Class 11 Biology – Pteridophyta Notes
Complete notes on Pteridophyta, general characteristics, Dryopteris, reproduction, prothallus, fertilization and alternation of generations.
Pteridophyta
The term Pteridophyta is derived from Greek words: pteris, meaning feather, and phyton, meaning plant.
Pteridophytes are plants having feather-like fronds.
They are also called vascular cryptogams because they are non-flowering plants possessing vascular tissues such as xylem and phloem.
According to the handwritten notes, 31 families, 105 genera and 385 species of ferns have been reported from Nepal.
They are mainly land plants growing in moist, shady and cool places. Some species are aquatic and a few are epiphytes.
General Characteristics of Pteridophytes
- The plant body is the sporophyte.
- The sporophyte is generally differentiated into roots, stem and leaves.
- They are non-flowering plants.
- They possess vascular tissues such as xylem and phloem.
- Reproduction takes place by spores produced inside sporangia.
- The gametophyte is monoecious, bearing both male and female sex organs, namely antheridia and archegonia.
- Pteridophytes show a clear alternation of generations.
Dryopteris
Systematic Position
Occurrence
The fern Dryopteris is commonly found growing in moist and shady places.
It is cosmopolitan in distribution.
Structure of Dryopteris
The plant body is a sporophyte which produces spores.
The sporophyte is differentiated into:
- Root
- Stem
- Leaves
Root
The plant possesses true roots.
Stem
The stem is highly reduced and underground. It is known as a rhizome.
Leaves
The leaf is known as a sporophyll because it bears spore-producing structures.
Young leaves are highly coiled. This condition is called circinate.
Young leaves are covered with brownish, hair-like or scale-like structures called ramenta.
The stalk of the leaf is known as the petiole.
The main axis of the leaf is called the rachis.
The leaf bears leaflets called pinnae. Each pinna is further composed of pinnules.
The entire leaf of a fern is also known as a frond.
Reproduction in Dryopteris
According to the handwritten notes, Dryopteris reproduces through:
- Vegetative reproduction
- Asexual reproduction
- Sexual reproduction
1. Vegetative Reproduction
Vegetative reproduction takes place by:
- Fragmentation of rhizome
- Adventitious buds
A. Fragmentation
The rhizome is dichotomously branched.
The rhizome becomes separated into fragments by the progressive death and decay of its older parts up to the dichotomy.
Each separated fragment grows and develops into a new independent plant.
B. Adventitious Buds
Adventitious buds arise on the axil of leaves.
They may become detached from the parent plant and develop into new plants.
2. Asexual Reproduction
Asexual reproduction takes place by means of spores.
The spores are produced inside sporangia.
The sporangia occur in groups known as sori.
The sori are described in the notes as kidney-shaped, brown-coloured structures found on the ventral surface of the pinnae.
Leaves bearing sori are called sporophylls.
Structure of Sorus and Sporangium
Each sorus contains numerous sporangia. The sporangia develop in association with a parenchymatous region called the placenta.
Each sporangium consists of a capsule and a long stalk.
The capsule is surrounded by a layer known as the jacket.
The jacket contains a characteristic thickened region called the annulus.
The annulus is discontinuous at a particular region called the stomium.
The sporangia in a sorus are covered by a protective covering called the indusium.
Inside the capsule are sporogenous cells called spore mother cells.
Formation and Release of Spores
Each spore mother cell undergoes meiosis and produces haploid spores.
According to the notes, approximately 32–64 spores are produced in each sporangium.
At maturity, the wall of the sporangium ruptures along the stomium, and the spores are released.
On reaching a suitable substratum, a spore develops into a heart-shaped gametophyte called the prothallus.
3. Sexual Reproduction
Sexual reproduction is described in the notes as a highly advanced oogamous type.
The spore represents the beginning of the gametophytic generation.
On germination, the spore gives rise to a minute, green and heart-shaped structure called the prothallus.
Prothallus
The cells of the prothallus contain chloroplasts and can prepare food by the process of photosynthesis.
The prothallus is monoecious, as it bears both male and female sex organs.
Rhizoids develop from its posterior end, and the prothallus can survive independently.
The male sex organs, antheridia, occur towards the posterior region of the prothallus.
The female sex organs, archegonia, occur towards the anterior region near the apical notch.
Antheridium
The male reproductive organ is called the antheridium.
Each antheridium is a multicellular structure.
It contains a mass of androgonial cells called androcytes.
At maturity, the androcytes are released and become multiflagellated antherozoids.
The antherozoids function as the male gametes.
Archegonium
The female reproductive organ is called the archegonium.
Each archegonium is flask-shaped and consists of:
- Venter
- Neck
Venter
The venter contains:
- A large egg cell
- A smaller ventral canal cell
Neck
The neck contains 4–6 rows of neck canal cells.
Fertilization
Fertilization takes place in the presence of water.
- Multiflagellated antherozoids are released from the antheridia.
- The ventral canal cell and neck canal cells of the archegonium disintegrate.
- The tip of the neck ruptures.
- The antherozoids swim through water towards the archegonium.
- An antherozoid reaches the venter.
- The male gamete fuses with the egg.
- Fusion results in the formation of a zygote.
Development of Sporophyte
The zygote divides mitotically to form a 2-celled embryo.
The embryo undergoes repeated mitotic divisions, and a young sporophyte is formed.
The young sporophyte later differentiates into:
- Roots
- Stem
- Leaves
This produces the mature fern plant and completes the alternation between the gametophytic and sporophytic generations.
Life Cycle of Dryopteris
Alternation of Generations
Pteridophytes show a distinct alternation between sporophytic and gametophytic generations.
| Feature | Sporophyte | Gametophyte |
|---|---|---|
| Ploidy | Diploid (2n) | Haploid (n) |
| Form | Mature fern plant | Heart-shaped prothallus |
| Nature | Main plant body | Small and independent |
| Reproductive Role | Produces spores in sporangia | Produces male and female gametes |
| Male Organ | — | Antheridium |
| Female Organ | — | Archegonium |
Quick Revision
- Pteridophytes are non-flowering vascular plants.
- They are also known as vascular cryptogams.
- Xylem and phloem are present.
- The main plant body is the sporophyte.
- The sporophyte is differentiated into roots, stem and leaves.
- Dryopteris is a common fern growing in moist and shady places.
- The underground stem is called a rhizome.
- A fern leaf is called a frond.
- The main axis of a frond is called the rachis.
- Leaflets are called pinnae, and pinnae are divided into pinnules.
- Young fern leaves show circinate coiling.
- Brownish hair-like or scale-like structures on young leaves are called ramenta.
- Vegetative reproduction occurs through fragmentation of the rhizome and adventitious buds.
- Asexual reproduction takes place through spores.
- Spores are produced inside sporangia.
- Groups of sporangia are called sori.
- The protective covering over a sorus is called the indusium.
- The thickened region of the sporangial wall is called the annulus.
- Spore mother cells undergo meiosis to produce haploid spores.
- A germinating spore develops into a heart-shaped prothallus.
- The prothallus is monoecious.
- Antheridia produce male gametes called antherozoids.
- Archegonia contain the female egg.
- Water is necessary for fertilization.
- Fusion of the antherozoid and egg produces a diploid zygote.
- The zygote develops into a young sporophyte.
Important Questions
- What are pteridophytes?
- Why are pteridophytes called vascular cryptogams?
- Write the general characteristics of Pteridophyta.
- Write the systematic position of Dryopteris.
- Describe the occurrence and habitat of Dryopteris.
- Describe the external structure of Dryopteris.
- What are rhizome, frond, rachis, pinnae and pinnules?
- What is circinate vernation?
- What are ramenta?
- Explain vegetative reproduction in Dryopteris.
- Explain asexual reproduction in Dryopteris.
- What are sori?
- Describe the structure of a sporangium.
- What are annulus, stomium and indusium?
- Explain the formation and release of spores.
- Describe the structure of a fern prothallus.
- Why is the prothallus called monoecious?
- Describe the structure and function of antheridium.
- Describe the structure of archegonium.
- Explain fertilization in Dryopteris.
- Describe the development of the sporophyte from the zygote.
- Explain alternation of generations in Dryopteris.
- Draw and explain the life cycle of Dryopteris.
Discussion
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