This document provides information about algae, including their definition, characteristics, habitats, and classification. Some key points: i. Algae are chlorophyll-bearing microorganisms that can be unicellular or multicellular. They are mostly aquatic but also occur in soils, rocks, snow, and other habitats. ii. Algae have simple plant-like bodies but lack vascular tissues and true roots/leaves. Reproduction occurs through mitosis or meiosis rather than embryogenesis. iii. Algae are classified into 11 major groups, with the first four - cyanobacteria, green algae, diatoms, and yellow-green algae - commonly found in soils. Blue-green al

1. WELCOME
BY A. HASAN SHAKIB

2. ALGAE
 Definition: The chlorophyll bearing ubiquitous
microorganism with a thallus like plant-body, which
may be unicellular and multicellular, are known as
algae.

3. CHARACTERISTICS OF ALGAE:
 1. Algae are chlorophyll-bearing autotrophic thalloid plant
body.
 2. Almost all the algae are aquatic.
 3. The plant body may be unicellular to large robust
multicellular structure.
 4. The multicellular complex thalli lack vascular tissue and
also show little differentiation of tissues.
 5. The sex organs are generally unicellular but, when
multicellular, all cells are fertile and in most cases the entire
structure does not have any protection jacket.
 6. The zygote undergoes further development either by
mitosis or meiosis, but not through embryo formation.
 7. Plants having distinct alternation of generations. Both
gametophyte and sporophyte generations - when present in
the life cycle are independent.

4. OCCURRENCE OF ALGAE:
The algae are ubiquitous (present everywhere) in
distribution, i.e., they are found in fresh water as
well as marine water, on soil, on rock, as epiphytes
or parasites on plants and animals, in hot springs,
in desert, on permanent snow-fields etc. But they
mainly dwell in aquatic environments.

5. BASED ON HABITAT THE ALGAE MAY BE
CATEGORIZED AS:
1. Aquatic algae.
2. Terrestrial algae, and
3. Algae of remarkable habitats.

6. 1. AQUATIC ALGAE:
Aquatic algae may be fresh water (when salinity is as low-as
10 ppm) or marine (when salinity is 33-40%). Again, certain
algae grow in brackish water which is unpalatable for
drinking, but less salty than sea water. The fresh water
algae usually grow in ponds, lakes, tanks, ditches etc.
The very common fresh water algae are Chlamydomonas,
Volvox, Ulothrix, Chara, Oedogonium, Spirogyra, Nostoc,
Oscillatoria etc. Some of the very common marine algae are
Sargassum, Laminaria, Ectocarpus, Polysiphonia, Caulerpa,
Bangia, Padina etc.
Fresh water algae may be termed as planktonic when they
grow and remain suspended on the upper part of water
(e.g., Volvox, diatom), while the benthic algae are bottom-
dwellers. The algae that grow at air-water interface are
called neustonic. The benthic algae may be epilithic, that
grow on stones; epipelic attached to sand or mud;
epiphytic- growing on plants; and epizoic- growing on
animal body surface.

7. 1. AQUATIC ALGAE:(CONTINUED)
The marine algae may be supralittoral or sub- aerial, as
they grow above the water level and in the spray zone.
The intertidal algae grow in such a depth so that they
are exposed periodically due to tides. Other marine
algae are sublittoral, meaning hat they are constantly
submerged at depths as great as 30-60 metres (100-
200 ft).
Again, the supralittoral algae may be edaphic- that grow
in and on the soil, epilithic- growing on stones,
epiphytic- growing on plants, epizoic- growing on
animal body surface, and corticolous - growing on tree
barks and parasitic on plants and animals. Some algae
(e.g., Chlorella) live endozoically in various protozoa,
coelenterates, molasses etc.

8. 2. TERRESTRIAL ALGAE:
Some algae are found to grow in terrestrial habitats like
soils,’ rocks, logs etc. The algae that grow on the surface
of the soil are known as saprophytes. Many blue-greens,
on the other hand, grow under the surface of the soil, and
are called cryptophytes.
The algae growing in the desert soil may be typified as
endedaphic (living in soil), epidaphic (living on the soil
surface), hypolithic (growing on the lower surface of the
stones on soil), chasmolithic (living in rock fissures) and
endolithic algae (which are rock penetrating).
The common terrestrial members are Oscillatoria sancta,
Vaucheria geminata, Chlorella lichina, Euglena sp.,
Fritschiella sp. and Phormidium sp.

9. WHERE ALGAE ARE FOUND?/WHERE FOUND?/
OCCURRENCE OF ALGAE:
Algae occur
i. Great abundance in oceans, seas, rivers, salt
lakes, fresh water lakes, ponds and streams.
ii. Many in damp soils; on rocks, stones & tree bark,
and in other plants and animals.
iii. Many on the snow and ice of polar regions and
mountains

10. ENVIRONMENTAL FACTORS FOR THE GROWTH
OF ALGAE:
The environmental factors for the growth of algae
are
i. presence of excessive soil moisture.
ii. presence of excessive light.
iii. pH about 7-7.5 i.e. the neutral media are
preferable.
iv. optimum temperature for the growth of algae is
350C . But they may grow at temperatures
ranging from 0- 700C temperature.

11. CLASSIFICATION OF ALGAE:
 There are 11 classes of algae of which 1 st 4 are
found in soils:
i. Cyanophyceae - Blue Green Algae
ii. Chlorophyceae- Green algae
iii. Bacillariphyceae- Diatoms
iv. Xanthopyceae-Yellow green algae
v. Rhodophyceae- Red algae
vi. Phaeophyceae-Brown algae
vii. Chrysophyceae-They are in sea
viii. Cryptophyceae- ,,
ix. Dinophyceae- ,,
x. Euglenophyceae- ,,
xi. Chlromonadaceae- ,,

12. SOME GENERA OF BLUE GREEN ALGAE FOUND
IN BANGLADESH
i.Anabaena,
ii.Nostoc,
iii. Calothrix,
iv. Tolypothrix,
v. Plectonema,
vi. Scytonema

13. CHIEF CHARACTERISTICS OF BLUE GREEN
ALGAE (PROCARYOTA):
 i. Blue green algae are generally blue green in
colour. The pigments being chlorophyll-a(green),
carotenes (orange), c-phycocyanine(blue), c-
phycoerythrene(red) and xanthophyll(yellow).
 ii. They are ubiquitous in their distribution
 iii. They have no chloroplast i.e. the definite plastid.
 iv. The cells of blue green algae lack well defined
nucleus.
 v. Location of pigments in the peripheral portion of
the protoplasm.
 vi. Lack of sexual reproduction.
 vii. Their photosynthetic product is glycogen.

14. FUNCTIONS OF ALGAE:
The important functions of algae are described below:
 i. Like other microorganisms, algae do not decompose organic matter but
they themselves act as the source of organic matter
 ii. They can fix nitrogen from atmosphere (Blue green algae).
 iii. They can reduce the alkalinity of soil by evolving CO2 to the soil.
 iv. Algae improve aeration by excreting oxygen to the soil.
 v. Algae increase the yield of rice.
 vi. Algae are used as bio-fertilizer to supplement nitrogenous fertilizer
mainly urea.
 vii. Algae liberate some growth promoting substances like auxins and
amino acids, which increase the number of tillers and panicle length of
rice.
 viii. Some of the red algae (agra and irish moss) are used as food.
 ix. Algae are used in medicine.
 x. Algae are source of iodine, bromine and potassium.
 xi. The importance of algae in plankton as food for marine animals is
beyond calculation.

15. WHY WE USE ALGAE AS FERTILIZER?
ADVANTAGE OF ALGAE AS FERTILIZER
WHY DO THE FARMERS USE BGA AS BIOFERTILIZER?
The major causes of algae to be specially used in agriculture as
biofertilizer are given below:
 i. Farmers can easily produce these BGA fertilizer/ materials
for their field application.
 ii. The sun-dried algal material can be stored for a long time in
dry state without loss in their viability.
 iii. These materials can be applied through broadcasting over
standing water.
 iv. Blue green algae can adjust with any climate and soil.
 v. Blue green algae can be used along with the high level of
nitrogenous fertilizer.
 vi. Recommended pest control measures and other
management practices do not interfere with the establishment
and activities of these algae.
 vii. These are very cheap in comparison with urea fertilizer.

16. DIFFERENCE BETWEEN BACTERIA AND ALGAE:

17. LICHEN:
 Lichens are composite organisms
consisting of algae and fungi.