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Climate change, food and disease vectors

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Which explanation links cattle production to a required greenhouse gas?

  1. The methane is released mainly when feed plants photosynthesise.
  2. Cattle production affects climate only through the fossil fuel used in transport.
  3. Microbial digestion in ruminants releases methane.
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Microbial digestion in ruminants releases methane.

This is an important gas-specific link between production and climate.

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Which sequence correctly describes a warming feedback?

  1. Released methane cools the soil and stops further thaw.
  2. Thaw slows microbial decomposition in the soil, so less greenhouse gas reaches the air and warming eases.
  3. Warming causes thaw, decomposition releases greenhouse gases, and further warming follows.
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Warming causes thaw, decomposition releases greenhouse gases, and further warming follows.

Each link reinforces the initial warming.

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Why can a seawall worsen the risk to a mangrove stand under rising sea level?

  1. It prevents the trees from moving seawards into permanently deeper water.
  2. It may block landward establishment as the suitable coastal zone shifts.
  3. Salt tolerance means rising water depth cannot affect mangrove survival.
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It may block landward establishment as the suitable coastal zone shifts.

A physical barrier can prevent adjustment even where inland habitat could otherwise become suitable.

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Why can a long marine heatwave kill a reef-building coral?

  1. The coral expels its zooxanthellae and starves without their sugars.
  2. Warm water dissolves the calcium carbonate skeleton directly.
  3. The tissue turns white because the coral cells have already died.
  4. The zooxanthellae photosynthesise faster and use up the oxygen in the coral.
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The coral expels its zooxanthellae and starves without their sugars.

Heat breaks the mutualism. Without zooxanthellae the coral loses most of its sugar supply, and it can starve if the heat lasts.

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Which can cause coral bleaching? 1: A long period of high sea temperature. 2: Low salinity after heavy rain. 3: Clear, calm water. 4: Loss of zooxanthellae from coral tissue.

  1. 2 and 3 only
  2. 1, 2 and 4 only
  3. 1, 3 and 4 only
  4. 1 and 4 only
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1, 2 and 4 only

Heat and low salinity stress corals, and bleaching is the loss of zooxanthellae. Clear, calm water is not a stress.

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Which explanation directly accounts for a mangrove carbon store?

  1. Fixed carbon is returned at once by respiration, so the store is the living leaves and nothing else.
  2. Photosynthesis adds biomass and some organic carbon is retained in slowly decomposing sediment.
  3. Wave drag directly removes atmospheric CO2 without photosynthesis.
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Photosynthesis adds biomass and some organic carbon is retained in slowly decomposing sediment.

This links carbon input to storage.

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What most weakens a claim that new bioethanol production is carbon neutral?

  1. The crop photosynthesises, so it took in carbon while it grew.
  2. Its feedstock contains carbon atoms, which are released as CO2 when the fuel burns in an engine.
  3. The project clears a carbon-rich forest and uses fossil energy in processing, but excludes those emissions.
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The project clears a carbon-rich forest and uses fossil energy in processing, but excludes those emissions.

Omitting major life-cycle stages makes the neutrality claim incomplete.

Check your understanding

Which comparison is most defensible?

  1. Ignore land clearance because it happened before the food was sold.
  2. Compare the same nutritional output with the same included production stages.
  3. Rank foods by how far they travel, because transport is the stage people can most easily see.
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Compare the same nutritional output with the same included production stages.

This makes the meaning of the footprint difference clear.

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Invented life-cycle values per kg of protein: beef 300 kg CO2-equivalent, beans 10, with transport making up 1% of the beef value and 20% of the beans value. Which conclusion is best supported?

  1. Beans have the larger footprint because of transport.
  2. Production, not transport, explains most of the gap.
  3. The two foods have similar footprints.
  4. Buying local beef would bring it close to the beans.
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Production, not transport, explains most of the gap.

Transport is only 3 kg for beef and 2 kg for beans, so production causes nearly all the difference.

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Why might flooding reduce root function?

  1. Roots stop respiring under water, because respiration takes place in the leaves, which stay in air.
  2. Water entering soil pores supplies oxygen as effectively as the air it replaces.
  3. Waterlogged soil can restrict oxygen supply and reduce aerobic respiration in roots.
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Waterlogged soil can restrict oxygen supply and reduce aerobic respiration in roots.

This links the environmental stress to energy-dependent root functions.

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Which conclusion fits faster development but lower survival at a higher temperature?

  1. Faster development always means more mosquitoes and more disease at any temperature.
  2. Temperature affects different components of population growth, so one rate does not establish the total result.
  3. Development time alone shows which condition produces the most adults, because faster growth means more generations.
  4. Lower survival can be ignored because all surviving adults emerge sooner.
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Temperature affects different components of population growth, so one rate does not establish the total result.

Development and survival must be considered together.

Check your understanding

Which statement best explains possible spread beyond the tropics?

  1. Warming spreads dengue by making the dengue bacterium reproduce faster in standing water, where people pick it up.
  2. Warming can extend suitable conditions for vectors and pathogen development, if the other transmission requirements are met.
  3. A suitable vector population guarantees disease even if the pathogen is absent.
  4. Once winters warm, mosquitoes survive year-round, so breeding habitat and vector control stop mattering to transmission.
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Warming can extend suitable conditions for vectors and pathogen development, if the other transmission requirements are met.

This gives both the mechanism and its conditions.

Explain your thinking

Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 14

Judge a warming claim from two tables

5 marks

Invented laboratory data for Aedes aegypti. Table 1 (eggs to adults): 24 degrees C, 12 days, 80% survive; 28 degrees C, 9 days, 75%; 32 degrees C, 7 days, 50%; 36 degrees C, 6 days, 15%. Table 2 (adults): adult lifespan 30, 24, 14 and 6 days; bites per day 0.3, 0.5, 0.6 and 0.6; extrinsic incubation period of dengue virus 14, 10, 8 and 7 days at 24, 28, 32 and 36 degrees C. A student claims: "Warmer temperatures always increase dengue transmission." (a) For each temperature, calculate the infectious bites per adult mosquito, using (lifespan - extrinsic incubation period) x bites per day. (b) Use both tables to judge the claim. Give data that support it and data that do not, and state your verdict. (c) Give one limitation of the data. [5]

Quote figures with units. A judgement needs evidence on both sides and a verdict word.

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