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Life On Earth National 5 Biology
1
2. Biotic and Abiotic factors
2.1 The Effect of Abiotic Factors on the Distribution of Organisms
in an Ecosystem
2.1.1 Measuring Abiotic Factors
2.1.2 Effect of Abiotic Factors on Distribution of Organisms
2.2 The Effect of Biotic Factors on the Distribution of Organisms
in an Ecosystem
2.2.1 Competition
2.2.2 Grazing
2.2.3 Predators and Prey
2.2.4 Parasitism and Disease
Learning Intentions
By the end of this section you should be able to:
describe the difference between abiotic and biotic factors
give named examples of abiotic and biotic factors
design an investigation to measure the effects of abiotic and biotic
factors on the distribution of organisms
use sampling equipment to measure abiotic factors in a habitat
identify possible sources of error in your investigation and how to
minimize them
explain the relationship between abiotic and biotic factors and population
size, giving named examples
Describe the relationship between grazing and biodiversity
An organism will only live in a particular habitat if the conditions are
suitable for it. These conditions, or factors, are either biotic or abiotic
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2.1 The Effect of Abiotic Factors on the Distribution of
Organisms in an Ecosystem
Abiotic factors are non-living physical and chemical factors which affect the
ability of organisms to survive and reproduce. Some abiotic factors include light
intensity, temperature, pH level, availability of water, oxygen/carbon dioxide
levels and levels of pollution. Abiotic factors vary in the environment and
determine the types and numbers of organisms that exist in that environment.
Biotic factors are all the living things that directly or indirectly affect an
organism in its environment. This would include competition for resources like
food or light between organisms, availability of food, parasitism, disease, and
predation.
Factors which determine the types and numbers of organisms of a species in an
ecosystem are called limiting factors. Abiotic factors often act as limiting
factors by restricting the growth of populations in nature. An example of this
would include low annual average temperature, common to the Arctic region,
which restricts the growth of trees and insects. Biotic factors can also act as
limiting factors, for example competition for light and water between trees in a
forest can limit the number or type of trees present.
Carrying capacity is the maximum number of organisms the resources of an
ecosystem can support. The carrying capacity of the ecosystem is limited by a
combination of abiotic and biotic factors.
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Learning Activity 1 – Show you know!
1. Describe the difference between abiotic and biotic factors, giving a named
example of each.
2. Re-organise the information into a table of Abiotic and Biotic factors giving 4
examples of each
3. Why are competition and disease classed as biotic factors?
4. What effect do limiting factors have on the size of a population?
5. How do biotic and abiotic factors act as limiting factors?
Extension - Attempt activity 3.1.16 on p249 of National 5 biology book
2.1.1 Measuring Abiotic Factors
During the study of an ecosystem the abiotic factors can be measured. Your
teacher will demonstrate/discuss some of the techniques that can be used to
measure abiotic factors, e.g. light intensity, moisture level, pH, water content.
They will also point out what can go wrong with the techniques and how these
problems are overcome.
Learning Activity 2 – Measuring Light intensity and Moisture
Your task is to use the equipment you have been shown to measure and then
compare the light intensity and moisture level between at least two different
areas (habitats) around the school.
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You will record your results in tables like the ones shown below:
Measuring Light intensity
1st Reading 2nd Reading 3rd Reading
1.
2.
Measuring Moisture
Area Moisture level
Average
Moisture
Level 1st Reading 2nd Reading 3rd Reading
1.
2.
Once you have your results complete the following tasks:
1. If possible, compare area one and two in terms of both light intensity and
moisture level.
2. Explain why it was necessary to take three reading in each area.
3. Explain what errors could have occurred while using the equipment
4. Describe what you did to minimise these errors.
5. Insert and complete the Measuring Abiotic Factors diagram from your
pack into your notes.
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2.1.2 - Effect of Abiotic Factors on the Distribution of Organisms
Learning Activity 3 – Investigating the effect of abiotic factors of seed
germination
How do abiotic factors affect germination of seeds?
Choose one of the following factors to investigate:
Temperature
Moisture
pH
Your teacher will show you some of the equipment available to you. Working with
a partner, you need to come up with a plan for this investigation. In the plan you
need to identify:
your aim
the equipment that you will need
how you will alter the independent variable
how you will measure the dependent variable
other variables that you will need to control
how you will obtain and record your results
Show your plan to your teacher. If the teacher agrees, you can set up the
investigation.
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Learning Activity 4 – Effect of Light Intensity on Plant Distribution
1. You will carry out a line transect survey to investigate the effect of
moisture on the distribution of daisies. Your teacher will demonstrate
how to carry out a line transect.
You can record your results in a table like this.
Sample
site
1 2 3 4 5 6 7 8 9 10
Abundance
of daisies (out of 25)
Moisture
2. Share your results with other groups and work out a class average.
3. Discuss the following questions in pairs:
What do the results tell you about the relationship between light
intensity and the abundance of daisies?
What was the point of sharing the results to make a class average?
Apart from light intensity, what other factors could be affecting the
abundance of daisies?
Learning Activity 5 – Effect of light intensity on the abundance of daisies
A group of students carried out transect survey to measure the abundance of
daisies in a small clearing in the middle of a wood. They used quadrats and light
meters to obtain their results.
Study the information in the table below then complete the questions
underneath the table.
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Abundance of Daisies
Sample
site
1 2 3 4 5 6 7 8 9 10
Abundance
of daisies (out of 25)
19 20 18 21 12 8 4 1 0 0
Light
Intensity (A=low
H=high)
H H H H G F E D C C
A. Present the information in the table as a two separate bar charts. Once
you have drawn one of the bar charts check the success criteria below
to judge how good it is. Decide if you need to make any improvements.
B. Using the data from your bar charts, describe the relationship between
light intensity and the abundance of daisies.
C. Predict how many daisies would be found if the light intensity was ‘B’.
Explain your answer.
D. Suggest a reason why the light intensity decreased between sample site 1
and sample site 10.
E. Name at least two variables that would need to be controlled during the
investigation to make these results valid.
Success Criteria for a Bar Chart
All lines must be drawn in pencil with a ruler
The labels for the Y (vertical) axis and X (horizontal) axis must
match up to the headings in the table, including any units
Each scale must have equal integers (i.e. each space on the scale
should be worth the same numerical value)
The bars should be accurately drawn, i.e. tops of the bars should
be straight; bars should be same width; height of each bar
should match a value given in the table
The bar graph should have a title
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2.2 The effect of Biotic Factors on the Distribution of
Organisms in an Ecosystem
2.1.2 - Competition
Learning Activity 6 – what do you already know?
What sort of things might organisms living in the same habitat compete for?
Make a list of as many things as you can.
There are two types of competition:
Interspecific competition is when individuals of different species compete for
similar resources in an ecosystem.
Intraspecific competition is when individuals of the same species compete for
exactly the same resources in an ecosystem.
Which type of competition is more intense? Discuss with your partner.
Learning Activity 7: Investigating competition between cress seedlings
You will investigate the effect of competition for moisture on the growth of a
population of cress seedlings.
100 cress seeds will germinate successfully on 2g of cotton wool soaked with
20ml of cold tap water in a yoghurt carton. Under these conditions there is
little or no competition between the seedlings as they develop. If they are left
in a propagator for 5 days, they will grow tall and develop healthy green leaves.
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Working with a partner, you need to come up with a plan for this investigation.
In the plan you need to identify:
your aim
the equipment that you will need
how you will alter the independent variable
how you will measure the dependent variable
other variables that you will need to control
how you will obtain and record your results
Show your plan to your teacher. If the teacher agrees, you can set up the
investigation.
Learning Activity 8 - Research task: Interspecific competition
Brown v Rainbow Trout – Rainbow trout from North America have been
introduced into British Rivers and are invading the natural habitat of the native
brown trout.
Use resources available to use to research more about inter-specific
competition. The links below will help you find out more about competition
between the two species of trout but you can chose other organisms if you wish.
Write a short report describing competition between the organisms you have
chosen. Include information about the resources they compete for, which of
the organisms is most successful and why you think this is.
Go to http://www.gov.scot/Topics/marine/marine-
environment/species/fish/freshwater/btrout and
http://www.gov.scot/Topics/marine/marine-
environment/species/fish/freshwater/rainbow
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2.2.3 Effect of Grazing on Biodiversity
Grazing is a biotic factor which affects biodiversity in an ecosystem.
Natural grassland normally contains a rich diversity of plant species. Some are
especially strong and vigorous while others are much more delicate. Rabbits are
relatively unselective grazers eating most types of grassland plants. This
maintains a high biodiversity of plant species as the stronger, more vigorous
grasses are kept in check.
If disease or human activity decreases the number of rabbits from an area of
grassland the dominant, more vigorous grasses will be able to grow freely and
this will prevent the weaker species surviving and plant biodiversity will be
reduced.
When rabbits return to the area, they keep the grass closely cropped, keeping
the dominant grasses in check, allowing the weaker species to return again, and
so increasing biodiversity.
However if grazing becomes very intense (overgrazing) the biodiversity of
plants may be slightly reduced as the more delicate species can no longer
survive.
Learning Activity 9 – Data Handling
Use the information in the table to draw a line graph to show the effect of
grazing pressure.
Average number of plant species Grazing Pressure
(Number of rabbits per Km2)
10 100
20 200
50 300
20 400
a. Present the information as a line graph. Refer to the success criteria to
help you complete it correctly.
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b. Using the information from the passage above and the data from your
graph, compare the effect of increasing grazing pressure with the
average number of plant species found.
If two marks were available in an exam for question b, how many marks is your
answer to question b worth? How could you improve your answer? Share your
answer with the people at your table until you think you have come up with the
perfect answer.
Show your answer to your teacher and ask for his/her feedback.
Line Graph Success Criteria
All line must be drawn using a pencil and a ruler
A suitable scale must be used for the Y- axis (vertical) and
the x-axis (horizontal)
The scale for each axis must have regular integers (i.e. spaces
between the numbers should have equal numerical values)
The scale should have an origin (i.e. start at zero)
Each axis should have a label, including units, that matches the
headings in the table
All points must be plotted accurately
The graph should have an appropriate title
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2.2.3 - Predator Prey Interactions
Predation is a biotic factor which affects biodiversity in an ecosystem.
The graph below shows the typical relationship between predator and prey
populations.
Learning Activity 10 – Data Interpretation
Collect a copy of the graph and paste it into your notes.
What do you notice when you look at the graph? Discuss this with your partner.
Make a list of as many observations as you can. Share these with the people at
your table.
Learning Activity 11 – Data Interpretation
The graph below shows the interaction between the population of Moose and the
population Wolves. Collect a copy of the graph and complete the following
questions in full sentences.
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1. What was the Moose population in 1970?
2. What was the Moose population in 1980?
3. What was the Wolf population in 1970?
4. What was the Wolf population in 1980?
5. Suggest a reason for the decline in the Moose population between 1973
and 1982. You should use the evidence from the graph to support your
answer.
6. Using the data from the graph, describe what happens to the Wolf
population between 1980 and 1982. Suggest a possible reason for this.
7. Predict what would have happened to the size of the Wolf population
after 1995.
8. Explain what the graph tells us about the relationship between the size of
a predator population and the size of a prey population.
Formatted: Font: Comic Sans MS, 12pt
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2.2.4 - Parasites and Parasitism
A parasite is an organism that lives off of another organism (called the host
organism). Parasitism is a biotic factor that describes the relationship between
the parasite and its host organism.
The picture opposite shows a honey
bee larva that has been infected
by a parasite called Varroa
Destructor (Varroa mite).
Watch the film below to get some perspective on this issue. Consider the
questions below while you watch the film.
http://www.abc.net.au/7.30/content/2013/s3911559.htm
The key questions:
How does the varroa mite affect the honey bee?
Why is the varroa mite such a problem for honey bees?
What impact could this have on humans?
Learning Activity 12 – Parasites
Your task is to use the internet or other resources to research the effect of
the varroa mite on the honey bee population. Your report should be one or two
sides of A4 at most.
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It must include five of the following pieces of information:
A description of what a varroa mite is
A description of how the varroa mite affects the honey bee
An explanation of why the varroa mite is such a problem for honey bees
Some data to show the effect it has on the size of the honey bee
population
A description of the effect this is having on the population of honey bees
An explanation of the effect that this could have on humans
An explanation of the effect that this could have on biodiversity
A description of what can be done by humans to help protect the honey
bee from the varroa mite
Choice Extension
Task You must complete at least two of these activities Completed
1 Design a board game based on competition.
2 Produce a collage of pictures demonstrating different types of competition in nature.
3 Produce a poster on a particular habitat – Where in the world is it? What sort of animals or plants live there? What abiotic and biotic factors affect them?
4 Find out a parasite that affects humans. Produce an information poster or leaflet about it
5 Produce a helpful checklist or advice to help people to draw graphs
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Self Evaluation - How well did I do?
How well can you describe the key words/phrases below? Take turns at
explaining what they mean to the person sitting next to you, and then let them
explain them to you.
Use the success criteria sheet to reflect on and evaluate your learning from
this section.
Think carefully and answer the following questions:
1. What skills have you developed over the past few lessons? How do you
know and how could you prove it to someone?
2. What areas have you found difficult? What strategies are you going to
use to overcome these problems?
Discuss this with your teacher and set yourself a learning target – this is what
you will do to improve your knowledge and skills. Update Didbook with a
comment about what you have done well, what you want to improve at doing and
how you will do this.
Abiotic, biotic, intense, overgrazing, abundance, parasite, competition,
limiting factor, habitat, biodiversity, population, ecosystem, source of error,
independent variable, dependent variable, interspecific, intraspecific
