Olfactory Imprinting in Smolt Development

Free to try, no login

In the text below some words are missing. Drag words from the box below to the appropriate place in the text. There are more words than you need.

Young salmon undergo a critical physiological transition known as smoltification before migrating to the sea. During this brief window, juveniles unique chemical signatures from their home streams into neurological memory. Elevated hormone levels heighten their olfactory sensitivity, enabling them to minute concentrations of organic compounds. Years later, returning adults rely on these stored chemical cues to their natal tributaries with extraordinary precision.

Drag a word into a gap, or tap a word and then a gap. Tap a filled gap to empty it.

Questions 2–5

In the text below some words are missing. Drag words from the box below to the appropriate place in the text. There are more words than you need.

Read them here; log in to answer and check them.

Geomagnetic Orientation at Sea

While oceanic feeding grounds may lie thousands of kilometres from freshwater spawning grounds, salmon navigate open waters using geomagnetic cues. Specialised cells containing magnetic minerals act as an internal 1, allowing fish to perceive variations in the Earth's magnetic field. This sensory system provides both directional orientation and positional 2, helping the fish establish their geographic coordinates and maintain a consistent 3 across featureless marine environments.

compass
aquatic
accelerate
trajectory
current
awareness

Physiological Costs of River Ascent

Re-entering freshwater triggers profound anatomical and physiological changes as adult salmon cease feeding entirely. To fuel their strenuous upstream journey, they 1 stored lipids and muscle tissues, rapidly depleting bodily reserves. Concurrently, reproductive organs mature while the digestive tract begins to 2. This irreversible investment ensures that remaining energy is 3 exclusively into migration and spawning before the individuals inevitably perish.

metabolise
dissolved
wandering
expand
channelled
degenerate

Genetic Isolation Across River Basins

Precise homing behaviour restricts gene flow between different river basins, promoting reproductive 1 among salmon stocks. Over generations, natural selection drives local adaptation, shaping distinct morphological traits and emergence timing suited to specific watershed conditions. Although occasional straying occurs, the high fidelity to natal streams maintains genetic 2 across populations, ensuring that advantageous traits remain 3 within their native habitats.

isolation
combined
preserved
dilution
diversity
migratory

Anthropogenic Disruption of Homing Cues

Human alterations to river systems can severely 1 the sensory mechanisms that salmon depend on for homing. Hydroelectric dams physically block upstream passage, while artificial reservoirs alter water flow and temperature gradients. Furthermore, agricultural runoff and industrial contaminants can mask natural olfactory signatures, causing returning adults to experience spatial 2 and fail to reach their ancestral grounds, ultimately reducing overall spawning 3.

disorientation
navigation
success
elevated
enhance
disrupt

Want to answer the other 4?

Log in to practise Reading: Fill in the Blanks in the BandLadder app: the full question bank, instant scoring the way Pearson marks it, and answer explanations.

Ready for the whole test?

Take a full PTE mock with every question type, the real timings and a score on Pearson's 10–90 scale the moment you finish.

Try a free PTE mock →

Keep practising

Mechanisms of Salmon Homing