ECONOMIC IMPORTANCE AND CLASSIFICATION OF ALGAE

1. 1. Algae as green manure
o Blue green algae, bio fertilizer has proved to be most efficient source of organic
nitrogen in low level paddy
o Algae fertilizer is especially useful because it is a living organism.
o When we use algae as a manure, it quickly begins to break down, releasing its
abundant nitrogen.
o In addition, fertilizers have a high concentration of nitrogen. In some plants,
atmospheric nitrogen is not readily available and hence blue green algae are used
as bio fertilizers due to its nitrogen fixing ability, except for the plants that have
endosymbiotic nitrogen fixing bacteria.
o An example of a cyanobacteria used as a green manure is Nostoc, Azolla.
o Being photosynthetic, algae play an important part in introducing organic matter
in to the soil and excrete polysaccharides which increase soil aggregation.
2. Algae in agriculture
Algae play an important role in agriculture where they are used as bio fertilizers
and soil stabilizers. Marine algae are used as fertilizers on farmlands close to the sea,
examples include large brown and red algae, which are richer in potassium content.
3. Algae as bio fertilizers
• Many algae increase the water holding capacity besides the addition of their
chemical
• constituent in the soil
• In India, Turbinaria is used around palm tree while as sea weeds are used as
compost.
• The species of Nostoc, Scytonema, Aulosira, Lyngobya, Anabaena etc. most of
these can fix atmospheric nitrogen and increase the soil fertility.
REVISION NOTES -
ECONOMIC IMPORTANCE OF ALGAE

2. • Due to their mucilaginous sheath, they are able to prevent soil erosion by binding
the soil particles firmly.
• Blue green algae are treated as bio fertilizers from olden days.
• Nostoc, Oscillatoria, Scytonema, Spirulina etc. are used as fertilizers to rice
fields.
• Cultivation of spirulina is gaining importance as feed for fish, poultry and cattle.
4. Algae as food
o Algae species are used as food in several countries and in several forms.
o Algae species have proteins, vitamins (A, B, C and E), lipids and minerals.
o Laminaria species is the important edible seaweed in Japan and the food item
(kombu) is prepared from it.
o Aonori from Monostroma Asakusa Nori from porphyra are prepared in different
countries. Porphyra has 35% protein, 45% carbohydrates, vitamins B and C.
o Nostoc is used as food material in south America.
5. Algae as fodder
• Many sea weeds such as Fucus, Laminaria, Ascophyllum, etc. species are used as
fodder.
• Rhodymenia plamata is used as food for sheep in narvey.
• Laminaria saccharina, Pelvitia, Ascophyllum etc. species are used as food for
cattle.
• Sea weeds contain larger amount of iodine so they are used as fodder for milk
cattle and hens.
6. Algae in industry
Many products of commercial and pharmaceutical importance have been derived from
algae
➢ Agar –Agar
• Agar is obtained commercially from species of Gelidium, Gracilaria and condrus.
• Japan and South East Asia are the main production centres of agar.
• The greatest use of agar in food, pharmaceutical and cosmetic industry.
• It is used as a stiffering agent in culture media.
➢ Carrageenan
• It is obtained from the cell walls of Chondrus crispus and Gigartina stellata.

3. • It is utilized in textile, leather and brewing industries.
• In alcohol and sugar industry it is used as a clearing agent.
➢ Alginate
• They are found in cell wall of brown algae
• Alginate are nontoxic and viscous and readily form gel, useful as thickener,
emulsifier and gelling agent.
• Flame proof fabrics are also prepared from alginates.
7. Role of algae in medicine
o Algae is used one of the most important medicinal sources due to its anti-oxidant,
anti-cancer, anti-viral properties.
o A biotech company is applying brown sea weed that produces an incredible amount
of poly saturated fatty acid to reduce blood pressure, alleviate chronic
inflammation and reduce cholesterol level.
o Dunaliella primolecta C-525 exhibiting highest antibiotic activity.
o Phycobili proteins from red macro algal species have an important role as
anticancer agents due to their high efficiency and low toxicity.
8. Biological importance of Planktons
▪ Companies such as Climos and Planktos have invested in phytoplankton as a means
of reducing carbon-dioxide emissions.
▪ They are investigating fertilizing phytoplankton communities with iron, a vital
nutrient, to promote their growth.
▪ As political and economic pressures to provide carbon-dioxide emissions offsets
increases, the potential profit of companies like these increases.
▪ Some phytoplankton have a direct impact humans and other animals.
▪ Dense blooms of some organisms can deplete oxygen in coastal waters, causing
fish and shellfish to suffocate. Other species produce toxins that cause can cause
illness or death among humans and even whales that are either exposed to the
toxins or eat shellfish that accumulate toxins.
▪ Such harmful algal blooms (HABs) cause significant economic loss every year in
the seafood industry and in tourist communities, and scientists are working to

4. understand the causes of these blooms and to devise ways to predict and prevent
them.
▪ Though they are microscopic in size, organisms called plankton play a big role in
marine ecosystems.
▪ As photosynthetic organisms, they are able to convert solar energy into chemical
energy and store it as sugars
▪ They provide the base for the entire marine food web- providing food to a wide
variety of species from tiny bivalves to whales.
Global Ecosystems
They are responsible for half of the photosynthetic activity on the planet.
This means that of the carbon dioxide in the atmosphere that gets fixed into
sugars, phytoplankton are doing half of the work- makes them important to global
carbon-dioxide levels.
Carbon sequestration
Without phytoplankton to pull carbon dioxide out of the atmosphere, carbon-
dioxide levels would rise, because carbon dioxide would continue to be produced
in both biological and industrial sources.
❖ CHLOROPHYTA {green algae}
Generally fresh water.
▪ Thallus structure
o Shows a range of variation in the structure of plant body (thallus)
o It ranges from unicellular e.g., Chlamydomonas, Chlorella, etc. to multicellular
structure. The multicellular forms may be of different types. They may have a
number of cells arranged in colonies of definite shape, the coenobium.
REVISION NOTES -
General account of thallus structure, cell ultra-structure, reproduction,
relationships and evolutionary trends in the following groups:
Chlorophyta, Xanthophyta, Bacillariophyta, Phaeophyta & Rhodophyta

5. o In multicellular forms the cells may be arranged in a single row to form the
filament. The filament may be branched (e.g., Pithophora, Cladophora etc.) or
unbranched (e.g., Oedogonium, Spirogyra, Ulothrixetc.). The multicells may
aggregate and form an expanded sheet-like structure as found in Coleochaete.
o It shows heterotrichous habit where the erect system is well-developed. In some
algae like Ulva, the plant body is leaf-like. The highly organised plant body in
Chlorophyceae is found in Chara, where the plant is very much complicated in
structure with well protected sex organs.
o From simple to complicated forms, various types of thalli evolved in green algae
along different lines. They may be grouped as follows:
1. Unicellular (Motile or non-motile)
2. Aggregates (Palmelloid or Dendroid)
3. Colonial (Motile or Non-motile)
4. Filamentous (Unbranched or Branched) [Branched filaments may be
simple, heterotrichous or pseudoparenchymatous.]
5. Siphonaceous,
6. Foliaceous, and
7. Parenchymatous
o Typical example of unicellular non-motile green alga is Chlorella. It is spherical in
shape, about 2 to 10 μm in diameter, and is without flagella. Example of motile
unicellular green alga is Chlamydomonas.

6. ▪ Cell ultra-structure
o Eukaryotic
o considered as a renewable source of valuable chemicals for
biofuel, nutraceutical or pharmaceutical industries.
o Microalgae store most of their valuable components inside the cell behind a thick
and resistant cell wall.
o Green microalgae accumulate carotenoids, vitamins or unsaturated fatty acids in
appreciable amounts.
o The chloroplasts may be discoid (Chara), plate-like (Mougeoutia), reticulate
(Oedogonium), cup-shaped (Chlamydomonas), spiral (Spirogyra) or ribbon-shaped
in different species.
o Photosynthetic pigments are chlorophyll a, chlorophyll b, carotenes and
xanthophylls. The green colour is due to the excess of chlorophyll pigments.
o They have storage bodies called pyrenoids containing protein besides starch. The
reserve food is starch, composed of amylose and amylopectin.
o Eye Spots occur in motile or flagellate forms. An eye spot is a photosensitive area
associated with the chloroplast.
o They have a rigid cell wall made of an inner layer of cellulose and an outer layer
of pectose. Many forms like Spirogyra and Zygnema secrete mucilage around the
cell wall.

7. o In Chara, the cell wall is encrusted with calcium and magnesium carbonate.
o Semipermeable cell membrane is present.
o Usually there is only one nucleus in each cell, but in Siphonales and Cladophorales
many nuclei are present in their coenocytic body.
o Flagella are 1-many, equal in size and inserted either apically or sub-apically. The
flagella show typical 9+2 arrangement when viewed under electron microscope.
▪ Reproduction
o Vegetative –
• Portions of the plant body become separated off to give rise to new individuals
without any obvious changes in the protoplasts. Fragmentation into two or more
pieces or through an accidental or natural separation of its parts.
• The process of multiplication by ordinary cell division is also characteristic of
some unicellular algae.
o Asexual –
• Formation of zoospores (flagellate spores that are formed singly or in numbers
either in a vegetative cell or in a specialized part of the plant body known as a
sporangium).
• In some species non-motile spores are formed which are called aplanospores,
but if these should then secrete a thick wall they are known as hypnospores.
All these spores produce new plants.
o Sexual –
• Gametic union ranges from isogamy to anisogamy, and even oogamy with a
relatively advanced stage of evolution having a tendency of retention of the
products of gametic fusion in the mother plant and to develop a mechanism to
afford protection against unfavorable conditions.
• Depending on species, union of gametes both of which may be non-flagellate
(aplanogamy) or flagellate (piano- gamy). Normally the two gametic nuclei fuse
immediately after fusion of gametes, but in many cases, they do not fuse until
just before germination of the zygote.
• Meiosis generally takes place during the germination of the zygote.
• Practically in all fresh-water algae the diploid phase in the life cycle is
restricted to the zygospore or oospore which is comparable with the
sporophyte of the higher plants.

8. ▪ Relationships & Evolutionary trends
o Evolutionary Trend in the Development of Plant Body in the Chlorophyta:
Members of the Chlorophyta exhibit a wide degree of variation in their external
form, ranging from very simple unicellular motile and non-motile on the one hand
to a highly developed complex structure with clear distribution of labour on the
other.
o Trend of evolution can be traced broadly along four lines with a starting point from
the Chlamydomonad type.
(i) the motile coenobial line
(ii) non-motile net-like line
(iii) the coenocytic line
(iv) the filamentous line.
o The evolutionary trend indicated based on the observation of E. F. Blackman, who in
1900 traced the evolution in the construction of plant body in the Chlorophyta from
one-celled flagellated Chlamydomonad type of condition.
o The filamentous line has again given rise to:
(i) simple parenchymatous form, (Ulva)
(ii) a line terminating in the Conjugates
(iii) the elaborately developed heterotrichous line.
o The heterotrichous line has further developed in two directions with the suppression
of one form or the other.
(i) a line having the tendency to develop thalloid structure at the cost of
the aerial portion which turns out to be very rudimentary, (Coleochaete,
Fritschiella)
(ii) a very elaborately branched aerial portion with very insignificant
prostrate portion (Draparnaldia, Draparnaldiopsis, Chara, Nitella).

9. ❖ XANTHOPHYTA {yellow-green algae}
Include only one class Xanthophyceae. Both marine and fresh-water forms. Has close
relationship with the Chlorophyta.
▪ Thallus structure
o A variety of cell organizations.
o Most Xanthophyta are coccoid or filamentous, but some are siphonous, meaning that
they are composed of multiple tubular cells with several nuclei. What makes up the
cell wall is unknown but inside some there are two silica valves similar to those in

10. diatoms. For the species that are filamentous the interlocking halves are in the shape
of a H.
o Single flagellated cells (e.g., Chloromeson).
o Solitary and coenobial coccal types are much more common in freshwater euplankton
and epiphyton. However, their presence is often overlooked since they are easily
mistaken for coccal green algae because of the similar morphology and their yellow-
greenish color, which is due to the lack of fucoxanthin, an accessory pigment typical
of other heterokontophytes.
o Sessile coccal genera, e.g., Ophiocytium.
o Species grow on drying mud, on trunk of trees, on damp walls, and similar other
habitat.
▪ Cell ultra-structure
o Each vegetative cell has a cell wall composed chiefly of pectic substances which,
depending on species, may be impregnated with silica.
o Their photosynthate is stored as oils and the storage polymer chrysolaminarin.
o Xanthophyceae are "secondary endosymbionts" -- they evolved from protists that
engulfed algae and assimilated their chloroplasts.
o The cell contains one to several discoid chromatophores.
o Except in the siphonaceous forms each vegetative cell is uninucleate.
o Due to the presence of excess of carotenoids, the colour of chromatophores is
yellow-green. Chlorophyll a and chlorophyll e are present.
o The chromatophores lack pyrenoids.
o One of the outstanding features of the Xanthophyta is the presence of motile cells
bearing two flagella of unequal length.
▪ Reproduction
o For the majority of Xanthophyceae only vegetative reproduction is known, which can
occur by vegetative cell division or by filament fragmentation. Although free-
swimming xanthophytes are very few, reproduction by flagellated spores is very
common in the whole class. Several taxa (e.g., Tribonema and Botrydium) can also
produce akinetes, modified vegetative cells with thickened cell wall that can survive
adverse environmental conditions.

11. o Asexual reproduction in most species is by zoospores with a few exceptional cases
where aplanospores are formed for asexual reproduction.
o Sexual reproduction is less common and has been reported only in
1) Tribonema, where isogamous union of gametes produces a dormant zygote.
2) Botrydium, with isogamous or anisogamous gametes.
3) Vaucheria, which presents a very characteristic oogamy (FIG) with male and
female reproductive structures arising near the apex of vegetative filaments
on monoecious or dioecious thalli.
▪ Relationships & Evolutionary trends
o One line may have descended from a unicellular motile ancestor, giving rise to
solitary or colony non-motile unicells.
o Another tendency is for the plant to take on a tubular, or siphonaceous, shape.
o The third leads to the creation of multicellular filamentous type organisms.
o This division was previously classified as Chlorophyta.
▪ They were included in the 'Heterokontae' subgroup because to their uneven
flagella.
▪ Others with similar flagella were labelled 'Isokontae' (Chlorophyceae).

12. ❖ BACILLARIOPHYTA {diatoms} golden brown algae
Members are commonly known as diatoms and are commonly found in fresh water, saline
water, in air or on soil.
▪ Thallus structure
o Thallus is represented by an iso-bilaterally symmetrical diploid unicells.
o Structurally, it can be differentiated into two parts:
(i) A siliceous cell wall (called frustule) and
(ii) the protoplast.
The cell wall is made of pectic substances which are impregnated with silica
(SiO2). Cell wall consists of two overlapping halves called epitheca and
hypotheca. Epitheca remains fitted over the hypotheca as a lid over the box.
Each theca is further divided into two parts:
(i) The main surface called valve.
(ii) the incurved margin known as connecting band or cingulum. The two
connecting bands of the two thecas are fitted together. The connecting
band of the epitheca overlaps that of the hypotheca and the two bands
remain united in the overlapping region (called girdle) by a connecting
cement present between them.
o A frustule can be seen in two views:
(i) Valve view
(ii) Girdle view.
o In top view or valve view it appears as boat shaped. Girdle view or side view more
or less rectangular. The valve view shows marking or striations which spread out
laterally in two parallel series, one on either side of the axial strip. The axial strip
pears a longitudinal cleft known as raphe.
o The raphe extends from one end of the valve to the other. It also bears three
enlargements or rounded nodules, one central nodule and two polar nodules. Due to
presence of raphe Navicula shows gliding movement. This movement is caused “by
streaming cytoplasm by circulation within the raphe, and by the extrusion of the
mucilage”.

13. ▪ Cell ultra-structure
o Thallus is unicellular, uninucleate diploid and show radial or bilateral symmetry.
o Cell wall is silicified. It shows characteristic secondary structures. It is often
called the frustule.
o Frustule is made up of two overlapping halves.
o The upper larger half is called as the epitheca, and the lower smaller overlapped
half is called hypotheca.
o Cells generally possess many discoid or two plate like chromatophores.
o Members of this class are also called as golden-brown algae because of their
characteristic pigments which include carotenoids, fucoxanthin, diatomin
(diatoxanthin, diadinoxanthin), beside chlorophyll a and chlorophyll C.
o The stored food products are in the form of oil, volutin and chrysolaminarin.
o Cell shows gliding movement.
o Reproduction occurs by cell division and auxospore formation.
o Motile stages possess a single, anterior pantonematic flagellum.
o The raphe is a structure that allows diatom cells to move over surfaces. The raphe
system is composed of one or two slits, or fissures, that penetrate the valve of
some diatoms. If two slits are present, each is called a branch of the raphe.
Branches may be separated by a silica thickening called the central nodule.

14. o Types of Diatoms
(i) Pennate Diatoms - These types of diatoms are elongated in shape. These
diatoms can be divided bilaterally. Therefore, they have bilateral symmetry.
Pennate diatoms are motile in nature. They move by the gliding movement.
(ii) Centric Diatoms - These types of diatoms are round-circular in shape. They
possess radial symmetry. These forms of diatoms are non-motile in nature.
▪ Reproduction
o Vegetative Reproduction:
It takes place by the mitotic cell division or fission. Successive cell division takes
place very rapidly at night. Presence of aluminium silicate in water is essential for
cell division to occur. As the cell division starts, the cell protoplast increases in
diameter. The cell also increases in size. The diploid nucleus divides mitotically and
produces two daughter nuclei. Two chromatophores divide. The single
chromatophore spits longitudinary in such a manner that one chromatophore comes
to lie in each half. Now the protoplasm cleaves into two uninucleate portions by
division in longitudinal plane parallel to valve surface.
One daughter protoplast now lies in epitheca and the other in
hypotheca.
Now both the daughter protoplasts with one daughter nucleus secrete the new
siliceous wall on the two fresh protoplasmic surfaces exposed along the cleavage

15. plane. The new valves developed always become hypotheca while the older theca
(which may be epitheca or hypotheca of the parent cell) becomes the epitheca of
the new or daughter cell.
When this cell again divides, it produces a daughter ceil which is again smaller than
the present parent. Thus, in a population of diatom cells during successive divisions
there is normally a progressive decrease in the average cell size. It is called
Macdonald-Pfitzer law. The smaller cells of later series of division lose their
vitality and capacity of division.
o Diatoms mainly reproduce by the asexual mode of reproduction, by binary fission.
o Sexual Reproduction:
It takes place by the formation of auxospores. The successive decrease of cell
size in vegetative reproduction is prevented by the auxospore formation. The
auxospore formation is actually a ‘restorative process’ because the reduction in
the original size of the cells, during the cell division is restored. During the process
only those cells which have diminished sufficiently in size can act as sex cells or
conjugating cells. Those cells which do not decrease in size by cell division
apparently do not show sexual reproduction. Two sex cells come together, pair up
longitudinally (called gamontogamy) and secrete a common mucilaginous envelope.
The diploid nucleous of each cell undergoes meiosis to form 4 haploid nuclei. Out
of these two nuclei degenerate and only two remain functional. The protoplasm of
each cell now cleaves into two portions each obtaining one haploid nucleus. The
functional nuclei ultimately metamorphose into gametes. The parent cell fuses
(cytogamy) and the fusion of gametes occurs in a copulatory jelly.
• Relationships & Evolutionary trends
o Little is known of the evolution of the group from the earliest cell to the
myriad of taxa known today.
o Relationships among taxa at the family or generic level have been recognised
in some diatoms.
o However, relationships at higher taxonomic levels are poorly understood and
have often been strongly influenced by the first appearances of key taxa in
the fossil record.

16. o An independent assessment of relationships among the diatoms at these
higher taxonomic levels has been made using rRNA sequence data to infer
phylogenetic relationships.
o Ribosomal RNA data indicate that both the centric and araphid pennate
lineages may not be monophyletic.
o Diatom feature that suggests that the diatoms may have emerged before
the other pigmented forms in this lineage is their ploidy state. The diatoms
are virtually unique in the chromophyte algae in having only a diploid stage.
❖ PHAEOPHYTA {brown algae}
They are found in cold water. They are abundantly present in Arctic and Antarctic oceans.
Many species are grown in intertidal zone. These algae grow best 10-20 meters below the
water surface. Some species are epiphytes and endophytes.
• Thallus structure
o They have different type of plant bodies. It ranges from simple filamentous to
giant microscopic kelps. Filaments forms may be erect or prostrate. They may be
heterotrichous (both erect and prostate branches). The kelps may be 25-30
meters long. The tissues of kelps are differentiated into outer cortex and inner
medulla. Plant body has three parts:
1) Hold fast: It is root like structure. It anchors the plant.
2) Stipes: These are stem like branches.
3) Blades: These leave like. They are present at the apex of stipe. 3. Cell wall: The
cell wall has two portions. The inner portion is composed of cellulose. The outer
portion is gelatinous. It is formed of algin. Algin is pectic substance of calcium
salts of alginic and fucinic acids.

17. • Cell ultra-structure
o The cell is uninucleate. It has large vacuole. Centrosome is present in them.
Therefore, nuclei divide by animal like mitosis.
o Pigments: Its photosynthetic pigments are chlorophyll a, chlorophyll b, carotenoids
and xanthophylls in the form of fucoxanthin and diatoxanthin. Fucoxanthin is a
golden-brown pigment. It masks the colour of chlorophyll. Pigments are present in
chloroplast. Pyrenoids are absent.
o Reserve food material: Their reserve food material is in the form of dissolved
sugars, alcohols, fats and complex polysaccharides. Starch is absent in them. Some
other reserve products are laminarin (a polysaccharide), mannitol and alcohol. Fat
like, colourless fucosan granule or physole compounds are also found in them.
• Reproduction
o Sexual reproduction: Sexual reproduction may be isogamous, anisogamous, or
oogamous. The gametophyte may be homothallic or heterothallic. In case of
oogamous type, single motile antherozoids are produced in gametangia or
antheridia. Oogonium has single egg. In some cases, egg is discharged from oogonia.
So, fertilization occurs in water. But in some cases, eggs are not discharged and
fertilization occurs in oogonia.

18. o Alternation of generation: Regular alternation of generation occurs in
phaeophytes. Diploid sporophyte generation alternates with haploid gametophyte
generation. The two generations may isomorphic or heteromorphic.
• Relationships & Evolutionary trends
o Phaeophyta evolved about 150-200 million years ago.
o The Phaeophyta form a well-marked taxon not very closely related to the other
algae. The nature of swarmer’s suggests that the Phaeophyta possibly arose from
flagellate unicellular organisms.
o The Phaeophyta are often considered parallel to the Chlorophyta in the nature of
plant body and in the method of reproduction, although the Phaeophyta have
evolved multicellular reproductive organs and a higher type of vegetative body.
o The apically growing thallus of the Phaeophyta developing into an elaborate
structure is often differentiated into epidermis, cortex, and medulla. Besides this,
the development of sieve-tube cells and in some cases development of a cambium-
like region are the features which can very well justify a very high position for the
Phaeophyta in the evolutionary scale.
o Since they lack xylem for conduction and sup-port, a cuticle for protection against
evaporation, jacket layers around their multi-cellular reproductive organs for
protection against desiccation, and the mode of sexual reproduction is not well
advanced, the Phaeophyta did not receive any higher position although they
possess high degree of specialization in their plant body.
o The pigmentation of the Phaeophyta suggests a relationship to both the
Chrysophyta and the Pyrrophyta. All these groups have an excess of carotenoid
pigments over chlorophylls, as compared to the Chlorophyta. Chlorophyll c is known

19. only in the Phaeophyta, Chrysophyta and Pyrrophyta. Fucoxanthin, the principal
xanthophyll of the Phaeophyta occurs also in the Chrysophyta but is unknown among
the Pyrrophyta.
o The sum of the evidence indicates that the Phaeophyta originated from a
prechrysophytan stock after the pyrrophytan line had already diverged from the
ancestors of this same stock.
❖ RHODOPHYTA {red algae}
More than 98% members are marine and the rest grow in fresh water. The marine species
have the ability to live at greater depth (even at 30-90 meters) than the other members
of different classes.
They also exhibit a high degree of parasitism and epiphytism. The parasitic members show
great reduction in their size and pigmentation.
• Thallus structure
o The plant body may be unicellular (Porphyridium) or multicellular. The multicellular
forms: filamentous (Goniotrichum), parenchymatous (Porphyra, Crinellia), feathery
(Polysiphonia), pseudoparenchymatous (Helmin- thocladia), or ribbon like
(Chondrus).
o They do not attain the size like that of the brown algae (Phaeophyceae), but may
reach up to 2 meters in Schizymenia.

20. o The growth may be diffused or apical.
o In the order Bangiales, Porphyra and Asterocystis any cell of the thallus may divide
in any direction. This is called diffused growth.
o The apical growth is strictly restricted to sub-class Florideae.
o The flagellated motile stages are totally absent.
• Cell ultra-structure
o The cell wall is two layered.
o The cell wall consists of outer pectic and inner cellulosic layer.
o The mucilaginous material of the outer layer mainly consists of agar-agar
and carrageenans and constitute major portion of dry weight of the cell wall.
o In multicellular forms, the cell walls have pits, through which cytoplasmic
connections are maintained. These cytoplasmic threads are the so-called
plasmodesmata.
o The members of Rhodophyceae show much variation in the number of nuclei in a
cell. In the subclass Bangioideae, cells are uninucleate, but in the subclass
Florideae most of the members are multinucleate.
o The cells may have one chromatophore with a central pyrenoid (Bangioideae) or
many discoid and parietal chromatophores with pyrenoids (Florideae).
o The photosynthetic pigments are chlorophyll a, chlorophyll b; α- and β-carotene;
xanthophylls and Bili proteins such as r-phycoerythrin and r-phycocyanin.
o The characteristic red colouration of the algae is due to the sufficient presence
of r-phycoerythrin which completely masks the chlorophyll a.
o The reserve food is floridean starch, floridi- side and mannoglycerate.

21. • Reproduction
o Reproduction takes place by all the three means: vegetative, asexual and sexual.
▪ Vegetative reproduction takes place only in unicellular form.
▪ Asexual reproduction takes place by monospore, neutral spore, carpospore,
bispore, and tetraspore.
▪ Sexual reproduction is of advanced oogamous types.
i. The male sex organs are known as spermatangium. Single non- flagellate male
gamete is produced in each spermatangium, called spermatium.
ii. The female sex organs are called carpogonia or procarp. Carpogonia are flask-
shaped with a long neck, the trichogyne.
During fertilisation, the spermatium comes in contact with the trichogyne with
the help of water current.
Post fertilization changes:
• The post-fertilization changes are highly elaborate.
• They develop carposporophyte.
• Carposporangia are developed from each carposporophyte and each
carposporangium produces single carpospore.
o Life cycle: Most of the Rhodophycean members show biphasic or triphasic life
cycle patterns.
• Relationships & Evolutionary trends
o All these features of the Rhodophyta may be regarded as evolutionary advances
over the condition in the Cyanophyta.

22. o It is possibly justifiable to consider both Cyanophyta and Rhodophyta as living
representatives of evolutionary lines of descent which have diverged considerably
from the same common ancestor in the extremely distant past.
o Some consider Rhodophyta to have derived from a member of the Chlorophyta.
But the structure of the plant body and pigment composition in both these taxa
are so different from each other that it is difficult to justify such an evolutionary
line. But in Prasiola, the structure of chloroplast and the similarity in morphological
structure and reproduction make it possible to suggest as an ancestor of the
Rhodophyta.
o Two alternatives have been suggested by Klein and Cronquist (1967) about the
ancestry of the Rhodophyta:
I. They originated from some simple procaryotic blue- green algae.
II. They were derived from some archaic eucaryotic algae which them-selves
originated from blue-green algae.
o But the fundamental differences between the eucaryotic and procaryotic cellular
organizations rule out the existence of any direct link between the red algae and
the blue-green algae. Further, the Bili proteins of Rhodophyta differ in spectral
properties from those of Cyanophyta. It may be speculated that the red algae
probably originated from some primitive non-flagellate eucaryotic ancestor
possessing Bili proteins.