Biology Notes
BIOLOGICAL
CLASSIFICATION
Class 11ᵗʰ
Biological Classification
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Biological classification: the video explanation here click here
Biological classification is defined as the process of grouping organisms according to
certain similarities.
THINGS TO KEEP IN MIND:
Aristotle was the earliest to attempt a more scientific basis
of classification
Simple morphological characters for Classification.
plants Animals
Animals without Red
Animals with Red Blood
Trees Shrubs Herbs Blood
e.g. Mammals Lizards
e.g. Insects
Birds
Jellyfish
Fishes
Carolus Linnaeus made two kingdom systems of
classification.
He classified organisms in the animal kingdom which is called Animalia, and in the
plant kingdom which is called Plantae.
Linnaeus system did not distinguish between the Eukaryotes and Prokaryotes Unicellular
and Multicellular Organisms, Photosynthetic and non-photosynthetic organisms.
Two kingdom classification included under plants
Linnaeus placed
Prokaryotic bacteria, blue - green algae and other groups under eukaryotes.
The character that unified the whole kingdom was the presence of cell wall in
their cells.
Two kingdom system included unicellular and multicellular organisms under one group.
e.g. Chlamydomonas and Spirogyra were placed together under algae.
The classification did not differentiate between the heterotrophic group
(Fungi) and the autotrophic green plants.
The cell wall in fungi is made up with chitin while, in green plants it has a cellulosic
cell wall.
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,
reproductionand phylogenetic relationships.
TABLE 2.1 Characteristics of the Five Kingdoms
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Kingdom Monera the video explanation here click here
Bacteria are the sole members of the Kingdom Monera
They can be found in extremely harsh environments like deep
oceans, snow, deserts, and hot springs.
Structure of bacteria is very simple but, very complex in behavior.
Bacteria are grouped under four categories based on their shape:
shapes of bacteria
Spherical Coccus (pl.: cocci)
Rod-shaped Bacillus (pl.: bacilli)
Comma-shaped Vibrium (pl.: vibrio)
Spiral Spirillum (pl.: spirilla)
Bacterial structure is very simple, they are very complex in behaviour.
All monerans are prokaryotes, i.e., do not have a definite nucleus.
They can be autotrophs, heterotrophs moreover as parasites.
Cell wall is present.
The vast majority of bacteria are heterotrophs, i.e., they depend on other
organisms or on dead organic matter for food.
Archaebacteria
These bacteria are special because they live in some of the most harsh habitats
There are three types of archaebacteria:
extreme salty areas (halophiles),
hot springs (thermoacidophiles)
and marshy areas (methanogens)
cell wall structure is different from other bacteria.
Methanogens aid in the production of biogas from animal
excrement and are present in the intestines of several
ruminants, including cows and buffalo
Eubacteria
Called "true bacteria".
They are characterised by having a stiff cell wall and a movable flagellum.
The cyanobacteria (also referred to as blue-green algae)
They are similar to plants as they contain chlorophyll a. For this reason, they are
called photosynthetic autotrophs.
Cyanobacteria are filamentous, unicellular algae that grow into colonies encased in a
gelatinous sheath.
They often form blooms in polluted water bodi
Some have special structures known as heterocysts that help in
nitrogen fixation in place.
example Nostoc and Anabaena
Nitrogen fixation is a chemical process that converts
atmospheric nitrogen into ammonia, which is absorbed by
organisms. Nitrogen fixation is essentially converting
atmospheric nitrogen into a form that plants can more readily
utilize.
Bacteria
Autotrophic Heterotrophic
Chemosynthetic Photosynthetic Parasitic Saprophytic
Chemosynthetic Autotrophs
Oxidize various inorganic substances such as nitrates, nitrites and ammonia and use
the released energy for ATP production.
Plays important role in recycling of
nutrients like nitrogen, phosphorus, iron
and sulphur.
Heterotrophic bacteria
Majority of heterotrophic bacteria are Saprophytes or Decomposers.
Making curd from milk
Production of antibiotics Many bacteria are pathogen causing
various diseases of plants and animals,
Fixing nitrogen in legume roots
e.g. citrus canker, tetanus, typhoid,
cholera.
Reproduction
Bacterias Reproduce by binary fission, spore / sexual reproduction.
If conditions are unfavourable, they can also proliferate through spores.
They also reproduce by a sort of sexual reproduction
Mycoplasma
Organisms that completely lack a cell wall.
Many mycoplasma are pathogenic in animals and plants
Smallest living cells can survive without oxygen.
Previously called pleuropneumonia like organisms (PPLO)
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Kingdom Protista the video explanation here click here
Protista are Single celled eukaryotic with a well defined nucleus and membrane -
bound organelles.
But, the boundaries of this kingdom are not well defined.
This kingdom forms a link with others (plants, animals and
fungi).
Reproduction assembles by fission or by the formation of
spores.
Sexual reproduction by a process involving cell fusion and
Zygote formation.
Protista includes following members….
Chrysophytes Euglenoids Protozoans
Dinoflagellates Slime Moulds
Chrysophytes
includes diatoms and golden algae (desmids)
They are microscopic and float passively in water currents (planktons).
They are found in fresh water as well as in marine environment
Most of the chrysophytes are photosynthetic.
In diatoms the cell walls form two thin overlapping shells epitheca over hypotheca.
The walls are embedded with silica and thus walls are indestructible.
Diatoms
Accumulation of large amounts of silica in the cell walls of diatoms referred as
diatomaceous earth.
Diatoms are the Chief Producers in oceans.
The soil of (diatomaceous earth) being used in polishing, filtration of oils and syrups.
This accumulation over a billion year was referred as diatomaceous earth
Dinoflagellates
Mostly marine and photosynthetic.
Cells of dinoflagellates, appear in different colours
Green, Brown, Blue, Red or Yellow.
The cells of dinoflagellates have 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.
Red Dinoflagellates undergo rapid multiplication that they make the
sea appear in red.
Toxins released by large numbers of dinoflagellates kill other marine
animals such as fishes. (Example: Gonyaulax)
Euglenoids
Majority of them are fresh water organisms.
Found in Stagnant Water
Insted of cell wall, Euglenoids have protein rich layer called
pellicle which makes their body flexible.
They have two flagella a short and long one.
Euglenoids are photosynthetic in the presence of sunlight and heterotrophs in the
absence of light.
Slime Moulds
saprophytic protists
Under favorable condition slime molds form an aggregation called plasmodium.
Bearing Spores at their tips
The spores possess true walls and extremely resistant
and survive for many years.
Spores survive under adverse conditions.
Spores are dispersed by air currents.
Protozoans
All protozoans are heterotrophs.
primitive relatives of animals.
The four major groups of protozoans
Amoeboid Protozoan
Organisms live in fresh water, sea water or moist soil.
These protozoans use their false feet (pseudopodia) to capture the prey.
Marine forms have silica shells on their surface. Some of them such as
Entamoeba are parasites.
Flagellated Protozoans
either free-living or parasitic.
They have flagella
The parasitic forms cause diseases
e.g. Diseases such as sleeping sickness caused by trypanosoma
Ciliated Protozoans
These are Aquatic.
Coordinated movement of rows of cilia causes the water laden with food,
that passes inside gullet.
Actively moving organisms because of the presence of thousands of cilia.
Ciliated protozoans have cavity (gullet) that opens to the outside of cell
surface.
Sporozoans
This includes diverse organisms that have an infectious
spore-like stage in their life cycle.
Plasmodium (malarial parasite) causes malaria
Didn’t understand? Watch
Fungi the video explanation here click here
Heterotrophic organisms
The common edible mushroom and toadstools (poisonous)
are also fungi.
Fungi on a moist bread and rotten fruits
Fungi cause diseases in plants and animals; wheat rust-causing Puccinia
some are the source of antibiotics eg : penicilliumi
Fungi are cosmopolitan and occur in air, water, soil and on animals and plants.
Fungi are filamentous, with the exception of unicellular yeasts.
Fungi 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 or aseptate and 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.
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 Mycorrhizae.
Reprodution
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.
Sexual cycle
Fusion of protoplasms between two motile or non-motile gametes called plasmogamy.
Fusion of two nuclei called karyogamy.
Meiosis in zygote resulting in haploid spores.
sexual cycle follow three steps
The fusion of two haploid cells immediately results in
diploid cells (2n), but in some fungi such as
ascomycetes and basidiomycetes, an intervening
dikaryotic 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 sexual cycle involves the following three steps:
Kingdom fungi is divided into various classes based on the morphology of the
mycelium, mode of spore formation and fruiting bodies such as
Phycomycetes
Ascomycetes
Basidiomycetes
Deuteromycetes
Phycomycetes
They are called algal fungi.
Members of phycomycetes are found in aquatic habitats and on decaying
wood in moist and damp places or as obligate parasites on plants.
Sexual reproduction
Asexual reproduction takes place by zoospores (motile) or by aplanospores (non-
motile).
These spores are endogeneously produced in sporangium.
Zygospores are formed by fusion of two gametes
Some common examples are Mucor, Rhizopus (the bread mould) and Albugo (the
parasitic fungi on mustard). These gametes may be similar
Some common examples are Mucor, Rhizopus (isogamous) or dissimilar
(the bread mould) and Albugo (the parasitic (anisogamous or oogamous)
fungi on mustard). in morphology
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 on conidiophores.
Reproduction
Sexual spores are called ascospores which are produced endogenously in sac
like asci arranged in different types of fruiting bodies called ascocarps.
Examples are Aspergillus, Claviceps, Pencillium and Neurospora.
Neurospora is used extensively in biochemical and genetic work
Neurospora is used extensively in biochemical and genetic work.
Many members like morels and truffles are edible and are
considered delicacies.
Basidiomycetes
They are commonly known as club fungi.
Commonly known forms of basidiomycetes are mushrooms, bracket fungi or puffballs
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 genotype.
The resultant structure is dikaryotic and produces a dikaryotic secondary
mycelium which ultimately gives rise to basidia.
Karyogamy and meiosis take place in the basidium producing four
basidiospores wich are exogenously produced on basidium.
The basidia are arranged in fruiting bodies called basidiocarps.
Some common members are Agaricus (mushroom) , Ustilago
(smut) and Puccinia (rust fungus).
Deuteromycetes
They are known as ‘Imperfect Fungi’ because in this group, only 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 are saprophytes or parasites while a large number of them are
decomposers of litter and help in mineral cycling.
Examples - Alternaria, Colletotrichum and Trichoderma
Didn’t understand? Watch
Kingdom Plantae
the video explanation here click here
Kingdom Plantae includes all plants.
Almost all plants are autotrophic, but some are heterotrophic, for
example, Venus fly trap and bladderwort are insectivorous plants.
Some plants are parasitic too. Example: Cuscuta
The plant cells contain a cell wall made of cellulose.
Cells of photosynthetic plants contain the photosynthetic pigment
called chlorophyll.
The life cycle of plants has two phases—a diploid sporophytic phase
and a haploid gametophyticphase which alternate with each other. This
phenomenon is called alternation of generations.
Kingdom Animalia
Kingdom Animalia includes all heterotrophic, eukaryotic, multicellular
organisms.
They lack a cell wall and chlorophyll.
They depend on plants for food directly or indirectly.
The food is digested inside the body cavity.
Nutrition is holozoic.
Animals exhibit a definite growth pattern.
Most of the animals exhibit embryonic development after fertilisation
Viruses, Viroids & Lichens Didn’t understand? Watch
the video explanation her click here
In five-kingdom classification, acellular organisms (viruses & viroids) and lichens are
not mentioned.
Viruses are non-cellular and not truly ‘living’. So they are not included in five-
kingdom classification.
Viruses have an inert crystalline structure outside the living cell.
Viruses are obligate parasites.
When they infect a cell they take over the machinery of host cell to replicate
themselves, killing the host.
A virus is a nucleoprotein, i.e, it has a protein coat (capsid) & genetic material
(RNA or DNA).
No virus contains both RNA & DNA.
The genetic material is infectious.
Generally, viruses that infect plants have single stranded RNA.
Viruses that infect animals have either single or double stranded RNA or double
stranded DNA.
Bacteriophages (viruses that infect bacteria) usually have double stranded DNA.
The protein coat (capsid) made of small subunits (capsomeres) protects
nucleic acid.
Capsomeres are arranged in helical or polyhedral geometric forms.
Viruses cause diseases like mumps, small pox, herpes, influenza & AIDS
In plants, the symptoms can be mosaic formation, leaf rolling & curling, yellowing &
vein clearing, dwarfing & stunted growth.
Virus
Virus means venom or poisonous 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.
Viroids
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.
The RNA of the viroid was of low molecular weight. 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.
Lichens
Lichens: Lichens are symbiotic associations (mutually useful
associations) between algae & fungi.
The algal component is called phycobiont (autotrophic) and fungal
component is mycobiont (heterotrophic).
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. cllass 11th podhenge
