Biological classification class 11th, Study notes of Biology

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Aristotle was the earliest to attempt a more scientific basis for classification of organisms. He classified plants into trees, shrubs & herbs and animals into 2 groups, those which had red blood and those that did not.

It is proposed by Linnaeus (1758). This system classifies organisms into Two Kingdoms- Plantae & Animalia.

Carl Linnaeus

Aristotle

Bacteria are the most abundant microorganisms.

Hundreds of bacteria are present in a handful of soil.

They also live in extreme habitats such as hot springs, deserts, snow & deep oceans.

Many are parasites.

Bacterial structure is very simple but they

are complex in behaviour and show

metabolic diversity.

Some bacteria are autotrophic (synthesize

food from inorganic substrates).

Majority are heterotrophs (they do not

synthesize the food but depend on other

organisms or on dead organic matter for

food).

They live in harshest habitats such as extreme salty areas (halophiles), hot springs (thermoacidophiles) and marshy areas (methanogens).

Archaebacteria have a different cell wall structure for their survival in extreme conditions.

Methanogens are present in the guts of ruminant animals (cows, buffaloes etc). They produce methane (biogas) from the dung of these animals.

They have a rigid cell wall and a flagellum (if motile).

They include Autotrophs (photosynthetic & chemosynthetic) and Heterotrophs.

Bacteria reproduce mainly by fission.

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.

They are organisms without a cell wall.

They are the smallest living cells known.

They can survive without oxygen.

Many are pathogenic in animals and

plants.

It includes single-celled eukaryotes. Protists are primarily aquatic. It forms a link with plants, animals and fungi. Cell contains well defined nucleus and other

membrane-bound organelles. Some have flagella or cilia. Reproduce asexually and sexually by a process involving cell fusion & zygote formation.

They are found in fresh water and marine environments. They are microscopic and float passively in water currents (plankton). Most of them are photosynthetic. It includes diatoms & golden algae (desmids). Diatoms They have siliceous cell walls forming two thin overlapping shells, which fit together as in a soap box. The cell wall deposit of diatoms over billions of years in their habitat is known as ‘diatomaceous earth’. This is used in polishing, filtration of oils and syrups. Diatoms are the chief ‘producers’ in the oceans.

Mostly marine and photosynthetic. They appear yellow, green, brown, blue or red depending on the main pigments in cells. Cell wall has stiff cellulose plates on the outer surface.

They are heterotrophs (predators or parasites).

They are believed to be primitive relatives of animals.

Amoeboid Protozoans

Flagellated Protozoans

Ciliated Protozoans

Sporozoans

Live in fresh water, sea water or moist soil. They move and capture prey by putting out pseudopodia (false feet). E.g. Amoeba. Marine forms have silica shells on their surface. Some are parasites. E.g. Entamoeba.

Free-living or parasitic. They have flagella. Parasitic forms cause diseases like sleeping sickness. E.g. Trypanosoma

Aquatic, actively move using cilia. They have a cavity (gullet) that opens to outside. Due to the movement of cilia, water with food enters into gullet. E.g. Paramecium

infectious spore- like stage in their life cycle. E.g. Plasmodium (malarial parasite). It causes malaria.

It is a unique kingdom of heterotrophic organisms. Fungi are cosmopolitan and occur in air, water, soil and on animals and plants. They prefer to grow in warm and humid places. E.g. Bread Mould, Orange Rots, Mushroom, Toadstools etc. White spots on mustard leaves are due to a parasitic fungus

Some fungi are the source of antibiotics, e.g.,Penicillium.

Some unicellular fungi (e.g. Yeast) are used to make bread and beer.

Other fungi cause diseases in plants and animals. E.g. wheat rust-causingPuccinia.

Penicillium Yeast

Puccinia

Except yeasts, 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 hyphae. Fungal cell wall is made of chitin & polysaccharides

Asexual reproduction Takes place by zoospores (motile) or by aplanospores (non-motile). These are produced in sporangium.

Sexual reproduction :- Zygospores are formed by fusion of two gametes. These gametes are isogamous (similar) or anisogamous or oogamous (dissimilar).

Unicellular (e.g. yeast, Sacharomyces) or multicellular (e.g. Penicillium). They are saprophytic, decomposers, parasitic or coprophilous (growing on dung). Mycelium is branched and septate.

Asexual reproduction By conidia produced exogenously on the special mycelium called conidiophores. Conidia germinate to produce mycelium.

Sexual reproduction By ascospores produced endogenously in sac like asci (sing. ascus). Asci are arranged to form ascocarps (fruiting bodies). Examples Aspergillus, Claviceps & Neurospora. Neurospora is used in biochemical and genetic work. Many members like morels & buffles are edible and are delicacies.

Includes mushrooms, bracket fungi or puffballs. They grow in soil, on logs and tree stumps and in living plant bodies as parasites (e.g. rusts & smuts). Mycelium is branched & septate. The asexual spores are generally not found, but vegetative reproduction by fragmentation is common.

Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of different strains or genotypes. The resultant structure is dikaryotic. It gives rise to basidium. Karyogamy & meiosis occur in basidium producing 4 basidiospores exogenously. Basidia are arranged in fruiting bodies called basidiocarps. E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus).

Sex organs are absent, but plasmogamy occurs by fusion of two vegetative or somatic cells of different strains or genotypes. The resultant structure is dikaryotic. It gives rise to basidium. Karyogamy & meiosis occur in basidium producing 4 basidiospores exogenously. Basidia are arranged in fruiting bodies called basidiocarps. E.g. Agaricus (mushroom), Ustilago (smut) and Puccinia (rust fungus).

Deuteromycetes reproduce only by asexual spores (conidia). Mycelium is septate and branched. Some are saprophytes or parasites. Majority are decomposers of litter and help in mineral cycling. E.g. Alternaria, Colletotrichum and Trichoderma.

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.

Louis Pasteur : Gave the name ‘virus’ {means venom or poisonous fluid}

D.J Ivanowsky : Discovered virus. He recognised certain microbes that cause mosaic disease of tobacco. They were smaller than bacteria because they passed through bacteria – proof filters

M.W. Beijernick : Demonstrated that the extract of the infected plants of tobacco could cause infection in healthy plants and

called the fluid as ‘ Contagium vivium fluidum’ {infectious living

fluid}

W.M. Stanley : Showed that viruses could be crystallized and crystals consist largely of proteins

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.

Helical

Polyhedral

geometric

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.