Introduction, characteristics, classification,Thallus organisation,reproduction and its types, algal blooms, causes of algal blooms, biological and economic importance of algae.
B.SC 1st Year (BOTANY)
3. “Alga is a term that describes a large and incredibly diverse group of
eukaryotic, photosynthetic lifeforms”.
These organisms do not share a common ancestor and hence, are not
related to each other (polyphyletic).
It is an important group of Thallophyta (Gr. Thallos — a sprout;
phyton — a plant), the primitive and simplest division of the plant
kingdom.
The orderly systematic study of algae is called Phycology (Gr.phycos
— seaweeds; logos — study or discourse).
4. Characteristics of Algae
•Algae are photosynthetic organisms
•Algae can be either unicellular or multicellular organisms
•Algae lack a well-defined body, so, structures like roots, stems or leaves are absent
•Algae are found where there is adequate moisture.
•Reproduction in algae occurs in both asexual and sexual forms. Asexual reproduction
occurs by spore formation.
•Algae are free-living, although some can form a symbiotic relationship with other
organisms.
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8. Thallus Organisation in Algae:
The algal thalli are grouped into the
following, based on their organization:
A. Unicellular Algae:
Unicellular forms of algae are also called
acellular algae as they function as complete living
organisms.
Unicellular forms are common in all the groups
of algae except Rhodophyceae, Phaeophyceae
and Charophyceae.
The unicells may be motile or non-motile.
The motile unicells are either rhizopodial or
flagellated.
9. The non-motile cells may be
spiral filament as found in
Spirulina (Cyanophyceae)
The coccoid unicellular algae are
the simplest forms of algae found
in
o Cyanophyceae,
o Chlorophyceae etc., e.g.,
Gloeocapsa, Chlorella
10. B. Multicellular Algae:
1. Colonial:
o The colonial habit is achieved by loose
aggregation of cells within a common
mucilaginous investment.
o The cells of these usually remain connected
with each other by cytoplasmic threads.
a. Coenobium:
When a colony has a definite number of cells
with a definite shape and arrangement, it is
called coenobium.
11. Coenobium may be:
i. Motile, or
ii. Non- motile.
• i. In motile form, cells are flagellated and
whole coenobium can move by the
organised beating action of flagella, e.g.,
Volvox , Pandorina, Eudorina etc.
• In Volvox the coenobium is a hollow
sphere.
ii. In non-motile form, the cells are without
flagella, thereby the coenobium is non-
motile,
e.g., Scenedesmus (Fig. 3.3C), Hydro-
dictyon
12. Aggregated Form:
Unlike coenobium the cells are
aggregated irregularly showing a
colonial mass of various size and
shape.
It is of three types:
i. Palmelloid,
ii. Dendroid, and
iii. Rhizopodial.
13. i. Palmelloid:
In this type the non- motile cells
remain embedded in an amorphous
gelatinous or mucilaginous matrix.
Each and every cell of the
organisation is independent and
can perform all the functions as an
individual.
Chlamydomonas and Chromulina
represent palmelloid as a
temporary feature in their life cycle.
14. ii. Dendroid:
o In this type the number, shape and
size of the cell is variable.
o They look like microscopic trees (e.g.,
Prasinocladus, Ecballocystis,
Chrysodendron, .
o A mucilaginous thread is present at
the base of each cell, thus showing a
sort of polarity.
iii. Rhizopodial:
In this type the cells are united through
rhizopodia. e.g., Chrysidiastrum
15. Filamentous:
The filamentous plant body is formed through repeated
cell divisions in a single plane and in a single direction,
where the cells remain firmly attached to each other —
end to end forming a chain or a thread.
The filaments may be unbranched or branched.
a. Unbranched Filament:
It may be free-floating (e.g., Spirogyra,) or attached to
the substratum (e.g., Ulothrix, Oedogonium, etc.).
The free-floating unbranched filaments are not
differentiated into basal and apical ends.
All the cells in the filament are alike.
But the Unbranched filaments that remain attached to
the substratum are differentiated into base and apex.
16. b)Branched Filament:
It is formed when a filament occasionally starts
division in a second plane.
It is of two types:
i. Falsely branched, and
ii. Truly branched.
i. Falsely Branched:
The trichomes of blue greens may break either
due to death or decay of the intercalary cells.
The broken ends emerge out of the mucilaginous
sheath in the form of a branch.
They do not arise as lateral outgrowths, e.g.,
Scytonema
17. ii. Truly Branched:
When a cell in the filament
occasionally starts division in
a second plane, true branch is
formed.
Thus true branches arise as
lateral outgrowths of the
main filament.
True branches are of the
following three types: Simple
filament, Heterotrichous
habit, and
Pseudoparenchymatous
habit.
18. Reproduction in Algae
(A) Vegetative Reproduction:
Vegetative reproduction in algae takes place by the
following methods:
(i) Fragmentation:
o The filamentous thallus breaks into fragments, and
each fragment is capable of forming new thallus.
o Fragmentation can take place due to mechanical
pressure, insect bite etc.
o The common examples are Ulothrix, Spirogyra,
Oedogoniwn, Zygnema, Oscillatoria etc.
19. (ii) Fission:
Fission is common in desmids, diatoms and other
unicellular algae. The cell divides mitotically into two the
cells are separated by septum formation
(iii) Adventitious branches:
Adventitious branches like protonema develop on
rhizoids of Chara. On detachment they form new thalli.
Similar adventitious structures are formed on thalli of
Dictyota and Fucus.
(iv) Hormogonia:
In blue green algae like Nostoc, Cylindrospermum, the
main filament breaks into small fragments of varying
length called hormogonia. The hormogonia may be
formed at the place of heterocyst in the filaments.
20. (B) Asexual Reproduction:
o Asexual reproduction takes place with
the help of some spores and
structures.
o Fertilization and fusion of nuclei does
not take place.
o The reproduction takes place only by
protoplasm of the cell.
Different methods of asexual
reproduction are:
o Aplanospores - are formed under
unfavorable conditions.
o Aplanospores are non-motile
structures, in which protoplasm gets
surrounded by thin cell wall.
o The aplanospores on release form new
plants, e.g., Ulothrix.
21. Hypnospores - are thick walled structures.
These are formed during unfavorable
conditions.
Under prolonged unfavorable conditions, the
protoplasm of hypnospores divides to make
cysts.
The cysts are capable of forming new thallus.
e.g., Chlamydomonas nivalis.
o Tetra spores - are non-motile spores formed
in some members of Rhodophyceae and
Phaeophyceae.
o In Polysiphonia, tetra spores are formed in
tetra sporangia by reduction division on
special tetrasporophytic plants.
22. Sexual reproduction takes place by fusion of gametes of different sexuality.
The gametes are formed in gametangia by simple mitotic division or by
reduction division.
The haploid gametes fertilize to make diploid zygote
Sexual reproduction
Hologamy:
In hologamy the unicellular thallus of opposite
strains (-) and (+) behaves as gametes directly. The
thalli fuse to make diploid zygote e.g.,
Chlamydomonas.
Autogamy:
In autogamy two gametes of same mother cell fuse
to form diploid zygote. Since both gametes are
formed by same cell there is no genetic
recombination e.g., diatoms.
25. An algal bloom or algae bloom is a rapid increase or
accumulation in the population of algae in freshwater or
marine water systems, and is often recognized by the
discoloration in the water from their pigments.
The term algae encompasses many types of aquatic
photosynthetic organisms, both macroscopic, multicellular
organisms like seaweed and microscopic, unicellular
organisms like cyanobacteria.
Algal bloom commonly refers to rapid growth of microscopic,
unicellular algae, not macroscopic algae.
An example of a macroscopic algal bloom is a kelp forest.
26. Algal blooms are known to be mainly composed of
bio-toxins and are characterized by a distinct
discoloration of water due to a large number of
pigmented algae cells.
The colors range from green, red, brown, and
yellow. The major types of algal blooms are
cyanobacteria (blue-green algae) and red tides
(red algal blooms).
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28. Causes of Algal Bloom in Aquatic Ecosystems
1. Runoff of Nutrients
An algal bloom is mostly caused by the presence of
large amounts of nitrogen and phosphorus present in
water. These nutrients are washed away from lands
and farms that are heavily riddled with nitrogenous
and phosphatic fertilizers.
Rain acts as an agent by washing these leachable
nutrients from the soil into water bodies such as rivers
and streams, which eventually end up in large
reservoirs such as lakes and oceans.
29. 2. High Temperatures
The global world is facing the destruction of the ozone layer caused by global
warming. This is one of the main reasons algal bloom is thriving at a fast rate.
Conducive temperature is needed for certain bacteria to survive both in and out of
water.
3. Presence of Dead Organic Matter
Generally, there are many kinds of bacteria present in the atmosphere, as well as in
water. They are all in search of suitable media for growth and nutrition.
4. Slow-moving Water
Algal blooms need large masses of water, which are almost still to thrive. Most of the
blue-green algae prefer stable water conditions with low flows, long retention times,
light winds and minimal turbulence; other prefer mixing conditions and turbid
environments.
30. 5. Light
When blue-green algae populations are exposed to long periods of high light
intensity (photo-inhibition), these are diminished but have optimal growth when
intermittently exposed to high light intensities. These conditions prevail under the
water surface, where the light environment is fluctuating.
6. Turbidity
The presence of suspended particles and organic matter (flocs) in the water column
cause turbidity. High turbidity occurs when a lot of water is running through the
system (high discharge after a rain event). Low turbidity occurs when there is only a
small amount of suspended matter present in the water column.
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32. 1.Algae Constitute the Link of Food
Chain
2.Algae is Useful in Fish Culture
3.Algae is Used for Recreational
Purposes
4.Algae is Useful in Sewage
Treatment Plants
5.Algae and Water Supplies
6.Algae as the Origin of Petroleum
and Gas
7.Algae and Limestone Formation
33. 1.Algae is Used in Space Research
and Other Fundamental Studies
2.Algae is Used as Food
3.Algae is Used as Fodder
4.Algae is Used as Fertilizers
5.Algae is Used as Medicine
6.Industrial Utilization of Algae
