ALGAE
Habit &
Habitat: Algae are chlorophyll-bearing, simple, thalloid, autotrophic and
largely aquatic (both fresh water and marine) organisms. They occur in a
variety of other habitats: moist stones, soils and wood. Some of them also
occur in association with fungi (lichen) and animals (e.g., on sloth bear).
Size: The
size ranges from the microscopic unicellular forms like Chlamydomonas, to
colonial forms like Volvox and to the filamentous forms like Ulothrix and
Spirogyra. A few of the marine forms, such as kelps, form massive plant bodies.
Reproduction:
The algae reproduce by vegetative, asexual and sexual methods.
Vegetative
Reproduction: Vegetative reproduction is by fragmentation. Each fragment
develops into a thallus.
Asexual
Reproduction: Asexual reproduction is by the production of different types of
spores, the most common being the zoospores. They are flagellated (motile) and
on germination gives rise to new plants.
Sexual
reproduction: Sexual reproduction takes place through fusion of two gametes.
The fusion of gametes can be of following types in algae:
Isogamous
Fusion: These gametes can be flagellated and similar in size (as in
Chlamydomonas) or non-flagellated (non-motile) but similar in size (as in
Spirogyra). Such reproduction is called isogamous.
Anisogamous
Fusion: Fusion of two gametes dissimilar in size, as in some species of
Chlamydomonas is termed as anisogamous.
Oogamous
Fusion: Fusion between one large, non-motile (static) female gamete and a
smaller, motile male gamete is termed oogamous, e.g., Volvox, Fucus.
Economic
Importance of Algae: Algae are useful to man in a variety of ways. At least a
half of the total carbon dioxide fixation on earth is carried out by algae
through photosynthesis. Being photosynthetic they increase the level of
dissolved oxygen in their immediate environment. They are of paramount
importance as primary producers of energy-rich compounds which form the basis
of the food cycles of all aquatic animals. Many species of Porphyra, Laminaria
and Sargassum are among the 70 species of marine algae used as food. Certain
marine brown and red algae produce large amounts of hydrocolloids (water holding
substances), e.g., algin (brown algae) and carrageen (red algae) are used
commercially. Agar, one of the commercial products obtained from Gelidium and
Gracilaria are used to grow microbes and in preparations of ice-creams and
jellies. Chlorella and Spirullina are unicellular algae, rich in proteins and
are used as food supplements even by space travellers.
The algae
are divided into three main classes:
Chlorophyceae
Phaeophyceae
Rhodophyceae
Chlorophyceae
Characteristics:
The members of chlorophyceae are commonly called green algae. The plant body
may be unicellular, colonial or filamentous. They are usually grass green due
to the dominance of pigments chlorophyll a and b. The pigments are localised in
definite chloroplasts. The chloroplasts may be discoid, plate-like, reticulate,
cup-shaped, spiral or ribbon-shaped in different species. Most of the members
have one or more storage bodies called pyrenoids located in the chloroplasts.
Pyrenoids contain protein besides starch. Some algae may store food in the form
of oil droplets. Green algae usually have a rigid cell wall made of an inner
layer of cellulose and an outer layer of pectose.
Reproduction:
Vegetative reproduction usually takes place by fragmentation or by formation of
different types of spores. Asexual reproduction is by flagellated zoospores
produced in zoosporangia. The sexual reproduction shows considerable variation
in the type and formation of sex cells and it may be isogamous, anisogamous or
oogamous.
Common
Examples: Chlamydomonas, Volvox, Ulothrix, Spirogyra and Chara
Phaeophyceae
Characteristics:
The members of phaeophyceae or brown algae are found primarily in marine
habitats. They show great variation in size and form. They range from simple
branched, filamentous forms (Ectocarpus) to profusely branched forms as
represented by kelps, which may reach a height of 100 metres. They possess
chlorophyll a, c, carotenoids and xanthophylls. They vary in colour from olive
green to various shades of brown depending upon the amount of the xanthophyll
pigment, fucoxanthin present in them. Food is stored as complex carbohydrates,
which may be in the form of laminarin or mannitol. The vegetative cells have a
cellulosic wall usually covered on the outside by a gelatinous coating of
algin. The protoplast contains, in addition to plastids, a centrally located
vacuole and nucleus. The plant body is usually attached to the substratum by a
holdfast, and has a stalk, the stipe and leaf like photosynthetic organ – the
frond. Vegetative reproduction takes place by fragmentation.
Reproduction:
Asexual reproduction in most brown algae is by biflagellate zoospores that are
pear-shaped and have two unequal laterally attached flagella. Sexual
reproduction may be isogamous, anisogamous or oogamous. Union of gametes may
take place in water or within the oogonium (oogamous species). The gametes are
pyriform (pear-shaped) and bear two laterally attached flagella.
Common
Examples: Ectocarpus, Dictyota, Laminaria, Sargassum and Fucus
Rhodophyceae
Characteristics:
Rhodophyta are commonly called red algae because of the predominance of the red
pigment, r-phycoerythrin in their body. Majority of the red algae are marine
with greater concentrations found in the warmer areas. They occur in both
well-lighted regions close to the surface of water and also at great depths in
oceans where relatively little light penetrates. The red thalli of most of the
red algae are multicellular. Some of them have complex body organisation. The
food is stored as floridean starch which is very similar to amylopectin and
glycogen in structure.
Reprodcution:
The red algae usually reproduce vegetatively by fragmentation. They reproduce
asexually by non-motile spores and sexually by non-motile gametes. Sexual
reproduction is oogamous and accompanied by complex post fertilisation
developments.
Common
Examples: Polysiphonia, Porphyra, Gracilaria and Gelidium.
Economic
importance of Algae
Many algae
are used by human beings for food, manufacture iodine in some other purposes
from ancient times. Many researches are being done in phycology (study of
algae) and many workers are trying to find out the food value of algae, their
importance in industries and importance in agriculture. The importance of role
played by algae in the world is be coming more appreciated each day because of
the increased utilization that many of them are valuable to man. Value is as
under.
(1) Algae
as food: Large numbers of Algae are used as source of food by human beings.
They are rich in carbohydrates, inorganic substances and vitamins. Vitamins A C
D and E are main constituents of these plants. Parphyratenesa is very popular
and eaten throughout Japan. Kambu is another product of algae. Laminarta is
used in Japan as standard food. Spirogyra is chief source of food ulva (sea
lettuce) is also used be man as food. Recently green algae chlorena has drawn
attention of psychologists. Percentage of Protein in this algae is too much
than other vegetable or egg. It contains vitamins A to D. Algae is used to
decorate pastries, sandwiches, rice, fish, cakes and jelly cakes in Japan. Agar
Agar is also used in preparation of ice-cream and jellies. Geliduim,
Gracillaria algae are chief source of agar agar. Another algae Rhodomenia
palmata is chewed like tobacco in Scotland. Hair vegetable is eaten in China
and algae Nostoc commune is one of its constituents. Minute algae chlorella has
also been found as food source for human and animal. Many algae are used as
food for animals like sheep, goat and cattle in New Zealand.
(2) Algae
in industry: Diatoms (an algae) prepare diatomaceous earth and is extensively
used in sugar refineries and soap manufacture. It is also helpful in cement industry,
in the manufacture of dynamite, rubber and blotting paper. It is also used in
isolation of boilers, blast furnaces and at various other places where very
high temperature (1000°C) is required.
Algin is
extracted by boiling algae I washing soda solution and rollers of type writers
are prepared from it. Japanese prepare artificial wool from sargassum.
Agar-Agar obtained from algae like Geliduim is used I sizing of textiles. Algae
chondrius and careragaenium which yields a mucilage is used in manufacture of
left hats as stiffening agent. It has the properties of agar and therefore used
as ingredient of cosmetics, shaving creams, shoe polishes and shampoos. Various
red algae like lamineria yields Iodine. Several sea weeds also yield bromine,
acetic acid, formic acid and acetone.
(3) Algae
in Agriculture: Presence of mucilage in most of the members of Myxophyceae
helps in development and better nourishment for nitrogen fixing bacteria. Some
of them like Anebena, Nostoc etc are able to utilize and fix atmospheric
nitrogen, thus increasing soil fertility. Some members of myxophyceae were able
to fix 20 Lbs. of atmospheric nitrogen per acre in rice field.
(4)
Medicinal Use of Algae: Green unicellular algae chlarella yield an antibiotic
known as chlorellin. It is crystalline and stable at 120°C. With an average
composition of carbon 77.3%, Hydrogen 16.6% and oxygen 10.99%. It has marked
effect on gram positive and gram negative bacteria. Presence of chara and
Nitella algae in a pond cause death of mosquito larvae thus helping in control
of malaria to some extent.
(5) Algae
in Biological research: Photosynthesis and metabolism are based on studies of
unicellular algae such as chlorella. Certain algae like chlamydomonas are being
used in genetical studies. Chlamydomonas was the first haploid organism on
which successful hydridization was accomplished.
Certain
algae like Aceta bularia, Valonia and Nitella show great success in studies on
morphogenesis, nuclear function, nuclear cytoplasmic relationship and ionic
exchange with the environment.
From above
discussion it is clear that algae are great importance for human being.
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