FUNGI-THE KINGDOM OF RECYCLERS
MULTIPLE CHOICE QUESTIONS
Q.01: Each question has five options. Encircle the correct option.
(i) Which statement about fungal nutrition is not true?
(a) Some fungi are active predators.
(b) Some fungi are mutualists.
(c) Facultative parasitic fungi can grow only on their specific host.
(d) All fungi require mineral nutrients.
ANSWER: (c) Facultative parasitic fungi can grow only on their specific host.
EXPLANATION: Facultative parasites can grow parasitically on their host as well as by themselves on artificial growth media.
(ii) The absorptive nutrition of fungi is aided by:
(a) Spore formation
(b) Their large surface area-volume ration
(c) They are all parasites.
(d) They form fruiting bodies.
ANSWER: (b) Their large surface area-volume ration
EXPLANATION: Extensive spreading system of hyphae provides large surface area to volume ratio that aids to the absorptive nutrition of fungi.
(iii) The zygomycetes:
(a) Have hyphae without regularly occurring cross walls.
(b) Produce motile gametes.
(c) Are haploid throughout their life.
(d) Answer ‘a’ & ‘c’ are both correct.
ANSWER: (a) Have hyphae without regularly occurring cross walls.
EXPLANATION: Zygomycetes have multinucleate septate hyphae while Ascomycetes & Basidiomycetes have septate hyphae.
(iv) Which of the following cells/structures are associated with asexual reproduction in fungi?
(a) Ascospores
(b) Conidia
(c) Zygospores
(d) Basidiospores
ANSWER: (b) Conidia
EXPLANATION: Conidia (singular conidium) are non- motile, asexual spores which are cut of at the end of modified hyphae called conidiophores, and not inside the sporangia, usually in chains or clusters.
(v) The closest relatives of fungi are probably:
(a) Animals
(b) Slime molds
(c) Brown algae
(d) Vascular plants
ANSWER: (b) Slime molds
EXPLANATION: Fungus-like protists or slime molds resemble fungi in their absorptive mode of nutrition, decomposition of organic matter, hyphal growth, and the presence of cell walls. So, they are considered the closest relatives of fungi.
(vi) E. Coli of fungi are the:
(a) Rusts
(b) Brown mold
(c) Green mold
(d) Saccharomyces cerevisiae
ANSWER: (d) Bacilli
EXPLANATION: The fungal equivalent of E. coli, in terms of being a widely used model organism for research, is often considered to be Saccharomyces cerevisiae, commonly known as baker’s yeast.
(vii) An ascus is to ascomycetes as is a _______ to basidiomycetes.
(a) Basidiospore
(b) Basidiocarp
(c) Basidium
(d) Haustorium
ANSWER: (c) Basidium
EXPLANATION: Four haploid basidiospores are produced on the club-shaped structures called basidia.
(viii) Which statement is not true about deuteromycetes?
(a) They are also called imperfect fungi.
(b) Their asexual spores are called conidia.
(c) It is a heterogenous polyphyletic group.
(d) They have both sexual and asexual reproduction.
ANSWER: (d) They have both sexual and asexual reproduction.
EXPLANATION: Deuteromycetes include all those fungi in which sexual phase has not been observed.
Q.02: SHORT QUESTIONS
(i) What is a hypha? What is the advantage of having incomplete septa?
ANSWER:
Hyphae: “The body of a fungus or mycelium consists of long, slender, branched tubular thread-like filaments called the hyphae (singular hypha).” Hyphae may be septate, i.e., having cross walls or septa or non-septate, i.e., without cross walls. They spread over the substratum.
Advantage of Incomplete Septa: The cross walls or septa of many septate fungi are incomplete, i.e., they have a pore through which cytoplasm flows from cell to cell. This helps in carrying the materials to growing tips and enabling the hyphae to grow rapidly when food and water are abundant and temperature is favourable.
(ii) What is the composition of fungal cell wall and how is this composition advantageous to fungi?
ANSWER:
Composition of Fungal Cell Wall: The major component of the cell wall of fungi is chitin, a material that is also found in the exoskeleton of arthropods. Other constituents are glucans and glycoproteins.
Advantage: The advantage of having chitin in their cell wall is that chitin is more resistant to decay than are cellulose and lignin,which make up the plant cell wall.
(iii) To which phyla do yeasts belong? How do they differ from other fungi?
ANSWER:
“Yeasts are unicellular microscopic fungi, derived from all the three different groups of fungi (Ascomycetes, basidiomycetes & deuteromycetes) but mostly ascomycetes.”
Difference from Other Fungi: Yeasts are different from other fungi because:
(1) Yeasts are the unicellular microscopic fungi consisting of round oval-shaped cells, while all other fungi are multicellular consisting of tubular, filamentous hyphae.
(2) Yeasts usually reproduce asexually by a special method called budding. However, they may also reproduce sexually by forming ascospores or basidiospores, under favourable conditions. Other fungi normally reproduce by sexual spore formation.
(3) They obtain energy by fermenting carbohydrates into alcohol and CO2.
(iv) Name sexual and asexual spores of Ascomycetes.
ANSWER:
Sexual spores of ascomycetes ___ ascospores.
Asexual spores of ascomycetes are conidia.
(v) What are mycorrhizae?
ANSWER:
Mycorrhizae: “Mycorrhizae are mutualistic association between certain fungi and roots of vascular plants (about 95% of all kinds of vascular plants).”
Types: There are two main types of mycorrhizae:
(1) Endomycorrhizae, in which the fungal hyphae penetrate the outer cells of the plant root, forming coils, swellings, and minute branches.
(2) Ectomycorrhizae, in which the hyphae surround and extend between the cells but do not penetrate the cell walls of the roots. These are mostly formed with pines, firs etc.
However, the mycelium extends far out into the soil in both kinds of mycorrhizae.
(vi) By what means can individuals in imperfect fungi be classified?
ANSWER:
Deuteromycetes or imperfect fungi are a heterogenous group that includes all such fungi in which sexual phase has not been observed. If sexual structures are found on an imperfect fungus, it is then reassigned to the appropriate phylum. Biologists now can classify most imperfect fungi on the basis of DNA sequences, though sexual structures may not be found.
(vii) Give a single characteristic that differentiates Zygomycota from Basidiomycota.
ANSWER:
Zygomycota have non-septate hyphae whereas Basidiomycota have septate hyphae.
(viii) Why is green mold more likely to contaminate an orange kept in a refrigerator than are bacteria?
ANSWER:
An orange kept in a refrigerator is more likely to be contaminated by a green mold than by bacteria because many fungi can tolerate extreme temperatures like -5°C below freezing and 50°C or more. Whereas, bacteria cannot tolerate such extreme temperatures, so cannot grow there.
(ix) What is a fungus?
ANSWER:
Fungus: “A fungus is a member of the kingdom Fungi that includes eukaryotic, heterotrophic organisms that are absorptive in their nutritional mode.” Most of them are decomposers that live on organic material, secrete digestive enzymes and absorb small organic molecules which are produced by digestion. Mostly, they are multicellular like molds, mushrooms etc., but a few are unicellular like yeasts.
Examples: Mushrooms, morels, truffles, Rhizopus or black bread mold, yeasts etc.
(x) State two parallel characteristics of Ascomycetes and Basidiomycetes.
ANSWER:
Parallel Characters of Ascomycetes & Basidiomycetes:
(1) Both have septate hyphae.
(2) Both produce haploid sexual spores.
Q.03: EXTENSIVE QUESTIONS
(i) Discuss taxonomic status of fungi.
ANSWER:
Taxonomic Status of Fungi:
Taxonomic status of fungi has changed from that of “a group of Plant kingdom” to a separate kingdom “Fungi”.
Resemblance with Plants: They resemble plants in some respects:
(1) Have cell wall
(2) Lack centrioles
(3) Are non-motile.
Resemblance with Animals: But fungi resemble more animals than plants.
(1) Unlike plants and like animals, fungi are heterotrophs.
(2) They lack cellulose in their cell wall and contain chitin – the chemical found in external skeleton of arthropods.
For this reason, some mycologists (scientists who study fungi) think that fungi and animals probably arose from a common ancestor.
Differences with Animals: But fungi are different from animals because of:
(1) Having cell wall
(2) Being absorptive heterotrophs
(3) Non-motile
So, fungi are neither plants nor animals.
Separate Kingdom Fungi: Fungi are neither plants nor animals because:
(1) Their DNA studies also confirm that they are different from all other organisms.
(2) They show a characteristic type of mitosis, called ‘nuclear mitosis’. During nuclear mitosis, nuclear envelope does not break. Instead, the mitotic spindle forms within the nucleus and the nuclear membrane constricts between the two clusters of daughter chromosomes.
Because fungi are distinct from plants, animals and protists in many ways, they are assigned to a separate kingdom ‘Fungi’.
(ii) Summarize differentiating/distinguishing characteristics of four main groups of Fungi, and give two common examples of each group.
ANSWER:
Consult textbook at page 119, table 8.1.
(iii) State various features of fungi that adapt them to terrestrial mode of life.
ANSWER:
Consult textbook at page 124 — 125.
(iv) What is ecological importance of saprotrophic fungi, of lichens and mycorrhizae?
ANSWER:
Ecological Importance of Fungi: Fungi have great ecological impact as:
(1) Decomposers: Fungi, along with saprobic bacteria, play vital role in the recycling of inorganic nutrients in the ecosystem. Without their activity all the essential nutrients would soon become locked up in the mounds of dead animals, plants, would be unavailable for use by organisms, and life would cease.
(2) Symbionts:
(i) Mycorrhizal fungi improve the growth of plants with which they are associated. 95% of all kinds of vascular plants have this association.
(ii) Lichens growing on rocks break them, setting stage for other organisms during the course of ecological succession. Lichens are very good bioindicators of air quality as they are very sensitive to pollution.
(3) Bioremediators: Some fungi are also used for bioremediation (degrading/removing environmental poisons/pollutants by organisms).
(v) Same enzymes of fungi are useful on one hand and harmful on other. Discuss.
ANSWER:
Many enzymes produced by fungi serve beneficial purposes, such as aiding in decomposition, nutrient recycling, and food production (e.g., brewing and baking).
However, some of these same enzymes can be harmful when they contribute to fungal infections in humans, animals, or plants. For example, enzymes involved in breaking down organic matter can also degrade tissues in host organisms, causing diseases such as athlete’s foot in humans or crop diseases like rusts in plants.
(vi) Name any four important fungal diseases of plants and four fungal diseases of humans, and briefly describe any one of the plant diseases and any one of the diseases of humans.
ANSWER:
Fungal Diseases in Plants: Powdery mildews, ergot of rye, red rot of sugar cane, potato wilt, cotton root rot, apple scab, brown rot etc.
Rust Disease of Plants: “Rusts are plant diseases caused by certain pathogenic fungi belonging to order Puccinales.” The disease is characterized by numerous rusty, orange-yellow coloured spots on the host surface (mostly stem & leaves), which later release brick or rust-red spores. That’s why, it is called rust. Rust infects all sort of plants like wheat, oat, corn, soyabean, pines, apple, coffee, sugarcane etc.
Example: Puccinia species are the most common rust fungi. Some common infections caused by them are; Brown wheat rust, common rust of corn, crown rust of oats, etc.
Fungal Diseases in Animals: Ringworm, Athlete’s foot, Histoplasmosis, Aspergillosis, ergotism etc.
Histoplasmosis: “Histoplasmosis is a serious infection of lungs, caused by inhaling spores of a fungus which is common in soil contaminated with bird’s feces.”
Effects: If its infection spreads into blood stream and then to other organs (which is very occasional), it can be serious and even fatal.
(vii) Describe, giving examples, different ways in which fungi are useful to humans.
ANSWER:
Consult textbook at page 125 — 126.
(viii) Differentiate between the members of each of the following pairs:
(a) Spore/Conidium
(b) Ascus/Basidium
(c) Dikaryotic/Diploid
(d) Ascocarp/Ascus
(e) Obligate parasite/Facultative parasite
(f) Endomycorrhizae/Ectomycorrhizae
(g) Plasmogamy/Karyogamy
ANSWER:
Difference between:
(a) Spore & Conidium:
(1) Spores are units of sexual or asexual reproduction, produced inside reproductive structures called sporangia, which are cut off from the hyphae by complete septa.
(2) They are haploid, non-motile, small, produced in very large number and are dispersed by wind.
(3) Spores are produced by almost all groups of fungi.
(b) Spores & Conidium:
(1) Conidia or naked spores are a type of asexual spores which are cut off at the tips of special modified hyphae called conidiophores. They are not produced within sporangia, but are in the form of chains or clusters at the tips of conidiophores.
(2) Conidia are generally haploid, comparatively larger in size, produced in large number and most commonly dispersed by wind.
(3) Conidia are the characteristic of Ascomycota and Deuteromycota.
(c) Ascus & Basidium:
Ascus:
(1) Ascus is the sac-like structure in which haploid sexual spores in ascomycetes, called ascospores, are produced.
(2) Usually, eight (8) ascospores are formed inside each ascus.
(3) They are the characteristic of ascomycetes.
Basidium:
(1) Basidia are the characteristic club-shaped sexual reproductive structures on which haploid sexual spores in basidiomycetes, called basidiospores, are produced.
(2) Usually, four (4) basidiospore are formed on each basidium.
(3) They are the characteristic of basidiomycetes.
(d) Dikaryotic & Diploid:
Dikaryotic Hyphae: A fungal hypha or cell having two nuclei of different genetic types is called dikaryotic or heterokaryotic hypha or cell. It is the characteristics of basidiomycetes and ascomycetes.
Diploid: A cell having two sets of chromosomes is called diploid.
(c) Ascocarp: In most sac-fungi or Ascomycota, the sexual spore producing structures or asci are packed into special macroscopic fruiting bodies called ascocarps. E.g.,Visible morels, etc.
Ascus: Ascus is the sac-like structure in which haploid sexual spores in ascomycetes, called ascospores, are produced. Usually, eight (8) ascospores are formed inside each ascus.
(e) Obligate parasite & Facultative parasite:
Obligate parasites can grow only on their living host and cannot be grown on available defined growth culture medium.
Example: Various mildews and most rust species are obligate parasites.
Facultative parasites can grow parasitically on their host as well as by themselves on artificial growth media.
Example: ‘Armillaria’ species do parasitize living trees, but if the tree dies, the fungus continues to eat the dead wood without parasitic activity.
(f) Endomycorrhizae & Ectomycorrhizae:
Endomycorrhizae: In endomycorrhizae, the fungal hyphae penetrate the outer cells of the plant root, forming coils, swellings, and minute branches, and also extend out into surrounding soil.
Ectomycorrhizae: In ectomycorrhizae, the hyphae surround and extend between the cells but do not penetrate the cell walls of the roots. These are mostly formed with pines, firs etc. However, the mycelium extends far out into the soil in both kinds of mycorrhizae.
(g) Plasmogamy & Karyogamy:
Plasmogamy:
(1) Plasmogamy means the fusion of cytoplasm.
(2) Plasmogamy occurs before karyogamy.
(3) In zygomycetes, plasmogamy is immediately followed by karyogamy.
Karyogamy:
(1) Karyogamy means the fusion of nuclei.
(2) Karyogamy occurs after plasmogamy.
(3) In ascomycetes and basidiomycetes, karyogamy does not take place immediately after plasmogamy.
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