Reading: Diagram Label Completion: IELTS Academic 9990 (IELTS Academic)

A canal that crosses hilly or uneven ground cannot simply be dug at a single level, since water will not stay in a channel that slopes continuously downhill. Engineers solve this problem with a device called a pound lock, a mechanism that lifts or lowers boats between two stretches of canal, known as pounds, that sit at different heights.

A pound lock consists of a rectangular chamber built between two sets of watertight gates. At the upstream end, where the chamber meets the higher pound, stand the upper gates; at the downstream end, where it meets the lower pound, stand the lower gates. Each gate is a heavy timber or steel structure hinged at one edge and closes against a stone ledge, called the cill, set into the floor of the chamber; the cill prevents water from forcing the gates open from the wrong side. Fixed to the top of each gate is a long wooden balance beam, which projects out over the towpath; a lock keeper, or on quieter canals a boater, pushes against this beam to swing the heavy gate open or shut, since the beam's length provides enough leverage for one person to move it.

Built into the lower part of each gate is a small sliding panel called a paddle. Raising a paddle in the upper gates allows water to flow from the upper pound into the chamber, gradually raising the water level inside until it matches the upper pound; only then can the upper gates be opened safely, since gates can never be opened while there is a difference in water level across them. To lower a boat, the process is reversed: with both gates shut, the paddles in the lower gates are raised instead, draining water out of the chamber into the lower pound until the level inside falls to match it, at which point the lower gates can be swung open and the boat continues on its way.

The diagram below shows a lengthwise cross-section of a pound lock, running from a higher stretch of canal on the left to a lower stretch of canal on the right, with the chamber in between.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the stretch of open water at the higher level, to the left of the lock
2. the gates at the left-hand (upstream) end of the chamber
3. the ledge set into the floor of the chamber that each gate closes against
4. the long wooden arm fixed to the top of each gate, used to push it open
5. the small sliding panel built into the lower part of each gate
6. the enclosed section of water between the two sets of gates
7. the stretch of open water at the lower level, to the right of the lock

Beneath the bright colours that attract pollinating insects, a flower is a highly organised reproductive structure in which every part occupies a precise position for a functional reason. At the base of the flower, the stalk widens into a small swelling called the receptacle, from which all of the flower's other parts grow in a series of concentric rings.

The outermost ring consists of small, often green, leaf-like structures called sepals, which enclose and protect the developing bud before it opens; together the sepals are known as the calyx. Just inside the sepals sits the next ring, the petals, whose colour, scent and shape have evolved primarily to attract pollinators such as bees and moths rather than to serve any structural role.

Moving further inward, the third ring is made up of the male reproductive organs, the stamens. Each stamen consists of a slender stalk, the filament, topped by a swollen structure called the anther, inside which pollen grains are produced. When an insect brushes against the anther while feeding, pollen grains stick to its body and may later be carried to another flower.

At the very centre of the flower lies the female reproductive structure, the carpel. The carpel's uppermost part, the stigma, is often sticky or feathery so that pollen grains landing on it will adhere rather than fall away. Below the stigma runs a narrow tube-like section called the style, which connects the stigma to the swollen base of the carpel, the ovary, where the ovules that will develop into seeds are contained. Small glands located near the base of the petals, called nectaries, produce the sugary liquid that rewards visiting insects for transferring pollen between flowers.

The diagram below shows a vertical cross-section through the centre of a flower, arranged from the outer edge of the flower inward to its centre, and from the base of the flower upward to the tip of the central carpel.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the small swelling at the base of the flower stalk, from which all the other parts grow
2. the outermost ring of small, leaf-like structures enclosing the unopened bud
3. the ring of parts just inside the outermost ring, coloured to attract pollinators
4. the slender stalk at the base of a male reproductive organ
5. the swollen structure at the top of that slender stalk, where pollen is produced
6. the sticky or feathery structure at the very top of the central female organ
7. the narrow tube connecting the top of the central female organ to its swollen base
8. the swollen base of the central female organ, containing the seed-forming structures

Long before steam or electricity became available, watermills used the force of flowing water to grind grain, and the most efficient design for doing so was the overshot wheel. Unlike simpler wheels that are pushed round by the current striking their lower edge, an overshot wheel is turned by the weight of water falling onto it from above, a difference that allows it to extract far more energy from the same stream.

Water bound for the wheel first passes through a headrace, an artificial channel that carries it from a point upstream, often diverted from the river by a low dam called a weir. Where the headrace reaches the wheel, a hinged wooden or metal gate known as the sluice controls how much water is allowed through; opening the sluice further increases the flow reaching the wheel and therefore its turning speed. Just beyond the sluice, the water enters a narrow wooden trough called the launder, which is angled so that it delivers the water directly into a series of buckets fixed around the wheel's outer rim rather than letting it spill onto the wheel's flat face.

As each bucket fills, its weight pulls that side of the wheel downward, and the wheel rotates continuously as successive buckets fill on one side and empty on the other. At the centre of the wheel runs a solid horizontal axle, which turns together with the wheel and carries the rotational motion into the mill building, where a system of wooden gears steps the axle's slow, powerful turning up to the much faster speed needed to drive a millstone. Once the water in each bucket has emptied out, it falls into a channel below called the tailrace, which carries the spent water back to rejoin the main river some distance downstream of the mill.

The diagram below shows a side-on cross-section of an overshot water wheel and its water supply, viewed from upstream on the left to downstream on the right.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the low dam across the river that diverts water into the channel supplying the wheel
2. the artificial channel that carries water from upstream to the wheel
3. the hinged gate that controls how much water reaches the wheel
4. the narrow angled trough that delivers water into the wheel's buckets
5. the containers fixed around the outer rim of the wheel that fill with falling water
6. the solid horizontal bar running through the centre of the wheel
7. the channel below the wheel that carries the spent water back to the river

Limestone caves form when slightly acidic rainwater, having absorbed carbon dioxide from the soil as it seeps downward, dissolves the calcium carbonate in the surrounding rock over thousands of years, gradually enlarging cracks into passages and eventually into large underground chambers.

Water often enters the cave system through a vertical shaft called a sinkhole, a depression on the surface formed where the roof of a passage below has collapsed or where surface water has steadily dissolved a channel straight down through the rock. Rainwater seeping through the cave roof carries dissolved minerals with it, and as each droplet reaches the ceiling of a chamber, a small amount of water evaporates before the droplet falls, leaving behind a tiny deposit of calcium carbonate; over centuries, countless droplets falling in the same spot build up a tapering, icicle-like formation hanging from the ceiling, known as a stalactite.

Droplets that fall from a stalactite before evaporating completely often land in the same spot on the cave floor below, where the remaining minerals are deposited in a similar way, building upward instead of downward to form a stalagmite. Where a stalactite and a stalagmite growing directly beneath it eventually meet after many thousands of years, they fuse into a single continuous formation running from floor to ceiling called a column.

Beneath the cave's dry upper passages, water that has percolated all the way through the rock collects in the pore spaces and fractures of the limestone, forming an underground reservoir; the upper surface of this saturated zone is known as the water table, and any passage that lies below it stays permanently flooded. Where a passage remains above this level, water draining through it instead gathers into a flowing underground river that carves the passage floor even wider as it makes its way toward a distant resurgence, the point where the water finally re-emerges at the surface.

The diagram below shows a cross-section through a limestone hillside containing a cave system, running from the surface downward to the underground river, and from the cave entrance on the left toward the distant hillside resurgence on the right.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the vertical opening at the surface through which water enters the cave system
2. the icicle-like formation hanging down from the chamber ceiling
3. the upward-growing formation on the cave floor, directly beneath it
4. the single formation running from floor to ceiling where the two meet
5. the upper surface of the water-saturated zone beneath the dry upper passages
6. the flowing body of water below that level, which carves the passage floor
7. the point where the underground water finally re-emerges at the surface

Most birds produce a rushing or whooshing sound as they fly, generated where fast-moving air spills off the wing's trailing edge and where feathers rub against one another during each wingbeat. Owls, however, are able to fly and dive almost silently, an ability that depends on three separate structural features rather than on any single adaptation.

The first feature is found along the wing's leading edge, the forward-facing border that meets the oncoming air first. In most birds this edge is smooth, but along an owl's leading edge, the primary feathers end in a row of stiff, comb-like points known simply as the comb, which breaks up the large, noisy vortices that would otherwise form as air rushes over the wing into a mass of much smaller, quieter ones.

The second feature lies at the opposite side of the wing, the trailing edge, the rear border from which air finally leaves the wing. Here, instead of ending in a stiff, well-defined line, an owl's flight feathers taper into a soft, irregular fringe, which breaks up the airflow gradually rather than letting it separate abruptly, the main source of the rushing noise in an ordinary bird's wing.

The third feature covers the wing's upper surface, which in an owl is coated in a layer of fine down. This down absorbs high-frequency sound rather than reflecting it, and also reduces the friction noise produced as adjacent feathers slide across one another during a wingbeat.

Together, these three features shift the noise an owl's wing does produce down to frequencies below around two kilohertz, which happens to lie outside the hearing range of the small mammals owls typically hunt, allowing the bird to approach its prey without being detected until the final moment of an attack.

The diagram below shows the upper surface of an outstretched owl wing, viewed from above, with the forward border of the wing at the top and the rear border at the bottom.

Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1. the forward-facing border of the wing that meets the oncoming air first
2. the row of stiff, comb-like points along that forward border
3. the rear border of the wing, from which air finally leaves
4. the soft, irregular texture along that rear border
5. the broad face of the wing lying between the forward and rear borders
6. the fine feather layer coating that broad central face

Run-of-river hydroelectric schemes generate electricity by diverting a portion of a river's natural flow through a low, compact dam, rather than storing enormous volumes of water behind a high one. The scheme built across the Kestrel River in 2021 by the regional utility Marrowvale Power illustrates the basic arrangement shared by most such dams.

At the upstream end of the structure, a concrete spillway allows excess floodwater to pass safely over the crest of the dam whenever the reservoir behind it rises above its normal operating level, preventing the structure from being overtopped in an uncontrolled way. Immediately beside the spillway, water destined for power generation first passes through a trash rack, a steel grille of closely spaced bars that stops branches, leaves and other floating debris from reaching the machinery further downstream. Water that clears the trash rack enters an intake channel, a short, gently sloping passage cut into the dam that funnels the flow toward the generating equipment and gradually narrows to increase its speed.

From the base of the intake channel the water is forced into a penstock, a large steel pipe that carries it under considerable pressure down to the turbine hall at the foot of the dam. Engineers at Marrowvale Power chose a steel penstock over a concrete one because steel tolerates the sudden pressure surges that occur whenever the flow is throttled quickly. Inside the turbine hall, the pressurised water strikes the curved blades of a turbine, spinning a shaft connected to a generator on the floor above; the turbine's rotational energy is converted into electrical energy at this point, and cables carry the output to a substation on the riverbank.

Having passed through the turbine, the water is not stored again but is released into a tailrace, a wide open channel that returns it to the natural riverbed a short distance downstream of the dam. Because the dam interrupts the river's natural course, a fish ladder, a stepped series of pools running alongside the main structure, allows migratory fish such as salmon to bypass the dam and continue upstream to their spawning grounds, a feature required by Marrowvale Power's environmental operating licence.

The diagram below shows a cross-section of the Kestrel Gorge dam, viewed from upstream to downstream (left to right). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The structure at the top of the dam that lets floodwater pass over the crest when the reservoir is too full 2 ____________________. A steel grille positioned beside it that stops debris before it can reach the generating equipment 3 ____________________. The narrowing passage that funnels water from the grille toward the generating equipment 4 ____________________. The large steel pipe that carries pressurised water down to the turbine hall 5 ____________________. The part inside the turbine hall struck directly by the pressurised water, turning the connected generator shaft 6 ____________________. The open channel that returns water to the riverbed after it leaves the generating equipment 7 ____________________. The stepped series of pools beside the dam that lets migratory fish continue upstream

A basin-type solar still is one of the simplest technologies available for turning contaminated or saline water into drinking water, and it needs no power source beyond sunlight itself. Trials of a small still at a coastal research site in Tarrant Bay, conducted between 2018 and 2020, showed that a single square metre of still can reliably produce between two and four litres of clean water per day in sunny conditions.

At the base of the still sits a shallow basin, lined with a black liner that maximises the amount of solar radiation converted into heat rather than reflected away. Untreated water, whether drawn from the sea or from a brackish well, is poured into the basin to a depth of only a few centimetres, since a shallow layer heats and evaporates far more quickly than a deep one. As the sun warms the black liner, water evaporates from the surface of the basin, leaving behind salts, minerals and other dissolved contaminants, which are not carried upward in vapour form.

The rising water vapour condenses on the underside of a sloped glazing cover, a sheet of glass or clear plastic mounted at an angle above the basin. The slope of the glazing cover is not simply for appearance: it ensures that condensed droplets run downhill under gravity rather than dripping straight back into the basin and re-mixing with the untreated water. At the lower edge of the glazing cover, a narrow collection trough catches the runoff, and an outlet pipe then carries this clean water out of the still into a storage container standing beside it.

Because the still must retain heat rather than lose it to the surrounding air, the basin sits within an insulated frame, which reduces heat loss through the sides and base and keeps the internal temperature high enough for continuous evaporation. Left inside the basin, the increasingly concentrated leftover liquid, known as the brine, must eventually be drained away through a brine outlet at the base of the still and replaced with a fresh batch of untreated water.

The diagram below shows a cross-section of the solar still, from the base upward. Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The shallow container at the base of the still that holds the untreated water 2 ____________________. The dark layer inside the basin that absorbs sunlight and converts it into heat 3 ____________________. The sloped, transparent surface above the basin on which water vapour condenses 4 ____________________. The narrow fitting at the low edge of the sloped surface that collects the condensed runoff 5 ____________________. The fitting that carries the collected clean water out to a storage container 6 ____________________. The layer surrounding the basin that reduces heat loss through the sides and base 7 ____________________. The fitting at the base of the still used to drain away the concentrated leftover liquid

Passive solar design uses a building's orientation, materials and geometry to capture, store and release the sun's heat without any mechanical heating or cooling system, and a single-storey demonstration house, the Aldermoor House, completed in 2022 by the architect Priya Ostrander, illustrates the main features found in most passive solar homes in temperate climates.

The house is oriented so that its longest wall, made almost entirely of glass, faces south, maximising the amount of low-angle winter sunlight that enters through the glazing during the coldest months. Because the sun sits much higher in the sky in summer, a wide roof overhang projects out above the glazing and is calculated to block the more overhead summer sun while still admitting the lower winter sun, keeping the interior comfortably cool once the weather turns hot.

Sunlight that passes through the glazing strikes a mass wall built from dense, dark-coloured concrete blocks positioned directly opposite the windows. This wall absorbs solar energy throughout the day, slowly warming to the touch, and then releases that stored heat back into the room by radiation for several hours after sunset, smoothing out the difference between daytime and night-time temperatures without any need for a furnace. A similar principle applies underfoot: a storage floor of unfinished tiled concrete performs the same absorb-and-release function for sunlight that lands directly on the floor rather than on the vertical wall.

Higher up, a row of small clerestory windows sits just below the roofline on the north side of the house, admitting additional daylight deep into the interior without the unwanted heat gain that a large north-facing window would allow, since north-facing glass in this hemisphere receives very little direct sun. On hot days, opening the clerestory windows together with vents low down near the floor allows warm air to escape from the top of the room while drawing cooler air in near the ground, creating a natural convection current through the house.

Finally, opposite the glazing, the house's north wall is heavily insulated with thick layers of mineral wool and contains no windows at all, minimising the heat that escapes from the building on cold nights, when the temperature difference between indoors and outdoors is at its greatest.

The diagram below shows a cross-section of the Aldermoor House, viewed from south (left) to north (right). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The large glass surface on the long south-facing wall that lets in low winter sunlight 2 ____________________. The structure projecting above it, sized to block high summer sun but admit low winter sun 3 ____________________. The dense, dark-coloured concrete wall opposite the windows that absorbs and later releases solar heat 4 ____________________. The unfinished concrete surface underfoot that absorbs sunlight falling directly on it 5 ____________________. The row of small windows below the roofline on the north side that admits extra daylight 6 ____________________. The openings low near the floor that, together with the windows above, create a convection current 7 ____________________. The heavily insulated wall opposite the glazing that has no windows at all

A simple refracting telescope gathers and focuses light using nothing but a pair of lenses mounted at opposite ends of a long tube, a design essentially unchanged since amateur astronomers began building their own instruments in home workshops during the nineteenth century. A basic 900-millimetre refractor assembled by the Hallowick Astronomy Club for its outreach programme in 2019 demonstrates every part typically found in an entry-level instrument of this kind.

At the front, or "sky", end of the main tube sits the objective lens, a large glass lens whose job is to gather incoming light from a distant object and bend it inward so that the rays converge to form a small, sharp image partway down the tube. The wider the objective lens, the more light the telescope can collect, which is why serious observers judge a refractor chiefly by the diameter of this front lens rather than by its magnifying power.

Because the image formed by the objective lens does not always land at exactly the same distance down the tube, the correct focal point shifts slightly depending on what is being observed, the rear section of the telescope includes a draw tube, a narrower sliding sleeve that can be moved in and out of the main tube to bring the image into sharp focus. A focus knob mounted on the side of the draw tube turns a fine gear that moves the sleeve smoothly and precisely, allowing an observer to sharpen the image without touching, and so accidentally shifting, the rest of the telescope.

At the very end of the draw tube sits the eyepiece, a small, removable lens assembly that the observer looks through directly; it takes the small image formed by the objective lens and magnifies it further before it reaches the eye, and swapping in an eyepiece of a different focal length changes the telescope's overall magnification.

Because the main tube's narrow field of view makes it difficult to locate faint objects directly, a small finder scope is mounted alongside the main tube, giving a wider, lower-magnification view that helps the observer aim the main instrument at the right patch of sky before switching to the eyepiece. The whole assembly rests on a tripod mount, a three-legged stand with a pivoting head that lets the observer swing the tube smoothly to track a target as it moves slowly across the night sky.

The diagram below shows the layout of the Hallowick Astronomy Club's refracting telescope, from front (sky end) to rear (eyepiece end). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The large lens at the front, or "sky", end of the tube that gathers and bends incoming light 2 ____________________. The narrower sliding sleeve at the rear of the tube that moves in and out to focus the image 3 ____________________. The control on the side of the draw tube that turns a gear to move the sleeve smoothly 4 ____________________. The small lens assembly at the very end of the draw tube that the observer looks through 5 ____________________. The smaller, wide-view instrument mounted alongside the main tube, used for aiming at the right patch of sky 6 ____________________. The three-legged stand with a pivoting head that supports the whole assembly

A leaf's internal structure, viewed in cross-section, reveals several distinct layers, each fine-tuned by evolution to maximise the amount of light captured for photosynthesis while limiting the loss of water to the surrounding air. Botanists studying leaf anatomy at the Fenmarsh Plant Sciences Institute in 2020 used thin-sectioned samples from a broad-leaved shrub to illustrate the arrangement common to most flowering plants.

Covering the entire outer surface of the leaf is a waxy cuticle, a thin, transparent layer secreted by the cells beneath it that dramatically reduces water loss through evaporation while still allowing sunlight to pass through largely unhindered. Directly beneath the cuticle on the upper surface lies the upper epidermis, a single layer of tightly packed, transparent cells that contains no chloroplasts of its own but instead acts chiefly as a protective barrier, letting light pass down into the tissue below.

Immediately under the upper epidermis sits the palisade mesophyll, a layer of tall, closely packed, column-shaped cells crammed with chloroplasts and oriented so that their long axes run perpendicular to the leaf surface, an arrangement that captures the maximum amount of direct sunlight for photosynthesis. Below this dense layer lies the spongy mesophyll, made up of loosely arranged, irregularly shaped cells with large air spaces between them; these air spaces allow carbon dioxide and oxygen to diffuse freely through the tissue and reach the photosynthesising cells above.

Running through the spongy mesophyll is a vascular bundle, which bundles together the xylem, carrying water and dissolved minerals up from the roots, and the phloem, carrying the sugars produced by photosynthesis away to the rest of the plant. On the lower surface of the leaf sits the lower epidermis, broadly similar to its upper counterpart but interrupted at intervals by small pores called stomata; each stoma is flanked by a pair of guard cells, which change shape to open or close the pore and so control the movement of water vapour and gases into and out of the leaf.

The diagram below shows a cross-section of a leaf, from the upper surface (top) to the lower surface (bottom). Label the diagram below. Choose NO MORE THAN TWO WORDS from the passage for each answer.

1 ____________________. The thin, waxy, transparent layer covering the entire outer surface of the leaf, which reduces water loss 2 ____________________. The single layer of tightly packed, transparent cells directly beneath this waxy layer on the upper surface 3 ____________________. The layer of tall, column-shaped cells packed with chloroplasts, arranged perpendicular to the leaf surface, just below the upper layer 4 ____________________. The layer of loosely arranged cells with large air spaces between them, lying below the column-shaped layer 5 ____________________. The structure running through this loosely arranged layer that bundles together the leaf's water- and sugar-transporting tissues 6 ____________________. The layer on the lower surface of the leaf, broadly similar to its upper counterpart 7 ____________________. The small pore within this lower layer, through which gases and water vapour move into and out of the leaf 8 ____________________. The pair of specialised cells flanking this pore that change shape to open or close it