Chlamydomonas
Sr. Kaslin Juliat SAL
Assistant Professor
St. Xavier’s College, Mahuadanr,
Nilamber Pitamber University

Structure of Chlamydomonas
 Chlamydomonas is unicellular, motile green algae.
 The thallus is represented by a single cell.
 The shape of thallus can be oval, spherical, oblong,
ellipsoidal or pyriform.
 The pyriform or pear shaped thalli are common, they
have narrow anterior end and a broad posterior end.

Structure

Cell Wall
 The cell is surrounded by a smooth, thin and firm cell
wall made of cellulose.
 The detailed structure of cell wall shows that it is
multilayered and is made of cellulose fibrils.
 Inner to the wall lies the plasma lemma (plasma
membrane).
 It is made of two membranes separated by an opaque
zone.

Cytoplasm
 The cytoplasm is present in thallus between the cell wall
and the chloroplast.
 The cytoplasmic structure includes the nucleus,
mitochondria, endoplasmic reticulum, dictyosomes,
ribosomes etc.
 The thallus contains single large, dark nucleus lying inside
the cavity of the cup shaped chloroplast.
 Each cell contains two contractile vacuoles.

Flagella
 The anterior part of thallus bears two flagella. Both the
flagella are whiplash or acronematic type, equal in size.
 The flagella are mostly longer than the thallus but in
some species they can be equal or shorter than the
thallus.
 Each flagellum originates from a basal granule and
comes out through a fine canal in cell wall.

Chloroplast
 In Chlamydomonas generally a large, cup shaped parietal
chloroplast is present in cytoplasm.
 The chloroplast is generally associated with pyrenoid
covered with starch plates.
 The pyrenoids are concerned with synthesis of starch.
 In chloroplast there are 2-6 thylakods which join to form
a granum.

Stigma or Eyespot
 The anterior side of the chloroplast contains a tiny spot
of orange or reddish colour called stigma or eyespot.
 It is photoreceptive organ concerned with the direction
of the movement of flagella.

Reproduction in Chlamydomonas
Reproduction
Asexual Sexual

Asexual
Reproduction
zoospores Aplanospores Hypnospores
Palmella
Stage
Asexual
Reproduction

By zoospores
 The protoplast contracts. The parent cell loses flagella.
 The contractile vacuoles and the neuro-motor
apparatus disappear.
 The protoplasm divides longitudinally by simple
mitotic division forming two daughter protoplasts.
 The second longitudinal division of protoplasm takes
place at right angle thus making four daughter
protoplasts.
 Sometimes the protoplasm may further divide to make
8-16-32 daughter protoplasts.

 The contractile vacuoles also develop in daughter protoplasts.
 Each daughter cell develops cell wall, flagella and transforms into
zoospore.
 The zoospores are liberated from the parent cell.
 The zoospores are identical to the parent cell in structure but
smaller in size.
 The zoospores simply enlarge to become mature Chlamydomonas.
 Under favourable conditions the formation of zoospores can take
place every 25 hours.

Aplanospores
 The aplanospores are formed slightly under
unfavorable conditions.
 The parent cell loses flagella.
 The protoplast rounds off and secretes a thin wall
outside but does not develop.
 These non-motile structures are called aplanospores.
 On approach of favourable conditions aplanospores
may germinate either directly or divide to produce
zoospores.

Hypnospores
 In extreme unfavorable conditions the protoplast
develops thick wall and the structure developed is
called Hypnos pore.
 The hypnospores also germinate like aplanospores on
approach of favourable conditions.

Rounded up
protoplast
Aplanospor
e
(A) Parent cell (B) Aplanospore formation (C) Hypnospore
Cell wall

Palmella Stage
 The palmella stage is formed under unfavorable conditions as shortage
of water, excess of salts etc.
 The protoplast of parent cell divides to make many daughter
protoplasts but they do not form zoospores.
 The daughter protoplasts develop gelatinous wall around themselves
but do not develop flagella. These protoplast segments are called
palmellospores.
 The division and red visions of these protoplast ultimately forms
amorphous colony with indefinite number of spores and it is called
palmella stage.
 When favourable conditions return the gelatinous wall is dissolved,
palmellospores develop flagella, and the spores are released to make
new thalli.

Mucilaginous sheath
Chlamydomonas Palmella stage

Sexual Reproduction
Isogamous Anisogamous oogamous

Isogamy
 Most of the Chlamydomonas species are isogamous in nature.
 In isogamous reproduction the fusion of gametes, which are similar in size,
shape and structure, take place. These gametes are morphologically similar but
physiologically dissimilar.
 These are vegetative cells which may directly function as gametes without
undergoing any division.
 The two gametes fuse by their anterior ends and later fusion proceeds to lateral
sides. The contact wall dissolves and fertilization occur which leads to the
formation of quadriflagellate zygote.
 The zygote later on loses flagella and gets covered by a thick wall and is now
called zygospore.

Anisogamy
 In anisogamous reproduction the gametes are unequal in size.
 The male gametes or microgametes are smaller, the female gametes
or macrogainetes are larger.
 The macrogametes are formed in female gametangium in which the
protoplast divides to make 2 to 4 gametes only.
 The microgametes are formed in male gametangium where the
protoplast divides to make 8-16 gametes. The microgametes are
more active than macrogametes.
 The microgametes come close to the macrogamete, the protoplast of
microgamete enters into macrogamete and after fusion a diploid
zygote is formed. The zygote secretes a thick wall and transforms
into zygospore.

Anisogamy
Chlamydomonas Anisogamous
reproduction
Diploid
nucleus
Zygote
Anisogamy
Microgamete
Macrogamete
Male gametangium
Female gametangium

Oogamy
 The oogamous sexual reproduction takes place in C. coccifera and C.
ooganum.
 The vegetative thallus functioning as female cell withdraws its
flagella and directly functions as non-motile macrogamete or egg.
 The microgametes are formed by four divisions of protoplast as in
case of anisogamous reproduction.
 The microgamete reaches the female gamete and unites by anterior
ends.
 The contact wall between the two dissolves. After plasmogamy and
karyogamy a diploid zygote is formed.
 The zygote secretes a thick wall and transforms into zygospore.

Chlamydomonas Oogamous reproduction
Antheridiu
m
Antherozoid Antherozoids
Oogonium

Zygote/Zygospore
 The zygote is resting diploid spore. The zygote secretes a thick wall which is
smooth or ornamented.
 The zygote accumulates large amount of oils and starch.
 The zygospore survives long period of unfavorable conditions and germinates
on approach of favourable season.
 When the resting period is over and the favourable conditions reappear the
zygospore germinates.
 Its diploid nucleus divides by meiosis to make four haploid nuclei which are
called as haploid zoospores or meiozoospores.
 Each zoospore contains neuro-motor apparatus, eye spot, two flagella and
contractile vacuoles.
 In 4 zoospores two may be of (+) type and two (-) type in heterothallic forms.

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