Spirogyra is a genus of green algae that forms long, filamentous colonies visible as green mats in ponds and slow streams. The filaments are made of cylindrical cells containing ribbon-like chloroplasts arranged in a spiral pattern. Spirogyra reproduces through both asexual fragmentation and sexual conjugation between filaments. During conjugation, gametes from adjacent filaments fuse within connecting tubes to form zygospores, which later germinate into new filaments. This allows Spirogyra to alternate between haploid and diploid generations as part of its life cycle in aquatic environments.
3. • Member of division
Chlorophyta, also called
green algae
• Derived from two Greek
words: Speria (meaning
coil) and gyras (meaning
twisted); named after
spirally arranged
chloroplasts in cell
• Looks like a mass of long
shining silky filaments in
running water, that is why
it is called pond silk
4. Habitat
• Widely distributed and found
throughout the world
• It commonly grows in fresh water
including stagnant reservoirs, slow
running streams and rivers
• It grows as free-floating mass, so it is
commonly called pond scum
• Suitable season for its growth is
spring, but it grows well throughout
the year
• It develops reproductive stage if
temperature rises and develops
vegetative stage if temperature lowers
5. Thallus structure
• Plant body consists of green-colored
filaments
• Filaments are unbranched,
measuring approximately 10 to
100μm in width and may grow up to
several centimeters in length
• Individual cells in a filament are
cylindrical (much longer than broad)
and joined end to end
• No distinction between basal and
distal ends in free-floating species
• Attached forms have modified basal
cells called hapteron or holdfast
6. Cell structure
• Cell wall: Consists of
three layers; with inner
two layers made of pectin
and outer layer composed
of cellulose. The slimy
mucilaginous sheath
surrounding the filament
of Spirogyra cell is formed
due to the dissolution of
pectin in water and is
slippery to touch.
7. • Cell Membrane: Situated just beneath the cell wall, it is selectively
permeable in nature that protects the inner cell content from the
outside environment.
• Cytoplasm: Mostly distributed to the periphery of cell, forming thin
lining along the cell wall. It contains most other organelles such as
endoplasmic reticulum, Golgi bodies, mitochondria, ribosomes, and
other cytoplasmic inclusions. It is traversed by several cytoplasmic
strands.
• Vacuole: A centrally located large organelle that is filled with fluid, and
maintains the water and salt balance inside the cell. The vacuole is
separated from the surrounding cytoplasm by a semi-permeable
membrane called tonoplast.
8. • Chloroplast: A ribbon-shaped organelle that is arranged spirally. It
contains the green pigment chlorophyll that helps them to perform
photosynthesis for producing their own food. There are
approximately 1 to 16 chloroplasts present in a typical Spirogyra cell.
A dense, highly refractive, granular protein body called pyrenoids is
found within the chloroplast at very short intervals. Pyrenoids helps
the cell to store starches and proteins, also providing a distinctive
identifiable feature to Spirogyra.
• Nucleus: A membrane-bound organelle that contains the genetic
material of the cell. The nucleus resides at the center of the cell,
being supported by the cytoplasmic strands. It also contains a
distinct nucleolus that helps the cell to synthesize proteins.
9. Movement
• Spirogyra forms long
filaments that are capable
of bending, twisting and
straightening their
filaments, enabling
locomotion
• Move slowly in the liquid
medium
• Also move towards light
sources (which they need
for photosynthesis)
11. Reproduction
• Broadly Spirogyra perform
three modes of
reproduction
• Vegetative reproduction
is common
• Asexual reproduction is
rare mode, only exhibited
by some species
• Sexual reproduction is
also common
12. • Fragmentation is the common
method, when favorable
environmental conditions,
water and nutrients are
available
• Accidental breaking or injury
may occur
• It breaks the filament into 2-3
cell portions
• Each portion germinates to
produce a new plant
Vegetative Reproduction
13. Asexual Reproduction
Akinetes: When environmental condition become
harsh, some vegetative cells of filament lose water
get shrunk and rounded. They deposit thick wall
and act as resting spore. On return of favorable
condition, akinete germinate into new filament.
Aplanospore: Vegetative cell after losing water get
rounded up, secrete thin wall around and develop
into spore. Single aplanospore formed in single
cell. Aplanospore are released after decay of
mother filament and germinate into new filament
on arrival of favorable condition
Azygospore: It is also known as parthenospore. In
some species, due to physiological condition
gametes fail to fuse and behave as spore.
14. Sexual
Reproduction
• Isogamous type: Spores
of similar size fuse to
form new filaments
• Takes place by
conjugation
• Entire protoplasmic
contents of vegetative
cells (viz., gametangia)
function as gametes
• Two types: Scalariform
and Lateral conjugation
16. • Two filaments come close, lie opposite and parallel to each other held in
mucilage
• Opposite cells of both filaments develop outgrowths called protuberances
• At the point of contact, tips of protuberance dissolve to form conjugation tube
between opposite cells
• When conjugation tube is forming, protoplasts of conjugating cells (gametangia)
recede, round up and function as gametes
• Male gametes transfer through the conjugation tube into opposite cell (female
gametangia) and fuse with female gamete to form zygote (2n)
• Zygote secretes a thick wall to become zygospore
• Therefore, in the late stage of conjugation, male gametangia remain empty and
the female gametangia contain zygospores
• Due to several conjugation tube formation between two filamentous cells, its
appearance is like a ladder. Hence, it is called scalariform (Greek, scala = ladder;
forma = shape) or H-shape conjugation.
17. Lateral Conjugation
• Rare occurrence
• Involves the fusion of gametes from two adjacent cells of the same filament
• Occur in monoecious or homothallic species
Indirect lateral conjugation
• Two outgrowths emerge on
both side of a transverse
septum of two adjunct cells
and after some growth the two
protuberances unite to form a
conjugation tube
• Of the two adjacent cells, one
behaves as male gametangium
whiles the other as female
gametangium
18. • The content (now behaving as gamete) from male gametangium passes
through conjugation tube and enters into female gametangium
• By the fusion of male and female gametes a diploid zygospore is formed
• Thus, in each second cell of a filament, a zygospore is formed
Direct lateral conjugation
• In this type of conjugation,
male gametangium after
passing through an aperture in
the transverse septum of
adjoining gametangium enters
the female gametangium
• It fuses with female gamete,
and diploid zygospore is formed
19. Zygospore
Germination
• Zygospore is the only diploid phase
in sexual life cycle
• Decay of female gametangia causes
liberation of zygospore which
remains dormant in pond bottom
• On return of favorable condition,
diploid nucleus of zygospore
undergo meiosis to produce 4
haploid nuclei out of which 3
degenerate
• Zygospore with one haploid nucleus
gradually enlarges and burst open
to release a germ tube
• Repeated transverse divisions of
germ tube form a new filament
20. Life Cycle
• Haplontic life cycle, with no true
alternation of distinct plants
• Rather, alternation of
chromosome numbers from
haploid to diploid and back to
haploid conditions can be noticed
• Involves haploid vegetative
filament (gametophyte) and a
diploid zygospore, towards the
end of growing season
• Gametes fuse to form a zygospore
(2n)
• Zygospore gives rise to a haploid
new filament
