Life cycle of bryophytes.

Bryophytes, which include mosses, liverworts, and hornworts, have a life cycle that alternates between a haploid gametophyte stage and a diploid sporophyte stage. This life cycle is known as alternation of generations.

1. Gametophyte stage:
- The life cycle of bryophytes begins with the germination of a haploid spore, which grows into a multicellular, photosynthetic gametophyte.
- The gametophyte produces both male and female gametangia (structures that produce gametes). The male gametangia, called antheridia, produce sperm cells, while the female gametangia, called archegonia, produce egg cells.
- Water is required for fertilization in bryophytes, as the sperm cells must swim to the egg cells for fertilization to occur. Once fertilization occurs, a diploid zygote is formed.

2. Sporophyte stage:
- The zygote develops into a diploid sporophyte, which remains attached to the gametophyte and is dependent on it for nutrients.
- The sporophyte consists of a foot, seta (stalk), and capsule. The capsule contains spores, which are produced through meiosis.
- When the sporophyte is mature, the capsule ruptures, releasing the spores into the environment.

3. Spore dispersal and germination:
- The spores are dispersed by wind or water and can germinate under suitable conditions to form new gametophytes.
- The cycle then repeats, with the gametophyte producing gametes, fertilization occurring, and a new sporophyte developing.

Overall, the life cycle of bryophytes is characterized by the alternation of generations between a haploid gametophyte and a diploid sporophyte, with spores serving as the means of dispersal and reproduction.

Bryophytes are non-vascular plants that reproduce through alternation of generations. Their life cycle consists of two distinct phases: a gametophyte phase and a sporophyte phase.

Gametophyte Phase

1. Spore Germination: A spore germinates and grows into a juvenile gametophyte.
2. Protonema: The juvenile gametophyte develops into thread-like filaments called protonema.
3. Buds: Buds form on the protonema, developing into leafy gametophytes.
4. Gametangia: Leafy gametophytes produce specialized structures called gametangia.
5. Archegonia (female): Archegonia are flask-shaped structures that house female gametes (eggs).
6. Antheridia (male): Antheridia are club-shaped structures that produce male gametes (sperm).

Fertilization and Sporophyte Development

1. Sperm Release: Sperm from antheridia are released into water or air.
2. Fertilization: Sperm swim to the archegonia and fertilize the eggs.
3. Zygote: The fertilized egg develops into a diploid zygote.
4. Embryo: The zygote undergoes cell division to form an embryo within the archegonium.
5. Sporophyte: The embryo develops into a sporophyte (diploid plant).

Sporophyte Phase

1. Spore Production: The sporophyte consists of a stalk (seta) and a capsule (sporangium).
2. Meiosis: Within the sporangium, the diploid cells undergo meiosis to produce haploid spores.
3. Spore Dispersal: The spores are released into the environment.

Return to Gametophyte Phase

1. Spore Germination: A spore germinates and grows into a juvenile gametophyte, restarting the life cycle.

Significance of Alternation of Generations

- Genetic Variation: Meiosis during spore production creates genetic variation in the spores.
- Environmental Adaptation: The gametophyte phase is dominant in moist habitats, while the sporophyte phase is better adapted to drier conditions.
- Dispersal: The production of numerous spores by the sporophyte ensures the survival and spread of the species.