• The earliest systems of classification were based on the gross
morphological characters such as habitat, colour, number and shape of
the leaves etc.
• They were based mainly on vegetative structure (System given by
Linnaeus). Such systems were Artificial Systems. They separated closely
related species as they were based on a few characteristics only.
• Moreover the Artificial system gave equal weightage to the
vegetative and sexual characteristics which is not acceptable now.
• The Natural Classification Systems on the other hand are based on
natural affinities among the organisms and consider not only External
features but also the Internal features, like the Ultra structure,
Anatomy, Embryology and Phytochemistry.
• Such a system of classification was given by George Bentham and
Joseph Dalton Hooker.
•According to the 5 Kingdom Classification, The Plant Kingdom
includes: Algae, Bryophyta, Pteridophyta, Gymnospermae and
• These days Taxonomists even use the other systems of
• Phylogenetic Classification: It is based on the evolutionary
relationships between various organisms which are
acceptable. That means organisms belonging to the same
Taxa have a common ancestor.
• Numerical Taxonomy: It can be easily carried out using
computers is based on all observable characteristics. Number
and codes are assigned to all the characters and the data is
then processed, so hundreds of characters can be considered
• Cytotaxonomy: It is based on the cytological information like
chromosome number, structure, behavior of the
• Chemotaxonomy: It uses the chemical constituents of the
plant to resolve confusions.
General Characteristic features of Algae:
• The term ‘Algae’ was coined by Carolus Linnaeus.
• The study of algae is called Phycology.
• Algae occur in both fresh water as well as marine water, on wet rocks, wet
tree trunks etc.
• They may be unicellular such as Chlamydomonas, Chlorella, Porphyra
(red alga) etc. or they may be multi-cellular filamentous: e.g. Spirogyra,
Ulothrix or Colonial e.g. Volvox.
• The size may vary from simple microscopic to even several meters long as
the Brown algae. e.g. Macrocystis.
• The plant body is undifferentiated into root, stem or leaves, such an
undifferentiated plant body is called Thallus.
• They do not have any vascular tissues such as xylem and phloem. They
do not need even mechanical tissues as they are supported by water.
Their body is flexible and does not resist water.
• They are photosynthetic.
• Plastids are present. The green plastids are called
Chloroplasts and the coloured ones are called
• The photosynthetic pigments present in algae are – Chl-a, Chl-
b, Chl – c, Carotenes (orange), Xanthophylls (yellow),
Fucoxanthin (brown) Phycobillins usually red in colour.
• The cell wall is cellulosic.
• Their whole body is covered by a mucilage layer ( so that
body does not get rotten).
• The reserve food materials in algae is usually Floridean starch
(red algae), Laminarin, Mannitol (brown algae).
• They may have one or more Pyrenoid bodies for storing
starch and protein.
• Reproduction in algae may be of following types.
Reproduction in algae may be of following types.
1) Vegetative reproduction by fragmentation is very
2) Asexual reproduction takes place by different types of
spores like – Zoospores, Aplanospores, Monospores,
Tetraspores, Carpospores and so on.
3) Sexual reproduction may be:
a) Isogamy i.e. fusion of similar gametes.
b) Anisogamy i.e. the fusion of dissimilar gametes.
c) Oogamy: Here the male gamete is small and motile
while the female gamete is large and immotile.
E.g. Volvox, Fucus.
Economic importance of Algae:
1) 50% of earth’s CO2 fixation is done by algae.
2) They also increase the amount of dissolved oxygen in
3) They are the primary producers of many aquatic eco-
4) Some algae such as Laminaria, Sargassum are used as
5) Many algae are consumed as food by many aquatic
6) Certain red and brown algae produce Hydrocolloids (water
holding substances) e.g. Algin is produced by brown algae,
Carragin is produced by red algae. Agar which are used as
jellying agents in the cosmetic industry, for making ice-
creams, medicines. Agar is one such material which is
extensively used as a medium for the growth of microbes.
Agar is obtained from Gelidium, Gracelaria (Red Algae).
6) Spirullina is the richest source of protein used as food
supplement by space travellers.
7) Many algae yield minerals like Iodine, Potash, Bromine
8) Codium, Chlorella, Laminaria and many others have
9) Several (brown algae) algae which grow several meters
long get tangled with the hull of the ships and pose
danger to them.
10) Aerobic algae are grown in the sewage tanks to
provide Oxygen to the decomposer organisms.
Algae are divided into 3 classes:
2. Phaeophyceae and
Chlorophyceae: (Green Algae)
• They may be unicellular such as Chlamydomonas, Chlorella,
Multicellular: Filamentous – Spirogyra, Ulothrix, Colonial – Volvox.
• They are mostly found in fresh waters, very few in salt waters.
• The photosynthetic pigments are Chl – a and Chl – b.
• The Chloroplast are of various shapes – disc like, cup shaped or
ribbon like, reticulate etc.
• They have one or more Pyrenoid bodies for storing starch and
• Vegetative Reproduction by Fragmentation or by formation of
different types of spores.
• Asexual reproduction by formation of Flagellated Zoospores
produced in Zoosporangia.
• Sexual reproduction shows variation in the type and formation of
Gametes, which may Isogamous, Anisogamous or Oogamous.
Phaeophyceae: (Brown Algae):
• The group includes multi-cellular forms of different sizes some
of them are called giant – Kelps which reach the length of
even 100 meters, such as Macrocystis (100 m approx),
Nereocystis (60 m).
• They are mostly marine. These algae are attached to the
substratum with the help of an adhesive structure called
Holdfast. The thallus even consists of a stalk called Stipe,
which holds the photosynthetic lamina called Fronds.
• A few species are free floating such as Fucus, Sargassum.
• Some species are even epiphytic or endophytic such as
• The Western part of North Atlantic Ocean is called Sargasso
sea because of abundance of free floating Sargassum.
• These Kelps pose danger to the ships by getting entangled at
the bottom of the ships.
• They have a cellulosic cell wall.
• There is a covering of Phycocollids such as Alginic acid and
Fucoidin. They are responsible for:
a) Protecting Brown Algae from drying or freezing on exposure
to cold air.
b) Protecting the Brown algae form damage when these algae beat
against the rocks by the waves, otherwise the waves may cause
mechanical damage to these algae.
• The photosynthetic pigments are present in Phaeoplasts.
• The photosynthetic pigments are Chl-a, Chl-c, Carotenes, Fucoxanthin
• The reserve food materials are Laminarin, Mannitol.
• Vegetative reproduction by fragmentation.
• Asexual reproduction by different types of spores like Tetraspores,
Monospores, Zoospores etc.
• Sexual reproduction may be Isogamous, Anisogamous or Oogamous.
E.g. Laminaria, Fucus, Ectocarpus, Sargassum, Dictyota, Macrocystis,
Rhodophyceae: (Red Algae):
• They are mostly marine.
• A few freshwater forms are such as Batrochospermum and
• They have graceful, delicate, lace-like appearance, generally called
• The only unicellular red alga is Porphyridium.
• The freshwater forms are generally bluish green. The marine
forms are generally red in the deep water forms. Near the shore,
they change the colour to purple, pink or violet.
• One or two members are even parasitic and colour less e.g.
• The cell wall consists of cellulose and pectic compounds.
• The Phycocolloids of red algae are usually made of Agar or
• The Chromatophores of red algae are called Rhodoplasts.
• The photosynthetic pigments of red algae are Chl-a,
Chl-d and Phycobillins such as r-Phycoerythrin (red),
r-Phycocyanin (blue) and Allophycocyanin.
• The reserve e food in them is Floridian starch which is
similar to Glycogen and Amylopectin.
• Vegetative reproduction is very common and occurs by
• Asexual reproduction occurs by non-motile spores such
as Monospores, Tetraspores, Carpospores, etc.
• Sexual reproduction takes place by formation of non-
motile gametes and it is usually of Oogamous type.
E.g. of red algae: Polysiphonia, Porphyra, Gelidium,
Gracelaria, Chondrus, etc.
Note on Phycocolloids:
i) The Phycocolloids of red algae are usually Agar and
ii) Agar is one of the main products obtained from these
iii) The Agar producing red algae such as Gracelaria,
Galidium, Gigatina, Chondrus etc. are together
included in a group called Agarophyta.
iv) The largest producer of Agar is China.
v) Agar is used as a culture medium, as a stabilizer,
as a thickener of many food items.
vi) Agar has a property of forming a gel at room
temperature. Therefore it is used in the preparation of
Gelatin capsules as a laxative base for pills.
vii) It is also used as a base for cosmetics, for
toothpaste, for making dental impressions and
also as a jelling agent in the preparation of ice-
viii) Carragenin is obtained from Chondrus,
ix) It is used as a cleaning agent in liquors,
x) It is also used in the preparation of emulsions
of ice-creams, chocolates, toothpastes and
xi) Carragenin also has medicinal value, as it
hastens blood coagulation.
Important Questions for Weekend Assignment:
1. Mention 5 distinguishing characteristic features of Division ‘Algae’.
2. Give one example of unicellular Green alga and Red alga.
3. What is the importance of Pyrenoid bodies in Chlorophyceae?
4. What are ‘Kelps’? Give two examples.
5. Why are Brown Algae named so, inspite of having Chlorophylls in them?
6. Name two parasitic Red algae.
7. Name two Red Algae used as a source of Agar.
8. What are Phycocolloids? How are they important for Brown Algae?
9. How are Hydrocolloids commercially useful?
10. State three differences between all the three groups of Algae, with
reference to their: a) Photosynthetic pigments, b) Reserve food materials,
c) Cell wall.
11. Give one example each of unicellular, filamentous and colonial Green
12. Mention any 5 points of ‘Economic Importance’ of Algae.
• Chapter:3 ‘Plant Kingdom’ (Algae): NCERT Text
Book of Biology, Class XI.
• Chapter:3 ‘Plant Kingdom’ (Algae): Rachna
Sagar’s Together With Biology for Class XI.
• Chapter:3 ‘Plant Kingdom’ (Algae): Dhanpat Rai’s
Move Fast With Biology, Class XI.
• Chapter:3 ‘Plant Kingdom’ (Algae): Modern’s abc
Biology, Class XI.
• Chapter: 3 from printed notes prepared by
A. Jayashree, Biology Dept DPS Hyderabad.
• Flow Charts & pictures from Google Chrome.
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