De la encuesta a Directivos

6.2.2 Structure of a typical fungus 6.2.3 Types of fungi and nutrition

6.2.4 Classification and Characteristics of fungi 6.2.5 Uses of fungi

6.3.0 Conclusion 6.4 Summary 6.5 TMA 6.7-) 6.6 References

6.2.1 Fungi General Description

Fungi are a large group of organisms. They range from unicellular yeast to toadstool, puffballs, stinkhorns. Toadstool and puffballs are a kind of mushrooms.

You must have seen some mushrooms or even eaten some. Some of them are poisonous. They are very numerous, about 80,000 species have been identified.

They have some benefits to man. We have just mentioned the mushrooms that are used for food. Others are used for medicine. Yeast is used as raising agents in bread baking..

You must have seen bread with some growth on it. We usually refer to such as moulds. There are different kinds of moulds. Some grow on leather products, like shoes, handbags, rotten vegetable etc. Some grow on fruits causing damage to such fruits while others grow on plants causing the disease of plant called mildews, smuts and rusts. Those who study fungi in detail are called Mycologists and the filed itself is called Mycology.

6.2.1 Structure of a Typical Fungus figure I

Fig 6.1: (a) A scanning electron micrograph of part of the mycelium of Mucor hiemalis showing sporangia (x 85). (b) Mycelium of Mucor as seen with low power of a light microscope.

Source: Taylor et al., (1998) p. 28

Mucor is a typical fungus. It is made up of hyphae- branches that are like twigs, a single one is called hypha. The hypha is hollow inside. The collection of hyphae is called mycellium. The structure of hyphae is segmented like, this segment is called septa. It divides the hyphae into compartments similar to cells, but in this case the hyphae are not divided into true cells. The hyphae contains chitin. Chitin is a nitrogen containing polysaccharide. A hypha may have walls (septate) as in penicillium or lack cross-walls (aseptate) as in mucor. The cytoplasm like any Eukaryotes cell contains mitochondria, golgi apparatus, endoplasmic reticulum, ribosomes and vacuoles.

Sporangium –black when ripe, colourless/white when immature;

produces spores for asexual reproduction

Branching, aseptate hyphae forming a large white mycelium

Sporangiophore Vertically growing hypha bearing sporangium

100ųm

Spores exposed when sporangium splits (dehisces)

You learnt in the forgoing section that fungi have over 80,000 species. We will talk about the very common ones around us.

a. Penicillium, Mucor and Rhizopus-they are the ones we often see on stale bread, rotten food, etc. You do not need a scientist to culture them. If you have eba in the kitchen after two days you will find mould growing on it. If your tutor mount this under a microscope, you will notice the branching threads we call hyphae.

(c) (a)

(c)

Septate, branching mycelium

(a) Penicillium growing on nutrient agar in a Petri dish. It typically produces a relatively small circular mycelium. The young outer edge of the mycelium appears white, whereas the mature central portion appears darker where coloured spores have been produced.

(b) Penicillium showing asexual reproduction. It has a characteristic brush-like arrangement of conidia.

(c) Scanning electron micrograph of conidiophore and conidia (spores) of Pencillium. (d) LS hypha showing fine structure visible with electron microscope.

6.2.3 Types of Fungi and Nutrition

Fig 6.2

b. Penicillium Species - there are many types of these and they are identified by their colour - blue, green, yellow and orange. They grow on bread, ripe fruits, etc.

Their colour is as a result of the mycelia. Reproduction here is by spores called conidia. When any falls on favourable surface it develops. The spores are produced at the tips of special hyphae called conidiophones. Penicillium is of special interest to scientist because they have been able to produce antibiotic from it called Penicillin.

c. Mucor is the common one we find around. They are the white cotton wool-like structure you see growing profusely on bread, smoked fish, etc. The structure of mucor is different from that of others. It produces spores too, like penecillium but in this case the spores are produced on a spherical sporangia borne on very long stalks known as sporangi ophores.

d. Yeast are the simplest of the fungi group because they are unicellular. Yeast can be found on ripe fruits, they give that characteristic sour smell or flavour in cereals. Yeast has a very high economic importance in the brewing industries.

Yeast cells multiply by budding rapidly. Bakers use yeast to bake bread. It helps the bread to rise, i.e. by the budding process.

6.2.4 Classification and Characteristics of Fungi Kingdom Fungi - General Characteristics

Heterotrophic nutrition because they lack chlorophyll and are therefore non-photosynthetic. They can be parasites, saprotrophs or mutualists. Nutrition is absorptive, digestion takes place outside the body and nutrients are absorbed directly. Digestion does not take place inside the body, unlike animals. Rigid cell walls containing chitin as the fibrillar material. Chitin is a nitrogen containing polysaccharide, very similar in structure to cellulose. Like cellulose it has high tensile strength. It therefore give shape to the hyphae and prevents osmotic busting of cells. Body is usually a mycellium, a network of fine tubular filaments called hyphae. These may be septate (have cross-walls), e.g. Penicillium, or

aseptate (no cross-walls, e.g. Mucor. If carbohydrate is stored, it is usually as glycogen, not starch. Reproduce by means of spores. Non-motile.

Table 6.2.4 Classification and Characteristics of Fungi

Phylum Zygomycota Phylum Ascomycota Phylum

Basidiomycota Asexual reproduction by

conidia or sporangia containing spores

Asexual reproduction by conidia.

No sporangia

Asexual

reproduction by formation of spores.

Not common.

Non-septate hyphae and large well-developed branching mycelium

Septate hyphae Septate hyphae

e.g Rhizopus stolonifer, Common bread mould, a saprotroph, Mucor, common moulds, saprotroph

e.g Penicillium Aspergillus, saprotrophic moulds Saccharomyces (yeast), unicellular saprotrophs, Erysiphe, obligate parasites causing powdery mildews, e.g of barley

e.g Agaricus campestris, field mushroom

saprotroph Source: Taylor et. al. (1998) p 25

6.2.5 Uses of Fungi

1. Yeast - different species and strains of yeast are used in the brewing industry for alcoholic fermentation.

2. Penicillium - a blue-green mould is the source of the world famous penicillin (an antibiotic). Certain species of penicillium are used industrially in making various organic acids and in making special types of flavoured cheese.

3. Aspergillus - is economically an important fungus. Some species are used industrially in the manufacture of alcohol from rice starch, and manufacture of certain organic acids (e.g. citric, gluconic acid) on a commercial basis. Some species are sources of certain antibiotics.

4. Agaricus (Mushroom) use as food by humans.

6.3 Conclusion

You have learnt about the general description of fungi. There are many types of fungi. The drawing of a fungus is just an example. You learnt that the most common fungi that you can easily observe on your own are the mucor, penicillium and rhizopus. You have also learnt that they digest their food outside their body and absorb what is digested. They feed on alsmost anything. They are referred to by the method of their feeding as saprotrophs, parasites and mutualists.

6.4 Summary

Fungi are diverse in nature. There are about 80,000 species known. They could be more. Some of them are very beneficial to man like the mushrooms„ while some are destructive. If you leave your eba or bread outside for long, the spores fall on it and start to grow. The spores are found in the air, even in your refridgerator.

The refridgerator does not destroy them but slow down their activity.

6.5 TMA (See attached) 6.6 References

Talor et. al. (1998) has been referred to extensively. All the figures present in this unit have been adopted form Taylor et. al.

6.7 Further Reading - You are advised to read variety of biology textbooks.

In unit 6, you learnt about Fungi as an example of Eukaryotes. You learnt that the fungi lack chlorophyll because of that they do not make their food, instead they feed on already made food. You learnt about the three different types of feeding in fungi i.e. parasitic, saprotrophic and mutualism.

In this unit we are going to study another group of organisms called Algae.Algae are plant-like, photosynthetic and mainly aquatic. They are named or classified on the basis of the pigment they contain, like blue-green, brown and green algae.

7.1 Objectives

By the time you complete this unit, you will be able to:

1. Draw a typical Alga and label the drawing correctly.

2. List and discuss the characteristics of two main groups of algae.

3. Differentiate types of algae on the basis of their nutrition, reproduction and biological importance.

4. Differentiate between algae and fungi 7.2. Algae

7.2.1 General description of Algae

7.2.2. Classification and Characteristics of Algae 7.2.3 Structure of a typical Algae

7.2.4 biological importance of Algae

7.2.5 Types of Algae on the basis of their nutrition and reproduction.

7.2.5.1 Differences between Algae and Fungus 7.3 Conclusion

7.4 Summary

7.5 TMA

7.6 References and further readings 7.2 Algae

7.2.1 General Description

The flow-chart below shows the place of algae among the Protoctista Protoctista

Phylum Chlorophyta

Algae Plant-Like Photosynthetic

and mainly

animal-like, unicellular and acquatic

Slime Moulds, Motile like

animals, produce spores Phylum:

Oomycota Furgus-like

7.0 Introduction