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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

green algae e.g Chlorella

Phylum: Phaeophyta brown algae

e.g focus laminaria Phylum: Rhodophyta Red algae

Plylum: Bacilliariophyta e.g diatons

Source: Taylor et al. Figure 7.2 (other features of figure 7.2 p.31 has been left out).

Algae belong to the group Protoctist. They are believed to have evolved in water and have remained in water. Some alga have escaped unto land and have successfully lived on land but they are not plants since they lack true stern and leaves. Instead of stem, roots and leaves, they have undifferentiated body called Thallus. They are grouped according to the pigment they contain. They make their own food (photosynthetic) like the plants.

Common green algae you see around are spirogyra, Chlorella, etc.

7.7.2 Classification and characteristics of two of the main groups of Algae

Alge

General Characteristics

Almost all are specialized for an aquatic existence. Great range of size and form, including unicellar, filamentous, colonial and thallaoid forms. A thallus is a body which is not differentiated into true roots, stems and leaves and lacks a true vascular system (xylem and phloem). It is often flat. Photosynthetic, eukaryotic. Phylum Chlorophyta (‘green algae’) Phylum Phaeophyta (‘brown algae’) Dominant photosynthetic pigment is

chlorophy II; therefore green in appearance.

Chlorophylls a and b present (as in plants)

* Dominant Photosynthetic pigment is Brown and called fucoxanthin.

Chlorophylls a and c present.

Store carbohydrate as starch (insoluble) * Store carbohydrate as soluble laminarin and mannitol. Also store fat.

Mostly freshwater Nearly all marine (3 freshwater genera only)

Large range of types e.g unicellular, Filamentous, colonial thalloid

Filamentous or thalloid, often large e.g Chlorella, a unicellular, non-motile alga,

Chlamydomanas, a unicellular, motile alga, e.g Fucus, a thalloid, marine alga Laminaria, large thalloid, marine

thallaoid marine alga

Source: Taylor et al (1998:33) * a diagnostic feature 7.2.3 Structure of a Typical Alga Chlorella

Chlorella

Fig 7.1 Structure of Chlorella, a green alga.

Source: Taylor el. al., (1998, 34)

Chlorella is atypical algae. It is unicellular non-motile green alga. It is a aquatic, found in fresh water ditches and ponds.

Activities

Go round your environment, look out for ditches and ponds. Using a container, collect water containing green substance found in water. Some of them are slimy.

When there are a lot of them, they appear like green threads in the water.

Spirogyra is a common algae. Your tutor will show you the structure of algae under the microscope. You will be able to see different types of algae from that collection. Draw the structure or appearance of at least five. You will enjoy this exercise. Note any stagnant water during rainy season could contain a lot of algae.

They are in their peak when the rains have stopped and before the dry season.

Your instructor will also show you prepared slide of types of algae. Compare what you see on the slide with what you see under the microscope.

7.2.4 Types of Algae on the basis of their nutrition and reproduction Algae are classified into six classes on the basis of their pigments:

1. Blue-green algae 2. Euglena

3. Green algae 4. Diatoms 5. Brown algae 6. Red algae

Cell Wall contains cellulose Cell surface membrane

Cytoplasm contains usual eukaryotic organelles. E.g Golgi apparatus, ribosomes, ER, small vacuoles Chloroplast large, cup-shaped, contains photosynthetic pigments chlorophyll a and b

Pyrenoid

Site of starach formation and storage

Algae are autotrophic plants, they manufacture their own food with the help of chlorophyll. Reproduction is vegetative by cell division or by detachment of a portion of the mother plant or asexual.

7.2.5.1 Biological Importance of Algae

Algae are useful to man in many ways. Some serve as food in many parts of the world. Algae start a very good point in food chain. The example you saw earlier, i.e. chlorella, a non-motile alga is a good starting point for the evolution of higher green plants, since it has lost motility. Various algae have various biological importance.

Table 7.0 Difference between Algae and Fungi

Algae Fungi

Green thallophytes with chloerophyll Do not have chlerophyll

Autotrophic-make their own food Heterotrophic, feed on already made food.

Have diverse mode of nutrition parasitic or saprophytic in habit

Have a true parenchymatous tissues False tissue (hyphae) Cell-wall-true cellulose Cell-wall, chitin

Live in water or wet substrata Live as parasites on other plants or on animals as saprophytes on decaying animal or vegetable matter

Reserve carbohydrate is starch Glycogen