For non-mobile organisms, like plants, reproduction can be a bit tricky. Two plants cannot come together to mate. Instead, they have to find different ways in which to reproduce. One such way is with spores.
What Is a Sporangium?
A sporangium is a structure in certain plants and other organisms that is charged with making and storing spores. Spores are haploid structures created in organisms that help to germinate and form new organisms. In other words, they help organisms to reproduce.
But, what does it mean that they’re haploid? Well, it simply means that there’s only half of the required chromosomes to form a full diploid organism. The spores produced and released by the sporangia are able to divide via mitosis, or cell division.
Alternation of Generations
As previously stated, spores are haploid structures. They contain one half of the required chromosomes for a particular organism. Unlike other haploid cells, they don’t need another spore or another half of the chromosomes in order to create a new organism; they do it through a different form of reproduction.The spores that are created by the sporangia are a form of asexual reproduction, which means that they don’t need two different gametes, or sex cells, in order to reproduce.
The spore can divide and copy itself, creating a new organism. What occurs in plants, fungi, and similar organisms is known as an alternation of generations, which is just another way that an organism can create many more organisms.An alternation of generations has two main phases: the sporophyte phase and the gametophyte phase. The sporophyte phase creates spores via a sporangium. These spores are haploid and must divide and copy via mitosis. As they do, they’ll begin to form gametophytes, which is part of the gametophyte phase.
These can divide via meiosis, or sex cell division, to create gametes. We need one male and one female gamete in order to fuse and form a zygote. This then forms a sporophyte, starting the whole process over again.
Many different types of plants and some mosses are what we refer to as homosporous, where they only make one type of spore. In other types of mosses and fungi, for example, we see two different types of spores, one male, and one female spore, which are referred to as heterosporous.The male spores are called microspores, and their corresponding sporangia are referred to as microsporangia.
The female spores are called megaspores, and those corresponding sporangia are called megasporangia. In plants that are heterosporous, we see the microspores forming male gametophytes and the megaspores forming female gametophytes. Once the gametophyte is formed, the gametes inside can be created and released. The male gametophyte makes male gametes, and the female gametophyte makes female gametes. This allows them to fuse together, forming a fertilized cell, or zygote.
Sporangia are the structures that house and create spores in certain organisms. As many of these organisms are non-mobile, they have no choice but to release the spores out into the environment.
This allows the spores, which are haploid, the opportunity to germinate and form gametophytes. The gametophyte then forms male and female gametes, which when given the proper conditions, will fuse together, forming a zygote. This zygote will have half of its chromosomes from the male gamete and half from the female gamete.The zygote then grows into a sporophyte, which creates a sporangium for itself, and the cycle continues.
In homosporous organisms there exists only one kind of sporangium, and in heterosporous organisms there exists two: a male sporangium is called a microsporangium and a female is called a megasporangium.