What you need to know
- 5.9–5.10GPP, NPP and trophic-transfer efficiency.
- 5.16–5.19Evidence, greenhouse effectWarming of the Earth’s surface because gases in the atmosphere absorb infrared radiation emitted by the Earth and re-emit some of it back., carbon cycleThe movement of carbon between the atmosphere, organisms, oceans and rocks by photosynthesis, respiration, decomposition and combustion., models.
- 5.20–5.26Biological impact, Q10Temperature coefficient: the rate at (T + 10) °C divided by the rate at T °C., evolution, interests, reforestationPlanting trees where forest has been cut down. and biofuelFuel made from recently living biomass, such as ethanol from sugar cane..
Core Practical 12 has the method page.
By the end, you should be able to…
- Calculate NPP and a transfer efficiency from given kJ values.
- Keep correlationA relationship in which two variables change together. A correlation does not prove that one causes the other., cause and author interest distinct.
- Use Q10 and speciationThe formation of a new species, when populations become reproductively isolated and their gene pools change. language precisely.
Build your understanding
Show the equation
NPP = GPP − R. Efficiency = (energy in next level / energy in previous level) × 100. Q10Temperature coefficient: the rate at (T + 10) °C divided by the rate at T °C. = rate(T+10) / rate(T). Fictional numbers in the questions are labelled as such.
Name the process
photosynthesisThe process in which plants use light energy to make glucose from carbon dioxide and water, releasing oxygen., combustion, infrared absorption, gene flowMovement of alleles between populations when individuals migrate and interbreed., reforestationPlanting trees where forest has been cut down.. A slogan without a process is not a 5C answer.
Make your reasoning visible
Do not dump 5B sampling here
Quadrats belong in 5B unless the question brings them.
Keep 4C calculations in 4C
Hardy–Weinberg is available as a link, not a hidden extra here.
Avoid this misconception
The claim: If a model is uncertain, greenhouse gases do not absorb infrared.
The correction: Model limitation (5.19) is not the same as the absorption mechanism (5.17).
Check your understanding
Try each question before opening the suggested answer.
Check your understanding (continued)
Check your understanding (continued)
Practice question
Retrieval and explanation · suggested answer
GPP = 30 000 kJ m⁻² year⁻¹, R = 11 000 kJ m⁻² year⁻¹. Calculate NPP.
Show suggested answer
NPP = 19 000 kJ m⁻² year⁻¹.
Practice question
Retrieval and explanation · suggested answer
That NPP is 19 000 and herbivores store 1 710 kJ m⁻² year⁻¹. Calculate percentage efficiency.
Show suggested answer
(1 710 / 19 000) × 100 = 9.00%.
Practice question
Retrieval and explanation · suggested answer
Why is NPP, not GPP, the energy available to primary consumers?
Show suggested answer
Herbivores eat producer biomass; plant respiration has already used part of GPP.
Practice question
Retrieval and explanation · suggested answer
Describe how extra carbon dioxide can cause warming.
Show suggested answer
CO₂ is a greenhouse gas that absorbs outgoing long-wave infrared, enhancing the greenhouse effect.
Practice question
Retrieval and explanation · suggested answer
Give one use and one limitation of dendrochronology as climate evidence.
Show suggested answer
Use: annual rings can reconstruct past growing conditions. Limitation: width responds to several factors, or not all trees produce clear annual rings.
Practice question
Retrieval and explanation · suggested answer
Rates 6 and 15 at temperatures 10 °C apart. Calculate Q10.
Show suggested answer
Q10 = 15/6 = 2.5.
Practice question
Retrieval and explanation · suggested answer
How can isolation lead to speciation?
Show suggested answer
Reduced gene flow lets mutation and selection change allele frequencies independently; if fertile offspring can no longer be produced, allopatric or sympatric speciation has occurred.
Practice question
Retrieval and explanation · suggested answer
Give one carbon-cycle method to reduce atmospheric CO₂ and one conservation conflict it can create.
Show suggested answer
Reforestation stores carbon in biomass but uses land that might be food or existing habitat; or biofuels can replace fossil carbon but displace food and wild communities.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Fictional seedling rates: 10 mm day⁻¹ at 16 °C and 9 mm day⁻¹ at 26 °C. A student calculates Q10 = 0.9 and concludes climate change will slow all development. Evaluate.
Show a hint
Which limb of the curve?
Explore the reasoning
Q10 = 9/10 = 0.9 is arithmetically correct but sits on a falling limb, so enzymes may already be denaturing or water stress may be limiting. You cannot generalise to “all development” or to organisms whose optimum is higher. A 5.20 distribution answer still needs rainfall and seasons, not only this pair of numbers.
Recall this lesson
Lesson recall questions
Question 1 of 5: List four types of evidence used to reconstruct past climate or recent climate change.
Evidence for climate change
Practice question
Retrieval and explanation · suggested answer
List four types of evidence used to reconstruct past climate or recent climate change.
Lesson: 5C 5: Looking at the Evidence
Try this from memory first.
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
One report, many chapters
5C · Exam PracticeThe IPCC Sixth Assessment Synthesis Report brings physical evidence, impacts and mitigation into one assessed document. Use it as a map of where professional conclusions come from, not…Specification 5.19(ii)Read & use the scienceClose article
Why this matters
The IPCC Sixth Assessment Synthesis Report brings physical evidence, impacts and mitigation into one assessed document. Use it as a map of where professional conclusions come from, not as a quotation bank for 5C answers. Your calculations still use the fictional kJ in the question. A synthesis report connects evidence from different fields, but its headline does not supply the uncertainty, baseline or pathway for every figure. A good interpretation checks the underlying claim before applying it to a new scenario.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.19(ii) understand that models for climate change have limitations
Use the science
Why is copying a headline number from a summary for policymakers a weak 5.19 answer?
Explore a possible response
Without the pathway, baseline and uncertainty, the number is an unsourced extrapolation. 5.19 wants those limitations named.
Explore the source
A climate model is tested against yesterday
5C · Models of Climate Change and Their LimitationsNOAA explains that climate models can be tested by seeing whether they reproduce historical patterns before using them with possible future emissions pathways. This process is called hindcasting.…Specification 5.19(i) · 5.19(ii)Read & use the scienceClose article
Why this matters
NOAA explains that climate models can be tested by seeing whether they reproduce historical patterns before using them with possible future emissions pathways. This process is called hindcasting. A model that matches a past global average can still have regional biases, especially for rainfall or clouds. Future scenarios also depend on human decisions that physics alone cannot predict. That is why a range of models and scenarios is more informative than one precise-looking number. Extrapolation is useful, but its limitations should travel with the result. A model is neither an untested guess nor an infallible forecast.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.19(i) understand that data can be extrapolated to make predictions and that these are used in models of future climate change
- 5.19(ii) understand that models for climate change have limitations
Use the science
Why might two valid models project different rainfall for one region even if both simulate past global warming well?
Explore a possible response
They may represent regional processes differently, and future rainfall also depends on scenario and natural variability.
Explore the source
- Climate modelsNOAA Climate.gov
The offset advert leaves out the land
5C · What Can Be Done?The IPCC assesses bioenergy and tree planting alongside land use, food production, water and the carbon already stored in soil and vegetation. An advert may count carbon taken…Specification 5.26Read & use the scienceClose article
Why this matters
The IPCC assesses bioenergy and tree planting alongside land use, food production, water and the carbon already stored in soil and vegetation. An advert may count carbon taken up by young trees while omitting what was cleared to plant them or whether the trees will survive. This does not mean all reforestation is ineffective. It means the outcome depends on location, previous land use, timescale and management. A responsible claim distinguishes emission reduction from carbon removal and includes the full system boundary. The biological mechanism of photosynthesis is necessary, but it is not an entire climate policy.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 4, pp. 29–32. The application extends beyond required recall.
- 5.26 understand how reforestation and the use of sustainable resources, including biofuels, are examples of the effective management of the conflict between human needs and conservation
Use the science
Why could planting an energy crop on a high-carbon natural habitat increase net emissions despite photosynthesis?
Explore a possible response
Clearing the original habitat can release stored carbon, while cultivation and transport add emissions. These may outweigh the crop’s uptake or displaced fuel.