PTE · Reorder Paragraphs

The Science of Caffeine

5 original Reorder Paragraphs questions. Question 1 is free to answer and check right here; log in free to practise the rest in the BandLadder app.
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1

Botanical Defence Mechanisms

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  1. AThis soil contamination prevents competing seeds from germinating nearby, thereby securing vital moisture and nutrients for the parent flora.
  2. BWhen herbivorous insects feed on these tissues, the concentrated compound disrupts their nervous systems and discourages further consumption.
  3. CIn addition to deterring pests, shed leaves release the stimulant into surrounding topsoil as they gradually decompose.
  4. DSeveral wild plant species naturally synthesise caffeine within their seeds, foliage, and young seedlings as a biochemical defence mechanism.

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2

Decaffeination via Carbon Dioxide

  1. AOne widely adopted technique involves pumping carbon dioxide under high pressure into sealed extraction chambers.
  2. BCommercial coffee processors rely on specialised chemical methods to extract caffeine from raw green beans.
  3. CThis fluid selectively dissolves the target alkaloid molecules while leaving essential flavour precursors completely intact.
  4. DUnder these extreme conditions, the gas enters a supercritical state that combines liquid density with gaseous diffusion.
  5. EOnce separated, the remaining liquid is depressurised, allowing the gas to evaporate and leave behind decaffeinated beans.
3

Adenosine Receptor Blockade

  1. AHowever, ingested caffeine possesses a three-dimensional molecular structure remarkably similar to adenosine, allowing it to occupy those same binding sites.
  2. BAs this compound steadily accumulates, it binds to specialised neural receptors, progressively promoting drowsiness and slowing cellular activity.
  3. CBy blocking these neural receptors without activating them, the stimulant effectively prevents fatigue signals from registering across the central nervous system.
  4. DThroughout waking hours, human brain cells continuously generate and release a regulatory metabolic byproduct known as adenosine.
4

Aquatic Environmental Contamination

  1. AThese artificial aquatic concentrations alter the baseline swimming behaviours and metabolic rates of local freshwater fish.
  2. BMassive global consumption of caffeinated beverages has inadvertently introduced chemical residues into urban wastewater streams.
  3. CStandard municipal sewage treatment facilities cannot entirely filter out these persistent dissolved compounds.
  4. DOver time, such physiological disruptions can destabilise vulnerable aquatic food webs and diminish reproductive success in native species.
  5. EConsequently, treated effluent discharged into nearby rivers and coastal waters carries detectable levels of the stimulant.
5

Pollinator Memory Enhancement

  1. AInstead, the low chemical dosage acts directly on the insect brain to reinforce olfactory memory during foraging visits.
  2. BBees conditioned in this manner recall floral scents far more accurately, ensuring frequent return visits and significantly improving pollination efficiency.
  3. CAlthough high doses deter herbivores, these mild concentrations do not repel visiting honeybees or alter nectar taste.
  4. DMany flowering plant species secrete minute traces of naturally occurring caffeine into their floral nectar alongside sweet sugars.

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