We are providing a clear cut notes on biological classification chapter 2 from NCERT BIOLOGY books,helpful for NEET,board examinations…etc
1️⃣ INTRODUCTION
✅Aristotle was the earliest to attempt a more scientific basis for classification. He used simple morphological characters to classify plants into trees, shrubs and herbs. He also divided animals into two groups, those which had red blood and those that did not.
✅Linnaeus’ classified a Two Kingdom system of classification with
Plantae and Animalia. drawback;This system did not distinguish between the eukaryotes and prokaryotes, unicellular and multicellular organisms
and photosynthetic (green algae) and non-photosynthetic (fungi)
organisms.
✅ R.H. Whittaker (1969) proposed a Five Kingdom Classification. The kingdoms defined by him were named Monera, Protista, Fungi, Plantae
and Animalia. The main criteria for classification used by him include cell
structure, body organisation, mode of nutrition, reproduction and
phylogenetic relationships.
In Five Kingdom Classification.All prokaryotic organisms were grouped
together under Kingdom Monera and the unicellular eukaryotic organisms
were placed in Kingdom Protista . Kingdom Protista has brought together
Chlamydomonas, Chlorella (earlier placed in Algae within Plants and both having cell walls) with Paramoecium and Amoeba (which were earlier placed in the animal kingdom which lack cell wall).
2️⃣ kingdom monera
●Bacteria are the sole members of the Kingdom Monera.
●They are the most abundant micro-organisms.
●Rigid cell wall of murein or peptidoglycan.
●Histones are absent. Ribosomes are of 70S type.
●Bacteria occur almost everywhere. Hundreds of bacteria are present in a handful of soil.
• They also live in extreme habitats such as hot springs,
deserts, snow and deep oceans where very few other life
forms can survive.
• Many of them live in or on other organisms as parasites.Some of the bacteria are
autotrophic,(they synthesise their own food from inorganic substrates.)
They may be photosynthetic autotrophic or chemosynthetic autotrophic.
•The vast majority of bacteria are heterotrophs(they depend on other
organisms or on dead organic matter for food.)
•Bacteria are grouped under four categories based on their shape: the
spherical Coccus (pl.: cocci), the rod-shaped Bacillus (pl.: bacilli), the
comma-shaped Vibrium (pl.: vibrio) and the spiral Spirillum (pl.: spirilla)
Archaebacteria
- These bacteria are live in some of the most harsh habitats
- CLASSIFICATION; extreme salty areas (halophiles), hot springs (thermoacidophiles) marshy areas (methanogens).
- Archaebacteria differ from other bacteria in having a different cell wall structure and this feature is responsible for
their survival in extreme conditions. Methanogens are present in the gut
of several ruminant animals such as cows and buffaloes and they are
responsible for the production of methane (biogas) from the dung of these
animals.
eubacteria
- There are thousands of different eubacteria means true
bacteria’. - They are characterised by the presence of a
rigid cell wall, and if motile, a flagellum - The cyanobacteria (also referred to as blue-green algae)
have chlorophyll a similar to green plants and are
photosynthetic autotrophs .The cyanobacteria are unicellular, colonial or filamentous, freshwater/marine or terrestrial algae. The colonies
are generally surrounded by gelatinous sheath. They
often form blooms in polluted water bodies. - Some of these organisms can fix atmospheric nitrogen in
specialised cells called heterocysts, e.g., Nostoc and
Anabaena. - Chemosynthetic autotrophic bacteria
oxidise various inorganic substances such as
nitrates, nitrites and ammonia and use the released
energy for their ATP production. They play a great role
in recycling nutrients like nitrogen, phosphorous,
iron and sulphur. - Heterotrophic bacteria are most abundant in
nature. The majority are important decomposers.
They are helpful in making curd from milk,
production of antibiotics, fixing nitrogen in legume. - Cholera, typhoid, tetanus, citrus canker are well
known diseases caused by different bacteria - Bacteria reproduce mainly by fission. Sometimes, under unfavourable conditions,they produce spores. They also reproduce by a
sort of sexual reproduction by adopting a primitive type of DNA transfer from one bacterium to the other.
The Mycoplasma are organisms that completely lack a cell wall. They are the smallest living cells known and can survive without oxygen
3️⃣ KINGDOM PROTISTA
- All single-celled eukaryotes are placed under Protista
- It include Chrysophytes, Dinoflagellates, Euglenoids,
Slime moulds and Protozoans.
- Members of Protista are primarily aquatic.
- This kingdom forms a link with the others dealing with plants, animals
and fungi - 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.
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.
- The walls are embedded with silica and thus the walls are indestructible.
- diatoms have left behind large amount of cell wall(silica) deposits in their habitat; 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.
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).
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.
- they are photosynthetic and heterotrophs .
- the pigments of euglenoids are identical to those present in
higher plants. Example: Euglena
Slime Moulds
Slime moulds are saprophytic protists. The body moves
along decaying twigs and leaves engulfing organic
material.The spores possess true walls.
The spores are dispersed
by air currents.
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,
▶️Amoeboid protozoans: 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. Eg:Entamoeba
▶️Flagellated protozoans: they are free-living
or parasitic. They have flagella. The parasitic forms cause diaseases such
as sleeping sickness. Example: Trypanosoma.
▶️Ciliated protozoans: These are aquatic, actively moving due to cilia. They have a cavity (gullet) that opens
to the outside of the cell surface. Example:Paramoecium
▶️Sporozoans: They are infectious
spore-like stage in their life cycle. The most notorious is Plasmodium
(malarial parasite) which causes malaria,
4️⃣ Kingdom Fungi
The fungi constitute a unique kingdom of heterotrophic organisms.
Some unicellular fungi, e.g., yeast are used to make bread and beer.
Other fungi cause diseases in plants and animals; wheat rust-causing Puccinia is an important example.
Some are the source of antibiotics, e.g., Penicillium. Fungi are cosmopolitan. They prefer to grow in warm and humid
places.
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 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.
Most fungi are heterotrophic and absorb soluble organic matter from
dead substrates and hence are called saprophytes. They can also live as
symbionts – in association with algae as lichens and with roots of higher
plants as mycorrhiza.
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.
Sexual reproduction includes
(i) Fusion of protoplasms between two motile or non-motile gametes called plasmogamy.
(ii) Fusion of two nuclei called karyogamy.
(iii) Meiosis in zygote resulting in haploid spores.
When a fungus reproduces sexually, two haploid
hyphae of compatible mating types come together and
fuse. In some fungi the fusion of two haploid cells
immediately results in diploid cells (2n), However, in other
fungi (ascomycetes and basidiomycetes), an interveningdikaryotic stage (n + n, i.e., two nuclei per cell) occurs;
such a condition is called a dikaryon and the phase is
called dikaryophase of fungus. Later, the parental nuclei
fuse and the cells become diploid. The fungi form fruiting
bodies in which reduction division occurs, leading to formation of haploid spores.
The morphology of the mycelium, mode of spore formation and fruiting bodies form the basis for the division of the kingdom into various classes.
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).
examples are Mucor, Rhizopus (the bread
mould mentioned earlier) and Albugo (the parasitic fungi
on mustard).
Ascomycetes
Commonly known as sac-fungi, the ascomycetes are mostly
multicellular, e.g., Penicillium, or rarely unicellular, 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.
examples Aspergillus, Claviceps and Neurospora.
Neurospora is used extensively in biochemical and genetic work. Many
members like morels and truffles are edible and are considered delicacies.
Basidiomycetes
Commonly known forms of basidiomycetes are mushrooms, bracket fungi
or puffballs. e.g., rusts and smuts. The mycelium is branched
and septate. 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. Some common members
are Agaricus (mushroom) Ustilago (smut) and Puccinia (rust
fungus).
Deuteromycetes
Commonly known as imperfect fungi because only the asexual or
vegetative phases of these fungi are known. 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. 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.
examples :Alternaria, Colletotrichum and Trichoderma.
5️⃣ Kingdom PLANTAE
Kingdom Plantae includes all eukaryotic chlorophyll-containing
organisms commonly called plants. A few members are partially
heterotrophic such as the insectivorous plants or parasites. Bladderwort
and Venus fly trap are examples of insectivorous plants and Cuscutais a
parasite. The plant cells have an eukaryotic structure with prominent
chloroplasts and cell wall mainly made of cellulose.
Life cycle of plants has two distinct phases — the diploid sporophytic
and the haploid gametophytic — that alternate with each other. The lengths
of the haploid and diploid phases, and whether these phases are free—
living or dependent on others, vary among different groups in plants.
This phenomenon is called alternation of generation.
6️⃣Kingdom Animalia
This kingdom is characterised by heterotrophic eukaryotic organisms, multicellular and their cells lack cell walls. They directly or
indirectly depend on plants for food. They digest their food in an internal
cavity and store food reserves as glycogen or fat. Their mode of nutrition
is holozoic — by ingestion of food. They follow a definite growth pattern
and grow into adults that have a definite shape and size. Higher forms
show elaborate sensory and neuromotor mechanism. Most of them are
capable of locomotion.
The sexual reproduction is by copulation of male and female followed
by embryological development.
7️⃣Viruses, Viromws, Prions and LICHENS
In the five kingdom classification of Whittaker there is no mention of lichens
and some acellular organisms like viruses, viroids and prions.
Viruses did not find a place in classification since they are not
considered truly ‘living’, if we understand living as those organisms that
have a cell structure. The viruses are non-cellular organisms that are
characterised by having an inert crystalline structure outside the living cell.
Viroids : 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.
Prions : In modern medicine certain infections neurological diseases were
found to be transmitted by an agent consisted of abnormally folded
protein,called
prions. Disease including bovine spongiform
encephalopathy (BSE) commonly called mad cow disease in cattle and
its analogous variant Cr-Jacob disease (CJD) in humans.
Lichens : 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. Algae prepare food for fungi and fungi
provide shelter and absorb mineral nutrients and water for its partner.
Lichens are very good pollution indicators — they do not grow in polluted areas.
