decay of
bodies of dead mammals, and the stages of succession and colonisation by numerous
organisms of dead bodies; and how this can be used for estimating time of death.
Finally, we must come to appreciate the subtleties of A-level Biology.
Throughout topics 5, 6, 7 and 8, we come to consider the biochemical mechanisms
underpinning all of the above events, and that all of Biology can be reduced purely to
physicochemical interactions. We try to understand:
 how cells function by looking at their structure (eg. microbial life forms and their
adaptations; sliding filaments in muscle cells of higher eukaryotes)
 how cells harness and store energy (eg. photosynthesis, respiration…)
 how hereditary information is passed on, from cell to cell, from generation to
generation (vertical transfer)…
 how cells control gene expression (via transcription factors incl. hormones) and
 how they communicate information with each other (eg. immune system cell
responses; endocrine (hormonal) chemical messaging; electric impulses in neural
networks, etc), and how these can be affected by drugs.
We break down all bodily processes to metabolic sequences (sequences of chemical
reactions) that exist to maintain homeostasis. They occur as a consequence of external and
internal stimuli, which in turn affects the organism’s physiology and behaviour, and hence
also affects the environment of this organism and other organisms too.
So one must come to appreciate the complexity of biological interrelationships at all
levels of biological organisation (from the molecule, the cell, the organism, the
population/ecosystem). This is actually very simple:
We understand the multi-factorial nature of biological events and how these are regulated by
the interaction between both biotic and abiotic factors. Abiotic factors provide a framework
for biotic factors, all of which is then dependent on the changing environment and changing
organisms; so if a specific feature of an organism changes (eg. one or more genes mutate
and therefore a makes a lion’s legs slightly longer) or the climate gets slightly warmer by a
few degrees, it becomes relatively indeterminate to model precisely what will happen further
down the line to a group of organisms, as the ecosystem as a whole and all the species within
it will need to change, not just a particular feature of the ecosystem.

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5.10. Explain that the numbers and distribution of organisms in a
habitat are controlled by biotic and abiotic factors.
This is very straightforward and self-explanatory: organisms are adapted to specific
conditions and need to adapt to new conditions if they change.
What you need to know for 5.10:
Abiotic factors
(non-living, physical, chemical)
They take three forms, the physical states of matter: Liquid, gas, solid
The list below is not exhaustive.
Square brackets indicate how to measure this factor (this is for 5.11)
I also include mnemonics at the end.
Climatic factors
Solar energy input / Light (duration of exposure, intensity) [light sensor]
Temperature [thermometer; digital sensor and data logger]
Rainfall [rain gauge; beaker for volume over time]
(Air) Humidity – this is actually just ‘humidity’ (water vapour in air) [electronic/whirling
hygrometer]
Wind (ie. speed)
Atmospheric
CO2/O2 levels
Exposure to air
Pollution – water, air, land
Topography – shape/features of Earth’s surface
Slope (the angle/steepness) [clinometer – a string with a weight, attached to a protractor
centre]
Aspect (direction slope faces) [compass]
Relief/Altitude (how land height changes) [GPS; maps with contour lines]
(Height above sea level)
(Drainage)
Environmental
Space
Water availability; Water (quantity, submersion time, etc)
Chemical composition of surroundings
Nature of rock (see edaphic)
(Wave action)
Ground/edaphic
Salinity
pH [indicator liquid & chart; pH probe/monitor; soil test kit]
Organic matter [burnt in crucible]
Minerals [gardener’s test kit]
Moisture content of soil [dried sample at 80-100oC until constant mass - get %age change]
Soil texture [hand assessment, charts]
(Toxicity)
Substrata
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Aquatic
Water flow/supply [observation; seasonal changes in water levels]
Oxygen availability - O2 dissolved in water [oxygen centre/probe]
(Natural disturbances)
(Earthquakes, floods, volcanic eruptions, fires, etc)
Examples of mnemomics:
Note: I tend to use a lot of acronym mnemonics for my own
learning. I found it particularly useful transferring large amounts of
information from paper and uploading it into my brain. Do not
underestimate how powerful they are. I’m sure you use them
yourselves. Clearly, not only do you need to condense whole
textbooks into short notes, but you must further condense these to
really make sure you can memorise and remember everything you
need to learn. And so in the exam, when prompted with a question,
you should be able recall these mnemonics quickly and expand them
at will to score as many marks as possible. I didn’t actually use
mnemonics for 5.10 – 5.12 back then, but there’s an attempt below,
but please be creative and produce some which may be more
meaningful to you.
CATEGA
(climatic, atmospheric, topography, environment, ground, aquatic)
STRAW
(sunlight, temp, rainfall, (air) humidity, windspeed)
Or visual imagery: think of the sun and a cloud: the light and heat of the sun, clouds pouring
rain and ‘wetness’ of the air, and blowing wind.
Biotic (living, biochemical, other organisms)
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Competitors (Inter or intraspecific) – competition for resources like food, space, water
Predators (Interspecific)
Disease: Pathogenic microbes and other parasites (one benefits at the other’s
expense)
Plant activity
Food
(Grazing)
(Symbiotic relationships; mutualism where both benefit) (eg. bee pollinating
flowering plants; natural skin bacteria outcompeting pathogenic bacteria for human
host’s welfare in exchange for nutrients and a place to live (the skin), etc.)
(Anthropogenic factors) – biotic factor affecting many other biotic factors via abiotic
factors (eg. ecological footprint, pollution, global warming, hunting, farming, building,
urban areas, wildlife conservation, deforestation, etc.). This can be detrimental for
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many existing species and ways of life but it also opens there the way for new ways of
life to thrive.
Population size
Abiotic
factors:
The most suitable conditions mean organisms
can grow faster and reproduce
successfully, and thereby increasing the
overall population faster (eg. an ideal
temperature of the surrounding for mammals
entails an optimal for metabolic reactions as
less energy is used to maintain body
temperature by processes of homeostasis)
Distribution
Organisms can only exist
where they can survive
Eg. Plants grow on southfacing slopes in northern
hemisphere.
Inter-specific competition: different species
compete for the same resources (eg. red
and grey squirrels in the UK)
Biotic:
Intra-specific: Resources are plentiful, the
population grows, but soon resources
become limiting (space/food) so the pop.
declines (the maximum stable population is
the carrying capacity)
Predation: We can look at the pattern of
snowshoe hare and lynx populations.
(see below)
One species will need to
adapt to another
environment due to interspecific competition
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
5.11. Describe how to carry out a study on the ecology of a
habitat to produce valid and reliable data (including
the use of quadrats and transects to assess abundance
and distribution of organisms and the measurement
of abiotic factors, eg solar energy input, climate,
topography, oxygen availability and edaphic factors).
This is slightly more advanced than 5.10, but is based on a sequential understating of the
processes of ecological investigation, where each stage is clearly defined and purposeful:
A study on ecology of a habitat:
An exam question may ask you to describe a study to investigate ecology (for 4-8 marks), in
which case you can efficiently touch upon the main points:
1) Named organism and named habitat
Method
2) Sampling: Using random sampling (sampling to save time, and random to avoid bias). This
is obtained by dividing a uniform field into a grid and using a random number generator on a
calculator to select coordinates.
3) Technique used:
Quadrats are for defining samples.
 Frame quadrats (square frame with strings or tape to create a grid) – for measuring
abundance.
 Point quadrats (horizontal bar on two legs with holes at set length interval; pins are
dropped through holes and the touched plants are recorded).
Transects are for distribution and only for when there are changes along an environmental
gradient.
 Belt Transect - they are for selecting samples, for linear habitats; frame quadrats are
placed along a transect line, to obtain more data, and it is used for abundance.
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
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Line transect – a tape measure touches species and these are recorded, which saves
time
Interrupted transect – measurements are taken at intervals with a point quadrat at
right angle to the transect line
Mention of other apparatus/equipment
4)
DV – Abundance and/or Distribution
IV – Abiotic factor
Example of investigation: are there more plants where there is more light?
5) Control variables to take into account!!! – all the other relevant abiotic factors.
6) Quantifying data:
 The number of individuals is counted in each quadrat, divided by the total area
sampled to give mean density
 State measurements for distribution/abundance
 Reference to abiotic measurements
7) Reference to safety
8)
Increasing accuracy and precision of instrumental data and methods allows for more efficient
data collection, but mainly a more reliable set of results and therefore a valid conclusion.
Make a reference to taking many samples and readings, as so getting a more reliable est. of
whole area.
The typical experiment often requires repeats: usually 3 trials (repeats) for 5/8 IV values
(subject to context).
Talk about this when you talk about the method and data collection.
Standardisation is also important: the investigation and trend obtained must be replicable.
Also bear in mind:
9) Specific details and precision must go into describing/explaining steps eg, names,
temperature values, time periods, etc.
10) All of this must be done in a logical sequence for the examiner to follow.
Mnemonic for pts 1-8: NSTVQSR
eg. “Name some things very quiet since racing”
Name Sampling Technique Variables Quantifying Safety Reliability
Coursework:
Obviously you have coursework and whether it’s for U4 experimental investigations or the big
U6 dissertation, as you know, the main steps of the criteria are as follows: (in bold is for the
exam)
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A well-researched rationale, defining the investigation clearly, a structured and detailed
methodology with evidence of preliminary testing, controlling of variables (very
important!!), conscientious safety practices; and then the collection, processing and
presenting of data, analysing the pattern, looking at anomalies, interpreting with inferential
statistics, putting together a conclusion, evaluation and feedback.
I have lots of exemplars including my own if you need any help with this.

5.12. Explain how the concept of niche accounts for distribution and
abundance of organisms in a habitat.
Finally, we have the niche, which is even more straightforward than 5.10, and we need a
good understanding of the terminology, which you have already gone through in U2.
What is a niche?
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The lifestyle and relative position of a species within an ecosystem (the habitat it lives
in, how it exploits the abiotic components of its environment, and its interactions with
other organisms).
Every species has its own unique niche.
2 species may live in the same habitat (habitat niche), but there may be variation in
what they eat (nutrition niche).
If they both occupy the same niche, they will compete until the more successful one is
left.
“Explain the concept” means being able to say that the idea of niche means they need to live
in specific places. Draw on biological knowledge to give reasons and don’t merely restate the
information given.
It accounts for:
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Distribution, because there are specific habitat types – eg. bats live in
woodland/farmland but not deserts
Abundance – eg. inter-specific competition for food reduces numbers in each
population.
Bear in mind that if the environment changes too much too quickly for extended periods of
time, the group of organisms may not be able to adapt, and either they will die or relocate to
a different viable niche, to which they can adapt.

Book references:
5.10
5.11
5.12
Green CGP revision
guide
p12-13
p14
p15-17
Purple/green
p13,15
p14-15
p13
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Edexcel A2 Biology
revision guide
Green concept-led
Edexcel A2 Biology
Orange context-led
Edexcel A2 Biology
p18-19,24-33 p22,24-27
p18-19,30-33
p4-8
p4-5
p6-8
Mapping to How science works:
5.11 only maps to HSW (2, 3, 4, 5 & 8), which tells you to use scientific knowledge to pose
questions and using appropriate experimental skills, all explained above.
(see specification for more detail)
U4 Past exam questions:
5.10
Question bank pre2008. “C cycle and
ecology past
questions”
Sept 2008 Specimen
(Sample Assessment
Material)
Jan 2010
Jun 2010
Jan 2011
Jun 2011
5.11
5.12
Q2, ~3
Q2
~Q2, ~3
Q1, 2, 3, 7
Q3
Q2, 6, 7
Q7
Q2, 3, 6, 10, 13
?
Not yet released
Access these via:
QEGS Moodle / Edexcel website / LC
(including the markschemes and examiners’ reports)
If you want the questions relevant to topic 6, let me know.
Snapshot of U4 Jan10 Q3:
Q6
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Commentary on examples of exam questions and exam techniques:
5.10: This particular LO, seeing from past Qs, is likely to be woven into more thorough
questions which involve a specific organism and habitat. That could be an organism/species
from a range of possible organisms/species, but tends to be more like plant species,
sometimes algae-type life forms, and also invertebrates. They will deliberately put in
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something which you may not have met before to get you to think. There is no need to be
alarmed, as the basic principles you learnt can always be applied to all these Qs; but be sure
to read the question properly, and acknowledge that abiotic factors might differ greatly
depending on the organism mentioned.
They may quiz on how organisms are distributed and you will be asked to not only deduce
how they are distributed but why that is the case, and follow up with the wider implications
that has. It may also ask to describe, given specific factors, how the life forms develop and
how they evolve, as we look at the specific adaptations that organisms have to their
surroundings.
But there are some very easy points to gain: eg. Name 3 abiotic factors that would affect that
species’ distribution; this should be ‘give-away’ marks and quickly obtained, and likely to be
about 3 marks, but the mark scheme may usually have a possible 8. I suggest you learn
about 15-20, some will be more relevant than others, and would safely get you the marks if
appropriate to the question. Here we just want to get the marks and move on to the longer
questions.
It seems these questions on abiotic/biotic factors involve a lot of graphs too. And they may
ask to describe and explain the graphed data. Here talk about the trend(s): the general
pattern, the range of values, then compartmentalise parts of the graph to look for increases
and decreases, fluctuations, rates of change, differences which may be or not significant, and
finally correlation and causation. Here often mentioning specific values to quantify your point
will entail an extra mark, but you need to do something with it (“manipulation of figures”)
Most likely though, they will give you data, a graph, or a combination of graphs and tables, to
use and say: Using data from the graph/chart/table(s), explain which species of these
invertebrates is more apt at living under water, in which case you would need to not only
state the right answer, but also give a specific clear reason for it. That is linked to 5.11.
For 5.11, previous examples include:
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Deducing and explaining which factor affects this bird the most and how the
distribution of this species can be affected by that abiotic factor.
Percentage cover of different species of seaweeds based on distance from the sea
along a rocky shore. Reference to graphs.
Invertebrates on sea shores.
Mussel on a rocky shore and freshwater stream.
Species of plants and mammals in woodland areas.
They might also ask for you to discuss the validity of different statements based on a graph
and data, by asking if statements are valid and why, or even which ones are more valid than
others. (see snapshot on page 10)
So they may ask to describe how to investigate X and Y, or even explain a specific stage of a
specific investigation.
But know all the 5 practicals extremely well by the time you finish them, because one or two
or three will come up. Each of them being a set of 5-10 main points, in a simple logical order,
which I believe are also ‘give-away’ marks and shouldn’t be problem for you.
Here, we go back to an efficient and productive revision system, and where the information
you learn is consolidated so well that you should be able to retrieve it from your memory
store as quickly as possible and write down all the relevant information on the exam paper as
quickly and concisely as possible.
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This is important as they may also have pre-prepared experiment questions, like above;
these range from simple lab experiments about a plant with light and CO2 levels, much alike
GCSE and AS, or you may need to talk about numerous species of invertebrates in an whole
ecosystem and less familiar abiotic factors; broken down into simpler parts, these questions
should not be the hardest at all.
The understanding of niche for 5.12 usually ties in understanding selection pressures and
how that shapes organisms’ characteristics as well as their abundance and distribution, but
also stages of succession, as you can see the way that every way of life opens there to be a
new way of life, and there is an incremental build up of complexity of the ecosystem.
In exams, you occasionally see synoptic elements being introduced, especially looking at
mammalian adaptations; but there are also references to plant physiology.
Also let me know if you want any more help related to exam work.