DIVISION BRYOPHYTA:
Definition:
Bryophytes can be defined more precisely as plants with the distinguishing characters as follows:
Characters:
1) First Land Plants:
The first plants to colonize land were bryophytes.
2) Origin:
They are generally thought to have evolved from green algae.
3) Habitat Adaptation:
The Bryophytes are poorly adapted to life on land and are mainly confined to damp shady places.
4) Non-vascular Plants:
These plants are devoid (lacking in) of specialized conducting (xylem and phloem) and strengthening tissues.
5) Transportation by Diffusion:
Only the process of diffusion helps in the transportation of water minerals as well as in transportation of prepared food and other substances.
6) Cuticle:
The plant body is with a proper cuticle, without cuticle or has a very thin one.
The water is absorbed by the general surface of the plant.
7) Amphibious Plants:
The bryophytes are said to be the amphibians of the plant world because they cannot live away from water.
They need water for reproduction.
8) Non-flowering:
The bryophytes are non-vascular, flowerless plants.
9) Alternation of Generation:
These plants show a regular alternation of heteromorphic (morphologically different) generations.
They have a dominant independent free living gametophyte.
10) Thalloid:
This may be thalloid as in many liverworts or is differentiated into structures resemble with stem, leaves and absorbing and anchoring organs, rhizoids as in mosses and source liverworts.
11) Reproduction:
i. Gametophyte Generation:
The gametophyte produces a sporophyte, which is a less conspicuous generation, partially or totally dependent upon the gametophyte for its nutrition.
ii. Sporophyte Generation:
The sporophyte generally consists of foot, seta and capsule.
The sporophyte is diploid (2n) which produces in sporangia one kind one kind of haploid spores (i.e. it is homosporous) by meiosis.
The spores germinate and give rise to gametophyte which is also haploid.
iii. Sex Organs:
ANTHERIDIA multicellular male sex organs and ARCHEGONIA female sex organs both are born on gametophyte either on same or different plants.
iv. Protection of Sex Cells:
These sex organs are multicellular and protected by a sterile covering of cells.
v. Gametes:
Gametes are produced by Mitosis.
vi. Antherozoid:
Male gametes produced by antheridia are called antherozoid; antherozoids are motile and always produced in large number.
vii. Eggs:
Female gametes formed within archegonia are termed as eggs.
A single egg is formed in each archegonium.
viii. Fertilization:
Fertilization takes place in water.
Antherozoids (n) are towards archegonia (n) Chemotactically.
A single antherozoid fuses with an egg (n) thus accomplishing fertilization which results in the formation of the diploid zygote (2n)
ix. Zygote is Retained with in Archegonium:
Definition:
Bryophytes can be defined more precisely as plants with the distinguishing characters as follows:
- Vascular system absent
- Gametophyte dominant
- Sporophyte attached to gametophyte
- Homosporous.
1) First Land Plants:
The first plants to colonize land were bryophytes.
2) Origin:
They are generally thought to have evolved from green algae.
3) Habitat Adaptation:
The Bryophytes are poorly adapted to life on land and are mainly confined to damp shady places.
4) Non-vascular Plants:
These plants are devoid (lacking in) of specialized conducting (xylem and phloem) and strengthening tissues.
5) Transportation by Diffusion:
Only the process of diffusion helps in the transportation of water minerals as well as in transportation of prepared food and other substances.
6) Cuticle:
The plant body is with a proper cuticle, without cuticle or has a very thin one.
The water is absorbed by the general surface of the plant.
7) Amphibious Plants:
The bryophytes are said to be the amphibians of the plant world because they cannot live away from water.
They need water for reproduction.
8) Non-flowering:
The bryophytes are non-vascular, flowerless plants.
9) Alternation of Generation:
These plants show a regular alternation of heteromorphic (morphologically different) generations.
They have a dominant independent free living gametophyte.
10) Thalloid:
This may be thalloid as in many liverworts or is differentiated into structures resemble with stem, leaves and absorbing and anchoring organs, rhizoids as in mosses and source liverworts.
11) Reproduction:
i. Gametophyte Generation:
The gametophyte produces a sporophyte, which is a less conspicuous generation, partially or totally dependent upon the gametophyte for its nutrition.
ii. Sporophyte Generation:
The sporophyte generally consists of foot, seta and capsule.
The sporophyte is diploid (2n) which produces in sporangia one kind one kind of haploid spores (i.e. it is homosporous) by meiosis.
The spores germinate and give rise to gametophyte which is also haploid.
iii. Sex Organs:
ANTHERIDIA multicellular male sex organs and ARCHEGONIA female sex organs both are born on gametophyte either on same or different plants.
iv. Protection of Sex Cells:
These sex organs are multicellular and protected by a sterile covering of cells.
v. Gametes:
Gametes are produced by Mitosis.
vi. Antherozoid:
Male gametes produced by antheridia are called antherozoid; antherozoids are motile and always produced in large number.
vii. Eggs:
Female gametes formed within archegonia are termed as eggs.
A single egg is formed in each archegonium.
viii. Fertilization:
Fertilization takes place in water.
Antherozoids (n) are towards archegonia (n) Chemotactically.
A single antherozoid fuses with an egg (n) thus accomplishing fertilization which results in the formation of the diploid zygote (2n)
ix. Zygote is Retained with in Archegonium:
The zygote is retained within the female sex organ (archegonium) for some time.
x. Embryo Formation:
After a resting period the zygote develops by mitotic division into a diploid embryo.
xi. Sporophyte Depend on Gametophyte:
The embryo ultimately develops into a sporophyte which is also diploid.
The entire development of sporophyte thus takes place within the gametophyte plant body.
Even when the sporophyte is fully developed it remains attached to the gametophyte for nourishment and protection because it does not contain chloroplast and is unable to perform photosynthesis.
IMPORTANCE OF ALTERNATION OF GENERATION:
There is an alternation of generation in the life cycle of bryophytes i.e. multicellular haploid gametophytic (gamete producing) generation alternates with the multicellular diploid sporophytic (spore producing) generation.
It is a very important phenomenon, which provides continuous genetic variabilities and selection for the best genetic make up for survival and adaptation in the changing environment.
General Characters of Bryophytes
Reviewed by SaQLaiN HaShMi
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5:39 AM
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Reviewed by SaQLaiN HaShMi
on
5:39 AM
Rating:
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