Biological Classification 3 Flashcards
describe phycomycetes
Members of phycomycetes are found in aquatic habitats
and on decaying wood in moist and damp places or as
obligate parasites on plants. The mycelium is aseptate
and coenocytic. Asexual reproduction takes place by
zoospores (motile) or by aplanospores (non-motile). These
spores are endogenously produced in sporangium. A
zygospore is formed by fusion of two gametes. These
gametes are similar in morphology (isogamous) or
dissimilar (anisogamous or oogamous). Some common
examples are Mucor (Figure 2.5a), Rhizopus (the bread
mould mentioned earlier) and Albugo (the parasitic fungi
on mustard).
describe ascomycetes
Commonly known as sac-fungi, the ascomycetes are mostly
multicellular, e.g., Penicillium, or rarelyunicellular, e.g., yeast
(Saccharomyces). They are saprophytic, decomposers,
parasitic or coprophilous (growing on dung). Mycelium is branched and septate. The asexual spores are conidia produced
exogenously on the special mycelium called conidiophores. Conidia on
germination produce mycelium. Sexual spores are called ascospores
which are produced endogenously in sac like asci (singular ascus). These
asci are arranged in different types of fruiting bodies called ascocarps.
Some examples are Aspergillus (Figure 2.5b), Claviceps and Neurospora.
Neurospora crassa is used extensively in biochemical and genetic work. Many
members like morels and truffles are edible and are considered delicacies.
explain conidia
conidia are borne exogenously. conidia are present on an erect hypae called conidiophore
explain ascomycetes sexual repro
The ascomycetes have fruiting bodies called ascocarps which bear sac like structures called ascus which undergo meiotic division to give rise to haploid ascospores endogenously
describe basidiomycetes
Commonly known forms of basidiomycetes are mushrooms, bracket fungi
or puffballs. They grow in soil, on logs and tree stumps and in living
plant bodies as parasites, e.g., rusts and smuts. The mycelium is branched
and septate. The basidia are
arranged in fruiting bodies called basidiocarps. Some common members
are Agaricus (mushroom) (Figure 2.5c), Ustilago (smut) and Puccinia (rust
fungus).
explain repro in basidiomycetes
The asexual spores are generally not found, but vegetative
reproduction by fragmentation is common. The sex organs are absent,
but plasmogamy is brought about by fusion of two vegetative or somatic
cells of different strains or genotypes. The resultant structure is dikaryotic
which ultimately gives rise to basidium. Karyogamy and meiosis take
place in the basidium producing four basidiospores. The basidiospores
are exogenously produced on the basidium (pl.: basidia).The basidia are
arranged in fruiting bodies called basidiocarps.
explain basic features of deuteromycetes
Commonly known as imperfect fungi because only the asexual or
vegetative phases of these fungi are known. The deuteromycetes reproduce only by asexual spores
known as conidia. The mycelium is septate and branched. Some members
are saprophytes or parasites while a large number of them are
decomposers of litter and help in mineral cycling. Some examples are
Alternaria, Colletotrichum and Trichoderma.
explain repro of deuteromycetes
When the sexual forms of
these fungi were discovered they were moved into classes they rightly
belong to. It is also possible that the asexual and vegetative stage have
been given one name (and placed under deuteromycetes) and the sexual
stage another (and placed under another class). Later when the linkages
were established, the fungi were correctly identified and moved out of
deuteromycetes. Once perfect (sexual) stages of members of
dueteromycetes were discovered they were often moved to ascomycetes
and basidiomycetes
give the history of viruses
Louis Pasteur gave the name virus meanign venom or poisonoous fluid.
Dmitri Ivanowsky (1892)
recognised certain microbes as causal organism of the mosaic disease of
tobacco (Figure 2.6a). These were found to be smaller than bacteria
because they passed through bacteria-proof filters.
M.W. Beijerinek
(1898) demonstrated that the extract of the infected plants of tobacco
could cause infection in healthy plants and named the new pathogen
“virus” and called the fluid as Contagium vivum fluidum (infectious living
fluid).
W.M. Stanley (1935) showed that viruses could be crystallised
and crystals consist largely of proteins. They are inert outside their specific
host cell. Viruses are obligate parasites
what are viruses
The viruses are non-cellular organisms that are
characterised by having an inert crystalline structure outside the living cell.Once they infect a cell they take over the machinery of the host cell to replicate
themselves, killing the host.
what genetic material does virus have
In addition to proteins, viruses also contain genetic material, that could
be either RNA or DNA. No virus contains both RNA and DNA. A virus is
a nucleoprotein and the genetic material is infectious. In general, viruses
that infect plants have single stranded RNA and viruses that infect animals
have either single or double stranded RNA or double stranded DNA.
Bacterial viruses or bacteriophages (viruses that infect the bacteria) are
usually double stranded DNA viruses
describe the structure of the protein coat
The protein coat
called capsid made of small subunits called capsomeres, protects the
nucleic acid. These capsomeres are arranged in helical or polyhedral
geometric forms. Viruses cause diseases like mumps, small pox, herpes
and influenza. AIDS in humans is also caused by a virus. In plants, the
symptoms can be mosaic formation, leaf rolling and curling, yellowing
and vein clearing, dwarfing and stunted growth.
describe viriods
: In 1971, T.O. Diener discovered a new infectious agent that
was smaller than viruses and caused potato spindle tuber disease. It was
found to be a free RNA; it lacked the protein coat that is found in viruses,
hence the name viroid. The RNA of the viroid was of low molecular weight.
describe prions
In modern medicine certain infectious neurological diseases
were found to be transmitted by an agent consisting of abnormally folded
protein. The agent was similar in size to viruses. These agents were called
prions. The most notable diseases caused by prions are bovine spongiform
encephalopathy (BSE) commonly called mad cow disease in cattle and
its analogous variant Cr–Jacob disease (CJD) in humans.
describe structure of lichen
Lichens are symbiotic associations i.e. mutually useful
associations, between algae and fungi. The algal component is known as
phycobiont and fungal component as mycobiont, which are autotrophic
and heterotrophic, respectively.
