Biology · Kingdom Plantae. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
A seed is a fertilised ovule: an embryo with a food store inside a protective coat. The seed habit began with heterospory, the making of small microspores and large megaspores. Next the megaspore was kept inside its sporangium, which gained protective coats called integuments. Selaginella shows the early steps.
Gymnosperms such as Pinus have naked seeds on the scales of cones. Angiosperms have their ovules closed inside an ovary, which becomes the fruit. Only angiosperms have flowers and double fertilisation.
Pollen tubes carry the male gametes to the egg, so seed plants do not need water for fertilisation. Angiosperm families are recognised by their flowers and fruits.
Students give Pinus a triploid endosperm. Triploid endosperm comes from double fertilisation, which happens only in angiosperms; in Pinus the endosperm is haploid.
Answer: Endosperm cell 12, embryo cell 24.
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