Petunia axillaris is a plant with flowers that are pollinated by night-flying moths. To attract moths, P. axillaris synthesises compounds at night that are released as scents (attractive smells).

Figure 8.1 shows a flower of P. axillaris. Figure 8.2 shows a moth with large sensory structures known as antennae.

Figure 8.1, a photograph of a single white Petunia axillaris flower, showing its broad trumpet-shaped petals and central reproductive structures.

Figure 8.2, a photograph of a moth viewed head-on, showing its two large feathery antennae spread outward and its furry head and thorax.

Moths detect scent chemicals using sensory receptor cells on their antennae. Outline the role of sensory receptor cells.

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8(a)(ii)Gene RegulationMedium3 marks

The compounds that are released as scents by P. axillaris are lipids. Outline how P. axillaris could control the production of scent chemicals by regulating gene expression, so that scent chemicals are synthesised only at night.

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8(b)Gene RegulationMedium3 marks

Microarrays could be used to investigate whether gene expression in P. axillaris is different during the day compared to the night. Figure 8.3 shows some steps that would be performed in this microarray analysis.

Figure 8.3, a flow diagram of a microarray analysis: separate day-sample and night-sample flower cells each have chemical A extracted from them, chemical B synthesised from A, and a fluorescent label added to B (green for the day sample, red for the night sample); both labelled samples are then applied to a microarray chip, a grid of spots shown at the bottom, where C labels one individual spot on the chip.

Identify A, B and C on Figure 8.3.