Q1: Describe the habit, structure and differentiation of cells in ... - CEC

Q1: Describe the habit, structure and differentiation of cells in the filament of
Oedogonium.
Ans. Oedogonium thallus is a long, unbranched, filamentous structure
consisting of a single row of elongated, cylindrical cells arranged end to
end. The filament usually occurs attached with the substratum at the
lower end by means of a basal cell, the rhizoidal cell or holdfast,
expanded into a flattened disc with outgrowths. Certain cells in every
filament possess one or more ring like markings of hemicellulose at their
distal ends are called cap cells. The free end of the distal cells of the
filament is broadly rounded in case of majority of the species. In few
casces, however it ends in a fine, slender, hairlike process (O. ciliata )
Q2: Give an account of the vegetative structure and modes of reproduction in
Oedogonium.
Ans. The plant body is thallus in habit. The thallus is filamentous,
unbranched consists of single now of elongated, cylindrical cells. The
filaments remain attached with the substratum by means of rhizoidal cell
or holdfast.
It reproduces vegetatively by fragmentation, asexually by zoospore
and akinete formation and sexually by advanced oogamy.
Q3: How are akinetes different from zoospores in Oedogonium ?
Ans: Akinetes are thick walled, reddish brown, more or less rounded,
non- motile structures, develop with the approach of unfavorable period
for vegetating growth.
The mature zoospore is surrounded by a delicate mucilaginous
vesicle. It has a ring of short flagella at the base of the colourless beak.
The liberated zoospores are deep green, spherical or pear shaped
structure.
Q4: What are suffultory cells?
Ans: Suffultory cells subtend the oogonium in the Oedogonium thallus.

These cells remain undivided. In some species, these cells again
function as oogonium mother cells and undergo further segmentation to
form a chain of two, three or four oogonia. In the monoecious species,
the suffultory cells may divide to give rise to antheridia.
Q5: The cell division in Oedogonium is peculiar and unique. Elaborate the
statement.
Ans. The mode of cell division is unique as it occurs in the following way:
Just before the cell division, a ring-like scar is developed near the anterior
end of the cell. The ring gradually increases in thickness and becomes
grooved with the open part covered by the outer layer. In the next step the
nucleus of the parent cell divides into two fallowed by the formation of a
cytoplasmic strained just below the anterior ring. At the level of the ring,
the outer and the middle layers external to the groove rupture all round,
permitting the thickened portion to be stretched out. Consequently, the cell
elongates to about double its normal length. At the same time, the septum
is pushed upwards and finally becomes fixed near the lower end of the
intercalated membrane. Thus upper daughter cell thus formed has now a
new bounding wall. As successive divisions always occur at the same
place, a number of apical rings develop there, giving a characteristic
striated appearance to the cap cells. Thus the number of apical rings the
cap cell contains denotes the number of divisions the cell has undergone.
Q6: Describe the germination of zoospore?
Ans. The liberated motile zoospores after settling down on some solid
object, withdraws its flagella and secretes a cell wall, lacks the superficial
chitinous material. The colourless anterior end of zoospores develop in to a
simple or branched holdfast. The one celled germling divides transversely
by an apical ring. The basal colourless cell does not divide again, where as
the apical cell divides repeatidly to form the Oedogonium filament.
Q7: Give an account of Macrandrous species of Oedogonium?
Ans. Depending on the distribution of sex organs, the species of

Oedogonium are grouped into two major categories, macrandrous and
nannandrous.
Macrandrous: In the macrandrous species, antheridia occur on filaments of
normal size. These may be (a) monoecius or (b) dioecious. In monoecius
Macrandrous species both antheridia and oogonia occur on the same
filament which is, thus, bisexual where as in dioeceious species the sex
organs occur in separate filaments are called Macrandrous dioeceious.
Q8: What are Nannandrous species in Oedogonium?
Ans. Some dioecious species of Oedogonium exhibit dimorphism. The
male and the female filaments show distinct morphological differences. The
antheridia (a) are produced by special, much reduced male filaments called
the dwarf male plants or nannandria. The latter grow epiphytically attached
to the female filaments.
Q9: Describe the structure of antheridia in Oedogonium with illustration?
Ans: The antheridia are flat, short, cylindrical, disc-like cells or segments
of the filament. They lie in a row or series, consisting of a variable number
of 2 to 40 cells. The contents of each antheridium commonly develop into
two sperms, rarely into one. The antheridia are either terminal or intercalary
in position. The antheridia in the macrandrous species are developed by
the rapid and repeated transverse divisions of a vegetative cell, called the
antheridial mother cell. It is one of the cap cells (A). It divides into two
unequal cells (B), the upper much smaller antheridium (a), and the lower
larger sister cell (b). The sister cell divides again (C). The process is
repeated a number of times, so that a row of antheridia are formed. The
protoplast within each antheridium commonly divides by a transverse or
vertical wall to form two sperms.

Fig. 8(A-F) Odogonium: stages in the development of antheridia and liberation of
antherdiozooids
Q10: What are the structural and developmental features of oogonium? Give
illustrations
Ans. The oogonia are highly differentiated female gametangia. Each
oogonium develops from an actively growing cap cell, called the oogonial
mother cell. It divides by a transverse wall into two daughter cells; the upper
or distal one is richer in cytoplasm. It contains a larger nucleus than the lower
and functions as an oogonium. The oogonium gets distended to form a rounded or
oval structure. It always has one or more caps at the upper end (A). The lower or
sister daughter cell forms the supporting cell or suffultory cell. It often remains
undivided. In some species, it again functions as an oogonium mother cell and
undergoes further segmentation to form a chain of two, three or four oogonia. The

protoplast of the oogonium stores reserve food materials and forms a single egg.
In the macrandrous monoecious species,
the antheridia and oogonia are borne on the same
filament. To ensure cross fertilisation the
antheridia usually develop one day after than the
oogonia. The macrandrous dioecious species
have the antheridia and oogonia developed on
distinct filaments.
Fig. Oedogonium: development of oogonium (A and B)
with the upper one in B ready for fertilization.