Ecology
Ecology is the study of how organisms interact with each other and with their non-living environment, spanning individual organisms, populations of one species and communities of interacting species up to whole ecosystems. It covers how abiotic and biotic factors affect where organisms are found, how materials such as carbon cycle through ecosystems, and how human activity affects biodiversity.
Before you start
Make sure you're comfortable with these topics first:
Method
- Learn the levels of ecological organisation in order, smallest to largest: organism, population, community, ecosystem, and be ready to identify which level a scenario describes.
- Split every factor-affecting-distribution question into abiotic, non-living, for example light intensity, temperature, moisture level, soil pH, and biotic, living, for example availability of food, competitors, predators, a new pathogen, and name at least one specific example of each.
- For adaptation questions, sort the adaptation into structural, a body feature such as thick fur, behavioural, something the organism does such as migrating, or functional, something inside the body that works differently such as producing antifreeze proteins, and always link it to the specific survival advantage it gives in that named environment.
- For the required practical on sampling species distribution or abundance, learn the method: lay a transect line across the area being studied, and at regular intervals place a quadrat next to the line, counting or estimating the percentage cover of the species of interest in each quadrat, before working out a mean or plotting the change along the transect.
- Learn the carbon cycle as a cycle of processes, not a list of facts: photosynthesis removes carbon dioxide from the atmosphere into plants and algae; respiration and combustion return carbon dioxide to the atmosphere; feeding passes carbon compounds along a food chain; decomposers break down dead organisms and waste, releasing carbon dioxide and returning mineral ions to the soil.
- For human-impact questions, always give both a cause and a specific consequence for biodiversity, rather than the cause alone, for example naming a reason for deforestation and then explaining its effect on species numbers and on carbon dioxide levels.
- For biodiversity or conservation questions, be ready to name specific measures, such as breeding programmes for endangered species, protecting and regenerating rare habitats, replanting hedgerows and field margins, reducing deforestation, and recycling materials to reduce demand for raw resources.
Worked example
A student uses ten quadrats, each 0.5 m by 0.5 m, placed randomly across a school field to estimate the population of daisy plants. The mean number of daisies per quadrat is 6.4. The total area of the field is 800 m^2. Estimate the total population of daisies in the field.
- Calculate the area of one quadrat: 0.5 m x 0.5 m = 0.25 m^2.
- Calculate how many quadrats of this size would be needed to cover the whole field: 800 / 0.25 = 3200.
- Multiply this by the mean number of daisies counted per quadrat: 3200 x 6.4.
- Calculate: 3200 x 6.4 = 20480.
- Final answer: the estimated population of daisies in the field is approximately 20480, assuming the quadrats were placed randomly and daisies are evenly distributed.
Practice questions
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Q1Define community, in ecological terms.Show answer
Answer: All the populations of different species living and interacting together in a habitat.
Q2Give one example of an abiotic factor that could affect where a plant species grows.Show answer
Answer: Any valid example, for example light intensity, temperature, moisture or water availability, or soil pH.
Q3Give one example of a biotic factor that could affect a population of rabbits.Show answer
Answer: Any valid example, for example the availability of food (grass), a new predator, a new disease, or competition with another species for food.
Q4Name the equipment used to measure the abundance of a small plant species within a sample area.Show answer
Answer: A quadrat.
Q5State one structural adaptation of a polar bear that helps it survive in a cold environment.Show answer
Answer: Any valid example, for example a thick layer of fur and blubber for insulation, or a small surface-area-to-volume ratio to reduce heat loss.
Q6Name the group of organisms that break down dead plant and animal matter, returning mineral ions to the soil.Show answer
Answer: Decomposers, such as bacteria and fungi.
Q7A student counts 3, 5, 4 and 8 dandelion plants in four separate 1 m^2 quadrats. Calculate the mean number of dandelions per quadrat.Show answer
Answer: 5 dandelions per quadrat ((3 + 5 + 4 + 8) / 4 = 20 / 4 = 5).
Q8Explain why deforestation to create land for cattle grazing can reduce biodiversity.Show answer
Answer: It destroys the habitat that many species of plants and animals depended on, so fewer species can survive in that area, reducing the variety of living organisms in that ecosystem.
Exam-style questions
Written in the style of a GCSE Science exam paper, with a full mark scheme.
State three abiotic factors that could be measured when investigating the distribution of a plant species across a school field.
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A student investigates the distribution of clover plants along a 20 m transect line running from the shaded edge of a wood into an open, sunny field, placing a quadrat every 2 m. Near the wood, the mean count is 1.2 clover plants per quadrat. In the open field, the mean count is 9.6 clover plants per quadrat. (a) Calculate how many times greater the mean number of clover plants per quadrat is in the sunny area compared with the shaded area. (b) Suggest a reason for this difference, in terms of an abiotic factor.
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A local council plans to drain a wetland area to build new housing. Evaluate the likely effects of this development on the biodiversity of the area, and suggest one measure that could reduce the impact.
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See real GCSE Science past-paper questions, with official mark schemes →
Free printable worksheet
Want more practice on paper? Download the ecology worksheet pack - 17 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
This topic is chapter 7 of GCSE Biology Workbook, the whole course as one free printable PDF.
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