4.1Ecology and the Environment
The organism in the environment — Edexcel Modular - OL Revision Notes & Topical Questions
10 min read 16 parts Lesson 2 of 5 2 quizzes
Lesson summary
The organism in the environment Edexcel O Level Modular Biology notes: understand the terms population, community, habitat and ecosystemTwo species cannot share exactly the same niche for long (competitive exclusion).Biomestundra, desert, rainforest, grassland, taiga, deciduous f…
- The organism in the environment Edexcel O Level Modular Biology: what to do next
- Give / State / Name
- Evaluate / Assess
- Keywords the mark scheme looks for in this lesson
- How to get full marks (examiner guidance)
- Link ideas
Section 1 of 16Process & sequence
- Organism
- Population
- Community
- Ecosystem
- Biome
- Biosphere
Factors
Biotic predators, competitors, food
Abiotic temperature, water, light, soil
Section 2 of 16Keep going
The organism in the environment Edexcel O Level Modular Biology: what to do next
These The organism in the environment Edexcel O Level Modular Biology notes covered the key ideas, worked examples and exam technique for this topic. Check your The organism in the environment Edexcel O Level Modular Biology understanding with the practice questions below, then reread any The organism in the environment Edexcel O Level Modular Biology point you were unsure about before moving on.
2
Previous lesson: 3.2 Inheritance — Notes
3
Next lesson: 4.2 Feeding relationships — Notes
4
Course: Edexcel Modular - OL — all units
5
Official syllabus: Pearson Edexcel International GCSEs
Section 3 of 16Quadrat sampling
When completing an ecological study, data must be random and representative of the survey area.
Quadrat sampling
Choose the position of each quadrat randomly (for example by random numbers as coordinates on a tape grid) and take a minimum of 10 readings in each survey area.
Using CORMS: C - the area surveyed (for example shaded versus open); O - count the number of different plant species or individuals; M1 - count the number of different plant species found across all quadrats; S - control the size of the quadrat, the random way quadrats are placed on the ground,
- and the day the results were collected.
1
Mark out the area with two tape measures at right angles.
2
Use a random number generator for coordinates.
3
Place the quadrat at each coordinate and count species or individuals.
4
Repeat at least ten times in each area.
5
Calculate the mean per quadrat and compare areas.
For a gradient of conditions, use a belt transect, placing quadrats at regular intervals along a line.
Section 4 of 16Abiotic factors
An abiotic factor is a non-living factor in an environment, such as temperature, light intensity and wind speed. Their effect on population size and distribution is summarised below.
| Abiotic factor | How it affects populations | Example |
|---|---|---|
| Light intensity | Limits photosynthesis, so plant growth and food for consumers | Fewer plants under dense canopy |
| Temperature | Affects enzyme activity and metabolic rate | Fewer species at cold altitudes |
| Water availability | Needed for photosynthesis and support | Desert plants are sparse |
| Oxygen concentration | Needed for respiration | Low-oxygen polluted water supports few species |
| Carbon dioxide | Reactant in photosynthesis | Higher concentration gives more biomass |
Lichens are found in areas with low air pollution, so their presence indicates clean air.
Abiotic factors
Experiment: scientists set up five glasshouses each containing 100 wheat plants, with carbon dioxide at different concentrations (starting at 0.03%), keeping all other conditions such as light intensity, temperature and water supply the same, measured dry biomass and calculated the mean biomass for each concentration.
Result: mean biomass increases as carbon dioxide concentration increases,
- because carbon dioxide is a reactant in photosynthesis;
- a higher concentration increases the rate of photosynthesis,
- producing more glucose for growth.
Section 5 of 16Biotic factors
| Biotic factor | Description | Example |
|---|---|---|
| New pathogen | If a new pathogen enters an ecosystem, the populations may have no immunity or resistance | Ash dieback, caused by a fungus, has infected millions of ash trees in Europe |
| Competition | If two species compete for the same resource(s) and one is better adapted, it will outcompete the other | North American grey squirrels introduced to the UK in the 1800s outcompeted red squirrels for food and nesting sites; they also carry a virus red squirrels are susceptible to |
| Predation | Predator and prey numbers rise and fall in linked cycles | Foxes and rabbits |
Exam comment on squirrel data (five of the following): the red squirrel population increases at first, then decreases after grey squirrels are introduced; the grey squirrel population increases after introduction; at the end grey squirrels are many and red squirrels few or none; this is likely due to competition for food and disease.
Section 6 of 16Compare
| Level | Includes | Example | Living only? | Scale | Study focus |
|---|---|---|---|---|---|
| Organism | One individual | One lion | Yes | Smallest | Adaptations |
| Population | One species | Lions in Serengeti | Yes | — | Growth, density |
| Community | All species | Lions, zebras, grass | Yes | — | Interactions |
| Ecosystem | Community + abiotic | Serengeti plains | No | — | Energy, cycles |
| Biome | Similar ecosystems | Savanna | No | — | Climate |
| Biosphere | All life on Earth | Earth | No | Largest | Global change |
Section 7 of 16Worked examples
Describe how to compare the number of plant species in two areas. [4]4 marks
Place quadrats at random positions (at least 10 per area), identify and count species in each, calculate the mean number of species per quadrat for each area.
Scientists grew wheat with 0.03% to 0.12% CO2 and measured dry biomass. Explain a result showing increased biomass. [3]3 marks
Carbon dioxide is a reactant in photosynthesis; more CO2 raises the rate of photosynthesis, so more glucose is made for growth.
Explain why grey squirrels replaced red squirrels. [3]3 marks
They compete for food and nest sites and are better adapted; they also carry a virus that harms red squirrels.
Give two variables to control in the glasshouse experiment. [2]2 marks
Light intensity and temperature (or water supply).
Section 8 of 16Abiotic and biotic factors
Abiotic factors
Abiotic factors are non-living environmental conditions, such as light intensity, temperature, water availability, soil pH and carbon dioxide concentration. They affect where organisms can survive and how quickly they grow or reproduce.
Biotic factors
Biotic factors arise from living organisms. Examples include food supply, predation, competition and pathogens. A change in any of these factors can alter the size or distribution of a population.
Section 9 of 16Carbon dioxide and plant growth
Carbon dioxide and plant growth
Carbon dioxide is a raw material for photosynthesis. If it is in short supply, increasing its concentration can raise the rate of photosynthesis, produce more glucose and increase plant biomass. This explanation links the environmental factor to the observed growth.
In one investigation, wheat plants were grown in glasshouses at several carbon dioxide concentrations while light, temperature, water and growth time were controlled.
- Mean dry biomass rose most at lower concentrations and then levelled off.
- The levelling off suggests another resource became limiting,
- so a claim that extra carbon dioxide will always increase growth would be too broad.
Section 10 of 16Living factors and population change
Living factors and population change
A larger food supply can improve survival and reproduction.
- A newly introduced predator can reduce prey numbers.
- A novel pathogen may spread through a population with little resistance.
- Where two species need the same food or nesting sites, the better competitor can reduce the other species' population.
Population change usually has more than one possible cause. When interpreting a graph, describe the trend first, then propose a mechanism supported by the context. A statement such as “the species is better adapted” needs a named advantage, such as a wider food range or greater disease resistance.
Section 11 of 16Worked example: squirrels
Worked example: squirrels
Suppose grey squirrels enter a woodland in year 6. After their introduction, their numbers rise while red squirrel numbers fall. That is a description of the data; a complete answer must also explain why the populations may change.
Grey squirrels can compete with red squirrels for food and nesting places.
- A wider range of usable food can give grey squirrels an advantage, and disease carried by grey squirrels may further harm red squirrels.
- These are plausible biological mechanisms;
- a graph showing opposite trends alone does not prove which mechanism acted.
Section 12 of 16Answering ecological data questions
For a “comment on” question, state when a change begins, describe the direction of change in both populations, and quote relevant values if the graph provides them. Then explain the trends using competition, predation or disease as appropriate.
Check:
Check Why might wheat biomass stop increasing even while carbon dioxide continues to rise? Answer: A different factor, such as light, water or mineral availability, may become limiting.
Section 13 of 16Key terms
| Term | Meaning |
|---|---|
| Abiotic factor | A non-living factor in the environment. |
| Biotic factor | A living factor, such as predation or competition. |
| Quadrat | A square frame used for sampling. |
| Transect | A line along which samples are taken. |
| Competition | Rivalry for the same resource. |
| Indicator species | A species whose presence shows environmental conditions. |
Section 14 of 16Syllabus checklist
Syllabus points
understand the terms population, community, habitat and ecosystem
practical: investigate the population size of an organism in two different areas using quadrats practical: investigate the distribution of organisms in their habitats and measure biodiversity using quadrats
understand how abiotic and biotic factors affect the population size and distribution of organisms
Section 15 of 16Command terms
Command terms
Give / State / Name
Recall a fact; one idea per mark.
Define
Give the exact meaning using the specification keywords.
Describe
Give an account of what happens / the pattern in data, quoting values; no reasons needed.
Explain
Give reasons with linked statements (cause → effect). Each linked step is usually a separate marking point.
Suggest
Use knowledge in a new context; more than one answer may be accepted.
Compare
Similarities and differences; each point must refer to both items.
Calculate
Show working; include units; check significant figures. Method marks are given even if the final answer is wrong.
Discuss
Explore the issue from different angles and link the points.
Evaluate / Assess
Weigh strengths and weaknesses and reach a supported judgement.
Deduce
Draw a conclusion from the information given.
Justify
Support a statement/choice with evidence.
Section 16 of 16Exam technique
1
Choosing quadrat positions by hand.
2
Counting too few quadrats.
3
Forgetting to calculate a mean.
4
Mixing abiotic and biotic factors.
Marked practiceQuizzes for this lesson
Last updated: