B22: Human Impact on the Environment
Biodiversity, pollution and sustainability
📋 Key Concepts
Human Impact: Human activities such as deforestation, pollution and burning fossil fuels are reducing biodiversity and contributing to global warming. Conservation and sustainable practices are essential to protect ecosystems for future generations.
Key Terms
- biodiversity
- deforestation
- peat destruction
- global warming
- greenhouse effect
- greenhouse gases
- pollution
- conservation
- sustainable development
- recycling
- quadrat
- transect
- random sampling
📝 Biodiversity
Biodiversity: The variety of different species of living organisms in an ecosystem. High biodiversity means many different species are present. Biodiversity is important because it makes ecosystems more stable and provides resources (food, medicines, raw materials).
Why biodiversity matters:
- Ecosystems with high biodiversity are more stable and resilient to changes
- Many medicines are derived from plants and other organisms — losing species means losing potential cures
- Biodiversity provides food resources, raw materials and genetic variation for crop breeding
- Organisms are interdependent — losing one species can affect the whole food web
Example 1
Explain why a reduction in biodiversity could affect food security.
Solution:
Reduced biodiversity means fewer species available for food. Many crops rely on a small number of varieties, making them vulnerable to disease (e.g. potato famine). With fewer species, if one crop fails, there may be no alternative food source. Also, fewer species means less genetic variation for breeding disease-resistant or climate-adapted crops in the future.
📝 Deforestation
Deforestation: The large-scale removal of trees from forests. Trees are cut down for timber, to clear land for farming (crops and cattle), and for building developments.
Consequences of deforestation:
- Less CO₂ absorbed: Fewer trees means less photosynthesis, so less CO₂ is removed from the atmosphere, contributing to global warming
- More CO₂ released: Burning felled trees or decomposing wood releases stored carbon as CO₂
- Reduced biodiversity: Forest habitats are destroyed, leading to loss of species and extinction
- Soil erosion: Tree roots hold soil together; without trees, soil is washed away by rain, leading to flooding and loss of fertile land
- Disruption of the water cycle: Less transpiration means less rainfall in the region
Example 2
Explain how deforestation in tropical rainforests contributes to global warming.
Solution:
Deforestation reduces the number of trees available to absorb CO₂ through photosynthesis, so less CO₂ is removed from the atmosphere. When trees are cut down and burned or left to decompose, the carbon stored in their wood is released as CO₂. Both effects increase atmospheric CO₂ concentration, which enhances the greenhouse effect and contributes to global warming.
📝 Peat Destruction
Peat bogs are wetland areas where dead plant material has accumulated over thousands of years without fully decomposing (due to acidic, anaerobic conditions). Peat is a major store of carbon.
Destruction of peat bogs:
- Peat is dug up and sold as compost for gardens and agriculture
- Peat is burned as a fuel in some countries
- When peat bogs are drained and exposed to air, decomposers can break down the peat aerobically, releasing large amounts of CO₂
- Burning peat also releases CO₂ directly into the atmosphere
- Peat bog destruction destroys the habitat of many specialised organisms, reducing biodiversity
📝 Global Warming
The greenhouse effect: Greenhouse gases (CO₂ and methane) in the atmosphere trap heat from the Sun, preventing it from escaping back into space. This keeps the Earth warm enough for life. However, human activities are increasing the concentration of greenhouse gases, causing the Earth to warm more than normal (global warming).
Consequences of global warming:
- Rising sea levels: As the Earth warms, ice caps and glaciers melt, adding water to the oceans. Water also expands as it warms. This can cause flooding of low-lying land and coastal areas.
- Habitat loss: Organisms adapted to cold conditions (e.g. polar bears) lose their habitat as ice melts
- Migration and distribution changes: Species may need to move to cooler areas to survive, changing the distribution of organisms. Some species cannot migrate fast enough.
- Changes in weather patterns: More extreme weather events (droughts, floods, storms) affect agriculture and ecosystems
- Biodiversity loss: Species unable to adapt or migrate may become extinct
Example 3
Explain how increasing CO₂ concentration in the atmosphere leads to global warming.
Solution:
CO₂ is a greenhouse gas. It absorbs heat (infrared radiation) that the Earth's surface radiates back towards space, and re-radiates some of it back towards the Earth. As CO₂ concentration increases due to human activities (burning fossil fuels, deforestation), more heat is trapped in the atmosphere. This enhanced greenhouse effect causes the average global temperature to rise, which is global warming.
📝 Pollution
| Type of Pollution | Sources | Effects |
|---|---|---|
| Landfill waste | Household and industrial waste buried in the ground | Takes up land space; toxic chemicals can leak into soil and groundwater; produces methane as waste decomposes anaerobically |
| Water pollution | Sewage, fertilisers (nitrates and phosphates), chemicals from industry | Eutrophication (algal blooms from excess fertilisers → oxygen depletion → fish death); contamination of drinking water; harm to aquatic organisms |
| Air pollution | Smoke from factories and vehicles; sulfur dioxide from burning fossil fuels | Acid rain (formed when SO₂ dissolves in rainwater) damages trees, acidifies lakes, erodes buildings; respiratory problems in humans |
📝 Conservation and Sustainability
Conservation: Protecting ecosystems and the species within them. Strategies include:
- Protecting habitats (e.g. nature reserves, national parks, marine conservation zones)
- Captive breeding programmes for endangered species (breeding in zoos, then reintroducing to the wild)
- Seed banks (storing seeds of rare plants to prevent extinction)
- International agreements (e.g. CITES — regulates trade in endangered species)
- Reducing waste, recycling and reusing materials
- Education programmes to raise awareness
Sustainable development: Meeting the needs of the present generation without compromising the ability of future generations to meet their own needs. This means using resources at a rate that allows them to be replenished.
Ways to be more sustainable:
- Reduce use of fossil fuels — switch to renewable energy (solar, wind, hydroelectric)
- Recycle and reuse materials (reduces landfill waste and need for raw materials)
- Use biodegradable or compostable packaging
- Reduce deforestation — use sustainable forestry (plant new trees for each one cut down)
- Reduce peat use in compost — use peat-free alternatives
- Control pollution with legislation and technology
Example 4
Explain why recycling helps protect the environment and conserve resources.
Solution:
Recycling reduces the amount of waste sent to landfill, which reduces soil and water pollution and reduces methane emissions from decomposing waste. It also reduces the need to extract raw materials (e.g. mining for metals, cutting down trees for paper), which reduces habitat destruction and loss of biodiversity. Recycling uses less energy than making products from raw materials, which reduces CO₂ emissions from fossil fuel burning.
📝 Field Investigations
Quadrats: Square frames (usually 0.5 m × 0.5 m or 1 m × 1 m) used to sample the distribution and abundance of organisms in an area. Used for plants and slow-moving animals.
Random sampling using quadrats:
- Divide the study area into a grid using two tape measures at right angles
- Use a random number generator to select coordinates
- Place the quadrat at each coordinate
- Count the organisms inside the quadrat (or estimate percentage cover)
- Repeat many times and calculate a mean
- Population size = mean count per quadrat × (total area ÷ quadrat area)
Transects: A line (tape measure) placed across a habitat to study how the distribution of organisms changes along an environmental gradient (e.g. from a field into a woodland). Place quadrats at regular intervals along the transect and record the organisms found.
Example 5
A student wants to estimate the population of dandelions in a 100 m² field. They place a 0.5 m × 0.5 m quadrat 10 times at random positions and count: 3, 5, 2, 4, 6, 3, 5, 4, 3, 5 dandelions. Estimate the total population.
Solution:
Mean count per quadrat = (3+5+2+4+6+3+5+4+3+5) ÷ 10 = 40 ÷ 10 = 4
Quadrat area = 0.5 × 0.5 = 0.25 m²
Number of quadrats that fit in the field = 100 ÷ 0.25 = 400
Estimated population = 4 × 400 = 1,600 dandelions
❓ Practice Questions
Q1: Define biodiversity and explain why it is important.
Q2: Explain three consequences of deforestation.
Q3: Describe the greenhouse effect and explain how human activities are increasing global temperatures.
Q4: Give three strategies for conservation and explain how each helps protect biodiversity.
Q5: Higher A student uses a 1 m × 1 m quadrat to estimate the population of buttercups in a 500 m² field. The mean number of buttercups per quadrat from 20 random samples is 8. Estimate the total population of buttercups in the field.
✅ Answers
- Biodiversity is the variety of different species of living organisms in an ecosystem. It is important because: ecosystems with high biodiversity are more stable; many medicines come from organisms; it provides food resources and raw materials; organisms are interdependent so losing one species can affect the whole food web.
- Three consequences of deforestation: (1) Less CO₂ is absorbed (fewer trees for photosynthesis), contributing to global warming. (2) Burning or decomposing felled trees releases CO₂. (3) Habitat destruction reduces biodiversity and can lead to species extinction. (4) Soil erosion increases (no tree roots to hold soil), leading to flooding and loss of farmland. (5) Disruption of the water cycle (less transpiration → less rainfall).
- The greenhouse effect is where greenhouse gases (CO₂ and methane) in the atmosphere absorb and re-radiate heat back to Earth, keeping the planet warm. Human activities (burning fossil fuels, deforestation, farming) are increasing greenhouse gas concentrations. More greenhouse gases trap more heat, enhancing the greenhouse effect and causing global temperatures to rise (global warming).
- Any three from: (1) Protecting habitats (nature reserves, national parks) — preserves the environment where species live, preventing habitat loss. (2) Captive breeding programmes — breed endangered species in zoos to increase numbers, then reintroduce to the wild. (3) Seed banks — store seeds of rare plants to prevent extinction and allow future replanting. (4) Recycling and reducing waste — reduces pollution and habitat destruction from resource extraction. (5) International agreements (CITES) — regulate trade in endangered species to prevent over-exploitation.
- Quadrat area = 1 × 1 = 1 m². Mean count per quadrat = 8. Number of quadrats that fit in the field = 500 ÷ 1 = 500. Estimated population = 8 × 500 = 4,000 buttercups.
🎯 Exam Tips
- Biodiversity = variety of species, NOT number of individual organisms
- When discussing deforestation, always link it to BOTH increased CO₂ (less photosynthesis + burning) AND reduced biodiversity (habitat loss)
- Peat destruction releases CO₂ because draining peat bogs allows aerobic decomposition to occur
- The greenhouse effect is NATURAL and necessary — human activities ENHANCE it
- Global warming consequences: rising sea levels, habitat loss, migration changes, extreme weather, biodiversity loss
- Eutrophication: fertilisers → algal blooms → oxygen depletion → fish death — learn this sequence
- Sustainable development = meeting present needs WITHOUT compromising future generations
- For quadrat calculations: population = mean per quadrat × (total area ÷ quadrat area)
- Random sampling avoids bias — use random number generators for coordinates
- Transects are used to study changes along a gradient (not for estimating total population)
🔬 Required Practical
Required Practical: Quadrats and Transects
Aim: Investigate the effect of an environmental factor on the distribution of a species using quadrats along a transect.
Method: 1. Choose a transect line across an environmental gradient (e.g. from a shaded area into full light, or from dry to damp ground). 2. Lay a tape measure along the transect. 3. Place a 0.5 m × 0.5 m quadrat at regular intervals (e.g. every 2 m) along the transect. 4. Record the number of the target species in each quadrat (or estimate percentage cover). 5. Also measure the environmental factor (e.g. light intensity using a light meter) at each quadrat position. 6. Repeat with additional transect lines for reliability.
Variables: IV: distance along transect (environmental gradient), DV: number/percentage cover of species, Control: quadrat size, species counted, time of day
🔢 Maths Skills
Mathematical Skills
You need to calculate population sizes from quadrat data, use random number generators for sampling coordinates, and interpret data on CO₂ concentrations and temperature changes over time.
Maths Example
A student uses a 0.5 m × 0.5 m quadrat to sample a 250 m² field. The mean count of a plant species is 3 per quadrat. Estimate the total population.
Quadrat area = 0.5 × 0.5 = 0.25 m². Number of quadrats in field = 250 ÷ 0.25 = 1,000. Population = 3 × 1,000 = 3,000 plants
Maths Example 2
Global CO₂ emissions from fossil fuels were 5 GtC/yr in 1950 and 10 GtC/yr in 2020. Calculate the percentage increase.
Percentage increase = ((10 − 5) ÷ 5) × 100 = 100% increase
⚠️ Common Misconceptions
Watch Out!
1. Wrong: Biodiversity means the total number of organisms Correct: Biodiversity means the VARIETY of different species — an area with 100 of one species has lower biodiversity than an area with 10 each of 10 species
2. Wrong: The greenhouse effect is entirely caused by humans Correct: The greenhouse effect is NATURAL and keeps Earth warm enough for life — human activities are ENHANCING it, causing global warming
3. Wrong: Deforestation only affects the area where trees are cut down Correct: Deforestation affects global CO₂ levels (less photosynthesis + burning releases CO₂), disrupts the water cycle (less transpiration → less rainfall), and reduces biodiversity globally
4. Wrong: Eutrophication is caused by oil pollution Correct: Eutrophication is caused by excess NITRATES and PHOSPHATES from fertilisers — these cause algal blooms that block light and deplete oxygen when they decay
✍️ 6-Mark Question
Extended Answer
6 marks: Explain how human activities are reducing biodiversity and describe how conservation can help protect it.
Human activities are reducing biodiversity in several ways. Deforestation destroys forest habitats, removing the homes of many species and causing extinction. Burning felled trees or leaving them to decompose releases CO₂, contributing to global warming, which causes habitat loss as ice caps melt and climate zones shift. Peat bog destruction releases stored carbon as CO₂ and destroys the habitat of specialised species. Pollution also reduces biodiversity — for example, fertilisers running into rivers cause eutrophication: algal blooms block sunlight, plants die, decomposers use up oxygen, and fish and other organisms die. Over-exploitation of resources such as overfishing reduces species numbers. Conservation strategies can protect biodiversity: nature reserves and marine conservation zones protect habitats; captive breeding programmes increase numbers of endangered species; seed banks preserve genetic diversity; recycling reduces the need for raw material extraction, reducing habitat destruction; and international agreements like CITES regulate trade in endangered species. Sustainable development ensures resources are used at a rate that allows them to replenish, so future generations can also meet their needs.
Mark scheme: 1 mark for deforestation reducing biodiversity; 1 mark for global warming effects; 1 mark for pollution/eutrophication; 1 mark for a specific conservation strategy explained; 1 mark for a second conservation strategy explained; 1 mark for linking conservation to maintaining biodiversity for future generations
📊 AO3: Analyse & Evaluate
Analysis and Evaluation
Data was collected on CO₂ concentration and global average temperature over the past 60 years:
- 1960: CO₂ = 317 ppm, Temperature anomaly = +0.00°C
- 1980: CO₂ = 339 ppm, Temperature anomaly = +0.26°C
- 2000: CO₂ = 369 ppm, Temperature anomaly = +0.42°C
- 2020: CO₂ = 414 ppm, Temperature anomaly = +1.02°C
(a) Describe the relationship shown by the data.
(b) A politician argues that "temperature has always changed naturally, so human activity is not the cause." Evaluate this claim.
(c) Suggest two ways to reduce the rate of increase in atmospheric CO₂ and explain how each works.
Answers: (a) As CO₂ concentration has increased from 317 to 414 ppm over 60 years, the temperature anomaly has also increased from 0 to +1.02°C. This shows a positive correlation between CO₂ concentration and global temperature. (b) While natural climate variation does occur, the RATE of temperature increase since the mid-20th century is unprecedented. The rapid rise in CO₂ coincides with increased fossil fuel burning and deforestation. The greenhouse effect is well-established scientifically — CO₂ absorbs infrared radiation and re-radiates it, warming the atmosphere. The politician's claim does not account for the speed and scale of current changes compared to natural cycles. (c) 1. Reduce fossil fuel use / switch to renewables — burning fewer fossil fuels releases less CO₂ into the atmosphere. 2. Reduce deforestation / plant more trees — more trees absorb more CO₂ through photosynthesis, removing it from the atmosphere.
📝 Exam Questions by Topic
🎬 Video Resources
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