#bryophytes_class_11 #life_cycle_of_bryophytes #alternation_of_generation
You can read the detailed article on the same topic by clicking the following link:-
[ Ссылка ]
0:00 Intro
0:15 Features and Habitat
0:30 Life cycle of Mosses
0:45 Spore dispersal
1:00 Germination of Spores
1:10 Protonema
1:28 Leafy gametophyte
2:08 Male branch
2:55 Antherozoids
3:25 Female branch
4:10 Transfer of gametes
4:50 Development of Sporophyte
5:40 Capsule and Peristome teeth
HABITAT- Moist, damp and shady places like river beds, rock crevices etc.
BODY STRUCTURE-
Gametophyte-
• It is the main (dominant) plant body.
• In juvenile form, the gametophyte is green, photosynthetic and filamentous called Protonema.
• In mature form, the gametophyte is erect and leafy having root like, stem like and leaf like structures called Rhizoid, Cauloid and Phylloid respectively.
Sporophyte-
• It grows as a parasite on the Gametophyte body.
• Sporophyte is photosynthetic but obtains its water and nutrients from Gametophyte body.
{ Bryophytes lacks vascular tissues i.e. Xylem and Phloem }
REPRODUCTION- Both asexual (budding, fragmentation) and sexual mode are present.
Life Cycle of Mosses
Gametophyte
On finding a suitable site, these spores starts to germinate and divides by mitotic divisions. This results in development of juvenile gametophyte called Protonema (n). The development of this filamentous stage helps in rapid growth as the Protonema (n) divides asexually by fragmentation.
The juvenile gametophyte now starts producing buds which grows vertically to form the Leafy Gametophyte (n) having slight differentiation of body parts. Each leafy gametophyte develops two branches, one bearing male sex organs (Antheridium) at its tip called Male branch and the other bearing female sex organs (Archaegonium) at its tip called Female branch.
Male branch
The tip of male branch is surrounded by a group of leaves called Perichaetial leaves (n). Numerous male sex organs called Antheridia are also present at the tip. These antheridia are surrounded by layer of sterile cells (n) called Jacket and contains Androcytes (n) that are fertile haploid cells and will mature into male gametes later. Long thread like structures called Paraphyses (n) arises from the tip which helps in accumulation of water and helps in release and transfer of male gametes. During rainy season, the water gets accumulated at the tip due to paraphyses. The Antheridium (n) releases the Androcytes (n) into the accumulated water and these Androcytes (n) now transform into male gametes called Antherozoids (n). Each Antherozoid is a long, spirally coiled and bi-flagellated male gamete.
Female branch
The tip of female branch is also surrounded by Perichaetial leaves (n) and bears Paraphyses (n). The female sex organs Archaegonium (n) are surrounded by sterile layer of cells forming Jacket. Each Archaegonium has a long and narrow upper part called Neck (n) and a swollen base called Venter (n). The neck contains 6-10 cells called Neck Canal Cells (n) and the venter contains a single Venter Canal Cell (n) and a single large Egg cell (n). During rainy season water gets accumulated at tip of female branch too.
Transfer of male gametes and fertilization
The Antherozoids (n) may be transferred from a male branch to a female branch along with the splashes of water drops. The NCC (n) and VCC (n) of Archaegonium dissolves to release chemicals. This clears the path for entry of male gametes inside the Archaegonium and also directs the chemotactic movement of male gametes.
The Antherozoid (n) fuses with Egg (n) which results in formation of a diploid cell called Zygote (2n). The zygote represents the first cell of Sporophytic generation. The zygote now divides mitotically to produce Embryo (2n) and as the developing embryo is retained in the Gametophyte permanently so the Sporophyte plant body develops over the Gametophyte plant body as a partial parasite (as it obtains water and nutrients from gametophyte).
Sporophyte
The Sporophyte plant body is divided into 3 parts:-
Foot (2n)- Penetrates the Gametophyte to provide anchor and absorb water and nutrients.
Seta (2n)- Long part which helps to expose the Capsule for spore dispersal.
Capsule (2n)- Swollen tip of Sporophyte which is protected by a haploid structure called Calyptra (n) during initial stages of development. The Capsule contains diploid cells called Spore Mother Cells (2n) which divides by meiosis and results in formation of haploid Spores (n). When the spore formation is complete, the tip of Capsule called Operculum ruptures and exposes teeth like structures called Peristome teeth.
These spores are now dispersed through wind and germinates to develop new Gametophyte.
