Posts Tagged ‘Alternation of Generations’

The life cycle of plants is quite different from the life cycle of animals. Plants go through a cycle called alternation of generations which means that there are two multicellular stages. One is diploid, called the sporophyte, and one is haploid, called the gametophyte. In contrast, our animal life cycle has only one multicellular stage, the adult that we are all in as we read/write this.

These two multicellular stages mean that there are a lot of other facets in the plant life cycle that may be unfamiliar to those of us with animal life cycles. The one that I am going to focus on here is the difference between spores and gametes. In dipoid organisms, like us, we have no spores. Our only single cell stage are our gametes. But plants have both spores and gametes and this can lead to some confusion because there are some similarities between the two. Spores and gametes are singles celled, and they are both haploid. But these are pretty much the only similarities you will find.

Fundamentally, spores and gametes are very different. One difference is in the type of reproduction that each are involved in. Spores are used in asexual reproduction, while gametes are used in sexual reproduction. Another difference is in what each needs to develop into the next stage in the life cycle. A spore has the ability to grow into the adult gametophyte all by itself. It does not need to interact with any other cell to do this, all it needs is to find favorable growing conditions. A gamete has to fuse with another gamete before it can form a zygote that then can grow into the adult sporophyte. A third difference is in the life span of these cells. Spores have a very tough outer layer that allows them to remain dormant, but viable, for extremely long periods of time (sometimes decades or even longer) in order to persist through periods of poor conditions until better growing conditions arise. Gametes are much more delicate and generally only remain viable for a matter of days, and so must find another gamete quickly. A fourth difference, related to the how long each cell lasts, is dispersal ability. Especially in more basally derived plant lineages, spores can disperse very, very long distances. They are small and light, and so can be carried by the wind for hundreds, or even thousands, of miles. Gametes, on the other hand can only disperse very short distances. The egg, the larger gamete, is generally retained and so does not disperse at all while the sperm, the small gamete, will swim to find an egg, but will generally only swim a few inches. Yet another difference between spores and gametes is the process by which they are created. Spores are created through meiosis. The structure that produces a spore is diploid and so must go through a process of chromosome reduction in order to create the haploid spores. Gametes are produced by mitosis. The structure that produces a gamete is already haploid and so does not need to change the number of chromosomes it has in order to produce haploid gametes.

So, hopefully this post explains how different spores and gametes are. I wanted to highlight this information because I see it as a common source of error.

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