What you need to know
- 5.11populationAll the individuals of one species living in one area at the same time., communityAll the populations of different species living in one habitat at the same time., habitatThe place where an organism lives., ecosystemA community together with the non-living (abiotic) parts of its environment, interacting..
- 5.12–5.13abioticNon-living. Abiotic factors include light, temperature, water and soil pH. and bioticLiving. Biotic factors include competition, predation and disease. control; nicheThe role of a species in its habitat: how it uses biotic and abiotic resources and interacts with other organisms. and abundance.
- 5.14–5.15Habitat study methods and successionThe gradual change in the community of an area over time, as each set of species changes the conditions for the next..
Core Practical 11 has the field method. GPP, climate change and Q10 remain 5C.
By the end, you should be able to…
- Keep 5.11 terms distinct.
- Choose sampling and tests that match the question.
- Explain maps of speciesA group of organisms that can interbreed to produce fertile offspring. using niche plus biotic and abiotic factors.
Build your understanding
Start with the noun
If the question says populationAll the individuals of one species living in one area at the same time., name one speciesA group of organisms that can interbreed to produce fertile offspring.. If it says ecosystemA community together with the non-living (abiotic) parts of its environment, interacting., include abioticNon-living. Abiotic factors include light, temperature, water and soil pH. interactions. If it says climax, you are in successionThe gradual change in the community of an area over time, as each set of species changes the conditions for the next., not evolution of new species. If it says random, you are not on a transectA line across a habitat along which samples are taken, to show how organisms change with conditions. unless the gradient is the point.
All questions below are original. Fictional counts are labelled in the question.
Finish the mechanism
Light → photosynthesisThe process in which plants use light energy to make glucose from carbon dioxide and water, releasing oxygen.. nitrateNO₃⁻, a mineral ion taken up by plant roots and used to make amino acids, proteins and nucleic acids. → amino acidThe monomer of proteins: a central carbon with an amine group, a carboxyl group, a hydrogen and an R group.. Predation → death rate. nicheThe role of a species in its habitat: how it uses biotic and abiotic resources and interacts with other organisms. overlap → competition → possible exclusion. χ² → association, not causationWhen a change in one variable directly causes a change in another. Showing it needs controlled experiments or a known mechanism..
Make your reasoning visible
Do not import 5C
Leave greenhouse gases and Q10 unless the question brings them.
Show the comparison
Primary versus secondary; random versus transectA line across a habitat along which samples are taken, to show how organisms change with conditions.; range versus standard deviation.
Avoid this misconception
The claim: A significant correlation proves a named abioticNon-living. Abiotic factors include light, temperature, water and soil pH. factor caused the zonation.
The correction: It shows the two variables change together. Cause still needs a biological mechanism and a sampling design that fits.
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
Define ecosystem.
Show suggested answer
A community interacting with the abiotic conditions of its habitat, including energy flow and material cycling.
Practice question
Retrieval and explanation · suggested answer
Why is secondary succession usually faster than primary?
Show suggested answer
Soil, nutrients and often a seed bank or surviving organisms are already present.
Practice question
Retrieval and explanation · suggested answer
Give one abiotic and one biotic factor that could limit a limpet population.
Show suggested answer
Abiotic: desiccation time, temperature or wave action. Biotic: competition with other grazers, predation, or disease.
Practice question
Retrieval and explanation · suggested answer
How does niche overlap help explain why two similar birds might not be equally abundant in one wood?
Show suggested answer
If they use slightly different food, height or time, each peaks where its role fits better. Strong overlap can reduce one species through competition.
Practice question
Retrieval and explanation · suggested answer
When is a belt transect more appropriate than random quadrats?
Show suggested answer
When recording how distribution and abundance change along an environmental gradient.
Practice question
Retrieval and explanation · suggested answer
A 2 × 2 χ² = 4.2. The stated critical value at p = 0.05, 1 d.f. is 3.84. Interpret.
Show suggested answer
4.2 > 3.84, so there is significant evidence of an association at p = 0.05. This is not proof of a causal mechanism.
Practice question
Retrieval and explanation · suggested answer
Why use standard deviation rather than range to compare spread of ten cover estimates?
Show suggested answer
Range uses only two values and is easily inflated by one outlier; standard deviation uses all ten.
Practice question
Retrieval and explanation · suggested answer
What is a climax community?
Show suggested answer
A more stable community that persists under the prevailing conditions if major disturbance does not reset succession.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Fictional ranks of soil moisture and species cover for n = 6 give Rs = 0.89. The stated critical value is 0.83. A student concludes “moisture causes the plant to grow”. Rewrite a specification-level conclusion.
Show a hint
Association, then a mechanism offered as a hypothesis.
Explore the reasoning
There is significant evidence of a positive correlation at p = 0.05. Moisture and cover change together. A causal claim needs a mechanism (for example water potential affecting growth) and should admit that a third factor, such as soil depth, could drive both.
Recall this lesson
Lesson recall questions
Question 1 of 5: What is meant by a biotic factor?
Biotic and abiotic control of distribution
Practice question
Retrieval and explanation · suggested answer
What is meant by a biotic factor?
Lesson: 5B 4: The Effect of Biotic Factors on Populations
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
Frames, tapes and honesty about bias
5B · Exam PracticeFSC vegetation-sampling pages separate random frames for comparing areas from transects along gradients, and they treat frequency and cover as different records. That professional distinction is exactly what…Specification 5.14Read & use the scienceClose article
Why this matters
FSC vegetation-sampling pages separate random frames for comparing areas from transects along gradients, and they treat frequency and cover as different records. That professional distinction is exactly what 5.14 is for. Their worked frequencies are examples, not your results. The method must fit the question. Random positions can estimate average cover across an area; regularly spaced positions along a line can reveal a gradient. Neither design repairs an incorrectly identified plant species.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.14 CORE PRACTICAL 11: carry out a study of the ecology of a habitat, such as using quadrats and transects to determine the distribution and abundance of organisms, and measuring abiotic factors appropriate to the habitat
Use the science
Why would copying an FSC frequency calculation into your book as “our result” fail 5.14?
Explore a possible response
You would be reporting someone else’s sample. The practical requires your habitat, your frames and your abiotic readings, with their limitations.
Explore the source
- Field Studies Council: using quadratsField Studies Council
A quadrat size can change the answer
5B · Investigating Abundance and Distribution of OrganismsUS Geological Survey ecologists compared quadrat sizes and transects for long-term monitoring of streamside vegetation. Very small frames missed useful frequencies for many species, while large frames and…Specification 5.14Read & use the scienceClose article
Why this matters
US Geological Survey ecologists compared quadrat sizes and transects for long-term monitoring of streamside vegetation. Very small frames missed useful frequencies for many species, while large frames and repeated transects captured different parts of the community. In school, choosing a quadrat is often presented as a routine step. In research it is a design decision tied to plant size, rarity and the question being asked. A quadrat that counts grasses well may be poor for sparse shrubs. More measurements do not remove a bias introduced by always placing frames in the easiest patch to reach.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.14 CORE PRACTICAL 11: carry out a study of the ecology of a habitat, such as using quadrats and transects to determine the distribution and abundance of organisms, and measuring abiotic factors appropriate to the habitat
Use the science
Why might doubling the number of tiny quadrats still fail to estimate the abundance of scattered shrubs?
Explore a possible response
The frame size may systematically miss shrubs; more of the same biased measurement does not fix the sampling scale.
Explore the source
- Field evaluations of riparian sampling techniquesUS Geological Survey
A buried forest waiting for disturbance
5B · How Ecosystems EvolveUS Forest Service researchers describe the soil seed bank as a hidden reserve of living seeds that can survive a disturbance. Fire, browsing by deer and gaps in…Specification 5.15Read & use the scienceClose article
Why this matters
US Forest Service researchers describe the soil seed bank as a hidden reserve of living seeds that can survive a disturbance. Fire, browsing by deer and gaps in the canopy change which plants return. The first visible seedlings do not necessarily arrive from outside; some were already below ground. That complicates the simple school succession diagram in a useful way. Where soil and a seed bank remain, recovery resembles secondary succession, with a biological legacy from the previous community. A site stripped to new bare rock has a very different starting point and may need pioneers to build soil first.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.15 understand the stages of succession from colonisation to the formation of a climax community
Use the science
Why might two burned forest patches develop different plant communities even if they receive the same rainfall afterward?
Explore a possible response
They may have different surviving seed banks, soil, browsing pressure and light after the fire. Initial biological legacies alter the sequence.
Explore the source
- How fire, deer and canopy gaps shape seed banksUS Forest Service