8. 9/7/2022
8
CYANOPHYTA
DISTRIBUTION:
It is a primitive group of algae consisting of 150 genera and about
2,000 species all over the world.
In India, this group is represented by 98 genera and 833 species.
12. 9/7/2022
12
CYANOPHYTA-Range of Thallus Organization
The thallus may be of unicellular or colonial forms:
1. Unicellular Form:
In unicellular form, the cells may be oval or spherical. Common members
are Gloeocapsa, Chroococcus and Synechococcus.
13. 9/7/2022
13
2. Colonial Form:
In most of the members the cells after division remain attached by their
cell wall or remain together in a common gelatinous matrix, called a
colony.
The colonies may be of two types:
a. Non- filamentous, and
b. Filamentous.
CYANOPHYTA-Range of Thallus Organization
14. 9/7/2022
14
a. Non-Filamentous Type:
The cells of this type divide either alternately or in three planes, thereby they
form
Spherical (Gomphosphaera, Coelosphaerum),
Cubical (Eucapsis alpine, Merismopedia) or
Irregular (Microcystis).
CYANOPHYTA-Range of Thallus Organization
Eucapsis Microcystis
15. 9/7/2022
15
b. Filamentous Type:
By the repeated cell division in one plane, single row of cells are formed,
known as trichome e.g., Oscillatoria, Spirulina, Arthospora etc.
The trichome when covered by mucilaginous sheath is called a filament.
The filament may contain single trichome (Oscillatoria, Lyngbya) or several
trichomes (Hydrocoleus, Microcoleus).
CYANOPHYTA-Range of Thallus Organization
16. 9/7/2022
16
CYANOPHYTA
The trichomes may be
Unbranched (Oscillatoria, Lyngbya),
Branched (Mastigocladus limilosus, and
Falsely branched (Scytonema and Tolypothrix).
Oscillatoria Mastigocladus Scytonema
18. 9/7/2022
18
Cyanobacterial cells are larger and more
elaborate than bacteria.
Cell structure is typically prokaryotic— one
envelope organisation with peptidoglycan wall,
naked DNA, 70S ribosomes and absence of
membrane bound structures.
The cell wall is four layered with peptidoglycan
present in the second layer. The outer part of
the protoplast contains a number of photosyn-
thetic thylakoids. It is called chromoplasm.
The thylakoids lie freely in the cytoplasm.
Their membranes contain chlorophyll a,
carotenes and xanthophyll’s. Chlorophyll b is
absent.
CYANOPHYTA-Cell structure
27. 9/7/2022
27
Nostoc are filamentous and
unbranched.
Numerous filaments are found in a
gelatinous mass as a colony.
The filament consists of a chain of
cells, which appear like a bead.
They are called trichomes
Cells are oval, spherical or
cylindrical.
Some of the cells in the filament are
differentiated, they are called
heterocyst. They are sites for
nitrogen fixation. Nitrogenase
enzyme fixes nitrogen.
NOSTOC-MORPHOLOGY
28. 9/7/2022
28
Each filament is covered in a
mucilaginous sheath, which is a
protective layer. It absorbs and
retains water.
The gelatinous sheath is made up of
polysaccharides and also contains
proteins
Colonies are of different shapes,
sizes and colours.
They are mostly greenish or bluish-
green in colour and also have red-
brown or yellow-green colour.
NOSTOC-MORPHOLOGY
29. 9/7/2022
29
Nostoc reproduce vegetatively or asexually by spore
formation.
The vegetative reproduction is by fragmentation.
Small colonies can grow attached to a large colony
and later form separated colonies.
Hormogonia are short and free filaments. They are
formed when a filament breaks. It retains the
gelatinous sheath. New trichomes are developed
inside the colony.
Asexual reproduction is by the formation of resting
spores known as akinetes.
Nostoc also reproduce by heterocysts.
NOSTOC-REPRODUCTION