This video, we're going to talk about the Laminaria life cycle and alternation of generations. Laminaria is a type of brown algae that lives in aquatic ecosystems, commonly known as kelp. It is an example of a multicellular protist and plays very important roles in coastal ecosystems. It also exhibits alternation of generations, a life cycle that alternates between multicellular diploid and multicellular haploid forms of the organism.
The multicellular diploid form of the organism is called the sporophyte, which produces haploid spores via meiosis. The multicellular haploid form is called the gametophyte. It produces gametes, but via mitosis. Below, we have a diagram representing the Laminaria life cycle. Let's enlarge this diagram so we can see it more clearly, noting the 5 steps numbered throughout.
Let's wipe this diagram clean so we can approach this one step at a time. Before we get started, the bluish arrow on the left represents the diploid stage of the life cycle. Therefore, we put 2 in this blank, and the purplish arrows on the right represent the haploid stage. Let's place n in this blank. We'll start with the mature sporophyte, which contains structures called sporangia that produce spores, undergoing meiosis to produce specifically called zoospores. These zoospores are haploid.
These zoospores will undergo mitosis to produce multicellular haploid organisms called gametophytes. About half of the zoospores will produce male gametophytes, and the other half will produce female gametophytes. The male gametophyte produces sperm and releases them into the aqueous environment, allowing them free movement. In contrast, the female gametophyte produces eggs that remain attached to her. The sperm can merge with the egg in the process of fertilization to produce a zygote, which will be diploid. This zygote undergoes mitosis to produce a developing sporophyte and then a younger sporophyte. The main goal is to return to the mature sporophyte form. And that completes the Laminaria life cycle.
The last thing I want to do is draw your attention to the numbers for each of these steps in the diagram, shown in this table below the diagram on your worksheet. This table lists all steps, providing a brief description of what occurs in each, just as we have discussed. This concludes this video on the Laminaria life cycle and alternation of generations, applying these concepts in problems moving forward. I'll see you all in our next video.
