what is the symbiotic relationship between the lichens and algae?

Answer 1

LICHENS AND THEIR RELATIONSHIP WITH ALGAE

Lichens are symbiotic associations of a fungus with a photosynthetic partner (called a photobiont or phycobiont) that can produce food for the lichen from sunlight.

The photobiont is usually either green algae or cyanobacteria.

A few lichens are known to contain yellow-green algae or, in one case, a brown alga.

Some lichens contain both green algae and cyanobacteria as photobionts; in these cases, the cyanobacteria symbiont component may specialize in fixing atmospheric nitrogen for metabolic use. The word is pronounced as though it is spelled "liken" .

The body (thallus) of most lichens is quite different from that of either the fungus or alga growing separately, and may strikingly resemble simple plants in form and growth

The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations; however, the algal cells are never enclosed inside the fungal cells themselves.
The fungus may or may not penetrate into the algal cells with fine hyphal protrusions.

In general, the symbiosis is considered obligatory for successful growth and reproduction of the fungus; however, the significance for the algal symbiont is less clear.

For some algae, the symbiosis may be obligatory for survival in a particular habitat; in other cases, the symbiosis might not be advantageous for the alga.

Thus, there is some controversy as to whether the lichen symbiosis should be considered mutualistic or parasitic. Nonetheless, the lichen is typically a highly stable association which probably extends the ecological range of both partners.

There is evidence that lichens might involve a controlled form of parasitism of the algal cells.

In laboratory settings, cyanobacteria grow faster when they are alone rather than when they are part of a lichen.

But there is also a mutualistic side to the relationship: the fungus part of the lichen provides the alga with water and minerals that the fungus absorbs from whatever the lichen is growing on.

As for the alga, it uses the minerals and water to make food for the fungus and itself.

Lichens take the external shape of the fungal partner and hence are named based on the fungus.

The fungus most commonly forms the majority of a lichen's bulk, though in filamentous and gelatinous lichens this may not always be the case.

The lichen fungus is typically a member of the Ascomycota—rarely a member of the Basidiomycota.

Formerly, some lichen taxonomists placed lichens in their own division, the Mycophycophyta, but this practice is no longer accepted because the components belong to separate lineages.

The algal or cyanobacterial cells are photosynthetic, and as in higher plants they reduce atmospheric carbon dioxide into organic carbon sugars to feed both symbionts.

Both partners gain water and mineral nutrients mainly from the atmosphere through rain and dust.

The fungal partner protects the alga by retaining water, serving as a larger capture area for mineral nutrients and, in some cases, provides minerals obtained from the substratum.

If a cyanobacterium is present, as a primary partner or another symbiont in addition to green alga as in certain tripartite lichens, they can fix atmospheric nitrogen, complementing the activities of the green alga.

For pictures , click the links below--

1) http://tecfa.unige.ch/perso/lombardf/calvin/botanique-8-9avril-02/image/lichen-1.jpg

2) http://faculty.clintoncc.suny.edu/faculty/Michael.Gregory/files/Bio%20102/Bio%20102%20Laboratory/fungi/img021.jpg

Answer 2

They are partners in photosynthesis...The lichens are made of a fungus and an algae. Without the algae the lichen cannot make photosynthesis.The algae is called the photobiont, the photosynthesis partner.In the lichen, the fungus surrounds the algae cells, enclosing them, almost in their complex tissue formations.The algae acts as the food supplier and the fungus is the support.So, you cannot call this a symbiotic relationship, between the lichens and the algae, the symbiosis is between the algae and the fungus that work together to form a new organism.The lichens are usually formed of cyanobacteria or green algae.Some might contain brown algae or yellow green algae, and some contain both the cyanobacteria and the green algae.

Answer 3

A lichen is made up of a fungus and an alga that live together. The alga uses the sunlight to produce food. The fungus provides the alga with water and minerals that the fungus absorbs from whatever the lichen is growing on . The alga part of the lichen uses the minerals and water to make food for the fungus itself. The two organisms live in close association with each other and both benefit from the association.....symbiosis.

Answer 4

algae are aquatic plants. the fungus builds a protective structure that the alga can live in and photosynthesize. the alga provides carbohydrates and the fungus provided habitat the relationship is thought to be more of an exploitation or balanced parasitism rather than mutualistic symbiosis, since 50% of the food produced by the alga is pirated by the fungus, which has formed a tight cage around the algal cells (more like they are captured). in fact, it seems that only algal cells in debilitated condition will allow the relationship to occur (healthy cells will shut down and die when engulfed by the fungus). the algae consists of about 5% to 10% of the total size of the lichen.