Class 9th Science: Chapter 7 Diversity in Living Organisms

Classification of Living Organisms

Organisms differ in their form, structure and mode of living.  Hence, based on their similarities they should be grouped.  The grouping of related organisms helps us in studying their evolutionary relationships. Classification is the division of organisms on the basis of characteristics into groups and sub-groups. A characteristic may be a particular form or function.

History of classification
•  Aristotle, the Greek philosopher, classified animals based on whether they live on land, in water or in the air.
•  Charles Darwin put forward the idea of evolution in 1859, in his book, The Origin of Species.
•  Ernst Haeckel, Robert Whittaker and Carl Woese have tried to classify living organisms into broad categories, called kingdoms.
•  Carolus Linnaeus classified all the living organisms into two kingdoms namely, ‘Plantae’ and ‘Animalia’.
•  Robert Whittaker, in 1969 proposed ‘Five kingdom classification’ of living organisms.

Hierarchical classification
The hierarchy can be represented as Kingdom subgrouping into Phylum for animals or Division for plants, Class, Order, Family, Genus and Species. Hence, the basic unit of classification is species. Species includes all the organisms that are similar to breed and produce fertile offspring.

The scientific naming of an organism is called as nomenclature. Binomial nomenclature, introduced by Carolus Linnaeus is the method of naming an organism with the genus name first and species name later.

Conventions followed while writing scientific names
•  Name of the genus begins with a capital letter.
•  Name of the species should begin with a small letter.
•  Scientific name should be in Italics when printed.
•  Genus name and the species name should be underlined separately while handwritten.

Five kingdom classification
The five kingdom classification was proposed by R.H. Whittaker in 1969. The five kingdoms were formed on the basis of characteristics such as cell structure, mode of nutrition, source of nutrition and body organisation. It includes Kingdom Monera, Kingdom Protista, Kingdom Fungi, Kingdom Plantae, and Kingdom Animalia.

Kingdom Monera:
It includes prokaryotic cells lacking organised nucleus and membrane bound cell organelles. Some of the Monerans are autotrophic and some of them are heterotrophic forms.Bacteria, cyanobacteria, blue-green algae, mycoplasma are some of the examples of Kingdom Monera.

Kingdom Protista:
It includes algae, diatoms and protozoans. These are unicellular and the simplest form of eukaryotes exhibiting both autotrophic and heterotrophic mode of nutrition. Locomotion and movement are possible by whip-like flagella and hair-like cilia or finger-like pseudopodia.

Kingdom Fungi:
These are multicellular, eukaryotic saprophytes. The cell wall of fungi is made up of chitin.
They feed on dead and decaying matter. They include mushrooms, rhizopus and mucor. Some fungi are symbiotic forming an association with algal cells. These symbionts are termed to be lichens.

Kingdom Plantae:
It includes all the plants that are non-motile, multicellular and eukaryotic organisms with their cell walls made up of cellulose.
These are complex organisms which can perform photosynthesis.
Plants comprise cells with thick cell walls.
Plant cells are rigid nd cannot be comprssed
Plants are immobile, they cannot move from one place to another.
Plants have unlimited growth.

Kingdom Animalia:
It includes all the animals that are motile, multicellular, eukaryotic organisms with their cells possessing no cell walls. It exhibits species diversity.
Members of this kingdom are complex oganisms with tissue differentiation.
Nutrition is heterotrophic .
Well developed organ systems with division of labour.
animals are ecologically meant to be consumers.

The Plant Kingdom

Members of the plant kingdom are called Plantae.  Plant kingdom mainly comprises of eukaryotic organisms which can produce their own food by the process of photosynthesis.

Photosynthesis:  This is the process by which plants use energy from the sun to convert water and carbon dioxide into sugar and release oxygen into the atmosphere.

Plant kingdom is classified based on some criteria.  Features forming the basis of classification are elucidated.
•  Plants having distinct parts like stem, roots and leaves.
•  Plant parts have tissues to transport food and water.
•  Plants bearing enclosed seeds or naked seeds.

Classification of plant kingdom
Eichler classified the plant kingdom into two sub-kingdoms - Cryptogamae and Phanerogamae.

Cryptogamae:  This sub-kingdom includes plants with hidden reproductive organs and plants do not bear flowers or seeds. Cryptogams are further divided into three groups: Thallophyta, Bryophyta and Pteridophyta.
•  Thallophyta are the simplest of plants that do not have a well-differentiated body design. e.g. Algae do not have leaves, stems or roots.
•  Bryophyta are often called amphibians of the plant kingdom as they require both aquatic and terrestrial conditions for the completion of their life cycle. e.g. Moss or Funaria belongs to the group Bryophyta.
•  Pteridophyta include fern plants which possess the plant body differentiated into stem, leaves and roots. They also possess naked embryos in the form of spores underneath the leaf.

Phanerogamae:  This sub-kingdom includes plants that develop seeds and have well-formed stem, leaves and roots. Phanerogams are further classified into Gymnosperms and Angiosperms.
•  Gymnosperms were the first plants to have a seed habit.  These are the plants which possess naked seeds. e.g. Pinus, cycas and other coniferous trees are gymnosperms.
•  Angiosperms are highly evolved plants with flowers, fruits and seeds.  They are also called as flowering plants.  These plants possess seeds enclosed inside the fruit.  The seed germinates develops into a new plant.  Angiosperms are divided into two groups, namely, monocots and dicots based on the number of cotyledons that they have.

Differences between monocots and dicots plants: 
 These include the variation in seed, root and in leaves.
•  Monocots are the plants whose seed possesses single cotyledon while dicots are the plants which possess seeds with two cotyledons.  Cotyledons are also called as seed leaves.  Cotyledons supply food to the growing embryos, when the seeds germinate.
•  The leaves in monocot plants exhibit parallel venation while that of dicot plants include reticulate venation.
•  In monocots, the primary root perishes quite early and gets replaced by a cluster of adventitious roots, while in dicots, the primary root becomes the most prominent root of the plant.  This is called as the tap root, from which several lateral roots branch out.

The Animal Kingdom

Animals are the multicellular eukaryotic organisms which belong to the kingdom Animalia.

Criteria for classification
Animals are classified on the basis of different features.
•  Cellular or tissue level of body organization
•  Body symmetry
•  Type of body cavity called as coelom
•  Presence or absence of segmentation
•  Presence or absence of a backbone.

Classification of animal kingdom
Classification of the kingdom Animalia includes Invertebrata and Vertebrata.

Invertebrata:  It includes group of animals that do not possess a vertebral column. Invertebrata is classified into different phyla such as Porifera, Coelenterata, Platyhelminthes, Nematoda, Annelida, Arthropoda, Mollusca and Echinodermata.

•  Porifera are multicellular organisms exhibiting minimal level of tissue organization. They lack nervous system. Porifera get their name from two words, “pori,” meaning “holes,” and “fera,” meaning “bearing”.   Porifera includes Sycon, Spongilla and Euplectella.  e.g.  Sponges.
•  Coelenterates are radially symmetrical organisms which live in marine habitat except for hydra.  Some are solitude and some are colonial.  Coelenterates get their name from two Greek words - “koilos,” meaning “hollow,” and “enteron,” meaning “intestine”.  e.g. Corals,  Hydra.
•  Platyhelminthes are either free living or parasitic.  They are triploblastic animals. Platyhelminthes get their name from two Greek words - “platy,” meaning “flat,” and “helminthes,” meaning “worms”.  e.g. Planaria.
•  Nematoda are bilaterally symmetrical, triploblastic parasitic worms.  Nematoda get their name from two Greek words - “nema,” which means “thread,” and “ode,” which means “like”.  Nematodes can be free living or parasitic.  e.g. Ascaris.
•  Annelida are bilaterally symmetrical, triploblastic, schizocoelomates with segmented body.  Annelida get their name from the Latin word “anellus,” which means "little ring".  Annelids are characterised by the presence of a circulatory system.  e.g. Earthworm
•  Arthropoda are bilaterally symmetrical, triploblastic animals with true coelom. Arthropoda means “joint legs”.  This phylum gets its name from the Greek words arthron, meaning “joint”, and podos, meaning “foot”.  e.g. Insects. These insects breathe through their tracheae.  Their circulatory system is open, so blood does not flow through blood vessels.
•  Molluscs are bilaterally symmetrical, triploblastic gastropods with reduced coelom. Mollusca is derived from a Latin word, which means “thin-shelled and soft”. Locomotion in molluscs is by means of a muscular foot.  Water molluscs breathe through their gills, while land molluscs have lungs and their circulatory system is open.
•  Echinodermata are triploblastic animals with true coelomic cavity.  Echinodermata are spiny skinned organisms which get their name from the Greek words “echinos,” meaning protective “spines,” and “derma,” meaning “skin”. Skeletons of echinoderms are hard calcium carbonates. They exhibit radial symmetry.

Protochordata:  These are the organisms belonging to the phylum Chordata, and are primitive chordates.  Protochordates possess a notochord during their early stage of development.  The notochord is a long rod-like support that runs all along the back of the animal separating the nervous tissue from the gut. e.g.Balanoglossus, Herdmania.

Vertebrata: These are the most advanced group of animals with true vertebral column and strong endoskeleton.  Vertebrates are grouped into different classes based on bilateral symmetry, notochord, dorsal nerve cord, paired gill pouches, triploblastic, and coelomate. These classes are Pisces, Amphibia, Reptilia, Aves and Mammalia.
•  Pisces includes all fish. These are aquatic cold blooded organisms with a spindle-shaped body covered by scales. Fish breathe through their gills. Skeleton may be cartilaginous or bony in nature. Fish comprise two-chambered heart and reproduce by laying eggs.
•  Amphibians are cold-blooded animals. Amphibians can live both on land and in water. They are the first vertebrates to have four limbs, each with five digits and are called tetrapods. Respiration is by skin and lungs. They possess a three-chambered heart. Amphibians reproduce by laying eggs.
•  Reptilia are cold-blooded animals. They have four limbs with five fingers or toes each, and hence, are called pentadactyle tetrapods. Respiration is through lungs. Hearts are three-chambered except for crocodiles. Reptiles also reproduce by laying eggs.
•  Aves are warm-blooded animals. Birds bear three clawless digits. Their hind limbs are strong and are developed for walking. Bones are hollow. Body is covered by feathers. Respiration is through lungs. They have four-chambered heart. They lay eggs which hatch into chicks.
•  Mammals are warm-blooded animals. Their skin is covered by hair, sweat glands and oil glands that regulate body temperature, thereby allowing them to live in diverse habitats. Breathing is through lungs. Four-chambered heart is present. Mammals give birth to young ones through different modes. Mammals like platypus lay eggs. Kangaroos give birth to under-developed young ones that are carried in their mother’s abdominal pouch. Humans, elephants and lions produce live offspring. Mammals have milk-producing glands called as mammary glands to nourish their young ones.
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