🍄 Kingdom Fungi: The Decomposers 🍄
Understanding Fungal Characteristics
Fungi constitute a unique kingdom of heterotrophic organisms, exhibiting immense diversity in their morphology and habitats. Unlike plants, they do not perform photosynthesis.
Assertion: Fungi are heterotrophic organisms.
Reason: They cannot synthesize their own food and depend on other organisms or dead organic matter for nutrition.
- Diversity: Show great diversity in morphology and habitat.
- Examples: Common mushrooms, toadstools, white spots on mustard leaves (parasitic fungi), yeast (unicellular).
- Cosmopolitan Distribution: Found in air, water, soil, on animals, and plants.
- Preferred Habitat: Thrive in warm and humid places. This is why food is refrigerated to prevent fungal growth.
Assertion: Food is often kept in refrigerators to prevent spoilage by fungi.
Reason: Fungi prefer to grow in warm and humid conditions, and refrigeration inhibits their growth and metabolic activity.
Structure of Fungi
- Filamentous Nature: With the exception of yeast (which is unicellular), most fungi are filamentous.
- Hyphae: Their bodies consist of long, slender, thread-like structures called hyphae.
- Mycelium: The network of hyphae is known as mycelium.
- Coenocytic Hyphae: Some hyphae are continuous tubes filled with multinucleated cytoplasm; these are called coenocytic hyphae.
- Septate Hyphae: Others have septae or cross walls in their hyphae.
- Cell Walls: Composed of **chitin** and **polysaccharides**.
Assertion: Fungal cell walls are chemically distinct from plant cell walls.
Reason: Fungal cell walls are primarily composed of chitin and polysaccharides, whereas plant cell walls are mainly made of cellulose.
Mode of Nutrition
- Saprophytes: Most fungi are heterotrophic and absorb soluble organic matter from dead substrates.
- Parasites: Those that depend on living plants and animals for nutrition.
- Symbionts: They can also live in mutually beneficial associations:
- With algae as **lichens**.
- With roots of higher plants as **mycorrhiza**.
Assertion: Lichens are examples of symbiotic associations involving fungi.
Reason: In lichens, fungi live in a mutually useful association with algae, where algae provide food and fungi provide shelter and absorb nutrients.
Assertion: Mycorrhiza represents a symbiotic relationship between fungi and plants.
Reason: In mycorrhizal associations, fungi colonize the root system of a host plant, providing increased water and nutrient absorption capabilities for the plant, while the plant provides carbohydrates to the fungus.
Reproduction in Fungi
Fungi reproduce through various means:
- Vegetative Means:
- Fragmentation
- Fission
- Budding (e.g., in yeast)
- Asexual Reproduction: By spores called:
- Conidia
- Sporangiospores
- Zoospores
- Sexual Reproduction: By spores called:
- Oospores
- Ascospores
- Basidiospores
- Fruiting Bodies: The various spores (sexual and asexual) are produced in distinct structures called fruiting bodies.
Assertion: Fungi can reproduce both asexually and sexually.
Reason: Asexual reproduction often involves spores for rapid dispersal, while sexual reproduction involves gamete fusion to create genetic variation and adapt to changing environments.
Sexual Cycle in Fungi (Three Steps):
- Plasmogamy: Fusion of protoplasms between two motile or non-motile gametes.
- Karyogamy: Fusion of two nuclei.
- Meiosis: Reduction division in the zygote, resulting in haploid spores.
When a fungus reproduces sexually, two haploid hyphae of compatible mating types come together and fuse. In some fungi, this immediately results in diploid cells (2n). However, in other fungi (like Ascomycetes and Basidiomycetes), an intervening **dikaryotic stage (n+n)** occurs, where each cell contains two nuclei. This phase is called **dikaryophase**. Later, the parental nuclei fuse, and the cells become diploid. The fungi then form fruiting bodies where reduction division occurs, leading to the formation of haploid spores.
Assertion: The dikaryotic stage is a unique feature in the sexual cycle of some fungi.
Reason: In Ascomycetes and Basidiomycetes, plasmogamy occurs without immediate karyogamy, leading to a stage where each cell has two haploid nuclei (n+n) before they eventually fuse.
Basis for Fungi Classification
The morphology of the mycelium, mode of spore formation, and the type of fruiting bodies form the basis for the division of the kingdom into various classes.
🔬 Classes of Kingdom Fungi: A Detailed Look 🔬
Kingdom Fungi is broadly divided into four main classes.
1. Phycomycetes (Algal Fungi)
Assertion: Phycomycetes are often found in aquatic habitats.
Reason: Many members produce motile zoospores for asexual reproduction, which require water for dispersal.
- Habitat: Found in aquatic habitats, on decaying wood in moist and damp places, or as obligate parasites on plants.
- Mycelium: **Aseptate** (lacking cross-walls) and **coenocytic** (multinucleated cytoplasm without septa).
- Asexual Reproduction:
- By **zoospores** (motile, flagellated).
- By **aplanospores** (non-motile).
- These spores are produced **endogenously** (inside) in sporangium.
- Sexual Reproduction: A **zygospore** is formed by the fusion of two gametes.
- Gametes can be similar in morphology (**isogamous**).
- Or dissimilar (**anisogamous** or **oogamous**).
- Examples: Mucor, Rhizopus (the bread mould), and Albugo (the parasitic fungi on mustard).
🧠 Test Your Knowledge: Phycomycetes! 🧠
Click on a card to reveal the answer.
What is the characteristic structure of the mycelium in Phycomycetes?
The mycelium is **aseptate and coenocytic**.
Name two types of asexual spores found in Phycomycetes.
**Zoospores** (motile) and **aplanospores** (non-motile).
Where are asexual spores produced in Phycomycetes?
They are produced **endogenously in sporangium**.
What is formed by the fusion of two gametes in Phycomycetes?
A **zygospore** is formed.
Give an example of a parasitic Phycomycete on mustard.
**Albugo** is a parasitic Phycomycete on mustard.
What kind of gametes can Phycomycetes have during sexual reproduction?
Gametes can be **isogamous, anisogamous, or oogamous**.
Where are Phycomycetes commonly found in terms of habitat?
They are found in **aquatic habitats** and on decaying wood in moist places.
Is Rhizopus (bread mould) a member of Phycomycetes?
Yes, **Rhizopus** is a common example.
What does 'coenocytic' mean in the context of hyphae?
It means the hyphae are **continuous tubes filled with multinucleated cytoplasm** without cross-walls.
Do Phycomycetes produce motile spores?
Yes, they produce **zoospores** which are motile.
What type of parasitic relationship do some Phycomycetes exhibit?
They can be **obligate parasites on plants**.
What is the term for non-motile asexual spores in Phycomycetes?
They are called **aplanospores**.
Is Mucor an example of Phycomycetes?
Yes, **Mucor** is a common example.
Do Phycomycetes have septa in their hyphae?
No, their mycelium is **aseptate**.
What is the primary characteristic that gives Phycomycetes their common name "Algal Fungi"?
Their **aquatic habitat** and the presence of **motile zoospores**, similar to some algae.
What is the ploidy of the zygospore in Phycomycetes?
The zygospore is **diploid (2n)**.
Are the asexual spores of Phycomycetes produced internally or externally?
They are produced **endogenously** (inside the sporangium).
What is the mode of nutrition for Phycomycetes found on decaying wood?
They act as **saprophytes**.
Can Phycomycetes exhibit all three types of sexual reproduction (isogamous, anisogamous, oogamous)?
Yes, their gametes can be **isogamous, anisogamous, or oogamous**.
Are Phycomycetes generally considered primitive or advanced fungi?
They are considered **primitive fungi** due to their simple mycelial structure and presence of motile spores.
2. Ascomycetes (Sac-Fungi)
Assertion: Ascomycetes are commonly known as sac-fungi.
Reason: Their sexual spores, ascospores, are produced endogenously in sac-like structures called asci.
Assertion: Neurospora is widely used in biochemical and genetic research.
Reason: Its rapid growth, simple life cycle, and well-characterized genetics make it an ideal model organism for studying metabolic pathways and genetic mutations.
- Common Name: Sac-fungi.
- Morphology: Mostly multicellular (e.g., Penicillium), but rarely unicellular (e.g., yeast - Saccharomyces).
- Mode of Nutrition: Saprophytic, decomposers, parasitic, or coprophilous (growing on dung).
- Mycelium: Branched and **septate** (with cross-walls).
- Asexual Spores:
- **Conidia**, produced **exogenously** (externally) on special mycelia called **conidiophores**.
- Conidia on germination produce mycelium.
- Sexual Spores:
- Called **ascospores**, produced **endogenously** in sac-like **asci** (singular: ascus).
- These asci are arranged in different types of fruiting bodies called **ascocarps**.
- Examples: Aspergillus, Claviceps, Neurospora.
- Economic Importance: Neurospora is used extensively in biochemical and genetic work. Many members like morels and truffles are edible and considered delicacies.
🧠 Test Your Knowledge: Ascomycetes! 🧠
Click on a card to reveal the answer.
Why are Ascomycetes commonly called sac-fungi?
Because their sexual spores (ascospores) are produced in **sac-like asci**.
Name a unicellular Ascomycete.
**Yeast (Saccharomyces)** is a unicellular Ascomycete.
What kind of mycelium do Ascomycetes possess?
Their mycelium is **branched and septate**.
Where are conidia produced in Ascomycetes?
Conidia are produced **exogenously on conidiophores**.
What are the fruiting bodies of Ascomycetes called?
They are called **ascocarps**.
Name an Ascomycete used extensively in biochemical and genetic work.
**Neurospora** is widely used.
Are morels and truffles edible fungi?
Yes, they are **edible delicacies** among Ascomycetes.
What is the mode of nutrition for Ascomycetes that grow on dung?
They are **coprophilous**.
How do conidia reproduce in Ascomycetes?
Conidia on germination produce **mycelium**.
Are Ascomycetes typically multicellular or unicellular?
They are mostly **multicellular** (e.g., Penicillium), rarely unicellular.
What are the sexual spores of Ascomycetes called?
They are called **ascospores**.
Where are ascospores produced?
Ascospores are produced **endogenously in asci**.
Is Aspergillus an example of an Ascomycete?
Yes, **Aspergillus** is a common example.
What is the ploidy of ascospores?
Ascospores are **haploid (n)**.
Do Ascomycetes have a dikaryotic stage?
Yes, they exhibit an **intervening dikaryotic stage (n+n)**.
What is the term for the specialized mycelium that bears conidia?
It is called a **conidiophore**.
Are Ascomycetes capable of both asexual and sexual reproduction?
Yes, they reproduce by **conidia (asexual)** and **ascospores (sexual)**.
What is the common name for Saccharomyces?
It is commonly known as **yeast**.
Are all Ascomycetes saprophytic?
No, they can also be **decomposers, parasitic, or coprophilous**.
What is the term for the sac-like structure containing ascospores?
It is called an **ascus** (plural: asci).
3. Basidiomycetes (Club Fungi)
Assertion: Basidiomycetes are commonly known as club fungi.
Reason: Their sexual spores, basidiospores, are produced on club-shaped structures called basidia.
Assertion: Sex organs are absent in Basidiomycetes.
Reason: Plasmogamy is achieved directly by the fusion of two vegetative or somatic cells of different strains or genotypes, bypassing the need for specialized sex organs.
- Common Forms: Mushrooms, bracket fungi, puffballs.
- Habitat: Grow in soil, on logs and tree stumps, and in living plant bodies as parasites (e.g., rusts and smuts).
- Mycelium: Branched and **septate**.
- Asexual Spores: Generally **not found**.
- Vegetative Reproduction: Common by **fragmentation**.
- Sex Organs: **Absent**.
- Plasmogamy: Brought about by fusion of two vegetative or somatic cells of different strains or genotypes.
- Resultant Structure: The fusion leads to a **dikaryotic** structure (n+n), which ultimately gives rise to a **basidium**.
- Karyogamy and Meiosis: Take place in the basidium, producing four **basidiospores**.
- Basidiospores: Produced **exogenously** on the basidium (plural: basidia).
- Fruiting Bodies: The basidia are arranged in fruiting bodies called **basidiocarps**.
- Examples: Agaricus (mushroom), Ustilago (smut), and Puccinia (rust fungus).
🧠 Test Your Knowledge: Basidiomycetes! 🧠
Click on a card to reveal the answer.
What are Basidiomycetes commonly known as?
They are commonly known as **club fungi**.
Name two common forms of Basidiomycetes.
**Mushrooms, bracket fungi, or puffballs**.
What is the structure of the mycelium in Basidiomycetes?
The mycelium is **branched and septate**.
Are asexual spores generally found in Basidiomycetes?
No, asexual spores are **generally not found**.
How does vegetative reproduction occur in Basidiomycetes?
It is common by **fragmentation**.
Are sex organs present in Basidiomycetes?
No, sex organs are **absent**.
How is plasmogamy achieved in Basidiomycetes?
By fusion of two **vegetative or somatic cells** of different strains.
What is the resultant structure after plasmogamy in Basidiomycetes?
A **dikaryotic** structure (n+n) which forms a basidium.
Where do karyogamy and meiosis take place in Basidiomycetes?
They take place in the **basidium**.
How many basidiospores are produced from a basidium?
**Four** basidiospores are produced.
Are basidiospores produced endogenously or exogenously?
They are produced **exogenously** on the basidium.
What are the fruiting bodies of Basidiomycetes called?
They are called **basidiocarps**.
Give an example of a parasitic Basidiomycete that causes rust disease.
**Puccinia** (rust fungus) is an example.
What is the common name for Agaricus?
It is commonly known as **mushroom**.
What is the ploidy of basidiospores?
Basidiospores are **haploid (n)**.
Where can Basidiomycetes grow as parasites?
They grow in **living plant bodies**.
What is the common name for Ustilago?
It is commonly known as **smut**.
Do Basidiomycetes form a dikaryotic stage during their sexual cycle?
Yes, they have a prominent **dikaryotic stage**.
What is the shape of the basidium?
It is typically **club-shaped**.
Are all Basidiomycetes macroscopic?
Many common forms like mushrooms are macroscopic, but the mycelium is microscopic.
4. Deuteromycetes (Imperfect Fungi)
Assertion: Deuteromycetes are commonly known as imperfect fungi.
Reason: Only their asexual or vegetative phases of reproduction are known; their sexual forms have not been discovered or identified.
Assertion: Deuteromycetes play a significant role in mineral cycling.
Reason: A large number of them are decomposers of litter, breaking down organic matter and releasing nutrients back into the ecosystem.
- Common Name: Imperfect fungi.
- Reason for Name: Only the asexual or vegetative phases of these fungi are known. When their sexual forms are discovered, they are moved to the classes they rightly belong to (e.g., Ascomycetes or Basidiomycetes).
- Reproduction: Reproduce only by **asexual spores** known as **conidia**.
- Mycelium: **Septate** and **branched**.
- Mode of Nutrition: Some members are saprophytes or parasites. A large number of them are **decomposers of litter** and help in **mineral cycling**.
- Examples: Alternaria, Colletotrichum, and Trichoderma.
🧠 Test Your Knowledge: Deuteromycetes! 🧠
Click on a card to reveal the answer.
Why are Deuteromycetes called "imperfect fungi"?
Because only their **asexual or vegetative phases are known**.
What type of spores do Deuteromycetes reproduce by?
They reproduce only by **asexual spores called conidia**.
Describe the mycelium of Deuteromycetes.
The mycelium is **septate and branched**.
What happens when the sexual forms of Deuteromycetes are discovered?
They are **moved to the classes they rightly belong to** (e.g., Ascomycetes or Basidiomycetes).
Name an example of a Deuteromycete that is a decomposer of litter.
**Alternaria, Colletotrichum, or Trichoderma** are examples.
Do Deuteromycetes play a role in mineral cycling?
Yes, a large number of them **help in mineral cycling** as decomposers.
Can Deuteromycetes be parasitic?
Yes, some members are **parasites**.
What is the term for the asexual spores of imperfect fungi?
They are called **conidia**.
Is the mycelium of Deuteromycetes coenocytic?
No, it is **septate**.
Why is it difficult to classify Deuteromycetes definitively?
Because their **sexual reproductive stages are unknown**.
If a sexual stage is found for a Deuteromycete, where might it be reclassified?
Often to **Ascomycetes or Basidiomycetes**.
Are all Deuteromycetes saprophytes?
No, some are **parasites**, and many are **decomposers**.
What is the primary ecological role of many Deuteromycetes?
They are important **decomposers of litter**.
Give an example of a Deuteromycete that causes plant disease.
**Colletotrichum** is an example (causes anthracnose).
Are there any known sexual stages for Deuteromycetes?
No, their sexual stages are **unknown** or have not been observed.
Can Deuteromycetes be beneficial to the environment?
Yes, by **helping in mineral cycling**.
What is the term for the asexual spores produced by Deuteromycetes?
**Conidia**.
Is Trichoderma a common example of Deuteromycetes?
Yes, **Trichoderma** is a well-known example.
What is the characteristic of their mycelium that allows them to be classified?
Their **septate and branched mycelium**.
If a Deuteromycete's sexual stage is found, does it remain in Deuteromycetes?
No, it is **moved out** to its rightful class.
📊 Kingdom Fungi: Comparative Table of Classes 📊
Here's a quick comparison of the four main classes of Kingdom Fungi:
| Classes | Common Name | Mycelium Type | Asexual Spores | Sexual Spores | Fruiting Body | Key Features |
|---|---|---|---|---|---|---|
| Phycomycetes | Algal Fungi | Aseptate, Coenocytic | Zoospores (motile), Aplanospores (non-motile) | Zygospores | Absent | Aquatic habitats, obligate parasites, gametes can be isogamous/anisogamous/oogamous. |
| Ascomycetes | Sac-Fungi | Branched, Septate | Conidia (exogenous) | Ascospores (endogenous in asci) | Ascocarps | Mostly multicellular (yeast unicellular), dikaryotic stage, edible forms (morels, truffles). |
| Basidiomycetes | Club Fungi | Branched, Septate | Generally absent (vegetative by fragmentation) | Basidiospores (exogenous on basidia) | Basidiocarps | Mushrooms, bracket fungi, puffballs; sex organs absent, prominent dikaryotic stage. |
| Deuteromycetes | Imperfect Fungi | Septate, Branched | Conidia only | Unknown/Absent | Absent | Only asexual/vegetative stages known, decomposers of litter, help in mineral cycling. |
💡 Did You Know? Click to Reveal! 💡
The largest living organism on Earth is a fungus! A single specimen of Armillaria ostoyae (honey mushroom) in Oregon spans over 2,200 acres and is estimated to be thousands of years old.