Bryophyta - Plant Kingdom, Class 11, Biology PDF Download

BRYOPHYTA

General characteristics : 

1. Bryophytes are the first land plant. It is believed that they originated from aquatic plant and they come on land through water. Because some bryophytes have characters similar to aquatic plants (eg. presence of air canal)

2. Bryophytes are known as amphibians of the plant kingdom because they need water to complete their life cycle. Mostly bryophytes are found on land.

3. Bryophytes are not considered as the successful land plants because the vascular tissue is absent and they need water for fertilization. Due to the absence of vascular tissue bryophytes cannot grow very tall. The process of water conduction in bryophytes takes place with the help of parenchyma. Parenchyma is a living tissue.

4. Roots are absent in bryophytes. Stem and leaves of bryophytes are functionally similar to the stem and leaves of higher plants.

5. Bryophytes are sciophytes, i.e. bryophytes prefer to grow in moist (wet) and shady places.

Life cycle of Bryophytes :

1. The plant in bryophyte is gametophyte. It is haploid.

2. Sex organs are formed on gametophyte. Sex organs are multicellular and jacketed in bryophytes. Male sex organs are called as antheridium and female sex organs are called as archegonium.

3. The male gametes of bryophytes are motile. These motile male gametes are called as antherozoids. Antherozoids are comma-shaped and biflagellate. Female gamete is called egg.

4. In Bryophyta, fertilization is performed by zoodiogamy i.e. male gamete reaches the female gametes and fertilizes it.

5. As a result of fertilization, a diploid zygote is formed. This zygote initiates the sporophytic generation. Sporophytic generation is a diploid stage.

6. Zygote is developed by mitosis and forms sporophyte, which is known as sporogonium or embryo (2N)

7. During the development first division is transverse in zygote and second division is vertical. Third division is also vertical but at right angle to second division, therefore an eight-celled embryo is formed.

Now a periclinal division takes place in every cell of the eight-celled embryo. As a result of it, a 16 celled embryo is formed. Now, these sixteen cells are arranged in two layers.

(i) Outer 8 cells - Called Amphithecium

(ii) Inner 8 cells - Called Endothecium

8. Now cells of endothecium divide and form many cells which are known as sporogenous cells. Some sporogenous cells become sterile and called nurse cells.

Remaining sporogenous cells function as spore mother cells. Now meiosis takes place in spore mother cells, result of it haploid spores are formed. Nurse cells provide nutrition to spores mother cells.

9. The germination of spores is direct or indirect. In Liverworts & Hornworts the germination of spore is direct i.e. each spore forms a gametophyte after germination i.e. each spore forms one thallus.

But the germination of spores in Mosses is indirect. In mosses, a multicellular filament is formed after the germination of spore. This filament is known as protonema. Now buds are formed on protonema.
Each bud develops and forms a gametophyte plant. Indirect germination is best for survival. Mosses are gregarious in nature because they appear in the group.

Bryophyta is divided into three classes

HEPATICOPSIDA – LIVERWORTS

(i) All the bryophytes included in this class have a shape like liver, so they are known as liverworts.

(ii) Plant body of this group is thallus like. Rhizoids and scales are present on thallus.. Rhizoids are unicellular and unbranched. Scales are multicellular.

(iii) The sporophyte of Liverworts is completely dependent on gametophyte i.e. it depends on gametophyte for food, water and habitat.

iv) The sporophyte of Liverworts is made up of foot, seta and capsule. (Except Riccia sporophyte is made up of only capsule).

(v) In this class formation of spores and nurse cells takes place by the cells of endothecium. Cells of amphithecium form only wall of sporophyte.
Amphithecium = Wall of sporophyte

Endothecium = sporogenous cells = spore mother cells + nurse cells

(vi) Elaters are present in sporophyte of some members of liverworts. (eg. Marchantia - In Marchantia nurse cells are modified in to elaters) Elaters are hygroscopic and they help in dispersal of spores.
Eg. of LiverwortsRiccia, Marchantia , Cryptothallus, Riella, Pellia, Porella

Note : In Bryophytes, sporophyte of Riccia is the simplest.

ANTHOCEROTOPSIDA – HORNWORTS

(i) The plant body of this group is also thallus like. Scales are absent but rhizoids are present on thallus. Rhizoids are unicellular and unbranched.

(ii) The sporophyte of Hornworts is divided into foot and capsule.

(iii) The sporophyte of Hornworts is not completely dependent on its gametophyte i.e. it is semiparasite because its sporophyte is photosynthetic therefore it can manufacture its own food. So it does not depend on gametophyte for food, it depends only for water and habitat.

(iv) In horn worts wall of sporophyte and spores are formed by cells of amphithecium. Cells of endothecium formed only elaters.

Amphithecium = Wall of sporophyte and Spores

Endothecium = Elaters

(v) In hornworts spore-forming cells and elaters forming cells are separate, so elaters are known as pseudoelaters.
Pseudoelaters are structurally and functionally similar to true elaters.

(vi) In hornworts on the basal part of sporophyte, a special, type of meristem is present. Due to the activeness of this meristem, the sporophyte grows rapidly. It grows like the horn of animals. eg. Notothylus, Anthoceros

Note: Anthoceros have some Algae like characters such as –

(i) Archegonia is jacketless

(ii) In each cell of Anthoceros, only one chloroplast is present which is a character of green algae. In the cells of higher plants, many chloroplast are present.

(iii) Pyrenoides (starch storing granules) are present in the chloroplast of Anthoceros, which is an algal character.

(iv) Anthoceros shows ancestral characters which prove that bryophytes have originated from green algae.

Note : Due to these reasons Anthoceros also termed as synthetic-archegoniatae.