Question 2: Explain Merit

The honey bee (Apis mellifera) is active by day, and its pollen foraging is tied to its circadian rhythm. Bees find their way around and back to the hive by cues from their surroundings, including the Sun’s position as a compass, and can forage 5 km out and still get home when cloud hides the Sun. In a total solar eclipse the Moon covers the Sun completely, so bees meet darkness at a time they normally would not. Biologists compared foraging on an ordinary day with the day of a total eclipse. Their graph (Figure 4) is greyed out in NZQA’s public copy; as the schedule reads it, ordinary-day foraging climbs through the morning to a peak near 1:30 pm and eases off slowly in the late afternoon, while on the eclipse day it is normal until the eclipse, falls to a handful of bees in totality, comes back only slowly, and stays under the ordinary day until after 3 pm, when it rises above it.

Explain how the circadian rhythm is linked to the sun compass, which homing cues bees use on sunny and on overcast days, and the foraging on each of the two days.

The 2025 paper, page 6 ↗ Marking schedule, page 4 ↗

Work it out

Try it on paper first. Stuck? Take one hint at a time.

1 The describe answer said bees fly at an angle to the Sun. The Sun moves across the sky, so why does that angle need a clock?
The Sun’s position changes through the day, so a fixed angle would take a bee further off course as the hours pass. Its circadian clock tells it the time, so it can keep adjusting the angle to where the Sun is: a time-compensated sun compass.
2 Which cues get a bee home on a sunny day, and why?
The Sun itself, read with that clock, and the landmarks and hive scent it knows near home. The Sun is only usable when it can be seen.
3 Which cues get it home on an overcast day, and why do they still work?
Polarised light, because the pattern sunlight makes in the sky still gives the Sun’s direction through thinner cloud and gaps; landmarks and scent, which do not need the Sun at all; and possibly the magnetic field, which cloud does not change. Having several cues means a forager 5 km away can still get home.
4 Why does foraging on a normal day rise to a peak and then fall?
The circadian rhythm starts foraging as the light comes up, activity builds as it gets lighter and warmer and flowers open, peaks in the early afternoon, and falls off as the light fades, so foragers are home by dark.
5 Why did foraging collapse during the eclipse, and why did it recover slowly?
The sudden darkness is read like dusk, the sun compass is useless, so most bees stopped going out and many came home. Afterwards bees went back out gradually, and the later rise above normal may be the colony making up for lost foraging time.
6 Why were a few bees still foraging in the dark?
Their internal clock still said midday: it is entrained by light but does not switch over the moment light drops, so a few minutes of darkness were not read as night by every bee.

Answer The Sun’s position changes through the day, so a bee using it as a compass must allow for the time; its circadian clock does this, keeping the angle it flies at matched to where the Sun is (a time-compensated sun compass). On sunny days bees home by the Sun, with landmarks and hive scent near home. On overcast days they use polarised light, which still shows the Sun’s direction through cloud gaps, together with landmarks, scent and possibly the magnetic field, none of which need the Sun, so a forager can get home from 5 km away in any weather. On a normal day the circadian rhythm starts foraging in the morning light; it builds to an early-afternoon peak and falls as the light fades. On the eclipse day the sudden darkness was read like dusk and the sun compass failed, so most bees stopped and returned; activity recovered slowly, then rose above normal, perhaps making up lost time. A few bees kept foraging because their clock, entrained by light but not reset instantly, still read the time as midday.

What the marker wanted

Achieved The describe points: diurnal, circadian rhythm with its clock, each homing cue, and foraging on each day.
Merit Explains, not just names: why the circadian rhythm is tied to the sun compass; the homing cues for sunny days; the homing cues for overcast days; the foraging pattern on a normal day; the foraging pattern on the eclipse day; and why some bees forage during the eclipse’s darkness. Three make M6.

One answer, N0 to E8. Merit points sit above the Achieved ones: two give M5, three M6.

In our words, from NZQA’s 2025 marking schedule.

Common mistake

Leaving out why some bees kept foraging in the dark. NZQA’s 2025 report singles out that reason as one candidates need, and it is a Merit point on its own.

How did it go?

Got it moves it further out. Review brings it back tomorrow.