Biological Classification

Attempts at Classifying Living Organisms

• Early classification was instinctive, based on usage for food, shelter, and clothing
• Aristotle used morphological characteristics to classify plants into trees, shrubs, and herbs
• Animals were categorized into those with and without red blood

Two Kingdom Classification

• Linnaeus developed a system with Plantae and Animalia kingdoms
• The system did not differentiate between eukaryotes and prokaryotes
• It also failed to distinguish unicellular from multicellular organisms
• Photosynthetic organisms (green algae) were not separated from non-photosynthetic organisms (fungi)
• This system proved inadequate as it failed to accommodate a large number of organisms

Need for Change

• Gross morphology was not sufficient
• Characteristics such as cell structure, wall nature, nutrition mode, habitat, reproduction methods, and evolutionary relationships needed consideration
• Classification systems experienced multiple revisions over time
• Plant and animal kingdoms remained constant
• The understanding of included groups and organisms evolved
• Varying interpretations emerged from different scientists

Whittaker's Five Kingdom Classification

• Proposed in 1969 by R.H. Whittaker
• Kingdoms included Monera, Protista, Fungi, Plantae, and Animalia
• Classification based on cell structure, body organization, nutrition mode, reproduction, and phylogenetic relationships

Three-Domain System

• Divides Kingdom Monera into two domains
• Eukaryotic kingdoms are placed in the third domain
• Resulting in a six-kingdom classification system

Issues with Earlier Systems

• Previous systems grouped bacteria, blue-green algae, fungi, mosses, ferns, gymnosperms, and angiosperms under 'Plants'
• The unifying characteristic was the presence of a cell wall
• This put together widely different groups, such as prokaryotic bacteria and eukaryotic blue-green algae

Drawbacks Cont.

• Unicellular and multicellular organisms were grouped, like Chlamydomonas and Spirogyra under algae
• No distinction was made between heterotrophic fungi and autotrophic green plants
• Fungi have chitin, while green plants have a cellulosic cell wall

Resulting Changes

• Fungi were placed in a separate kingdom
• Prokaryotic organisms went into Kingdom Monera
• Unicellular eukaryotic organisms were placed in Kingdom Protista

Impact of New Classifications

• Kingdom Protista includes Chlamydomonas and Chlorella (previously in Algae) alongside Paramoecium and Amoeba (previously in the animal kingdom)
• Organisms from different kingdoms were grouped together due to changed criteria
• Future changes are expected with improved understanding

Focus moving forward

• Modern attempts consider morphological, physiological, and reproductive similarities
• Phylogenetic aspects are also considered, reflecting evolutionary relationships
• The chapter studies Kingdoms Monera, Protista and Fungi
• Kingdoms Plantae and Animalia are covered in later chapters

Kingdom Monera

• Bacteria are the sole members
• They are the most abundant microorganisms and are found everywhere
• Hundreds are present in a handful of soil
• They thrive in extreme habitats like hot springs, deserts, and deep oceans
• Many live in or on other organisms as parasites

Bacterial Shapes

• Coccus (spherical)
• Bacillus (rod-shaped)
• Vibrium (comma-shaped)
• Spirillum (spiral)

Bacterial Diversity

• Simple structure but complex behavior
• Exhibit the most extensive metabolic diversity compared to other organisms
• Some are autotrophic, synthesizing their own food from inorganic substrates
• They may be photosynthetic or chemosynthetic autotrophic
• The majority are heterotrophic, depending on other organisms or dead organic matter

Archaebacteria

• Live in harsh habitats like salty areas (halophiles), hot springs (thermoacidophiles), and marshy areas (methanogens)
• Differ in cell wall structure, aiding survival in extreme conditions
• Methanogens are in the gut of ruminant animals and produce methane from dung

Eubacteria

• Thousands of different types
• Characterized by a rigid cell wall and a flagellum if motile
• Cyanobacteria (blue-green algae) have chlorophyll a, similar to green plants, and are photosynthetic autotrophs

Features of Cyanobacteria

• Unicellular, colonial, or filamentous
• Found in freshwater, marine, or terrestrial environments
• Colonies are surrounded by a gelatinous sheath
• They can form blooms in polluted water bodies
• Some fix atmospheric nitrogen in specialized cells called heterocysts

Chemosynthetic Autotrophic Bacteria

• Oxidize inorganic substances like nitrates, nitrites, and ammonia
• Use released energy for ATP production
• Play a role in recycling nutrients like nitrogen, phosphorous, iron, and sulphur

Heterotrophic Bacteria

• The most abundant in nature
• Important decomposers
• Helpful in making curd from milk
• Active in antibiotic production
• Involved in fixing nitrogen in legume roots
• Some are pathogens, causing damage to humans, crops, and animals

Bacterial Reproduction

• Mainly by fission
• Under unfavorable conditions, they produce spores
• They also reproduce via a primitive form of DNA transfer

Mycoplasma

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

Kingdom Protista

• Includes single-celled eukaryotes
• Kingdom boundaries are not well defined
• Includes Chrysophytes, Dinoflagellates, Euglenoids, Slime moulds and Protozoans
• Primarily aquatic

Defining Features of Protista

• Link between plants, animals, and fungi
• Eukaryotic cell body containing a well-defined nucleus and membrane-bound organelles
• Some possess flagella or cilia
• Reproduction through asexual and sexual processes involving cell fusion and zygote formation

Chrysophytes

• Includes diatoms and golden algae (desmids)
• Found in freshwater and marine environments
• Microscopic and passively float in water (plankton)
• Mostly photosynthetic

Diatom Characteristics

• Cell walls form overlapping shells fitting like a soap box
• Walls are embedded with silica, making them indestructible
• Accumulation of cell wall deposits over billions of years forms 'diatomaceous earth'
• Diatomaceous earth is used in polishing, and filtration of oils and syrups
• Diatoms are chief producers in the oceans

Dinoflagellates

• Mostly marine and photosynthetic
• Appear yellow, green, brown, blue, or red based on main pigments
• Cell wall has stiff cellulose plates on the outer surface
• Usually have two flagella: one longitudinal, one transverse

Red Dinoflagellates

• Capable of rapid multiplication, causing "red tides"
• Toxins released can kill other marine animals

Euglenoids

• Mostly freshwater organisms found in stagnant water
• Possess a protein-rich layer called pellicle instead of a cell wall, allowing flexibility
• Have two flagella, one short and one long

Nutritional Modes of Euglenoids

• Photosynthetic in the presence of sunlight
• Heterotrophic when sunlight is absent, preying on smaller organisms
• Pigments are identical to those in higher plants

Slime Moulds

• Saprophytic protists
• Move along decaying matter, engulfing organic material
• Form a plasmodium aggregation under suitable conditions
• Plasmodium differentiates into fruiting bodies with spores during unfavorable conditions
• Spores are resistant and dispersed by air currents

Protozoans

• Heterotrophs living as predators or parasites
• Believed to be primitive relatives of animals

Amoeboid Protozoans

• Live in fresh water, sea water, or moist soil
• Move and capture prey using pseudopodia (false feet)
• Marine forms have silica shells on their surface
• Some are parasites, such as Entamoeba

Flagellated Protozoans

• Free-living or parasitic
• Possess flagella
• Parasitic forms cause diseases like sleeping sickness, e.g., Trypanosoma

Ciliated Protozoans

• Aquatic and actively moving due to thousands of cilia
• Have a cavity (gullet) that opens to the cell surface
• Cilia movement steers food-laden water into the gullet, e.g., Paramoecium

Sporozoans

• Diverse organisms with an infectious spore-like stage in their life cycle
• Plasmodium (malarial parasite) causes malaria, a disease with a staggering effect on the human population

Kingdom Fungi

• Unique kingdom of heterotrophic organisms
• Exhibit great diversity in morphology and habitat
• Examples include mushrooms, toadstools, and parasitic fungi

Fungi

• Some unicellular fungi, like yeast, are used to make bread and beer
• Some cause diseases in plants and animals, e.g., wheat rust (Puccinia)
• Others, like Penicillium, are a source of antibiotics
• Cosmopolitan, occurring in air, water, soil, and on animals and plants
• Prefer warm and humid environments

Fungal Structure

• Most are filamentous except for unicellular yeasts
• Bodies consist of hyphae, slender thread-like structures
• Network of hyphae is called mycelium
• Some have continuous tubes with multinucleated cytoplasm (coenocytic hyphae)
• Others have septae or cross walls in their hyphae
• Cell walls are made of chitin and polysaccharides

Fungal Nutrition

• Most are heterotrophic and absorb soluble organic matter from dead substrates (saprophytes)
• Others depend on living plants and animals (parasites)
• Can live as symbionts, in association with algae as lichens, and with roots of higher plants as mycorrhiza

Fungal Reproduction

• Vegetative reproduction through fragmentation, fission, and budding
• Asexual reproduction by spores (conidia, sporangiospores, or zoospores)
• Sexual reproduction by oospores, ascospores, and basidiospores

Sexual Cycle in Fungi

• Plasmogamy: fusion of protoplasms between two gametes
• Karyogamy: fusion of two nuclei
• Meiosis in zygote resulting in haploid spores

Dikaryotic Stage

• In some fungi (ascomycetes and basidiomycetes)
• An intervening dikaryotic stage (n + n) occurs, with two nuclei per cell
• The parental nuclei fuse later, and the cells become diploid

Phycomycetes

• Found in aquatic habitats, on decaying wood, and as parasites on plants
• Mycelium is aseptate and coenocytic
• Asexual reproduction by zoospores (motile) or aplanospores (non-motile) endogenously produced in sporangium
• A zygospore is formed by fusion of two gametes (isogamous or anisogamous)
• Examples: Mucor, Rhizopus, and Albug

Ascomycetes

• Commonly known as sac-fungi
• Mostly multicellular (e.g., Penicillium) or rarely unicellular (e.g., yeast/Saccharomyces)
• Saprophytic, decomposers, parasitic, or coprophilous
• Mycelium is branched and septate

Ascomycete Reproduction

• Asexual spores are conidia produced exogenously on conidiophores
• Sexual spores are ascospores produced endogenously in sac-like asci
• Asci are arranged in fruiting bodies called ascocarps
• Examples: Aspergillus, Claviceps and Neurospora
• Neurospora is used in biochemical and genetic work; morels and truffles are edible delicacies

Basidiomycetes

• Familiar forms include mushrooms, bracket fungi, and puffballs
• Grow in soil, on logs, and as parasites (e.g., rusts and smuts)
• Mycelium is branched and septate

Reproduction in Basidiomycetes

• Asexual spores are generally not found
• Vegetative reproduction by fragmentation is common
• Plasmogamy occurs by fusion of vegetative or somatic cells of different strains
• The resulting dikaryotic structure gives rise to a basidium and karyogamy
• Four basidiospores are produced exogenously on the basidium, which is arranged in fruiting bodies called basidiocarps
• Examples: Agaricus, Ustilago, and Puccinia

Deuteromycetes

• Known as imperfect fungi because only asexual or vegetative phases are known
• When sexual forms are discovered, they are moved to other classes
• Deuteromycetes reproduce only asexually by conidia
• Mycelium is septate and branched
• Saprophytes and parasites are included, as are decomposers
• Examples: Alternaria, Colletotrichum and Trichoderma

Kingdom Plantae

• Includes all eukaryotic chlorophyll-containing organisms (plants)
• Some members are partially heterotrophic, such as insectivorous plants (e.g., Bladderwort, Venus fly trap) and parasites (e.g., Cuscuta)
• Plant cells have a eukaryotic structure with chloroplasts and a cellulose cell wall
• Includes algae, bryophytes, pteridophytes, gymnosperms, and angiosperms

Plant Life Cycle

• Two distinct phases: diploid sporophytic and haploid gametophytic
• Exhibit alternation of generation, with varying lengths and dependencies