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  • My textbook says that in both groups of seedless plants (vascular plants, non-vascular plants) the gametophyte is a free-living plant, independent of the sporophyte. I don't understand this statement and am now wondering if the sporophyte and gametophyte are stages in a plant's lifecycle, or are they individual parts of the plant, or are the sporophyte and the gametophyte different plants altogether? Secondly, does this differ depending on the organism?

Different plants or different structures that make up the same organism?

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The sporophtye is the diploid stage in the life cycle. In comparison, with humans, you and I would be sporophytes.

The Gametophyte is the haploid stage in the life cycle. In comparison, with humans, spermatozoids and ovules are gametophytes.

Independence

Note for what follows: "independent" can be understood in terms of "ability to survive". Being independent according to its ability to survive. One might use the word "independent" for other concerns though! For example: "Independent" in the sense "no nutrient exchange between the two"

Therefore, one could say that in humans, the gametophyte is not independent (in it's ability to survive) of the sporophyte. Similarly, in moss (bryophyta), the gametophyte is not independent of the sporophyte because the gametophyte grows on the sporophyte using its nutrients (one could say that the gametophyte parasitize the sporophyte but that would be a bit misleading!). If the sporophyte is independent of the gametophyte (or vice-versa), it means that there is alternation of generations. In other words, sporophyte and gametophyte live separately (like two different individuals).

Life-cycle

You can find tons of examples of weird life cycles, in particular in plants, fungi and parasites but not only. And you may find many examples for which the type of sexual reproduction or the type of life-cycle are hard to defined with these relatively simple concepts.

Identity

The question of identiy (how separate or genetically different should two individuals be so that we consider them to be two different individuals) is rather a question of philosophy. Such discussions about identity occur when we talk about clones (ramet and genet), about life cycle or about level of organisation/level of selection. The book Major Transition in Evolution (Revisited) provides many of the philosophical discussion on the subject of identity in population genetics.

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    $\begingroup$ great answer.. but your book reference link is not recognised by Amazon? Do you have the title of the book instead? Thanks $\endgroup$ – user9846 Oct 19 '14 at 13:24
  • $\begingroup$ Oops I missed your comments 2 months ago. I edited the link. Thanks you! $\endgroup$ – Remi.b Dec 31 '14 at 9:32

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