Crustose lichen stage - xerarch, Biology

Assignment Help:

Crustose Lichen Stage - Xerarch

On bare rocks, conditions are inhospitable for life, as there is extreme deficiency of water and nutrients, great exposure to sun, and extremes of temperature. Crustose lichens alone are usually able to grow in such situations. Some examples of these pioneering species are, Rhizocarpon, Rhinodina, Lecidea and Lecanora. These plants flourish during periods of wet weather and remain in a state of desiccation for very long periods during drought. During the wet weather they rapidly absorb moisture by their sponge-like action. Mineral nutrients are obtained by the secretion of carbon dioxide which, with water forms a weak acid that slowly eats into the rock into which the rhizoids sometimes penetrate for a distance of several millimetres.

Nitrogen is brought by rain or by wind-blown dust. Thus all the life requirements of this simple, crust-like species is met with. Thus, lichens help corrode and decompose the rock, supplementing the other forces of weathering. And by mixing the rock particles with their own remains, make conditions favourable for - growth of other organisms. Thus, a thin layer of soil is formed. The rapidity with which a small amount of soil is formed is controlled largely by the nature of the rock and by the climate. On quartzite or basalt rocks in a dry climate, the crustose-lichen stage might persist for hundreds of years. But on limestone or sandstone in a moist climate, sufficient changes permit the invasion of foliose lichens, and all this may occur within a life time.


Related Discussions:- Crustose lichen stage - xerarch

Embryological evidences of evolution, EMBRYOLOGICAL EVIDENCES - A co...

EMBRYOLOGICAL EVIDENCES - A comparative study of embryology of different groups of animals reveals certain features that provide evidences for organic evolution. There ar

What body systems respond to resist the changes, Jennifer has the "stomach ...

Jennifer has the "stomach flu" that is going around campus and has been vomiting profusely for the past 24 hours. Not only has she been unable to keep down fluids or food but she h

Symptoms and complications of atherosclerosis, Q. Symptoms and Complication...

Q. Symptoms and Complications of atherosclerosis? Symptoms Excessive weight, hypertension, high levels of cholesterol and triglycerides. Complications Myocardia

Similaritie and difference between lamarckism and darwinism, What are the f...

What are the fundamental similarities and differences between lamarckism and darwinism? Both darwinism and lamarckism are evolutionary theories as opposed to fixism, both admit

Importance of meiosis, Meiosis becomes significant for the following reason...

Meiosis becomes significant for the following reasons. Constant Number of Chromosomes: It brings about a reduction in the chromosome number from a diploid (2n) condition to

Clinic blood pressure management, Raised blood pressure is a major risk fac...

Raised blood pressure is a major risk factor for cardiovascular disease. The higher the blood pressure, the higher the risk of stroke, coronary heart disease, kidney disease, heart

Explain the nerve centres which control the body temperature, The nerve cen...

The nerve centres which control the body temperature and the urge for eating recontained in: 1.  Hypothalamus 2. Pons 3. Cerebellum 4. Thalamus Hypothalamus is the

Male reproductive disorders-congenital disorders, Congenital disorders ...

Congenital disorders Poor fertilizing quality of semen could be due to impaired spermatogenesis. When such a condition is due to genetic congenital causes the treatment is not

Determine about the multicellular organisms, Another possible way to classi...

Another possible way to classify organisms would be to separate them into unicellular and multicellular organisms. Explain why this is not a useful classification system. Other

Ribosome in the translation of one mrna molecule, Q. How many of the same p...

Q. How many of the same proteins are made at the same time by each ribosome in the translation of one mRNA molecule? How does successive protein production occur in translation?

Write Your Message!

Captcha
Free Assignment Quote

Assured A++ Grade

Get guaranteed satisfaction & time on delivery in every assignment order you paid with us! We ensure premium quality solution document along with free turntin report!

All rights reserved! Copyrights ©2019-2020 ExpertsMind IT Educational Pvt Ltd