Ultra structure and reproductive nature of Chlamydomonas

2. KINGDOM : Plantae
CLASS : Chlorophyceae
ORDER : Volvocales
FAMILY : Chlamydomonadaceae
GENUS : Chlamydomonas

3. Chlamydomonas is one of the most primitive genus comprises
of about 350species and is unicellular, spherical in shape
Distributed and grows very well in stagnant water, pools,
ponds and ditches.
Chlamydomonas nivalis imparts red coloration to the
substratum causing “ Red snow” in alpine and arctic regions.
Chlamydomonas yellowstonensis is found in the yellow stone
National park of America where the snow gets yellow
coloration.
A drop of fresh pond water observed under the microscope
show hundreds of these structures moving to and fro in the
field of the microscope.

4. The cell wall is made up of seven layers which is thickened and
stratified at the anterior end.
A pectose layer external to the cell wall is called as capsule layer.
The plasma membrane internal to the cell wall is made by lip of
two opaque layers separated by a less opaque zone.
There are two flagella and each flagellum is attached to a basal
granule or blepheroplast.
Each flagellum consists of eleven fibrils with typical 9+2
arrangement.
The two central fibrils are single fibrils, while the nine peripheral
fibrils are double fibrils.

5. The two granules are joined by thin protoplasmic fibrils known as “
Paradesmos”.
One of the basal granules is connected to the central nucleus by a
thread called “ Rhizoplast”.
The nucleus regulates the flagellar movement through the rhizoplast.
The entire structure is given the name “Neuromotor apparatus”.
Near the basal granule there are two contractile vacuoles, which are
osmoregulatory in function.
A little away from the vacuole is the stigma or eyespot, which is orange
red in colour.
The stigma possesses a lens which is thick as cell wall and is
photosensitive in function.

6. The eyespot is composed of two or three parallel rows of fat droplets
called granules.
The function of stigma is photoreception.
If a beam of intense light is made to fall on the stigmatic surface it is
observed that the cell swims away from light.
The stigma is situated within the chloroplast.
Towards the broader end of the cell occupying ¾ the area is a large cup
shaped chloroplast with a centrally placed pyrenoid.
The chloroplast has a double membrane envelope containing lamellae
arranged in the form of stacks.
The stacks form the grana and the matrix constitutes the stroma.
The chloroplast matrix contains DNA, Ribosome and microtubules.

7. The pyrenoid consists of
a central protein body
surrounded by a number
of starch grains, the
number of pyrenoids
ranges from one to many
Filling the cup of the
chloroplast is the
cytoplasm.
A single nucleus lies in
the cytoplasm.
Nutrition is autotrophic.

8. ASEXUAL REPRODUCTION
ZOOSPORE FORMATION
During rainy season, when there is
sufficient moisture zoospores are formed.
The flagella are usually discarded and
the cell becomes non motile.
The contractile vacuoles disappear and
the protoplast divides
The protoplast divides several times
producing 2-16 bits of small protoplasts.
Each bit secretes its own wall and
develops two flagella.
Contractile vacuoles and pigments
also appear forming a full fledged
zoospore.
The parent cell wall at this stage
ruptures liberating the zoospores.
The zoospores swim about in water
and develop into new individuals.
A single cell of Chlamydomonas would
produce two lakhs individuals.

9. ASEXUAL REPRODUCTION - APLANOSPORES
If conditions are not
favorable for
the formation of
zoospores the bits
of protoplasts may round
up and
envelope themselves
with thick wall
and develop into
aplanospores.
If there is no water the
They may either germinate directly into a new plant or
produce zoospores at the return of the favorable season.

10. ASEXUAL REPRODUCTION – PALMELLA STAGE
When the pond is drying up the cells
living in damp soil divide but the
protoplasts do not form, flagella.
They remain inactive within the parent
cell.
All the daughter cells get surrounded
by mucilage which protects these cells
from desiccation.
These daughter cells may divide further
producing large number of cells.
In this way, a large number of small
non – motile cells may be formed
covered by the gelatinous mucilage
resembling a large colony.
This stage is known as the palmella stage.
At the favorable season the mucilage wall dissolves, the daughter cells become
motile and develop into new individuals.

11. SEXUAL REPRODUCTION
Sexual reproduction is highly variable.
Low nitrogen content favors gamete formation.
Chlamydomonas exhibits three
types of Sexual reproduction namely
1. Isogamy
2. Anisogamy
3. Oogamy
The gametes with cell wall is called as Cryptogametes
The gametes without cell wall is called as Gymnogametes.

12. SEXUAL REPRODUCTION - ISOGAMY
Iso = Similar, gamy = fusion
The protoplast of the cell
divides to form
32 or 64 biflagellate gametes,
all gametes
are similar in size and
structure.
Generally isogametes
produced from
different parent cells fuse.

13. SEXUAL REPRODUCTION - ANISOGAMY
The gametes that take part in
fusion are different in size. Usually
one cell produces large number of
smaller gametes while another
produces less number of large
sized gametes. One large and one
small gamete fuse resulting in the
formation of zygote.

14. SEXUAL REPRODUCTION - OOGAMY
In this type, one cell produces
only one large non – motile
female gamete (Egg) which
does not come out of the cell.
In another cell, functioning as
male, small but large number
of motile male gametes are
formed.
The cell wall ruptures and
male gametes are released
into water.
They approach the female and
fuse with the egg forming the
zygote.

15. DEVELOPMENT AND GERMINATION OF
ZYGOSPORE
The zygospore develops a thick wall and
undergoes a period of rest. It generally
sinks to the bottom of the pond and
develops haematochrome pigment so that
it looks red in color. The zygospore will be
rich in reserve food material, particularly
fat is abundant. The zygospore consists of
a diploid nucleus. At the favorable season
the nucleus undergoes meiosis forming
four haploid nuclei.
Meanwhile, the protoplasm also divides into four bits each incorporating one
nucleus. Each bit eventually develops into a zoospore. The zygospore wall cracks
open releasing the zoospores. The zoospores swim about and develop into new
individuals.

16. REPRODUCTION OF
CHLAMYDOMONAS