Environmental Biology
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Environmental Biology
Summary — What This Chapter Covers
1 · Evidence for Climate Change
1Why "climate" isn't just "weather"
Weather is what's happening outside right now — rainy today, sunny tomorrow. Climate is the average pattern of weather over decades. Climate change means that long-term average has genuinely shifted, not just that we had one hot summer.
Today, "climate change" almost always refers to global warming — the rise in average global temperature caused by human activity.
2The four lines of evidence
Think of these as four independent "witnesses" that all tell a consistent story. That's what makes the case so strong — it's not just one dataset.
🧊 Ice cores (atmospheric CO₂): As snow falls and compacts into ice over thousands of years, it traps tiny air bubbles. The deeper you drill, the older the air. By measuring CO₂ in these bubbles, scientists have built a CO₂ record stretching back hundreds of thousands of years. Before industrialisation, CO₂ peaked around 300 ppm. Today it's above 400 ppm — higher than at any point in that record.
🌡️ Thermometer records: Direct air temperature measurements from the mid-1800s onward show an overall upward trend in global average temperature, even though there are short dips along the way (e.g. some cooling in the 1940s–1970s doesn't cancel the long-term trend).
🌿 Pollen in peat bogs: Peat forms when dead plant matter partially decomposes under waterlogged, acidic, low-oxygen conditions and compacts in layers — like a sedimentary "photo album," with the oldest layers at the bottom. Pollen grains are unique to each plant species and get trapped in these layers. By identifying which pollen appears at which depth, scientists can reconstruct which plants were growing at any point in time — and since different plants favour different climates, this tells us about past climate.
🌳 Dendrochronology (tree rings): Trees grow a new ring every year — a pale, wide ring in spring/summer (fast growth) and a dark, narrow ring in autumn (slow growth). Warmer years = wider rings, because growth is faster. Counting and measuring rings in old tree trunks gives a year-by-year climate record going back centuries.
2 · Anthropogenic Climate Change
1The greenhouse effect (a good thing, gone too far)
Sunlight hits Earth's surface and gets radiated back out as heat (infrared radiation). A greenhouse gas absorbs that outgoing heat and re-emits it in all directions — some of it back down towards Earth — trapping warmth in the atmosphere, just like the glass roof of a greenhouse traps heat inside.
This is not inherently bad — without any greenhouse effect at all, Earth would swing wildly in temperature like Mars does (20°C down to −153°C). The problem is that human activity is adding extra greenhouse gas, trapping extra heat, and warming the planet beyond its natural balance.
Global warming = the rise in temperature caused mainly by humans intensifying the greenhouse effect.
Climate change = the broader, long-term shifts in rainfall, wind, and temperature patterns that result from global warming.
2Carbon dioxide: where does it come from?
- Burning fossil fuels (factories, transport, homes) since the industrial revolution (late 1700s)
- Damaging carbon sinks — natural carbon stores like trees, soils, peat bogs, and oceans — through deforestation, soil degradation, peat harvesting, and ocean warming
3Methane: a smaller gas, a bigger punch per molecule
Methane (CH₄) is a simple hydrocarbon, the main component of natural gas. Sources include:
- Guts of ruminant mammals (cattle) — intensive farming has massively increased this
- Landfill sites — decomposing organic waste
- Extraction of fossil fuels underground
- Anaerobic bacteria in waterlogged rice paddies
- Melting permafrost (ground frozen all year round) — a dangerous feedback loop, since warming releases stored methane, which causes more warming
3 · The Carbon Cycle & Environmental Management
1Pools and fluxes — the two things you must be able to name
Every carbon cycle diagram is really just two types of thing:
- Carbon pools = where carbon is stored (atmosphere, oceans, biomass, fossil fuels)
- Carbon fluxes = the processes that move carbon between pools (photosynthesis, respiration, feeding, combustion, decomposition, dissolving)
2Using the carbon cycle to manage the climate
Once you understand the cycle as a diagram of arrows in and out of pools, environmental management becomes obvious: you either slow the arrows going into the atmosphere, or speed up the arrows taking carbon out.
- Reduce inflow: burn less fossil fuel, burn less biomass, disturb carbon sinks (soils, peat) less
- Increase outflow: plant more trees to raise the rate of photosynthesis
4 · Models for Predicting Climate Change
1Extrapolation
Extrapolating means extending a trend from existing data to make a prediction about the future — essentially, continuing the line on the graph past the data you actually have. The IPCC (Intergovernmental Panel on Climate Change) uses this to build models under different future scenarios:
- If humans cut fossil fuel use immediately → warming might be limited to around +2°C
- If nothing changes → warming could exceed +4°C
2Why models have limits (this is a favourite exam topic)
- We don't know which emissions scenario humans will actually follow
- We don't know if future carbon-capture technology will work
- We don't know exactly how much a given gas concentration will raise temperature
- Climate is a complex system — many interacting factors make prediction hard
- Tipping points could cause sudden acceleration (e.g. melting permafrost suddenly releasing large amounts of methane)
- Unpredictable natural events (volcanic eruptions releasing ash that reflects sunlight) could cool things unexpectedly
5 · How Climate Change Affects Species
1The chain of cause and effect
It helps to see this as a chain: more greenhouse gas → more heat trapped → changed climate patterns → direct impacts on species. Let's break down the impacts:
🌍 Distribution shifts: Species move toward the poles or to higher altitudes to stay in their preferred temperature range. Risk: they may compete with (or out-compete) species already living there, reducing biodiversity. Slow-moving species (especially plants) may not be able to shift fast enough and could go extinct.
💧 Water availability: Species relying on seasonal rains (e.g. some desert plants) suffer if rainfall patterns change or seasonal events stop happening reliably.
📅 Seasonal cycle mismatches: Flowering and breeding are happening earlier. This can desynchronise food chains — e.g. a migratory bird arrives expecting a peak in insect abundance, but the insects already peaked earlier due to warmer spring temperatures, so the bird's food source has moved on.
🧊 Ice and sea level: Polar ice and glaciers are retreating, threatening water supplies dependent on glacial melt. Sea levels are rising due to (a) thermal expansion of warmer water and (b) melting polar ice — putting coastal humans and wildlife at flood risk.
6 · The Effect of Temperature on Enzyme Reactions
1Why this links to climate change
Almost every biological process depends on enzymes — and enzymes are exquisitely sensitive to temperature. As global temperatures shift, enzyme-driven processes across all of biology shift with them. This is the molecular-level reason climate change affects living things.
2Below the optimum: slow and steady
Lower temperature → molecules have less kinetic energy → they move more slowly → fewer successful collisions between substrate and active site → fewer enzyme-substrate complexes form → reaction proceeds more slowly. Collisions also happen with less force, making bond formation/breakage less likely.
3Above the optimum: fast, then catastrophic
Higher temperature → more kinetic energy → faster movement → more frequent, more forceful collisions → faster reaction rate — up to a point. Beyond the optimum, the increased vibration puts strain on the weak hydrogen and ionic bonds holding the enzyme's tertiary structure together. These bonds break, the enzyme's shape changes permanently, and the active site is no longer complementary to the substrate. This is denaturation — and it's irreversible.
4The temperature coefficient, Q₁₀
5Real-world consequences of shifting temperatures
- Cyanobacteria photosynthesise faster in warmer water (more rubisco activity), increasing harmful algal blooms
- Photorespiration increases at high temperatures — this competing reaction (also using rubisco) actually slows down photosynthesis, reducing crop yields as the world warms
- Fish eggs can develop more slowly at higher temperatures; extreme fluctuations reduce hatching rates in some invertebrates
- In species like alligators, the temperature during egg incubation determines the sex of the offspring — so warming can skew sex ratios in a population
7 · Core Practical 12: Effect of Temperature on Development
1Method A — Seedling growth rate
- Plant identical seeds in several pots of compost, all kept in identical conditions initially
- Allow germination and a few initial days of growth
- Measure the initial height of every seedling
- Place each pot in an incubator at a different temperature for the same duration (e.g. 5 days), keeping all other variables constant (soil moisture, pH, light intensity)
- Measure the final height of every seedling
- Calculate average growth rate
2Method B — Brine shrimp hatching rate
- Place equal numbers of brine shrimp eggs (e.g. 40) into water baths at different temperatures, using non-chlorinated water with 2g salt per 100 cm³
- Keep everything else constant (egg age, water pH, volume, dissolved oxygen)
- Count hatched shrimp at regular time intervals (e.g. every 12 hours)
- Calculate hatching rate
3The pattern in both results
Both growth rate and hatch rate increase with temperature up to around 25°C, then decrease beyond that. This mirrors the enzyme rate-vs-temperature curve exactly — because both growth and hatching are ultimately controlled by enzyme-catalysed metabolic reactions, which slow down past their optimum due to denaturation.
8 · Mutation, Natural Selection & Evolution
1Defining evolution precisely
2The five-step natural selection chain
This exact sequence is one of the most commonly examined processes in biology — learn it as a chain, not a list, so you can apply it to any scenario:
- Variation exists in a population (from mutation, meiosis, random fertilisation)
- Selection pressures act on the population (predation, competition, disease, etc.)
- Individuals with advantageous alleles are more likely to survive and reproduce
- These advantageous alleles are passed on to offspring
- The advantageous allele increases in frequency in the population over generations
3Worked example: rabbits and fur colour
Variation in fur colour exists (brown allele vs white allele). Foxes act as a selection pressure. Brown rabbits camouflage better, so are more likely to survive and reproduce → they pass on the brown allele more often → over many generations, the frequency of the brown allele increases in the population, while the white allele frequency decreases.
9 · Isolation & Speciation
1What speciation actually requires
2Allopatric speciation — separated by geography
"Allo" = other/different, "patric" = homeland — different homelands. This is the most common type. A physical barrier (mountain range, river, ocean, even a motorway) splits one population into two, stopping gene flow completely.
Worked example — trees split by a new mountain range:
- A single tree population lives across a mountainous habitat
- A new mountain range forms, physically dividing the population into two
- The barrier stops interbreeding → no gene flow between the two groups
- Each population faces slightly different environments → different alleles become advantageous in each
- Different alleles increase in frequency in each population (natural selection + genetic drift)
- Over thousands of years, the two populations diverge enough that they can no longer interbreed to produce fertile offspring → two separate species now exist
3Sympatric speciation — separated without geography
"Sym" = same, "patric" = homeland — same homeland, no physical barrier at all. Instead, a random mutation/change in phenotype prevents interbreeding directly. Three common mechanisms:
- Seasonal changes: different mating/flowering times mean reproductive timing no longer overlaps
- Mechanical changes: changes in genitalia physically prevent successful mating
- Behavioural changes: changes in courtship behaviour mean individuals can no longer attract mates from the other group
The two populations can still live in the same physical location — the isolation is reproductive, not geographic.
Sympatric = same location, but a phenotype change stops successful interbreeding.
10 · Contentious Issues in Environmental Science
1The scientific consensus
There is a strong consensus among scientists that (1) rising greenhouse gases cause global warming, and (2) human activity is the direct cause of that rise. But some individuals — including a small number of scientists — dispute that the correlation between fossil fuel burning and warming is causal.
2How to evaluate any climate claim like a scientist
Ask about the evidence: Does the claim address all the data, or cherry-pick convenient parts? Is the data reliable? Does it come from multiple independent studies? Is it statistically significant?
Ask about the source: Does the person making the claim have a financial or political interest in a particular outcome? An oil company scientist, a passionate conservationist, and a renewable energy employee could all have biases pulling in different directions — that doesn't make them automatically wrong, but it means their claims need extra scrutiny.
| Claim (often used to dismiss human causation) | Scientific evaluation |
|---|---|
| "CO₂ has changed naturally throughout Earth's history — this is just another natural cycle" | Current CO₂ levels are higher than at any point in Earth's recorded history, suggesting natural causes alone cannot explain it |
| An oil company said the evidence linking fossil fuels to climate change was "inconclusive" | Oil companies have a financial interest in people continuing to burn fossil fuels, so may be motivated to downplay the evidence |
| "Temperatures cooled slightly at some points in the last 50 years, so warming has stopped" | CO₂ is not the only factor influencing temperature in any given year; short-term fluctuations don't override the strong overall long-term trend |
11 · Examples of Sustainable Conservation
1The two-lever approach
Just like environmental management of the carbon cycle earlier, sustainability boils down to two levers: reduce carbon emissions and increase carbon removal.
2Reducing emissions — biofuels vs renewables
| Option | Pros | Cons |
|---|---|---|
| Biofuels (from recently living plant biomass) | Cheaper than oil; arguably "carbon neutral" (only releases recently-absorbed carbon, not ancient stored carbon); renewable, can be regrown quickly | Still releases CO₂ when burned; land used to grow them could instead grow food; growing them often destroys other habitats (e.g. rainforest) — bad for biodiversity; cutting mature trees for land reduces photosynthesis |
| Wind / Solar / Geothermal / Tidal | Technology advancing fast, getting cheaper; releases no CO₂ during generation | No single source is reliable everywhere: geothermal needs volcanic activity nearby, solar needs sunshine hours, wind needs consistent wind speeds (and can affect birds/bats and landscape views), tidal only works near coasts |
3Increasing carbon removal
Advanced carbon capture technology does not yet exist at scale — so for now, we rely on the mechanism nature already gave us: photosynthesis.
- Stopping deforestation — preserves existing carbon-absorbing capacity
- Reforestation — planting new trees; mature trees store huge amounts of carbon in their biomass
Example: Costa Rica now plants seven times more trees than it cuts down — but this required significant government investment through benefits to landowners.
What to Memorise
These are the facts, terms, and formulas that should be instantly recallable — no hesitation.
Concepts Checklist
Tick off each concept only once you could explain it out loud to someone else without checking your notes.
Exam Tips — Mark-Scheme Traps to Avoid
- 3 · The Carbon Cycle & Environmental Management
- 8 · Mutation, Natural Selection & Evolution
- 9 · Isolation & Speciation
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