Q.19. How many types of reproduction found in lichens ? Describe in detail.
Related Questions -
Q. Describe vegetative reproduction in lichens. (2009)
Q. Discuss asexual reproduction in lichens in brief. (2005, 08)
Q. Describe sexual reproduction in lichens. (2003, 06, 08)
Q. Write short notes on (2007)
(i) Isidia (ii) Soredia
Ans. Structure (Internal): -
The structure of lichen is very complex. The thallus of lichen is partly made up of algae and partly of fungi and such thallus is called consoritum. In the center is medull made up of closely twisted hyphae. Space between the outer ring and medulla is occupied by cortex which is again made up of interwoven fungal hyphae. Towards the upper surface are algal cells forming gonidal layer.
1. Vegetative reproduction: -
It takes place by the following methods
(i) By fragmentation: - When accidentally, the thallus of lichens break into many fragments (small portion). These small pieces blow away to new areas and give rise to new thalli.
Q.20. Write in brief economic importance of Lichen. (2001, 02, 04, 07, 10)
Related Questions -
Q. Write short note on importance of Lichen. (2013)
Ans. Economic importance of lichens or uses of lichens : -
Related Questions -
Q. Describe vegetative reproduction in lichens. (2009)
Q. Discuss asexual reproduction in lichens in brief. (2005, 08)
Q. Describe sexual reproduction in lichens. (2003, 06, 08)
Q. Write short notes on (2007)
(i) Isidia (ii) Soredia
Ans. Structure (Internal): -
The structure of lichen is very complex. The thallus of lichen is partly made up of algae and partly of fungi and such thallus is called consoritum. In the center is medull made up of closely twisted hyphae. Space between the outer ring and medulla is occupied by cortex which is again made up of interwoven fungal hyphae. Towards the upper surface are algal cells forming gonidal layer.
1. Vegetative reproduction: -
It takes place by the following methods
(i) By fragmentation: - When accidentally, the thallus of lichens break into many fragments (small portion). These small pieces blow away to new areas and give rise to new thalli.
Fig. - Lichen : V.S. of thallus
Fig. - Lichen : Different modes of vegetative reproduction
(ii) By soredia: - Many lichen produce bud like outgrowths on the upper surface of thallus having both fungal and algal cells. These structures are called soredia. In each soredium, many algal cells are present which are surrounded by fungus hyphae. The soredia after sperating from thallus are taken from one place to another by wind which on getting favourable conditions, they germinate to produce new thalli.
(iii) By isidia: - They consist of cortical layer of fungal hyphae with an internal algal layer. Isidia are usually constricted at the base and thus can easely be broken off. Under favourable conditions each isidium grows into a new lichen thallus. The isidium differs from a soredium in being covered by cortex.
2. Asexual reproduction: - In Ascolichens, the asexual reproduction occurs by pycnidiospores. These spores are formed in the flask-shaped pycnidia. The pycnidial wall is made of fungal hyphae from which spores are formed. On liberation, these pycnidiospores are taken from one place to another by wind. Under favourable conditions, they germinate and forms fungal hyphae. Algal cells come in contact with fungal hyphae and in this manner fungus and algae together forms a new thalli.
3. Sexual reproduction: - In most lichens, the fungus component belongs to the Ascomycetes, the sexual reproduction involves the formation of ascopores in special structure, called asci which are borne in apothecia or perithecia. Thus frtification like apothecia and perithecia occur inlichens as end product of sexual reproduction. The female reproductive organ is called carpogonium. It is coiled and multicellular. The male organ is a flask-shaped structure and is called spermogonium. It produces non-motile spermatia. The male nucleus fuses with female nucleus. The fusion cell produces ascgenous hyphae within which develop eight ascaspores and asci. The hymenium is made up of asci and paraphysis. The fruiting body may be either an apothecia or perithecia. The ascopores germinate to produce hyphal branches which on coming in contact with an appropriate algal cell, initiate the development of a new lichen thallus.
Q.20. Write in brief economic importance of Lichen. (2001, 02, 04, 07, 10)
Related Questions -
Q. Write short note on importance of Lichen. (2013)
Ans. Economic importance of lichens or uses of lichens : -
1. Formation of soil or ecological importance: - Most of the crustose lichens growing on rocks dissolve and disintegrate them into soil particals. Limestone rocks are dissolved by the action of certain chemical secreted by lichens and the disintegration of rocks is due to stresses and strain including contraction and expansion of the gelatinous thalli. When the lichens die and decay, they form humans together with rock particles on which mosses, ferns and other plants grow. Thus they prepare ground for succession of vegetation.
2. Food value: - Numerous small creatures like insects, mosses, fern and other plants e.g. mites, slugs, snail, caterpillars Lecanora saxicola. Some lichens, e.g. Cladonia rangiferina, the well known ‘reindeer moss’ is an important source of food reindeer, caribou (musk ox) and other animals of the arctic and subarctic regions. Their plentiful storage of a starch-like carbohydrate also makes some of them usefull for human food. In Tamil Nadu a species of parmelia known in Telgu as rathapu or rock flower has been used in curry preparation and is famous for its delicacy.
3. Medicinal value: - Several species of lichens were of use in earlier times in the treatment of various disease, but today they have been replaced by more effective drugs. Several lichens contain usunic acid and other lichen acids which have been shown to have an antibacterial properties.
4. For dyes: - Several lichens such as Rocelia tinctoria give purple dye, which has been used for centuries.
5. The sweet scented thalli of some lichen species are used in the manufacture of dhup, hawan samagris and other perfumeries.
6. These are indicator of sulphur pollution.