Biological Classification 2 Flashcards
explain general features of protistans
All single-celled eukaryotes are placed under Protista, but the boundaries
of this kingdom are not well defined.
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.
describe chrysophytes
This group includes diatoms and golden algae (desmids). They are found
in fresh water as well as in marine environments. They are microscopic
and float passively in water currents (plankton). Most of them are
photosynthetic. In diatoms the cell walls form two thin overlapping shells,
which fit together as in a soap box. The walls are embedded with silica
and thus the walls are indestructible. After the diatoms die, theiry decompose but cell walls remain intact and get accumulated; this accumulation over
billions of years is referred to as ‘diatomaceous earth’. Being gritty this
soil is used in polishing, filtration of oils and syrups. Diatoms are the
chief ‘producers’ in the oceans.
describe 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, giving an armoured appearance.
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.They release neurotoxins that paralyse the fishes and other animals.
describe 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 one tucked inside the cell and a long one, protruding out. 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
describe slime moulds
Slime moulds are saprophytic protists. The body moves
along decaying twigs and leaves engulfing organic
material.
Under suitable conditions, they form an multinucleated
aggregation called plasmodium which may grow and
spread over several feet.
During unfavourable conditions,
the plasmodium differentiates and forms fruiting bodies
bearing spores at their tips.
The spores possess true walls.
They are extremely resistant and survive for many years,
even under adverse conditions. The spores are dispersed
by air currents.
introduce protozoans
All protozoans are heterotrophs and live as predators or
parasites. They are believed to be primitive relatives of
animals. There are four major groups of protozoans.
describe ameoboid organisms
These organisms live in fresh
water, sea water or moist soil. They move and capture their prey by putting out pseudopodia (false feet) as in Amoeba. Marine
forms have silica shells on their surface. Some of them such as Entamoeba
are parasites.
They may be freeliving and parasite.
describe 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.
describe ciliated protozoans
These are aquatic, actively moving organisms because
of the presence of thousands of cilia. They have an oral cavity (gullet) that opens
to the outside of the cell surface. The coordinated movement of rows of
cilia causes the water laden with food to be steered into the gullet. Example:
Paramoecium
describe sporozoans
This includes diverse organisms that have an infectious
spore-like stage in their life cycle.They have multiple nuclei enclosed in a cyst.The most notorious is Plasmodium
(malarial parasite) which causes malaria, a disease which has a staggering
effect on human population.
describe the basic features of fungi
With the exception of yeasts which are unicellular, fungi are
filamentous. Their bodies consist of long, slender thread-like structures
called hyphae. The network of hyphae giving a mat-like appearance is known as mycelium. Some hyphae
are continuous tubes filled with multinucleated cytoplasm – these are
called coenocytic hyphae. Others have septae or cross walls in their
hyphae. The cell walls of fungi are composed of chitin and polysaccharides.
what is mode of nutrition of fungi
Most fungi are heterotrophic and absorb soluble organic matter from
dead substrates and hence are called saprophytes. Those that depend
on living plants and animals are called parasites. They can also live as
symbionts – in association with algae as lichens and with roots of higher
plants as mycorrhiza.
what is mode of reproduction of fungi
Reproduction in fungi can take place by vegetative means –
fragmentation, fission and budding. Asexual reproduction is by spores called conidia or sporangiospores or zoospores, and sexual reproduction
is by oospores, ascospores and basidiospores. The various spores are
produced in distinct structures called fruiting bodies
what are the types of sexual reproduction
isogamy:
fusion of morphologically similar gametes
anisogamy
fusion of gametes whcih are not morphololigcally similar ( female larger)
oogamy:
fusion of gametes whcih are morphologically similar such tht female is larger and non motile while male is smaller and motile.
describe sexual reproduction in fungi
(i) Plasmogamy, during the onset of plasmogamy, two compatible hyphae come in close contact, putting forth protuberances, enabling the cross walls to dissolve for protoplasmic fusion called plasmogmay
Fusion of protoplasms between two motile or non-motile gametes
called plasmogamy.
(ii) Karyogmay- fusion of two haploid nuclei of the 2 compatible hyphae giving rise to diploid zygote.
(iii) Zygotic Meisosis:The diploid zygote undergos reductional divsion giving rise to haploid spores which gereminate under sutiable conditions giving rise to new mycelium.
