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Lichen are plant-like organisms that act as a symbiosis between diverse species such as fungi and cyanobacteria or algae. Despite the fact that cyanobacteria are not algae, they are sometimes referred to as blue-green algae.
- Lichens are important producers that feed on many trophic feeders, such as mites, reindeer, nematodes, and springtails.
- The fungal component is known as the mycobiont, and the non-fungal component, which includes chlorophyll, is known as the photobiont.
- Many lichen partners consist of one photobiont and one mycobiont, but this is not universal.
- The fungal partner is thought to be made up of filamentous cells, each of which is referred to as a hypha.
- These hyphae can branch but keep their distance constant and expand via extension.
Key Terms: Lichens, Fungi, Cyanobacteria, Algae, Types of Lichens, Characteristics of Lichens, Sexual Reproduction, Crustose, Foliose, Fruticose
What is Lichen?
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Lichen is a single-celled organism found on tree bark, exposed rock, and the biological soil crust. Few photobiont species have filamentous structures, while others are made up of chains of more or fewer cells.
- The most prevalent fungus in lichens is ascomycetes or basidiomycetes species.
- Green algae (Chlorophyta) or blue-green bacteria (Cyanophyceae) are the most common algal partners.
- In most cases, fungal partners cannot survive without their phycobiont.
- Although algae may often survive on their own in water or wet soil.
- The biggest lichens may produce thallus up to 3 feet long, although most are just a few centimetres long.
- They are vibrant, with colours ranging from yellow to green to black.
Lichens
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| Keystone Species | Types of Receptors | Gametophyte |
Characteristics of Lichens
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Lichens are characterized by several distinctive features, some of which are listed below for your reference,
- Lichens are a type of composite thalloid plant that is created by the union of algae and fungus.
- Both of them use the carbohydrates generated by the algal partner through photosynthesis.
- The fungal partner performs water absorption and retention functions.
- Thalli are classified into three kinds based on their morphological structure: crustose, foliose, and fruticose.
- Lichen reproduces in three ways: vegetative, asexual, and sexual reproduction.
- Basidiospores are generated by Basidiolichen and resemble bracket fungi.
- Basidiospores are formed near the bottom of the fruit body.
- Lichen grows slowly and may live in harsh environments such as high temperatures and dry weather.
Types of Lichens
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Lichens are classified into various categories based on different factors. Some of the types of lichens are as follows:
Based on the Growth
Lichens are divided into the following categories based on the growth:
- Crustose: Crustose is a type of lichen that grows across different substrates.
- Foliose: Foliose are leaf-like species of tissues that are not bound closely.
- Squamulose: Squamulose is a cluster of units that consist of flattened pebble units.
- Fruticose: Fruticose are easily available in branching tubes.
- Gelatinous: Gelatinous form a jelly-like structure
- Leprose: Leprose is a type of lichen with a powdery appearance.
Based on Habitat
Lichens are divided into the following categories based on the habitat:
- Lignicolous: Lignicolous lichens are mainly found in the woods.
- Corticolous: Corticolous lichens reside on bark from trees
- Saxicolous: Saxicolous lichens live on stones or rocks.
- Marine: Marine lichens are found around the coasts of the ocean.
- Freshwater: Freshwater lichens are found on siliceous rocks near freshwater.
- Terricolous: Terricolous lichens, also known as terrestrial lichens, are found on the soil.
Based on Internal Structure
Lichens are divided into the following categories based on the internal structure:
- Heteromerous Lichens: Heteromerous Lichens are a type of algal component of the thallus that is well-differentiated and forms a layered structure.
- Homoiomerous Lichens: Homoiomerous Lichens is a type of algal component that is uniformly distributed uniformly and is not well-differentiated.
Based on Fungal Companion
Lichens are divided into the following categories based on the fungal companion:
- Ascolichens: Ascolichen lichens consist of fungal components and belong to ascomycetes.
- Basidiolichens: Basidiomycetes is a type of lichen that consists of fungal components of lichens.
- Hymenolichens: Hymenolichens lichens consist of fungal components and belong to hymenomycetes
Importance of Lichens
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Lichens are significant for a variety of reasons. The importance of Lichens is listed below,
- One of the most evident benefits is that they are appealing to the eye.
- These lichens play an important role in converting rocks into soil and help in soil formation.
- They also help improve the quality of the soil by supplying important nutrients that are useful for plant growth.
- Our natural environments would be a lot more monotonous and lifeless if these live animals weren't hanging from trees or clinging to rocks.
- Another significant role of lichens is that they provide a way for algae to live in hostile settings where they would otherwise perish.
- These typically water-dependent creatures may survive in dry, sunny conditions as long as there are infrequent rain showers or flooding.
- They also provide a way to convert carbon dioxide in the atmosphere into oxygen, which we all need to exist.
- With the help of lichens, geologists and petrologists calculate the age of species.
- They are used in pharmaceutical industries to prepare cosmetic products to treat skin-related diseases like rashes.
Also Read:
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| Microsporangia | Living Fossil | Biome |
| Fertilization in Plants | Terrestrial Ecosystem | What is Triple Fusion? |
Things to Remember
- Lichens have the same internal anatomy regardless of the diversity of fundamental development.
- The filaments are packed tightly together at the outer surface to create a cortex, which aids in interaction with the environment.
- The filaments of the fungal partner make up the majority of the lichen's body.
- The medulla is located under the algal layer, which is made up of loosely woven fungal filaments.
- The relative density of these filaments defines the lichen's layers.
Sample Questions
Ques: What is the definition of lichen? (2 marks)
Ans: Lichens are a tiny group of unusual plants with a body made up of both an algal and a fungal component that coexist in a symbiotic relationship. The biggest lichens may produce thallus up to 3 feet long, although most are just a few centimeters long. They are vibrant, with colors ranging from yellow to green to black.
Ques: What is the structure of lichens? (3 marks)
Ans: Lichens don't have a waxy cuticle on their leaves as plants do, and they don't have vascular tissue like xylem and phloem to transport nutrients and water throughout their thalli like plants do. Everything that comes into contact with the lichen's surroundings gets absorbed into its structure. Lichens obtain their water and nutrients from the air and rain in their surroundings.
Ques: How do lichens grow? (2 marks)
Ans: Lichens develop slowly in most cases. The one with a blue-green bacteria as the phycobiont has the capacity to convert nitrogen gas into ammonia. Some people, especially those who live in harsh settings like the arctic tundra or the alpine, can live for centuries.
Ques: What is the cortex in lichens? (2 marks)
Ans: The cortex is the lichen thallus' outer covering. These cells are thicker and more densely packed than the rest of the lichen's fungal cells. In certain species, this layer provides a little amount of protection as well as color.
Ques: What are the different types of lichen on the basis of growth? (4 marks)
Ans: Lichens are divided into three categories based on their growth:
- Crustose: Crustose is a type of lichen that grows across different substrates.
- Foliose: Foliose are leaf-like species of tissues that are not bound closely.
- Squamulose: Squamulose is a cluster of units that consist of flattened pebble units.
- Fruticose: Fruticose are easily available in branching tubes.
- Gelatinous: Gelatinous form a jelly-like structure
- Leprose: Leprose is a type of lichen with a powdery appearance.
Ques: What is the medulla in lichens? (2 marks)
Ans: The medulla, or fungal threads, make up the bulk of the lichen thallus. It's made up of threadlike fungal cells that are loosely packed in the centre of the lichen thallus and have thin cell walls. A cotton-like material forms underneath the outer cortex as a result.
Ques: What is reproduction in lichens? (3 marks)
Ans: Lichens are unique. Lichens do not have a simple mechanism to reproduce themselves, unlike plants that can generate seeds that develop into new plants. The fungus gets to develop its fruiting bodies and generate spores because it is the dominant partner in the relationship. These spores can form a new fungus, but the alga does not have the potential to reproduce. Either the new fungus will die or it will find an algae companion.
Ques: What are the uses of lichens? (3 marks)
Ans: The uses of lichens are as follows:
- Lichens have been used as a food source for centuries in many parts of the world.
- They have been used to produce a variety of dyes for centuries.
- The species have been used in traditional medicine for centuries to treat a variety of ailments.
- Lichens are used in some cosmetics, such as sunscreens and lotions.
- They can be used as a nitrogen source for plants.
- Some lichen extracts have been shown to have UV-protective properties.
Ques: How do lichens react to environmental stress? (2 marks)
Ans: Lichens serve as nature's silent sentinels, offering a natural way to monitor air quality. Their sensitivity to pollutants makes them a valuable tool for environmental scientists and policymakers working to ensure clean air for all. A decline in lichen populations can be a strong signal of increasing air pollution.
Ques: What is photobiont? (2 marks)
Ans: A photobiont is the photosynthetic partner in a lichen symbiosis. It's most commonly an alga or a cyanobacteria, but in some rare cases, it can even be a green yeast. Photobionts capture sunlight and convert it into energy through photosynthesis. This energy is then used by both the photobiont and the fungal partner in the lichen for survival and growth.
Ques: Is lichen a fungus? (2 marks)
Ans: Lichens are not single entities, but rather a complex life form resulting from the intimate partnership of two distinct organisms: a fungus and an alga. In this partnership, the fungus plays the dominant role. It dictates the outward appearance of the lichen, influencing everything from the shape of its body (thallus) to the structures it produces for reproduction (fruiting bodies). This influence gives rise to the incredible diversity seen in lichens, ensuring no two are exactly alike.
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