BiologyCBSE Class 11 · Biological Classification

Kingdom Fungi: Structure, Reproduction and the Four Classes

Updated 17 October 2026 · Fact-checked

Fungi are heterotrophic eukaryotes with a cell wall of chitin and polysaccharides, made of hyphae forming a mycelium. They reproduce vegetatively (fragmentation, fission, budding), asexually (conidia, sporangiospores, zoospores) and sexually (plasmogamy, karyogamy, meiosis). The four classes are Phycomycetes, Ascomycetes, Basidiomycetes and Deuteromycetes.

Understand Kingdom Fungi: Classes and Reproduction

Fungi. Heterotrophic, eukaryotic organisms with a wide variety of habitats (air, water, soil, on and in plants and animals). They are saprophytes (decaying matter), parasites or symbionts (lichens and mycorrhiza). Examples: yeast, mushrooms, bread mould, *Penicillium*. Cell wall: chitin and polysaccharides. Body: thread-like hyphae, forming a network, the mycelium. Hyphae may be septate (cross walls) or coenocytic (continuous multinucleate cytoplasm, no septa). Reserve food: glycogen and oil droplets. Yeast is unicellular.

Reproduction.

Vegetative: fragmentation, fission and budding.
Asexual: conidia, sporangiospores or zoospores (aquatic fungi).
Sexual: oospores, ascospores, basidiospores, produced in a distinct fruiting body. Three steps: plasmogamy (fusion of protoplasm), karyogamy (fusion of nuclei) and meiosis. In some fungi (ascomycetes and basidiomycetes) a dikaryon stage (n+n, two nuclei per cell) occurs between plasmogamy and karyogamy; the fungus is then called dikaryotic. Later the two nuclei fuse (karyogamy) and the zygote undergoes meiosis to give haploid spores.

Classes.

Phycomycetes (algal fungi): aquatic habitats, decaying wood, obligate parasites on plants. Mycelium aseptate and coenocytic. Asexual zoospores (motile) or aplanospores (non-motile) in sporangium; sexual by zygospore after fusion of two gametes (isogamous, anisogamous or oogamous). *Mucor*, *Rhizopus* (bread mould), *Albugo* (parasite on mustard).
Ascomycetes (sac fungi): mostly multicellular (e.g. *Penicillium*), rarely unicellular (yeast). Saprophytic, decomposers, parasitic or coprophilous (growing on dung). Mycelium branched and septate. Asexual spores: conidia on conidiophores. Sexual: ascospores in sac-like asci, grouped in ascocarps. *Aspergillus*, *Claviceps*, *Neurospora* (used in biochemical and genetic work).
Basidiomycetes: mushrooms, bracket fungi, puffballs; grow in soil, on logs and tree stumps, and as parasites (rusts and smuts). Mycelium branched and septate. Asexual spores are generally not found, but vegetative reproduction by fragmentation is common. Sex organs are absent; plasmogamy by fusion of two vegetative or somatic cells of different strains, forming a dikaryotic structure. Basidiospores form externally on the basidium, which is grouped in basidiocarps. *Agaricus*, *Ustilago*, *Puccinia*.
Deuteromycetes (imperfect fungi): only the asexual (conidial) or vegetative phases are known; when the sexual form is discovered they are moved to the proper class. Septate mycelium. Some are saprophytes or parasites, many decomposers that help in mineral cycling. *Alternaria*, *Colletotrichum*, *Trichoderma*.

Table: spores. Phycomycetes: zoospores/aplanospores, zygospores. Ascomycetes: conidia, ascospores in asci. Basidiomycetes: none asexual, basidiospores on basidium.

Draw and label: an ascus with ascospores in an ascocarp. Checklist: ascocarp, asci with ascospores. Title: 'Sac fungus fruiting body'.

Kingdom Fungi: Classes and Reproduction: key facts

Cell wall: $C hi t in + p o l y s a cc ha r i d es ∣ h y p ha e ∣ m y ce l i u m$; Fungal body
Sexual cycle: $P l a s m o g am y ∣ d ik a r y o n (n + n) ∣ k a r y o g am y ∣ m e i os i s$; Three steps
Classes: $P h y co m y ce t es ∣ A sco m y ce t es ∣ B a s i d i o m y ce t es ∣ D e u t er o m y ce t es$; Four classes
Spores: $A scos p or es (a sc i) ∣ B a s i d i os p or es (ba s i d i u m) ∣ Z y g os p or es (P h y co m y ce t es)$; Sexual spores

How to answer Kingdom Fungi: Classes and Reproduction questions

Questions give a fungus or spore and ask for the class, or a feature and ask for the example.

1Identify the key clue: aseptate hyphae = Phycomycetes; sac = Ascomycetes; basidium = Basidiomycetes; no sexual stage known = Deuteromycetes.
2Name the spore and where it forms.
3For sexual reproduction give the three steps in order, and mention the dikaryon where applicable.
4Always give the example for each class named in the syllabus.
5Note exceptions: yeast is unicellular, and Basidiomycetes lack asexual spores.

Kingdom Fungi: Classes and Reproduction in real life

The idea, met in an everyday situation. Answer the question in your own words, then compare with the model answer. The one-line hook is what to remember.

Bread kept in a damp box

Suppose a slice of bread develops a cotton-like mould with black dots after three days.

Name the likely class, the structure producing the dots, and how the fungus spreads.

Try it first, then show the solutionSolution

A bread mould such as Rhizopus belongs to Phycomycetes.
The black dots are sporangia packed with sporangiospores.
Spores released in air land on food and grow into new mycelia.

Answer: Phycomycetes; sporangia with sporangiospores.

Memory hook: Black dots on bread are sporangia.

Tricks to remember Kingdom Fungi: Classes and Reproduction

Short memory aids. Say each one aloud once, then use it on a question the same day.

PABD
Phycomycetes, Ascomycetes, Basidiomycetes, Deuteromycetes.
Use it when: Order of classes
PKM
Plasmogamy, Karyogamy, Meiosis.
Use it when: Sexual cycle
Sac, club, none
Ascus = sac fungi, basidium = club fungi, imperfect fungi = no sexual stage.
Use it when: Class clue

Kingdom Fungi: Classes and Reproduction: solved examples

Ordered from board level to HOTS. Try each one before you open the solution.

Example 1: Hyphae · 2 marks · Very short answerBoard level

Distinguish septate from coenocytic hyphae and name a class of each.

Try it first, then show the solutionSolution

Septate hyphae have cross walls; coenocytic hyphae are multinucleate and continuous (1 mark).
Coenocytic: Phycomycetes (Mucor); septate: Ascomycetes (Penicillium) (1 mark).

Answer: Septa present vs absent; Ascomycetes vs Phycomycetes.

Example 2: Sexual cycle · 3 marks · Short answerBoard level

Describe the three stages of sexual reproduction in fungi.

Try it first, then show the solutionSolution

Plasmogamy: fusion of protoplasm of two cells (1 mark).
Dikaryon may form, and karyogamy fuses the two nuclei (1 mark).
Meiosis in the zygote gives haploid spores (1 mark).

Answer: Plasmogamy, karyogamy, meiosis.

Example 3: Class comparison · 4 marks · Short answerHarder board level

Contrast the spore-bearing structures of sac fungi and club fungi (position of spores, fruiting body, one example each).

Try it first, then show the solutionSolution

Ascomycetes: ascospores inside asci, endogenous (1 mark).
Basidiomycetes: basidiospores outside on a basidium, exogenous (1 mark).
Fruiting bodies: ascocarp versus basidiocarp (1 mark).
Examples: Neurospora, Aspergillus versus Agaricus, Puccinia (1 mark).

Answer: Ascospores in sacs versus basidiospores on clubs.

Example 4: Dikaryotic phase · 3 marks · Short answerHarder board level

Explain what a dikaryon is and in which two classes it is prominent. Why does it exist between plasmogamy and karyogamy?

Try it first, then show the solutionSolution

A dikaryon is a cell with two nuclei, one from each parent (n+n) (1 mark).
Prominent in Ascomycetes and Basidiomycetes (1 mark).
Plasmogamy joins cytoplasm but nuclei fuse only later, so the cell stays dikaryotic until karyogamy (1 mark).

Answer: n+n stage between cytoplasm fusion and nuclear fusion.

Example 5: Deuteromycetes · 4 marks · Short answerHOTS / competency

Why are Deuteromycetes called imperfect fungi, and what happens when the sexual stage is found? How can they still be identified?

Try it first, then show the solutionSolution

Only vegetative or asexual stages are known (1 mark).
When the sexual stage is later discovered, the fungus is moved to Ascomycetes or Basidiomycetes (1 mark).
Identification relies on septate mycelium and conidia (1 mark).
Examples: Alternaria, Trichoderma, Colletotrichum (1 mark).

Answer: Class of fungi with unknown sexual stage; reclassified when found.

Where students lose marks in Kingdom Fungi: Classes and Reproduction

The slips examiners see most often, and what to write instead.

Mistake: Chitin as cellulose
Plant wall is assumed.
Wrong working
Fungal cell wall is cellulose.
Right working
Fungal wall is chitin and polysaccharides.
Do this: Fungi: chitin.
Usually costs: 1 mark.
Mistake: Basidiospores inside basidium
Ascus confusion.
Wrong working
Basidiospores form endogenously.
Right working
Basidiospores form exogenously on the basidium.
Do this: Basidium: outside.
Usually costs: 1 mark.
Mistake: Yeast as multicellular
Most fungi are.
Wrong working
All Ascomycetes are multicellular.
Right working
Yeast is unicellular; others are multicellular.
Do this: Remember the exception.
Usually costs: 1 mark.

Exam tips

Learn one example for each class.
Quote the order plasmogamy, karyogamy, meiosis.
Say that Basidiomycetes lack asexual spores.
Add chitin when describing the wall.

Practice questions on Kingdom Fungi: Classes and Reproduction

Write each answer on paper first. Open the hint only if you are stuck, and the answer only when you have finished.

Q1 · 1 mark · MCQBoard level
Mushrooms belong to
(a) Phycomycetes (b) Ascomycetes (c) Basidiomycetes (d) Deuteromycetes
Hint
Basidiocarp.
Answer
(c).
Q2 · 1 mark · Assertion-reasonHarder board level
Assertion (A): Basidiomycetes show no asexual spores.
Reason (R): Plasmogamy in Basidiomycetes occurs without sex organs.
(a) Both A and R are true and R is the correct explanation of A.
(b) Both A and R are true but R is not the correct explanation of A.
(c) A is true but R is false.
(d) A is false but R is true.
Hint
Two separate facts.
Answer
(b).
Q3 · 2 marks · Very short answerHarder board level
Name a fungus in which zoospores are produced, and the class it belongs to. Why are zoospores found in aquatic fungi?
Hint
Motility needs water.
Answer
Albugo (or other aquatic Phycomycetes). Zoospores have flagella and swim in water to colonise new places.
Q4 · 4 marks · Case-basedHarder board level
Read and answer.
Suppose a plate shows fungus P with aseptate hyphae and sporangia; Q with sac-like structures containing spores; R with club-shaped basidia on a cap.
(a) Name classes of P, Q, R. (1)
(b) Give one example of each. (1)
(c) Which has no asexual spores? (1)
(d) Which spore is formed exogenously? (1)
Hint
Match the structures.
Answer
(a) Phycomycetes, Ascomycetes, Basidiomycetes. (b) Rhizopus, Neurospora (or Aspergillus), Agaricus. (c) R. (d) Basidiospores of R.
Q5 · 3 marks · Short answerHOTS / competency
Suppose a fungus has septate hyphae, no known sexual spores, and decomposes leaf litter in a forest. Place it in a class, justify it and say what would change its classification.
Hint
Imperfect fungi.
Answer
Deuteromycetes: septate mycelium with only asexual conidia known. It helps in mineral cycling. If its sexual stage is discovered, it would be moved to Ascomycetes or Basidiomycetes.

Test your recall

Answer in your head or on paper first, then open the card. Pulling an answer out of memory makes it stick far better than re-reading.

1.What is the fungal wall made of?Show answer
Chitin and polysaccharides.
2.What is a mycelium?Show answer
A network of hyphae.
3.Name two Ascomycetes.Show answer
Penicillium, Neurospora.
4.Where are basidiospores borne?Show answer
Exogenously on the basidium.
5.What is a dikaryon?Show answer
A cell with two nuclei (n+n).
6.Which fungi are called imperfect?Show answer
Deuteromycetes.

Kingdom Fungi: Classes and Reproduction: frequently asked questions

What are fungi?

Heterotrophic eukaryotes with chitinous walls and a body of hyphae.

How do fungi reproduce?

Vegetatively, asexually by spores, and sexually in three steps.

What are sac fungi?

Ascomycetes, which form ascospores in asci.

What is the difference between plasmogamy and karyogamy?

Plasmogamy fuses cytoplasm; karyogamy fuses nuclei.

What are imperfect fungi?

Deuteromycetes, whose sexual stage is unknown.