A Moss Life Cycle: Dominant Gametophyte

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  • 0:05 Introduction to Mosses
  • 0:56 Review of Alternation…
  • 2:28 The Haploid Stage
  • 3:30 The Diploid Stage
  • 4:26 Lesson Summary
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Lesson Transcript
Instructor: Danielle Weber

Danielle teaches high school science and has an master's degree in science education.

Mosses are unique because they spend most of their lives with only one set of genetic material rather than the normal two sets. We will look at this cycle and how the alternation of generations takes place in these non-vascular plants.

Introduction to Mosses

Peat and other mosses serve many important purposes.
Moss Example

Mosses are non-vascular plants that do not have flowers or seeds. These simple plants typically grow in damp areas such as forests or wetlands. You may have seen large patches of moss growing on a tree or rock or even on the forest floor. While we may think of mosses as small, forgettable plants, they actually serve several vital roles. For example, peat moss can be used as a fuel, carbon sink, and habitat for many unique organisms. You may also see moss used in flower arrangements or hanging flower baskets. Mosses are also useful to many ecosystems because they can survive in very high or low temperatures and can even help make soil. As for the life cycle of these plants, mosses are unique because they spend most of their lives with only one set of genetic material rather than the normal two sets. This would be like living the majority of your life cycle with only half of your genetic information.

Review of Alternation of Generations

Now that we know a little bit about these non-vascular plants, let's quickly review the concept of alternation of generations before looking at this process in mosses.

Alternation of generations is a life cycle that includes both diploid and haploid multicellular stages. Remember that 'diploid' means 'two sets of chromosomes' and is commonly abbreviated as 2N, where the N stands for 'chromosomes.' In diploid cells, one copy of the chromosomes comes from each parent. For example, in humans you get one copy of chromosomes from your dad and one copy of chromosomes from your mom. The same idea is found in plants. Each diploid cell contains one copy of chromosomes from the male parent and one copy of chromosomes from the female parent. 'Haploid' means 'one set of chromosomes' and is commonly abbreviated as N because there is only one copy of the chromosomes.

Let's look at a diagram of the basic idea of alternation of generations. We can see in this diagram that the life cycle is broken into N - on the top - and 2N - on the bottom. In plants, the gametophyte is N and the sporophyte is 2N.

Diagram of the alternation of generations life cycle
Alteration of Generations Diagram

Previously, we used the Garblinx to illustrate the oddity of this. Remember that the diploid or 2N organism looks like this.


However, when it moves into the haploid stage, the Garblinx looks completely different!

Image of haploid

Two of these haploid organisms will get together and mate in order to produce a new 2N organism that looks similar to our first Garblinx. This Garblinx will then eventually produce a new haploid organism, and so on.

Now that we have a good review of the basics of alternation of generations, let's look at how this process is completed in mosses.

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