Protista and Fungi into major groups; Lichens

Introduction

Protista and fungi are two distinct kingdoms of the five-kingdom classification, proposed by R.H. Whittaker. Each kingdom comprises organisms that differ in their structure and functional activities. However, lichens show a symbiotic relationship between two diverse kingdoms. A symbiotic relationship signifies the benefits of both organisms involved. Thus, lichens possess the characteristics of green algae (protist) or cyanobacteria and fungi. Because of this relationship, lichens are often referred to as “dual organisms.” Lichens are a group of approximately 13,500 to 17,000 species that resemble plants. They come in a variety of colours, shapes, and sizes. They can grow on different surfaces and cover about 6% to 8% of the Earth’s surface. The study of Protista and Fungi into major groups; Lichens is an important topic that comes under the field of biological science. Let us understand Protista and Fungi into major groups; Lichens study material in brief.

Symbiotic Relationship of Protista and Fungi into major groups; Lichens

Lichens are an example of a successful symbiotic relationship between algae (protists) or cyanobacteria and fungi. The fungal part of lichens is called mycobiont, whereas the algal or cyanobacterial part is called photobiont. The fungi are heterotrophs, i.e., they depend on autotrophs for their nutrition. Whereas the algae are autotrophs, thus they can synthesise their food via photosynthesis. The fungal partner depends on the algal partner for its food, and it delivers water and minerals to its algal partner in return. Approximately 20% of fungal species take part in symbiosis. These species may belong to either the Ascomycete or Basidiomycete phylum. However, Ascomycetes are more prominent in forming symbiotic relationships. There are around 100 different species of photobionts taking part in the symbiosis. They may include classes like Cynophyceae, Phaeophyceae, Chlorophyceae, etc. One species of fungi is capable of forming a symbiotic relationship with a variety of algae. Similarly, one species of algae can form a symbiotic relationship with different fungi. Around 90% of lichens have green algae as their photobiont.

Habitat of Protista and Fungi into major groups; Lichens

Lichens can grow in different habitats. They are slow-growing organisms but can survive in extremely harsh conditions too. They may be present on the bark of trees or as epiphytes on the leaves of tropical trees. You can also spot them growing on cooled lava. Lichens can also grow on rocks. They cause the breaking of rocks, leading to soil formation. They are capable of growing and surviving even in deserted areas. Lichens are present everywhere, from arctic regions to tropical and temperate climatic areas.

Types of Lichens

Based on their growth forms, lichens can be of three categories:

• Foliose: Foliose lichens possess a flat, leafy, like lettuce structure. The foliose lichens occur attached over rocks and twigs by rhizoids

Examples of foliose lichen are Cetraria, Xanthoria, and Parmelia.

• Fruticose: These lichens are pendant, hair-like, and upright (shrubby or cup-like). They can have round branches either with a central core or maybe hollow. Some may also have flat branches. They grow on the tree branches, foliage, and rocks

Examples of fruticose lichen are Cladonia fimbriat and Usnea longissima.

• Crustose: Crustose lichens are flat without any differentiated lobes. They are available in many vibrant colours like yellow, orange, red, green, and grey. These lichens are present over tree trunks, stones, rocks, or barks

Examples of crustose lichens are Lecanora garovaglii and Pleopsidium chlorophanum.

Reproduction of lichens

Lichens usually reproduce by vegetative propagation. They can reproduce by breaking off the dry thallus. When the conditions are favourable, this thallus starts growing on its own. The lichens also reproduce by means of soredia. The soredia are the powdery photosynthetic cells enveloped inside the fungal hyphae. They are easily dispersed by winds, and they start growing when the conditions are favourable. The fungal partner grows sexually through spore (ascospore) formation. These spores germinate and find a new algal partner to form the symbiotic relationship. This process is called the “reassembly” of the lichens.

Economic importance of lichens

Lichens have a very diverse significance in different industrial fields. Given below are some of the ways in which lichens are important:

• Lichens cause soil formation by breaking the bare rocks on which they grow
• They act as bio-indicators of air quality and are used in climate change studies
• They can survive in harsh climates and are also useful in determining the age of their substrate
• They play a vital role in the nitrogen cycle, as they fix nitrogen from the environment
• They act as a source of food for aquatic animals
• They are often used as colouring agents and dyes, like in pH indicators
• They are very useful in the pharmaceutical industry as they help treat different skin issues
• In famines, they act as a source of food. However, lichens are eaten as a staple food in some areas

Conclusion

Protista and Fungi are into major groups; Lichens are a very important part of the environment. Protists and fungi have a symbiotic relationship, in which both partners are benefited. There are approximately 13,500 to 17,000 species of lichens. Based on structure and growth, there are three major groups of lichens – foliose, fruticose, and crustose. The fungal part of lichens is called mycobiont, whereas the algal or cyanobacterial part is called photobiont. They usually reproduce through vegetative propagation. They play an important role in the soil formation and determination of air quality.