Download FAQs Q.1. Explain alternation of generations in Ectocarpus. Ans

FAQs
Q.1. Explain alternation of generations in
Ectocarpus.
Ans. There occur two distinct plant generations in the
life-cycle - the diploid sporophyte and the haploid
gametophyte. The sporophyte bears both unilocular
and plurilocular sporangia. The unilocular sporangia
produce haploid meiozoospores and the plurilocular
sporangia
produce
diploid
zoospores.
The
meiozoospores, on germination, give rise to the
alternate haploid plant -the gametophytes. The diploid
zoospores, on the other hand, develop into other
sporophytes.
The
gametophyte
plants
bear
multicellular
reproductive
structures,
called
plurilocular gametangia. Each cell of these plurilocular
gametangia produces a single pyriform gamete. The
gametes from two different Ectocarpus plants fuse to
form a zygote, which on germination gives rise to
diploid or sporophyte plant. The sporophyte is diploid
plant whereas gametophyte is a haploid plant. These
two plant generations with different functions and
different genetic constitution regularly alternate with
each other in the life cycle. This is called alternation of
generations.
Q.2. Discuss distribution and occurrence of
Ectocarpus.
Ans. This marine alga is worldwide in distribution with
many species. A few of them (at least 6) have also
been reported to occur in fresh water.The marine
species are cosmopolitan in distribution, but are more
abundant in colder seas of temperate and polar
regions. The genus is common along the Atlantic coast
but scarce along the pacific coast. The algae occur as
lithophytes along coasts in littoral and sublittoral
zones. Some species occur in shallow water on the
sides of the tidal pool. Some species grow as
epiphytes on the other algal genera, especially on the
members of Fucales and Laminariales (e.g. E.
tomentosus); E. fasciculatus has been found growing
on fins of certain fishes (epizoic). Some species are
endophytic (E. dermonematis) or endozoic (E.
fasciculatus) (wholly or partly).
Q.3. Write briefly about plastid genome in
Ectocarpus.
Ans.The chloroplast genomes of Ectocarpus is circular,
has 139,954 base pairs and two inverted repeat
regions (IR). Gene content of the plastid consists of
139-148 protein-coding genes, 28-31 tRNA genes,
and 3 ribosomal RNA genes. The tRNA-Leu gene of E.
siliculosus lacks an intron. The cpDNA IRs contain two
ribosomal operons, encoding 16S, 23S and 5S rRNA.
E. siliculosus plastid genomes are predicted to encode
a total of 139 and 144 protein-coding genes, and 26
and 27 tRNA genes, respectively.
Q.4. Highlight the role of pheromones in sexual
reproduction of Ectocarpus.
Ans. Soon after release, the originally motile female
gametes begin to settle on a surface and start to
secrete a chemical signal -a pheromone. The biological
function of this pheromone is to improve the mating
efficiency by attracting the flagellated, motile male
gametes. The chemical structure of the chemical
signal has been established as 6-(1Z)-(butenyl)
cyclohepta-1,4-diene, popularly called as ectocarpene.
Q.5.What is clump formation?
Ans. During fertilization many male gametes encircle
the female gamete and get entangled by their anterior
large flagella. This stage is called clump formation.
Out of the many, only one male gamete fuses with the
female gamete and the remaining gametes go astray
and gradually get destroyed.
Q.6. Differentiate between zoospores and
meiozoospores.
Ans. The meiozoospores also called gonozoospores are
haploid spores formed by unilocular sporangia
developed on sporophyte plants. The plants developed
on the germination of these haploid meiozoospores
are gametophytes. The zoospores are diploid and
formed in plurilocular sporangia developed on
sporophyte plants. On germination they develop into
sporophyte plants.
Q.7. Discuss the fate of germination of zygote.
Ans. The zygote undergoes germination without any
reduction division and rest. On germination it
develops into a sporophytic (2n) plant, which is
morphologically similar to the haploid or gametophytic
plant. Diploid sporophyte in some species of
Ectocarpus (E. siliculosus) bears both unilocular and
plurilocular sporangia on the same plant where as
other species (E. reptans and E. confervoides)
produce only either of them.
Q.8. write briefly on the position and formation
of sporangia on dwarf or small species of
Ectocarpus.
Ans.In the small or dwarf species of Ectocarpus with
short erect threads, the sporangia may arise
terminally upon them as in E. faeroensis, but in such
other species they are borne directly on the prostrate
base, which is usually well- developed and may
branch so profusely as to become pseudoparenchymatous. Apart from the fertile branches, it
may bear ordinary photosynthetic threads which may
exhibit a trichothallic meristem and terminate in long
hairs. This pseudo-parenchymatous disc then bears
only plurilocular sporangia with unicellular stalks.
Q.9. Illustrate with the help of diagram isogamy
in Ectocarpus.
Ans. In isogamy the
male
and
female
gametes
which
are
morphologically similar,
fuse to form the diploid
zygote
which
germinates
to
sporophyte.
Fig.10. Isogamy in Ectocarpus