IELTS Academic Practice Test 21

Beneath every forest floor, grassland, and garden lies an invisible network of extraordinary importance—a web of fungal threads connecting trees, plants, and soil in ways that were only recently understood by science. These are mycorrhizal fungi, organisms that form one of nature's most fundamental partnerships, yet remain almost completely unknown to the general public. The word "mycorrhiza" comes from Greek, meaning "fungus-root," and it perfectly describes the intimate relationship between these fungi and plant roots. This partnership is not a modern discovery; fossil evidence suggests that mycorrhizal associations have existed for over 450 million years, long before plants first colonized land. Without these fungi, the terrestrial world as we know it would not exist. The mechanics of mycorrhizal partnership are elegantly simple yet profoundly effective. The fungal partner extends threadlike structures called hyphae into the soil, dramatically expanding the reach of the plant's root system. A single fungal network can extend across an area many times larger than the plant's own roots could access, allowing the fungus to absorb water and nutrients—particularly phosphorus and nitrogen—from far-flung soil regions. In return, the plant provides the fungus with sugars produced through photosynthesis, energy that the fungus cannot generate on its own. It is a transaction of mutual benefit, refined over millions of years of co-evolution. Around 90 percent of plant species on Earth engage in some form of mycorrhizal relationship, a statistic that underscores just how central this partnership is to terrestrial life. There are several distinct types of mycorrhizal associations, each suited to different environments and plant families. Arbuscular mycorrhizal fungi (AMF) penetrate the cell walls of plant roots and form branching structures inside the root cells, maximizing the surface area for nutrient exchange. These fungi are generalists, forming relationships with a wide variety of plants, from wheat and corn to legumes and most tropical species. Ectomycorrhizal fungi, by contrast, do not penetrate root cells; instead, they form a sheath around the root and extend into the spaces between cells. This type is particularly common in temperate forests, where they associate with trees like oaks, pines, and birches. A third category, ericoid mycorrhizae, specializes in plants of the heath family, helping them survive in acidic, nutrient-poor soils where few other plants can thrive. The benefits of mycorrhizal fungi extend far beyond simple nutrient delivery. These fungal networks facilitate communication between plants, sometimes called the "wood wide web" by researchers. Through fungal connections, one plant can receive chemical signals from neighbors, alerting it to pest attacks or disease threats. Recent experiments have demonstrated that plants connected through fungal networks can transfer defensive compounds to vulnerable neighbors, effectively sharing immunity information. Furthermore, mycorrhizal associations increase plants' resistance to drought and salinity stress, crucial abilities as climate patterns shift and soil conditions change. In agricultural contexts, mycorrhizal fungi can reduce the need for synthetic fertilizers by making soil nutrients more available to crops. Despite their importance, mycorrhizal fungi face unprecedented challenges in the modern world. Agricultural practices, particularly the use of fungicides and the heavy tilling of soil, severely disrupt fungal networks and reduce fungal diversity. Monoculture farming, where vast areas are planted with a single crop species, eliminates the diversity of plant hosts that fungi require to thrive. Pollution, habitat fragmentation, and climate change further threaten these delicate underground ecosystems. Some scientists worry that we are inadvertently dismantling the biological foundation upon which terrestrial ecosystems depend, often without realizing what we are losing. The future may bring renewed appreciation and active restoration of mycorrhizal communities. Agricultural researchers are investigating ways to reintroduce beneficial fungi to depleted soils and to develop farming practices that protect existing fungal networks. Some organic and regenerative agriculture movements explicitly prioritize soil health and fungal diversity as cornerstones of sustainable food production. As climate change accelerates, the role of mycorrhizal fungi in helping plants adapt to new conditions becomes increasingly critical. By understanding and protecting these hidden networks, we invest not only in agricultural productivity but in the stability of ecosystems that sustain all life on land.

Vertical farming, the practice of growing crops in vertically stacked layers within controlled indoor environments, has emerged as a promising solution to food security challenges in densely populated urban areas. Unlike traditional agriculture, which depends on vast tracts of land and favourable weather conditions, vertical farms utilise sophisticated hydroponic or aeroponic systems to cultivate vegetables, leafy greens, and herbs year-round in cities where agricultural land is scarce or prohibitively expensive. The concept itself is not entirely new; controlled environment agriculture has existed since the 19th century in the form of greenhouses. However, technological advances in LED lighting, climate control systems, and automation have only recently made vertical farming economically viable at scale. The Netherlands, Japan, and Singapore have become global pioneers in this field, with Singapore in particular viewing vertical farming as a strategic component of its food independence policy, having devoted approximately 30 hectares of land to vertical farming by 2023. A typical vertical farm operates with minimal water consumption—roughly 95% less than conventional agriculture—because water is recycled through closed-loop systems rather than lost to evaporation or soil absorption. This efficiency, combined with the elimination of pesticide use and the reduction of transportation distances from farm to consumer, makes vertical farming an environmentally attractive proposition. Proponents argue that vertical farms can reduce the carbon footprint associated with food production and distribution while simultaneously creating employment opportunities in urban centres. However, the sector faces significant challenges. Initial capital costs remain prohibitively high, with some commercial facilities requiring investments exceeding $10 million. Energy consumption is another critical concern; despite improvements in LED efficiency, lighting accounts for 30% to 50% of operational costs in most vertical farms. The profitability of vertical farming currently hinges on growing high-value crops such as specialty herbs, microgreens, and premium lettuces, rather than staple grains or legumes. Scaling to produce calorie-dense staple foods remains technically and economically unfeasible with existing technology. Furthermore, the sector requires skilled labour for system maintenance and crop management, and many vertical farms operate at relatively small scales, limiting their impact on municipal food supply chains. Research institutions, including those at the University of Tokyo and Wageningen University, are investigating methods to improve crop yields per unit area and reduce energy requirements through optimised light wavelengths and nutrient delivery systems. Some experimental facilities have begun exploring renewable energy integration, particularly solar panels and wind turbines, to offset electrical costs. Despite these ongoing improvements, most industry analysts suggest that vertical farming will complement rather than replace conventional agriculture in the foreseeable future. Its greatest potential lies in augmenting local food production in regions with severe land constraints, extreme climates, or limited agricultural infrastructure. The technology also offers opportunities for research into future food systems, as climate change continues to disrupt traditional farming patterns and increase uncertainty in global food supply networks.

The contemporary metropolis presents a profound ecological paradox: despite centuries of systematic environmental degradation, cities are increasingly becoming sites of deliberate ecological restoration and species reintroduction. This phenomenon, termed 'urban rewilding,' represents a fundamental shift in how societies conceptualize the relationship between human settlement and natural systems. Rather than viewing cities as inherently antithetical to nature, urban planners and ecologists now recognize that carefully managed urban environments can function as critical refuges for biodiversity, particularly as anthropogenic climate change and habitat fragmentation render traditional wilderness areas increasingly precarious. Urban rewilding differs markedly from conventional conservation efforts in that it operates within the constraints of densely populated human landscapes. The restoration of tidal wetlands in Rotterdam, the reintroduction of wolves to the Carpathian periphery of Bucharest, and the creation of pollinator corridors through London's derelict railway infrastructure exemplify how cities are being reimagined as dynamic ecological systems rather than biological deserts. These interventions rest upon an emerging scientific understanding that urban ecosystems possess unique characteristics that can be leveraged for conservation purposes. The heat-island effect, for instance, traditionally viewed as an environmental liability, creates microhabitats suitable for thermophilic species displaced from warming landscapes elsewhere. Similarly, the fragmented patchwork of parks, green roofs, and urban gardens provides stepping-stone habitats that facilitate species dispersal across otherwise hostile urban matrices. However, urban rewilding initiatives face substantial conceptual and practical obstacles. A fundamental tension exists between the ecological imperative to restore 'authentic' or historically baseline ecosystems and the pragmatic reality that cities cannot simply revert to pre-anthropogenic conditions. The species composition of urban rewilded areas often reflects available propagule sources, funding priorities, and political preferences rather than rigorous historical or ecological criteria. Furthermore, urban rewilding frequently privileges charismatic megafauna and visually appealing botanical specimens over less conspicuous but ecologically essential organisms. The widespread enthusiasm for reintroducing urban beavers in European cities, for example, contrasts starkly with minimal investment in restoring populations of soil microorganisms or fungal networks—elements far more critical to soil health and nutrient cycling yet utterly invisible to public perception. The socio-political dimensions of urban rewilding warrant particular scrutiny. These initiatives consistently attract substantially greater funding and public engagement than traditional conservation efforts in remote areas, partly because they offer immediate recreational and aesthetic benefits to urban populations. This redistribution of conservation resources raises troubling questions about environmental equity: should biodiversity protection prioritize the lived experience of privileged urban dwellers over the pressing conservation needs of less-developed regions where most terrestrial biodiversity actually persists? Some conservation biologists argue that urban rewilding, despite its ecological benefits, may inadvertently undermine broader conservation agendas by concentrating resources on demonstrable but ultimately marginal habitat interventions whilst neglecting the protection of biodiverse but economically marginal regions in the Global South. Nevertheless, urban rewilding initiatives have catalyzed significant advances in ecological science and practice. Research on urban-adapted species has illuminated evolutionary processes operating at previously unstudied temporal and spatial scales. Studies of how organisms respond to rapid environmental change in urban settings have provided crucial insights applicable to climate change adaptation more broadly. Additionally, the engagement of urban populations with rewilding projects has demonstrably increased ecological literacy and environmental advocacy, creating constituencies more likely to support broader conservation policies. Cities like Singapore, which has systematically integrated ecological corridors into urban infrastructure planning, have achieved remarkable results: native species populations have stabilized or increased even as the city-state has experienced unprecedented human population growth and development intensity. Looking forward, the trajectory of urban rewilding remains uncertain. Its long-term ecological efficacy depends heavily upon sustained political commitment and financial investment—resources perpetually vulnerable to budgetary constraints and shifting policy priorities. Furthermore, climate change itself introduces profound uncertainties into rewilding design: species reintroductions planned according to historical baseline conditions may prove maladaptive if climatic regimes shift dramatically within the timescale of restoration efforts. Some researchers suggest that urban rewilding should embrace a more explicitly adaptive framework, treating restored ecosystems as experimental laboratories wherein species assemblages and management protocols are continuously adjusted based on real-time ecological monitoring. This approach represents a significant departure from conventional conservation philosophy, which typically assumes relatively stable target conditions. Ultimately, whether urban rewilding constitutes a promising frontier in global biodiversity conservation or an elaborate but ultimately insufficient substitute for protecting intact wild ecosystems remains contested—a tension unlikely to be resolved without substantially more longitudinal ecological research and honest engagement with the equity implications of where and how conservation resources are deployed.