PTE Listening Practice Test 3

"Bioluminescence — the ability of living organisms to produce their own light through chemical reactions — is remarkably common in the deep ocean, where sunlight cannot penetrate. Scientists estimate that as many as ninety percent of deep-sea animals are capable of producing light in some form, making it one of the most widespread traits in that environment. The light is generated when a molecule called luciferin reacts with oxygen, a process catalysed by an enzyme known as luciferase, releasing energy as visible light rather than heat. Different species use this ability for very different purposes: some anglerfish use a glowing lure to attract prey directly into their jaws, while certain squid release glowing ink to confuse predators during an escape. Other creatures use bioluminescence for communication, flashing specific patterns of light to attract mates or signal to members of their own species in the darkness. Researchers have also found that some deep-sea organisms use counter-illumination, producing light on their undersides that matches the faint light filtering down from the surface, effectively making them invisible from below. Understanding these chemical processes has practical applications beyond marine biology; the genes responsible for producing light in certain jellyfish are now used widely in medical research as markers to track gene activity in cells."

বায়োলুমিনেসেন্স (নিজস্ব আলো তৈরি) গভীর সমুদ্রে সাধারণ — প্রায় ৯০% প্রাণী আলো তৈরি করতে পারে (luciferin+অক্সিজেন বিক্রিয়া)। শিকার ধরতে, শত্রু বিভ্রান্ত করতে, যোগাযোগে ও ছদ্মবেশে ব্যবহৃত হয়। জেলিফিশের জিন মেডিকেল গবেষণায় ব্যবহৃত হয়।

"A growing body of research has examined how sleep deprivation affects the brain's ability to make sound decisions. Studies consistently find that people who have slept fewer than six hours show a marked increase in risk-taking behaviour, often underestimating the likelihood of negative outcomes. Sleep-deprived individuals also show reduced activity in the prefrontal cortex, the brain region responsible for weighing long-term consequences, while emotional responses driven by the amygdala become comparatively stronger. Interestingly, most sleep-deprived people are unaware of how impaired their judgement has become, often rating their own decision-making as unaffected even when objective tests show significant decline. Some hospitals and transport companies have introduced mandatory rest periods for staff in safety-critical roles specifically in response to this body of research."

"Community gardens have become an increasingly common feature in cities around the world, and research suggests they offer a range of measurable benefits. Residents who participate report eating more fresh vegetables than before, since produce grown in a shared plot is both free and conveniently located near home. Community gardens also strengthen neighbourhood ties, giving people from different backgrounds a shared reason to interact regularly, which some studies link to reduced feelings of isolation, particularly among older residents. In addition, converting vacant urban lots into gardens has been shown to reduce local crime rates in several city studies, possibly because a well-tended, frequently visited space discourages illicit activity. City governments increasingly view community gardens as a low-cost way to improve public health and social cohesion simultaneously."

"Desalination — the process of removing salt from seawater to produce fresh drinking water — has expanded rapidly in regions facing water scarcity, particularly in the Middle East. The most common method, reverse osmosis, forces seawater through a fine membrane that filters out salt and other minerals, leaving fresh water behind. However, the process is highly energy-intensive, and the leftover concentrated brine, if discharged back into the sea without treatment, can harm marine ecosystems near the outflow point. Some newer desalination plants have begun combining the process with solar power to reduce both costs and carbon emissions, though this technology remains more expensive to install than conventional plants."

"Made up of nearly three thousand individual reefs, the Great Barrier Reef stretches for over two thousand kilometres along the Australian coast, making it the largest living structure on Earth."