Pearson Edexcel International A Level Biology: Climate Change, Evolution, Speciation and Sustainable Resources (YBI11) – Revision Notes

These are condensed notes for statements 5.16 to 5.26 of Topic 5 in the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2, including Core Practical 12. Topics 1 to 4 are International AS (IAS) and Topics 5 to 8 are International A2 (IA2), so this is A2 content. There are no tiers. For full explanations go to the study guide, then test yourself with the practice questions. The course hub, printable checklist and free diagnostics show where this fits.

5.16 Evidence for climate change

Evidence	What it records	Reliability point
Ice cores	Carbon dioxide in trapped air bubbles; deeper means older	Direct sample of past air
Atmospheric measurements	Recent carbon dioxide concentration	Direct and accurate
Temperature records	Thermometer data	Direct, but limited in length
Pollen in peat bogs	Plant community at each depth, so past climate	Needs dating; assumes tolerances unchanged
Dendrochronology	Annual ring width: wide in good years, narrow in poor	One tree may reflect disease, not climate

• Peat is waterlogged, acidic and low in oxygen, so decay is slow and pollen is preserved. Pollen shape identifies the species.
• Correlation means the variables change together. Causation means one change produces the other. To argue causation you need a mechanism, repeated independent evidence and control of other variables.

Reminder (rings). Rings of 1.4, 1.6, 0.6 and 1.8 mm have a mean of 5.4 ÷ 4 = 1.35 mm. The 0.6 mm ring is the poor year: cold, dry or disease. Compare many trees before inferring climate.

5.17 Greenhouse effect and anthropogenic causes

Method in steps:

1. Sunlight, mostly short-wavelength, reaches the surface.
2. The surface emits longer-wavelength infrared.
3. Greenhouse gases absorb infrared and re-emit it, some back to the surface.
4. More greenhouse gas means more heat retained.

Gas	Main human sources
Carbon dioxide	Fossil fuel combustion, deforestation
Methane	Livestock, rice paddies, landfill
Nitrous oxide	Fertiliser use

Anthropogenic means caused by humans. The greenhouse effect itself is natural; the human contribution is the enhancement.

5.18 Carbon cycle and reducing carbon dioxide

• Inputs: respiration, combustion, decomposition. Removal: photosynthesis, and storage in wood, soil, peat and oceans.
• Cut inputs: renewable energy, less fossil fuel, capture of methane and of carbon dioxide from power stations.
• Increase removal: reforestation, protecting forests, peat and wetlands.

Quick calculation. A scheme plants 100 ha and the trees store 5 tonnes of carbon per hectare per year (data supplied). Carbon stored = 100 × 5 = 500 tonnes. Mass of carbon dioxide = 500 × 44 ÷ 12 = 1,830 tonnes (3 s.f.).

5.19 Extrapolation and models

(i) Extrapolation	(ii) Limitations of models
Extend a trend beyond measured data	Many variables and feedback loops
Used in models to predict future climate	Assumptions about future emissions
Rate = change ÷ time	Incomplete past data
Predicted value = last value + rate × years	Trend may change, so predictions have uncertainty

Reminder. If the concentration rises from 380 to 420 ppm in 10 years, the rate is 40 ÷ 10 = 4 ppm per year, and 20 years on the predicted value is 420 + 80 = 500 ppm, provided the rate stays constant.

5.20 Effects of climate change

• Distribution: species shift towards the poles or to higher altitude.
• Development and lifecycles: faster enzyme-controlled development; earlier hatching, flowering, migration.
• Seasonal mismatch: a predator and its food respond at different rates, so timing no longer overlaps.
• Rainfall change: drought lowers plant growth; flooding damages roots.

5.21 Temperature, enzymes and Q₁₀

• Rate rises with temperature: more kinetic energy, more frequent and more energetic collisions.
• Above the optimum: hydrogen bonds break, the tertiary structure and active site change, the enzyme denatures.
• Q₁₀ = rate at (T + 10) ÷ rate at T. For any interval: Q₁₀ = (R₂ ÷ R₁)^(10 ÷ (T₂ − T₁)).
• Impact: plant, animal and microorganism metabolism follows environmental temperature, so growth and development speed up, then fail above the optimum.
• Rate can be taken as 1 ÷ time taken.
• Q₁₀ close to 2 means the rate doubles for each 10 °C rise. Q₁₀ is not valid across the optimum, where denaturation lowers the rate.

Reminder. Rates 3 at 20 °C and 12 at 40 °C: interval 20 °C, so Q₁₀ = (12 ÷ 3)^(10/20) = 4^0.5 = 2.0.

Exam link. When a question gives a graph of rate against temperature, describe the rise, the peak and the fall, and explain each part with enzyme action. Quote values from the axes.

5.22 Core Practical 12

Aim: the effect of temperature on development, such as seedling growth rate or brine shrimp hatching, with ethical use of organisms.

Item	Detail
Independent variable	Temperature (water baths or incubators, at least five values)
Dependent variable	Number or percentage hatched in a set time; or seedling length per day
Controlled variables	Number and batch of organisms, volume and salinity, light, time, pH
Repeats	At least three per temperature, then a mean
Ethics	Smallest number needed, suitable conditions, no avoidable suffering, humane disposal
Check	Temperature held steady with a thermometer in each bath

Percentage hatched = hatched ÷ eggs × 100. For example, 36 hatched from 60 eggs is 60%. Hatching falls above the optimum because enzymes denature.

5.23 Evolution

Evolution is a change in allele frequency in a population over generations.

1. Mutation produces a new allele, at random.
2. Variation and overproduction of offspring mean not all survive.
3. A selection pressure favours individuals with the advantageous allele.
4. They survive, reproduce and pass on the allele, so its frequency rises.

Allele frequency = number of copies of the allele ÷ total number of alleles. Reminder: 20 copies among 200 alleles is 0.10. If later there are 70 copies among 200, the frequency is 0.35, so the population has evolved.

5.24 Isolation and speciation

	Allopatric	Sympatric
Location	Separate areas	Same area
Cause	Geographical barrier	Behavioural, ecological or seasonal isolation, or polyploidy
Process	Gene flow stops; different mutations and selection; allele frequencies diverge	Same, but isolation arises without a physical barrier
End point	Cannot interbreed to produce fertile offspring: separate species	Same

Exam link. To explain why a population evolved, name the selection pressure and the allele, say what the survivors did, and show the frequency changed across generations.

5.25 Controversial issues

Conclusions can depend on who reaches them. Look at: funding source, vested interests, whether work is peer-reviewed and replicated, selective use of data, and whether values rather than evidence drive the recommended action.

5.26 Reforestation, sustainable resources and biofuels

Approach	Benefit	Limitation
Reforestation	Habitat, carbon storage, less soil erosion	Slow; plantations support less biodiversity
Sustainable forestry	Replanting keeps the supply	Needs regulation
Biofuels	Close to carbon neutral	Land competes with food and forest; fertiliser and machinery energy

Evaluating a source. Ask: who wrote it, who paid for it, what data were used and over what period, was it reviewed by other scientists, and does the conclusion go further than the data?

Must-know distinctions

• Correlation versus causation.
• Weather versus climate.
• Natural greenhouse effect versus enhanced greenhouse effect.
• Mutation (creates alleles) versus natural selection (changes their frequency).
• Gene flow reduced by a barrier (allopatric) versus without one (sympatric).

Quick self-test

1. Why is peat good at preserving pollen?
2. The carbon dioxide concentration rises from 280 to 415 ppm. Calculate the percentage increase.
3. An enzyme-controlled rate is 4 units at 20 °C and 9 units at 30 °C. Calculate Q₁₀.
4. Explain why infrared, not visible light, is the radiation that greenhouse gases absorb.
5. Give two reasons why extrapolating a trend may be unreliable.
6. State two ways in which temperature affects an enzyme.
7. Why are brine shrimp eggs counted in several tubes at each temperature?
8. Give one ethical precaution for Core Practical 12.
9. What term describes a change in allele frequency across generations?
10. Distinguish allopatric from sympatric speciation.
11. Give two reasons why biofuels are not fully carbon neutral.
12. Why might a report funded by an industry body need checking?

Answers

1. Waterlogged, acidic, low oxygen, so decay is slow.
2. (415 − 280) ÷ 280 × 100 = 48.2%.
3. 9 ÷ 4 = 2.25, about 2.3.
4. The surface is cooler than the Sun, so it emits longer-wavelength infrared; the gases absorb infrared, while Sun’s shorter wavelengths pass through.
5. The trend may change; many variables and feedback loops interact; assumptions about emissions may be wrong.
6. Increasing temperature increases kinetic energy and collisions, so rate rises; above the optimum it denatures the enzyme.
7. To find a mean and spot anomalies, increasing reliability.
8. Use the smallest number of organisms, or dispose of them humanely.
9. Evolution.
10. Allopatric: geographical barrier separates populations. Sympatric: speciation within the same area.
11. Fertilisers and machinery use fossil fuel energy; land use change releases stored carbon.
12. The funder may have an interest, so data or interpretation may be selective.

Where marks are usually lost

• Writing “correlation proves” instead of “supports” and not naming a mechanism.
• Saying greenhouse gases “trap heat” without stating that infrared is absorbed and re-emitted.
• Giving Q₁₀ without showing rate as a ratio, or forgetting the exponent when the interval is not 10 °C.
• Quoting units for a ratio (Q₁₀ has none).
• Omitting control variables, repeats or the number of eggs in Core Practical 12.
• Saying individuals evolve, or that mutation happens because an organism needs it.
• Describing speciation without isolation and the end point, interbreeding to give fertile offspring.
• Calling biofuels carbon neutral without a limitation.

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, February 2021, Topic 5, statements 5.16 to 5.26, published by Pearson Education Limited.