Lichens

Hello everyone ,

 Today I will be writing about lichens

Lichens are unusual creatures. A lichen looks like a single organisms, but a lichen is not a single organism the way most other living things are, but rather it is a combination of two organisms which live together intimately. lichens actually a form of  symbiotic relationship between an alga and fungus.

It is composed of a fungal partner (Mycobiant) and one or more photosynthetic partner (Photobiont), generally green algae or cyanobacteria. there are about 20,000 species of lichens on the earth. Lichens will grow almost anywhere that a stable and reasonably well-lit surface occurs. This may include soil, rock, or even the sides of trees. A lichen may absorb certain mineral nutrients from any of these substrates on which it grows, but is generally self-reliant in feeding itself through photosynthesis in the algal cells. Thus, lichens growing on trees are not parasites on the trees and do not feed on them, any more than you feed on the chair you sit in. Lichens growing in trees are simply using the tree as a home. 

Mutualistic or Parasitism.

It is debated whether the relationship in a lichen is mutualistic or part of a controlled parasitism. On one hand, the fungus and photobiont seem to be in a mutualistic relationship because when they combined, they have the ability to deal with ecological  conditions, it also seem that  neither partner is damaged by other . Upon taking a closer look at a lichens, some might say that the photobiont is captive of the mycoboint, not a partner . the fungal partner 'enslaves ' the photobiont to feed from the photobionts photosynthesis.

Lichens; as biological indicator of pollution

Lichens absorbs most of it's mineral nutrients from air and rainfall. They have been used to monitor the amount of pollutants in an environment. This is done by  observing condition of lichens as well as their chemical composition sulfur dioxide is lethal to lichens as it damage chlorophyll  that cause photosynthesis to cease. 

Lichens are often strikingly colorful because of presence of pigments that protects the photosynthetic partner .

Lichens occur in one of four basic growth forms, as illustrated below:

• crustose - crustlike, growing tight against the substrate.
• squamulose - tightly clustered and slightly flattened pebble-like units.
• foliose - leaflike, with flat sheets of tissue not tightly bound.
• fruticose - free-standing branching tubes.
• leprose- powdery
• gelatinous – jelly like
• byssoid – whispy, like teased wool
• structureless.

-Dixy