Q1: Describe the habit, structure and differentiation of cells in ... - CEC
Q1: Describe the habit, structure and differentiation of cells in ... - CEC
Q1: Describe the habit, structure and differentiation of cells in ... - CEC
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<strong>Q1</strong>: <strong>Describe</strong> <strong>the</strong> <strong>habit</strong>, <strong>structure</strong> <strong>and</strong> <strong>differentiation</strong> <strong>of</strong> <strong>cells</strong> <strong>in</strong> <strong>the</strong> filament <strong>of</strong><br />
Oedogonium.<br />
Ans. Oedogonium thallus is a long, unbranched, filamentous <strong>structure</strong><br />
consist<strong>in</strong>g <strong>of</strong> a s<strong>in</strong>gle row <strong>of</strong> elongated, cyl<strong>in</strong>drical <strong>cells</strong> arranged end to<br />
end. The filament usually occurs attached with <strong>the</strong> substratum at <strong>the</strong><br />
lower end by means <strong>of</strong> a basal cell, <strong>the</strong> rhizoidal cell or holdfast,<br />
exp<strong>and</strong>ed <strong>in</strong>to a flattened disc with outgrowths. Certa<strong>in</strong> <strong>cells</strong> <strong>in</strong> every<br />
filament possess one or more r<strong>in</strong>g like mark<strong>in</strong>gs <strong>of</strong> hemicellulose at <strong>the</strong>ir<br />
distal ends are called cap <strong>cells</strong>. The free end <strong>of</strong> <strong>the</strong> distal <strong>cells</strong> <strong>of</strong> <strong>the</strong><br />
filament is broadly rounded <strong>in</strong> case <strong>of</strong> majority <strong>of</strong> <strong>the</strong> species. In few<br />
casces, however it ends <strong>in</strong> a f<strong>in</strong>e, slender, hairlike process (O. ciliata )<br />
Q2: Give an account <strong>of</strong> <strong>the</strong> vegetative <strong>structure</strong> <strong>and</strong> modes <strong>of</strong> reproduction <strong>in</strong><br />
Oedogonium.<br />
Ans. The plant body is thallus <strong>in</strong> <strong>habit</strong>. The thallus is filamentous,<br />
unbranched consists <strong>of</strong> s<strong>in</strong>gle now <strong>of</strong> elongated, cyl<strong>in</strong>drical <strong>cells</strong>. The<br />
filaments rema<strong>in</strong> attached with <strong>the</strong> substratum by means <strong>of</strong> rhizoidal cell<br />
or holdfast.<br />
It reproduces vegetatively by fragmentation, asexually by zoospore<br />
<strong>and</strong> ak<strong>in</strong>ete formation <strong>and</strong> sexually by advanced oogamy.<br />
Q3: How are ak<strong>in</strong>etes different from zoospores <strong>in</strong> Oedogonium ?<br />
Ans: Ak<strong>in</strong>etes are thick walled, reddish brown, more or less rounded,<br />
non- motile <strong>structure</strong>s, develop with <strong>the</strong> approach <strong>of</strong> unfavorable period<br />
for vegetat<strong>in</strong>g growth.<br />
The mature zoospore is surrounded by a delicate mucilag<strong>in</strong>ous<br />
vesicle. It has a r<strong>in</strong>g <strong>of</strong> short flagella at <strong>the</strong> base <strong>of</strong> <strong>the</strong> colourless beak.<br />
The liberated zoospores are deep green, spherical or pear shaped<br />
<strong>structure</strong>.<br />
Q4: What are suffultory <strong>cells</strong>?<br />
Ans: Suffultory <strong>cells</strong> subtend <strong>the</strong> oogonium <strong>in</strong> <strong>the</strong> Oedogonium thallus.
These <strong>cells</strong> rema<strong>in</strong> undivided. In some species, <strong>the</strong>se <strong>cells</strong> aga<strong>in</strong><br />
function as oogonium mo<strong>the</strong>r <strong>cells</strong> <strong>and</strong> undergo fur<strong>the</strong>r segmentation to<br />
form a cha<strong>in</strong> <strong>of</strong> two, three or four oogonia. In <strong>the</strong> monoecious species,<br />
<strong>the</strong> suffultory <strong>cells</strong> may divide to give rise to an<strong>the</strong>ridia.<br />
Q5: The cell division <strong>in</strong> Oedogonium is peculiar <strong>and</strong> unique. Elaborate <strong>the</strong><br />
statement.<br />
Ans. The mode <strong>of</strong> cell division is unique as it occurs <strong>in</strong> <strong>the</strong> follow<strong>in</strong>g way:<br />
Just before <strong>the</strong> cell division, a r<strong>in</strong>g-like scar is developed near <strong>the</strong> anterior<br />
end <strong>of</strong> <strong>the</strong> cell. The r<strong>in</strong>g gradually <strong>in</strong>creases <strong>in</strong> thickness <strong>and</strong> becomes<br />
grooved with <strong>the</strong> open part covered by <strong>the</strong> outer layer. In <strong>the</strong> next step <strong>the</strong><br />
nucleus <strong>of</strong> <strong>the</strong> parent cell divides <strong>in</strong>to two fallowed by <strong>the</strong> formation <strong>of</strong> a<br />
cytoplasmic stra<strong>in</strong>ed just below <strong>the</strong> anterior r<strong>in</strong>g. At <strong>the</strong> level <strong>of</strong> <strong>the</strong> r<strong>in</strong>g,<br />
<strong>the</strong> outer <strong>and</strong> <strong>the</strong> middle layers external to <strong>the</strong> groove rupture all round,<br />
permitt<strong>in</strong>g <strong>the</strong> thickened portion to be stretched out. Consequently, <strong>the</strong> cell<br />
elongates to about double its normal length. At <strong>the</strong> same time, <strong>the</strong> septum<br />
is pushed upwards <strong>and</strong> f<strong>in</strong>ally becomes fixed near <strong>the</strong> lower end <strong>of</strong> <strong>the</strong><br />
<strong>in</strong>tercalated membrane. Thus upper daughter cell thus formed has now a<br />
new bound<strong>in</strong>g wall. As successive divisions always occur at <strong>the</strong> same<br />
place, a number <strong>of</strong> apical r<strong>in</strong>gs develop <strong>the</strong>re, giv<strong>in</strong>g a characteristic<br />
striated appearance to <strong>the</strong> cap <strong>cells</strong>. Thus <strong>the</strong> number <strong>of</strong> apical r<strong>in</strong>gs <strong>the</strong><br />
cap cell conta<strong>in</strong>s denotes <strong>the</strong> number <strong>of</strong> divisions <strong>the</strong> cell has undergone.<br />
Q6: <strong>Describe</strong> <strong>the</strong> germ<strong>in</strong>ation <strong>of</strong> zoospore?<br />
Ans. The liberated motile zoospores after settl<strong>in</strong>g down on some solid<br />
object, withdraws its flagella <strong>and</strong> secretes a cell wall, lacks <strong>the</strong> superficial<br />
chit<strong>in</strong>ous material. The colourless anterior end <strong>of</strong> zoospores develop <strong>in</strong> to a<br />
simple or branched holdfast. The one celled germl<strong>in</strong>g divides transversely<br />
by an apical r<strong>in</strong>g. The basal colourless cell does not divide aga<strong>in</strong>, where as<br />
<strong>the</strong> apical cell divides repeatidly to form <strong>the</strong> Oedogonium filament.<br />
Q7: Give an account <strong>of</strong> Macr<strong>and</strong>rous species <strong>of</strong> Oedogonium?<br />
Ans. Depend<strong>in</strong>g on <strong>the</strong> distribution <strong>of</strong> sex organs, <strong>the</strong> species <strong>of</strong>
Oedogonium are grouped <strong>in</strong>to two major categories, macr<strong>and</strong>rous <strong>and</strong><br />
nann<strong>and</strong>rous.<br />
Macr<strong>and</strong>rous: In <strong>the</strong> macr<strong>and</strong>rous species, an<strong>the</strong>ridia occur on filaments <strong>of</strong><br />
normal size. These may be (a) monoecius or (b) dioecious. In monoecius<br />
Macr<strong>and</strong>rous species both an<strong>the</strong>ridia <strong>and</strong> oogonia occur on <strong>the</strong> same<br />
filament which is, thus, bisexual where as <strong>in</strong> dioeceious species <strong>the</strong> sex<br />
organs occur <strong>in</strong> separate filaments are called Macr<strong>and</strong>rous dioeceious.<br />
Q8: What are Nann<strong>and</strong>rous species <strong>in</strong> Oedogonium?<br />
Ans. Some dioecious species <strong>of</strong> Oedogonium exhibit dimorphism. The<br />
male <strong>and</strong> <strong>the</strong> female filaments show dist<strong>in</strong>ct morphological differences. The<br />
an<strong>the</strong>ridia (a) are produced by special, much reduced male filaments called<br />
<strong>the</strong> dwarf male plants or nann<strong>and</strong>ria. The latter grow epiphytically attached<br />
to <strong>the</strong> female filaments.<br />
Q9: <strong>Describe</strong> <strong>the</strong> <strong>structure</strong> <strong>of</strong> an<strong>the</strong>ridia <strong>in</strong> Oedogonium with illustration?<br />
Ans: The an<strong>the</strong>ridia are flat, short, cyl<strong>in</strong>drical, disc-like <strong>cells</strong> or segments<br />
<strong>of</strong> <strong>the</strong> filament. They lie <strong>in</strong> a row or series, consist<strong>in</strong>g <strong>of</strong> a variable number<br />
<strong>of</strong> 2 to 40 <strong>cells</strong>. The contents <strong>of</strong> each an<strong>the</strong>ridium commonly develop <strong>in</strong>to<br />
two sperms, rarely <strong>in</strong>to one. The an<strong>the</strong>ridia are ei<strong>the</strong>r term<strong>in</strong>al or <strong>in</strong>tercalary<br />
<strong>in</strong> position. The an<strong>the</strong>ridia <strong>in</strong> <strong>the</strong> macr<strong>and</strong>rous species are developed by<br />
<strong>the</strong> rapid <strong>and</strong> repeated transverse divisions <strong>of</strong> a vegetative cell, called <strong>the</strong><br />
an<strong>the</strong>ridial mo<strong>the</strong>r cell. It is one <strong>of</strong> <strong>the</strong> cap <strong>cells</strong> (A). It divides <strong>in</strong>to two<br />
unequal <strong>cells</strong> (B), <strong>the</strong> upper much smaller an<strong>the</strong>ridium (a), <strong>and</strong> <strong>the</strong> lower<br />
larger sister cell (b). The sister cell divides aga<strong>in</strong> (C). The process is<br />
repeated a number <strong>of</strong> times, so that a row <strong>of</strong> an<strong>the</strong>ridia are formed. The<br />
protoplast with<strong>in</strong> each an<strong>the</strong>ridium commonly divides by a transverse or<br />
vertical wall to form two sperms.
Fig. 8(A-F) Odogonium: stages <strong>in</strong> <strong>the</strong> development <strong>of</strong> an<strong>the</strong>ridia <strong>and</strong> liberation <strong>of</strong><br />
an<strong>the</strong>rdiozooids<br />
<strong>Q1</strong>0: What are <strong>the</strong> structural <strong>and</strong> developmental features <strong>of</strong> oogonium? Give<br />
illustrations<br />
Ans. The oogonia are highly differentiated female gametangia. Each<br />
oogonium develops from an actively grow<strong>in</strong>g cap cell, called <strong>the</strong> oogonial<br />
mo<strong>the</strong>r cell. It divides by a transverse wall <strong>in</strong>to two daughter <strong>cells</strong>; <strong>the</strong> upper<br />
or distal one is richer <strong>in</strong> cytoplasm. It conta<strong>in</strong>s a larger nucleus than <strong>the</strong> lower<br />
<strong>and</strong> functions as an oogonium. The oogonium gets distended to form a rounded or<br />
oval <strong>structure</strong>. It always has one or more caps at <strong>the</strong> upper end (A). The lower or<br />
sister daughter cell forms <strong>the</strong> support<strong>in</strong>g cell or suffultory cell. It <strong>of</strong>ten rema<strong>in</strong>s<br />
undivided. In some species, it aga<strong>in</strong> functions as an oogonium mo<strong>the</strong>r cell <strong>and</strong><br />
undergoes fur<strong>the</strong>r segmentation to form a cha<strong>in</strong> <strong>of</strong> two, three or four oogonia. The
protoplast <strong>of</strong> <strong>the</strong> oogonium stores reserve food materials <strong>and</strong> forms a s<strong>in</strong>gle egg.<br />
In <strong>the</strong> macr<strong>and</strong>rous monoecious species,<br />
<strong>the</strong> an<strong>the</strong>ridia <strong>and</strong> oogonia are borne on <strong>the</strong> same<br />
filament. To ensure cross fertilisation <strong>the</strong><br />
an<strong>the</strong>ridia usually develop one day after than <strong>the</strong><br />
oogonia. The macr<strong>and</strong>rous dioecious species<br />
have <strong>the</strong> an<strong>the</strong>ridia <strong>and</strong> oogonia developed on<br />
dist<strong>in</strong>ct filaments.<br />
Fig. Oedogonium: development <strong>of</strong> oogonium (A <strong>and</strong> B)<br />
with <strong>the</strong> upper one <strong>in</strong> B ready for fertilization.