Biology / Bio 2185 · Atom · ~20 seconds
Seed Evolution: Three Key Innovations
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The seed habit combines three innovations: heterospory, per Bio 2181, an ovule protecting the megaspore, and pollen replacing swimming sperm.
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Pollen carries sperm to an ovule without standing water, freeing seed plants from the fertilization constraint bryophytes and ferns face.
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A seed is not a mere spore with a shell — it is a fertilized embryo packaged with stored food.