Diversity in Living Organisms

   Diversity: It refers to the variety and variability among living organisms from all sources including land, water, and other ecosystems.

   Classification: It refers to the identification, naming, and grouping of organisms into a formal system based on similarities in internal and external structures or evolutionary history.

Characteristic: A feature that helps to identify or describe a person or a thing.

 Principles of classification:

*Nature of cell (Fundamental characteristic): prokaryotes and eukaryotes

* Cellularity: unicellular and multicellular

* Mode of nutrition: autotrophs and heterotrophs

# Primitive organism or lower organism has a simple body structure and ancient body design

 #Advanced organism or higher organism has a complex body structure and organization                                         

 Evolution: The process of gradual and continuous change in primitive or simple organisms to give rise to advanced organisms

 Biodiversity: The variety of life forms present in various ecosystems

 Hierarchy of classification: Kingdom à  Phylum (for animals)/ Division (for plants) à Class à   Order à  Family à  Genus à  Species.

   {Tips to learn this hierarchy: King Prabin’s Class OF General Science}                                                                                     

   Species is the basic unit of classification

 Carolus Linnaeus developed the hierarchy of classification. Linnaeus also developed the concept of binomial nomenclature. In this system, the name of a species is made up of two words: the genus name and the species name. E.g. Homo sapiens

 R.H. Whittaker (in 1969) proposed a five-kingdom classification of living organisms- Monera, Protista, Fungi, Planate and Animalia

 Kingdom Plantae: It includes five divisions:

 Division Thallophyta: Plant body is not differentiated into true root, stem, and leaves.  Includes Spirogyra, Cladophora, Ulva  

 Division Bryophyta (also called amphibians of plant kingdom):  Specialised vascular tissues (such as xylem) for the conduction of water are absent. Body is differentiated into stem and leaf like structures.  Naked embryo i.e. spores are present. Includes mosses, Riccia, Marchantia

 Division Pteridophyta:  Specialised vascular tissues for the conduction of water are present. Don’t produce seeds. Includes ferns, Marsilea, Equisetum

Plants that do not have well differentiated reproductive organs and produce naked embryo (spores) are called cryptogams. Thallophyta, Bryophyta and Pteridophyta all possess naked embryo. Plants that have well developed reproductive organs that finally make seeds are called Phanerogams. Gymnosperms and angiosperms belong to Phanerogams. 

 Division Gymnospermae:  Bear naked seeds, not enclosed inside fruits. Seed bearing, non-flowering plants.  Includes Pinus, cedar, fir, Juniper, Cycas, etc

 Division Angiospermae: Includes all flowering plants. Seeds are enclosed inside fruits. Seeds develop inside the ovary, which develops into a fruit. It is of two types:

o Monocotyledons: Seeds that have one cotyledon. E.g. maize, wheat etc

o Dicotyledons: Seeds that have two cotyledons. E.g.  Sunflower, gram etc 

 Kingdom Animalia: it can be divided into two major groups on the basis of the presence or absence of notochord: non-chordata and chordate.  Non-chordata can be further divided into the following phyla:

 Phylum Porifera: Cellular level of organization. Mainly found in marine habitats.  Possess canal system for circulating water. Includes sponges such as Spongilla, Euplectella, etc

 Phylum Coelenterata: Tissue level of organization. Diploblastic i.e. body is made of two layers of cells. 

 Phylum Platy helminthes: Includes flatworms, liver flukes and planarians o Bilateral symmetry o Triploblastic i.e. three layers of cells are present

 Phylum Nematoda (Aschelminthes): Includes roundworms - Ascaris o bilaterally symmetrical o Triploblastic o Pseudocoelom (false coelom) is present

 Phylum Annelida: Includes segmented worms such as earthworms and leeches o bilaterally symmetrical o Triploblastic o Body is segmented

 Phylum Arthropoda: Includes crabs, prawns, insects, spiders, scorpions, etc o largest group of the animal kingdom. o bilaterally symmetrical and segmented o Coelomic cavity is blood-filled o Presence of Jointed legs

 Phylum Mollusca: Includes snails, octopus, Pila, etc o Bilaterally symmetrical, little segmentation o Coelomic cavity is reduced o Open circulatory system and kidney like organ for excretion is present. 

 Phylum Echinodermata: Includes marine animals such as starfishes, sea urchins, etc o Spiny skinned organisms o Free living marine organisms o Triploblastic and coelomate o Skeleton is made of calcium carbonate

 Chordata can be further divided into sub-phyla Protochordata and Vertebrata o Notochord is a flexible rod like structure that forms the supporting axis of the body in the chordates. 

 Protochordata: Includes Herdmania and Amphioxus o Triploblastic, and have a coelom cavity o Bilaterally symmetrical o Notochord at some stages of life is present.

  Vertebrata: The sub-phylum Vertebrata is further divided into five classes:

  Class Pisces: Includes all fishes o Exclusively aquatic animals o Body is streamlined and covered with scales o They are cold blooded animals  o Heart is two chambered o Skeleton is bony or cartilaginous o Oviparous. They lay eggs in water.

  Class Amphibia: Includes frogs, toads, and salamanders o Scales are absent o Cold blooded animals o Heart is three chambered o Oviparous. They lay eggs in water o Have a dual mode of life (in water and land); respire through gills, skin and lungs

  Class Reptilia: Includes reptiles such as lizard, snake, turtle, etc o Cold blooded animals o Most of them have three chambered heart (Crocodiles have four chambered heart) o Skin is covered with scales o These animals are completely terrestrial. They breathe through lungs o Lay eggs on land (oviparous)

 Class Aves: Includes all birds o Warm-blooded animals with four chambered heart o They breathe through lungs o Have feathers and forelimbs modified for flight o Exclusively egg-laying animals

 Class Mammalia: Includes kangaroo, rat, dolphin, elephant, horse, human, tiger, etc o Warm-blooded animals with four chambered heart o Most of them are viviparous except for platypus and echidna. They both are oviparous o These animals have milk-producing glands (mammary glands) to nourish their young ones