Topics:Biological Classification
- Aristotle was the first scientist to classify living organisms (plants and animals) scientifically.
- Aristotle used simple morphological characters to classify
Two Kingdom Classification
- Proposed by C. Linnaeus
- Hedivided organisms into two kingdoms- Plantae and Animalia.
Shortcomings of the system
- A large number of organisms did not fall into either of the kingdoms.
Three Kingdom Classification
- Proposed by E. Haeckel
- He introduced a separate kingdom for all unicellular eukaryotes, Protista.
- He included fungi, protozoans, algae, bacteria and slime moulds in Protista.
Shortcomings of the system
- Prokaryotes and eukaryotes were placed together in Protista.
- Heterotrophic bacteria and fungi placed along with autotrophic algae.
Four Kingdom Classification
- Proposed by Copeland
- He introduced a separate kingdom, Monera for all unicellular prokaryotes.
- The term Monera was given by Daugherty and Allen.
Shortcomings of the system
- No proper place in this system for fungi.
- Other characteristics such as cell structure, mode of nutrition, habitat, methods of reproduction, evolutionary relationships etc. were not included.
Five Kingdom Classification
- It is the advanced and most popular system of classification.
- It was proposed by R. H. Whittaker (1969)
- The five kingdoms are Monera, Protista, Plantae, Fungi and Animalia.
- It is a phylogenetic system but mainly based on mode of nutrition.
- Other criteria for five kingdom classification − cell structure, thallus organization, reproduction and major ecological role.
Shortcomings of the system
- Both the kingdoms, Monera and Protista include autotrophic as well as heterotrophic organisms.
- The three higher kingdoms (Plantae, Animalia and Fungi) do not have a single ancestor.
- Members of algae are placed in different kingdoms.
- No proper place in this system of classification for viruses.Topics:Kingdom Monera (Including Virus and Viroids)Kingdom MoneraBacteria
- Sole members of this kingdom
- Most abundant microorganisms
- Occur almost everywhere including extreme environments such as hot springs, deep oceans, snow, and deserts
- Many live in or on other organisms as parasites
- Can be classified in four groups based on shape
- Cell structure is very simple but complex in behaviour
- Show the most extensive metabolic diversity as shown below
Archaebacteria- Unique since they live in the most harsh habitats
- Bacteria based on habitat can be named as
- Different from other bacteria in having a different cell wall structure which provides capacity to survive in these extreme conditions
- Methanogens present in the guts of ruminants are responsible for methane (biogas) production from their dung.
Eubacteria (True Bacteria)- Characteristic feature − presence of rigid cell wall and if motile, a flagellum
Cyanobacteria (Blue green Algae)- Have chlorophyll a similar to green plants; hence, they are photosynthetic autotrophs
- Unicellular, colonial or filamentous, marine or terrestrial algae
- Colonies surrounded by gelatinous sheath
- Some can fix atmospheric nitrogen in specialized cells called heterocysts.
Example − Nostoc and Anaebaena
Chemosynthetic Autotrophs- Oxidize various inorganic substances such as nitrites, nitrates, ammonia, etc.
- Play key role in recycling nutrients such as nitrogen, sulphur, iron, etc.
Heterotrophic Bacteria- Most abundant in nature
- Important decomposers
- Helpful in making curd from milk, production of antibiotics, fixing nitrogen in legumes
- Some are pathogens, causing damage to humans, crops, cattle, and pets.
- In humans, they cause diseases such as cholera, typhoid while they cause citrus canker in crop plants and anthrax in cattle.
Mycoplasma- Smallest known living creature
- Devoid of cell wall
- Can survive without oxygen
- Many are pathogens of humans, animals, and plants.
Reproduction in Bacteria- Reproduce asexually mainly by fission
- Under unfavourable conditions − reproduction through spores
- Sexual reproduction may also take place in a special way by DNA transfer from one bacterium to another.Viruses and ViroidsViruses
- Being acellular, they are not placed anywhere in Whittaker’s five kingdom classification.
- Viruses are not truly ‘living’ as they are living only inside the host body, else inert.
- They are non-cellular organisms characterized by inert crystalline structure outside the living cells.
- Obligate (compulsory) parasites
- Once inside a living cell, they take over the host cell machinery to replicate themselves, killing the host.
- Meaning of virus - venom or poisonous fluid
- Term coined by Pasteur
- D. J. Ivanowsky (1892) led the foundation of discovery of virus. He identified causative agent of Mosaic disease, which are smaller than bacteria as they can pass through bacteria-proof filters.
- M. W. Beijerinek (1898) found that the extract of infected plant causes disease in healthy plants.
He called the fluid as Contagium vivum fluidum (infectious living fluid). - W. M. Stanley (1935) crystallized viruses and demonstrated that crystals contain largely proteins, inert outside the host cell.
Structure of Viruses- In addition to proteins, viruses also contain genetic material, either DNA or RNA, never both.
- It is a nucleoprotein and the genetic material is infectious.
- The protein coat is called capsid. It protects the nucleic acid and is made up of small subunits called capsomeres, which are arranged in helical or polyhedral geometric forms.
- Viruses cause diseases such as mumps, small pox, herpes influenza, and AIDS in humans.
- In plants, they cause mosaic, leaf rolling and curling, yellowing, vein clearing, dwarfing and stunted growth.
Viroids- Discovered by T.O. Diener in 1971
- Smaller than viruses and responsible for spindle fibre disease in potato
- Unlike viruses, they lack protein coat and exist as free RNA, hence named viroids.
- Viroid RNA is of low molecular weight.
Video(s) by teachers
Example :Match the contents of column I with the contents of column II. Each of the options, in column I,has only one correct answer in column II.Column IColumn II(a)Methanogens(i)Smallest known agent of infectious disease(b)Thermoacidophiles(ii)Proteinaceous infectious particle(c)Viroid(iii)AnaerobicGram-negative bacteria(d)Prion(iv)Aerobic Gram-negative bacteria(a)(b)(c)(d)(iii)(iv)(i)(ii)
Example :Assertion and ReasonDirections: The following question has two statements, Assertion and Reason.Answer the question by choosing any one of the four responses.Assertion: Viruses are not included in any system of classification.Reason: Some biologists consider virus as living while others do not.Viruses are not included in any system of classification because they do not have a proper cellular structure and organisation.Topics:Kingdom ProtistaGeneral Characteristics- Contains all unicellular eukaryotes
- Primarily aquatic
- Cell body contains well-defined nucleus and other membrane-bound organelles
- Reproduce asexually and sexually, by a process involving cell fusion and zygote formation
Classes of ProtistaChrysophytes (Planktons)- Includes diatoms and golden algae (desmids)
- Found in fresh water as well as marine environments
- Microscopic; float passively in water currents
- Mostly photosynthetic
Diatoms- Cell wall forms two thin overlapping shells
- Walls embedded with silica, and thus, indestructible
- Fossilised remains of diatoms are referred to as ‘diatomaceous earth’
- Chief producers of the ocean
Dinoflagellates- Mostly marine and photosynthetic
- Appear yellow, green, brown, blue or red, depending on pigments present in their cells
- Cell wall has stiff cellulosic plates on the outer surface
- Most of these have two flagella—one lies longitudinally and the other transversely, in a furrow between the wall plates
- Red dinoflagellates (Example − Gonyaulax) rapidly multiply and make the sea appear red (red tides)
- Toxins released by these organisms may kill other marine animals
Euglenoids- Majority are fresh-water organisms
- Found in stagnant water
- Have protein-rich layer called pellicle, instead of cell wall, which makes their body flexible
- In the presence of sunlight, they behave like autotrophs; in the absence of sunlight, they behave like heterotrophs, predating on smaller organisms
- Pigments are similar to those present in higher plants
Slime Moulds- Saprophytic protists
- Move along decaying twigs and leaves
- Under suitable conditions, they form an aggregation called plasmodium, which grows and spreads
- Under unfavourable conditions, plasmodia differentiate to form fruiting bodies bearing spores at their tips
- Spores possess extremely resistant true walls, which make them capable for surviving for a long time under adverse conditions
- Spores disperse by air currents
Protozoans- All are heterotrophs
- Live as predators or parasites
- Believed to be the primitive relatives of animals
Amoeboid Protozoans- Live in freshwater, sea water or in moist soil
- Move and capture their prey by putting out pseudopodia (false foot); Example: Amoeba
- Marine forms have silica shells on their surface
- Some of them, such as Entamoeba, are parasites
Flagellated Protozoans- Either free-living or parasitic
- Bear flagella
- The parasitic forms cause diseases such as sleeping sickness;
Example: Trypanosoma
Ciliated Protozoans- Aquatic and actively moving
- Show presence of thousands of cilia
- Have a cavity (gullet) which opens on the outside
- Movement of cilia causes food-laden water to enter the gullet
Example: Paramoecium
Sporozoans- Include diverse organisms with spore-like infectious stage in their life cycle
- Example: Plasmodium,which causes malariaExample :Assertion and ReasonDirections: The following question has two statements, Assertion and Reason.Answer the question by choosing any one of the four responses.Assertion: The protozoan cell body is either naked or surrounded by rigid pellicle.Reason: Cellulose is absent in the pellicle. Some protozoans secrete shells of various inorganic compounds as external covers.The protozoan cell body is either naked or surrounded by non-rigid pellicle.Topics:Kingdom FungiGeneral Characters
- Constitute a unique kingdom of heterotrophic organisms
- Show great diversity in morphology and habitat
- Some are parasitic while most are saprophytic (feed on dead organisms).
- Except Yeasts (which are unicellular), other are multicellular and filamentous.
- The body consists of long, slender, thread-like structures called hyphae.
- A network of hyphae is known as mycelium.
- Some hyphae are continuous and multinucleate known as coenocytic hyphae while others have sepatae (cross walls).
- Cell wall is composed of chitin and polysaccharides.
- Shows symbiotic association
- with algae in lichens
- with roots of higher plants in mycorrhiza
- Sexual reproduction involves
- plasmogamy − fusion of protoplasm of two gametes
- karyogamy − fusion of two nuclei
- meiosis in zygote resulting in haploid spores
- During sexual reproduction in fungus,
- fusion of two haploid hyphae of compatible mating types takes place which may result
- in a diploid cell (2n) in some fungi or
- an intervening dikaryotic stage (n + n) called dikaryon and a phase called dikaryophase occurs - mainly in classes Ascomycetes and BasidiomycetesThe dikaryotic phase of the fungal life cycle is unique. During this unusual phase, which is common in many species of fungi, cells contain two distinct nuclei. These two nuclei divide simultaneously as the mycelium grows; growth continues until fusion occurs during karyogamy resulting in diploid condition.
- Formation of fruiting bodies takes place
- Production of haploid spores occurs in fruiting bodies as a result of meiosisClasses of FungiPhycomycetes
- Found in aquatic as well as damp habitats
- Some are obligate parasites on plants
- Mycelium − aseptate and coenocytic
- Asexual reproduction − by motile zoospores or non-motile aplanospores
- Spores produced endogenously in sporangium
- Zygospores formed by fusion of two gametes which may be isogamous, anisogamous, or oogamous
Example: Mucor, Rhizopus (Bread mould), Albugo (Plant parasite)
Ascomycetes- Commonly called sac-fungi
- Unicellular (Yeast) or multicellular
- They are saprophytic, decomposers, parasitic or coprophilous (growing on dung)
- Mycelium − branched and septate
- Asexual spores (conidia) produced exogenously on special mycelium called conidiophores
- Sexual spores (Ascospores) produced exogenously in sac-like asci, arranged in different types of fruiting bodies called ascocarps
- Example: Aspergillus, Claviceps,
Neurospora − Used extensively in biochemical and genetic work - Several members such as morels and buffles are edible (considered as delicacies).
Basidiomycetes- Commonly known members are mushrooms, puff balls, or bracket fungi
- Grow in soil, on logs and tree stumps, or as plant-parasites (rusts and smuts)
- Mycelium − branched and septate
- Asexual spores absent and most common means of vegetative reproduction is fragmentation
- Sex organs absent, but plasmogamy takes place through fusion of vegetative cells of different strains
- Resultant structure is a dikaryon, which gives rise to basidium
- Basidia are arranged in fruiting bodies called basidiocarps
Example: Agaricus (mushroom), Ustilago (smut), Puccinia (rust)Deuteromycetes- Known as imperfect fungi because sexual phase is absent
- On recognition of sexual phase, the member is shifted to either class Ascomycetes or class Basidiomycetes
- Reproduce only by asexual spores (conidia)
- Mycelium is septate and branched.
- Some are saprophytic while others are parasitic.
- Being decomposers, these help in mineral cycling.
Example: Alternaria, Colletotrichum, TrichodermaExample :Why are slime moulds not included in kingdom Fungi?Slime moulds are consumer decomposer protists. Formerly, they were included among fungi but now they are not because fungi are described as immotile, heterotrophic organisms with chitinous cell walls.Slime moulds move and lack chitin in their cell walls. So, they are now included in Kingdom Protista. Also, slime moulds are slimy masses during their vegetative phase and not moulds in true sense as in the case of fungi.
Example :Column I lists some spores found in fungi and column II lists some of their properties. Match the contents of column I with the contents of column II. Each of the options, in column I, has only one correct answer in column II.Column IColumn II(a)Conidia(i)Motile, thin, endogenously produced(b)Oidia(ii)Non-motile, thin, endogenously produced(c)Chlamydospore(iii)Non-motile, thin, exogenously produced(d)Zoospore(iv)Non-motile, thick, produced during unfavourable conditions(e)Sporangospore(v)Non-motile, thin, produced during unfavourable conditions(a)(b)(c)(d)(e)(iii)(v)(iv)(i)(ii)
Example :(i) Identify the given structure and the parts labelled as I, II and III associated with it.(ii) What are fairy rings?(iii) Which kind of spores are formed in it?(iv) What is mushroom?(i) The given figure illustrates the fungus, Agaricus.In the given figure, the part labelledI → StalkII → AnnulusIII → Gills(ii) Fairy ring refers to naturally occurring ring or arc of mushrooms found in many forested areas or grasslands. They are called so because, according to folklore, fairy ring appears when a fairy appears.(iii) Agaricus produces basidiospores.(iv) Mushroom is the edible portion of Agaricus which is only the aerial fructification (the basiodiocarp) of the fungi.Topics:Kingdom Plantae (Including Lichens) and AnimaliaKingdom Plantae- Contains all eukaryotic-photosynthetic organisms
- Few are partially heterotrophic (insectivorous plants such as Venus flytrap) or parasites (Cuscuta).
- Plant cells − eukaryotic with prominent chloroplasts and cellulosic cell wall
- Exhibit alternation of generation
- Major divisions included are
Kingdom Animalia- Heterotrophic, eukaryotic, multicellular organisms
- Animal cells lack cell wall.
- Directly or indirectly depend on plants for food
- Digestion is internal and store food reserve as glycogen or fat.
- Follow definite growth pattern, grow into adults having definite shape and size
- Higher forms show elaborate sensory and neuromotor mechanism.
- Most capable of locomotion
- Sexual reproduction is by copulation of male and female followed by embryological development.
Lichens- Symbiotic associations between fungi and algae
- Algal component − phycobiont (autotrophic)
- Fungal component − mycobiont (heterotrophic)
- Algae prepare food for fungi; in return, fungi absorb water and minerals and provide shelter to the algae
- Very good pollution indicators − do not grow in polluted areas
Example :Assertion and ReasonDirections: The following question has two statements, Assertion and Reason.Answer the question by choosing any one of the four responses.Assertion: Cladonia rangiferina is called the reindeer moss and Cetraria islandica is called the Iceland moss.Reason: Cladonia rangiferina, a moss found in the arctic region, is eaten by reindeer and cattle and Cetraria islandica, an edible moss found in Iceland, is consumed by the people of Iceland.If both Assertion and Reason are true and Reason is the correct explanation of assertion.
Example :Column I lists some types of lichens and column II lists their habitat. Match the contents of columnI with the contents of column II. Each of the options, in column I, has only one correct answer in column II.Column IColumn II(a)Lignicolous(i)Soil(b)Corticolous(ii)Stones(c)Saxicolous(iii)Bark(d)Terricolous(iv)Wood(a)(b)(c)(d)(iv)(iii)(ii)(i)
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