OCR GCSE Biology A: Field investigations, biodiversity and human impact on ecosystems (J247) – Revision Notes

These notes condense OCR GCSE (9-1) Gateway Science Biology A (J247), Version 4.0 (August 2026), topic B6.1, statements B6.1a to B6.1d. Statement B6.1d is printed in bold in the specification, so it is Higher Tier only; the others are assessed in both tiers. Full explanations are in the study guide. Test yourself with the practice questions, track coverage on the checklist, see the course hub, and find gaps with the free 10-minute diagnostics.

Key definitions

Term	Meaning
Distribution	Where organisms are found
Abundance	How many organisms there are
Biodiversity	The variety of living organisms in an ecosystem or on Earth
Random sampling	Every position has an equal chance of being chosen, which avoids bias
Systematic sampling	Samples at regular intervals, for example along a transect
Transect	A line across a habitat along which samples are taken
Percentage cover	Estimated fraction of a quadrat covered by a species
Indicator species	A species whose presence or absence shows an environmental condition
Ecotourism	Tourism designed to bring income while limiting damage to wildlife and habitats
Conservation	Protecting species and habitats, and restoring them where damaged

B6.1a: Field investigations

Choosing the method

Situation	Best choice	Reason
Even habitat, overall abundance	Random quadrats	No bias
Gradual change, such as away from a path or up a shore	Transect with quadrats at fixed intervals	Matches distribution to the changing factor
Overlapping plants such as grass	Percentage cover	Individuals cannot be counted
Animals that move	Capture-recapture	Counting every animal is impossible

Equipment

• Quadrat: counts plants or slow animals in a known area.
• Pooter: collects small insects by suction without crushing.
• Net: sweep net for vegetation, pond net for water.
• Key: identifies organisms from features.
• Tape measure: sets out transects and measures area.

Method in steps: random quadrats

1. Lay tapes along two adjacent sides to make axes.
2. Generate random coordinates.
3. Place the quadrat at each point, count and record.
4. Repeat for enough quadrats.
5. Calculate the mean, scale up and state that the answer is an estimate.

Formulas

Quantity	Formula
Mean per quadrat	total count ÷ number of quadrats
Number per m²	mean per quadrat ÷ quadrat area in m²
Estimated population	number per m² × total area in m²
Capture-recapture	(number first marked × number in second sample) ÷ number of marked animals recaptured
Percentage	part ÷ whole × 100
Percentage change	(new − old) ÷ old × 100

Worked reminder: scaling up

A hillside of 800 m² is sampled with eight quadrats of 0.25 m². The counts of a plant are 6, 2, 0, 9, 3, 4, 5 and 1.

• Total = 30, mean = 30 ÷ 8 = 3.75 per quadrat
• Per m² = 3.75 ÷ 0.25 = 15
• Estimate for the hillside = 15 × 800 = 12 000

Check that you have used the area from the question each time.

Worked reminder: capture-recapture

Thirty-five snails are marked. A later sample has 30 snails, of which 7 are marked.

• Estimate = (35 × 30) ÷ 7 = 1050 ÷ 7 = 150 snails

Assumptions: marks stay, marking does no harm, animals mix evenly, and no migration, births or deaths of note.

Worked reminder: reading a transect

Moss cover is 40% at 1 m from a path and 5% at 9 m from the path. Say that cover is much lower far from the path (5% < 40%), then link it to a factor that changes with distance, such as trampling or light. Then add that other factors may also change, so the data show a pattern rather than proof of cause.

Percentiles

The pth percentile is the value below which about p% of results fall. For 20 ordered results, the 25th percentile is in position 5 and the 75th percentile in position 15.

Symbols

Use =, <, <<, > and >> accurately. A single < is “less than”. A double << is “much less than”.

Must-know distinctions

Idea	Compare
Random vs systematic	Random avoids bias; systematic follows a gradient
Distribution vs abundance	Where vs how many
Estimate vs count	Sampling gives an estimate only
Correlation vs cause	A pattern does not by itself show cause

B6.1b: Human interactions and biodiversity

Negative

• Land use: forest clearance, building, drainage of wetlands and ploughing of meadows destroy or break up habitats.
• Monoculture: few species can live in the area.
• Hunting and poaching: numbers fall and species may become extinct.
• Pollution: acid rain and sewage change conditions so sensitive species cannot survive.

Positive

• Protecting individual species: laws against hunting, captive breeding, reintroduction and seed banks.
• Protecting habitats: nature reserves, restoring hedgerows and ponds, controlling pollution.

Graph reminders

Independent variable on the x-axis, dependent variable on the y-axis. Scales should use more than half the grid, with even steps. Label axes with quantity and unit.

Data reminder: acid rain and germination

Out of 25 seeds, 23 germinated at pH 7 and 4 at pH 3. Percentages are 92% and 16%, a fall of 76 percentage points. Acidity reduces germination, so acid rain can reduce which plants establish.

Indicator species

Crusty lichens tolerate more sulfur dioxide. Bushy lichens need cleaner air. Mapping lichen types shows an air-quality gradient.

B6.1c: Maintaining biodiversity

Benefits	Challenges
More stable ecosystems	Agreements between countries are hard to reach and enforce
Foods, materials and medicines from wild species	Monitoring needs money, trained staff and regular surveys
Pollinators and other wild species support crops	Local people may lose income from land, hunting or fishing
Recreation and income	Remote areas make illegal activity hard to detect

Ecotourism

Ecotourism links conservation to income, so the people who live near wildlife gain from keeping it. Benefits: income for rangers and monitoring, jobs for local people, and a reason for communities to protect habitats. Limit: too many visitors can disturb wildlife.

B6.1d: Environmental change (Higher Tier only)

Factor	Effect on distribution	Evidence you may be given
Low dissolved oxygen in water	High-oxygen species such as mayfly nymphs decline; bloodworms can remain	Invertebrate counts upstream and downstream
Warmer water	Holds less dissolved oxygen	Temperature and oxygen readings
Sulfur dioxide in air	Sensitive lichens disappear	Lichen survey along a distance gradient
Rising carbon dioxide and temperature	Species ranges can shift	Records of where species occur over time

How to evaluate evidence

1. State the pattern with figures.
2. Link it to the factor in biology terms.
3. Comment on sample size and repeats.
4. Comment on other variables that were not controlled.
5. Say what extra evidence would improve the conclusion.

Quick self-test

1. A field is 30 m by 20 m. What is its area?
2. One quadrat is 0.5 m by 0.5 m. What is its area?
3. A mean of 4 plants per quadrat of 0.25 m². How many per m²?
4. Using that density, estimate the number in the 600 m² field.
5. In capture-recapture, 20 are marked, a second sample is 30, and 5 are marked. Estimate the population.
6. Give one reason why quadrats should be placed randomly.
7. Name one piece of equipment for collecting small flying insects from vegetation, and one for small insects by suction.
8. Name one negative and one positive human interaction with ecosystems.
9. A population falls from 800 to 600. What is the percentage change?
10. Give one challenge of monitoring a conservation scheme.
11. (Higher Tier only) Why might mayfly nymphs be absent from a polluted stretch of river?
12. (Higher Tier only) Give one weakness of using a single sample at each site.

Answers

1. 30 × 20 = 600 m².
2. 0.5 × 0.5 = 0.25 m².
3. 4 ÷ 0.25 = 16 per m².
4. 16 × 600 = 9600.
5. (20 × 30) ÷ 5 = 120.
6. It avoids bias, so each position has an equal chance of being sampled.
7. A sweep net for flying insects in vegetation; a pooter for small insects by suction.
8. For example, forest clearance (negative) and nature reserves or seed banks (positive).
9. (600 − 800) ÷ 800 × 100 = −25%, a 25% decrease.
10. For example, remote areas are costly to survey, or illegal hunting may go unnoticed.
11. Sewage or fertiliser feeds microorganisms that use up dissolved oxygen, and mayfly nymphs need high oxygen levels.
12. It may not be typical, so a repeat is needed to see whether the pattern is reliable.

Where marks are usually lost

• Giving a mean per quadrat when the question asks for a number in the whole area.
• Using the wrong area, such as quadrat dimensions in metres instead of area in square metres.
• Describing a random method but placing quadrats by choice.
• Writing that a sample gives the exact population.
• Not stating the assumptions of capture-recapture.
• Writing “pollution kills things” without naming the factor and its effect on the organism.
• Listing conservation benefits without a link to biodiversity.
• Describing graph data without quoting figures.
• Stating that data prove a cause when they only show a pattern.
• Evaluating with “do more repeats” and no reason.

Official syllabus

Source: OCR GCSE (9-1) Gateway Science Biology A (J247), Version 4.0 (August 2026), for first assessment in 2018, published by OCR. Topic B6.1 Monitoring and maintaining the environment, statements B6.1a to B6.1d.