biological classification

• Aristotle used simple morphological characters to classify plants into trees, shrubs, and herbs
• Aristotle also divided animals into two groups based on whether they had red blood or not
• Carolus Linnaeus developed a Two Kingdom system of classification with Plantae and Animalia kingdoms
• Drawbacks of the two kingdom system:

  • Did not distinguish between eukaryotes and prokaryotes, unicellular and multicellular organisms
  • Did not differentiate between photosynthetic (green algae) and non-photosynthetic (fungi) organisms
  • Many organisms did not fit into the plant or animal categories
• R.H. Whittaker proposed a Five Kingdom Classification:

  • Monera, Protista, Fungi, Plantae, and Animalia
• Criteria for classification by Whittaker include cell structure, body organization, mode of nutrition, reproduction, and phylogenetic relationships
• Carl Woese proposed a six-kingdom classification
• Kingdom Monera:

  • Bacteria are the sole members
  • They are abundant and can survive in extreme habitats
  • Some bacteria are autotrophic, while most are heterotrophs
• Types of bacteria based on mode of nutrition:

  • Autotrophic bacteria can be photosynthetic or chemosynthetic
  • Heterotrophic bacteria depend on other organisms or dead organic matter for food
• Classification based on Shape of bacteria:

  • Spherical Coccus (pl.: cocci)
  • Rod-shaped Bacillus (pl.: bacilli)
  • Comma-shaped Vibrium (pl.: vibrio)
  • Spiral Spirillum (pl.: spirilla)
• Archaebacteria:

  • Live in extreme habitats like salty areas, hot springs, and marshy areas
  • Have a different cell wall structure compared to other bacteria
  • Methanogens in the gut of ruminant animals produce methane (biogas)
• Eubacteria:

  • Thousands of different eubacteria
  • Characterized by a rigid cell wall and flagellum if motile
• Chemosynthetic autotrophic bacteria:

  • Oxidize inorganic substances for ATP production
  • Play a role in recycling nutrients like nitrogen, phosphorous, iron, and sulfur
• Cyanobacteria:

  • Also known as blue-green algae
  • Have chlorophyll 'a' similar to green plants and are photosynthetic autotrophs
  • Can fix atmospheric nitrogen in heterocysts
• Heterotrophic bacteria:

  • Most abundant in nature
  • Majority are important decomposers
  • Helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots
  • Some are pathogens causing damage to human beings, crops, farm animals, and pets
  • Examples of diseases caused by bacteria: Cholera, typhoid, tetanus, and citrus canker
• Bacteria reproduction:

  • Mainly by fission
  • Under unfavourable conditions, they produce spores
  • Reproduce by a primitive type of DNA transfer from one bacterium to the other
• Mycoplasma:

  • Organisms that completely lack a cell wall
  • Smallest living cells known
  • Can survive without oxygen
  • Many are pathogenic in animals and plants
• Kingdom Protista:

  • Single-celled eukaryotes
  • Boundaries of this kingdom are not well defined
  • Primarily aquatic
  • Protistan cell body contains a well-defined nucleus and other membrane-bound organelles
  • Reproduce asexually and sexually by cell fusion and zygote formation
• Chrysophytes:

  • Includes diatoms and golden algae (desmids)
  • Found in fresh water and marine environments
  • Most are photosynthetic
  • Diatoms have indestructible cell walls embedded with silica
  • Diatoms are chief 'producers' in the oceans
• Dinoflagellates:

  • Mostly marine and photosynthetic
  • Cell wall has stiff cellulose plates
  • Most have two flagella
  • Rapid multiplication can cause red tides
  • Toxins released can kill marine animals
• Euglenoids:

  • Majority are fresh water organisms found in stagnant water
  • Lack a cell wall, have a protein-rich layer called pellicle
  • Have two flagella
  • Photosynthetic in sunlight, behave like heterotrophs in absence of sunlight
• Slime Moulds:

  • Saprophytic protists
  • Move along decaying twigs and leaves engulfing organic material
  • Form plasmodium under suitable conditions
  • Plasmodium differentiates to form fruiting bodies bearing spores
  • Spores are dispersed by air currents
• Protozoans:

  • All are heterotrophs living as predators or parasites
  • Believed to be primitive relatives of animals
  • Four major groups: Amoeboid, Flagellated, Ciliated, Sporozoans
• Kingdom Fungi:

  • Unique kingdom of heterotrophic organisms
  • Great diversity in morphology and habitat
  • Some unicellular fungi like yeast are used to make bread and beer
  • Fungi are cosmopolitan and occur in air, water, soil, and on animals and plants
  • Fungi prefer warm and humid places
• Reproduction in Fungi:

  • Vegetative means of reproduction: fragmentation, fission, budding
  • Asexual reproduction by spores: conidia, sporangiospores, zoospores
  • Sexual reproduction by oospores, ascospores, basidiospores
  • Various spores produced in fruiting bodies
• Sexual Reproductive Cycle in Fungi:

  • Fusion of protoplasms between two gametes (plasmogamy)
  • Fusion of two nuclei (karyogamy)
  • Meiosis in zygote resulting in haploid spores
  • Fungi form fruiting bodies for sexual reproduction
• Heterotrophic bacteria:

  • Most abundant in nature
  • Important decomposers
  • Helpful in making curd from milk, production of antibiotics, fixing nitrogen in legume roots
  • Some are pathogens causing damage to human beings, crops, farm animals, and pets
  • Examples of diseases caused by bacteria: Cholera, typhoid, tetanus, citrus canker
• Bacteria reproduction:

  • Mainly by fission
  • Under unfavourable conditions, they produce spores
  • Reproduce by a primitive type of DNA transfer from one bacterium to the other
• Mycoplasma:

  • Organisms that completely lack a cell wall
  • Smallest living cells known
  • Can survive without oxygen
  • Many are pathogenic in animals and plants
• Kingdom Protista:

  • Single-celled eukaryotes
  • Primarily aquatic
  • Protistan cell body contains a well-defined nucleus and other membrane-bound organelles
  • Reproduce asexually and sexually by cell fusion and zygote formation
• Chrysophytes:

  • Includes diatoms and golden algae (desmids)
  • Found in fresh water and marine environments
  • Most are photosynthetic
  • Diatoms have silica cell walls forming two thin overlapping shells
  • Diatoms are chief 'producers' in the oceans
• Dinoflagellates:

  • Mostly marine and photosynthetic
  • Cell wall has stiff cellulose plates
  • Most have two flagella
  • Rapid multiplication can cause red tides
  • Toxins released can kill marine animals
• Euglenoids:

  • Majority are fresh water organisms
  • Lack a cell wall, have a protein-rich layer called pellicle
  • Have two flagella
  • Photosynthetic in sunlight, behave like heterotrophs in darkness
  • Example: Euglena
• Slime Moulds:

  • Saprophytic protists
  • Move along decaying organic material
  • Form plasmodium under suitable conditions
  • Plasmodium differentiates into fruiting bodies bearing spores
  • Spores are dispersed by air currents
• Protozoans:

  • Heterotrophs living as predators or parasites
  • Amoeboid protozoans move and capture prey using pseudopodia
  • Flagellated protozoans have flagella, causing diseases like sleeping sickness
  • Ciliated protozoans have thousands of cilia and a gullet for food intake
  • Sporozoans have an infectious spore-like stage, causing diseases like malaria
• Kingdom Fungi:

  • Unique kingdom of heterotrophic organisms
  • Diversity in morphology and habitat
  • Most are filamentous except yeasts
  • Bodies consist of hyphae forming mycelium
  • Cell walls composed of chitin and polysaccharides
• Types of fungi based on nutrition:

  • Saprophytes absorb organic matter from dead substrates
  • Parasites depend on living plants and animals
  • Symbionts live in association with algae as lichens and with roots of higher plants as mycorrhiza
• Reproduction in Fungi:

  • Vegetative reproduction by fragmentation, fission, and budding
  • Asexual reproduction by spores like conidia, sporangiospores, and zoospores
  • Sexual reproduction by oospores, ascospores, and basidiospores
  • Sexual cycle involves plasmogamy, karyogamy, and meiosis in zygote resulting in haploid spores
• Sexual reproduction in fungi:

  • Fusion of protoplasms between gametes
  • Fusion of two nuclei
  • Meiosis in zygote leading to haploid spores
  • Formation of fruiting bodies where reduction division occurs