PLANTS (Bryophtes)
Objectives:
1. know features that distinguish the plant kingdom from other kingdoms
2. understand how brophytes differ from other plants
3. learn the basic difference between thalloid liverworts and mosses
4. know the structures involved in the life cycle of a moss and liverwort and in which structures meiosis and fertilization occur.
5. Learn some uses of bryophytes to man.
6. Know the basic structural differences between bryophytes and vascular plants
 

* Plants have cell walls made up of cellulose
* Surplus carbohydrate is stored as starch
*Chloroplasts contain chlorophyll b

Adaptations by land plants

A. Structural adaptations
* extensive development of roots,

* leaf bearing shoots,

*leaves with microscopic pores called stomata for gas exchange.

B. Chemical adaptations
* Plants have a waxy coating called a cuticle which prevents excessive water loss on land.

*Lignin produced, hardens the cell walls of woody tissues -function- for support.

* Sporopollenin -adds resistance to spores.

C. Reproductive adaptations
Embryophyte condition- protection and nourishment of embryos by maternal tissues of the parent plant.

The bryophytes include plants found in 3 divisions.
* Bryophyta (mosses)
* Hepatophyta (liverworts)
*Anthocerophyta (hornworts)

Division Bryophyta (mosses)

a. Need water to reproduce, a film of rain, water or dew is sufficient for fertilization to occur.

b. No vascular tissue (xylem and phloem) many mosses have:
* water conducting cells called hydroids in the centers of their stems,

* food conducting cells called leptoids surrounding the hydroids.

* hydroids and leptoids are not as efficient as xylem and phloem in water and food transport.
c. Alternation of haploid and diploid generations.

*The haploid gametophyte is the dominant generation.

* The diploid sporophyte is smaller short-lived and depends on the gametophyte for water and nutrients.

* Diploid sporophyte produces haploid spores via meoisis in a structure called the sporangium.

d. Lack woody tissue and cannot support tall plants on land.  Sprawl horizontally as mats.
e. rhizoids serve to anchor bryophytes to the substrate

Reproduction
Embryophyte condition -gametes develop within gametangia.

Female gametangia- archegonium cylindrical in shape, produces one egg

Archegonia release sugars, proteins, acids, etc. that attract sperm.

Male gametangia, antheridium - sausage shape to roundish produces flagellated sperm.

Absorbs water and swells releases sperm when mature.

Egg fertilized within the archegonium

Mature sporophyte consists of a capsule located at the tip of a slender stalk, the seta.

A little rimmed lid protects the free end of the capsule = operculum

Spores are released through peristome when the operculum has fallen off.

 Spores germinate and form protonema which eventually develops into male and female gametophytes.

Division Hepatophyta (liverworts)

Thalloid liverworts
have flattened, lobed, leaf-like bodies called thalli (thallus).

 Marchantia, example of a thalloid liverwort

Reproduction
Reproduce asexually by
a. Fragmentation

b. gemma.

*Gemma are tiny, lens-shaped pieces of tissue that become detached from the thallus.

* They are produced in small gemma cups scattered over the upper surface of the gametophyte.
 

Sexual reproduction
1. Separate male and female gametophytes.

2. Gametangia form in gametophores which are umbrella like structures.

3. Antheridia are borne on disk-like stalks called antheridiophores

4. Archegonia are borne on umbrella-like stalks called archegoniophores.

5. Antheridia are club-shaped gametangia with numerous sperms

6. Archegonia are flask-shaped gametangia each containing a single egg.

7. After fertilization zygote develops into a multicellular

8. Sporophyte develops suspended by a short thick stalk called the seta

The main part of the capsule is called a capsule

        *Within the capsule spore mother cells undergo meiosis producing haploid spores

        * Other capsule cells do not undergo meiosis but remain diploid and develop into long, pointed         elaters.

        * Elaters are sensitive to changes in humidity.
 

        * Spore dispersal occurs as elaters twist and untwist rapidly.

        * At maturity the capsule splits and air currents carry the spores away.

Under favorable conditions the spores germinate and develop into new gametophytes.

Ecological relevance of Bryophytes
The most important bryophytes to humans are peat mosses.
1 kg of dry peat moss will take up 25 kg of water.

Its extraordinary absorptive capacity makes it useful as a
*Soil conditioner in nurseries
*Component in potting mixtures

Its natural acidity gives it antiseptic properties
inhibits bacterial and fungal growth.