The life cycle of pteridophytes and alternation of generation in pteridophytes

Firstly, we will discuss the alternation of generation:

Simply it is the existence of two different stages in the life cycle of any organism. These stages are the sporophyte stage and the gametophyte stage. In pteridophytes, the main body is sporophyte.

Now, what is meant by the main body of Pteridophyte?
The simple meaning of this sentence is main or long-time pteridophytes live as sporophytes in nature or diploids in nature or the thallus of pteridophyte produces spores.

This sporophytic pteridophyte forms a gametophyte stage during its life cycle and the conversion of gametophyte to sporophyte or sporophyte to gametophyte is called alternation of generation.

In the case of pteridophytes, a special structure is formed on leaves which is called sporophyll. Spores are produced on sporophyll through meiosis.

Alternation of generation in pteridophyte:

Sporophytic stage is the main stage in pteridophytes.
Pteridophytes have a special structure called sporophyll, which produces spores.
Spores germinate on favorable conditions and form a structure called prothallus.
Prothallus is the gametophytic stage of pteridophyte.
Gametes are produced in prothallus which forms a new pteridophyte which is again a sporophytic stage

The life cycle of pteridophyte:

The life cycle of pteridophytes can be divided as:

Homosporous life cycle of pteridophyte
Heterosporous life cycle of pteridophyte

Homosporous life cycle

The main body is sporophyte in pteridophytes.
Pteriphytes have a special structure called sporophyll.
Sporophyll forms a special structure called sporangia.
Sporangia produce spores.
Spores produces by sporangia are diploid.
Spores after germination form a structure called prothallus.
Prothallus is free living body and not depends on pteridophyte because it is green in color and have chlorophyll which helps to prepare its food through photosynthesis.
Prothallus forms male and female sex organs,
These male and female structures are gametophytic in nature and hence produces haploid gametes.
Gametes fertized in the presence of water so, water is essential for gametes.
These gametes fuse to form a diploid zygote.
This zygote then forms a new pteridophyte.

Heterosporous life cycle

The main body is also sporophyte because it is a pteridophyte plant.
They have a special structure called sporophyll which produces spores.
In the heterosporous life cycle, two types of sporangia are formed:

Microsporangia
Macrosporangia

Microsporangia forms microspores which released out from microsporangia.
Macrosporangia form macrospores. These macrospores retained inside the macrosporangia.
Microspores from the male sex organ antheridium, which produces male gametes.
Macrospore forms the female sex part archegonium, which is involved in the formation of female gamete.
Microspore are free-living which means that they can prepare their own food through photosynthesis.
While macrospore are not free-living and depends on parent pteridophyte.
This means in the heterosporic life cycle, the gametophytic stage is dependent on the sporophytic stage, which was seen for the first time in the environment
An antherozoid comes from outside from antheridium and fertilizes this female gametophyte to form the zygote.
Water is also essential for this fertilization.
When a zygote is formed, this will come out from the parent pteridophyte and form a new diploid, sporophytic pteridophyte which is also free living in nature.

heteropsoric life cycle in pteridophytes

Points to be remembered:

Main body of pteridophyte is sporophyte.
Sporophytic stage is diploid and the Gametophyte stage is always haploid.
Mitosis occurs at gametophyte while meiosis takes place at sporophyte to produce spores.
Zygote is also diploid.
In the homosporous life cycle, the gametophyte stage is free-living.
In the heterosporic life cycle, female gametophyte depends on sporophytic body.