What you'll learn
This revision guide covers how human activities impact biodiversity and ecosystems, focusing on the AQA GCSE Biology specification. You'll understand the key threats to biodiversity including pollution, land use changes, and global warming, as well as the practical conservation methods used to protect species and habitats. This topic frequently appears in both Foundation and Higher tier papers, often combined with questions on food security or maintaining biodiversity.
Key terms and definitions
Biodiversity — the variety of all the different species of organisms on Earth, or within a specific ecosystem
Population — the total number of organisms of the same species living in the same geographical area
Pollution — the introduction of contaminants into the environment that cause harm or discomfort to organisms
Deforestation — the permanent removal of trees and forests, usually to create land for agriculture or development
Peat bog — waterlogged acidic ecosystem where partially decomposed plant material accumulates as peat
Eutrophication — the enrichment of water bodies with excess nutrients, causing algal blooms and oxygen depletion
Captive breeding programme — controlled breeding of endangered species in zoos or wildlife parks to increase population numbers
Reintroduction programme — the release of captive-bred or relocated individuals back into their natural habitat
Core concepts
Understanding biodiversity and its importance
Biodiversity encompasses three levels: genetic diversity within species, species diversity within ecosystems, and ecosystem diversity across the planet. High biodiversity indicates a healthy, stable ecosystem capable of withstanding environmental changes.
The importance of maintaining biodiversity includes:
- Ensuring ecosystem stability through complex food webs
- Providing resources for human use (medicines, foods, materials)
- Maintaining ecological services like pollination, decomposition, and nutrient cycling
- Preserving species that may have future value for scientific research or agriculture
Human activities over recent centuries have significantly reduced global biodiversity. The current rate of species extinction is estimated to be 100-1000 times higher than the natural background rate, primarily due to human impact.
Human activities that reduce biodiversity
Waste management and pollution
Humans produce substantial amounts of waste that can damage ecosystems:
Water pollution occurs through several mechanisms:
- Sewage and fertiliser runoff introduce excess nitrates and phosphates into water bodies
- This causes eutrophication: algae grow rapidly (algal bloom), blocking light to underwater plants
- Plants die and decompose; bacteria decomposing dead material use oxygen from the water
- Oxygen depletion kills fish and other aquatic organisms
- This creates "dead zones" with no biodiversity
Air pollution affects biodiversity through:
- Smoke and acidic gases (sulfur dioxide, nitrogen oxides) producing acid rain
- Acid rain lowers soil and water pH, harming plants and aquatic organisms
- Particulates reducing light availability for photosynthesis
- Toxic gases directly damaging plant tissues and reducing growth
Land pollution includes:
- Toxic chemicals from landfills leaching into soil and groundwater
- Pesticides and herbicides killing non-target species
- Plastic waste harming wildlife through ingestion and entanglement
Deforestation and habitat destruction
Deforestation is the large-scale removal of forests, primarily for:
- Timber production for construction and paper
- Agricultural land for crops (palm oil, soy) and livestock grazing
- Urbanisation and infrastructure development
- Mining operations
Consequences of deforestation include:
- Direct habitat loss for millions of species
- Fragmentation of remaining habitats, isolating populations
- Extinction of species with specialised habitat requirements
- Reduced biodiversity as complex forest ecosystems are replaced with simple agricultural systems
- Soil erosion as tree roots no longer stabilise soil
- Disruption of water cycles and increased flooding risk
- Release of stored carbon dioxide, contributing to climate change
Peat bog destruction
Peat bogs are unique wetland ecosystems where plant material accumulates faster than it decomposes due to waterlogged, acidic conditions. Peat formation stores carbon over thousands of years.
Peat extraction for use in compost causes:
- Destruction of rare peat bog habitats
- Loss of specialist species (carnivorous plants, specific insects)
- Release of stored carbon dioxide when peat is exposed to air
- Drainage of surrounding areas, affecting wider ecosystems
The environmental cost of peat extraction has led many gardeners to choose peat-free compost alternatives.
Global warming and climate change
Increased atmospheric carbon dioxide from burning fossil fuels and deforestation causes global temperature rises. This affects biodiversity through:
- Shifting climate zones faster than species can migrate
- Melting polar ice reducing habitat for Arctic species
- Coral bleaching as ocean temperatures rise
- Changing seasonal patterns disrupting breeding and migration
- Increased extreme weather events destroying habitats
- Ocean acidification affecting shell-forming organisms
Species unable to adapt or migrate face extinction. Studies predict that 15-40% of species could face extinction with temperature increases of 2-3°C.
Positive human impacts: conservation and protection
Recognising the biodiversity crisis, humans have developed various strategies to protect species and ecosystems:
Breeding programmes
Captive breeding programmes in zoos and wildlife parks aim to:
- Increase population numbers of endangered species
- Maintain genetic diversity through careful breeding records
- Prevent extinction when wild populations become critically low
- Educate the public about conservation
Examples include successful breeding of species like the Arabian oryx, California condor, and Mauritius kestrel. However, captive breeding has limitations:
- High costs and resource requirements
- Difficulty replicating natural habitats
- Animals may lose survival skills needed in the wild
- Genetic bottlenecks if starting from very small populations
Protection and regeneration of habitats
Effective habitat conservation includes:
Protected areas such as:
- National parks and nature reserves with restricted human access
- Marine protected areas limiting fishing and development
- Sites of Special Scientific Interest (SSSIs) in the UK
Habitat regeneration involves:
- Replanting hedgerows to connect fragmented habitats (wildlife corridors)
- Reforestation projects restoring native woodland
- Wetland restoration improving water quality and biodiversity
- Urban green spaces providing habitat in cities
Reintroduction programmes return species to areas where they've been extinct, such as:
- Red kites in England
- Beavers in Scotland
- Large blue butterflies in southwest England
Successful reintroductions require:
- Suitable habitat with sufficient resources
- Removal of original extinction causes
- Sufficient genetic diversity in reintroduced populations
- Monitoring and support during establishment
Field margins and hedgerows
Modern agricultural intensification reduced biodiversity by removing hedgerows and cultivating right to field edges. Conservation strategies include:
- Leaving field margins uncultivated to provide habitat for wildflowers, insects, and small mammals
- Maintaining and planting hedgerows connecting habitats
- Reducing pesticide use to protect beneficial insects
- Creating beetle banks (raised strips) for overwintering invertebrates
These measures support pollinator populations essential for crop production while increasing farmland biodiversity.
Reduction of waste and pollution
Reducing environmental damage includes:
Waste reduction strategies:
- Recycling programmes reducing landfill and resource extraction
- Composting organic waste rather than sending to landfill
- Reducing single-use plastics
- Properly treating sewage before discharge
Pollution control measures:
- Regulations limiting industrial emissions
- Catalytic converters reducing vehicle emissions
- Restrictions on pesticide and fertiliser use near waterways
- Wetland buffer zones filtering agricultural runoff
International cooperation
Biodiversity loss is a global problem requiring international action:
- CITES (Convention on International Trade in Endangered Species) regulates wildlife trade
- Protected areas spanning multiple countries
- Funding from developed nations supporting conservation in biodiversity hotspots
- International agreements on climate change mitigation
- Sharing scientific knowledge and conservation techniques
Programmes to reduce negative impacts
Governments and organisations implement various schemes:
Sustainable development aims to meet current needs without compromising future generations:
- Sustainable forestry with replanting and selective harvesting
- Sustainable fishing with quotas and protected breeding areas
- Renewable energy reducing fossil fuel dependence
- Green building standards minimising environmental impact
Education and awareness programmes encourage:
- Responsible consumer choices (sustainable products, reduced consumption)
- Support for conservation organisations
- Understanding of local and global biodiversity issues
- Citizen science projects monitoring wildlife populations
Worked examples
Example 1: Eutrophication process (6 marks)
Question: Describe how the use of fertilisers on farmland can lead to the death of fish in nearby rivers.
Answer:
- Fertilisers contain nitrates/phosphates that are washed from fields into rivers (1 mark)
- Excess nutrients cause algae to grow rapidly/algal bloom (1 mark)
- Algae block light from reaching plants below the water surface (1 mark)
- Plants cannot photosynthesise and die (1 mark)
- Bacteria decompose dead plants and algae, using oxygen from the water (1 mark)
- Oxygen concentration decreases so fish cannot respire and die (1 mark)
Examiner note: This is a classic 6-mark question requiring a logical sequence. Each step must be clearly stated; don't assume the examiner will fill in gaps. Use correct terminology like "algal bloom" and "decompose" rather than vague terms.
Example 2: Conservation methods (4 marks)
Question: Explain how captive breeding programmes help maintain biodiversity.
Answer:
- Breeding endangered species in controlled conditions like zoos increases their population numbers (1 mark)
- This prevents species from becoming extinct (1 mark)
- Careful breeding maintains genetic diversity within the species (1 mark)
- Individuals can later be released back into the wild/reintroduced to natural habitats (1 mark)
Examiner note: The command word "explain" requires you to give reasons, not just state facts. Link each point to how it maintains biodiversity.
Example 3: Evaluating conservation strategies (6 marks)
Question: A conservation group wants to protect an endangered butterfly species. Evaluate the advantages and disadvantages of creating a nature reserve compared to a captive breeding programme.
Answer: Nature reserve advantages:
- Protects the entire ecosystem including plants the butterfly feeds on and other species (1 mark)
- Butterflies remain in natural habitat with normal behaviours (1 mark)
Nature reserve disadvantages:
- Requires large area of land which may be expensive/difficult to obtain (1 mark)
- Cannot guarantee protection from all threats like disease or climate change (1 mark)
Captive breeding advantages:
- Close monitoring and protection from predators/disease increases survival (1 mark)
Captive breeding disadvantages:
- Difficult to replicate exact habitat conditions butterflies need (1 mark)
Examiner note: "Evaluate" questions require you to consider both positive and negative aspects. Structure your answer clearly with separate sections for each method. You don't need to reach a conclusion unless specifically asked.
Common mistakes and how to avoid them
Confusing biodiversity with population size: Biodiversity refers to the variety of different species, not just the number of individuals. A field with a million grass plants has lower biodiversity than a meadow with 50 different plant species even if it has fewer total individuals.
Incomplete eutrophication sequences: Students often miss steps in the eutrophication process. Remember the full chain: excess nutrients → algal bloom → light blocked → plants die → decomposition → oxygen depletion → fish death. Learn the sequence in order.
Vague descriptions of conservation methods: Saying "protect habitats" is insufficient. Specify how: creating protected areas, replanting native species, removing invasive species, establishing wildlife corridors, etc.
Confusing carbon dioxide and oxygen in pollution explanations: In eutrophication, bacteria use up oxygen (not produce carbon dioxide as the main problem). Keep gas exchanges clear in your explanations.
Not linking human activities to specific impacts: Always connect the activity to its consequence. For example, "deforestation reduces biodiversity because habitats are destroyed and species lose their food sources and shelter."
Mixing up captive breeding and reintroduction: Captive breeding is breeding in controlled conditions; reintroduction is releasing animals back to the wild. They're related but distinct processes.
Exam technique for "Biodiversity and the impact of human activity on ecosystems"
Command words matter: "Describe" requires you to state what happens; "explain" requires reasons why it happens; "evaluate" requires advantages and disadvantages; "suggest" means apply your knowledge to an unfamiliar context. Tailor your answer accordingly.
Mark-per-point guidance: Most biodiversity questions allocate 1 mark per distinct point. For a 6-mark question on eutrophication, give six separate, clear steps. Don't repeat the same point in different words.
Use data from graphs and tables: Questions often provide information about biodiversity changes or pollution levels. Reference specific values from the data ("the number of species decreased from 15 to 3") to support your explanations and gain marks.
Practice extended response questions: Biodiversity topics frequently appear as 4-6 mark questions requiring detailed, structured answers. Practice writing clear sequences with correct terminology under timed conditions.
Quick revision summary
Human activities including pollution, deforestation, and peat extraction reduce biodiversity by destroying habitats and disrupting ecosystems. Water pollution causes eutrophication through excess nutrients leading to algal blooms and oxygen depletion. Global warming shifts climate zones faster than species can adapt. Conservation strategies include captive breeding programmes, habitat protection and regeneration, reintroduction programmes, and reducing waste and pollution. Sustainable development and international cooperation are essential for maintaining biodiversity. Understanding the detailed sequences of processes like eutrophication and being able to evaluate different conservation methods are key exam skills.