Fungi: Classification, Characteristic, Structure, Reproduction and Facts

 

Fungi: Characteristic, Structure, Reproduction, Example and Facts

Fungi (singular: fungus) is a kingdom of its own. They are mainly non-motile organisms composed usually of thread-like structures called hyphae containing many nucleic members include moulds, mushrooms, toadstools, and slime moulds.

All fungi except slime moulds are non-motile. They do not possess chlorophyll and so cannot make their own food by photosynthesis. Instead, most fungi are sapiophytes which make use of the food present in the dead parts of plants and animals. They break down this food into smaller substances which they absorb and use, bringing about the decomposition of the dead organisms.

Thus, fungi, together with bacteria are important decomposers. We find them growing on logs, dead leaves, fruits, bread and leather. Some fungi are parasites, living and feeding on living organisms. These fungi cause diseases especially in plants.

The kingdom fungi too presents problems to biologists as they exhibit both plants and animal characteristics.

In another modern classification, the fungi are divided into two kingdoms. One containing the slime moulds (showing more animal-like features) and the rest of the fungi (showing more plant-like features). 


Classification of Fungi

Class one - Myxomyceies or slime fungi

Class two - Phycomycetes e.g. pythium

Class three Astomycetes or sac fungi e.g. yeast

Class four - Basidiomycetes or club fungi e.g. Ustilago

Class five - Deuteromycetes or fungi imperfecti e.g.Helminthosporium & Fusarium

In this article, you should be able to list at least six of the general characterisitcs of fungi, list at least seven general characteristics of fungi, state ten processes involved in the reproduction of fungi and explain the importance of fungi in industry, agriculture and medicine.

 

General Characteristic of Fungi

Let us consider these features that have made fungi to be in a kingdom of its own.

1. They are non-green plants.

2. They are simple multicellular plants.

3. Their body is not differentiated into root, stem and leaves.

4. The vegetative body (hyphae) is collectively known as mycelium.

5. Reproduction is by means of spores.

6. The cell wall is composed of cellulose and chitin.

7. Carbohydrate is stored in form of glycogen (and not starch) just as in animals.

8. They are either saprophytic or parasitic. Examples include Mucor; Rhizopus, Penicillium,

9. Some fungi form association with algae (as in lichens)

 

Mucor Mucedo (Black Mould) - Structure

Can you recall the black thread-like growth you have ever noticed on your exposed moist bread (food)? That is the black mould (Mucor mucedo). It is a fungi that is saprophytic on animal dung, wet shoes, moist bread, rotten fruits and other organic matter.

Let us look at the structure of a fungus.

Composed of a mass of white, delicate threads called mycelium (pl. mycelia).

It is coenocytic, non-septate and multinucleate.

Each thread in the mass is called the hypha.

There are three types of hyhae: horizontally growing, vertically upward-growing and vertically downward -growing.

Horizontally hypha is called the stolon.

Vertically upward growing hypha is the sporangiosphore.

Vertically downward growing hypha is rhizoid.

 

Read On: Bacteria: Characteristics, Occurrence, Structure, Different Shapes and Reproduction


Nutrition in Fungi

Unlike, green plants, fungi have no green (chlorophyll) pigments in their cells. They also do not have specialized structures like mouth or hypostomc for capturing food.

So, fungi cannot manufacture their own food.

However, fungi display two modes of nutrition. Some fungi live in, or on the tissues of other living organisms and from their they derive their nutrients directly by absorbing such through their hyphac that ramify the host tissue or substrate.

This mode of nutrition is said to be parasitic. The host does not benefit from this association, and in fact, may eventually be killed.

In some other fungi, as the hyphae grow on some dead or decomposing matter, copious amounts of enzymes are secreted unto such matter.

The complex food in the decomposing matter is digested into simpler and readily absorbable forms.

In this way, the hyphae of the fungus now absorb the soluble food.

This mode of nutrition is said to be saprophytic. The digestion of food that takes place outside the cells of the fungi is said to be extra-cellular.

 

Structure of a Mushroom

The macroscopic part of fungi is usually called the "fruiting body: A typical fruiting body of a mushroom fungus consists of an expanded umbrella-shaped structure called a pileus.

This is usually attached to the stripe (or stalk) by an annulus. The under part of the pileus bears gills which bear the reproductive structures (the basidiospores).

The mushroom is anchored on the substrate by rhitoids which are specialized hyphae that absorb nutrients from the substrate.

 

Reproduction in Fungi

You will find the process of reproduction in fungi very interesting. Now let see the details of the reproduction process. 

Reproduction is by asexual and sexual methods; Asexual reproduction.

This is by spores.

Developed in a container called sporangium.

Occurs under good conditions of moisture and temperature.

Mycelium develops into sporangiosphore.

The tip of the sporangiosphore develops the sporangium.

Vertical hypha swells at the tip.

Protoplasm migrates to tip. Central portion becomes dome-shaped and sterile; this is the columella. Peripheral protoplasm gives rise to small, mutinucleate masses by cleavage.

Each mass becomes the spore.

Spore wall thickens and darkens.

Sporangium wall becomes thin and brittle.

Columella swells due to fluid accumulation. It bursts open to liberate spores.

Spores are dispersed by wind and They germinate into slender mycelium, under a favourable condition. Hyphae sometime develop from the columella when the sporangiosphore happens to fall over and these hyphae then bear the sporangia.

 

Sexual Reproduction in Fungi

Takes place by conjugation. Occurs when food is exhausted Occurs through fusion of two similar gametes (isogametes).

Two hyphac of different plants of opposite strain (+ and -) lie side by side. Protuberances are produced by each plant to form programetes.

Each progamete enlarges to form club-shaped structure (progametangium).

Each is held by a suspensor.

Apex becomes gametangium (gamete store).

Gametes are multinucleate (coeno gametes).

Walls of gametangia in contact dissolve and gametes fuse to form zygospore.

The zygospore swells into a rounded body and its wall thickness, turns black in colour and becomes warted.

It contains an abundance of food, particularly fat globules.

The zygospore undergoes a period of rest and then germinates.

The outer wall bursts and the muter wall grows out into a tube called the sporangiosphore or promycellium which ends in a single sporangium.

The sporangiosphore may be branched, each branch bearing a sporangium

The sporangium contains numerous small spores but no columella.

 

Importance of Fungi

Do you know that Fungi play vital roles in the development of agriculture, medicine and industries? 


Read On: Viruses: Characteristics, Structures, Mode, Nutrition and Control


Diseases caused by Fungi

Plant diseases caused by fungi:

a. Late blight of Potato - The disease is caused by Phytophthora infestans. The symptom includes black patches on the under surface of leaves, less often on the upper, indicating diseased conditions of the plants. The diseases may spread to the entire leaf and to all parts of the plant body including the tubers. The fungus finally causes wilting of leaves and rotting of tubers. Control:

(i) Spraying the young plant with Bordeaux mixture (fungicide)

(ii) Selection of seed tubers from non-infected areas

(iii) Storage of seed tubers as a low temperature - 4.5°C

b. Smuts: This is a serious disease of wheat, barley, maize, oats and sugarcane caused by different species of ustilago. The fungus mainly attacks the stems, flower and often inflorescence. The infected parts turn black and all the grain is totally destroyed.

Control: (a) varieties of wheat or barley or maize already immune and resistant to smut should be cultivated.

(b) Cross-breeding with types immune or resistant to smut is possibly the best method.

(c) Hot water treatment of wheat grains and then drying them under strong sun may reduce the intensity of the disease.

c. Rusts: This is a disease of wheat, maize, - caused by different species of Puccinia The stem become yellowish or black depending on the species of Puccinia Control:

(a) Eradication of the barberry bush (alternate host) near a wheat field is a good established practice

(b) By cross-breeding with rust resist ant varieties

(c) Elimination of cultivation of wheat during summer may reduce the spread of the disease

(d) Cultivation of rust-resistant varieties.

d. Mildews: These diseases appear as whitish, yellowish or brownish sports on the leaves and also on other parts.

There are two kinds of mildews: Downy and Powdery

- Downy mildews are caused by cystopus, plasmopara and peropospora spp

- Powdery mildews are caused by Erysiphe and Uncinula spp.

Control: the disease is not a serious one; as such no control measures are taken.

 

Animal Diseases caused by Fungi

a. Ringworm - caused by Epidermophyton - located between outer and inner layers of the skin.

Symptoms: Circular red patch formed on the part of the skin infected. Later outer circular patch turns dark red. Small scales fall from the outer skin. Intense itching, disturbing sleep and general discomfort. - Ringworm of hairs causes hair to fall off.

Control: Good personal hygiene Avoid wearing wet shoes and clothes. Avoid contact with an infected person and his belongings. Spray infected materials with fungicides. See a medical doctor for medical advice and treatment.

b. AthleteN Foot - Also called Tinto pedis is located between skin and toes.

Symptoms - skin between toes becomes whitish. - at advanced stage, pains, and itchings, result. Offensive odour is produced.

Control:

 - Keep feet clean and dry all the time after bathing.

- rub dusting powder in between toes.

- Wear open sandals or loose shoes.

 

Benefits of Fungi to Man

1. In Medicine: Antibiotics (in form of capsules, syrup and injection) have been manufactured from saprophytic fungi for the cure of bacterial diseases, such as gonorrhoea, cholera, tuberculosis and dysentery. Penicilin is made from Penicillium notatum; Streptomycin is made from Streptonlyces and Aureomycin from Aureornyces.

Production of Antibiotics e.g. Penicilin from Penicilliuni notatum Streptomycin from Strepiornycesgrthesus (bacterium with fungi) Chloromycetin from Streptomyces yenezuclue Aureomycin from S. atireirfaciew Ferramycin from S. rimosus Erythromycin from S. erythreus Jaweharene from Aspergillus sp.

 2. In Industry

a. Alcoholic industry: Yeast is very important in the production of industrial spirit and be \ Ages. Yeast breaks down sugar to alcohol and carbon (IV) oxide. This is called fermentation. C611 1206 2H5OH + 2CO 2 + 28Kcal.

b. Bread Industry: In bread baking, yeast is used. Yeast produces carbon (IV) oxide which causes the dough to rise, making the bread spongy and easy to digest.

c. Fungi are used to ferment tobacco, in the curing of tobacco the carbohydrates in fresh leaves of tobacco are fermented by fungi to produce the special aromatic flavor and also for the retting of flax to obtain linen fibres.

The fungi break down the pectin that holds the fibres of flax together free for processing into linen.

• Fermentation: basis of industrial production of alcohol.

• Source of food e.g. Agaricus, volvariella, lepiata, Pleurotus spp and vitamin B.

• As saprophytes they help to decompose dead plants and enrich the soil.

• They cause superficial skin diseases of man e.g. ringworm and athlete's foot

• Internal diseases of man and other animals such as fungal tuberculosis and meningitis have been traced to fungi e.g. Aspergillus, thrush, moniliasis, etc.

• Cause decay and spoilage of valuable food.

• Yeast is an important source of vitamins and enzymes; it is used to make dough rise in bakery for making bread, etc. Useful for research work in cell biology, genetics and biochemistry.

In agriculture - soil inhabiting fungi play a major role in the decomposition of organic matter and in releasing minerals into the soil for plant growth and nutrition.

 

Conclusion on Fungi: Characteristic, Structure, Reproduction, Example and Facts 

The study of fungi is very important because of its significant importance to man in terms of human health, agriculture, and medicine.

In this article, you have learned that

1. Fungi are non-green plants.

2. Their vegetative body is collectively called mycellium.

3. Reproduction is both asexual and sexual.

4. Fungi cause diseases like smut, rust etc to man.

5. Fungi cause diseases in man and animals e.g. ringworm.

6. Fungi are highly important in medicine, industries and in agriculture.


Read On: Characteristics and Classification of Living Organisms

Post a Comment

0 Comments