ALGAE

 ALGAE

• Algae are chlorophyll bearing,simple thalloid,autotrophic and largely aquatic(both freshwater and marine) organism

• They occur in a variety of other habitats: moist stone,soil and wood.

• Some of them also occur in association with fungi called lichen.

Spirogyra

• The form and size of algae is highly variable.The size ranges from microscopic unicellular forms like chlamydomonas,colonial form like volvox and to filamentous forms like ulothrix and spirogyra.

ULOTHRIX IMAGES

• A few of the marine forms such as kelp,form massive plant bodies.

Reproduction in algae

• The algae reproduce by vegetativr,asexual and sexual method.

• Vegetative reproduction is by fragmentation. Each fragment develops into a thallus.

• Asexual reproduction is by thr productiom of diffetent types of spore,the most common being the zoospore.They are flagellated(motile) and on germinate give rise to new plant.

• Sexual reproduction takes place through fusion of two gamete.These gametes

 can be flagellated and similar in size(as in chlamydomonas) or non flagellated(non motile) but similar in size  asi in spirogyra. Such reproduction is called isogamous.

• Fusion of two gametes dissimilar in size, and in some species of chlamydomonas is termed as anisogamous.

• Fusion between one  large, non - motile(static) female gamete and a smallet, motile male gamete is termed oogamous,e.g., volvox, fucus.

Uses of Algae

• Algae are useful to man in a variety of ways. At least half of the total carbon dioxide fixation on earth is carried out by algae through photosynthesis.

• Being photosynthetic they increase the level of dissolved oxygen in their immediate environment.

• They are of paramount importance as primary producers of energy-rich compounds which form the basis of the food cycles of all aquatic animals.

• Many species of porphyra, laminaria and Sargassum are among the 70 species of marine algae used as food.

• Certain brown and red algae produce large amounts of hydrocolloid ( Water holding substance), e.g.,algin(brown algae) and carragene (red algae) Which are used commercially. 

• Agar is one of the commercial products obtained from  Gelidium and gracilaria that are used to grow microbes and in preparation of ice cream and jellies.

• Chlorella and spirulina are unicellular algae, rich in protein and are used as food supplements even by space travellers.

Algae are divided into three classes on the basis of pigments.

• Chlorophyceae

• Phaeophyceae

• Rhodophyceae

Chlorophyceae

• The members of chlorophyceae are commonly called green algae.

• The plant body may be unicellular, colonial or filamentous.

• They are usually grass green due to the dominant pigments chlorophyll a and b.

• The pigments are localised in definite chloroplast.

• The chloroplast may be discolid, plate-Like, reticulate, cup shaped, spiral or ribbon- shaped in different species.

• Most of the members have one or more storage bodies called pyrenoids located in chloroplast.

• Pyrenoids contain protein beside starch.

• Some algae may store food in the form of oil droplets.

• Green algae usually have a rigid cell wall made of an inner layer of cellulose and an outer layer of pectose.

• Vegetative reproduction usually takes place by fragmentation or by formation of different types of spore.

• Asexual reproduction by flagellated zoospore produced in zoosporangia.

• The sexual reproduction show considerable variation in the type of sex cell and it may be isogamous, anisogamous and oogamous.

• Some commonly found green algae are: chlamydomonas, volvox, ulothrix, spirogyra and Chara.

phaeophyceae

• The members of phaeophyceae or brown algae are found primarily in marine habitats.

• They show great variation in size and form. They range from simple branched, filamentous form in ectocarpus to profusely branched form as represented by kelp, which may reach a height of 100 meters.

• They possess chlorophyll a,c, carotenoids and xanthophylls.

• They vary in colour from olive green to various shades of brown depending upon the amount of the xanthophyll pigment, fucoxanthin present in them.

Sargassum

• Food is stored as complex carbohydrates, Which may be in the form of laminarin or mannitol.

• The vegetative cells have a cellulosic cell wall usually covered on the outside by a gelatinous coating of algin.

• The protoplast contains, in addition to plastid , a centrally located vacuole and nucleus.

• The plant body is usually attached to the substratum by a holdfast, and has a stalk, the stripes and leaf-like photosynthetic organ, the frond.

• Vegetstive reproduction takes place by fragmentation

• Asexual reproduction in most brown algae is by flagellated zoospore that are pear shaped and have two unequal laterally  attached flagella.

• Sexual reproduction may be isogamous, anisogamous and oogamous.

• Union of gamete may take place in water or within the (oogamous species).

• The gametes are pyriform ( pear shaped) and bear two laterally attached flagella.

• The common forms are ectocarpus, Dictyota, Laminaria, Sargassum, And fucus.

LAMINARIA

Rhodophyceae

• The members of rhodophyceae are commonly called red algae.

• The predominance of the red pigment, r-phycoerythrin in their body.

• Majority of the red algae are marine with greater concentration found in the warmer areas.

• They occur in both well- lighted regions close to the surface of water and also at great depth in oceans where relatively little light penetrates.

• The red thalli of most of the red algae are multicellular.

• The food is stored as floridean starch which is very similar to amylopectin and glycogen in structure.

• The red algae usually reproduce vegetative by fragmentation.

• They reproduce asexually by non-motile spore and sexually by non -motile gametes.

• Sexual reproduction is oogamous and accompained by comex post fertilisation develpoment.

• The common members are : polysiphonia, porphyra,gracilaria and gelidium.

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