Amphibean of land plants, Bryophytes

 

Ovrerview-

• Bryophytes are  in the next hierarchy to Algae. Their bodies are more diffrentisted and developed  than Algae.

Know more about the algae

• They are also thallus-like but their Thallus is prostrate and erect. 

• They are nonvascular embryophytes including  mosses, liverworts and hornworts. 

• Bryophytes are small plants and  they grow in moist, shady places.

• They have small height like shrubs  due to absence of roots, vascular tissues, mechanical tissues and cuticles.

• They are terrestrial but require water for fertilization to  complete their life cycle. Hence, they are called “Amphibians of plant kingdom”.

• The study of bryophytes is called bryology. Hedwig is called ‘Father of Bryology’. Shiv Ram Kashyap is the ‘Father of Indian Bryology’

• The fossil record indicates that bryophytes evolved on earth about  430 million years ago during the Silurian period of Paleozoic era

General  features of Bryophytes:

Occurence - 

• Bryophytes grow in humid ,damp and shady places and hilly areas.

Gametophyte stage -

• The dominant and main plant body is gametophyte which is haploid .

• The  gametophyte bears unicellular or multicellular rhizoids for attachment with the substrate.

• Sex organs - Gametophyte is well developed and bear sex organs. These sex organs  are multi-cellular and jacketed.

• The male sex organ is anthredia and female sex organ is archegonia.

• Anthredia produces antherozoids or male gamete whereas  archegonia produces eggs enclosed in its ventral canal cells.

• Antherozoid use water as medium and reach to the egg for fertilization.

• After the fusion, zygote is formed. This zygote  does not undergo reduction division and develops into multicellular sporophyte.

Sporophyte-

• Sporophyte is not  free living and depends on gametophyte for nutrition so it is attached with the gametophyte.

• Sporophyte is  differentiated into foot, seta and capsule.

• Capsule produces haploid spores by the reduction division. These spores germinate and form gametophyte.

👌👌Remember - Bryophytes have alternation of generation with the gametophyte and sporophyte.

Classification of Bryophytes-  

• Bryophytes are classified into  three classes - 
• Hepaticae or Liverworts  Anthocerotae  or Hornworts Musci  or Mosses 

General features of  Liverworts.

• Liverworts are present in moist areas , at banks of rivers, damp, soil, bark of trees etc.

• Generally the gametophytic plant body is  thalloid.

• Thallus is dorsiventral Sometimes it is foliose or having tiny leaves without midrib.

• The leafy members have tiny leaf like appandages in two row on stem like structure.

• Each cell in the thallus contains many chloroplasts; the chloroplasts are without pyrenoid.

• Asexual reproduction takes place by the fragmentaion of thallus.

• They also reproduce asexually by the special structure called gemmae or Gemma cup.

• These are asexual buds that are green and multicellular. Gemmae originated on the thallus of liverworts.

• Sexual reproduction takes place in antheridia and archegonia. Both are located on different thallus or same thallus at the dorsal surface.

• Sporophyte may be simple in Riccia having only a single capsule or differentiated into foot, seta and capsule in Marchantia.

• Spores are formed in capsule by meiosis. For Example - Riccia, Marchantia, Pallia and Porella.

General features of  Hornworts

• Gametophytic plant body is simple, thallus  like dorsiventral without air chambers.

• Each cell of the thallus possesses a single large chloroplast with a pyrenoid.

• Sporophyte is not completely dependent on gametophyte for its nourishment.

• It is differentiated into foot seta  and capsules. Seta is meristematic.

• Columella is present in a capsule.

• The sporophytes produce  spores, which play a key role in reproduction. 

• Hornworts do not have  vascular tissue.

• Thallus has thread-like rhizoids to attach the plant’s substrate.

• Rhizoids also absorb water and minerals from the environment. 

• Thallus also has a cyanobacteria called nostoc  as a symbiotic association with the hornwort.

Know about the Kingdom Monera including Cyanobacteria

• Nostoc supplies the hornwort with nitrogen in turn the hornwort supplies Nostoc with carbohydrates produced through photosynthesis.
• Hornworts have a life cycle that contains both sexual gametophyte and asexual sporophyte generations.

• The gametophyte stage is  the dominant generation Because it has  male sex organ or antheridium and the female sex organ, or archegonium.

Multiple Choice Questions on Bryophyte

• Male. gamete or  antherozoids release from the antheridium and travel through the water and reach the archegonium, where they fertilize the eggs.

• Each fertilized egg develops into a diploid embryo that gives rise to sporophyte.

• Sporophytes produce  haploid spores. The spores are released into the environment and form a thallus like gametophyte.

• They also exhibit the alternation of generations. For Example - Anthoceros, Dendoceros, Folioceros, Megaceros, Pheoceros, Notothylas etc.

General features of  Musci or moss

• The dominant stage of moss is gametophyte that is differentiated into two stages - Protonema and leafy stage.

• Protonema is creeping, green stage and developed directly from the spores.

• Leafy stages are developed from the protonema. Leafy stages bear leaves like appendages and are attached with the soil by multicellular rhizoids.

• They reproduce vegetatively by fragmentation and budding of protonema.

• They do sexual reproduction by producing antheridia and archegonia as a result zygote is formed.

• The zygote divides by  meiosis and produces spores that develop into sporophytes.

• In mosses, sporophytes are divided into foot seta capsules and  more developed than other groups.

• It's capsule has a more advanced mechanism of spore dispersal. For Ex- Funeria, Polytrichum Sphagnum,

Importance of Bryophytes:

• Bryophytes, especially mosses, prevent soil erosion caused  by running water.

• They are also involved in the process of succession.

• Mosses are an important link in plant succession on rocky areas.

• They take part in binding soil in rock crevices formed by lichens. Growth of Sphagnum ultimately fills ponds and lakes with soil.

• Peat is a dark spongy fossilized matter of Sphagnum.

• Peat is dried and cut as cakes for use as fuel.

• Peat used as good manure. 

• Mosses are a good source of animal food in rocky and snow covered  areas.

• Polytrichum  is used to remove kidney and gall bladder stones.

• Sphagnum is used for treatment of eye diseases.

• Marchantia polymorpha has been used to cure pulmonary tuberculosis.

• Bryophytes are used as packing material for fragile goods, glass wares etc. Some bryophytes act as indicator plants.