General characteristics of algae Basis for the classification of algae classification of algae

2.  Algae are photosynthetic eukaryotic organisms.
 They are commonly found in aquatic environments including
freshwater, marine and brackish water.
 They are either motile or non-motile.
 Some of the motile and non-motile algae may form a colony known as
Coenonbium.
 Algae possess the usual eukaryotic structures - Golgi apparatus,
mitochondria, Endoplasmic reticulum and a nucleus.
 The algae includes both the microscopic unicellular to macroscopic
multicellular organisms.
 Most of the algae are autotrophic characterized by their ability to use
the carbon-di-oxide as a carbon source and light as an energy source.
 They reproduce both sexually and asexually.

3. MORPHOLOGY OF AN ALGAL CELL

4. Algae are generally classified on the basis of the following
characteristics:
 Chemical and physical feature of the cell walls
 Nature and properties of pigments that contribute to
photosynthesis
 Morphological charactersitics of cells and thalli.
 Habitat
 Flagella number and the location of their insertion in motile
cells.
 Reproductive behaviour

5.  One of the best known algal classification was proposed by Fritsch
who divided them into 11 classes(1945).
 Classification is based on pigments, flagella and reserve food material.
Eleven classes proposed by Fritsch are as follows:
1. Chlorophyceae
2. Xanthophyceae
3. Chrysophyceae
4. Bacillariophyceae
5. Cryptophyceae
6. Dinophyceae
7. Chloromonadineae
8. Euglenineae
9. Phaeophyceae
10. Rhodophyceae
11. Myxophyceae.

6.  1980 - Lee used fine structural aspects of organelles such as
chloroplast, ER, flagellum, eyespot and nucleus to classify the algae
into 6 divisions and 15 classes.
 The 6 divisions are : Cyanophyta, Glaucophyta, Chromophyta,
Rhododphyta, Chlorophyta and Charophyta.
 Rosowski and Parker (1982) classified algae into 15 classes.
 Van den Hoek (1995) classified algae into 11 divisions:
 Cyanophyta
 Prochlorophyta
 Glaucophyta
 Rhodophyta
 Heterokontophyta
 Haptophyta
 Cryptophyta
 Dinophyta
 Euglenophyta
 Chloroarachniophyta
 Cholorphyta

7.  Chlorophyta is the division of the green algae.
 They are principally freshwater species.
 They are also found in sea water, and many other terrestial
ecosystems.
 This division contain around 500 genera and around 8000
species.
 There are many single celled forms and many colonial types of
green algae.
 Many unicellular green algae are motile by flagella action.
 Colonial types occur as spheres, filaments or plates.

8.  Some species have special structures called
holdfasts, which anchor them to submerged
objects or aquatic plants.
 The cells of the chlorophycophyta have a well-
defined nucleus and usually a cell wall and the
chlorophyll and other pigments are in
chloroplasts as in higher plants.
 Majority of the green algae contain one
chloroplasts per cell.
 The cholorplasts contains chlorophyll a and b.
 Green algae reproduce both sexually and
asexually.
 The cholorplasts are green because they are not masked by any
accessory pigments. Because of this character, the members of
chlorophyta are called as green algae.
 The chlorophyta has a characteristic set of acessory pigments such as
β-carotene and Xanthophylls.

9. Chlamydomonas:
 It is a typical unicellular motile green algae widely distributed in
stagnant water, damp soils and even in snow as “Snow algae”.
(Chlamydomonas nivalis - found in snow).
 They reproduce both sexually and asexually.
 Model organism

10. Volvox:
 Volvox is a colonial green algae.
 Found in freshwater habitats.
 It forms spherical colonies of up to 50,000 cells.
 The individual cells are biflagellate and are morphologically similar to
that of Chlamydomonas.

11. Chlorella:
 It is a green algae which is mainly found in freshwater habitats such as
ponds, ditches and lakes.
 It is globular in shape.
 It is non-motile in nature.
 Generally used in supplemental food supply - SCP.

12. Ulothrix:
 It is a filamentous green algae found in freshwater and marine water.
 They are found in flowing streams.
 They are attached to the twigs or stones by holdfasts at the bases of
the filaments.
 It reproduces by means of the flagellated zoospores. Each Zoospore
may become attached to a solid object and develop in to a filament.

13. Spirogyra:
 Also known as pond silk, water silk or blanket weed.
 It is a filamentous green algae.
 Named for the helical or spiral arrangement of the chloroplasts.
 Spirogyra is very common in relatively clean eutrophic water,
developing slimy filamentous green masses.

14. Acetabularia:
 The name, Acetabularia, derives from the Latin word acetabulum, a
broad, shallow cup used for dipping bread; the upturned cap of
Acetabularia resembles such a cup. For this reason, it is also
sometimes called mermaid's wineglass.
 Each Acetabularia cell is composed of three segments: the "foot" or
base which contains the nucleus, the "stalk," and the "cap."

15.  The members of this division
are red in colour. Hence they
are known as “Red Algae”.
 Red algae are red because of
the presence of the pigment
phycoerythrin.
 They are generally found in
frehwater or marine water.
 The members of this division
are generally multicellular
though unicellualr forms are
known.

16.  Some rhodophytes are also important in the formation of tropical reefs.
 These reef-building rhodophytes are called coralline algae, because
they secrete a hard shell of carbonate around themselves, in much the
same way that corals do.
 In many red algae, asexual reproduction takes place by non motile
spores called monospores.
 Sexual reproduction is oogamous type involving specialised female
cells called Carpogonia and specialised male cells called spermatia.
 Several red algae is of economic importance:
Carrageenan : It is extracted from the walls of several red algae. It is used
as a stabilizer or emulsifier in foods such as ice cream, custards and
evaporated milk.
Agar, a well-known solidifying agent used in the preparation of
microbiological media is extracted from Gelidium and Gracilaria.

17. Gelidium:
 Gelidium is a genus of
thalloid red algae comprising
124 species.
G.amansii - Used in making agar.
Gracilaria:
 Gracilaria is a genus of red
algae notable for its economic
importance in producing agar.
 It is generally used as a food
source for humans and certain
fishes such as tangs.

18.  The cryptomonads are a small
group of biflagellate organisms.
 They have two unequal flagella,
which arise from the base of
the groove.
 The cells are slipper shaped
and occur singly.
 Some forms have a cellulose
wall while others are naked,
being surrounded by
plasmalemma with a thin
granular material on the
outside.

19. There are one or two plastids, with or without pyrenoids
per cell.
Food reserve is stored as a true starch as well as oil.
The longer flagellum bears two rows of mastigonemes,
while the shorter flagellum bears a single row of
mastigonemes.
The choloroplasts contain chlorophylls a and c, but their
colour is masked by a variety of accessory pigments
which occur in different proportions.
The pigments include phycocyanin, phycoerythrin, α-
carotene and the Xanthophylls.
Reproduction is either by means of longitudinal cell
division or the formation of zoospores or cysts.

21. Cryptomonas:
 It is a very important member of the
cryptophyta division.
 They are widely distributed in freshwater
habitats.
 Cryptomonas is a dimorphic genus,
meaning it could be either protozoan
(Cryptomondida) or alga
(Cryptophyceae).
 The cells are usually brownish in color, and have a slit-like furrow
at the anterior.
 They are not known to produce any toxins and are used to feed
small zooplankton, which is the food source for small fish in fish
farming.
 Currently there are 26 species of Cryptomonas.

22.  The members of this algal division are commonly called as
euglenoids, because the best known genus of the group is Euglena.
 Most of the euglenophyta are freshwater organisms, but some are
marine.
 There are around 800 species of euglenophytes.
 They are unicellular flagellates.
 There are almost always two flagella, but one of these is often very
short.
 The members lack a cell wall but normally are surrounded by an
outer layer of pellicle composed of proteins and lipids.
 The euglenoid algae contain chlorophylls a and b like the green
algae and typically appear green because the chlorophylls are not
masked by any accessory pigments.

23.  Of the accessory pigments that are present, the most important are
β-carotene, neoxanthin and diadinoxanthin, although echinenone,
diatoxanthin and zeaxanthin are also found.
 This group is known to contain carbohydrate paramylon.
Nutrition:
A) Photosynthetic:
They can supplement photosynthesis by taking up the organic
compounds. Eg: Euglena.
B) Heterotrophic:
There are also many colourless euglenophytes which are completely
dependent on heterotrophic nutrition. Eg: Astasia.
C) Phagotrophic:
Few euglenophytes are phagotrophic and possess a special apparatus
for capturing the prey and a cytostome for ingesting them. Eg:
Peranema.

25. Euglena:
 They are both plant-like and animal-like.
 They are unicellular.
 They are motile by means of flagellum.
 They commonly occur in freshwater and salt water.
 There is no cell wall containing cellulose.
 The outer membrane is an organised periplast.
 Certain species develop a prominent stigma or eye spot.
 Contractile vacuoles are also present.
 Most species of Euglena have photosynthesizing chloroplasts
within the body of the cell, which enable them to feed by
autotrophy, like plants.

26.  In low moisture conditions, or when food is scarce, Euglena forms
a protective wall around itself and lies dormant as a resting cyst
until environmental conditions improve.
 All Euglenoids have two flagella rooted in basal bodies located in a
small reservoir at the front of the cell.
 In Euglena, one flagellum is very short, and does not protrude from
the cell, while the other is relatively long, and often easily visible
with light microscopy.

27.  It is a large group of algae
commonly found in the
freshwater.
 Species of chrysophycophyta
are predominantly flagellates.
 Some are amoeboid with the
psudopodial extensions of the
protoplasm.
 Most forms are unicellular, but
some form colonies.
 They differ from the green algae
in the nature of their pigments,
in storing reserve food as oil or
chrysolaminarin rather than
starch.

28.  Their characteristic colour is due to the masking of their
chlorophyll by brown pigments.
 Reproduction is commonly by binnary fission but occasionally
isogamous.
Ochromonas:
 It is an unicellular genus with
unequal flagellation.
 They are either spherical or
cylindrical in shape.
 They commonly appear in
freshwater, brackish or marine
waters.
 Some species (especially
Ochromonas danica) are important
in physiological and molecular
studies.

29. Chrysamoeba:
 They are unicellular flagellates.
 The flagella are unequal in length.
 There are two distinctive plastids in the photosynthetic forms.
 It is an amoeboid cell with a number of long rhizopodia radiating
from the central mass of protoplasm.

30. Thank
you