B6.1 Monitoring and maintaining the environment

Why this matters

Biodiversity is short for biological diversity — the variety of different species in a place. A coral reef can hold thousands of species; a ploughed wheat field essentially one. High biodiversity gives an ecosystem food-chain redundancy and resilience: lose one species and others can fill the gap. Low biodiversity makes a community fragile. Humans depend on biodiverse ecosystems for clean air and water, pollination of crops, fertile soil, fish stocks, timber and medicines. Since the Industrial Revolution the human population has climbed from one to over eight billion, and per-person resource use has climbed faster still — driving habitat conversion, pollution, climate change. To respond, ecologists need first to MEASURE what is happening (sampling, capture-recapture, quadrats) and then to ACT (protected reserves, breeding programmes, afforestation, ecotourism, sustainable quotas). OCR J247 B6.1 tests both halves of that loop, and expects internationally-coordinated answers because biodiversity is a global resource.

How to learn this topic

Build on what you already know

• GCSE B5: producers, consumers, decomposers, food webs and the carbon cycle.
• GCSE B4: aerobic respiration uses oxygen — needed to understand eutrophication.
• KS3: habitats, populations, photosynthesis, decomposition.
• Maths: ratios, simple algebraic rearrangement (for the capture-recapture formula).

1. Why we maintain biodiversity — ecosystem stability and human dependence.
2. Sampling: quadrats for plants and slow movers.
3. Capture-recapture for mobile animals — method, assumptions, formula.
4. Worked example with beetles and a water-vole context.
5. Human pressures that reduce biodiversity (deforestation, peat, pollution, climate).
6. Eutrophication chain — the five marking phrases.
7. Conservation strategies: protected reserves, captive breeding, afforestation.
8. Ecotourism — generates income, funds conservation, raises awareness.
9. Sustainable fishing quotas and international cooperation.

Key terms

biodiversity

The variety of all the different species of organisms in an ecosystem, or on Earth. (OCR wants 'variety of different organisms'. Don't write 'number of organisms' — it's about species variety, not population size.)

stability (of an ecosystem)

When populations and abiotic factors stay roughly constant over time. High biodiversity supports stability because the loss of one species can be absorbed by others. (Phrase: 'more stable ecosystem | loss of one species can cause others to decline'.)

sampling

Counting organisms in a small representative area (or a small sample of a population) and scaling up to estimate the total. Sampling must be random to avoid bias. (If asked about reliability, mention repeating the sample and taking a mean.)

quadrat

A square frame (typically 0.25 m² or 1 m²) used to sample plants and slow-moving animals by counting how many fall inside the frame. Quadrats are placed randomly to avoid bias. (Quadrats are for plants and SLOW movers only. For mobile animals you use capture-recapture.)

capture-recapture

A method for estimating the population size of mobile animals: catch a sample, mark and release them, allow time for redistribution, then catch a second sample. Population N = (M × C) ÷ R where M = first sample marked, C = second sample size, R = marked recaptured. (Four OCR phrases: capture a sample | mark and release them | leave time to mix back into the population | count marked and unmarked in second sample.)

deforestation

The clearing of large areas of forest, usually for agriculture, timber, or biofuel production. (Always link to habitat loss: 'organisms that depend on trees cannot survive'.)

eutrophication

The process in which excess nutrients (from fertilisers or sewage) in water cause algae to grow rapidly, blocking light. Plants die and decomposers use up the oxygen, killing fish. (Learn the five phrases in order: algae grow rapidly / light blocked / plants die / decomposers respire and use up oxygen / fish die.)

afforestation

Planting trees on land that was not previously forested (compare reforestation, which is replanting where forest used to be). (OCR phrase: 'more habitats created/restored | more species can live there | CO₂ removed from atmosphere | more stable environment allows more species to survive'.)

ecotourism

Tourism focused on visiting natural habitats responsibly, in which tourist money funds conservation of the habitat and its wildlife. (OCR phrase: 'generates income | fund conservation | maintains biodiversity | raises awareness'.)

captive breeding programme

A conservation programme in which endangered species are bred in zoos or reserves to increase their numbers, with offspring sometimes released into the wild. (Always give an example: giant panda, condor, Arabian oryx.)

SSSI (Site of Special Scientific Interest)

A protected area in the UK designated for its rare or important wildlife, geology or habitat. Development and damage are restricted.

sustainable fishing quota

A legal limit on the number or mass of fish that can be caught from a stock each year, set so the population can replace itself by breeding. (Combine with minimum mesh size so juveniles escape and can breed before being caught.)

Notes

Why maintain biodiversity

Biodiversity is the variety of all the different species of organisms in an ecosystem, or on Earth. A coral reef, a tropical rainforest and an ancient woodland all have high biodiversity. A monoculture wheat field has low biodiversity.

OCR wants four marking phrases for why we maintain high biodiversity:

• variety of different organisms — many species filling many roles
• more stable ecosystem — interdependence is spread across many species, not concentrated on one or two
• loss of one species can cause others to decline — food webs collapse when keystone species disappear
• preserves natural resources — clean water, fertile soil, fisheries, timber and medicines all depend on biodiverse systems

The future of the human species relies on us keeping biodiversity high.

Sampling — how we measure what's there

You cannot count every organism in an ecosystem, so ecologists sample — count organisms in small areas and scale up. Two methods you must know.

### Quadrats

A quadrat is a square frame (usually 0.25 m × 0.25 m or 1 m × 1 m) placed on the ground. Quadrats are used to sample plants and slow-moving animals (e.g. snails, limpets). The method:

1. Throw quadrats randomly (or use coordinates from a random-number table) to avoid bias.
2. Count the organisms in each quadrat, or estimate percentage cover.
3. Repeat many times and find the mean.
4. Multiply by the ratio of total area to quadrat area to estimate the total population.

For a belt transect (e.g. up a beach) you place quadrats at fixed intervals along a tape — used to study how distribution changes with an abiotic factor like distance from the shore.

### The capture-recapture method

Quadrats are no use for fast-moving animals — they walk in and out before you count them. For mobile animals (beetles, voles, butterflies, woodlice) we use capture-recapture.

The four steps the OCR mark scheme wants:

1. Capture a sample of beetles — using pitfall traps, sweep nets or live traps.
2. Mark and release them — with a small dot of harmless paint or a tag. Marks must be unobtrusive (a bright mark would expose them to predators) and durable enough to stay on for the second sample.
3. Leave time to mix back into the population — usually 24-48 hours so marked individuals redistribute themselves randomly.
4. Count marked and unmarked in the second sample — set traps again and record how many of those caught carry the mark.

The ratio of marked to total in the second sample reflects the ratio of marked to total in the whole population. That gives the Lincoln index formula:

> N = (M × C) ÷ R

where

• N = total population size (the answer we want)
• M = number marked and released in the first capture
• C = total number caught in the second sample
• R = number of marked individuals recaptured in the second sample

Worked example. You catch 40 beetles, mark them and release them. Two days later you catch 50 beetles and 8 of them carry the mark.

• M = 40, C = 50, R = 8
• N = (40 × 50) ÷ 8 = 2000 ÷ 8 = 250 beetles

The method assumes (a) marks do not fall off or harm the animals, (b) marked individuals mix evenly with unmarked ones, and (c) the population size does not change between samples — no births, deaths, immigration or emigration. If those assumptions are met, repeating the survey each year tracks whether a population is rising or falling, so conservation action can be taken in time.

Water-vole example. Water voles are declining in UK rivers. Conservationists trap them along the bank, mark each one with a tiny ear tag, release them, wait several days for redistribution, then trap again. The ratio of marked to unmarked in the second sample estimates total population size. Accurate estimates show whether the population is declining so conservation action (predator control, habitat restoration) can be taken.

Human pressures that reduce biodiversity

The human population is growing rapidly and the standard of living is rising, so more resources are used and more waste is produced. Habitats shrink as humans build, quarry, farm and dump waste.

Deforestation — large areas of forest are cleared for agriculture, timber and biofuels. Trees that thousands of species depend on are removed, so those organisms cannot survive and biodiversity falls. Cutting forests also reduces CO₂ removal by photosynthesis, worsening climate change.

Peat bog destruction — peat is dug up for compost. Specialist bog species (sphagnum moss, wading birds, sundew) lose their habitat. The peat dries out and decomposers release stored CO₂.

Water pollution and eutrophication. Fertilisers wash off fields into rivers and lakes. The OCR/AQA five-stage chain:

1. Algae grow rapidly — extra nutrients fuel a bloom.
2. Light cannot penetrate the water below.
3. Submerged plants and the algae themselves die.
4. Decomposers respire as they break down the dead matter and use up oxygen.
5. Fish and other animals die because there is not enough oxygen.

Air pollution and acid rain. Sulfur dioxide from burning fossil fuels dissolves in clouds to form acid rain — kills trees and acidifies lakes.

Global warming from CO₂ and methane causes rising sea levels, melting ice, changing weather and species migration / extinction.

Non-native (invasive) species brought to new areas have no natural predators, so they outcompete or prey on native species and biodiversity falls.

Conservation strategies

OCR examines six conservation strategies that work together.

Protected reserves. National parks, nature reserves and Sites of Special Scientific Interest (SSSIs) restrict development and damage. Marine reserves protect coastal and seabed habitats.

Captive breeding programmes. Zoos and reserves breed endangered species (giant panda, condor, Arabian oryx, scimitar oryx) and release offspring into protected wild populations. Without these programmes some species — e.g. the California condor — would already be extinct.

Afforestation and reforestation. Afforestation is planting trees on land that was not previously forested; reforestation is replanting where forest used to be. Both create or restore habitats — more habitats created/restored means more species can live there. New forests also absorb CO₂ (CO₂ removed from atmosphere) and stabilise temperature and rainfall, so a more stable environment allows more species to survive.

Ecotourism. Tourists pay to visit pristine habitats — safaris, rainforest walks, whale-watching trips. The money matters because it: generates income for local communities; that income can fund conservation (rangers, anti-poaching, reserve management); the ongoing need to protect wildlife maintains biodiversity; and contact with rare habitats raises awareness internationally. Ecotourism only works if visitor numbers stay low enough not to disturb the habitats.

Sustainable fishing quotas. Governments set legal limits on how many fish (cod, herring, tuna) can be caught each year, plus minimum mesh sizes so juveniles slip through. Quotas allow stocks to breed and recover, preventing collapse and protecting fishery-dependent species.

Recycling resources. Recycling reduces landfill waste, cuts demand for raw materials, and lowers land pollution.

Biodiversity is a global resource, so international cooperation matters. Treaties on whaling, fisheries, the ozone layer and CO₂ emissions only work when many countries sign up. OCR may credit answers that mention international agreements.

Exam tips

• For 'why maintain biodiversity?' use OCR's four phrases: variety of different organisms / more stable ecosystem / loss of one species can cause others to decline / preserves natural resources.
• Capture-recapture: write all four steps — capture, mark and release, leave time for mixing, recapture and count. Missing 'leave time' is the most common lost mark.
• Memorise the formula N = (M × C) ÷ R. In a numerical question, write it down, substitute, then calculate. Show working — partial marks are awarded.
• Quadrats are for plants and slow movers. Capture-recapture is for mobile animals. Choose the right method or you lose a mark in 'suggest a suitable sampling technique' questions.
• For ecotourism, hit all four OCR phrases: generates income / fund conservation / maintains biodiversity / raises awareness.
• For afforestation, hit all four phrases: more habitats created/restored / more species can live there / CO₂ removed from atmosphere / more stable environment allows more species to survive.
• For eutrophication (4 marks) the order is fixed: algae grow rapidly → light blocked → plants and algae die → decomposers respire and use up oxygen → fish and other animals die.
• If a question asks about water voles or other declining species, link your answer to 'accurate estimates show if the population is declining so conservation action can be taken'.

Mark-scheme phrasing

Common misconceptions

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Worked example

Question:

Answer:

Frequently asked questions

Related topics in OCR GCSE Biology A: Gateway Science (J247)

• B6.2 Feeding the human race
• B6.3 Monitoring and maintaining health