ALGAE
Algae are chlorophyll containing . simple, thalloid, autotrophic and
largely aquatic (both freshwater and marine) organisms.
The important salient features of algae are given below
These are found in both freshwater and marine habitats. Some
algal torms are also found in moist habitats like wet rocks and
soil, tree trunks, etc, Some of them are also found in close
association with fungi (lichen) and animals (e.g., on sloth
Few species are parasites.
Thallus Organisation
The plant body (thallus) is without differentiation. The
form and size of algae is highly variable, and ranges from
unicellular forms (Chlamydomonas), filamentous (e.g.,
and Spirogyra) to colonial (e.g., Volvox). Filamentous
attached on the substratum with the help of holdfast.
Structure of Algal Cell
It has a eukaryotic plant cell structure. The cytoplasm contains
membrane bound chloroplast, mitochondria, F.R. Golgi and
other cell organelles. The cell wall contains cellulose. The nucleus
contains nuclear membrane.
Food Material
Algae have main food reserve as starch. In brown algae, mannitol
and laminarin are the main reserve food material, whereas in red
algae floridean starch is the reserve food material.

Reproduction
The algae reproduces vegetatively, asexually and sexually.
i. Vegetative Reproduction
It occurs by fragmentation, tubers, stolons, advcntitious branches,
etc. Each fragment gets developed into an independent thalloid
plant body.
ii. Asexual Reproduction
It occurs by a number of accessory spores, such as zoospores
aplanospores, akinetes, carpospores, etc. The most common being
the zoospores, which arc flagellated. The cells which produce
spores are called sporangia which may be the vegetative cells
(e.g., in Chlamydomonas and {Ulothrix) or modified vegetative cells
(e.g., in Vaucheria).
iii. Sexual Reproduction
It occurs by fusion of two gametes.
On the basis of morphology of reproductive cells, sexual
reproduction is of two types
(a) Isogamous In this method, two morphologically similar
gametes fuse to form a zygote, e.g., Spirogyra.
(b) Anisogamous It is the fusion of structurally dissimilar
gametes, which differ in size and behaviour. Male gamete is
more active than female gamete. It is bigger in size also, e.g.
some species of Chlamydomonas.
(c) Oogamous In this process, the male gamete is motile,
active, small and without reserve food. The female gamete
is bigger, passive, non-motile and laden with food, e.g.,
Volvox, Fucus.

Life Cycle
Life cycle in algae can be haplontic, diplontic, diplohaplontic,
haplohaplontic, etc, An alternation of generation occurs in
diplohaplontic life cycle.

Economic Importance of Algae
(i) Algae are responsible for carrying out about a
half of the total carbon dioxide fixation on
earth by the process of photosynthesis.
(ii) Some forms of marine brown and red algae
produce large amount of hvdrocolloids. These
are algin (brown algae) and carrageenan (red
algae), which have many commercial uses.
(iii) The algae Gelidium and Gracilaria are used to
produce agar, which is used in preparation of
ice creams and jellies.
(iv) Some protein rich algae, like Chlorella and
Spirullina are used as food supplements by
sailors and space travellers.
(v) About 70 species of marine algae are used as
food, e.g., Porphyra, Laminaria and Sargassum.

Classification of Algae
Algae are divided into various classes based on
pigmentation, type of stored food materials and kind
of flagellation. The three main classes are
Chlorophyceae, Phaeophyceae and Rhodophyceae.
i. Class—Chlorophyceae (Green Algae)
The members of Chlorophyccae are commonly
called green algae. There are about species in
this class. The reserve fbod material is starch.
The characteristic features of Chlorophyceae are
discussed below
(a) Habitat These are mostly marine forms, only
some are freshwater. Chlorella can tolerate
moderately warm waters. Snow dwelling
forms are called cryophytes, e.g.,
Chlamydomonas nivalis, Scotiella, etc.
(b) Cell Organisation These are unicellular,
colonial, coenocytic and multicellular forms.
Cell walls contain cellulose (inner layer) and
pectose (outer layer) in most of the green
algae. The chloroplasts may be discoid,
plate-like, reticulate, cup-shaped, spiral or
ribbon-shaped.
The chloroplasts contain photosynthetic
pigments. Most of the members have one or
more storage bodies called pyrenoids located
in the chloroplasts. Pyrenoids contain protein
besides starch.
Some algae may store food in the form of oil droplets
also.

(c) Thallus Unicellular green algae can be flagellate,
(Chlamydomonas), non-flagellate (Chlorella).
Acetabularia (umbrella plant) has unicell upto 10 cm
long with distinction of nucleus containing rhizoid,
elongated stalk and umbrella-like cap.
A colony for fixed number of individual unicells
( Vilvox) is called coenobium. Coenocytic or
siphonaceaus thallus occurs in Caulerpa. Unbranched
filamentous thallus in Ulothrix and Spirogyra,
Cladophora, heterotrichous in Stigeoclonium and
parenchymatous in Ulva.
(d) Reproduction The members of Chlorophyceae
reproduce vegetatively, asexually and sexually by
various methods.
Vegetative reproduction occurs through cell division
(unicellular forms), fragmentation, stolons, tubers,
storage cells, etc.
Asexual reproduction occurs by zoospores,
aplanospores, hypnosporcs, akinetes and daughters
colonies.
Sexual reproduction may be isogamous, anisogamous
or oogamous.
(e) Life Cycle It can be haplontic, diplontic
and
diplohaplontic. In haplontic life cycle, there is a single
somatic phase, which is haploid. Diploid stage is
represented by a single cell or zygote, e.g., in Spirogyra.
ii. Class—Phaeophyceae (Brown Algae)
The members of Phaeophyceae contain
fucoxanthin
pigmant and include phycocolloid rich multicellular
eukaryotic algae. Its common members are seaweeds called
kelps. This class is comprised of about 2000 species.
(a) Habitat Brown algae are mostly marine. These are
found mostly in colder seas or during cold seasons in
tropical regions.
(b) Size They range from simple branched,
filamentous forms (Ectocarpus) to profusely
branched forms as represented by kelps.
These represent largest algae. The largest kelps are
Macrocystis (40-100m) and Nereocystis (20-30 m).
(c) Cell Organisation All members are multicellular.
Cell wall is composed of cellulose, pectose and
phycocolloids. The cellulosic wall of vegetative cells
is usually covered on the outside by a gelatinous
coating of algin.
(d) Thallus It is heterotrichous filament with both
prostrate and upright branches (Ectocarpl<).
The parenchymatous structure is found in highe
forms.
The plant body of large forms often
into holdfast (with which it usually attaches to the
substratum) a stalk called the stipe and lamina
(frond), which is photosynthetic. Conducting tubes
or trumpet hyphae are present in larger brown algae
or kelps. They help in conduction of food
materials.
(e) Photosynthetic Pigments and Colour These
include chlorophyll-a, c and carotenoids. They
range in colour from olive green to various shades
of brown depending upon the amount of the
xanthophyll and fucoxanthin present in them.
(f) Food Reserve It remains in the form of compla
carbohydrates such as laminarin or mannitol.
(g) Flagellation These contain heterokont flagellation
with one smooth (whiplash) and one tinsel flagella
(h) Reproduction Vegetative
reproduction occurs
through fragmentation
(e.g.,
adventitious branches and stolons (e.g., DictyoM)•
Asexual reproduction by biflagellate zoospo
res.
which are pear-shaped having two unequal latera
attached flagella.
Sexual reproduction is performed by isogamy,
anisogamy and oogatny. Union of gametes may take
place in water or within the oogonium (oogamous
species). ‘I •he gametes are pyriform (pear-shaped)
and have two laterally attached flagella.
(i) Life Cycle Isotnorphic alternation of generation is
found in some brown algae, e.g., Ectocarpus.
Dictyota. In many brown algae, the diploid
generation or phase is dominant. The haploid phase
is either microscopic or represented by gametes only
(e.g., Fucus).
Economic Importance of Phaeophyceae
The brown algae that are used as food are I-aminarta,
Nerocystis, Macrocystis, Alaria, etc.
Some brown algae like Fucus, Sargassam, laminar:a,
Macrocystis are important fodder för cattle.
Brown algae are collected from seashores and are also used
as manure. They improve mineral content of soils.
Alginic acid is a phycocolloid obtained from a number of
brown algae such as Alaria, Macrocysris, Ascophyllum,
Laminaria. It is used as emulsifier, thickener, gelating agent
in toothpastes, shaving creams, ice-creams, emulsion paints,
shampoo, cosmetics, etc.
Fucus and Laminaria are rich in iodine.
iii. Class—Rhodophyceae (Red Algae)
The members of Rhodophyceae are commonlv called red
algae because of the predominance of the red pigment, i.e.
r-phycoerythrin in their body.
(a) Habitat Most of the red algae are marine with
greater concentrations found in
the warmer areas.
They are found in both well-lighted regions close to
the surface of water and also at great dcpths in
oceans where relatively little light penetrates.
(b) Thallus The red thalli of most of the algae are
multicellular. Some of them have complex body
organisation like Astercnysns is pseudoiilamcntous,
Porphyridium is unicellular, Porphyra has
parenchymatous sheets, Chondrus is ribbon-like,
Gelidium is a multicellular sea weed.
(c) Cell Wall The cell wall contains cellulose, pectic
compounds and certain mucopolysaccharides called
phycocolloids, such as agar, carrageenan, etc. In
many algae, cell wall contains pits.
(d) Photosynthetic Pigments These include¯ CINCH o–
phyll-a, carotenes, xanthophylls and phycobilins.
Phycobilins are water soluble and are of two types,
i.e., red-coloured phycoerythrin and blue-coloured
phycocyanin.
is floridean starch similar in
(e) Reserve Food It
constitution to glycogen and amylopectin.
(f) Reproduction Vegetative reproduction occurs by
fragmentation, regeneration of hold fast and
gemmae. Asexual reproduction occurs by non-motile
spores (carpospores, monospores, tetraspores and
neutral spores).
Sexual reproduction occurs by non-motile gametes
and is oogamous type. The male sex organs is called
spermatogonium or antheridium. The male gamete
produced is non-flagellated, called as spermatium.
The fernale sex organ is called carpogonium. After
fertilisation, a new structure called carposporophyte
is produced. It remains attached to the parent alga.
(g) Life Cycle Life cycle has two or more phases such as
haplohaplontic, haplohaplohaplontic,
diplodiplohaplontic, etc.
Economic Importance of Red Algae
The red algae like Porphyra, Chondrus, Rhodymenia,
Centerella and Bostrychia are used as food in various parts of
the world.
Agar yielding algae are called agarophytes, such as
Gelidium, Gracilaria, Ceramium, Gelidiella, etc.
Algae like Rhodymenia are used as fodder for cattle.
Carrageenin a phycocolloid obtained from red algae like
Chondrus and Gigartina is used in preparations of emulsions
for ice cream, chocolates, sauces, toothpastes, cosmetics, etc.
It is also used in clearing liqueurs and finishing leather, etc.
Funori an adhesive phycocolloid is obtained from red alga
Gloiopeltis. It is used in sizing textiles, paper and as glue.
Some algae like Corallina, Polysiphonia have medicinal
properties.