7.2.5 General Characteristics of Fungi

Introduction

Fungi (singular: "fungus") are a diverse group of eukaryotic microorganisms. They are not differentiated into roots, stems and leaves. They play critical roles in ecosystems, obtaining nutrients through external digestion by secreting enzymes to break down organic matter. This group encompasses familiar organisms like mushrooms, as well as microscopic molds and yeasts. Fungi are essential decomposers, form symbiotic relationships with plants, and can cause diseases in humans and crops.

Definition

Fungi: Fungi are a diverse group of eukaryotic microorganisms that are not differentiated into roots, stems and leaves. They obtain nutrients through external digestion by secreting enzymes to break down organic matter.

In simple words: Fungi are eukaryotic organisms that digest their food outside their body and absorb it.

Core Concept

• Fungi are eukaryotic microorganisms.
• They are not differentiated into roots, stems and leaves.
• They obtain nutrients through external digestion.
• They secrete enzymes to break down organic matter.
• The study of fungi is called mycology.
• The person who studies fungi is called a mycologist.

Detailed Explanation

Habitat Diversity and Mode of Life

• Fungi exhibit amazing habitat diversity and occupy various environments.
• They can be found in terrestrial ecosystems like forests and grasslands.
• They can also be found in aquatic environments, such as lakes and rivers.
• Some fungi live in association with other organisms, forming mutualistic relationships.
• Others are parasites, decomposers, or even symbiotic partners with plants.

• Mycorrhizal fungi form mutually beneficial partnerships with most plants.
• The fungi help plants absorb nutrients, especially phosphorus.
• The plants provide the fungi with carbohydrates produced through photosynthesis.

Nutrition

• Fungi are heterotrophic, meaning they cannot produce their own food through photosynthesis.
• Instead, they obtain nutrients by external digestion.
• They secrete enzymes to break down organic matter, such as dead plants or animals.
• Fungi display diverse modes of life, including:
• Saprophytic (decomposers)
• Mutualists (both organisms benefit, as in mycorrhizal fungi)
• Parasitic (harming other organisms)
• Predatory (consuming other microorganisms)
• Their adaptability and varied lifestyles make fungi essential components of ecosystems.

Size

• The size of fungi can vary significantly, ranging from the microscopic to the macroscopic, depending on the species and their life stage.
• Many fungi are so small that they are only visible under a microscope.
• Yeasts, for instance, are unicellular fungi with sizes typically ranging from a few micrometers to around 10 micrometers.
• On the other hand, some fungi form extensive structures that can be quite large.
• For example, the fruiting bodies of certain mushrooms can reach sizes ranging from a few millimeters to several centimeters in diameter.
• The largest living organism on Earth, a fungus called *Armillaria ostoyae (honey mushroom), covers an area of over 2,385 acres* in Oregon, USA.

Nutrition in Detail

• Fungi are not able to prepare their own food as they lack chlorophyll.
• Hence, they are heterotrophic and rely on extracellular digestion.
• The complex organic substances like carbohydrates and proteins are broken down into simpler molecules, such as sugars and amino acids.
• These simpler molecules are absorbed directly through their cell walls.

Cell Wall and Thallus

• Fungi have rigid cell walls made up of chitin.
• This is in contrast to cellulose walls in typical plants.
• Chitin is a nitrogen-containing polysaccharide that is more resistant to decomposition than cellulose.
• Fungi can store carbohydrates, but unlike plants not in the form of starch but as glycogen like animals do.

Thallus or Body of Most Fungi:

• The thallus or the body of most fungi is a multicellular structure known as "mycelium."
• A mycelium (Gk: mycelium, fungus filaments; pl. mycelia) is a network of filaments called hyphae (Gk: hyphae, web).
• Hyphae increase surface area of mycelium for absorption of nutrients into body of fungus.
• Hyphae may be:
• Nonseptate (aseptate): without cross walls.
• Septate: divided by cross walls.
• Nonseptate hyphae are multinucleate and are called coenocytic hyphae, e.g., in Rhizopus.
• *Penicillium* is a common example of septate fungi.

Locomotion

• Fungi are non-motile.
• They lack basal bodies and do not have flagella at any stage of their life cycle.
• They move towards a food source by growing towards it.

Reproduction

• A fungus can reproduce both asexually and sexually.
• Common asexual methods include:
• Budding: e.g., yeasts reproduce by forming small outgrowths, or "buds."
• Fragmentation: where some fungi break into fragments, and each piece can grow into a new organism.
• Mitotic spores: certain fungi produce mitotic spores through mitosis, which can develop into genetically identical individuals.
• Sexual reproduction involves the fusion of specialized sexual cells, resulting in genetic diversity.

Why are Fungi Classified as Separate Kingdom?

Fungi were originally classified in plant kingdom but more recent studies showed that they resemble more to the animals.

Fungi are now classified as a distinct kingdom in biology according to five kingdom system of classification.

This is due to several fundamental differences setting them apart from plants, animals, and other organisms.

• Having a cell wall.
• Lacking a centriole.
• Being non-motile.
• Producing spores and sporangium.

• They have no chlorophyll.
• Do not have flagella at any stage of their life cycle.
• Fungi are saprotrophs.

• Fungi are heterotrophs.
• Their cell walls are made up of chitin in contrast to cellulose walls in typical plant cells.

Hence, fungi are neither plants nor animals. They show "nuclear mitosis." During nuclear mitosis, the nuclear envelope does not break instead the mitotic spindle forms within the nucleus. The nuclear membrane constricts between the two clusters of daughter chromosomes. In some fungi, the nuclear envelope dismantles late.

Summary Table of General Characteristics of Fungi

Intermediate Level

Habitat Diversity and Mode of Life in Detail

Nutrition in Detail

Cell Wall and Thallus in Detail

Locomotion in Detail

Reproduction in Detail

Why Fungi Are a Separate Kingdom

Conclusion: Fungi are neither plants nor animals. They show nuclear mitosis.

Important Points

• 1. Fungi (singular: "fungus") are a diverse group of eukaryotic microorganisms.
• 2. They are not differentiated into roots, stems and leaves.
• 3. They play critical roles in ecosystems, obtaining nutrients through external digestion by secreting enzymes to break down organic matter.
• 4. This group encompasses familiar organisms like mushrooms, as well as microscopic molds and yeasts.
• 5. Fungi are essential decomposers, form symbiotic relationships with plants, and can cause diseases in humans and crops.
• 6. Habitat Diversity and Mode of Life:
• - Fungi exhibit amazing habitat diversity and occupy various environments.
• - They can be found in terrestrial ecosystems like forests and grasslands, as well as aquatic environments, such as lakes and rivers.
• - Some fungi live in association with other organisms, forming mutualistic relationships, while others are parasites, decomposers, or even symbiotic partners with plants.
• 7. Mycorrhizal Fungi:
• - Mycorrhizal fungi form mutually beneficial partnerships with most plants.
• - The fungi help plants absorb nutrients, especially phosphorus, while the plants provide the fungi with carbohydrates produced through photosynthesis.
• 8. Nutrition:
• - Fungi are heterotrophic, meaning they cannot produce their own food through photosynthesis.
• - Instead, they obtain nutrients by external digestion, secreting enzymes to break down organic matter, such as dead plants or animals.
• - Fungi display diverse modes of life, including saprophytic (decomposers), mutualists (a type of symbiotic relationship where both participating organisms benefit as in the case of Mycorrhizal fungi), parasitic (harming other organisms), and predatory (consuming other microorganisms).
• - Their adaptability and varied lifestyles make fungi essential components of ecosystems.
• 9. Size:
• - The size of fungi can vary significantly, ranging from the microscopic to the macroscopic, depending on the species and their life stage.
• - Many fungi are so small that they are only visible under a microscope.
• - Yeasts, for instance, are unicellular fungi with sizes typically ranging from a few micrometers to around 10 micrometers.
• - On the other hand, some fungi form extensive structures that can be quite large.
• - For example, the fruiting bodies of certain mushrooms can reach sizes ranging from a few millimeters to several centimeters in diameter.
• - The largest living organism on Earth, a fungus called Armillaria ostoyae, (honey mushroom) covers an area of over 2,385 acres in Oregon, USA.
• 10. Nutrition:
• - Fungi are not able to prepare their own food as they lack chlorophyll, Hence, they are heterotrophic and rely on extracellular digestion.
• - The complex organic substances like carbohydrates and proteins are broken down into simpler molecules, such as sugars and amino acids with the help of enzymes and are absorbed directly through their cell walls.
• 11. Cell wall and Thallus:
• - Fungi have rigid cell walls made up of chitin in contrast to cellulose walls in typical plants.
• - Chitin is a nitrogen containing polysaccharide that is more resistant to decomposition than cellulose.
• - Fungi can store carbohydrates, but unlike plants not in the form of starch but as glycogen like animals do.
• - The thallus or the body of most fungi is a multicellular structure known as "mycelium".
• - A mycelium (Gk: mycelium, fungus filaments; pl. mycelia) is a network of filaments called hyphae (Gk: hyphae, web).
• - Hyphae increase surface area of mycelium for absorption of nutrients into body of fungus.
• - Hyphae may be nonseptate (aseptate) without cross walls or septate dived by cross walls.
• - Nonseptate hyphae are multinucleate and are called coenocytic hyphae e.g., in Rhizopus.
• - Penicillium is a common example of septate fungi.
• 12. Locomotion:
• - Fungi are non-motile, lack basal bodies and do not have flagella at any stage of their life cycle.
• - They move towards a food source by growing towards it.
• 13. Reproduction:
• - A fungus can reproduce both asexually and sexually.
• - Common asexual methods include budding e.g., yeasts reproduce by forming small outgrowths, or "buds", fragmentation where some fungi break into fragments, and each piece can grow into a new organism while certain fungi produce mitotic spores through mitosis, which can develop into genetically identical individuals.
• - Sexual reproduction involves the fusion of specialized sexual cells, resulting in genetic diversity.
• 14. Why are Fungi Classified as Separate Kingdom?
• - Fungi were originally classified in plant kingdom but more recent studies showed that they resemble more to the animals.
• - Fungi are now classified as a distinct kingdom in biology according to five kingdom system of classification.
• - This is due to several fundamental differences setting them apart from plants, animals, and other organisms.
• - Fungi share many characteristics with plants including:
• 1. having a cell wall
• 2. lacking a centriole
• 3. being non-motile
• 4. producing spores and sporangium.
• - Fungi differ from plants as:
• 1. they have no chlorophyll
• 2. do not have flagella at any stage of their life cycle
• 3. fungi are saprotrophs.
• - The common characters that make fungi resemble with animals include:
• 1. fungi are heterotrophs
• 2. their cell walls are made up of chitin in contrast to cellulose walls in typical plant cells.
• - Hence, fungi are neither plants nor animals. They show "nuclear mitosis". During nuclear mitosis, the nuclear envelope does not break instead the mitotic spindle forms within the nucleus. The nuclear membrane constricts between the two clusters of daughter chromosomes. In some fungi, the nuclear envelope dismantles late.

Remember

• - Fungi = eukaryotic microorganisms.
• - Not differentiated into roots, stems, leaves.
• - Nutrition = heterotrophic; external digestion.
• - Cell wall = chitin.
• - **Storage** = glycogen.
• - Body = mycelium (network of hyphae).
• - Hyphae = nonseptate or septate.
• - Coenocytic hyphae = nonseptate; multinucleate; e.g., Rhizopus.
• - Locomotion = non-motile; no flagella.
• - Reproduction = asexual and sexual.
• - Largest organism = Armillaria ostoyae.
• - Study of fungi = mycology.
• - Mycologist = person who studies fungi.

Common Mistakes

• 1. Thinking fungi are plants – Fungi are not plants; they are a separate kingdom.
• 2. Thinking fungi have cellulose in their cell walls – Fungi have chitin in their cell walls.
• 3. Thinking fungi store starch – Fungi store glycogen.
• 4. Thinking fungi are motile – Fungi are non-motile.
• 5. Confusing mycelium and hyphae – Mycelium = network of hyphae; Hyphae = individual filaments.
• 6. Confusing septate and nonseptate hyphae – Septate = divided by cross walls; Nonseptate = without cross walls.
• 7. Thinking all fungi are harmful – Many fungi are beneficial (decomposers, food, antibiotics).
• 8. Confusing mycorrhizal fungi with parasitic fungi – Mycorrhizal = mutualistic; Parasitic = harmful.
• 9. Thinking fungi reproduce only sexually – Fungi reproduce both asexually and sexually.
• 10. Forgetting the largest organism – Armillaria ostoyae covers over 2,385 acres.
• 11. Confusing mycology and mycologist – Mycology = study of fungi; Mycologist = person who studies fungi.
• 12. Thinking fungi have flagella – Fungi do not have flagella at any stage.

Quick Revision

• Fungi (singular: "fungus") are a diverse group of eukaryotic microorganisms.
• They are not differentiated into roots, stems and leaves.
• They play critical roles in ecosystems, obtaining nutrients through external digestion by secreting enzymes to break down organic matter.
• This group encompasses familiar organisms like mushrooms, as well as microscopic molds and yeasts.
• Fungi are essential decomposers, form symbiotic relationships with plants, and can cause diseases in humans and crops.
• Habitat Diversity and Mode of Life:
• Fungi exhibit amazing habitat diversity and occupy various environments.
• They can be found in terrestrial ecosystems like forests and grasslands, as well as aquatic environments, such as lakes and rivers.
• Some fungi live in association with other organisms, forming mutualistic relationships, while others are parasites, decomposers, or even symbiotic partners with plants.
• Mycorrhizal Fungi: Mycorrhizal fungi form mutually beneficial partnerships with most plants. The fungi help plants absorb nutrients, especially phosphorus, while the plants provide the fungi with carbohydrates produced through photosynthesis.
• Nutrition:
• Fungi are heterotrophic, meaning they cannot produce their own food through photosynthesis.
• Instead, they obtain nutrients by external digestion, secreting enzymes to break down organic matter, such as dead plants or animals.
• Fungi display diverse modes of life, including saprophytic (decomposers), mutualists (a type of symbiotic relationship where both participating organisms benefit as in the case of Mycorrhizal fungi), parasitic (harming other organisms), and predatory (consuming other microorganisms).
• Their adaptability and varied lifestyles make fungi essential components of ecosystems.
• Size:
• The size of fungi can vary significantly, ranging from the microscopic to the macroscopic, depending on the species and their life stage.
• Many fungi are so small that they are only visible under a microscope.
• Yeasts, for instance, are unicellular fungi with sizes typically ranging from a few micrometers to around 10 micrometers.
• On the other hand, some fungi form extensive structures that can be quite large.
• For example, the fruiting bodies of certain mushrooms can reach sizes ranging from a few millimeters to several centimeters in diameter.
• The largest living organism on Earth, a fungus called Armillaria ostoyae, (honey mushroom) covers an area of over 2,385 acres in Oregon, USA.
• Nutrition:
• Fungi are not able to prepare their own food as they lack chlorophyll, Hence, they are heterotrophic and rely on extracellular digestion.
• The complex organic substances like carbohydrates and proteins are broken down into simpler molecules, such as sugars and amino acids with the help of enzymes and are absorbed directly through their cell walls.
• Cell wall and Thallus:
• Fungi have rigid cell walls made up of chitin in contrast to cellulose walls in typical plants.
• Chitin is a nitrogen containing polysaccharide that is more resistant to decomposition than cellulose.
• Fungi can store carbohydrates, but unlike plants not in the form of starch but as glycogen like animals do.
• The thallus or the body of most fungi is a multicellular structure known as "mycelium".
• A mycelium (Gk: mycelium, fungus filaments; pl. mycelia) is a network of filaments called hyphae (Gk: hyphae, web).
• Hyphae increase surface area of mycelium for absorption of nutrients into body of fungus.
• Hyphae may be nonseptate (aseptate) without cross walls or septate dived by cross walls.
• Nonseptate hyphae are multinucleate and are called coenocytic hyphae e.g., in Rhizopus.
• Penicillium is a common example of septate fungi.
• Locomotion:
• Fungi are non-motile, lack basal bodies and do not have flagella at any stage of their life cycle.
• They move towards a food source by growing towards it.
• Reproduction:
• A fungus can reproduce both asexually and sexually.
• Common asexual methods include budding e.g., yeasts reproduce by forming small outgrowths, or "buds", fragmentation where some fungi break into fragments, and each piece can grow into a new organism while certain fungi produce mitotic spores through mitosis, which can develop into genetically identical individuals.
• Sexual reproduction involves the fusion of specialized sexual cells, resulting in genetic diversity.
• Why are Fungi Classified as Separate Kingdom?
• Fungi were originally classified in plant kingdom but more recent studies showed that they resemble more to the animals.
• Fungi are now classified as a distinct kingdom in biology according to five kingdom system of classification.
• This is due to several fundamental differences setting them apart from plants, animals, and other organisms.
• Fungi share many characteristics with plants including (1) having a cell wall, (2) lacking a centriole, (3) being non-motile, and (4) producing spores and sporangium.
• Fungi differ from plants as: (1) they have no chlorophyll, (2) do not have flagella at any stage of their life cycle, and (3) fungi are saprotrophs.
• The common characters that make fungi resemble with animals include (1) fungi are heterotrophs, and (2) their cell walls are made up of chitin in contrast to cellulose walls in typical plant cells.
• Hence, fungi are neither plants nor animals. They show "nuclear mitosis". During nuclear mitosis, the nuclear envelope does not break instead the mitotic spindle forms within the nucleus. The nuclear membrane constricts between the two clusters of daughter chromosomes. In some fungi, the nuclear envelope dismantles late.

60-Second Revision

• Fungi = eukaryotic microorganisms.
• Not differentiated into roots, stems, leaves.
• Nutrition = heterotrophic; external digestion.
• Cell wall = chitin.
• **Storage** = glycogen.
• Body = mycelium (network of hyphae).
• Hyphae = nonseptate or septate.
• Coenocytic hyphae = nonseptate; multinucleate; e.g., Rhizopus.
• Locomotion = non-motile; no flagella.
• Reproduction = asexual and sexual.
• Largest organism = Armillaria ostoyae.
• Study of fungi = mycology.
• Mycologist = person who studies fungi.
• Warning: Fungi are not plants. They have chitin in their cell walls, not cellulose. They store glycogen, not starch. They are non-motile and have no flagella. Mycelium = network of hyphae; Hyphae = individual filaments. Septate = divided by cross walls; Nonseptate = without cross walls. Fungi reproduce both asexually and sexually. Mycorrhizal fungi are mutualistic, not parasitic. Mycology = study of fungi; Mycologist = person who studies fungi. The largest organism is Armillaria ostoyae.