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Gametophyte: Definition & Explanation

Gametophyte: Definition & Explanation
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  • 0:00 Definition of Gametophyte
  • 0:32 What Do Gametophytes Do?
  • 2:02 How Are Gametophytes Produced?
  • 2:30 Gametophytes in Plants
  • 4:05 Lesson Summary
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Lesson Transcript
Instructor: Angela Lynn Swafford

Lynn has a BS and MS in biology and has taught many college biology courses.

Wouldn't it be weird if humans had entire generations in which individuals had half the normal number of chromosomes in their cells? Plants actually have this generation, and it is called a gametophyte. Learn more about gametophytes in this lesson.

Definition of Gametophyte

Alternation of generations is a type of life cycle found in all plants and some algae species. This process involves a multicellular diploid generation called a sporophyte and a multicellular haploid generation called a gametophyte. Diploid means having two sets of chromosomes in your cells and is usually written as '2n'. Haploid means having only one set of chromosomes in your cells and is written as 'n.'

Let's take a closer look at the gametophyte generation.

What Do Gametophytes Do?

Gamete production is the main job of a gametophyte. Gametes are haploid reproductive cells, such as eggs and sperm. They are produced in sex organs on the haploid gametophyte by mitosis, or cellular division without reduction of chromosome sets. There are two sex organs, or gametangia, found in gametophytes:

  • Archegonium (archegonia is plural): Multicellular female sex organ that produces eggs
  • Antheridium (antheridia is plural): Multicellular male sex organ that produces sperm

You can think of an archegonium as being like an ovary in human females because both structures produce haploid egg cells. An antheridium is like a testis in human males because both produce haploid sperm cells. However, both archegonia and antheridia are usually microscopic structures.

Some gametophytes have both archegonia and antheridia. These are called bisexual gametophytes because they have both female and male structures. A gametophyte that has only one type of gametangium (either an archegonium or an antheridium but not both) is called a unisexual gametophyte.

Gametophytes are necessary for sexual reproduction, which occurs when a sperm cell fertilizes an egg cell. Sexual reproduction produces a diploid unicellular zygote that will undergo mitosis to become multicellular. This multicellular diploid organism is the sporophyte.

How Are Gametophytes Produced?

A gametophyte is created when the sporophyte generation produces spores. Spores are made by meiosis or cell division that reduces the number of chromosomes by half. Remember, sporophytes are diploid, so if a diploid cell undergoes meiosis, it will produce haploid cells. These haploid cells produced by sporophytes are spores. Spores will then undergo mitosis to grow into a multicellular haploid gametophyte.

Gametophytes In Plants

Let's look at some examples of gametophytes in different groups of plants.

In nonvascular plants, like mosses, the gametophyte generation is the dominant generation. This means that the gametophyte is larger in size and lives longer than the sporophyte generation. So when you are looking at the green leafy part of a moss, this is the gametophyte generation. A moss sporophyte is short-lived and grows out of the gametophyte. It is also completely dependent upon the gametophyte for nutrients.

In vascular plants, like ferns and fronds, the gametophyte is small and not the dominant generation. This means that when you look at any vascular plant, you are looking at a sporophyte. You will have to work hard to see the gametophyte of a vascular plant.

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