From R3104 Feb 2018:
Q1 a) State what is meant by ‘seed dormancy’ in plants. [1 mark]
b) Describe THREE distinct primary (innate) dormancy mechanisms giving ONE NAMED plant example for EACH. [ 9 marks]
This question relates to the following part of the syllabus:
1.2 Describe the physiological and environmental factors in seed dormancy.
State what is meant by ‘primary’ (innate) dormancy: dormancy present when seed is shed.
State that ‘secondary’ (induced) dormancy develops from conditions that delay germination after primary dormancy is broken and will result in difficulties in subsequent germination.
State a range of primary dormancy mechanisms, giving ONE plant example for EACH mechanism:
seed coat: interference with water uptake due to impermeable seed coat (Lathyrus odoratus); Seed coat interferes with gas exchange (Beta vulgaris, Paeonia delavayi); Mechanical restraint of the embryo/hard testa (Prunus spp).
Fruit tissue inhibiting germination: Fruit tissue contains germination inhibitors (e.g. tomato (Solanum lycopersicum)).
Seed remains dormant even though seed coat is removed. Internal germination inhibitors (Fraxinus excelsior) Embryo may be immature (Ilex aquifolium)
State the role of abscisic acid, gibberellic acid and cytokinin in dormancy.
Part a) was looking for a statement about seed dormancy in general, and not specifically primary or secondary dormancy. The examiners’ comments suggest the following:
‘ the state, in viable seeds, where germination does not occur, even when the environmental conditions are met’.
The comments point out that the term ’viable’ was missed out by some candidates, and also the conditions optimal for seed germination.
Part b) requires the description of three primary dormancy mechanisms. A plant example is required for each, and the full botanical name should be used. As the question asks you to ‘describe’ a good amount of detail is required.
The examiners’ comments suggest the following as examples of suitable answers:
‘waterproofed testa, impervious epicarps, immature embryos and germination inhibitors’.
They continue to say that ‘Many answers which displayed a real knowledge included a description how these mechanisms delay germination, or of remedial actions to overcome the dormancy mechanisms’. This gives some idea of the detail to include in your answer.