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Bryophytes: General characteristics, Reproduction, Gemmae, Antheridium, Archegonium, Practice Problems and FAQs

On the wall and roof of the buildings we have always seen green patches growing and establishing the area in a short period of time. In our childhood days we used to wonder what they are? Now you know that they are Mosses.

But how do they grow easily there without fertilisers? You want to know the answer. Bryophyta is a division under subkingdom Cryptogamae. They include nonvascular land plants which live in moist conditions. They don't need soil like other higher plants. It is possible to grow mosses on surfaces including stones and bricks. Mosses were the first plants on Earth. They don’t have roots.

Let’s take a deep dive into the world of bryophytes and understand how they are able to survive in harsh conditions.


                                                                       Fig: Moss

Table of contents

  • Evolution of land plants
  • Common characteristics of bryophytes
  • Reproduction
  • Gemmae
  • Antheridium
  • Archegonium
  • Practice Problems
  • FAQs

Evolution of land plants

With the abundant growth of algae in shallow water, the nutrients in the shallow depths of the water bodies became gradually depleted. The land had a richer nutrient reservoir than water and hence aquatic plants had to gradually evolve into land plants.

The algae were protected against desiccation, temperature fluctuations and solar radiation by the surrounding water. When the land plants evolved, they had to acquire adaptations to protect themselves from these external factors. These adaptations were the following:

  • The development of the cuticle as a protective layer all over the exposed parts of the plant body.
  • Development of jacketed sex organs, that means sex organs are covered by a layer of sterile cells.

Common characteristics of bryophytes

They are the first land plants to have evolved and grow in damp and shady places. Haploid gametophytes form the dominant plant body. They normally grow densely together and form mats on damp soils, walls and rocks. The plant is thallus-like and prostrate or erect.

Prostrate

It means the downward position of the thallus which is stretched on the ground. It is attached to the substratum by unicellular or multicellular rhizoids. They lack true roots, stems or leaves. They may possess root-like, leaf-like or stem-like structures.


                                            Fig: Prostrate

Erect

Erect plant body is differentiated into rhizoids, axis and leaf like structures. Roots of plants give anchorage, absorb water and minerals whereas rhizoids provide only anchorage.


               Fig: Plant body of a bryophyte

Vascular tissues

They are absent. The thallus absorbs water and minerals directly from the ground or atmosphere. Hence they can survive only in moist places. The conduction of water and food takes place from cell to cell normally by diffusion.

Sex organs

Male sex organs are called antheridia and produce biflagellated male gametes called antherozoids by mitotic division. Female sex organ is called archegonium and produces a single egg by mitosis. They are called as amphibians of the plant kingdom as they can live in soil but depend on water for the transfer of gametes during sexual reproduction.

Life cycle of bryophytes

It shows alternation of generation between a diploid sporophyte (2n) generation and a haploid gametophyte (n) generation. The gametophyte is the independent, main plant body and the sporophyte depends on the gametophyte for survival and nutrition.

Reproduction

Reproduction occurs by asexual and sexual methods.

Asexual reproduction

It occurs by fragmentation of the thallus or by gemmae.

Gemmae

They are multicellular, green asexual buds. They develop on small receptacles called gemma cups. Once matured, gemmae detach from the parent body and germinate to form new plant bodies.


                                     Fig: Gemmae

Sexual reproduction

It occurs by the fusion of gametes which are produced in the sex organs present on the haploid gametophyte plant body. Sex organs are antheridium and archegonium.

Antheridium

It is the haploid male sex organ. It is a multicellular club-shaped structure which is born in clusters. It has a single layered jacket which encloses the sperm mother cells. Each haploid sperm mother cell undergoes mitotic division to produce a single haploid elongated sperm with two flagella.


                                      Fig: Antheridium

Archegonium

It is the haploid, multicellular female sex organ. It is a flask-shaped organ present on a stalk.

It has a tubular neck and a swollen venter. This venter encloses two types of cells, a venter canal cell and a haploid egg cell (female gamete). The neck has a single layered jacket. There is a lid made up of cover cells present at the tip of the archegonium. At maturity, the neck canal cells disintegrate and release mucilage. The egg cell remains in the venter. As the mucilage absorbs water and swells, the cover cells separate and the chemicals in the mucilage attract the antherozoids towards the venter where the egg is present.


             Fig: L.S of archegonium

Practice Problems

1. The sporophytes are not independent in which group?

(A) Bryophyta

(B) Pteridophyta

(C) Gymnosperm

(D) Angiosperm

Solution : The plants included in phylum Bryophyta are called the amphibians of the plant kingdom. The main plant body of a bryophyte is a haplid gametophyte which bears the male sex organ, antheridium and the female sex organ, archegonium. Antheridium produces male gametes called antherozoids and archegonium produces an egg. The antherozoid which is released into water fuses with egg and forms the zygote which develops into a multicellular sporophyte. This sporophyte remains attached to the gametophyte and is dependent on it for survival. Hence option (A) is correct.

2. The plant body in bryophytes is ______________.

(A) majorly gametophyte with sporophyte

(B) majorly sporophyte with gametophyte

(C) only gametophyte

(D) only sporophyte

Solution : The main plant body of a bryophyte is a haplid gametophyte which bears the male sex organ, antheridium and the female sex organ, archegonium. Antheridium produces male gametes called antherozoids and archegonium produces an egg. The antherozoid which is released into water fuses with egg and forms the zygote which develops into a multicellular sporophyte. Sporophyte grows on the gametophyte and depends on it for survival. Hence the correct option is (A).

3. Bryophytes are called as amphibians of the plant kingdom because they ______________.

(A) lack root

(B) lack vascular tissue

(C) require water for the transport of gametes

(D) all of the above

Solution : Bryophytes are considered as the amphibians of the plant kingdom. They can live in soil but always depend on water for the transfer of gametes during sexual reproduction.

4. In Bryophyta the archegonium is ___I____ and antheridium is ___II______.

(A) I - flask-shaped, II - club-shaped

(B) I - kidney-shaped, II - flask -shaped

(C) I heart-shaped, II - club-shaped

(D) I - rounded, II - kidney-shaped

Solution : In Bryophyta the sex organs are antheridium and archegonium. Antheridium is a multicellular club-shaped structure which is born in clusters. It has a single layered jacket which encloses the sperm mother cells. Archegonium is a multicellular flask-shaped organ present on a stalk. It has a tubular neck and a swollen venter. Hence the correct answer is option (A).

5. Define gemma cups?
Answer:
The gemma cup is a small receptacle present on the upper surface of bryophytes. Gemmae are multicellular, green asexual buds which are produced here.

6. Write a short note on the archegonium of bryophytes?
Answer:
Archegonium is the haploid, multicellular female sex organ. It is a flask-shaped organ present on a stalk. It has a tubular shaped neck and a venter which is swollen. This venter encloses two types of cells, a venter canal cell and a haploid egg cell (female gamete). The neck has a single layered jacket. There is a lid made up of cover cells present at the tip of the archegonium. At maturity, the neck canal cells disintegrate and release mucilage. The egg cell remains in the venter.

FAQs

1. What are the major characteristics of bryophytes?
Answer:
The major characteristics of bryophytes are as follows:

  • They grow in damp and shady places.
  • They are called as amphibians of the plant kingdom as they can live in soil but depend on water for the transfer of gametes during sexual reproduction.
  • Haploid gametophytes form the dominant plant body and vascular tissues are absent.
  • The plant is thallus-like and prostrate or erect.
  • Male sex organs are called antheridia and produce biflagellated male gametes called antherozoids by mitotic division.

Female sex organ is called archegonium and produces a single egg by mitosis.

2. Mosses will be able to produce flowers?
Answer:
No, mosses are non flowering plants. Angiosperms are flowering plants.

3. Which is the tallest moss in the world?
Answer:
Dawsonia superba is a moss belonging to the class Polytrichaceae. It is found in Australia, Malaysia, New Guinea, and New Zealand. It is considered the tallest moss in the world. It reaches a height of 60 cm.

4. Name the smallest bryophyte?
Answer:
Zoopsis genus belonging to the family Lepidoziaceae is considered the smallest Bryophyte. These plants are normally shiny, greenish, and spreading.

Related Topics

Classification of plants : Sexual system of classification, Eichler’s system of classification, Cryptogamae, Phanerogamae, Tracheophytes, Practice Problems and FAQs

Bryophytes: Life cycle, Classification, Economic importance, Practice Problems and FAQs

Pteridophytes: Alternation of generations, Reproduction, Life cycle, Practice problems and FAQs

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