OCR GCSE Biology B (Twenty First Century)
OCR GCSE Biology B B3.4 How are populations affected by conditions in an ecosystem? Exam Questions
Free OCR GCSE Biology B exam questions for B3.4 How are populations affected by conditions in an ecosystem?, with a mark scheme for every pack. Covers abiotic and biotic factors, distribution and abundance, sampling with quadrats and transects, capture and recapture, and adaptations to the environment.
B3.4 How are populations affected by conditions in an ecosystem? exam questions
2 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
StemUp mark scheme flashcards
GCSE Biology Triple Science Flashcards for 2027 Onwards
Every answer is written in mark scheme wording, so you learn exactly what examiners give marks for. Then test yourself with the questions on this page.
From £7.99View flashcards
About OCR GCSE Biology B B3.4 How are populations affected by conditions in an ecosystem?
B3.4 explains how living and non-living conditions affect where organisms live and how many there are. You need to identify abiotic factors such as light, temperature, water and pH, and biotic factors such as predation, competition and disease, and explain how they change population size. Field techniques are central: using quadrats and transects to estimate abundance and distribution, and capture and recapture for mobile animals. This builds on interdependence in B3.3 and leads to biodiversity and conservation in B6.4. Examiners often ask you to plan a sampling method or calculate a population estimate.
What you need to know
- Abiotic factors Non-living factors including light intensity, temperature, moisture, soil pH and mineral content, wind and carbon dioxide or oxygen concentration.
- Biotic factors Living factors including availability of food, new predators, new pathogens and competition between species.
- Quadrats Place quadrats randomly using coordinates from random numbers, count organisms or percentage cover, and scale up: estimated population = mean per quadrat x (total area / quadrat area).
- Transects A line transect with quadrats at regular intervals shows how distribution changes across a gradient, such as from a hedge into a field.
- Capture and recapture Estimated population = (number in first sample x number in second sample) / number marked in second sample. Marks must not harm the animal or make it more visible to predators.
- Predator and prey cycles Predator numbers rise after prey numbers rise and fall after prey numbers fall, so the cycles are out of phase.
Common mistakes in B3.4 How are populations affected by conditions in an ecosystem?
- Placing quadrats where organisms look common. Quadrats must be placed randomly to avoid bias.
- Using a transect to estimate total population. Transects show changes in distribution; random quadrats estimate abundance.
- Rearranging the capture and recapture formula wrongly. Divide by the number of marked animals recaptured.
- Listing predation as an abiotic factor. Abiotic factors are non-living.
- Assuming the population is closed when it is not. Capture and recapture assumes no births, deaths or migration between samples.
Try three B3.4 How are populations affected by conditions in an ecosystem? exam-style questions
1. State two abiotic factors that could affect the distribution of plants in a field. (2 marks)
Show the mark scheme answer
Any two from: light intensity; soil moisture; soil pH; temperature; mineral ion concentration.
2. Ecologists caught and marked 40 woodlice. A week later they caught 50, of which 8 were marked. Estimate the population. (2 marks)
Show the mark scheme answer
(40 x 50) / 8; = 250 woodlice.
3. Describe how to estimate the number of daisies in a 50 m by 20 m field using 1 m2 quadrats. (4 marks)
Show the mark scheme answer
Place quadrats at random coordinates using random numbers; count daisies in each quadrat; use at least ten quadrats and calculate the mean per m2; multiply by the field area of 1000 m2.
B3.4 How are populations affected by conditions in an ecosystem? FAQs
What does OCR GCSE Biology B B3.4 cover?
It covers abiotic and biotic factors, how they affect populations, and sampling methods such as quadrats, transects and capture and recapture.
Which paper is B3.4 examined in?
J257 has two papers at each tier, Breadth in Biology and Depth in Biology, and content from any chapter, including B3, can be assessed on either one. Expect it to be linked to ideas about science and to other chapters.
What fieldwork methods do I need for B3.4?
Learn random quadrat sampling, belt or line transects and capture and recapture, including the equations, the assumptions and how to reduce bias.
