Download Vaucheria

Frequently asked questions
Q. 1. Write a concise note on the occurrence of
Vaucheria.
Ans. Vaucheria grows on moist sand, soil, and salt marsh
banks, sometimes forming dark green mats, or is found
submerged
in
shallow
freshwater
or
marine
environments. It is common in streams, rivers, ponds,
lakes, ditches, and seeps. Growth is especially abundant
in waters with high nutrient levels, such as downstream
habitats affected by runoff and nutrient loading from
human land use. The genus is most often found in the
cooler months between fall and late spring. Some species
are habitat-specific, inhabiting only shallow lakes and
ponds or the mud of ditches and bogs, while others are
known from diverse habitats
Q. 2. Describe the external morphology of Vaucheria?
Ans. The plant body of Vaucheria consists of an aseptate,
tubular, siphonaceous, irregularly branched, coenocytic
filament. It is usually attached to the substratum by
means of a branched, colourless holdfast.
Q. 3. Discuss, in brief, the thallus structure of Vaucheria?
Ans. Vaucheria consists of thin, weak and inelastic wall.
It is composed of inner layer of cellulose and outer layer
of
pectic
substances.
Within
the
wall
it
contains
continuous layer of cytoplasm. The cytoplasm contains all
the essential cell organelles like mitochondria, small
vesicles,
chloroplast,
vacuole,
chromatophores,
innumerable minute nuclei. The cytoplasm of Vaucheria is
pushed to the cell periphery by large vacuole.The
chromatophores contain chlorophyll a, chlorophyll e,
carotenoids.Chlorophyll b is absent.Thallus is coenocytic.
Q. 4. Write a short note on cytoplasmic streaming in
Vaucheria?
Ans. It has been found that chloroplasts of Vaucheria are
accompanied by small vesicles and mitochondria, with
the streaming of cytoplasm along the longitudinal axis of
the
filament
in
dark.
In
Vaucheria,
longitudinally-
oriented cytoplasmic fibrils have been observed on the
cortical region of the cytoplasm in V. sessils. Feeble light
intensity causes the chloroplast to move into position to
receive maximum illumination and in high light intensity
they
are
provided
illumination.
The
with
device
photoreceptors
to
of
receive
light
minimal
oriented
movement of chloroplast are present in the cytoplasm
rather than in the chloroplast.
Q. 5. Is Vaucheria a unicellular or multi-cellular alga,
Explain?
Ans. Vaucheria possesses all the essentials of a multicellular organism, but the cytoplasm and the numerous
nuclei are not partitioned into distinct cells. The septa
remain suppressed in the vegetative condition. They
appear only during the formation of reproductive organs,
or when the filament is injured. Also in unicellular forms,
growth consists in increase in the size of the entire cell.
In Vaucheria growth is apical, where the cytoplasm is
colour-less and transparent. It is thus more appropriate
to call Vaucheria, in general, as an acellular, coenocytic
organism rather than a unicellular or multi-cellular form.
Q.
6.What
are
the
different
modes
of
asexual
reproduction found in Vaucheria?
Ans. In Vaucheria, asexual reproduction occurs entirely
by the method of sporulation. It occurs by the formation
of zoospores, aplanospores and akinetes, depending upon
the habitat in which alga lives.
When aquatic and terrestrial species of Vaucheria are
exposed to greater desiccation or low temperature, the
branched filaments divide into row of short segments by
thick, gelatinous cross walls. Their protoplast becomes
laden with oil. These resting, multinucleate thick- walled
segments are called the cysts, hypnospores or akinetes.
The cyst in a chain may remain connected by the parent
membrane of the filament, which appears like another
alga Gongrosira. Thus this stage of Vaucheria is also
called Gongrosira stage.
Q. 7. Write short note on synzoospores?
Ans. Zoospore formation is the commonest method of
asexual reproduction in aquatic forms. Zoospores are
large, multinucleate and multiflagellate structures. They
are
formed
singly
within
elongated,
club-shaped
zoosporangia, which develop at the end of side branch.
The
zoosporangia
get
swollen
into
a
club-shaped
structure. A large number of nuclei and chloroplasts
along with cytoplasm stream into and accumulate in the
swollen tip before it is separated from rest of the filament
by a transverse septum. The zoospore of Vaucheria is a
compound structure which is formed as a result of the
failure of the protoplast within the zoosporangium to
divide into uninucleate, biflagellate zoospores. Such a
compound structure is called synzoospore.
Q. 8. Write a precise note on sexual reproduction in
Vaucheria?
Ans. In Vaucheria, sexual reproduction is of oogamous
type. The male and female gametes are produced in
specialized sex organs. The antheridia produce numerous
colorless
uninucleate
sperms;
while
each
oogonium
develops a single uninucleate egg. These reproductive
structures may develop on special branches or on the
main thallus. The sperm unite with the egg within the
oogonium to form a thick-walled zygote. It is a resting
spore. After the dormant period, it under goes zygotic
meiosis and germinates to give rise to the new haploid
Vaucheria
meiospores.
filament
without
the
intervention
of