May/June 2026 Paper 43

2026 · 10 questions · 31 parts · 100 marks

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8(a)Plant Responses Growth RegulatorsMedium4 marks
Figure 8.1 is a diagram of a section through a barley seed.
Figure 8.1, a diagram of a section through a barley seed, labelled with four parts: the seed coat forms the thin outer layer; the aleurone layer is the layer just inside the seed coat, running around the upper/outer part of the seed; the endosperm is the large central region inside the aleurone layer; the embryo is the smaller, finger-shaped region at the base of the seed, separate from the endosperm.
Match the part of the seed from Figure 8.1 to the function it carries out. An item may be used more than once.
Gibberellin synthesis
Starch store
Amylase synthesis
Maltose production
8(b)(i)Plant Responses Growth RegulatorsMedium3 marks
The plant hormone auxin has an important role in the growth of plants. When auxin molecules bind to receptors in the cell surface membrane of young cells, a series of events is triggered that results in cell elongation. Figure 8.2 outlines this series of events.
Figure 8.2, a diagram of part of a cell surface membrane and cell wall showing three transport proteins in sequence: after auxin binds the receptor (triggering “stimulation”, shown by a dashed arrow), event 1 shows ion A pumped through the first protein from the cytoplasm, across the membrane, into the cell wall (arrow pointing outward/upward); event 2 shows ion B moving through the second protein from the cell wall into the cytoplasm (arrow pointing inward/downward); event 3 shows water (H2O) moving through the third protein from the cell wall into the cytoplasm (arrow pointing inward/downward).
Describe event 1 in Figure 8.2 and explain how this event is important for the process of cell elongation.

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8(b)(ii)Plant Responses Growth RegulatorsMedium3 marks
Explain how event 2 leads to event 3 and results in cell elongation.

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