ALGAE

NCERT Syllabus: Classification of Algae, Economic importance of Algae, Life cycle of

chlamydomonas, Life cycle of Ulothrix, Life cycle of Spirogyra.
Life cycle of Spirogyra.

THALLOPHYTA-ALGAE
 Alage and fungi (in Five Kingdom System, Fungi have their own Kingdom) are considered
together in thallophyta (having undifferentiated plant body), though there is basic difference in
the mode of nutrition (i.e., autotrophic in algae and heterotrophic in fungi).
 The term algae (L. alga - sea weed) was first introduced by Linnaeus (1755) but the present
day algae were delimited by de Jussieu (1789).
 Fritsch (1935) included algae under all holophytic organisms (as well as their numerous
colourless derivatives) that fail to reach the level of differentiation characteristic of
archegoniate plants The study of algae is called phycology or algology.

CHARACTERISTICS OF ALGAE
 Algae usually occur in a variety of habitats such as water, land as well as on the other plants
and even animals. Some grow in marine water called seaweeds.
 Plant body is unicellular, colonial, filamentous, parenchymatous or
pseudoparenchymatous.
 Vascular tissues are absent.
 A mechanical tissue is absent.
 Nutrition is autotrophic.
 A variety of pigments in algae provide different colours.
 Vegetative and asexual modes of reproduction are abundant.
 Sexual reproduction involves isogamy, anisogamy and oogamy. Sex organs are unicellular
and non- jacketed. An embryo stage is absent.
 Life cycle is various-haplontic, diplontic or diplohaplontic.

CLASSIFICATION OF ALGAE
 Algae are usually differentiated on the basis of their pigments and storage products. Algae
included under kingdom Plantae by Whittaker (1969) are of three types: red algae, brown
algae and green algae.

Table: Characteristics of Algae

Table: Characteristics of Algae
PHOTOSYNTHETIC PIGMENTS
Kingdom Name of algae Chlorophyll Others Food reserve Structure

Phycobilins-
Red algae Unicellular to
a+d phycoerythrin, Floridian starch
(Rhodophyceae) multicellular
phycocyanin

Plantae Special
Brown algae Lipid, Mannitol,
a+c carotenoids and Multicellular
(Phaeophyceae) Laminarin starch
fucoxanthin
 carotene and
Green algae Unicellular to
a+b other Starch
(Chlorophyceae) multicellular
carotenoids

RHODOPHYCEAE: RED ALGAE

 Red algae are an ancient group of algae with over 5,000 living species.
 They are marine except for a few fresh water species (e.g. Batrachospermum,
Compsopogon, Lemnaea).

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 Red algae are autotrophic with the exception of a few like Harveyella and Riccardia that are
colourless and parasitic on other red algae Harveyella is parasitic over Polysiphonia.
 A motile or flagellate stage is completely absent.
 The plant body varies from unicellular to multicellular forms.
 Cell wall possesses cellulose, pectic compounds and certain mucopolysaccharides called
phycocolloids.
 The latter are usually sulphated. The important phycocolloids of red algae are agar,
carrageenin and funori.
 The photosynthetic organelles are called chromatophor They have single thylakoid.
Photosynthetic pigments include chlorophyll a, carotenoids and phycobilins. Chlorophyll d has
been reported in some cases. Phycobilins are water soluble pigments of two types, red
coloured phycoerythrin and blue coloured phycocyanin.
 The red colour of red algae is due to abundant formation of phycoerythrin.
 Reserve food is floridian starch. In constitution, it is very much similar to glycogen.
 Vegetative reproduction takes place by fragmentation, gemmae, and regeneration of holdfast.
 Sexual reproduction takes place through a variety of spores.

Fig 1. Some Red Algae

 Sexual reproduction is an advanced type of oogamy The male sex organ is called
spermatangium or antheridium It produces non flagellate male gamete known as spermatium
The female sex organ is flask shaped and is termed carpogonium. Each carpogonium has a
long neck like structure called trichogyne and a bulbous base having female nucleus.
 Red algae have two or more phases in their life cycle so that they can be haplontic,
haplobiontic, diplohaplontic, etc.

ECONOMIC IMPORTANCE
Phycocolloids
 A number of phycocolloids are extracted for commercial use. These include agar, carrageenin
and funori. Agar is used in solidifying laboratory culture media and is added as stabilizer or
thickener in the preparation of jellies, puddings, creams, cheese, bakery, etc. Agar is obtained
from Gelidium and Gracilaria. Carrageenin is used as a clearing agent in liquors, leather
finishing and as emulsifier in chocolates, ice creams, toothpaste, paints, etc. It is extracted
from Chondrus crispus. Funori is a glue used as adhesive and in sizing textiles, papers, etc. It
is got from Gloiopeltis.

Food
 A number of red algae are edible, e.g., Porphyra (Layer), Rhodymenia (Dulse), Chondrus
(Irish moss). Rhodymenia (also called sheep’s weed) is also used as fodders. Porphyra is
cultivated in Japan for commercial exploitation.

Medicines
 Corallina has vermifuge properties while Polysephonia is antibacterial. Agar is employed as
laxative base and manufacture of pills. Carrageenin hastens blood coagulation.

PHAEOPHYCEAE: BROWN ALGAE

 Brown algae comprise about 2,000 species.
 Most of the brown algae are marine, except Pleurocladia, Heribaudiella and Bodanellia, which
are found in fresh water.
 Usually they grow in tidal or sub-tidal regions of colder seas. However, some grow in warm
waters, e.g., Ectocarpus, Dictyota, Sargassum, etc.

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 Unicellular forms are absent. The body consists of a branched filamentous structure in lower
forms (e.g., Ectocarpus) and parenchymatous structure in higher forms (e.g., Sargassum,
Laminaria, Fucus and Macrocystis).
 The size varies from 1 mm (e.g., Ectocarpus to 60 m (Macrocystis).
 Brown algae include the largest algae. The giant brown algae are called kelps. The largest
keips are Macrocystis (40-60 m), Nereocystis (20-30 m) and Laminaria (2-3m).
 The plant body is oflen differentiated into holdfast, stipe and lamina. The algae are commonly
found attached by means of their holdfasts. A few species of Sargassum and Fucus are free
floating.
 Sargassum species (e.g., S. natans, S.fluitans floating on the sea surface cover a large area
in parts of North Atlantic Ocean. The area is popularly called Sargasso sea. Free floating
forms, can be menace to shipping as they get attached to the bottom of the ships.
 Cell wall contains cellulose non glycan polysaccharides and phycocolloids. Phycocolloids of
brown algae are non sulphated mucopolysaccharides. The common ones are alginic acid,
fucoidin and fucin.
 The photosynthetic pigments are chlorophyll a, chlorophyll c, carotenes and xanthophylls
(e.g., lutein, flavoxanthin, violaxanthin). The brown colour of brown algae is due to the
presence of large amount of xanthophyll called fucoxanthin (c which masks the green colour
of chlorophyll.
 Food reserve is laminarin (starch) and D-mannitol (a sugar alcohol). Conducting tubes or
trumpet hyphae are present in larger brown algae or kelps. It is analogous structure to phloem
cells.
 Vegetative reproduction occurs through fragmentation (e.g., Sargassum), adventitious
branches, stolons(e.g., Dictyota) and propagules or specialized nests of cells. Asexual
reproduction occurs with the help of both motile (e.g., zoospores) and non motile spores (e.g.,
neutral spores, tetraspores, and monospores).
 Sexual reproduction varies from isogamy, anisogamy to oogamy
 There is no zygotic meiosis in brown algae. The diploid zygote produces a diploid thallus.
 Isomorphic alternation of generation is found in some brown algae, e.g., Ectocarpus and
Dictyota.

Fig 2. Some Brown Algae

ECONOMIC IMPORTANCE
Food
 A number of brown algae are used as food in some countries, e.g., Laminaria, Macrocystis
and Sargassum. The edible brown algae are also used as fodder. Food obtained from
Laminaria saccharina is known as kombu.

Iodine and Potash

 Fucus and Laminaria are rich source of iodine Potash is abundant in Macrocystis and
Nereocystis

Medicines
 Sodium larmnarin sulphate obtained from Laminaria is an effective blood anticoagulant
Laminaria Pelvetia and Ascophyllum have antibiotic properties, while Durvillea has worm
expelling properties.

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Alginic Acid
 It is phycocolloid which is obtained commercially from a large number of brown algae
including the giant ones (e g, Laminaria Macrocystis Nereocystis Fucus Sargassum) Alginic
acid and its salts are used in obtaining emulsions (icecreams, ointments, tooth pastes
cosmetics creams, shampoos etc.), sizing textiles, flame proof plastics and surgical threads.

CHLOROPHYCEAE: GREEN ALGAE

 About 90% of the total species grow in fresh water habitats and 10% are marine. They are
cosmopolitan in distribution. They may be
 Terrestrial- growing on moist soil, walls and rocks, e.g., Fritschiella.
 Epiphytes- growing on other plants, e.g., Trenteopohlia, Protococcus, etc.
 Endophytes- growing inside the other plants, e.g., Coleocheate nitellum inside the
thallus of Nitella.
 Epizoic- growing on the surface of animals, e.g., Cladophora and Charaeilum on
mollusc shells and crustaceans, respectively.
 Endozoic- living inside body of animals, e.g., Zoochlorella inside sponges, C’hlorella
in the body of Hydra.
 Cryophytes growing in the polar region on ice and snow, e.g., Chlamydomonas
nivalis,
 Ilaematococcus nivalis (causing red snow ball).
 Thermophilic- growing in hot springs, e.g., Chlorella sp.
 Parasitic- growing as pathogens and causing diseases, e.g., Cephaleuros (causing
red rust disease of tea and coffee).
 Symbionts - as components of certain lichens.
 Thallus is of various types: unicellular flagellate (e.g. Chlamydomonas), unicellular non
flagellate (e.g., Chlorella) flagellate colonies, (e.g., Volvox) unbranched filamentous (e.g.,
ulothrix), simple branched (e.g., Cladophora), heterotrichous with prostrate and vertical
branches, (e.g., Draparnaldia), and parenchymatous (e.g., Ulva).
 Cell wall contains cellulose with a few exceptions.
 Photosynthetic pigments are similar to those of higher plants: chlorophyll a, chlorophyll b,
carotenes and xanthopylls.
 Food reserve is Starch.
 Chloroplasts generally contain pyrenoids for storage of starch.
 Vegetative reproduction occurs by fragmentation, stolons and tubers.
 Asexual reproduction takes place by mitospores. The common asexual spores are zoospores,
aplanospores, hypnospores, akinetes, etc.
 Sexual reproduction is effected by isogamy, anisogamy and oogamy.
 Three types of life cycle occur in green algae: haplontic, diplontic and diplohaplontic.
 In haplontic life cycle the dominant phase is haploid. The diploid stage is present only
in the form of zygote or zygospore. Meiosis occurs at the time of its germination of
zygote (zygotic meiosis, e.g., Ulothrix, Spirogyra and Chlamydomonas).
 In diplontic life cycle, the dominant phase of the alga is diploid. It gives rise to haploid
gametes through meiosis (gametic meiosis, e.g., Caulerpa). The gametes fuse and
the fusion product or zygote regenerates the diploid phase.
 The haplodiplontic life cycle possesse well developed multicellular haploid and diploid
structures. The haploid gametophyte gives rise to haploid gametes. The fusion
product of gametes or diploid zygote grows directly into diploid sporophyte. The
sporophyte produces haploid spores through meiosis (sporic meiosis, e.g., Ulva.
Cladophora). Meiospores germinate into new gametophytes.

Fig 3. Some Green Algae

Economic importance

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 Certain green algae are components of sewage oxidation tanks (e.g., Chlorella.
Chlamydomonas, Scenedesmus, Pediastrum, etc.).
 Chlorella produces food rich in proteins (more than dried beef with similar digestibility), fats
and vitamins.
 It also yields an antibiotic chlorellin. Chlorella can be used in prolonged space flights for food,
oxygen, disposal of CO2 and organic matter.
 Cephaleuros is parasitic on a number of plants. C. virescens causes red rust of tea whereas
C. coffea is parasitic over coffee plants.

CHLAMYDOMONAS: LIFE CYCLE

HABITAT
 Chlamydomonas is widely distributed fresh water unicellular alga, commonly occurring in
standing or stagnant rainwater, ponds, pools, ditches and on moist soils. It grows, in
abundance in water rich in ammonium compounds. There are about 325 species.

PLANT BODY
 It is a simple, unicellular motile, green algae. The individuals are spherical or ellipsoidal. In
many species a papilla like out growth is visible in the anterior region.
 The protoplast is surrounded by a definite layer of glucoprotein wall and motile cells of some
species have a gelatinous pectic sheath outside the cellulose layer.
 Most of the species have a single large cup shaped chloroplast and occupies most of
protoplast. Chloroplasts of most of species have a single pyrenoid, which is a protein body
and is the site of starch storage. Some species like C. reticulata do not have pyrenoids.

Fig 4. Neuromotor apparatus of Chlamydomonas

 At the pointed anterior end of the cell, arise two flagella emerging through the same or
separate canals. The flagella are acronematic (whiplash) and are of equal length. Each
flagellum has a granule (blepharoplast) at the points of its origin. They are connected together
by a transverse fibre called paradesmos, which is again connected with the intranuclear
centrosome of the nucleus through a cytoplasmic strand, rhizoplast. The entire setup is well
coordinated to perform sensory as well as locomotory functions and is known as neuromotor
apparatus.
 Each cell typically possesses two contractile vacuoles located at the base of flagella in a
plane at right angles to them.
 A tiny spot of an orange or reddish colour, known as stigma or eyespot, lies at the anterior
end. It is a photoreceptive organ concerned with the direction of the movement.
 Each individual has a single nucleus lying in the colourless cytoplasm filling the cup. The
nucleus is typically of eukaryotic type.

REPRODUCTION
 Chlamydomonas reproduces both asexually and sexually.

ASEXUAL REPRODUCTION
 Zoospores: The protoplasm of each vegetative cell undergoes repeated longitudinal
divisions, either into 2, 4, 8 or 16 daughter protoplasts. The parent cell normally loses its
flagella before the onset of division. After the last series of divisions, each daughter protoplast
secretes a cell wall and neuromotor apparatus that develops two flagella, eyespot and
contractile vacuoles. The daughter cells (zoospores) are liberated by gelatinization or by the

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rupture of the cell wall. Thus, each daughter cell resembles the parent cell in all respects,
except that it is smaller in size. In nature the zoospore formation is very common when
conditions are favourable.

Fig 5. Chlamydomonas: Asexual Reproduction

 Palmella spores: In adverse condition of drought, when pond or pool dries up or when plant
grows on moist soil or on agar medium in laboratory, the daughter protoplast, formed as a
result of divisions, do not develop neuromotor apparatus and become motile. But the parent
cell wall gelatinizes and forms a matrix around the daughter protoplast. Divisions and
redivisions of these daughter protoplasts ultimately may produce an amorphous colony with
hundreds or thousand cells. All cells of such palmella stages (named after the genus
Palmella) develop flagella, become motile and escape from the gelatinous matrix when
flooded with water.
 Aplanospores: During unfavourable conditions, sometimes undischarged zoospores develop
into aplanospores. The aplanospores are thin walled, uninucleate, unicellular structure. Often
they develop singly in the cell and may germinate in situ (i.e., ‘before liberation). On
germination, each develops into a new filament.
 Hypnospores: In some species (e.g., C. nivalis), the protoplast withdraws from the cell wall,
rounds up and develops a thick wall under unfavorable conditions. These resting spores are
called hypnospores. Hypnospores usually develop red colour due to the formation of
haematochrome.
 Akinetes: Akinetes are formed during extreme conditions. They are formed in certain cells
that accumulate food and secrete a thick and resistant wall. During favourable condition each
germinates to produce a new cell.

SEXUAL REPRODUCTION
 Some species of Chlamydomonas are homothallic, while others are heterothallic. Gametic
union may be isogamous, anisogamous, or oogamous.

ISOGAMY
 Each Chlamydomonas cell may produce 8, 16, 32 or 64 biflagellate gametes that are (+)ve or
(-ve) in character. In C. longistigma, the gametes are naked (gymnogametes) whereas in C.
media, the gametes become covered with a wall, just before their emergence from the cell
(calyptogamete).

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Fig 6. Sexual reproduction-Isogamous in Chlamydomonas Longistigma

HOLOGAMY
 In most of the isogamous species any vegetative cell may function as gamete and their walls
fuse prior to the gametic union e.g., C. debaiyana.

PHYSIOLOGICAL ANISOGAMY
 In species where the two uniting gametes, though they are morphologically similar, behave
differently such as the cell contents of one gamete may pass into another gamete, the
process is called as physiological anisogamy.

ANISOGAMY
 In anisogamous species like C. braunii, 2-4 large female gametes are formed in one cell and
8-16 small male gametes are formed in another cell. Both the gametes are provided with a
wall. The male and female gametes join by their anterior ends. At the point of contact, their
membranes dissolve and contents of the male gamete pass into the female gamete with the
result of formation of zygote. The gametes do not shed their walls at the time of gametic
union.

OOGAMY
 In oogamous species, like C. coccifera the male cell divides to form 8, 16 or 32 small
biflagellate antherozoids. The large female cell loses its flagella and becomes an egg cell or
oogonium. Fusion takes place between a male gamete and an egg. Both the gametes are
covered with a cell wall and form a zygote.

ZYGOTE AND ITS GERMINATION

 Disappearance of flagella from quadriflagellate zygote of isogamous or anisogamous species
is followed by the formation of a wall around it. The two nuclei fuse and it becomes a
spherical structure, which undergoes a period of rest. It secretes a thick wall, which may be
smooth and spiny.
 When the resting period is over and the conditions are favourable, the zygote germinates.
The diploid nucleus undergoes reduction division and forms four nuclei and the cytoplasm
gets accumulated around each nucleus. The daughter protoplasts are liberated to the outside
by the breaking up of the zygote wall. Thus, the new cells formed are usually four in number,
from a single zygote.

ULOTHRIX: LIFE CYCLE

OCCURRENCE
 Ulothrix are largely found in fresh water ponds, pools, tanks and running streams. Some
species like U.zonata, are distinctly cold water forms.

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THE PLANT BODY

STRUCTURE OF THE THALLUS
 The plant body is a thallus consisting of an extremely fine unbranched filament. The filament
comprises of single row of cells placed end to end, and firmly united. The filaments appear
slender, thread like and may be upto 0.04 mm in diameter. Except for basal one, all the cells
of the filament are similar in structure and behaviour. The basal cell (holdfast) is slightly
elongated, hyaline or achlorophyllous and through it, the filament remains attached to the
substratum. The remaining cells of a filament are barrel shaped and are often wider than long.
Ulothrix is thus characterized by possessing filaments of unlimited growth exhibiting a
differentiation of base and apex.

STRUCTURE OF A CELL
 The cells are usually cylindrical, sometimes slightly swollen in middle, and often broader than
long as in U. zonata and most other species. Each cell consists of a cell wall enclosing the
protoplast. The cell wall consists of two layers:
 the inner layer consisting of cellulose, and
 the outer layer consisting of protopectin which is insoluble in water.
 The protoplast is differentiated into a cell membrane, cytoplasm, a single nucleus, chloroplast
with one or more pyrenoids and a central vacuole. Cytoplasm forms the lining layer or
primordial utricle and is closely invested by the cell membrane. The central portion of the cell
is occupied by a large vacuole containg a cell sap. The cells are always uninucleate and
possess a single girdle, collar or ring shaped chloroplast with one (e.g., U.variabilis) or more
(e.g., U.zonata) pyrenoids. The number of pyrenoids may increase during cell division. The
chloroplast may be closed (e.g., U.zonata) or open at one end.

Fig 7. Ulothrix: A. One filament, B. Detailed structure of one cell, C. A girdle shaped
chloroplast
 The cells are characteristically uninucleate. The nucleus in resting conditions possesses a
prominent nucleolus and only its little part is composed of chromatin reticulum.

REPRODUCTION
 Ulothrix reproduces by the following means:

VEGETATIVE REPRODUCTIONS
 Accidental breaking or the death of intermediate cell causes breaking of the filament into
fragments, the process is known as fragmentation. Each fragmented part then grows into a
new plant.

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ASEXUAL REPRODUCTION
 Following modes of asexual reproduction are known to occur in Ulothrix.
 Zoospores: The zoospores are formed during favourable conditions. All cells are capable to
form zoospores except the holdfast.
 During the formation of zoospores, the protoplast divides mitotically into number of daughter
protoplasts by repeated longitudinal divisions. Each develops into a zoospore. Following are
the two types of zoospores:
 Macrozoospores: They are quadriflagellate, uninucleate and pyriform (pear shaped)
with a pointed anterior end and are often fewer in number. Each macrozoospore
consists of a pair of contractile vacuoles, a single chloroplast with a pyrenoid and
almost anteriorly placed stigma. The zoospores resemble morphologically with
Chlamydomonas and are liberated from the parent cell through a pore in the lateral
wall. They are first liberated in a thin vesicle that soon disappears making zoospores
free in the water.
 After swimming for a short period the zoospores attach by the anterior pointed end on
some solid object. They discard their flagella, secrete a cell wall and divide by a
transverse division to produce a lower cell and an upper cell. The lower cell develops
into a holdfast while the upper cell by repeated transverse divisions forms the
filament.
 Microzoospores: Filaments of U. zonata produce microzoospores that are formed in
large number (4 to 32) similar to that of macrozoospores. They are smaller in size,
uninueleate, narrowly ovoid with a round posterior end and they may be quadri - or
biflagellate. They swim for a longer period for about 2 to 6 days.
 After swimming phase, they attach to some solid object by their anterior end. The
process of their development into a filament is similar to that of macro zoospores.
 Aplanospores: During unfavourable conditions, sometimes undischarged zoospores develop
into aplanospores. The aplanospores are thin walled, uninucleate, unicellular structure. Often
they develop singly in the cell and may germinate in situ (i.e.. before liberation). On
germination, each develops into a new filament.
 Hypnospores: During drought, the entire content of the cell rounds off and secretes a thick
wall and is called hypnospore. On the Onset of favourable conditions, the hypnospore
germinates to produce a new plant.
 Akinetes: Akinetes are formed during extreme conditions in U.idiospora. They are formed in
certain cells that accumulate food and secrete a thick and resistant wall. During favourable
conditions each germinates to produce a new filament.
 Palmella spores: Occasionally, the wall of the parent cell producing aplanospores
gelatinizes. Simultaneously, their aplanospore wall also gelatinizes resulting into number of
rounded bodies embedded in common mucilaginous mass. This is called palmella spore that
serves to protect against desiccation. With the return of favourable conditions, each rounded
body liberates as a zoospore. Palmella stage is commonly formed when the plant reaches
damp banks of the pools and ponds.

SEXUAL REPRODUCTION
 Isogamous type of sexual reproduction is found, in Ulothrix. They are generally heterothallic,
The gametes are formed in large number i.e., 32 to 64 in number in each gametangium. Each
gamete looks quite similar to biflagellate microzoospore. However, gametes are smaller in
size. These are formed and liberated in a way similar to zoospores. Each gamete is
biflagellate, pyriform and has prominent stigma and a chloroplast. They look like
Chlamydomonas but are naked. Since, male and female gametes are indistinguishable, they
are denoted as (+) or (-) strain gametes
 During fusion the two gametes fuse from anterior to lateral side. As a result, a quadriflagellate
zygospore is formed, which possesses a pair of nuclei, chloroplasts and eyespots.
Plasmogamy (fusion of protoplasm) takes place at this stage ‘that is followed by karyogamy
(nuclear fusion).

GERMINATION OF ZYGOSPORES
 With the return of favourable conditions, the diploid nucleus of zygospore divides meiotically
and generally produces four motile (zoospores) or non motile spores (aplanospores) of which’

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two develop into male filament (+ type) and other two into female ones (- type). Each spore
develops into a new plant.

SPIROGYRA: LIFE CYCLE

OCCURRENCE
 Spirogyra is a large genus consisting of about 300 species widely distributed throughout the
world. It grows as free floating extensive masses and hence commonly called pond scum. It
grows frequently in fresh water, stagnant reservoirs and in slow running streams and rivers. In
natural conditions, Spirogyra looks like a mass of shining silky long filaments and hence it is
popularly known as pond silk

THE PLANT BODY (THE GAMETOPHYTE)

STRUCTURE OF THE THALLUS
 The plant body consists of slender, unbranched filament. The young filament of Spirogyra is
found attached to some substratum by a modified basal cell, while adult plant is always free
floating. The basal cell that helps in the attachment is called as hapteron. Each filament
consists of a single row of cylindrical cells.

STRUCTURF OF A CELL
 Each cell consists of a firm cell wall enclosing a mass of protoplast Cell wall is commonly two
layered, the inner composed of cellulose while outer of pectic substances The pectic
substances gelatinize in the presence of water and render the plants slimy touch.

Fig 8. Spirogyra – A. Two filaments, B-C. Detailed structure of cell, D. T.S. of a cell, E. Hold fast
of Spirogyra, F. Holdfast of Spirogyra, G. Replicate septum

The protoplast consists of a single nucleus, mass of cytoplasm, variable number (1 to 2, sometime 24)
flat, ribbon shaped chloroplasts and a large central vacuole. The nucleus is found centrally suspended
by strands of cytoplasm or it may be parietal in position. The cytoplasm is peripheral due to presence
of large central vacuole but central vacuole is traversed by several cytoplasmic strands.

VEGETATIVE REPRODUCTION
Fragmentation is the common method of vegetative reproduction in Spirogyra. Accidental breaking or
injury breaks the filaments into 2-3 celled pieces, each germinates to produce a new plant. However,
in certain cases, cross walls also play a role in separating the two cells apart by the process of
invagination.
SEXUAL REPRODUCTION
The sexual reproduction in Spirogyra is called conjugation, which involves fusion of two
morphologically identical but physiologically dissimilar gametes. It is called as physiological

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anisogamy. The gametes are aflagellate (aplanogametes). For development of gametes some of the
cells start to act like male and female gametangia. The cell contents taking part in development of
gametangia become separated from the cell wall and shrink and are ultimately converted into
gametes. The process of conjugation involves following methods:

SCALARIFORM CONJUGATION
Scalariform conjugation takes place mostly during night in recently divided cells. The process begins
when two filaments getting intimately associated due to mucilage. Lateral outgrowths arise from the
cells of these two filaments, placed opposite one another and are called papillae. The outgrowths
enlarge because of the repulsion between the two conjugating filaments and result in the formation of
conjugation tubes. Later the common walls of the conjugation tubes dissolve and a free passage is
formed. Simultaneously, the protoplasts accumulate abundant starch. The male gamete moves in
amoeboid manner through the conjugation tube into the female cell of another filament. Ultimately the
nucleus of male gamete fuses with the nucleus of the female gamete involving plasmogamy followed
by karyogamy and forms a diploid zygospore. At the completion of scalariform conjugation, the cells of
the male filaments become empty while the cells of the female filament are filled with the zygospores.
Sometimes, even three filaments are involved in the scalariform conjugation, of which the central
filament acts as the female one in which male gametes from two other filaments move in and fuse to
form zygospores. This type of conjugation has been reported in S. indica and S. elongata.

LATERAL CONJUGATION
In Spirogyra lateral conjugation takes place by one of the following three methods:
Indirect lateral conjugation: In this process two adjacent cells of the filament take part. These cells
develop tube like outgrowths close to the common cross walls. These outgrowths extend laterally and
ultimately form conjugation tube like structure that connects the adjacent cells. The protoplast of
conjugating cells contracts and form gametes. The outgrowths of the adjacent cells fuse to form a
passage between them. The contracted protoplast of one cell (so called male gametangium) moves
through the conjugation passage into the adjacent cell (so called female gametangium). The fusion of
both the gametic protoplasts results in the formation of a diploid zygote. The male cells or male
gametangium becomes empty due to migration of its contents while zygospores occupies the female
gametangium. This type of conjugation has been reported in S. affinis.
Direct lateral conjugation: This type of lateral conjugation was reported in S.jogensis. The filament
is attached to the substratum by its basal cell. Lateral conjugation takes place between the two cells
placed immediately next to the basal cell. The protoplast of male cells pushes and pierces the septum
between the two cells and the whole protoplast of the male cells moves into the female cell through
the perforation. After fusion zygote is formed. It is believed that the secretion of an enzyme effects
perforation.

Formation of New filament

 Nucleus of zygospore undergoes reduction division to form 4 haploid daughter nuclei. Out of
4 daughter nuclei 3 degenerate, only one remains functional.
 Zygospore with one haploid nucleus forms germ tube like structure, which further gives rise to
new filament.

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SOLVED PROBLEMS

Subjective

Prob 1. Differentiate between direct and indirect lateral conjugations in Spirogyra.

Sol. In direct lateral conjugation, conjugation tube is not formed between the adjacent
conjugating cells. The male gamete moves into female gametangium through septal pore.

Prob 2. Where is zygospores are formed during Isogamous and physiological anisogamous
conjugations of Spirogyra?
Sol. In physiological anisogamous conjugation, the zygospores are formed in the cells of female
filament. In isogamous conjugation, the zygospores are formed in the conjugation tube.

Prob 3. Write about Pyrenoids present in Spirogyra cell.

Sol. In Spirogyra cell, the Pyrenoids are present attached to the chloroplast and are
equidistantly located along it mid—axial line. These are special proteinaceous structUres
which store starch.

Prob 4. How does Spirogyra reproduce vegetatively?

Sol. Spirogyra reproduces vegetatively by fragmentation It is a process of breaking the filament
into pieces due to mechanical injury or due to gelatinization of middle lamellae between
cells.

Prob 5. Which type of conjugation in Spirogyra is considered dioecious and which type
monoecious?
Sol. In Spirogyra, scalariform conjugation is considered as dioecious and lateral conjugation as
monoecious.

Prob 6. Distinguish between zygote and zygospore in Spirogyra?

Sol. In Spirogyra, the zygote is a diploid structure formed by the fusion of gametes. Zygospore is
a thick walled resting spore formed due to contraction of zygote.

Prob 7. Differentiate zygospore and azygospore of Spirogyra.

Sol. In Spirogyra, the zygospores are the thick walled diploid resting spores formed during
conjugation. The azygospores are thick walled spores which are haploid formed from
gametes when conjugation fails.

Prob 8. Give one example each to the two types of lateral conjugation in Spirogyra?
Sol. i) Indirect lateral conjugation - Eg: Spirogyra affinis.
ii) Direct lateral conjugation - E.g Spirogyra jogensis

Prob 9. Define parthenogenesis Mention the ploidy of Parthenospore in Spirogyra?

Sol. The formation of new individual from unfertilized gametes is known as parthenogenesis.
Parthenospores in Spirogyra are haploid.

Prob 10. Give the systematic position of Spirogyra.

Sol. Class: Chlorophyceae
Order: Conjugales
Family: Zygnemataceae

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Objective

Prob 1. Term ‘Algae’ was given by

(A) Lamarck (B) Fritsch
(C) Linnaeus (D) A P de Candolle

Sol. (C). Term ‘Algae’ was given by Linnaeus, derived from a Latin word Alga – meaning sea
weeds.

Prob 2. Which of the following is not a character of algae?

(A) Lack of vascular tissue (B) Little differentiation of true tissue
(C) No embryo formation (D) None of the above

Sol. (D). Algae are non-vascular, non-embryophytic cryptogams.

Prob 3. Simplest non-motile forms are found in

(A) Chlorophyceae (B) Dianophyceae
(C) Xanthophyceae (D) Cyanophyceae

Sol. (D). Cyanophyceae are unicellular in which flagella are absent. Cyanophyceae are
prokaryotic algae. e.g.: Chrococcus.

Prob 4. Algae which is the richest source of proteins is

(A) Prophyra (B) Ulva
(C) Rhodymenia (D) Chlorella

Sol. (D). Chlorella is richer in proteins as well as in lipids and vitamins. The nutritional value is
comparable to mixture of soybeans and spinach.

Prob 5. Which of the following algae is leaf-like and known as sea-lettuce.

(A) Nostac (B) Ulva
(C) Ulothrix (D) Spirogyra

Sol. (B). Ulva in Europe is called as Sea-lettuce.

Prob 6. In Ulothrix filaments appear as wet threads this is due to the presence of
(A) Pectin (B) Protopectin
(C) Cellulose (D) Chitin

Sol. (B). Outer layer of cell wall is made up of protopectin, which is insoluble in water.

Prob 7. The most distinguishing feature in the identification of spirogyra is

(A) Spiral chloroplast (B) Mucilage sheath
(C) Linear arrangement of pyrenoids (D) Uninucleate cells

Sol. (A). The chloroplasts are arranged spirally in the cytoplasm and hence the name spirogyra.

Prob 8. In which of the following stages of spirogyra one gametangium appears large with
zygospore and ribbed mucilage.
(A) Scalariform conjugation (B) Direct lateral conjugation
(C) Indirect lateral conjugation (D) Aplanospore formation

Sol. (B). Indirect lateral conjugation occurs between the two cells. Upper cell functions as male
gamete and the lower cell which is large is female gametangium.

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Prob 9. Species of spirogyra which grow attached to stones in water.

(A) S. Jogensis (B) S. Gratiana
(C) S. affinis (D) S. farlowii

Sol. (A). Generally spirogyra is found as free floating on surface of stagnant water. But some
species like S. adnata and S. jogensis grow attached to stones.

Prob 10. Direct lateral conjugation was recorded by R.S. Rattan in

(A) S. jogensis (B) S. mirabilis
(C) S. farlowii (D) S. aplanospora

Sol. (B). Direct lateral conjugation was first reported by prof. M.O.P. Iyenger. It was also
recorded by R.S. Rattan in S. mirabilis.

ASSIGNMENT

Subjective

Very short answer type questions

1. Give the systematic position of Spirogyra.
2. What is holdfast? What is its use? Mention the species of Spirogyra having holdfast.
3. How does holdfast cell differ from other vegetative cells of Spirogyra filament?
4. Why Spirogyra is called ‘pond scum’ and ‘pond silk’?
5. Why Spirogyra is named as such?
6. Write about pyrenoids present in Spirogyra cell.
7. What happens when conjugation fails to occur after the formation of gametes in Spirogyra?
8. Distinguish between akinete and aplanospore of Spirogyra.
9. What is haplontic life cycle? In which group of plant kingdom do you find such life cycle.
10. Distinguish between vegetative reproduction and asexual reproduction.

Short answer type questions

11. Describe the cell structure of Spirogyra.
12. Explain asexual methods of reproduction in Spirogyra.
13. Elucidate the dioecious conjugation in Spirogyra.
14. Write about monoecious conjugation in Spirogyra.
15. Differentiate between scalariform and lateral conjugation in Spirogyra.
16. Write about the germination of zygospore in Spirogyra.
17. Differentiate between asexual reproduction and sexual reproduction.

Long answer type questions

18. Explain the different types of conjugation in Spirogyra.
19. Describe lateral conjugation in Spirogyra.
20. Describe scalariform conjugation in Spirogyra.

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Objective

LEVEL – I
1. Which one of the following algae is endozoic?
(A) Ulva (B) ZooChlorella
(C) Volvox (D) Polysiphonia
2. Which of the following algae is leaf-like and known as sea-lettuce?
(A) Nostoc (B) Ulva
(C) Ulothrix (D) Spirogyra
3. The members of chlorophyceae are:
(A) Rarely terrestrial (B) Mostly aquatic
(C) Both (A) and (B) (D) None of these
4. Algae grow:
(A) On damp soil (B) In water
(C) As epiphytes (D) All of these
5. The zygospore of Spirogyra produces:
(A) 2-4 zoospores (B) 4 zoospores
(C) 2 zoospores (D) None of these
6. Which one of the following is a larvicidal alga?
(A) Euglena (B) Pandorina
(C) Oscillatoria (D) Polysiphonia
7. Meiosis in Chlamydomonas occurs in:
(A) Zygospore (B) Zoospore
(C) Aplanospore (D) Hypnospore
8. The cell wall of Spirogyra is made up of:
(A) Cellulose (B) Pectin
(C) Lignin (D) Chitin
9. An alga very rich in proteins is:
(A) Spirogyra (B) Ulothrix
(C) Oscillatoria (D) Chlorella
10. The nitrogen fixation by Nostoc takes place in:
(A) Vegetative cells (B) Akinetes
(C) Heterocysts (D) Hormogonia
11. Brown algae are characterised by the presence of:
(A) Phycocyanin (B) Phycoerythrin
(C) Fucoxanthin (D) Haematochrome
12. Which of the following is a parasite on tea plant?
(A) Cephaleuros (B) Nostoc
(C) Striga (D) Loranthus
13. Which algae occurs in still fresh water?
(A) Spirogyra (B) Laminaria
(C) Sargassum (D) Polysiphonia
14. The yield of paddy can be increased by the application of:
(A) Nostoc (B) Symbiotic bacteria
(C) Iron bacteria (D) Archaebacteria
15. Unicellular cyanobacteria reproduce asexually by:
(A) Conjugation (B) Fragmentation
(C) Binary fission (D) Hormogones
16. Which of the following has a coenocytic thallus?
(A) Spirogyra (B) Chlamydomonas
(C) Vaucheria (D) Nostoc
17. Blue-green algae associated with red tide phenomenon is:
Or
Red tides are caused by:
(A) Anabaena (B) Nostoc
(C) Gleocapsa (D) Trichodesmium
18. Green wavelength of sunlight is absorbed by:
(A) Phycoerythrin (B) Carotenoids
(C) Chlorophyll (D) Phycocyanin

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19. During monsoon ground becomes slippery because of:

(A) Green algae (B) Blue-green algae
(C) Mosses (D) Liverworts
20. Algae possess photosynthetic pigments and hence they are called as:
(A) Parasitic (B) Holophytic
(C) Saprophytic (D) Holozoic

LEVEL – II
1. Agar is used as
(A) Botting paper (B) Solidifying agent
(C) Sugar rich source (D) Poison
2. Which blue-green alga remains in symbiotic association with Anthoceros?
(A) Azolla (B) Spirochaete
(C) Spirulina (D) Nostoc
3. Fucoxanthin accessory pigment occurs in:
(A) Brown algae (B) Red algae
(C) Blue-green algae (D) Green algae
4. In Spirogyra meiotic division occurs in:
(A) Zygospore (B) Zoospore
(C) Pollen grain (D) Egg
5. The thermal algae can survive in a hot water spring at:
(A) 60°C (B) 70°C
(C) 80°C (D) 90°C
6. Parasitic alga is:
(A) Volvox (B) Vaucheria
(C) Cephaleuros (D) Oedogonium
7. Protoderma in alga is:
(A) Epizoic (B) Endozoic
(C) Epiphytic (D) Parasitic
8. The characteristic pigment of cyanobacteria is:
(A) Fucoxanthin (B) Cell
(C) Anthocyanin (D) Phycocyanin
9. Calcium encrustation and larvicidal properties are present in:
(A) Chara (B) Oscillatoria
(C) Diatoms (D) Caulerpa
10. Ulothrix filaments produce:
(A) Isogametes (B) Anisogametes
(C) Heterogametes (D) Basidiospores
11. Ancestor of land plants had:
(A) Prostrate habit (B) Heterotrichous habit
(C) Thorny habit (D) Arboreal habit
12. Oil is the reserve food in:
(A) Chlamydomonas (Chlorophyceae) (B) Vaucheria (Xanthophyceae)
(C) Nostoc (Myxophyceae) (D) Sargassum (Phaeophyceae)
13. Which of the following helps in N2-fixation?
(A) Albugo (B) Nostoc
(C) Peicillium (D) Puccinia
14. Agar-agar is obtained from:
(A) Chlorella (B) Chara
(C) Gelidium (D) Laminaria
15. Alga associated with Cycas root is:
(A) Anabaena (B) Chara
(C) Chlorella (D) Cladophora
16. Ulothrix can be described as a:
(A) Filamentous alga with flagellated reproductive stages
(B) Non-motile colonial alga lacking zoospores
(C) Filamentous alga lacking flagellated reproductive stages
(D) Membranous alga producing zoospores

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17. The food is stored in the form of oil in:

(A) Chlorophyceae (B) Rhodophyceae
(C) Xanthophyceae (D) Cyanophyceae
18. Some micro-organisms forming nuisance water blooms in lakes, ponds, oceans belong to:
(A) Brown and red algae (B) Desmids and myxomycetes
(C) Cyanobacteria and dinoflagellates (D) Aquatic angiosperms and algal fungi
19. Which type of ribosomes are found in Nostoc cells?
(A) 50S (B) 60S
(C) 70S (D) Eukaryotic
20. Spirogyra has a:
(A) Haplontic life cycle (B) Diplontic life cycle
(C) Haplobiontic life cycle (D) Diplobiontic life cycle

LEVEL – III
1. Algae are
(A) Chlorophyllous cryptogams (B) Non-chlorophyllous cryptogams
(C) Chlorophyllous phanerogams (D) Non-chlorophyllous phanerogams
2. Sex organs in algae are generally
(A) Unicellular and jacketed (B) Unicellular and non-jacketed
(C) Multicellular and jacketed (D) None of the above
3. Who is called ‘Father of modern Algology in India’?
(A) R.N. Singh (B) Y. Bharadwaj
(C) F.E. Fritsch (D) M.O.P. Iyenger
4. Which of the following is a cryophytic alga?
(A) Haematococcus nivalis (B) Scotiella
(C) Chlamydomonas yellowstonensis (D) All of the above
5. ‘Red snow’ is caused by
(A) Chlamydomonas nivalis (B) Haematococcus nivalis
(C) Both 1 and 2 (D) None of the above
6. The hypnospores in Chlamydomonas develop red colour in their wall due to
(A) Cytochrome (B) Phycoerythrin
(C) Haematochrome (D) None of these
7. Two fusing gametes of Spirogyra are
(A) Morphologically similar
(B) Morphologically dissimilar
(C) Morphologically and physiologically dissimilar
(D) Morphologically similar and physiologically dissimilar
8. In which sps. of Chlamydomonas, oogamy occurs?
(A) C. braunii (B) C. longistigma
(C) C. coccifera (D) C. media
9. Eye spot in Chlamydomonas contains
(A) Carotenoids (B) Chlorophyll
(C) Haematochrome (D) Xanthophyll
10. Which alga is found in mud?
(A) Rivularia (B) Spirogyra
(C) Chara (D) Polysiphonia
11. Diatomaceous earth is formed due to remains of which part of diatoms?
(A) Cellwall (B) Chloroplast
(C) Cytoplasm (D) Skeleton masses
12. Stomata are not found in:
(A) Algae (B) Mosses
(C) Ferns (D) Liverworts
13. Marine algae flourished well during which of the following period?
(A) Ordovician (B) Devonian
(C) Permian (D) Triassic
14. Cell wall of Chlamydomonas contains:
(A) Cellulose (B) Glycoproteins
(C) Protein (D) Hemicellulose

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15. Nitrogen fixers in Azolla are:

(A) Nostoc (B) Anabaena
(C) Aulosira (D) Azospirillum
16. Which of the following algae can be used as bacteriological filter?
(A) Batrachospermum (B) Gelidium
(C) Oscillatoria (D) Cymbehla
17. Life cycle of Ulothrix is:
(A) Haplobiontic (B) Diplobiontic
(C) Haplodiplobiontic (D) None of these
18. Blue-green algae are found in:
(A) Riccia (B) Pinus root
(C) Cycas root (D) Scales of Marchantia
19. Algae are useful because they:
(A) Are large in number (B) Purif the atmosphere
(C) Are used in alcoholic fermentation (D) Are used in study of photosynthesis
20. Algae used by Calvin et al. is
(A) Chlorella (B) Chlamydomonas
(C) Euglena (D) Chara

ANSWERS TO ASSIGNMENT
Objective
Level  I
1) B 2) B 3) C 4) D 5) D
6) C 7) A 8) A 9) D 10) C
11) C 12) A 13) A 14) A 15) C
16) C 17) D 18) A 19) B 20) B

Level  II
1) A 2) A 3) A 4) A 5) B
6) A 7) A 8) D 9) A 10) A
11) D 12) B 13) B 14) C 15) A
16) A 17) C 18) C 19) C 20) A

Level  III
1) A 2) B 3) D 4) D 5) C
6) C 7) A 8) C 9) A 10) C
11) A 12) A 13) A 14) A 15) B
16) D 17) A 18) C 19) B 20) A

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