Algae are chlorophyll-containing organisms that live in aquatic and moist habitats. They range from unicellular forms like Chlamydomonas to multicellular and colonial forms like Volvox. Algal thalli can take many forms including unicellular, filamentous, parenchymatous, and siphonous structures. More advanced forms have differentiated tissues. Evolutionary theories suggest simpler unicellular forms like Chlamydomonas preceded more complex colonial and multicellular algae.

1. ALGAE

2. What is algae?
• Algae are chlorophyll bearing
thallophytes in which the sex
organs are wither unicellular
or multicellular and not
presented by sterile envolope
• Algae – derived – latin word –
alga : washed away plants on
sea shore or sea weeds
• Can able to produce many
celled sex organs
• No sterile cell in sex organ
except chara.

3. • The study of algae is called algology or
phycology.
• Phycology – Greek word phycos – meaning
sea weeds
• First introduced by Linnaeus in 1754
• Algae – Greek word – Phykos
• Chinese – Tsau
• Hawaii – Limu
• Roman – Fucus
• Tamil - Pasigal

4. Salient features of algae
• Live in moist and aquatic habitats
• Unicellular or multicellular
• Plant body is thalloid
• Presence of chlorophyll and other
photosynthetic pigments in chromatophores
• Autotrophic in nutrition
• Cells may be uninucleate or multinucleate
• Cell wall rich in cellulose
• Cells motile due to the presence of flagella or
cilia

5. • Reserve food – starch
• Reproduction –
• Primitive algae – vegetative methods
• Higher forms – sexual and asexual
reproduction
• Asexual reproduction – motile zoospores
• In unicellular – entire organisms act as a
gametes
• In multicellular – gametes produced from
unicellular and multicellular gametangium [no
sterile jacket]

6. • Sexual reproduction –
isogamous, anisogamous
and oogamous
• Zygote develops a thick
wall to form an oospore
• Life cycle – isomorphic
or heteromorphic
• Life cycle – haplontic,
diplontic, diplohaplontic,
haplobiontic and
diplobiontic
• Alternation of
generations is common
in algae

7. Habits and Habitats of algae
• On the basis of habitats in which algae are
growing, there are seven groups –
»Aquatic algae
»Edaphic algae
»Aerial algae
»Cryophytic algae
»Symbiotic or endophytic algae
»Endozoic algae
»Parasitic algae

8. Aquatic algae
• Also called as hydrophilous algae
• Submerged or free – floating
• Living in fresh waters – ponds, rivers,
springs etc.
• Some in salt water – seas and oceans
• Still waters – ponds, pools etc Eg:
Zygnema, Oedogonium etc.
• Running water – Eg: Vaucheria and
Cladophora

9. Types of aquatic algae
i. Benthic algae
• Algae which are
found attached to
any substratum in
the bottom of water
bodies
• It is also called as
benthophytes
• Eg. Chara, Nitella,
Cladophora etc.

10. ii. Epactic algae
• Algae which are found attached
to the substrata along the
shores
• It is also called as epactiphytes
• Eg. Oedogonium, Spirogyra etc.
iii. Thermophilic algae
• Algae which lives in hot springs
at around 55⁰C and above
• It is also called thermophilic
algae or thermophytes
• Eg. Oscillatoria sps.

11. iii. Phytoplankton
• Algae that float on surface of water
• It is also called planktophytes
• Attached during early stages and then
become free floating – Tychoplanktophytes
• Eg. Oedogonium, Cladophora, Sargassum and
Nostoc
• Some others remain free floating throughout
the life – Euplanktophytes
• Eg. Chlamydomonas, volvox etc.

12. Epizoic algae
• Algae that live on
aquatic animals are
called epizoic algae
• It is otherwise
called epizoophytes
• Eg. Filaments of
Cladophora are
found attached to
the snail shells

13. Epiphytic algae
• Algae that live on other
aquatic plants are called
epiphytic algae or
epiphytes
• Eg. Oedogonium, Chara,
Nitella etc.
Halophytic algae
• Algae which are living in
salt water such as seas,
oceans
• It is called as halophytes
• Eg. Chlamydomonas etc.

14. Edaphic algae
• Algae which are living in or
on the moist soils
• It is also called
edaphophytes or terrestrial
algae
• Some sps. live in the suface
of soil where organic matter
is abundant – saprophytes
epiterranean. Eg. Vaucheria
• Algae which live bolow the
soil surface – cryptophytes
[subterranean]. Eg.
Anabaena, Nostoc etc.

15. Aerial algae
• Algae living in terrestrial
plants, animals, walls,
fencing wires, and rocks.
• Epiphyllophytes – live in
leaves. Eg. Phyllosiphon
• Epiphloeophytes – live in
bark. Eg. Trentipohlia
• Epizoophytes – live in
terrestrial animals. Eg.
Chaetophora
• Lithophytes – live in rocky
substratum. Eg. Scytonema

16. Cryophytic algae
• Algae that live in ice or snow – field
• It is also called cryophytes
• Ice fields – Ancyclostoma
• Ice – temporarily – Gleocapsa and Phormidium
• Ice and snow – Cylindrocystis and Trochiscia
• Alpine Snow fields – red colour –
Haematococcus
• Green colour – Raphidonema
• Red snow – Scotiella
• Yellow or Yellow green snow – Ulothrix and
Nostoc

17. Ancyclostoma TrochisciaPhormidium
Cylindrocystis Raphidonema Haematococcus
Scotiella Ulothrix Nostoc

18. Symbiotic or endophytic algae
• Algae that live in symbiotic association with
other plants
• It is called as symbionts or endophytes Eg.
Lichen.
• Some algae seems to be lichen Eg. Chrococcus,
Microsystis, Chlorella, Cytonema etc.
• Anabaena azollae – leaf tissue of aquatic fern
Azolla [Gymnosperm]
• A. cycade – corrolloid roots of Cycas
[Gymnosperm]
• Nostoc – cavities in the thallus of anthoceros
[Bryophytes]
• Chlorochytrium – inside Lemna [Angiosperm]

20. Endozoic algae
• Algae that live in the aquatic animals
• It is called endozoic algae or
endozoophytes
• Zooxanthellae is found in fresh water
sponges
• Zoochlorella – inside the body of Hydra
• Characium – seen in some body of insect
larvae

22. Parasitic algae
• Algae that live as parasite on other plants are
called parasitic algae
• Causes diseases in some plantation crops
• Eg. Caphaleuros virescens – parasitic algae of
tea and causes red rust disease

23. Range of thallus structure in Algae

25. I. Unicellular Algae: It is of two types
a. Motile forms or flagellated forms
a) Freely moving in water by flagella
b) They are of many shapes – spherical, oblong
or pear shaped and circular – Ex.
Chlamydomonas
c) Some are dorsiventrally differentiated
– Ex. Phacus
d) The number of flagella may to one to more
and it may be equal or unequal

26. • Euglena – one flagellum at its anterior
• Chlamydomonas – two flagella at its front end
• Heterochlorsis – two flagella and unequal
• Botrydiopsis – two flagella
i. acronematic or whiplash
ii. pantonematic
• Peridium – two flagella
»arises from transverse furrow and encircles
the cell
»arises from longitudinal furrow and faces
backward
• Trichloris – three flagella
• Carteria – four flagella
• Chloraster – five flagella
• Pocillomonas – six flagella

27. Amoeboid forms or periplasts or naked forms
• In some forms there is no true cell wall so that the
shape of the cells is flexible. Eg. Heterochloris
mutalis
Rhizopodial forms
• Some motile cells after shedding their flagella long
develop delicate cytoplasmic process called
rhizopodium. Eg. Synura
Encapsulated forms
• Some motile unicells are enclosed by thick,
variously shaped envolope. Eg. Phacotus
Colourless forms
• Some saprophytic motile unicells remain colourless

28. Euglena
Euglena Chlamydomonas Heterochlorsis
Carteria Synura Phacotus

29. b. Non flagellated or coccoid forms
• The unicellular non – flagellated forms are
called coccoid forms
• The cells are more or less round and bounded
by rigid cell wall Eg. Chlorella and
Chlorococcus
• The cell may be enclosed by sculptured
calcareous scales called coccolith. This form is
called cocosphere. Eg. Calcidiscus and diatoms
• The cell is elongated and spirally coiled in
Spirulina
• The cell is spindle shape in Closterium

30. Chlorella Chlorococcus
Spirulina Closterium

31. II. Multicellular Algae (or) colonial forms:
A group of individual cells of a species living in a
habitat is called a colony. It is of two types
a. Motile colonial forms (or) Coenobial forms
• Colony in juvenile and mature stages remains constant –
coenobium
• It is called as motile coenobium
• Motile Eg. Volvox, Gonium, Pandorina etc.
• A Volvox colony has many Chlamydomonas cells
interconnected by protoplasmic connections
• The surface of the colony is covered with mucilage –
lamella and the center remains hollow at several regions.
It is called hollow type coenobium

32. • Gonium colony consists of
4 – 32 closely arranged
Chlamydomonas type cells
surround by mucilaginous
cells
• Pandorina colony has 16 –
32 cells covered with a
common mucilaginous
sheath
Volvox
Pandorina
Gonium

33. b. Non Motile colonial forms
• If the individual cells are
non – flagellated, the
coenobium remains non –
motile. Eg. Hydrodictyon,
Pediastrum, Senedesmus
etc.
• The Coenobium of
Hydrodictyon consists of
many cylindrical cells which
are joined end to end like
hexagons.
• Hence the colony appears
to be a network
Hydrodictyon

34. • The colony of
Pediastrum is disc
shaped and is made
of closely arranged
cells
• In Scenedesmus, the
colony consists of 4 –
8 variously shaped
cells which are
parellely arranged
one above the other
as a stack of coins
Pediastrum
Scenedesmus

35. c. Palmelloid forms or Amorphous forms
• An algal colony in which non – motile cells are
embedded in an amorphous gelatinous matrix is
called palmelloid colony or palmelloid form.
• The gelatinous matrix may be secreted by
protoplasts of the individual cells of the colony
• Eg. Tetraspora, Chlorosaccus and Phaeocystis
Tetraspora Chlorosaccus Phaeocystis

36. Palmella – stage
• The division of the
protoplast of a cell
ultimately forms
amorphous colony
with indefinite
number of spores
and it is called
palmella stage.

37. d. Dendroid forms
• A colony, in which the
individual cells are jointed
end to end by producing
mucilage at their base end
which looks like a
branched tree.
• It is also called dendroid
family
• Eg. Prasinocladus,
Dendobryon etc.
Dendobryon
Prasinocladus

38. e. Rhizopodial form
• A colony in which the individual cells are
linked together by means of rhizopodia is
called rhizopodial forms or rhizopodial colony.
Eg. Chlorarachnion
Chlorachnion

39. f. Filamentous forms
• An algal thallus in which cells
are arranged in linear row
and are joined end to end by
middle lamella is called a
filament or filamentous form
Uniseriate filament – The
filament is made of single
row of cells. Eg. Ulothrix,
Oedogonium. [prokaryotic
cells]
Multiseriate filament – The
cells are arranged in more
than one linear row. Eg. Ulva

40. • The filamentous forms
may be branched or
unbranched
Unbranched types -
• simple with linear
row of cells Ex.
Ulothrix
• Leaf – like Ex. Ulva
• Tubular Ex.
Enteromorpha
Ulva
Enteromorpha

41. • Filamentous thalli with lateral
branches is called branched
filaments
Types of branched thalli
Pseudo branches
• In some algae, the filaments
breaks at certain points due to the
disintegration of cells
• The cells adjacent to the dead
cells grow out of the
mucilagenous sheath called
Pseudo branches
• The formation of Pseudo branches
is called false branching. Eg.
Scytonema
Scytonema

42. True branches
• The lateral branches arise
due to the transverse
division of cells in lateral
outgrowths. Ex.
Cladophora
Parenchymatous cells – Eg.
Ulva
Pseudoparenchymatous
cells – Eg. Polysiphonia and
Gracilaria
Cladophora
Polysiphonia
Gracilaria

43. g. Heterotrichous forms
• The filaments which contains both prostrate
system and erect system is called
heterotrichous form
• Hetero – different; trichous – filament
• The thallus was differentiated into creeping
system and projecting system
• Creeping system – consists of branched
filaments attached to the substratum
• Projecting system – arises from the creeping
system and grows erect

44. Eg:
• Fritschiella – both
creeping and erect
equally developed
• Coleochaete– creeping
system – disc like and
well developed.
Prostrate system –
poorly developed
• Drapernoldiopsis–
prostrate system – well
developed. Creeping
system – poorly
developed

45. h. Siphonous forms
• Here the thallus is an
elongated cell which
contains numerous nuclei,
chromatophores,
pheripheral cytoplasm
and a central narrow
vacuole.
• This type of thallus is
called siphon or
siphonous form Eg.
Vaucheria and
Protosiphon

46. i. Advanced type of Thalli
• The thallus consists of a
combination of filaments
and parenchymatous cells
• Thallus may be uniaxial or
multiaxial
• Uniaxial thallus – main
thread surrounded by
numerous lateral branches
as cortex. Eg.
Batrachospermum
• Multiaxial thallus – has the
main axis has many threads
surrounded by their lateral
branches. Eg. Polysiphonia

47. • In Chara, the thallus
bears rhizoids to attach
it with substratum and
the branched erect
system
• In Sargassum –
differentiated into root
– like, stem – like and
leaf – like structures
consists of
parenchymatous cells
• In Postelsia
palmaeformis – thallus
is palm – like and its
cells are
parenchymatous

48. Evolution of Thallus in Algae
• Acco’ to evolutionary theories, the motile
unicells are the simple and primitive type
of thalli
• The coccoid forms developed from the
flagellated forms by shedding their flagella
• The colonial forms developed by the
aggregation of motile or non – motile
forms
• The filamentous forms evolved from
unicells by the joining of many cells end to
end

49. • The leaf – like filamentous thalli evolved
from the uniseriate simple filaments by
lateral and transverse divisions of their
constituent cells.
• Heterotrichous filaments have evolved
from simple filamentous forms due to
the repeated cell division and
aggregation of resulting filaments.
• Heterotrichous forms are considered to
be the ancestors of advanced type of
thalli

50. THANK YOU