ALGAE

Characteristics:

• Majorityof algae are comprised of unicellular

microorganisms that may be spherical, rod-shaped,
club shaped and spindle shaped. Others are
multicellular and appear in a degree of complexity.
• Algal cells are eucaryotic. In most species the cell wall
is thin and rigid. Cell wall of diatoms are impregnated
with silica making them thick and rigid.
• These organisms are ubiquitous (found everywhere),
many live in aquatic environments but many also
thrive as terrestrial and subterranean algae.
• Algae contain chlorophyll and are photosynthetic like
plants but they differ from plants in having simple
reproductive structures for sexual reproduction. E.g.
unicellular algae may themselves function as
gametes. In asexual reproduction, many algae
produce flagellated spores and/or nonmotile spores in
• Algae contain a discrete nucleus. Other inclusions are starch
grains, oil droplets and vacuoles.
• Chlorophyll and other pigments are found in membrane
bound organelles known as chloroplasts. These chloroplasts
may be massive structures situated near the wall or
embedded in the midst of cytoplasm. They may occur as
one, two or many per cell; they may be ribbon like, bar like,
net like or in the form of discrete disks, as in green plants.
• Pyrenoid, a protein body found in the chloroplasts of algae
that is involved in carbon fixation and starch formation and
storage
• Motile algae also called as swimming algae have flagella
occurring singly, in pair or in clusters at the anterior or
posterior end of the cell. Some algae have no means of
locomotion and are carried about by tides, waves and
currents. Some attach themselves to the substrate which
move them to new locations. The small body, the eyespot is
often present near the anterior end of motile algae, other
structures are also found like spines and knobs by which
they may be anchored to some object.
 BIOLOGICAL
AND ECONOMIC
IMPORTANCE
OF ALGAE
Algae as primary producers:
• Mostalgae are aquatic organisms. Tiny floating algae
constitute the phytoplankton of the sea and serve as an
important food source for other organisms . These algae
form the base or beginning of most aquatic food chains
because of their photosynthetic activities and are
therefore called primary producers of organic matter.
Commercial products from algae:
• Many products of economic value are derived from algal
cell walls. Three of these, agar, alginic acid and
carrageenan are extracted from the walls of algae.
Another diatomaceous earth, is composed of millions of
diatoms glass walls deposited over time in either fresh
water or the ocean. Agar and carrageenan are polymers
of galactose or galactose containing compounds with
sulfate groups. hence, called as sulfated galactans.
Alginic acid consist of uronic acid residues.
• Carrageenan is extracted from the walls of several red
algae. It has been used as a stabilizer and emulsifier in
foods such as ice cream and other milk products. It is also
used as binder in toothpaste or in pharmaceutical
products. It is also useful as a finishing compound in textile
and paper industries, as a thickening agent in shaving
creams and lotions and in the soap industry.
• Agar is well known as a solidifying agent in the preparation
of microbiological media. It is obtained from red algae.it is
also important in food industry where it is valuable in the
manufacture of processed cheese, mayonnaise, pudding,
jellies, baking products and canned goods. In
pharmaceutical industry agar can be used as a carrier for a
drug. Lotions and ointments contain some agar.
• Alginic
acid is obtained from the walls of brown algae.
Alginates are incorporated into cheese and bakery
products, especially frostings. It is also used in paper
manufacturing, printing of fabrics and paint thickening. It is
used by dentists for making impressions of the teeth for
crowns, etc.
• Diatomaceous earth is used primarily for filters and filter
aids. It is suitable because it is not chemically reactive, is
not readily compacted and compressed during use and is
available in many grades.
Algae as food:
• Many species of algae mostly red and brown algae are
used as food in the far east.
• Of the red algae one of the most important is Porphyra; it
is used as a food in Japan, where it is called “nori” and is
processed into dried sheets. The algae are collected and
washed in fresh water to remove debris then chopped
and spread on frames to dry into thin sheets. Nori is
toasted over a flame and sprinkled in soup or rice , or it is
rolled around flavored rice with fish or vegetables to
make a popular luncheon snack called sushi.
• Red algae continue to be a significant food in china.
Porphyra and other red seaweeds are expected to be
increasingly important in Chinese diet.
Algae and diseases:
Although few algae are pathogenic, one, Prototheca,
has been found to be a probable pathogen of
humans. It has been found in systemic and
subcutaneous infections, as well as in bursitis
(inflammation and swelling of a bursa. A bursa is a
fluid-filled sac which forms under the skin, usually
over the joints).
Several species are parasitic on higher plants; e.g.
the green alga Cephaleuros attacks leaves of tea,
coffee, pepper and other tropical plants, causing
considerable damage.
Some planktonic algae produce toxins which are
lethal to fish and other animals. These toxins are
extracellular or they are liberated from the alga by
bacterial decomposition of water blooms.
 ALGAL
PIGMENTS
• There are three kinds of photosynthetic pigments in
algae:
1) Chlorophyll
2) Carotenoids
3) Biloproteins. (also called phycobilins)
Chlorophylls:

• There are five chlorophylls a, b, c, d and e.

• Chlorophylla is present in all algae, chlorophyll b is
present in Euglenophycophyta and Chlorophycophyta,
chlorophyll c is present in the members of
Xanthophycophyta, Bacillariophycophyta,
Chrysophycophyta, Pyrrophycophyta,
Cryptophycophyta and Phaeophycophyta, chlorophyll
d is present in Rhodophycophyta, chlorophyll e is rare
and is present in only two genera of
Xanthophycophyta.
Carotenoids:

• There are two kinds of carotenoids:

• Carotenes.

• Xanthophylls.
• Carotenes are linear, unsaturated hydrocarbons and
xanthophylls are oxygenated derivatives of these.
Biloproteins:

These are water soluble pigments whereas

chlorophylls and carotenoids are lipid soluble.
Phycobilins are pigment protein complexes and are
present in only two algal divisions: the
Rhodophycophyta and Cryptophycophyta.
There are two kinds of phycobilins: phycocyanin and
phycoerythrin.
REPRODUCTI
ON
• Algae may reproduce either sexually and asexually.
• Asexualprocesses in algae include the purely vegetative
type of cell division by which bacteria reproduce. A new
colony of algae or a filament may even start from a
fragment of an old multicellular type from which it has
broken.
• However, most asexual reproduction in algae is more
complex than this and involves the production of
unicellular spores, many of which especially in aquatic
forms have flagella and are motile; these are called as
zoospores. The non motile spores, or aplanospores, are
likely to be formed by the terrestrial type of algae.
• Allforms of sexual reproduction are found among algae.
In these processes there is fusion of sex cells, called as
gametes. The union of gametes forms a zygote.
• If
gametes are identical the fusion process is isogamous
but if they are unlike, differing in size, the process is
heterogamous.
• Aswe proceed to the higher, the sexual cells become
more characteristically male and female. The ovum
(female egg cell) is large and non motile and the
male gamete (sperm cell) is small and actively
motile. This type of sexual process is termed as
oogamy.
• Exclusivelymale or exclusively female thalli also
exist. Although these thalli may look alike, they are of
opposite sex types, since one produces male
gametes and the other produces ova. These are
called as unisexual or dioecious.
• Plants
in which gametes from the same individual
can unite are said to be bisexual or monoecious.
CLASSIFICATI
ON
• Algaeare classified on the basis of the following
characteristics:
1) Nature and properties of pigments.
2) Chemistry of storage products.
3) Chemistry and physical features of cell walls.
4) Morphological characteristics of cells and thalli.
5) Methods of reproduction.
Rhodophycophyta (red algae):
• It contains chlorophyll a and rarely d.
• Biloproteins are phycoerythrin and phycocyanin.
• Storage products include floridean, starch and oils.
• Flagella is absent.
• Asexualsexual reproduction is accomplished by
nonmotile spores . However, they reproduce sexually
heterogamously by the union of well differentiated
nonmotile male and female germ cells, the spermatia
and carpogonia.(female sex organs)
Xanthophycophyta (yellow green algae):
• It contains chlorophyll a,c and rarely e.
• Storageproducts are glucose polymers,
chrysolaminarin and oils.
•2 unequal and apical flagella.
• Asexualreproduction occur by cell division and
fragmentation of filaments and colonies. Sexual
reproduction is rarely observed.
Chrysophycophyta (golden algae):
• It contains chlorophyll a and c.
• Storage products are chrysolaminarin and oils.
•1 or 2 equal or unequal apical flagella: in some, cell
surface covered by characteristic scales.
Phaeophycophyta (brown algae):
• It contains chlorophyll a and c.
• Storageproducts are glucan (polymers of glucose),
laminarin, soluble carbohydrates and oils.
•2 lateral flagella.
Bacillariophycophyta (diatoms):
• It contains chlorophyll a and c.
• Storage products are chrysolaminarin and oils.
•1 apical flagellum in male gametes.
• Their hard silica containing walls consist of two halves
which fit together, like a petri dish and its cover. Deposits
of these shells are called diatomite or diatomaceous
earth, which is used in insulating material, as a filter for
clarifying fruit juices, wine, beverages etc. in cosmetic
bases and as polishing materials.
Euglenophycophyta (euglenoids):
• It contains chlorophyll a and b.
• Storage products are paramylon and oils.
• 1, 2 or 3 equal, slightly apical flagella.
• Reproduction is by longitudinal binary fission.
Chlorophycophyta (green algae):
• It contains chlorophyll a and b.
• Storage products are starch and oils.
• 1, 2, 4 to many , equal, apical or subapical flagella.
• Asexual reproduction occur by longitudinal fission of
the protoplast to form 2, 4 or 8 daughter protoplast.
• Sexual reproduction occur by isogamy or heterogamy.
Cryptophycophyta (cryptomonads):
• It contains chlorophyll a and c.
• Biloproteins include phycoerythrin and phycocyanin.
• Storage products are starch and oils.
•2 lateral flagella, gullet present in some species.
• Reproduction either by means of longitudinal cell
division or by the formation of zoospores or cysts.
• Sexual
reproduction has been confirmed in the genus
cryptomonas.
Pyrrophycophyta (dinoflagellates):
• It contains chlorophyll a and c.
• Storage products include starch, oils.
•2 lateral flagella present, there is a longitudinal and
transverse furrow and angular plates.
• Bothsexual and asexual reproduction is observed.
Asexual reproduction takes place through division of
the cell. Sexual reproduction is occasionally
observed.