Question: 100% NCERT covered from Particular Keyword.Explanations are 100% from NCERT | [Difficult level: Easy] From NCERT NEET Derived Question.
What is the number and positions of insertions of flagella in class Rhodophyceae?
(a) 2 – 8, equal, apical
(b) 2, unequal, lateral
(c) 2 – 6, equal, lateral
(d) Absent
Answer: (d) Absent
Flagella
👉A rod shaped
bacterium showing flagella
👉KINGDOM PROTISTA
All single-celled eukaryotes are placed under Protista, but the boundaries
of this kingdom are not well defined. What may be ‘a photosynthetic
protistan’ to one biologist may be ‘a plant’ to another. In this book we
include Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and
Protozoans under Protista. Members of Protista are primarily aquatic.
This kingdom forms a link with the others dealing with plants, animals
and fungi. Being eukaryotes, the protistan cell body contains a well defined
nucleus and other membrane-bound organelles. Some have flagella or
cilia. Protists reproduce asexually and sexually by a process involving
cell fusion and zygote formation.
👉Dinoflagellates
These organisms are mostly marine and photosynthetic.
They appear yellow, green, brown, blue or red depending
on the main pigments present in their cells. The cell wall
has stiff cellulose plates on the outer surface. Most of
them have two flagella; one lies longitudinally and the
other transversely in a furrow between the wall plates.
Very often, red dinoflagellates (Example: Gonyaulax)
undergo such rapid multiplication that they make the
sea appear red (red tides). Toxins released by such large
numbers may even kill other marine animals such as
fishes.
👉Euglenoids
Majority of them are fresh water organisms found in
stagnant water. Instead of a cell wall, they have a protein
rich layer called pellicle which makes their body flexible.
They have two flagella, a short and a long one. Though
they are photosynthetic in the presence of sunlight, when
deprived of sunlight they behave like heterotrophs by
predating on other smaller organisms. Interestingly, the
pigments of euglenoids are identical to those present in
higher plants. Example: Euglena
👉Flagellated protozoans: The members of this group are either free-living
or parasitic. They have flagella. The parasitic forms cause diaseases such
as sleeping sickness. Example: Trypanosoma.
👉Phaeophyceae
The members of phaeophyceae or brown algae are found primarily in
marine habitats. They show great variation in size and form. They range
from simple branched, filamentous forms (Ectocarpus) to profusely
branched forms as represented by kelps, which may reach a height of
100 metres. They possess chlorophyll a, c, carotenoids and xanthophylls.
They vary in colour from olive green to various shades of brown depending
upon the amount of the xanthophyll pigment, fucoxanthin present in
them. Food is stored as complex carbohydrates, which may be in the
form of laminarin or mannitol. The vegetative cells have a cellulosic wall
usually covered on the outside by a gelatinous coating of algin. The
protoplast contains, in addition to plastids, a centrally located vacuole
and nucleus. The plant body is usually attached to the substratum by a
holdfast, and has a stalk, the stipe and leaf like photosynthetic organ –
the frond. Vegetative reproduction takes place by fragmentation. Asexual
reproduction in most brown algae is by biflagellate zoospores that are
pear-shaped and have two unequal laterally attached flagella.
Sexual reproduction may be isogamous, anisogamous or oogamous.
Union of gametes may take place in water or within the oogonium
(oogamous species). The gametes are pyriform (pear-shaped) and bear
two laterally attached flagella. The common forms are Ectocarpus, Dictyota,
Laminaria, Sargassum and Fucus
👉
👉Bacterial cells may be motile or non-motile. If motile, they have thin
filamentous extensions from their cell wall called flagella. Bacteria show a
range in the number and arrangement of flagella. Bacterial flagellum is
composed of three parts – filament, hook and basal body. The filament
is the longest portion and extends from the cell surface to the outside.
👉Besides flagella, Pili and Fimbriae are also surface structures of the
bacteria but do not play a role in motility. The pili are elongated tubular
structures made of a special protein. The fimbriae are small bristle like
fibres sprouting out of the cell. In some bacteria, they are known to help
attach the bacteria to rocks in streams and also to the host tissues.
👉Cilia and Flagella
Cilia (sing.: cilium) and flagella (sing.: flagellum) are hair-like outgrowths
of the cell membrane. Cilia are small structures which work like oars,
causing the movement of either the cell or the surrounding fluid. Flagella
are comparatively longer and responsible for cell movement. The
prokaryotic bacteria also possess flagella but these are structurally
different from that of the eukaryotic flagella.
The electron microscopic study of a cilium or the flagellum show that
they are covered with plasma membrane. Their core called the axoneme,
possesses a number of microtubules running parallel to the long axis.
The axoneme usually has nine doublets of radially arranged peripheral
microtubules, and a pair of centrally located microtubules. Such an
arrangement of axonemal microtubules is referred to as the 9+2 array
(Figure 8.10). The central tubules are connected by bridges and is also
enclosed by a central sheath, which is connected to one of the tubules of
each peripheral doublets by a radial spoke. Thus, there are nine radial
spokes. The peripheral doublets are also interconnected by linkers. Both
the cilium and flagellum emerge from centriole-like structure called the
basal bodies.
👉
👉Centrosome and Centrioles
Centrosome is an organelle usually containing two cylindrical structures
called centrioles. They are surrounded by amorphous pericentriolar
materials. Both the centrioles in a centrosome lie perpendicular to each
other in which each has an organisation like the cartwheel. They are
made up of nine evenly spaced peripheral fibrils of tubulin protein. Each
of the peripheral fibril is a triplet.The adjacent triplets are also linked.
The central part of the proximal region of the centriole is also proteinaceous
and called the hub, which is connected with tubules of the peripheral
triplets by radial spokes made of protein. The centrioles form the basal
body of cilia or flagella, and spindle fibres that give rise to spindle
apparatus during cell division in animal cells.
👉Centrosome and centriole
form the basal body of cilia and flagella that facilitate locomotion.
👉Movement of cilia, flagella and tentacles are shown by many organisms
👉Flagellar movement helps in the swimming of
spermatozoa, maintenance of water current in the canal system of sponges
and in locomotion of Protozoans like Euglena.
